Francesca Vidotto

How to measure realistic Quantum Gravity observables: Primordial Black Holes

Francesca Vidotto

LOOPS17 Warsaw - July 6th, 2017 BH EXPLOSION See talks by Cristodoulou, Haggard, Rovelli

quantum g See talk by Singh n

l region - l

n “Planck Star” t

Vidotto, Rovelli 1401.6562 u

Quantum Gravity Phenomenology Francesca Vidotto WHERE are quantum effects?

r>2M r =2M r =0

Quantum Black Holes Francesca Vidotto WHEN are quantum effects?

r>2M r =2M r =0

Quantum Black Holes Francesca Vidotto HOW LONG IS THE BOUNCE FROM OUTSIDE?

Upper limit: Firewall argument (Almheiri, Marolf, Polchinski, Sully):“something” unusual must happen before the Page time (~ 1/2 evaporation time)

⟹ the hole lifetime must be shorter or of the order of ~ m3

Lower limit: For something quantum to happens, semiclassical approximation must fail. Vidotto, Rovelli 1401.6562 -2 Typically in quantum gravity: high curvature Curvature ~ (LP) Small effects can pile up: small probability per time unit gives a probable effect on a long time!

-1 Typically in quantum tunneling: Curvature × (time) ~ (LP)

⟹ the hole lifetime must be longer or of the order of ~ m2

Haggard, Rovelli 1407.0989

Quantum Gravity Phenomenology Francesca Vidotto HOW LONG IS THE BOUNCE FROM OUTSIDE?

Upper limit: Firewall argument (Almheiri, Marolf, Polchinski, Sully):“something” unusual must happen before the Page time (~ 1/2 evaporation time)

⟹ the hole lifetime must be shorter or of the order of ~ m3

-1 Typically in quantum tunneling: Curvature × (time) ~ (LP) m T 1 r3 b ⇠ ⟹ the hole lifetime must be longer or of the order of ~ m2

Haggard, Rovelli 1407.0989

Quantum Gravity Phenomenology Francesca Vidotto HOW LONG IS THE BOUNCE FROM OUTSIDE?

Upper limit: Firewall argument (Almheiri, Marolf, Polchinski, Sully):“something” unusual must happen before the Page time (~ 1/2 evaporation time)

⟹ the hole lifetime must be shorter or of the order of ~ m3

-1 Typically in quantum tunneling: Curvature × (time) ~ (LP) 1m TTb 1 mr23 b ⇠ ⟹ the hole lifetime must be longer or of the order of ~ m2

Haggard, Rovelli 1407.0989

Quantum Gravity Phenomenology Francesca Vidotto UNIVERSALITY OF BLACK HOLE EXPLOSION

LARGE EXTRA DIMENSIONS

1st order topological phase transition from black string to black hole Casadio and Harms 2000/01 Gubser 2002, Kol 2002 occurring because of the Gregory-Laﬂamme metrical instability Gregory and Laﬂamme 2002

BRANES Large black holes localized on inﬁnite Randall- Sundrum branes: period of rapid decay via Hawking radiation of CFT modes Emparana, Garcıa-Bellido, Kaloper 2003

Quantum effects shorten the lifetime of black holes!

For m ~ 1 024 Kg, m3~1050 Hubbl e t ime s, whil e m2~ H ubbl e t ime

Quantum Gravity Phenomenology Francesca Vidotto BLACK HOLES OF KNOWN MASS

106-1010: supermassive BH

Quantum Gravity Phenomenology Francesca Vidotto BLACK HOLES OF KNOWN MASS

106-1010: supermassive BH

3 > micro BH formed in the early universe

Quantum Gravity Phenomenology Francesca Vidotto PRIMORDIAL BLACK HOLES

All black holes are subject to quantum effects.

An explosion observed today, requires old black holes: primordial. Musco, Miller 1201.2379

(Quantum) PBH dark matter:

Today, black holes smaller than m ( t ) have already exploded. |t=tH It decreases with time. ( but for later accretion/merging )

Caution with constraints!

Carr, Kohri, Sendouda, Constraints from Hawking evaporation do not apply. Yokoyama 0912.5297 PBH mass spectrum beyond simple monochromatic models. PBH should exists, but not necessarily constitute all DM.

Quantum Gravity Phenomenology Francesca Vidotto QUANTUM PRIMORDIAL BLACK HOLES AS DARK MATTER

Structure formation Barrau, Moulin, Bellomo, Bernal, Chluba, Cholis, Raccanelli, Verde, Vidotto WIP

Preliminary result: Planck Stars compatible with constraints from early cosmology

First stars & Supermassive black holes Bambi, Freese, Vidotto WIP

Primordial black holes inside first-generation stars can provide the seeds for supermassive black holes

Quantum Gravity Phenomenology Francesca Vidotto EFFECTS IN THE LATE UNIVERSE 55 6 Raccanelli, Verde, Vidotto (to appear soon)

From galaxy-cluster surveys: 6

Observed galaxy over-density 22 Cosmic Magniﬁcation 0, ,41 6 0, ,41

Use of LATE UNIVERSE observations 0, ,41 to MEASURE quantum-gravity parameters!

7 88 , 7 ,0 21 531 21 531 7 21 531 Bellomo, Bernal, Chluba, Cholis, Raccanelli, Verde, Vidotto WIP Quantum Gravity Phenomenology Francesca Vidotto EFFECTS IN THE LATE UNIVERSE 55 6 Raccanelli, Verde, Vidotto (to appear soon)

From galaxy-cluster surveys: 6

Observed galaxy over-density 22 Cosmic Magniﬁcation 0, ,41 6 0, ,41

Use of LATE UNIVERSE observations 0, ,41 to MEASURE quantum-gravity parameters!

66 2=8B9C= ,CDBAC=8C 15 7 G

H+ H+ 88 31 G , 7 ,0 21 531 G 40CDB=DC 8CD9B=56/9C= 21 531 BB9DCDB=DC 7 21 531 G G G G G G 22 Bellomo, Bernal, Chluba, Cholis, Raccanelli, Verde, Vidotto WIP Quantum Gravity Phenomenology Francesca Vidotto PLANCK STAR SIGNAL EXPECTED SIGNALS

Barrau, Rovelli, Vidotto 1409.4031 fast process ( few milliseconds? ) the source disappears with the burst very compact object: big flux E = mc2 1.7 1047 erg ⇠ ⇥

tH 2Gm exploding today: m = 1.2 1023 kg R = 2 .02 cm r 4k ⇠ ⇥ c ⇠ 2Gm LOW ENERGY: size of the source ≈ wavelength R = . 02 . 05 cm cm (?) predictedc2 ⇠& HIGH ENERGY: energy of the particle liberated Tev ⇡

SYNCHROTRON EMISSION Kavic &al. 0801.4023

GRAVITATIONAL WAVES

Quantum Gravity Phenomenology Francesca Vidotto MAXIMAL DISTANCE Barrau, Bolliet, Vidotto, Weimer 1507.1198

shorter lifetime — smaller wavelength

Low energy channel High energy channel

1024 1028

1022 26 Hubble radius 10 Galactic scale ] ] 1020 m m 24 [ 10 [ R R Hadron decay 1018 1022 Galactic scale Direct emission 1016 1020

k 1 104 108 1012 1016 1020 k 1 104 108 1012 1016 1020 E [eV] 2.7 2.7×102 2.7×104 2.7×106 2.7×108 E [eV] 3.6×1013 3.6×1014 3.6×1015 3.6×1016 3.6×1017

