Sterile Neutrinos As Dark Matter

Alexey Boyarsky

October 23, 2018

1 / 36 Neutrino dark matter

Neutrino seems to be a perfect dark matter candidate: neutral, long-lived, massive, abundantly produced in the early Universe Cosmic neutrinos

I We know how neutrinos interact and we can compute their 3 primordial number density nν = 112 cm− (per ﬂavour)

I To give correct dark matter abundance the sum of neutrino masses, P m , should be P m 11 eV ν ν ∼

Tremaine-Gunn bound (1979)

I Such light neutrinos cannot form small galaxies – one would have to put too many of them and violated Pauli exclusion principle

I Minimal mass for fermion dark matter 300 400 eV ∼ − I If particles with such mass were weakly interacting (like neutrino) – they would overclose the Universe

2 / 36 ”Between friends”

I The ﬁnal blow to neutrino as dark matter came in mid-80s when M. Davis, G. Efstathiou, C. Frenk, S. White, et al. “Clustering in a neutrino-dominated universe”

I They argued that structure formation in the neutrino dominated Universe (with masses around 100 eV would be incompatible with the observations) http://www.adsabs.harvard.edu/abs/1983ApJ...274L...1W Abstract The nonlinear growth of structure in a universe dominated by massive neutrinos using initial conditions derived from detailed linear calculations of earlier evolution has been simulated The conventional neutrino-dominated picture appears to be ruled out.

3 / 36 Two generalizations of neutrino DM

I Dark matter cannot be both light and weakly interacting at the same time

I To satisfy Tremaine-Gunn bound the number density of any dark matter made of fermions should be less than that of neutrinos

I Neutrinos are light, therefore they decouple relativistic and their equilibrium number density is T 3 at freeze-out ∝

First alternative: WIMP One can make dark matter heavy and therefore their number density is m/T Boltzmann-suppressed (n e− ) at freeze-out ∝ Second alternative: super-WIMP One can make dark matter interacting super-weakly so that their number density never reaches equilibrium value

4 / 36 Sterile neutrino – super-weakly interacting particle

I Need a particle “like neutrino” but with larger mass and weaker interaction strength

I Sterile neutrino N: admixture of a new, heavier, state to the neutrino

I “Inherits” interaction from neutrino µ π Ds N νµ ± ϑ νµ µ ϑµ µ N ∓ . . . suppressed by a small parameter U

g + c ∗ µ − g c ∗ µ int = Wµ N U γ (1 γ5)`α + ZµN U γ (1 γ5)ν + ... L √2 − 2 cos θW −

5 / 36 Sterile neutrino + Okkam razor Sterile neutrinos can explain. . .

I Neutrino masses: Bilenky & Pontecorvo’76; Minkowski’77; Yanagida’79; Gell-Mann et al.’79; Mohapatra & Senjanovic’80; Schechter & Valle’80

I Baryon asymmetry: Fukugita & Yanagida’86; Akhmedov, Smirnov & Rubakov’98; Pilaftsis & Underwood’04-05;

I Dark matter: Dodelson & Widrow’93; Shi & Fuller’99; Dolgov & Hansen’00

A minimal model of particle physics and cosmology: νMSM

⇒

Sharing success of the Standard Model at accelerators and resolving major BSM observational problems Asaka & Shaposhnikov’05; Review: Boyarsky+’09 6 / 36 Properties of sterile neutrino dark matter

I Can be light (down to Tremaine-Gunn bound)

I Can be decaying (via small mixing with an active neutrino state)

The decay signal is proportional R to ρDM(r) The dark matter power spectrum I Can be warm (born relativisticUniversity of and Durham cool down later)

k3 P(k) The linear power spectrum (“power per octave” ) HDM Free streaming à cold

-1 λ cut α mx for thermal relic Dwarf P(k) P(k)