detection of arbitrarily far signals PBH: mass - temperature relation

better single-event detection different scaling

Quantum Gravity Phenomenology Francesca Vidotto maximal extension of the Schwarzschild metric for a The energy (and amplitude) of the signal emitted in mass M. Region (III) is where quantum gravity becomes the quantum gravity model considered here remains non-negligible. open. As suggested in [11] and to remain general, we consider two possible signals of di↵erent origins. Importantly, by gluing together the di↵erent part of The first one, referred to as the low energy signal, the e↵ective metric and estimating the time needed for is determined by dimensional arguments. When the maximal extension of the Schwarzschildquantum e↵ects metric to happen, for a it wasThe shown energy that the (and dura- amplitude)bounce of is the completed, signal emitted the black in hole (more precisely the mass M. Region (III) is wheretion quantum of the gravity bounce becomesshould not bethe shorter quantum than [10] gravity modelemerging considered white hole) here has remains a size (L 2M)determinedby its mass M. This is the main scale⇠ of the problem and it non-negligible. open. As suggested in [11] and to remain general, ⌧ =4kM2, (1) fixes an expected wavelength for the emitted radiation: we consider two possible signals of di↵erent origins. L. We assume that particles are emitted at the Importantly, by gluing togetherwith k> the di0↵.05erent a dimensionless part of The parameter. first one, We referred use toprorata⇠ as the of theirlow numberenergy signal, of internal degrees of freedom. is determined by dimensional arguments. When the the e↵ective metric and estimatingPlanck the units time where neededG = for~ = c = 1. The bounce (This is also the case for the Hawking spectrum at the quantum e↵ects to happen, ittime was shown is proportional that the to dura-M 2 andbounce not to isM completed,3 as in the the blackoptical hole limit, (morei.e. preciselywhen the the greybody factors describ- tion of the bounce should not be shorter than [10] emerging white hole) has a size (L 2M)determinedby Hawking process. As long as k remains small enough, ing the backscattering⇠ probability are spin-independent.) the bounce time is much smallerits mass thanM the. This Hawking is the main scale of the problem and it ⌧ =4kMevaporation2, time and the(1) evaporationfixesTHE an can SMOKING expected be considered wavelength GUN: DISTANCE/ENERGYThe for second the emitted signal, referred radiation: RELATION to as the high energy com- as a dissipative correction that can beL. neglected We assume in a thatponent, particles has are a very emitted di↵erent at origin. the Consider the history with k>0.05 a dimensionlessfirst order parameter. approximation. We use prorata⇠ of their number ofof internal the matter degrees emerging of freedom. from a white hole: it comes from Planck units where G = ~ = c = 1. The bounce (This distant is also signals the caseoriginated for the in younger bounce Hawking and of thespectrum smaller matter sources at that the formed the black hole by time is proportional to M 2 andThe not phenomenology to M 3 as in was the investigatedoptical in limit, [11] underi.e. thewhen thecollapsing. greybody In most factors scenarios describ- there is a direct relation be- Hawking process. As long asassumptionk remains that smallk takes enough, its smallesting possible the backscattering value, which probabilitytween the are formation spin-independent.) of a primordial black hole of mass M the bounce time is much smallermakes the than bounce the Hawking time as short as possible. The aim and the temperature of the Universe when it was formed evaporation time and the evaporationof the present can be article considered is to go beyondThe this second first signal, study in referred(see to [14] as for the ahigh review). energyM com-is given by the horizon mass as a dissipative correction thattwo can directions. be neglected First, we in generalize a ponent, the previous has a very results di↵erentMH origin.: Consider the history first order approximation. by varying k. The only conditionof the for matter the model emerging to be from a white hole: it comes from valid is that the bounce time remains (much) smaller M MH t. (2) the bounce of the matter that formed the black hole⇠ by⇠ than the Hawking time. This assumption is supported (Other more exotic models, e.g. collisions of cosmic The phenomenology was investigatedby the “firewall in [11] argument” under the presentedcollapsing. in [1]. We In most study scenarios in there is a direct relation be- strings or collisions of bubbles associated with di↵erent assumption that k takes its smallestdetail possible the maximal value, distance which at whichtween a the single formation black-hole of a primordial black hole of mass M vacua, can lead to di↵erent masses at a given cosmic time. makes the bounce time as shortbounce as possible. can be detected. The aim Second,and we go the beyond temperature this “sin- of the Universe when it was formed We will not consider them in this study.) The cosmic of the present article is to gogle beyond event this detection” first study and consider in (see the [14] di↵use for background a review). M is given by the horizon mass time t is related to the temperature of the Universe T by two directions. First, we generalizeproduced the by previous a distribution results of bouncingMH : black holes. by varying k. The only condition for the model to be 1 2 2 M MH t. t 0.3g(2)T , (3) valid is that the bounce time remains (much) smaller ⇠ ⇠ ⇠ ⇤ than the Hawking time. This assumptionII. SINGLE is supported EVENT DETECTION (Other more exotic models,wheree.g.g collisions100 is the of number cosmic of degrees of freedom. by the “firewall argument” presented in [1]. We study in ⇤ ⇠ strings or collisions of bubblesOnce associatedk is fixed, M with is fixed di↵ (byerent⌧ tH ) and T is therefore detail the maximal distance at which a single black-hole Quantum Gravity Phenomenology ⇠ Francesca Vidotto For detection purposes, wevacua, are interested can lead in to black di↵erentknown. masses at As a the given process cosmic is time. time-symmetric, what comes bounce can be detected. Second, we go beyond this “sin- holes whose lifetime is less thanWe the age will of not the consider Universe. themout in from this thestudy.) white The hole cosmic should be what went in the gle event detection” and consider the di↵use background For a primordial black hole detectedtime t is today, related⌧ to= thetH temperatureblack hole, of re-emerging the Universe at theT by same energy: a blackbody produced by a distribution ofwhere bouncingtH is black the Hubble holes. time. This fixes the mass M, as spectrum at temperature T . Intuitively, the bouncing a function of the parameter k (defined in the previous black1 hole plays the role of a “time machine” that sends 2 2 t 0.3g T , (3) section) for black holes that can be observed. In all⇠ the⇤ primordial universe radiation to the future: while the II. SINGLE EVENTcases DETECTION considered, M is very small compared to a solar surrounding space has cooled to 2.3K, the high-energy mass and therefore only primordialwhere blackg holes100 possibly is the numberradiation of emerges degrees from of freedom. the white hole with its original Once k is⇤ fixed,⇠ M is fixed (by ⌧ t ) and T is therefore formed in the early Universe are interesting from this energy.⇠ H For detection purposes, wepoint are of interested view. Although in black no primordialknown. black As the hole process has is time-symmetric, what comes holes whose lifetime is less thanbeen the detected age of the to date, Universe. various mechanismout from for the their white pro- hole shouldWhen be the what parameter wentk inis taken the larger that its smallest For a primordial black holeduction detected shortly today, after⌧ the= t BigH Bangblack have hole, been re-emerging suggested atpossible the same value, energy: that a blackbody is fixed for quantum e↵ects to be where tH is the Hubble time.(see, Thise.g. fixes, [12] the for mass anM early, as detailedspectrum calculation at temperature and [13] importantT . Intuitively, enough the to lead bouncing to a bounce, the bounce time a function of the parameter kfor(defined a review). in the Although previous their numberblack hole density plays might the be role ofbecomes a “time larger machine” for a thatgiven sends mass. If this time is assumed section) for black holes thatway can too be observed. small for direct In all detection,the primordial the production universe of radiationto be equal to the to future: the Hubble while the time (or slightly less if we cases considered, M is very smallprimordial compared black holes to a remains solar asurrounding quite generic spaceprediction has cooledfocus to on 2.3K, black the holes high-energy bouncing far away), this means mass and therefore only primordialof cosmological black holes physics possibly eitherradiation directly from emerges density from thethat white the holemass with has to its be original smaller. The resulting energy formed in the early Universeperturbations are interesting –possibly from this enhancedenergy. by phase transitions– will be higher for both the low energy and the high point of view. Although no primordialor through black exotic hole phenomena has like collisions of cosmic energy signals, but for di↵erent reasons. In the first been detected to date, variousstrings mechanism or bubbles for their of false pro- vacua. When the parameter k iscase, taken because larger that of the its smaller smallest size of the hole, leading to a smaller emitted wavelength. In the second case, duction shortly after the Big Bang have been suggested possible value, that is fixed for quantum e↵ects to be (see, e.g., [12] for an early detailed calculation and [13] important enough to lead to a bounce, the bounce time for a review). Although their number density might be becomes larger for a given2 mass. If this time is assumed way too small for direct detection, the production of to be equal to the Hubble time (or slightly less if we primordial black holes remains a quite generic prediction focus on black holes bouncing far away), this means of cosmological physics either directly from density that the mass has to be smaller. The resulting energy perturbations –possibly enhanced by phase transitions– will be higher for both the low energy and the high or through exotic phenomena like collisions of cosmic energy signals, but for di↵erent reasons. In the first strings or bubbles of false vacua. case, because of the smaller size of the hole, leading to a smaller emitted wavelength. In the second case,

2 maximal extension of the Schwarzschild metric for a The energy (and amplitude) of the signal emitted in mass M. Region (III) is where quantum gravity becomes the quantum gravity model considered here remains non-negligible. open. As suggested in [11] and to remain general, we consider two possible signals of di↵erent origins. Importantly, by gluing together the di↵erent part of The first one, referred to as the low energy signal, the e↵ective metric and estimating the time needed for is determined by dimensional arguments. When the maximal extension of the Schwarzschildquantum e↵ects metric to happen, for a it wasThe shown energy that the (and dura- amplitude)bounce of is the completed, signal emitted the black in hole (more precisely the mass M. Region (III) is wheretion quantum of the gravity bounce becomesshould not bethe shorter quantum than [10] gravity modelemerging considered white hole) here has remains a size (L 2M)determinedby its mass M. This is the main scale⇠ of the problem and it non-negligible. open. As suggested in [11] and to remain general, ⌧ =4kM2, (1) fixes an expected wavelength for the emitted radiation: we consider two possible signals of di↵erent origins. L. We assume that particles are emitted at the Importantly, by gluing togetherwith k> the di0↵.05erent a dimensionless part of The parameter. first one, We referred use toprorata⇠ as the of theirlow numberenergy signal, of internal degrees of freedom. is determined by dimensional arguments. When the the e↵ective metric and estimatingPlanck the units time where neededG = for~ = c = 1. The bounce (This is also the case for the Hawking spectrum at the quantum e↵ects to happen, ittime was shown is proportional that the to dura-M 2 andbounce not to isM completed,3 as in the the blackoptical hole limit, (morei.e. preciselywhen the the greybody factors describ- tion of the bounce should not be shorter than [10] emerging white hole) has a size (L 2M)determinedby Hawking process. As long as k remains small enough, ing the backscattering⇠ probability are spin-independent.) the bounce time is much smallerits mass thanM the. This Hawking is the main scale of the problem and it ⌧ =4kMevaporation2, time and the(1) evaporationfixesTHE an can SMOKING expected be considered wavelength GUN: DISTANCE/ENERGYThe for second the emitted signal, referred radiation: RELATION to as the high energy com- as a dissipative correction that can beL. neglected We assume in a thatponent, particles has are a very emitted di↵erent at origin. the Consider the history with k>0.05 a dimensionlessfirst order parameter. approximation. We use prorata⇠ of their number ofof internal the matter degrees emerging of freedom. from a white hole: it comes from Planck units where G = ~ = c = 1. The bounce (This distant is also signals the caseoriginated for the in younger bounce Hawking and of thespectrum smaller matter sources at that the formed the black hole by time is proportional to M 2 andThe not phenomenology to M 3 as in was the investigatedoptical in limit, [11] underi.e. thewhen thecollapsing. greybody In most factors scenarios describ- there is a direct relation be- Hawking process. As long asassumptionk remains that smallk takes enough, its smallesting possible the backscattering value, which probabilitytween the are formation spin-independent.) of a primordial black hole of mass M the bounce time is much smallermakes the than bounce the Hawking time as short as possible. The aim and the temperature of the Universe when it was formed evaporation time and the evaporationof the present can be article considered is to go beyondThe this second first signal, study in referred(see to [14] as for the ahigh review). energyM com-is given by the horizon mass as a dissipative correction thattwo can directions. be neglected First, we in generalize a ponent, the previous has a very results di↵erentMH origin.: Consider the history first order approximation. by varying k. The only conditionof the for matter the model emerging to be from a white hole: it comes from valid is that the bounce time remains (much) smaller M MH t. (2) the bounce of the matter that formed the black hole⇠ by⇠ than the Hawking time. This assumption is supported (Other more exotic models, e.g. collisions of cosmic The phenomenology was investigatedby the “firewall in [11] argument” under the presentedcollapsing. in [1]. We In most study scenarios in there is a direct relation be- strings or collisions of bubbles associated with di↵erent assumption that k takes its smallestdetail possible the maximal value, distance which at whichtween a the single formation black-hole of a primordial black hole of mass M vacua, can lead to di↵erent masses at a given cosmic time. makes the bounce time as shortbounce as possible. can be detected. The aim Second,and we go the beyond temperature this “sin- of the Universe when it was formed We will not consider them in this study.) The cosmic of the present article is to gogle beyond event this detection” first study and consider in (see the [14] di↵use for background a review). M is given by the horizon mass time t is related to the temperature of the Universe T by two directions. First, we generalizeproduced the by previous a distribution results of bouncingMH : black holes. by varying k. The only condition for the model to be 1 2 2 M MH t. t 0.3g(2)T , (3) valid is that the bounce time remains (much) smaller ⇠ ⇠ ⇠ ⇤ than the Hawking time. This assumptionII. SINGLE is supported EVENT DETECTION (Other more exotic models,wheree.g.g collisions100 is the of number cosmic of degrees of freedom. by the “firewall argument” presented in [1]. We study in ⇤ ⇠ strings or collisions of bubblesOnce associatedk is fixed, M with is fixed di↵ (byerent⌧ tH ) and T is therefore detail the maximal distance at which a single black-hole Quantum Gravity Phenomenology ⇠ Francesca Vidotto For detection purposes, wevacua, are interested can lead in to black di↵erentknown. masses at As a the given process cosmic is time. time-symmetric, what comes bounce can be detected. Second, we go beyond this “sin- holes whose lifetime is less thanWe the age will of not the consider Universe. themout in from this thestudy.) white The hole cosmic should be what went in the gle event detection” and consider the di↵use background For a primordial black hole detectedtime t is today, related⌧ to= thetH temperatureblack hole, of re-emerging the Universe at theT by same energy: a blackbody produced by a distribution ofwhere bouncingtH is black the Hubble holes. time. This fixes the mass M, as spectrum at temperature T . Intuitively, the bouncing a function of the parameter k (defined in the previous black1 hole plays the role of a “time machine” that sends 2 2 t 0.3g T , (3) section) for black holes that can be observed. In all⇠ the⇤ primordial universe radiation to the future: while the II. SINGLE EVENTcases DETECTION considered, M is very small compared to a solar surrounding space has cooled to 2.3K, the high-energy mass and therefore only primordialwhere blackg holes100 possibly is the numberradiation of emerges degrees from of freedom. the white hole with its original Once k is⇤ fixed,⇠ M is fixed (by ⌧ t ) and T is therefore formed in the early Universe are interesting from this energy.⇠ H For detection purposes, wepoint are of interested view. Although in black no primordialknown. black As the hole process has is time-symmetric, what comes holes whose lifetime is less thanbeen the detected age of the to date, Universe. various mechanismout from for the their white pro- hole shouldWhen be the what parameter wentk inis taken the larger that its smallest For a primordial black holeduction detected shortly today, after⌧ the= t BigH Bangblack have hole, been re-emerging suggested atpossible the same value, energy: that a blackbody is fixed for quantum e↵ects to be where tH is the Hubble time.(see, Thise.g. fixes, [12] the for mass anM early, as detailedspectrum calculation at temperature and [13] importantT . Intuitively, enough the to lead bouncing to a bounce, the bounce time a function of the parameter kfor(defined a review). in the Although previous their numberblack hole density plays might the be role ofbecomes a “time larger machine” for a thatgiven sends mass. If this time is assumed section) for black holes thatway can too be observed. small for direct In all detection,the primordial the production universe of radiationto be equal to the to future: the Hubble while the time (or slightly less if we cases considered, M is very smallprimordial compared black holes to a remains solar asurrounding quite generic spaceprediction has cooledfocus to on 2.3K, black the holes high-energy bouncing far away), this means mass and therefore only primordialof cosmological black holes physics possibly eitherradiation directly from emerges density from thethat white the holemass with has to its be original smaller. The resulting energy formed in the early Universeperturbations are interesting –possibly from this enhancedenergy. by phase transitions– will be higher for both the low energy and the high point of view. Although no primordialor through black exotic hole phenomena has like collisions of cosmic energy signals, but for di↵erent reasons. In the first been detected to date, variousstrings mechanism or bubbles for their of false pro- vacua. When the parameter k iscase, taken because larger that of the its smaller smallest size of the hole, leading to a smaller emitted wavelength. In the second case, duction shortly after the Big Bang have been suggested possible value, that is fixed for quantum e↵ects to be (see, e.g., [12] for an early detailed calculation and [13] important enough to lead to a bounce, the bounce time for a review). Although their number density might be becomes larger for a given2 mass. If this time is assumed way too small for direct detection, the production of to be equal to the Hubble time (or slightly less if we primordial black holes remains a quite generic prediction focus on black holes bouncing far away), this means of cosmological physics either directly from density that the mass has to be smaller. The resulting energy perturbations –possibly enhanced by phase transitions– will be higher for both the low energy and the high or through exotic phenomena like collisions of cosmic energy signals, but for di↵erent reasons. In the first strings or bubbles of false vacua. case, because of the smaller size of the hole, leading to a smaller emitted wavelength. In the second case,

2 THE SMOKING GUN: DISTANCE/ENERGY RELATION 4

by 1 1/2 other other 2Gm H0 1 ⌦⇤ =(1+z) . (6) 3/2 obs emitted ⟶ obs 2 (1 + z) 1/2 sinh (z + 1) ⇠ c v ⌦M u6 k⌦⇤ " # u ✓ ◆ The speciﬁc redshift dependence of our model makes t it possibly testable against other proposals. Obvi- 2 ously, detecting such a signal from far away galaxies is challenging but this work might precisely motivate some experimental prospects for the next generation of l gamma-ray for our satellites. signal: distance ∝ 1/wave length noise. There might be room for improvement. It is not

The order of magnitude of the number of bouncing impossible that the time structure of the bounce could black taking holes ininto the account galactic centerthe redshift region requiredthe to ac- countresulting for the observedfunction flux is very is 100 slowly per second. varying The asso- lead to a characteristic time-scale of the event larger than ciated mass is negligible when compared to the expected dark matter density, even when integrated over a long the response time of the bolometer. In that case, a time interval. If the mass spectrum of primordial black Barrau, Rovelli, Vidotto 1409.4031 FIG. 3. Best fit to the Fermi excess with bouncing black holes was known, which is not the case, it would in prin- specific analysis should allow for a dedicated search of holes. ciple be possible DISTANCE: to fix the total mass associated with bouncing black holes. ▫ As dispersion a reasonable relation? toy model, let us such events. We leave this study for a future work as assume that the mass ▫ spectrum hosting is galaxy? given by ▫ it requires astrophysical considerations beyond this first DISCRIMINATION WITH DARK MATTER AND 2 flux? z d N ↵ 2 4 6 8 10 MASS SPECTRUM = pM . (7) dMdV investigation. An isotropic angular distribution of the Quantum Gravity Phenomenology Francesca Vidotto The model presented in this work is unquestionably If the number of exploding black holes required to explain bursts, signifying their cosmological origin, could also be quite exotic when compared to astrophysical hypotheses. the data on a time interval d⌧ isFIG.Nexp, one 1: can estimate White hole signal wavelength (unspecified units) as But the important point is than it can, in principle, be the mass variation associated, considered as an evidence for the model. In case many distinguished both from astrophysical explanations and a function of z. Notice the characteristic flattening at large d⌧ from other “beyond the standard model” scenarios. The dM = . (8) 8kM events were measured, it would be important to ensure reason for that is the redshift dependance. When look- distance: the youth of the hole compensate for the redshift. ing at a galaxy at redshift z, the measured energy of With M0 the mass corresponding to a black hole explod- that there is no correlation with the mean cosmic-ray flux the signal emitted either by decaying WIMPS or by as- ing now, one then has trophysical objects will be E/(1 + z) if the rest-frame (varying with the solar activity) at the satellite location. energy is E. But this is not true for the bouncing black M0+dM N = pM ↵dM. (9) holes signal. The reason for this is that black holes that exp M0 The received signal is going to be corrected by standard Let us turn to something that has been observed. have bounced far away and are observed now must have Z a smaller bouncing time and therefore a smaller mass. This allows, in principe, to determinecosmologicalp and therefore to redshift. However, signals coming form far- Their emission energy – in the low energy channel we are normalize the spectrum. Fast Radio Bursts. Fast Radio Bursts are intense iso- considering in this article – is therefore higher and this ther away were originated earlier, namely by younger, partly compensates for the redshift e↵ect. Following [9], lated astrophysical radio signals with milliseconds dura- we can write down the observed wavelength of the signal CONCLUSIONand therefore less massive, holes, giving a peculiar de- from a host galaxy at redshift z, taking into account both tion. A small number of these were initially detected the expansion of the universe and the change of bouncing Black holes could bounce oncecrease they have reached of the the emitted wavelength with distance. The re- time, as: “Planck star” stage. This is a well motivated quantum only at the Parkes radio telescope [39–41]. Observations gravity idea. In this article, weceived have shown wavelength, that this taking into account both the expan- 2Gm phenomenon could explain the GeV excess measured by from the Arecibo Observatory have confirmed the detec- BH (1 + z) (5) obs ⇠ c2 ⇥ the Fermi satellite. This would opension the fascinating of the pos- universe and the change of time available for tion [42]. The frequency of these signals around 1.3 GHz, 1 1/2 sibility to observe (non perturbative) quantum gravity H0 1 ⌦⇤ 3/2 processes at energies 19 orders of magnitude below the 1/2 sinh (z + 1) , the black hole to bounce, can be obtained folding (1)into v ⌦M namely a wavelength u6 k⌦⇤ " # Planck scale. Interestingly the explanation we suggest is u ✓ ◆ t fully self consistant in the sense thatthe the hadronic standard “noise” cosmological relation between redshift and where we have reinserted the Newton constant G and due to decaying pions remains much below the observed the speed of light c; H0, ⌦⇤ and ⌦M being the Hubble background. Unquestionably, thereproper are other – less time. exotic A straightforward calculation gives constant, the cosmological constant, and the matter den- – ways to explain the Fermi excess. But the important observed 20 cm. (7) sity. On the other hand, for other signals the measured point we have made is that there is specific redshift de- ⇠ wavelength this just related to the observed wavelength pendance of this model which, in principle, can lead to2 aGm obs (1 + z) (6) These signals are believed to be of extragalactic origin, ⇠ c2 ⇥ because the observed delay of the signal arrival time with 1 1/2 H0 1 ⌦⇤ frequency agrees well with the dispersion due to ionized sinh (z + 1) 3/2 . 1/2 medium as expected from a distant source. The total v ⌦M u6 k⌦⇤ " # u ✓ ◆ energy emitted in the radio is estimated to be of the t 38 where we have reinserted the Newton constant G and order 10 erg. The progenitors and physical nature of the Fast Radio Bursts are currently unknown [42]. the speed of light c while H0, ⌦⇤ and ⌦M are the Hub- ble constant, the cosmological constant, and the matter There are three orders of magnitude between the pre- density. This is a very slowly varying function of the dicted signal (5) and the observed signal (7). But the redshift. The e↵ect of the hole’s age almost compesates black-to-white hole transition model is still very rough. It for the red-shift. The signal, indeed, varies by less than disregards rotation, dissipative phenomena, anisotropies, an order of magnitude for redshifts up to the decoupling and other phenomena, and these could account for the time (z=1100). See Figure 1. discrepancy. If the redshift of the source can be estimated by using In particular, astrophysical black holes rotate: one may dispersion measures or by identifying a host galaxy, given expect the centrifugal force to lower the attraction and sucient statistics this flattening represents a decisive bring the lifetime of the hole down. This should allow signature of the phenomenon we are describing. larger black holes to explode today, and signals of larger Do we have experiments searching for these signals? wavelength. Also, we have not taken the astrophysics of There are detectors operating at such wavelengths, begin- the explosion into account. The total energy (3) avail- ning by the recently launched Herschel instrument. The able in the black hole is largely sucient –9 orders of 200 micron range can be observed both by PACS (two magnitude larger– than the total energy emitted in the bolometer arrays and two Ge:Ga photoconductor arrays) radio estimated by the astronomers. and SPIRE (a camera associated with a low to medium Given these uncertainties, the hypothesis that Fast Ra- resolution spectrometer). The predicted signal falls in be- dio Burst could originate from exploding white holes is tween PACS and SPIRE sensitivity zones. There is also a tempting and deserves to be explored. very high resolution heterodyne spectrometer, HIFI, on- High energy signal. When a black hole radiates by board Herschel, but this is not an imaging instrument, it the Hawking mechanism, its Schwarzschild radius is the observes a single pixel on the sky at a time. However, the only scale in the problem and the emitted radiation has bolometer technology makes detecting short white-hole a typical wavelength of this size. In the model we are bursts dicult. Cosmic rays cross the detectors very of- considering, the emitted particles do not come from the ten and induce glitches that are removed from the data. coupling of the event horizon with the vacuum quan- Were physical IR bursts due to bouncing black hole regis- tum fluctuations, but rather from the time-reversal of tered by the instrument, they would most probably have the phenomenon that formed (and filled) the black hole. been flagged and deleted, mimicking a mere cosmic ray Therefore the emitted signal is characterized by second OBSERVED SIGNALS Thornton et al. 1307.1628 FAST RADIO BURSTS Spitler et al. 1404.2934 E. Petroff et al. 1412.0342

Short Observed width ≃ milliseconds No Long GRB associated No Afterglow

Punctual No repetition

Enormous flux density A real-time FRB 5 Energy ≲ 1038 erg

Likely Extragalactic Dispersion Measure: z≲0.5

104 event/day A pretty common object?