3 gals mCDM ~ 100GeV galaxy warm -6 susy; Mcut ~ 10 Mo clusters Log k

m ~ few keV amplitude Fluctuation Overdensity WDM 9 sterile ν; Mcut~10 Mo hot

mHDM ~ few eV light M ~1015 M ν; cut o -1 Large scales Log k [h Mpc ] small scales Institute for Computational Cosmology

7 / 36

1 Sterile neutrino – decaying dark matter

8 / 36 Signal from diﬀerent DM-dominated objects Boyarsky, Ruchayskiy et al. Phys. Rev. Lett. 97 (2006); Phys. Rev. Lett. 104 (2010)

6 Clusters of galaxies M - caustics, S - X-rays

) Groups of galaxies M - WL, S - WL

-2 Spiral galaxies M - WL, S - X-rays

pc Elliptical galaxies 5

sun dSphs Isolated halos, ΛCDM N-body sim. Signal: Subhalos from Aquarius simulation 4 Z = ρdm(r)dr 3 S

2 (Column

DM column density, lg (S/M density) 1

0 107 108 109 1010 1011 1012 1013 1014 1015 1016 DM halo mass [Msun]

9 / 36 Search for Dark Matter decays in X-rays

See “Next decade in sterile neutrino studies” by Boyarsky et al. [Physics of the Dark Universe, 1 (2013)]

1029

1028 [sec] τ 1027 XMM, HEAO-1 SPI Chandra Life-time

1026 τ 8

PSD exceeds degenerate Fermi gas = Universe life-time x 10 Available X-ray satellites: 1025 Suzaku, XMM-Newton, 10-1 100 101 102 103 104 Chandra, INTEGRAL, NuStar MDM [keV] signal z}|{ q Signal-to-noise DM texp Ωfov A ∆E ∝ S · · eff · | {z } signal over background − − All types of individual objects/observations have been tried: galaxies (LMC, Ursa Minor, Draco, Milky Way,

M31, M33,. . . ); galaxy clusters (Bullet cluster; Coma, Virgo, . . . ) with all the X-ray instruments

10 / 36 Detection of An Unidentiﬁed Emission Line

Bulbul et al. ApJ (2014) [1402.2301]

Boyarsky, Ruchayskiy et al. Phys. Rev. Lett. (2014) [1402.4119]

I Energy: 3.5 keV. Statistical error for line position 30 50 eV. 27 28 ∼ − I Lifetime: 10 10 sec (uncertainty: factor 3 5) ∼ − ∼ − Decaying dark matter?

11 / 36 InterpretationsI

There are 4 classes of interpretations

I Statistical ﬂuctuation (there is nothing there at all!)

I Unknown astrophysical emission line (emission line of some chemical element)

I Instrumental feature (systematics) (We do not know our telescopes well enough)

I Dark matter decay line

12 / 36 Signiﬁcance of the original signal

[Boyarsky, Ruchayskiy et al. Phys. Rev. Lett. (2014) [1402.4119]] M31 galaxy ∆χ2 = 13.0 3.2σ for 2 d.o.f. Perseus cluster (MOS) ∆χ2 = 9.1 2.5σ for 2 d.o.f. Perseus cluster (PN) ∆χ2 = 8.0 2.4σ for 2 d.o.f. M31 + Perseus (MOS) ∆χ2 = 25.9 4.4σ for 3 d.o.f. Global signiﬁcance of detecting the same signal in 3 datasets: 4.8σ

[Bulbul et al. ApJ (2014) [1402.2301]] 73 clusters (XMM, MOS) ∆χ2 = 22.8 4.3σ for 2 d.o.f 73 clusters (XMM, PN) ∆χ2 = 13.9 3.3σ for 2 d.o.f ...... Perseus center (XMM, MOS) ∆χ2 = 12.8 3.1σ for 2 d.o.f. Perseus center (Chandra, ACIS-S) ∆χ2 = 11.8 3.0σ for 2 d.o.f. Perseus center (Chandra, ACIS-I) ∆χ2 = 6.2 2.5σ for 1 d.o.f.

More detections followed!