Circular polarization Intrinsic Figure 2. The full-Stokes parameters of FRB 140514 recorded in the centre beam of the multibeam receiver with BPSR. Total intensity, and Stokes Q, U,andV are represented in black, red, green, and blue, respectively. FRB 140514 has 21 7% (3-)circularpolarisation Quantum Gravity Phenomenology ± Francesca Vidotto averaged over the pulse, and a 1- upper limit on linear polarisation of L<10%. On the leading edge of the pulse the circular polarisation is 42 9% (5-)ofthetotalintensity.Thedatahavebeensmoothedfromaninitialsamplingof64µsusingaGaussianﬁlteroffull-width ± half-maximum 90 µs.

source given the temporal proximity of the GMRT observa- 4.5 Gamma-Ray Burst Optical/Near-Infrared tion and the FRB detection. The other two sources, GMRT2 Detector and GMRT3, correlated well with positions for known ra- After 13 hours, a trigger was sent to the Gamma-Ray Burst dio sources in the NVSS catalog with consistent flux densi- Optical/Near-Infrared Detector (GROND) operating on the ties. Subsequent observations were taken through the GMRT 2.2-m MPI/ESO telescope on La Silla in Chile (Greiner et al. ToO queue on 20 May, 3 June, and 8 June in the 325 MHz, 2008). GROND is able to observe simultaneously in J, H, 1390 MHz, and 610 MHz bands, respectively. The second and K near-infrared (NIR) bands with a 100 100 field of epoch was largely unusable due to technical diculties. The ⇥ view (FOV) and the optical g0, r0, i0,andz0 bands with a search for variablility focused on monitoring each source for 60 60 FOV. A 2 2 tiling observation was done, providing flux variations across observing epochs. All sources from the ⇥ ⇥ 61% (JHK)and22%(g0r0i0z0) coverage of the inner part first epoch appeared in the third and fourth epochs with no of the FRB error circle. The first epoch began 16 hours af- measureable change in flux densities. ter FRB 140514 with 460 second exposures, and a second epoch was taken 2.5 days after the FRB with an identical 4.4 Swift X-Ray Telescope observing setup and 690 s (g0r0i0z0)and720s(JHK)exposures, respectively. Limiting magnitudes for J, H,andK The first observation of the FRB 140514 field was taken us- bands were 21.1, 20.4, and 18.4 in the first epoch and 21.1, ing Swift XRT (Gehrels et al. 2004) only 8.5 hours after the 20.5, and 18.6 in the second epoch, respectively (all in the FRB was discovered at Parkes. This was the fastest Swift AB system). Of all the objects in the field, analysis iden- follow-up ever undertaken for an FRB. 4 ks of XRT data tified three variable objects, all very close to the limiting were taken in the first epoch, and a further 2 ks of data magnitude and varying on scales of 0.2 - 0.8 mag in the NIR were taken in a second epoch later that day, 23 hours af- bands identified with di↵erence imaging. Of the three ob- ter FRB 140514, to search for short term variability. A final jects one is a galaxy, another is likely to be an AGN, and epoch, 18 days later, was taken to search for long term vari- the last is a main sequence star. Both XRT1 and GMRT1 ability. Two X-ray sources were identified in the first epoch sources were also detected in the GROND infrared imaging of data within the 150 diameter of the Parkes beam. Both but were not observed to vary in the infrared bands on the sources were consistent with sources in the USNO catalog timescales probed. (Monet et al. 2003). The first source (XRT1) is located at RA = 22:34:41.49, Dec = -12:21:39.8 with RUSNO =17.5 and the second (XRT2) is located at RA = 22:34:02.33 Dec =-12:08:48.2withR =19.7.BothXRT1andXRT2 USNO 4.6 Swope Telescope appeared in all subsequent epochs with no observable variability on the level of 10% and 20% for XRT1 and XRT2, An optical image of the FRB field was taken 16h51m after respectively, both calculated from photon counts from the the burst event with the 1-m Swope Telescope at Las Cam- XRT. Both sources were later found to be active galactic panas. The field was re-imaged with the Swope Telescope on nuclei (AGN). 17 May, 2 days after the FRB. No variable optical sources

c 0000 RAS, MNRAS 000,000–000 FAST RADIO BURSTS Barrau, Rovelli, Vidotto 1409.4031

!≈20 cm size of the source ≈ predicted & .02 cm Short synchrotron emission ≈ 20 cm Kavic, Vidotto WIP Observed width ≃ milliseconds fast process No Long GRB associated No Afterglow Very short GRB ? gravitational waves ? Punctual No repetition the source disappears with the burst Enormous flux density Energy ≲ 1038 erg very compact object ⟶ 1047 erg

Likely Extragalactic Dispersion Measure: z≲0.5 peculiar distance/energy relation

104 event/day A pretty common object? Are they bouncing Black Holes? Circular polarization Intrinsic Quantum Gravity Phenomenology Francesca Vidotto LIST OF FAST RADIO BURSTS

name date RA dec DM width peak notes FRB 010724 2001/07/24 01h18′ -75°12′ 375 4.6 30 "Lorimer Burst" FRB 010621 2001/06/2119:50:01.63 18h52′ -08°29′ 746 7.8 0.4 13:02:10.795 FRB 110220 2011/02/20 22h34′ -12°24′ 944.38 5.6 1.3 01:55:48.957 FRB 110627 2011/06/27 21h03′ -44°44′ 723.0 <1.4 0.4 FRB 110703 2011/07/0321:33:17.474 23h30′ -02°52′ 1103.6 <4.3 0.5 18:59:40.591 FRB 120127 2012/01/27 23h15′ -18°25′ 553.3 <1.1 0.5 FRB 011025 2001/10/2508:11:21.723 19h07′ -40°37′ 790 9.4 0.3 00:29:13.23 FRB 121002 2012/10/02 18h14′ -85°11′ 1628.76 2.1; 3.7 0.35 double pulse 5.1 ms apart FRB 121002 2012/10/0213:09:18.402 18h14' -85°11' 1629.18 <0.3 >2.3 13:09:18.50 FRB 121102 2012/11/02 05h32′ 33°05' 557 3.0 0.4 by Arecibo radio telescope 06:35:53.2442015 05h32′~ 33°05'~ 557~ 10 repeat bursts: 6 bursts in 10 minutes, 3 bursts weeks apart. FRB 131104 2013/11/04 06h44′ -51°17′ 779.0 <0.64 1.12 'near' Carina Dwarf Spheroidal Galaxy 18:04:01.2 FRB 140514 2014/05/14 22h34′ -12°18′ 562.7 2.8 0.47 21 ± 7 per cent (3σ) circular polarization FRB 090625 2009/06/25 03h07' -29°55′ 899.6 <1.9 >2.2 21:53:52.85 FRB 130626 2013/06/26 16h27' -07°27' 952.4 <0.12 >1.5 FRB 130628 2013/06/2814:56:00.06 09h03' +03°26' 469.88 <0.05 >1.2 03:58:00.02 FRB 130729 2013/07/29 13h41' -05°59' 861 <4 >3.5 09:01:52.64 FRB 110523 2011/05/23 21h45' -00°12' 623.30 1.73 0.6 700-900 MHz at Green Bank telescope, detection circular and linear polarization. FRB 150418 2015/04/18 07h16' −19° 00′ 776.2 0.8 2.4 Detection of linear polarization. The origin of the burst is disputed. FRB 160317 2016/03/17 07:53:47 −29:36:31 1165(±11) 21 >3.0 UTMOST, Decl ± 1.5° FRB 160410 2016/04/10 08:41:25 +06:05:05 278(±3) 4 >7.0 UTMOST, Decl ± 1.5° FRB 160608 2016/06/08 07:36:42 −40:47:52 682(±7) 9 >4.3 UTMOST, Decl ± 1.5° ﬁrst by ASKAP, high ﬂuence ~58 Jy ms. FRB 170107 2017/01/07 11:23 -05:01 609.5(±0.5) 2.6 27±4 In Leo. Galactic latitude 51°, Distance 3.1 Gpc, isotropic energy ~3 x 1034 J Quantum Gravity Phenomenology Francesca Vidotto TRANSIENTS AT SKA

Quantum Black Holes Francesca Vidotto DETECTION ON EARTH?

Quantum Gravity Phenomenology Francesca Vidotto INTEGRATED EMISSION 1 1 4 1 2 2⇡ (1 + z) H ⌦⇤ 3 meas 0 1 2 1 sinh (1 + z) 1 . (6) high 1 1/2 1 4 ⇠ kBT (0.3g ) 2 1 ⌦M 2 meas 2⇡ (1 + z) "6Hk0⌦ ⇤ 1 "✓⌦⇤ ◆ 3 ## ⇤ 2 high 1 1 1/2 sinh (1 + z) . (6) ⇠ kBT (0.3g ) 2 "6k⌦ " ⌦M ## ⇤ ⇤ ✓ ◆

This shows that although the mean wavelength does It is worth considering the n(R) term a bit more in decreases as a function of k in both cases, it does not detail. If one denotes by dn the initial di↵erential This shows that although the mean wavelength does1 It is worth considering the dMdVn(R) term a bit more in follow the same general behavior. It scales with k 2 mass spectrum of primordialdn black holes per unit volume, decreases as a function of k in both cases,1 it does not detail. If one denotes by dMdV the initial di↵erential 4 1 forfollow the low the energy same general component behavior. and as Itk scales for with thek high 2 massit is spectrum possible to of primordial define n(R black) as: holes per unit volume, 1 energyfor the one. low energy component and as k 4 for the high it is possible to define n(R) as: energy one. M(t+t) dn n(R)= dM, (8) The following conclusions can be drawn: M(t+t) dndMdV n(R)= ZM(t) dM, (8) The following conclusions can be drawn: dMdV The low energy channel leads to a better single- ZM(t) • eventThe low detection energy channel than the leadshigh to energy a betterchannel. single- leading to •Althoughevent detection lower energy than the diluteshigh the energy signalchannel. in a leading to higherAlthough astrophysical lower energy background, dilutes this the e signal↵ect is in over- a dn t n(R) dn t , (9) compensatedhigher astrophysical by the largerbackground, amount this of e photons.↵ect is over- n(R) ⇡ dMdV 8,k (9) compensated by the larger amount of photons. ⇡ dMdV 8k The di↵erence of maximal distances between the where the mass spectrum is evaluated for the mass cor- • low-Theand di↵erencehigh energy of maximalchannels distances decreases between for higher the whereresponding the mass to a spectrum time (t is evaluatedR ). If one for assumes the mass that cor- pri- INTEGRATED• EMISSION H R c valueslow- and of khigh, i.e. energy for longerchannels black-hole decreases lifetimes. for higher respondingmordial black to a time holes (t areH directlyc ). If one formed assumes by the that collapse pri- Barrau, Bolliet, Vidotto, Weimer 1507.1198 values of k, i.e. for longer black-hole lifetimes. mordialof density black fluctuations holes are directly with a formed high-enough by the density collapse con- In the low energy channel, for the smaller⌧ valuesm2 of density fluctuations with a high-enough density con- ⇠ trast in the early Universe, the initial mass spectrum is • ofInk, the a singlelow energy bouncechannel, can be for detected the smaller arbitrary values far trast in the early Universe, the initial mass spectrum is • of k, a single bounce can be detected arbitrary far directly related to the equation of state of the Universe away inLow the Universe.energy channel Highdirectlyat energy the formation related channel to theepoch. equation It is given of state by of [18, the 19]: Universe away in the Universe. at the formation epoch. It is given by [18, 19]: k=0.05 In all cases, the distances are large enough and ex- direct decayed • In all cases, the distances are large enough and ex- 1+3w perimental detection is far from being hopeless. dn 1 • dn = ↵M11+3 w1+w , (10) perimental detection is far fromk=0.05 being hopeless. k=100 = ↵M 1+w , (10) dMdVdMdV III. INTEGRATED EMISSION where w = p/⇢. In a matter-dominated universe the III. INTEGRATED EMISSION where w = p/⇢. In a1+3 matter-dominatedw universe the 1+3w exponentexponent 1 1 1+wtakestakes the the value value = =5/2.5/2. direct+decayed⌘ 1+w enlarged TheThe normalization normalization⌘ coe coecientcient↵ ↵willwill be be kept kept unknown unknown InIn addition addition to to the the instantaneous instantaneous spectrum emitted emitted by by a a asas it it depends depends on on the the details details of of the the black black hole hole formation formation singlesingle bouncing bouncing black black hole, hole, it it is is interesting interesting to to consider consider the the mechanism.mechanism. For For a a sizeable sizeable amount amount of of primordial primordial black black possiblepossible di di↵↵useuse background background due due to the integrated integrated emis- emis- holesholes to to form, form, the the power power spectrum spectrum normalized normalized on on the the sionsion of of a a population population of of bouncing bouncing blackk=10000 holes. holes. Formally, Formally, k=109 CMBCMB needs needs to to be be boosted boosted at at small small scales. scales. This This can can thethe number number of of measured measured photons photons detected per per unit unit time, time, bebe achieved, achieved, for for example, example, through through Staobinsky’s Staobinsky’s broken broken unitunit energy energy and and unit unit surface, surface, can can be written written as: as: scalescale invariance invariance (BSI) (BSI) scenario. scenario. The The idea idea is that is that the the dNdN massmass spectrum spectrumcharacteristic takes takes shape: a high a high distorted enough enough black value valuebody in the in the relevant relevant mesmes == ((1+((1+zz))E,RE,R)) nn(R)) AccAcc AbsAbs((E,RE,R))dR,dR, dEdtdS indind · · · rangerange whereas whereas it it is is naturally naturally suppressed suppressed at smallat small masses masses dEdtdS · · · depends on how much DM are PBL ZZ (7)(7) byby inflation inflation and and at at large large masses masses by by the the BSI BSI hypothesis. hypothesis. wherewhereindind(E,R(E,R)) denotes denotes the the individual individual flux flux emitted emitted WeWe will will not not study study those those questions questions here here and and just just consider consider by a single bouncing black hole at distance R and at thethe shape shape of of the the resulting resulting emission, emission, nor nor its its normalisation normalisation Quantumby a singleGravity Phenomenology bouncing black hole at distance R and at Francesca Vidotto energyenergyEE, ,AccAccisis the the angular angular acceptance acceptance of of the the detector detector whichwhich depends depends sensitively sensitively on on the the bounds bounds of ofthe the mass mass multipliedmultiplied by by its its e eciencyciency (in (in principle principle this this is is also also a a spectrum,spectrum, that that are are highly highly model-dependent. model-dependent. As As this this part part functionfunction of ofEEbutbut this this will will be be ignored ignored here), here), AbsAbs((E,RE,R)) ofof the the study study is is devoted devoted to to the the investigation investigation of the of the shape shape isis the the absorption absorption function, function, and and n(R)) is is the the number number of of ofof the the signal, signal, the they axisy axis on on the the figures figures are are not not normalized. normalized. blackblack holes holes bouncing bouncing at at distance distance R perper unit unit time time and and volume.volume. The The distance distance RR andand the the redshift redshift zz enteringentering Fortunately,Fortunately, the the results results are are weakly weakly dependent dependent upon upon thethe above above formula formula are are linked. linked. The The integration integration has has to to thethe shape shape of of the the mass mass spectrum. spectrum. This This is illustrated is illustrated in in be carried out up to cosmological distances and it is Fig. 5 where di↵erent hypothesis for the exponent are be carried out up to cosmological distances and it is Fig. 5 where di↵erent hypothesis for the exponent are therefore necessary to use exact results behind the linear displayed. The resulting electromagnetic spectrum is therefore necessary to use exact results behind the linear displayed. The resulting electromagnetic spectrum is approximation. The energy is also correlated with R almost exactly the same. Therefore we only keep one approximation.as the distance fixes The the energy bounce is also time correlated of the black with holeR casealmost ( = exactly5/2, corresponding the same. Therefore to w =1 we/3). only The keep black one as the distance fixes the bounce time of the black hole case ( = 5/2, corresponding to w =1/3). The black which, subsequently, fixes the emitted energy. holes are assumed to be uniformly distributed in the which, subsequently, fixes the emitted energy. Universe,holes are which assumed is a to meaningful be uniformly hypothesis distributed as long in as the Universe, which is a meaningful hypothesis as long as

5 5 1 1 4 1 2 meas 2⇡ (1 + z) H0 1 ⌦⇤ 3 2 high 1 1 1/2 sinh (1 + z) . (6) ⇠ kBT (0.3g ) 2 "6k⌦ " ⌦M ## ⇤ ⇤ ✓ ◆

This shows that although the mean wavelength does It is worth considering the n(R) term a bit more in decreases as a function of k in both cases, it does not detail. If one denotes by dn the initial di↵erential 1 dMdV follow the same general behavior. It scales with k 2 mass spectrum of primordial black holes per unit volume, 1 for the low energy component and as k 4 for the high it is possible to deﬁne n(R) as: energy one. 1 M(t+t) 1 4 dn 1 2 measThe following2⇡ (1 + conclusionsz) H0 can be drawn:1 ⌦⇤ 3 n(R)= dM, (8) 2 dMdV high 1 1 1/2 sinh (1 + z) . M((6)t) ⇠ kBT (0.3g ) 2 "6k⌦ " ⌦M ## Z The low energy⇤ channel⇤ leads to✓ a better◆ single- • event detection than the high energy channel. leading to