13 / 36 Signal from the Milky Way outskirts

I We are surrounded by the Milky Way halo on all sides

I Expect signal from any direction. Intensity drops with oﬀ-center angle

I Surface brightness proﬁle of the Milky Way would be a “smoking gun”

14 / 36 Signal from the Milky Way outskirts? Phys. Rev. Lett. (2014) [1402.4119]

Blank sky dataset 0.10 I No line is seen in 16 Msec observations of oﬀ-center Milky Way

[cts/sec/keV] I Conﬁrmed by Normalized count rate -3 – [(Sekiya et al. 2⋅10 2⋅10-3 [1504.02826])] with 1⋅10-3 5⋅10-4 Suzaku 0⋅100 -5⋅10-4 – [(Figueroa-Feliciano et al. [cts/sec/keV] ⋅ -3 Data - model -1 10 -2⋅10-3 [1506.05519])] with XQC -2⋅10-3 2.0 3.0 4.0 5.0 6.0 7.0 8.0 Energy [keV] Is this the end of the story?

15 / 36 Galactic center – a non-trivial consistency check Boyarsky, O.R.+ Phys. Rev. Lett. 115, (2014)

1.40

1.30 GC ON, MOS1 GC ON, MOS2 1.20 GC -1

1.10 s -2

1.00 10 Perseus [cts/sec/keV] 0.90

0.80 Normalized count rate photons cm 27 s M31

0.70 -6 -2 s s 3.0⋅10 27 27 28 s = 2 x 10 τ DM 2.0⋅10-2 = 6 x 10 = 8 x 10 -2 τ DM τ DM = 1.8 x 10 ⋅ Line flux, 10 1.0 10 1 τ DM Blank-sky 0 [cts/sec/keV] 0.0⋅10

-2 -1.0⋅10 0.01 0.1 3.0 3.2 3.4 3.6 3.8 4.0 2 Projected mass density, MSun/pc Energy [keV]

I 4σ+ statistical signiﬁcance

I Also in S. Riemer-Sorensen’14; Jeltema & Profumo’14

The observed signal ﬁts into the predicted range

16 / 36 Another X-ray satellite: NuStar

I Has small ﬁeld of view, would not be Optics Bench competitive with XMM, Chandra or Suzaku

I But! NuStar has a specical 0-bounce 2 photons mode where FoV is 30 deg Rays blocked by Rays from a Optics Bench stray light source

Aperture Stops

Focal Plane

Detectors

17 / 36 3.5 keV line in NuStar spectrum Milky Way halo. Neronov & Malyshev [1607.07328]. Also Ng+ [1609.00667]

I The 3.5 keV is present in the 0-bounce spectrum of the Cosmos ﬁeld and CDFS (total cleaned exposure 7.5 Msec)

I Combined detection has 11σ signiﬁcance

I The spectrum of NuStar ends at 3 keV, so this is a lower edge of sensitivity band

I The 3.5 keV line has been previously attributed to reﬂection of the sunlight on the telescope structure

I However, in the dataset when Earth shields satellite from the Sun the line is present with the same ﬂux

18 / 36 Line in Chandra from the same region of the sky Cappelluti+’17 [1701.07932]

that Ne↵ = 4 is permitted, there are no concrete CMB constraints on keV sterile neutrinos. Performing the line integral through the halo of the Milky Way taking into account the f.o.v and given that I Combined 10 Msec of Chandra all 3 deep fields included in this analysis are at roughly observation of COSMOS and 115 degrees, we compute the surface mass density along the line of sight. Similar to our assumption adopted CDFS fields (same as NuStar) above, the MW halo is once again modeled with an NFW profile and the current best-fit parameters are adopted I 3σ detection of a line at from Nesti & Salucci (2013). Using the formulation de- veloped in Abazajian et al. (2007), we use the measured 3.5 keV flux in the line to constrain the mixing angle sin2 2✓. Al- ∼ though we use the integrated surface mass density of dark I Flux is compatible with NuStar matter in the Milky Way halo integrated out to the virial radius, the dominant contribution comes from the inner I If interpreted as dark matter region - from within a few scale radii - of the density decay – this is a signal from profile due to the shape of the NFW profile. Using the higher bound and the lower bound estimates for the total Galactic halo outskirts ( 115◦ mass of the Milky Way, we obtain the following values off center) ∼ for ⌃the integrated surface mass density of DM: 2 ⌃DM,High =0.0362 gm cm ; 2 ⌃DM,Low =0.0109 gm cm . (5) Fig. 4.— 1 (continuous line)and2 (dashed line)limitsonthe expected 3.5 keV line flux as function of the angular distance from the GC by assuming a NFW profile with parameters from Nesti Using these values and the equation: &Salucci(2013). The profile is compared with our measurements m ⌃ from the deep fields (black filled circles)andwiththeNuSTAR sin2 2✓ ( ⌫ )4 DM = results (red/blue filled circles). The downward black arrow ⇥ 11keV ⇥ gm cm 2 represents the 3 limit derived from simulations. Thedownward 19 / 36 (6) blue arrow represents the 3 sensitivity to the 3.5 keV line with 50 I⌫ 2 1 2 ( ) photons cm s arcsec , Ms Chandra. 1.45 10 4 ⇥

and shape are still highly debated (Bland-Hawthorn & 2 10 we obtain that sin 2✓DM,High =6.92 10 and Gerhard 2016). 2 10 ⇥ sin 2✓DM,Low =2.29 10 . Furthermore, we can now Assuming that all the intervening dark matter is asso- estimate the lifetime⇥⌧ for this sterile neutrino species, ciated with a cold component that can be modeled with using equation 2 of Boyarsky et al. (2015): an NFW profile (Navarro et al. 1997) given by: 8 ⇢⇤ 10 1keV ⇢ = (4) 29 5 DM 2 ⌧DM =7.2 10 sec( 2 )( ) (7) x(1 + x) ⇥ sin 2✓ m⌫ 27 where x = r/rH ; here we adopt the parameters measured and find that it is ⌧DM,High =6.09 10 sec and 27 ⇥ by Nesti & Sallucci (2013): and therefore use d=8.02 0.2 ⌧DM,Low =1.83 10 sec respectively. These mixing an- +12.2 +20.7 6 3 ± ⇥ kpc, rH =16.1 5.6 , ⇢⇤=13.8 6.6 10 M /kpc and gle estimates are in very good agreement with Figures 13 2 ⇥ SDM,GC=0.63 0.11 ph/s/cm /sr. Using Eq. 2 we cal- and 14 of Bul14. They can also be overplotted and seen culated, with± Monte Carlo integration, the 1 and 2 clearly to be consistent with Figure 3 of Iakubovskyi et confidence levels of the flux from DM decay along the al. (2015). line of sight as a function of the angular distance from However, despite concordance with parameters ex- the GC. This is shown in Fig. 4, wherein we overplot our tracted from other observational constraints obtained measurement and the NuSTAR measurement. The two from X-ray data of stacked galaxy clusters and the Galac- fields investigated here are basically at the same angular tic center, due to the significance of our detection only at distance from the GC of ✓ 115 deg. Remarkably, our the 3 level, we cannot conclusively claim that this ob- measurements are consistent⇠ at the 1 level with such a served 3.51 keV line originates from decaying dark mat- profile. This means the ratio of fluxes at ✓=115 and ✓=0 ter. It would require a non-detection with at least 50 Ms is consistent with the NFW DM decay model. of Chandra observations to rule out this hypothesis (see In terms of constraints on the number of neutrino Fig. 4). species (allowing one additional species of a sterile neutrino along with the 3 other usual flavors), Planck Col- 6. SUMMARY laboration et al. (2015) report that with the CMB tem- In this paper, we have presented a 3 detection of an perature data alone it is dicult to constrain N , and unidentified emission feature at 3.5 keV in the spec- e↵ ⇠ data from Planck alone do not rule out Ne↵ = 4. At the trum of the CXB with extremely deep integration time. 95% C.L. combining Planck + WMAP + high l experi- Examining the sources of possible origin for this feature, +0.68 ments they obtain Ne↵ =3.36 0.64. The Planck collabo- we conclude that the line does not have a clear known ration has only investigated an eV mass sterile neutrino instrumental origin. The intensity and the energy of the as a potential additional species. So other than saying line is consistent with previous measurements that were Not systematics! By now the 3.5 keV line has been observed with 4 existing X-ray telescopes, making the systematic (calibration uncertainty) origin of the line highly unlikely