Although lower energy1 dilutes the signal in a 1 4 dn t 1 higher astrophysical2 background, this e↵ect is over- meas This2⇡ shows(1 + thatz) althoughH0 the1 mean⌦ wavelength⇤ does3 It is worth considering the n(R) term a bitn more(R) in , (9) 2 high 1 1 1/2 sinh compensated(1 by + z the) larger. amount of photons. (6) dn ⇡ dMdV 8k decreases⇠ kBT (0 as.3g a function) 2 "6k⌦ of k in both" ⌦ cases,M it does not## detail. If one denotes by dMdV the initial di↵erential ⇤ ⇤ ✓ ◆ 1 follow the same general behavior. It scales with k 2 mass spectrum of primordial black holes per unit volume, The di↵erence1 of maximal distances between the where the mass spectrum is evaluated for the mass cor- for the low energy component• and as k 4 for the high it is possible to define n(R) as: R low- and high energy channels decreases for higher responding to a time (tH c ). If one assumes that pri- energy one. values of k, i.e. for longer black-hole lifetimes. mordial black holes are directly formed by the collapse This shows that although the mean wavelength does It is worth considering the n(R) term a bit more inM(t+oft) densitydn fluctuations with a high-enough density con- dn n(R)= dM, (8) decreases as a function of k in bothThe following cases, it conclusionsdoes not candetail. beIn drawn: the If onelow denotes energy channel, by forthe the initial smaller di↵erential values trast in the early Universe, the initial mass spectrum is 1 PBH• MASS SPECTRUMdMdV M(t) dMdV follow the same general behavior. It scales with k 2 massof spectrumk, a single of primordial bounce can black be detected holes per arbitrary unit volume,Z far The low1 energy channel leads to a better single- directly related to the equation of state of the Universe 4 away in the Universe. for the low energy component and• aseventk detectionfor the high thanit the is possiblehigh energy to definechannel.n(R) as:leading to at the formation epoch. It is given by [18, 19]: energy one. Although lower energy dilutes the signal in a In all cases, the distancesM(t+t are) large enough and ex- higher astrophysical background,• this e↵ect is over- dn dn t dn 1 1+3w perimentaln(R detection)= is far from beingdM, hopeless.n(R(8)) , =(9)↵M 1+w , (10) The following conclusions can be drawn:compensated by the larger amount of photons. dMdV ⇡ dMdV 8k dMdV ZM(t) The low energy channel leads to a better single- • The di↵erence of maximalleading distances toIII. between INTEGRATED the where EMISSION the mass spectrum iswhere evaluatedw = forp/ the⇢. mass In a cor- matter-dominated universe the event detection than the high• energy channel. Low energy channel R 1+3w low- and high energy channels decreases for higher responding to a time (tH exponent). If one assumes1 that pri- takes the value = 5/2. Although lower energy dilutes the signal in a c 1+w values of k, i.e. for longer black-hole lifetimes. mordial black holes are directlyThe formed normalization by⌘ the coecollapsecient ↵ will be kept unknown higher astrophysical background, this e↵ect is over- In addition to the instantaneousdn spectrumt emitted by a n(R) of density, fluctuations(9) withas a high-enough it depends on density the details con- of the black hole formation compensated by the larger amount of photons.1 ⇡ dMdV 8k behavior. It scalesIn the withlowk 2 energyfor thechannel, lowsingle energy bouncing for compo- the smaller black hole, values it is interesting to consider the • 1 trast in the early Universe, themechanism. initial mass For spectrum a sizeable is amount of primordial black of4 k, a single bounce canpossible be detected di↵use arbitrary background far due to the integrated emis- The di↵erence ofnent maximal and as distancesk for the between high energy the one.Thewhere following the mass spectrum is evaluateddirectly for related the mass to the cor- equationholes of to state form, of the the Universe power spectrum normalized on the conclusions canaway be drawn: in the Universe. sion of a population of bouncing black holes. Formally, • low- and high energy channels decreases for higher responding to a time (t R ).at If the one formation assumes that epoch. pri- It isCMB given needs by [18, to 19]: be boosted at small scales. This can the number of measured photonsH c detected per unit time, values of k, i.e. for longerThe black-holelow energyIn all cases, lifetimes.channel the leads distances to amordial better are large single- black enough holes and are ex- directly formed by the collapse be achieved, for example, through Staobinsky’s broken • unit energy and unit surface, can be written as: 1+3w Different mass spectra • event detectionperimental than the detectionhigh energy is farofchannel. density from being fluctuations Al- hopeless. with a high-enough densitydn con- scale1 invariance (BSI) scenario. The idea is that the = ↵M 1+w , (10)gives qualitatively In the low energy channel,though for a the lower smaller energy values dilutes thedNtrast signal in the in early a Universe, the initial mass spectrumdMdV is mass spectrum takes a high enough value in the relevant • of k, a single bounce can be detected arbitrary far mes = ((1+z)E,R) n(R) Acc Abs(E,R)dR, same diffuse emission… higher astrophysical background, thisdEdtdSdirectly e↵ect is related over-ind to the equation· of state· · of the Universe range whereas it is naturally suppressed at small masses away in the Universe. compensated byIII. the larger INTEGRATED amount of photons. EMISSIONZ where w = p/⇢. In a matter-dominated universe the at the formation epoch. It is given by [18, 19]: (7)1+3w by inflation and at large masses by the BSI hypothesis. exponent 1 1+w takes the value = 5/2. In all cases, the distancesThe are di↵erence large enough of maximal and ex- distanceswhere betweenind(E,R the ) denotes the individual flux⌘ emitted We will not study those questions here and just consider • The1+3 normalizationw coecient ↵ will be kept unknown perimental detection• is far fromIn addition being hopeless. to the instantaneousby a single spectrum bouncing emitteddn black by a hole1 at distance R and at the shape of the resulting emission, nor its normalisation low- and high energy channels decreases for higher = ↵M as it1+ dependsw , on the(10) details of the black hole formation single bouncing black hole, itenergy is interestingE, Acc tois consider thedMdV angular the acceptance of the detector which depends sensitively on the bounds of the mass values of k, i.e. for longer black-hole lifetimes. mechanism. For a sizeable amount of primordial black possible di↵use backgroundmultiplied due to the by integrated its eciency emis- (in principle this is also a spectrum, that are highly model-dependent. As this part holes to form, the power spectrum normalized on the III. INTEGRATEDIn thesion EMISSIONlow of aenergy populationchannel, of for bouncing thefunctionwhere smaller blackw of values=E holes.p/but⇢. this Formally, In will a matter-dominated be ignored here), universeAbs(E,R the) of the study is devoted to the investigation of the shape • of k, a single bounce can be detected arbitrary far 1+3w CMB needs to be boosted at small scales. This can the number of measured photonsisexponent the detected absorption per function, unit1 time,1+w andtakesn(R the) is value the number = 5 of/2. of the signal, the y axis on the figures are not normalized. away in the Universe. The normalization⌘FIG. coe 5:cientLow energybe↵ will achieved,channel be kept forsignal unknown example, calculated through for di↵erent Staobinsky’s broken In addition to the instantaneousunit spectrum energy and emitted unit by surface, a Quantumblack can Gravity be holes written Phenomenology bouncing as: at distance R per unit time and Francesca Vidotto as it depends on themass details spectra. ofscale As the the black invariance mass hole spectrum formation (BSI) is not scenario. normalized, The the idea is that the single bouncing black hole, itIn is all interesting cases, the to distances consider are the largevolume. enough and The ex- distance R and the redshift z entering Fortunately, the results are weakly dependent upon • dNmes mechanism. For aunits sizeable of the amounty axismass are spectrum of arbitrary. primordial takes black a high enough value in the relevant possible di↵use backgroundperimental due to the detection= integratedind is((1+ far emis- fromz)E,R beingthe) aboven hopeless.(R) Acc formulaAbs(E,R are) linked.dR, The integration has to the shape of the mass spectrum. This is illustrated in dEdtdS range whereas it is naturally suppressed at small masses beholes· carried to· form, out· up the to power cosmological spectrum distances normalized and on it the is Fig. 5 where di↵erent hypothesis for the exponent are sion of a population of bouncing black holes.Z Formally, (7) by inflation and at large masses by the BSI hypothesis. CMB needs to bewhere boosted the mass at small spectrum scales. is evaluated This can for the mass cor- the number of measured photonswhere detected per(E,R unit) denotes time, therefore the individual necessary flux to emitted use exact resultsWe will behind not study the thoselinear questionsdisplayed. here and The just resulting consider electromagnetic spectrum is III. INTEGRATEDind EMISSIONbe achieved, for example,responding through to a time Staobinsky’s (t R ). The broken shape of the mass unit energy and unit surface, can be written as: approximation. The energy isthe also shape correlatedH of thec resulting with R emission,almost nor exactly its normalisation the same. Therefore we only keep one by a single bouncing black holescale at invariance distance (BSI)Rspectrumand scenario. at obviously The depends idea is on that the the details of the for- energy E, Acc is the angularas acceptance the distance of fixesthe detector the bouncewhich time of depends the black sensitively hole oncase the ( bounds= 5/2, of corresponding the mass to w =1/3). The black dNmes In addition to the instantaneous spectrumwhich,mass emitted subsequently, spectrum by a takesmation fixes a high the mechanism enough emitted value (see energy. [39] in the for relevant a review onholes PBHs are and assumed to be uniformly distributed in the = ind((1+z)E,R)multipliedn(R) Acc byAbs its(E,R e)ciencydR, (in principle this is also a spectrum, that are highly model-dependent. As this part dEdtdS single bouncing· black· · hole, it is interestingrange to consider whereas the it isinflation). naturally As suppressed an example, at we small shall masses assume thatUniverse, primor- which is a meaningful hypothesis as long as Z possible difunction↵use background of E but due this to(7) will the be integratedby ignored inflation emis- here), andAbs atdial large(E,R black masses) holesof by the are the study directly BSI is hypothesis. formed devoted by to the the collapse investigation of of the shape is the absorption function, and n(R) is the number of of the signal, the y axis on the figures are not normalized. where ind(E,R) denotession of the a population individual of flux bouncing emitted black holes.We will Formally, not studydensity those questions fluctuations here with and a high-enoughjust consider density contrast by a single bouncingthe black number holeblack of at measured holes distance bouncing photonsR and detectedat at distancethe per shape unitR per time, of unit the resulting timein the and early emission, Universe. nor The its normalisation initial mass spectrum5 is then energy E, Acc is the angularunit energy acceptancevolume. and unit The of surface, the distance detector can beR writtenandwhich the as: depends redshift sensitivelyz directlyentering related on the toFortunately, bounds the equation of the the of state results mass of arethe Universe weakly dependent upon multiplied by its eciency (inthe principle above formula this is also are linked. a spectrum, The integration that areat highly has the formation to model-dependent.the epoch. shape It of is As the given this mass by part [33, spectrum. 40]: This is illustrated in dNmes be carried out up to cosmological distances and it is Fig. 5 where di↵erent hypothesis for the exponent are function of E but this will be= ignoredind here),((1+z)AbsE,R()E,Rn(R)) A(ofE) thef(E,R study)dR, is devoted to the investigation of the shape dEdtdS · · · dn 1 1+3w is the absorption function, andthereforeZn(R) is necessary the number to use of exactof the results signal, behind the y theaxis linear on the figuresdisplayed. are not= ↵ TheM normalized. resulting 1+w , electromagnetic(14) spectrum is approximation. The energy is also correlated(11) with R almostdMdV exactly the same. Therefore we only keep one black holes bouncingwhere at distance (E,RR per) denotes unit time the individual and flux emitted indas the distance fixes the bounce time of the black hole case ( = 5/2, corresponding to w =1/3). The black volume. The distancebyR aand single the bouncing redshift blackz entering hole at distanceFortunately,R and at thewhere resultsw = arep/ weakly⇢. In a dependent matter-dominated upon universe the which, subsequently, fixes the emitted energy. exponent holes1 are1+3 assumedw takes the to value be uniformly = 5/2. distributed in the the above formula areenergy linked.E, A The(E) is integration the angular has acceptance to the of the shape detector of the mass spectrum.⌘ This 1+ isw illustrated in be carried out up tomultiplied cosmological by its distances eciency, andf(E,R it is) isFig. the absorption 5 where di↵erentThe hypothesis normalizationUniverse, for coe the exponent whichcient ↵ iswill a meaningfulare be kept unknown hypothesis as long as therefore necessary to usefunction, exact and resultsn(R) behind is the number the linear of blackdisplayed. holes bouncing The resultingas it depends electromagnetic on the details spectrum of the black is hole formation approximation. Theat energy distance is alsoR per correlated unit time with and volume.R almost The distance exactly themechanism. same. Therefore For a sizeable we only amount keep of one primordial black holes to form,5 the power spectrum normalized on the as the distance fixes theR and bounce the time redshift of thez entering black hole the abovecase formula ( = are5/2, corresponding to w =1/3). The black linked. The integration has to be carried out up to CMB needs to be boosted at small scales. The formula which, subsequently, fixes the emitted energy. holes are assumedgiven to be above uniformly might therefore distributed be correct in the only within a cosmological distances and it is thereforeUniverse, necessary which to is a meaningful hypothesis as long as use exact results behind the linear approximation. The limited interval of masses. The idea is that the mass energy is also correlated with R as the distance fixes the spectrum takes a high enough value in the relevant bounce time of the black hole which, subsequently,5 fixes range whereas it is naturally suppressed at small masses the emitted energy. by inflation. We will neither study those questions here (focusing on the shape of the resulting emission), It is worth considering the n(R) term a bit more into nor the normalisation issues which depend sensitively dn on the bounds of the mass spectrum, that are highly the details. If one denotes by dMdV the initial di↵erential mass spectrum of primordial black holes per unit volume, model-dependent. As this part of the study is devoted it is possible to define n(R) as: to the investigation of the shape of the signal, the y axis on the figures are not normalized. As we show M(t+t) dn below, the shape of the signal is quite independent on n(R)= dM, (12) the shape of the mass spectrum, so Eq. 14 does not play dMdV ZM(t) any significant role for the spectra computer. leading to The results are indeed very weakly dependent upon dn t the shape of the mass spectrum. This is illustrated in n(R) , (13) ⇡ dMdV 8k Fig. 5 where di↵erent hypothesis for the exponent are