I Line is changing with redshift I ACIS-I is a silicon CCD while the imagers of NuSTAR are two Cadmium-Zinc-Telluride detectors

I Chandra has mirrors made of Iridium (rather than Gold as XMM or Suzaku) – absorption edge origin becomes unlikely

I Diﬀerent orbits of satellites – cosmic ray origin is unlikely I Datasets accumulated over diﬀerent periods (15yrs for Chandra vs. 3yrs for Nustar) – not related to, e.g. solar activity

Is this a line from atomic transition(s)?

As argued by [Gu+; Carlson+; Jeltema & Profumo; Riemer-Sørensen; Phillips+]

20 / 36 Surface brigthness proﬁle of the 3.5 keV line in the Milky Way. PRELIMINARY Boyarsky, Iakubovskyi, Ruchayskiy. To appear (2018)

100 NuSTAR, Galactic Buldge ] r s / s

/ XMM-Newton,

2 Micro-X, 3 GC (B14) m sensitivity c 1 NuSTAR, / 10 h blank-sky p [

x u

l Chandra, f

e blank-sky n i L 2 XMM-Newton, 10 blank-sky (B14)

10 1 100 101 102 Angular distance from Galactic Centre [deg]

All detection in the Milky Way follow the same trend 21 / 36 Next step for 3.5 keV line: resolve the line

I A new microcalorimeter with a superb spectral resolution – Hitomi (Astro-H) was launched February 17, 2016

I During the ﬁrst month of observations (calibration phase) it observed the central part of the Perseus galaxy cluster where strong line was detected by XMM & Suzaku

I Spectrometer of Hitomi is able to resolve atomic lines, measure their positions and widths (due to Doppler broadening)

Unfortunately, the satellite was lost few weeks after the launch

22 / 36 What did we learn with existing Hitomi data?

I Even the short observation by Hitomi showed no astrophysical lines in Perseus cluster near da3.5 keV line ⇒ is not astrophysical [Hitomi collaboration, 1607.04487] Perseus halo mass I Astrophysical lines in the center are ← → Doppler broadened with velocity Lovell, Theuns, Frenk, Schaye+ [1810.05168] v 102 km/sec (measured by Hitomi) th ∼ I Width of DM decay line is determined by the virial velocity of the Perseus galaxy cluster, v 103 km/sec vir ∼ I For XMM/Chandra/Suzaku/Nustar there was no diﬀerence – they resolution did not allow to distinguish broad from narrow lines Hitomi sensitivity to broad lines is I [1705.01837] much weaker

23 / 36 Future of decaying dark matter searches in X-rays

Another Hitomi (around 2020) It is planned to send a replacement of the Hitomi satellite

Microcalorimeter on sounding rocket (2019)

2 I Flying time 10 sec. Pointed at GC only ∼ I Can determine line’s position and width

Athena+ (around 2028)

I Large ESA X-ray mission with X-ray spectrometer (X-IFU)

I Very large collecting area (10 that of XMM) × I Super spectral resolution

“Dark matter astronomy era” begins?

24 / 36 Sterile neutrino – warm dark matter

25 / 36 Lyman-α forest

I Neutral hydrogen absorption line at λ = 1215.67A˚ (Ly-α absorption 1s 2p) → I Absorption occurs at λ = 1215.67A˚ in the local reference frame of hydrogen cloud. I Observer sees the forest: λ = (1 + z)1215.67A˚

26 / 36 Suppression in the ﬂux power spectrum (SDSS)

1000

CDM What we want to detect 0.0 1.0 2.0 4.0 6.0 All of the above100 discussion applies to NRP sterile neutrinos in the DW 8.0 framework, as their I CMB and large scale observations ﬁx 10.0 phase-space distribution function is quasi-thermal and thus exhibits thermal-like 16.0 features notably in the matter power spectrum transfer function. Resonantly-produced (RP) sterile 20.0 neutrinos on the 3 50.0

other hand, suchP(k) as produced in an MSW -like resonance introduced by Shi and Fuller [20], feature a

matter power spectrum at large scales 3 120.0 non-Fermi componentk in their velocity-space distribution [21] and therefore display700.0 a di↵erent transfer function from the one illustrated in Fig. 1. Incorporating this resonant component requires running a dedicated Boltzmann10 code to compute the RP neutrino’s phase-space distribution and transfer I Based on this we can predict the functions, which is beyond the scope of this work. The authors of [22] have derived RP constraints from Ly-↵ forest data by approximating their transfer function at the relevant scales with a mixed Cold CDM matter power spectrum at + Warm Dark Matter model,M =7 where keV the relative abundance of the cold and warm species encodes Λ s the lepton asymmetry parameter . We plan on following their method in a forthcoming study. Mth=1.4 keV Refs [21, 23] provide an extensiveL overview of sterile neutrinos as dark matter and their impact on 1 small scales cosmology given several production mechanisms. 0.1 1.0 10.0 100.0 k [h Mpc−1] I WDM predicts suppression (cut-oﬀ) in 3 Flux Power Spectrum from the Ly-↵ Forest the matter power spectrum as 3D linear matter power spectra compared to the CDM

What we observe

I We observe ﬂux power spectrum – projected along the line-of-sight power

spectrum of neutral hydrogen 2 Figure 3. Dimensionless Ly-↵ ﬂux power spectra (k)=P'(k) k/⇡ from our selected sample in BOSS ' ⇥ DR9. Color encodes redshiftBOSS bin. Solid lines (SDSS-III) are the simulation results Ly- inα each redshift[1512.01981] bin from our benchmark absorption lines model described in Sec. 4.

This work is based on the one-dimensional flux power spectrum measured using the first release of BOSS quasar data [24]. From a parent sample consisting of 60, 000 SDSS-III/BOSS DR9 quasars [12–14, 25–27], we select the 13, 821 spectra that have high⇠ signal-to-noise ratio, no broad absorption line features, no damped or detectable Lyman-limit systems, and an average resolution27 / 36 1 in the Ly-↵ forest of at most 85 km s , where the Ly-↵ forest is defined as the region spanning 1050 <RF /A<˚ 1180, i.e., bounded by the Ly-↵ and Ly- emission peaks of the background quasar. The spectra in this sample are used to measure the transmitted flux power spectrum in 12 redshift bins from z =4.4to2.2, each bin spanning z =0.2, and in 35 equally-spaced spatial modes ranging h i 3 2 1 from k = 10 to 2.10 skm (cf. Fig. 3). To reduce correlations between neighboring z-bins, we split the Ly-↵ forest of each quasar spectrum into up to three distinct redshift sectors. Each sector

3Mikheyev-Smirnov-Wolfenstein

–6– High-resolution Ly-α forest

1000

CDM 0.0 1.0 2.0 4.0 6.0 100 8.0 10.0 16.0 20.0 50.0 P(k)

3 120.0 k 700.0

Ms=7 keV Mth=1.4 keV 1 0.1 1.0 10.0 100.0 k [h Mpc−1]

Warm dark matter predicts suppression (cut-oﬀ) in the ﬂux power spectrum derived from the Lyman-α forest data Lyman-α from HIRES data [1306.2314]

I HIRES ﬂux power spectrum exhibits suppression at small scales

I Is this warm dark matter?

28 / 36 But we measure neutral hydrogen!