6 GeV FERMI EXCESS Schutten, Barrau, Bolliet, Vidotto 1606.08031 4

by Low energy channel other other obs =(1+z)emitted. (6) Consider the longest possible lifetime of a quantum black hole. The specific redshift dependence of our model makes it possibly testable against other proposals. Obvi- ously, detecting such a signal from far away galaxies is challenging but this work might precisely motivate some experimental prospects for the next generation of gamma-ray satellites. Number of secondary gamma-rays is higher than the number of primary gamma-rays, but their The order of magnitude of the number of bouncing spectral energy density is much black holes in the galactic center region required to ac- lower. count for the observed flux is 100 per second. The associated mass is negligible when compared to the expected dark matter density, even when integrated over a long time interval. If the mass spectrum of primordial black FIG. 3. Best fit to the Fermi excess with bouncing black holes was known, which is not the case, it would in prin- Quantum Gravity Phenomenology Francesca Vidotto holes. ciple be possible to fix the total mass associated with bouncing black holes. As a reasonable toy model, let us assume that the mass spectrum is given by

DISCRIMINATION WITH DARK MATTER AND 2 d N ↵ MASS SPECTRUM = pM . (7) dMdV

The model presented in this work is unquestionably If the number of exploding black holes required to explain quite exotic when compared to astrophysical hypotheses. the data on a time interval d⌧ is Nexp, one can estimate But the important point is than it can, in principle, be the mass variation associated, distinguished both from astrophysical explanations and d⌧ from other “beyond the standard model” scenarios. The dM = . (8) 8kM reason for that is the redshift dependance. When looking at a galaxy at redshift z, the measured energy of With M0 the mass corresponding to a black hole explod- the signal emitted either by decaying WIMPS or by as- ing now, one then has trophysical objects will be E/(1 + z) if the rest-frame energy is E. But this is not true for the bouncing black M0+dM N = pM ↵dM. (9) holes signal. The reason for this is that black holes that exp M0 have bounced far away and are observed now must have Z a smaller bouncing time and therefore a smaller mass. This allows, in principe, to determine p and therefore to Their emission energy – in the low energy channel we are normalize the spectrum. considering in this article – is therefore higher and this partly compensates for the redshift e↵ect. Following [9], we can write down the observed wavelength of the signal CONCLUSION from a host galaxy at redshift z, taking into account both the expansion of the universe and the change of bouncing Black holes could bounce once they have reached the time, as: “Planck star” stage. This is a well motivated quantum gravity idea. In this article, we have shown that this 2Gm phenomenon could explain the GeV excess measured by BH (1 + z) (5) obs ⇠ c2 ⇥ the Fermi satellite. This would open the fascinating pos- 1 1/2 sibility to observe (non perturbative) quantum gravity H0 1 ⌦⇤ 3/2 processes at energies 19 orders of magnitude below the 1/2 sinh (z + 1) , v ⌦M u6 k⌦⇤ " # Planck scale. Interestingly the explanation we suggest is u ✓ ◆ t fully self consistant in the sense that the hadronic “noise” where we have reinserted the Newton constant G and due to decaying pions remains much below the observed the speed of light c; H0, ⌦⇤ and ⌦M being the Hubble background. Unquestionably, there are other – less exotic constant, the cosmological constant, and the matter den- – ways to explain the Fermi excess. But the important sity. On the other hand, for other signals the measured point we have made is that there is speciﬁc redshift de- wavelength this just related to the observed wavelength pendance of this model which, in principle, can lead to a …THE BEST IS YET TO COME! DETECTION ON EARTH?

Quantum Gravity Phenomenology Francesca Vidotto RADIO, MILLIMITERS AND SUB-MILLIMETER ASTRONOMY

10-20m

Quantum Gravity Phenomenology Francesca Vidotto NEWS IN FOCUS

ASTROPHYSICS Astronomers grapple with new era of fast radio bursts RADIO,Signals have progressedMILLIMITERS from astronomical AND peculiarity SUB-MILLIMETER to mainstream research area. ASTRONOMY

signals, lasting no more than a few thousandths of a second. They seem to come from sources across the sky and beyond our Galaxy. Some last longer than others, and the light from a few is polarized. A discovery last year caused further excitement. Astronomers reported2 that they had found a repeating FRB — a surprise,

ANDRE RENARD/DUNLAP INSTITUTE RENARD/DUNLAP ANDRE because all the other signals had been one-off blips. And in January this year, its origin was identified3: a faint, distant dwarf galaxy around 780 megaparsecs (2.5 billion light years) away, in a star-forming region that also hums with a steady radio source. The repeater has gone some way to focusing the FRB field, says Edo Berger, an astronomer CHIME at Harvard University in Cambridge, Mas- sachusetts. Astronomers have now observed nearly 200 signals from it; details of 20 have been published. It bolsters the hypothesis that The CHIME radio observatory in Canada will start looking for fast radio bursts this year. the signals are extragalactic, something most FRB researchers now agree on, and its location BY ELIZABETH GIBNEY origins and precise distances. The trajectory is reshaping theories about possible causes. mirrors that of astronomers 20 years ago when Dwarf galaxies host fewer stars than most, ne of the most perplexing phenom- they were getting to grips with γ-ray bursts, so tracking an FRB to one is surprising, says ena in astronomy has come of age. which are now a staple of astronomical observa- Berger. He thinks that the unusual environment The fleeting blasts of energetic cosmic tion, says Bing Zhang, a theoretical astrophysi- is more than coincidence, and that FRBs may Oradiation of unknown cause, now known as fast cist at the University of Nevada, Las Vegas. come from super-powerful magnetars — dense, radio bursts (FRBs), were first detected a decade “The meeting has really focused the field a magnetic stars thought to form after an abnor- ago. At the time, many astronomers dismissed lot,” says Sarah Burke Spolaor, an astronomer mally massive explosion, such as an extremely the seemingly random blasts as little more than at West10 Virginia-20m University in Morgantown. energetic supernova. Studies suggest that such glitches. And although key facts, such as what Debates continue over how to root out detec- events seem to be more common in dim dwarf causes them, are still largely a mystery, FRBs tion bias and coordinate observations and on galaxies, he says. Others think the bursts might are now accepted as a genuine class of celestial what can be learnt by studying patterns in the come from active galactic nuclei, regions at signal and have spawned a field of their own. existing FRB population. the centres of some galaxies that are thought The passage was marked this month by the The first FRB was co-discovered1 in 2007 by to host supermassive black holes. Streams of first major meeting on FRBs, held in Aspen, astronomer Duncan Lorimer at West Virginia plasma from these could comb nearby pulsars Colorado, on 12–17 February. As well as cel- University. He found in archived pulsar data to produce FRBs, says Zhang, which could also ebrating a fleet of searches for the signals, the a 5-millisecond radio frequency burst that was explain a recent, although tentative, observation meeting’s 80 delegates grappled with how best so bright it couldn’t be ignored. Astronomers of a faint γ-ray burst coinciding with an FRB. to design those hunts and pin down the signals’ have since seen 25 FRBs. All are brief radio At the meeting, some astronomers proposed

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Images of the ● These seven alien worlds could Migration special: month: fake help to explain how planets form a researcher seeks MORE stars, panda go.nature.com/2lpkldq refuge; smart ONLINE suits and a ● Bees learn football from their borders; and

dancing octopus buddies go.nature.com/2lupfu5 climate migration BARATHIEU 2017/GABRIEL YEAR go.nature. ● UK universities unlikely to be lured nature.com/nature/ com/2mab8ue to France go.nature.com/2lpxpwr podcast THE OF PHOTOGRAPHER UNDERWATER Quantum Gravity Phenomenology Francesca Vidotto 16 | NATURE | VOL 543 | 2 MARCH 2017 ǟ ƐƎƏƗ !,(++ - 4 +(2'#12 (,(3#"Ʀ / 13 .$ /1(-%#1 341#ƥ ++ 1(%'32 1#2#15#"ƥ ǟ ƐƎƏƗ !,(++ - 4 +(2'#12 (,(3#"Ʀ / 13 .$ /1(-%#1 341#ƥ ++ 1(%'32 1#2#15#"ƥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ ɥ NEWS IN FOCUS

ASTROPHYSICS Astronomers grapple with new era of fast radio bursts RADIO,Signals have progressedMILLIMITERS from astronomical AND peculiarity SUB-MILLIMETER to mainstream research area. ASTRONOMY

ANDRE RENARD/DUNLAP INSTITUTE RENARD/DUNLAP ANDRE because all the other signals had been one-off blips. And in January this year, its origin was identified3: a faint, distant dwarf galaxy around 780 megaparsecs (2.5 billion light years) away, in a star-forming region that also hums with a steady radio source. The repeater has gone some way to focusing the FRB field, says Edo Berger, an astronomer CHIME at Harvard UniversitySKA in Cambridge, Mas- sachusetts. Astronomers have now observed nearly 200 signals from it; details of 20 have been published. It bolsters the hypothesis that The CHIME radio observatory in Canada will start looking for fast radio bursts this year. the signals are extragalactic, something most FRB researchers now agree on, and its location BY ELIZABETH GIBNEY origins and precise distances. The trajectory is reshaping theories about possible causes. mirrors that of astronomers 20 years ago when Dwarf galaxies host fewer stars than most, ne of the most perplexing phenom- they were getting to grips with γ-ray bursts, so tracking an FRB to one is surprising, says ena in astronomy has come of age. which are now a staple of astronomical observa- Berger. He thinks that the unusual environment The fleeting blasts of energetic cosmic tion, says Bing Zhang, a theoretical astrophysi- is more than coincidence, and that FRBs may Oradiation of unknown cause, now known as fast cist at the University of Nevada, Las Vegas. come from super-powerful magnetars — dense, radio bursts (FRBs), were first detected a decade “The meeting has really focused the field a magnetic stars thought to form after an abnor- ago. At the time, many astronomers dismissed lot,” says Sarah Burke Spolaor, an astronomer mally massive explosion, such as an extremely the seemingly random blasts as little more than at West10 Virginia-20m University in Morgantown. energetic supernova. Studies suggest that such glitches. And although key facts, such as what Debates continue over how to root out detec- events seem to be more common in dim dwarf causes them, are still largely a mystery, FRBs tion bias and coordinate observations and on galaxies, he says. Others think the bursts might are now accepted as a genuine class of celestial what can be learnt by studying patterns in the come from active galactic nuclei, regions at signal and have spawned a field of their own. existing FRB population. the centres of some galaxies that are thought The passage was marked this month by the The first FRB was co-discovered1 in 2007 by to host supermassive black holes. Streams of first major meeting on FRBs, held in Aspen, astronomer Duncan Lorimer at West Virginia plasma from these could comb nearby pulsars Colorado, on 12–17 February. As well as cel- University. He found in archived pulsar data to produce FRBs, says Zhang, which could also ebrating a fleet of searches for the signals, the a 5-millisecond radio frequency burst that was explain a recent, although tentative, observation meeting’s 80 delegates grappled with how best so bright it couldn’t be ignored. Astronomers of a faint γ-ray burst coinciding with an FRB. to design those hunts and pin down the signals’ have since seen 25 FRBs. All are brief radio At the meeting, some astronomers proposed