Lyman-α forest method is based on the underlying assumption The distribution of neutral hydrogen follows the DM distribution

Baryonic eﬀects

I Temperature at redshift z (Doppler broadening) – increases hydrogen absorption line width

I Pressure at earlier epochs (gas expands and then needs time to recollapse even if it cools)

29 / 36 What is the origin of the cut oﬀ?

14 d.o.f z = 5.0

18000

I The shape of the ﬂux power 15000 spectrum can be explained 7 12000

keV sterile neutrino [K] 0 9000 T

I Can also be explained by CDM 6000 + (combination of) pressure CDM Planck Late 3000 and temperature eﬀects M7L12 Planck Late 0 0.75 1.00 1.25 1.50 1.75 2.00 2.25 τeff Garzilli, Magalich, Theuns, Frenk, Weniger, Ruchayskiy, Boyarsky [1809.06585] “The Lyman-α forest as a diagnostic of the nature of the dark matter”

I If IGM medium will be measured to be TIGM . 8 000 K at z 5 then we have discovered warm dark matter! ∼

I This data is actually suggesting this [Onorbe et al. [1607.04218]]

30 / 36 Current sterile neutrino DM parameter space

10-6 Too much Dark Matter

)] -7

θ 10 Non-resonant production Excluded by non-observation (2

2 of dark matter decay line 10-8 Lyman-α bound -9 L for NRP sterile neutrino 10 6 =12

10-10 L 6 =25 -11 L 10 6=70 BBN limit: L L max 10-12 6 =700

constraints BBN 6 = 2500 10-13 Phase-space density Interaction strength [Sin 10-14 Not enough Dark Matter 1 5 10 50 DM mass [keV]

By accident (or maybe not) the sterile neutrino dark matter interpre- tation of 3.5 keV line predicts exactly the amount of suppression of power spectrum observed in HIRES/MIKE (and fully consistent with all other structure formation bounds)

31 / 36 Backup slides

32 / 36 Flux power spectrum at z = 5 in CDM and sterile neutrino cosmologies

z = 5.0, CDM z = 5.0, mSN = 7 keV,L6 = 12 τ = 1.70, T0 = 8000 K τ = 1.88, T0 = 8000 K HIRES HIRES

100 100 ) ) k k ( ( 2 F 2 F ∆ ∆

1 1 10− 10− 3.0 2.5 2.0 1.5 1.0 3.0 2.5 2.0 1.5 1.0 − − log− k[s/km]− − − − log− k[s/km]− − Garzilli, Magalich, Theuns, Frenk, Weniger, Ruchayskiy, Boyarsky [1809.06585]

33 / 36 We keep seeing such plots. . .

[1701.07674]

[1609.00667]

However, these structure formation bounds should be understood diﬀerently that bounds in particle physics

[1704.01832]

34 / 36 What is known about the IGM thermal history? Current measurements of IGM temperature

1.6 Becker+11 (γ=1.0) 1.4 Becker+11 (γ=1.3) Becker+11 (γ∼1.5) 1.2 Bolton+12

1.0 K] 4

/[10 0.8 0 T 0.6

0.4 z-binned ev. [1708.04913] power-law ev. 0.2 I There are many measurements 3.5 4.0 4.5 5.0 5.5 6.0 6.5 at z < 5 z [1306.2314] I There is a single measurement above z = 6

I History of reionization at higher redshifts is poorly constrained

35 / 36 WDM and 21cm line

I EDGES signal means that stars f * = 0.09, fX = 1.0 already existed by z 17 0 ' 20

I Does this limit models with 40 K m

60 delayed structure formation , b T (e.g. WDM)? [1805.00021] 80

100 I No! Details of star formation CDM 120 WDM, 6 keV are not known and the results vMSM, L6=10 10 12 14 16 18 20 22 of analytical/numerical Redshift z estimates are controlled by [Boyarsky et al. to appear] parameters about which we have little knowledge

I These parameters were never determined for WDM cosmologies where star formation is known to be diﬀerent from CDM

I WDM (rather than CDM) can easily produce enough star light by z 17 [Boyarsky et al. to appear] '

36 / 36