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ASTROPHYSICS Astronomers grapple with new era of fast radio bursts RADIO,Signals have progressedMILLIMITERS from astronomical AND peculiarity SUB-MILLIMETER to mainstream research area. ASTRONOMY

ANDRE RENARD/DUNLAP INSTITUTE RENARD/DUNLAP ANDRE because all the other signals had been one-off blips. And in January this year, its origin was identified3: a faint, distant dwarf galaxy around 780 megaparsecs (2.5 billion light years) away, in a star-forming region that also hums with a steady radio source. The repeater has gone some way to focusing the FRB field, says Edo Berger, an astronomer CHIME at Harvard UniversitySKA in Cambridge, Mas- sachusetts. Astronomers have now observed nearly 200 signals from it; details of 20 have been published. It bolsters the hypothesis that The CHIME radio observatory in Canada will start looking for fast radio bursts this year. the signals are extragalactic, something most FRB researchers now agree on, and its location BY ELIZABETH GIBNEY origins and precise distances. The trajectory is reshaping theories about possible causes. mirrors that of astronomers 20 years ago when Dwarf galaxies host fewer stars than most, ne of the most perplexing phenom- they were getting to grips with γ-ray bursts, so tracking an FRB to one is surprising, says ena in astronomy has come of age. which are now a staple of astronomical observa- Berger. He thinks that the unusual environment The fleeting blasts of energetic cosmic tion, says Bing Zhang, a theoretical astrophysi- is more than coincidence, and that FRBs may Oradiation of unknown cause, now known as fast cist at the University of Nevada, Las Vegas. come from super-powerful magnetars — dense, radio bursts (FRBs), were first detected a decade “The meeting has really focused the field a magnetic stars thought to form after an abnor- ago. At the time, many astronomers dismissed lot,” says Sarah Burke Spolaor, an astronomer mally massive explosion, such as an extremely the seemingly random blasts as little more than at West10 Virginia-20m University in Morgantown. energetic supernova. Studies suggest that such glitches. And although key facts, such as what Debates continue over how to root out detec- events seem to be more common in dim dwarf causes them, are still largely a mystery, FRBs tion bias and coordinate observations and on galaxies, he says. Others think the bursts might are now accepted as a genuine class of celestial what can be learnt by studying patterns in the come from active galactic nuclei, regions at signal and have spawned a field of their own. existing FRB population. the centres of some galaxies that are thought The passage was marked this month by the The first FRB was co-discovered1 in 2007 by to host supermassive black holes. Streams of first major meeting on FRBs, held in Aspen, astronomer Duncan Lorimer at West Virginia plasma from these could comb nearby pulsars Colorado, on 12–17 February. As well as cel- University.ALMA He found in archived pulsar data to produce FRBs, says Zhang, which could also ebrating a fleet of searches for the signals, the a 5-millisecond radio frequency burst that was explain a recent, although tentative, observation meeting’s 80 delegates grappled with how best so bright it couldn’t be ignored. Astronomers of a faint γ-ray burst coinciding with an FRB. to design those hunts and pin down the signals’ have since seen 25 FRBs. All are brief radio At the meeting, some astronomers proposed

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ASTROPHYSICS Astronomers grapple with new era of fast radio bursts RADIO,Signals have progressedMILLIMITERS from astronomical AND peculiarity SUB-MILLIMETER to mainstream research area. ASTRONOMY

ANDRE RENARD/DUNLAP INSTITUTE RENARD/DUNLAP ANDRE because all the other signals had been one-off blips. And in January this year, its origin was identified3: a faint, distant dwarf galaxy around 780 megaparsecs (2.5 billion light years) away, in a star-forming region that also hums with a steady radio source. The repeater has gone some way to focusing the FRB field, says Edo Berger, an astronomer CHIME at Harvard UniversitySKA in Cambridge, Mas- sachusetts. Astronomers have now observed nearly 200 signals from it; details of 20 have been published. It bolsters the hypothesis that The CHIME radio observatory in Canada will start looking for fast radio bursts this year. the signals are extragalactic, something most FRB researchers now agree on, and its location BY ELIZABETH GIBNEY origins and precise distances. The trajectory is reshaping theories about possible causes. mirrors that of astronomers 20 years ago when Dwarf galaxies host fewer stars than most, ne of the most perplexing phenom- they were getting to grips with γ-ray bursts, so tracking an FRB to one is surprising, says ena in astronomy has come of age. which are now a staple of astronomical observa- Berger. He thinks that the unusual environment The fleeting blasts of energetic cosmic tion, says Bing Zhang, a theoretical astrophysi- is more than coincidence, and that FRBs may Oradiation of unknown cause, now known as fast cist at the University of Nevada, Las Vegas. come from super-powerful magnetars — dense, radio bursts (FRBs), were first detected a decade “The meeting has really focused the field a magnetic stars thought to form after an abnor- ago. At the time, many astronomers dismissed lot,” says Sarah Burke Spolaor, an astronomer mally massive explosion, such as an extremely the seemingly random blasts as little more than at West10 Virginia-20m University in Morgantown. energetic supernova. Studies suggest that such glitches. And although key facts, such as what Debates continue over how to root out detec- events seem to be more common in dim dwarf causes them, are still largely a mystery, FRBs tion bias and coordinate observations and on galaxies, he says. Others think the bursts might are now accepted as a genuine class of celestial what can be learnt by studying patterns in the come from active galactic nuclei, regions at signal and have spawned a field of their own. existing FRB population. the centres of some galaxies that are thought The passage was marked this month by the The first FRB was co-discovered1 in 2007 by to host supermassive black holes. Streams of first major meeting on FRBs, held in Aspen, astronomer Duncan Lorimer at West Virginia plasma from these could comb nearby pulsars Colorado, on 12–17 February. As well as cel- University.ALMA He found in archived pulsar data to produce FRBs, says Zhang, which could also ebrating a fleet of searches for the signals, the a 5-millisecond radio frequency burst that was explain a recent, although tentative, observation meeting’s 80 delegates grappled with how best so bright it couldn’t be ignored. Astronomers of a faint γ-ray burst coinciding with an FRB. to design those hunts and pin down the signals’ have since seen 25 FRBs. All are brief radio At the meeting, some astronomers proposed

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the white hole should eject particles at the same temperature as the particles that felt in the black hole limited horizon due to absorption ∼ 100 million light-years / z=0.01 Short Gamma Ray Burst ?

CTA

Quantum Gravity Phenomenology Francesca Vidotto TO CONCLUDE Hey astronomers! You can measure Quantum Gravity!

Quantum Gravity Phenomenology Francesca Vidotto SUMMARY

1. PHENOMENOLOGY depends mainly on the lifetime given as a function of the mass: as short as m2 * interesting to check prediction by different QG frameworks!

2. NEW EXPERIMENTAL WINDOWS for quantum gravity signals in the sub-mm, radio & TeV direct detection & diffuse emission peculiar energy distance relation

3. PRIMORDIAL BLACK HOLES

new features consequence in the early universe but also in the late one !!!

Quantum Gravity Phenomenology Francesca Vidotto PLANCK STARS: REFERENCES ON PHENOMENOLOGY

Planck stars Planck stars as observational probes of Carlo Rovelli, Francesca Vidotto quantum gravity Carlo Rovelli >>Int. J. Mod. Phys. D23 (2014) 12, 1442026 >>Nature Astronomy, March’17, comment

..Planck star phenomenology Aurelien Barrau, Carlo Rovelli Phys. Lett. B739 (2014) 405 ..Fast Radio Bursts and White Hole Signals Aurélien Barrau, Carlo Rovelli, Francesca Vidotto Phys. Rev. D90 (2014) 12, 127503 ..Quantum Gravity Effects around Sagittarius A* Hal Haggard, Carlo Rovelli Phys. Rev. D90 (2014) 12, 127503 ..Phenomenology of bouncing black holes in quantum gravity: a closer look Aurélien Barrau, Boris Bolliet, Francesca Vidotto, Celine Weimer JCAP 1602 (2016) no.02, 022 ..Bouncing black holes in quantum gravity and the Fermi gamma-ray excess Aurélien Barrau, Boris Bolliet, Marrit Schutten, FrancescaVidotto Phys. Lett. B 722 (2017) 58-62, Quantum effects of Primordial Black Holes on Galaxy Clustering Alvise Raccanelli, Licia Verde, Francesca Vidotto to appear soon

Quantum Gravity Phenomenology Francesca Vidotto Aurélien Barrau Nicola Bellomo

Borris Bolliet José Louis Bernal

Marios Christodoulou Jens Chluba

Fabio D’Ambrosio Ilya Cholis

Tommaso Di Lorenzo Michael Kavic

Hal Haggard Flora Moulin

Simone Speziale Alvise Raccanelli

Marrit Schutten Licia Verde

Alejandro Perez

Carlo Rovelli

Ilya Vilensky

Celine Weimer Aurélien Barrau Nicola Bellomo

Borris Bolliet José Louis Bernal

Marios Christodoulou Jens Chluba

Fabio D’Ambrosio Ilya Cholis

Tommaso Di Lorenzo Michael Kavic

Hal Haggard Flora Moulin

Simone Speziale Alvise Raccanelli

Marrit Schutten Licia Verde

Alejandro Perez

Carlo Rovelli

Ilya Vilensky

Celine Weimer Aurélien Barrau Nicola Bellomo

Borris Bolliet José Louis Bernal

Marios Christodoulou Jens Chluba

Fabio D’Ambrosio Ilya Cholis

Tommaso Di Lorenzo Michael Kavic

Hal Haggard Flora Moulin

Simone Speziale Alvise Raccanelli

Marrit Schutten Licia Verde

Alejandro Perez

Carlo Rovelli

Ilya Vilensky

Celine Weimer Aurélien Barrau Nicola Bellomo

Borris Bolliet José Louis Bernal

Marios Christodoulou Jens Chluba

Fabio D’Ambrosio Ilya Cholis

Tommaso Di Lorenzo Michael Kavic

Hal Haggard Flora Moulin

Simone Speziale Alvise Raccanelli

Marrit Schutten Licia Verde

Alejandro Perez

Carlo Rovelli

Ilya Vilensky

Celine Weimer PLANCK STARS: REFERENCES ON PHENOMENOLOGY

Planck stars Planck stars as observational probes of Carlo Rovelli, Francesca Vidotto quantum gravity Carlo Rovelli >>Int. J. Mod. Phys. D23 (2014) 12, 1442026 >>Nature Astronomy, March’17, comment

Quantum Gravity Phenomenology Francesca Vidotto