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The Quest for the Dark Matter Particle

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The Quest for the Dark Matter Particle The quest for the dark matter particle Alejandro Ibarra Technische Universität München ICTP-SAIFR October 23rd 2019 Dark matter is a likely solution to various long-standing puzzles in astronomy Coma cluster 1- Apply the virial theorem to determine the total mass of the Coma Cluster For an isolated self-gravitating system, 2- Count the number of galaxies (1000) and calculate the average mass 1- Apply the virial theorem to determine the total mass of the Coma Cluster For an isolated self-gravitating system, 2- Count the number of galaxies (1000) and calculate the average mass The modern technique: gravitational lensing Abell 1689 Abell 1689 Abell 1689 Evidence from galaxies Expectations from Newtonian theory Fcent Fgrav M31 Observed: constant velocity!! Expected Something else around M31? Fcent Fgrav M31 Something else around M31? Fcent Fgrav M31 Evidence from the Universe at large scale Cosmic microwave background temperature anisotropies Planck Collaboration CMB angular power spectrum Planck Collaboration There is evidence for dark matter in a wide range of distance scales Clusters Galaxies of galaxies Observable Solar system Universe pc kpc Mpc Gpc distance There is evidence for dark matter in a wide range of distance scales Clusters Galaxies of galaxies Observable Solar system Universe pc kpc Mpc Gpc distance M87 There is evidence for dark matter in a wide range of distance scales Clusters Galaxies of galaxies Observable Solar system Universe pc kpc Mpc Gpc distance Segue 1 There is evidence for dark matter in a wide range of distance scales Clusters Galaxies of galaxies Observable Solar system Universe pc kpc Mpc Gpc distance Abell 1689 There is evidence for dark matter in a wide range of distance scales Clusters Galaxies of galaxies Observable Solar system Universe pc kpc Mpc Gpc distance There is evidence for dark matter in a wide range of distance scales Clusters Galaxies of galaxies Observable Solar system Universe pc kpc Mpc Gpc distance What do we know about the dark matter? 1) It is (maybe?) not made of compact objects Brandt '16 Zumalacarregui, Seljak '17 1) It is (maybe?) not made of compact objects Brandt '16 Zumalacarregui, Seljak '17 Lots of discussions about the robustness and applicability of these limits... 1) It is (maybe?) not made of compact objects Brandt '16 Zumalacarregui, Seljak '17 Lots of discussions about the robustness and applicability of these limits... None of this limits apply if the dark matter distribution is smooth (rather than clumpy) 2) It is dark. It hardly interacts with visible matter. If it has positive charge, it can form a bound state X+e-, an “anomalously heavy hydrogen atom”. If it has negative charge, it can bind to nuclei, forming “anomalously heavy isotopes”. Perl et al. Millicharged dark matter? McDermott et al'10 3) It was “slow” at the time of the formation of the first structures. White'86 Hot Dark Matter Cold Dark Matter Relativistic Non-relativistic 3) It was “slow” at the time of the formation of the first structures. White'86 Hot Dark Matter Cold Dark Matter Relativistic Non-relativistic 4) It exists today. Current observations are consistent with dark matter being constituted by particles which have: No electric charge or color (or very small). Low velocity at the time of structure formation. Lifetime longer than the age of the Universe. Current observations are consistent with dark matter being constituted by particles which have: No electric charge or color (or very small). Low velocity at the time of structure formation. Lifetime longer than the age of the Universe. Current observations are consistent with dark matter being constituted by particles which have: No electric charge or color Low velocity at the time of structure formation. Lifetime longer than the age of the Universe. (or very small) . Evidence for physics beyond the Standard Model of Particle Physics What do we know about dark matter, from the particle physics point of view? DARK MATTER ? ? ? ? ? ? ? DARK MATTER ? ? ? ? ? ? ? DARK MATTER ? ? ? ? ? ? ? Goal for the 21st century: identify the properties of the dark matter particle DM DM The freeze-out mechanism freeze-out The annihilation production SM SM scattering The freeze-out mechanism production The probability of interaction controlled by the cross-section DM SM g Small interaction rate n i r e t t a c s DM SM Large interaction rate annihilation The freeze-out mechanism At very high temperatures, production dark matter particles are annihilated and regenerated at the same rate. DM SM g n i r e However, at low temperatures, t t a the Standard Model particles do not c DM SM s have enough kinetic energy to regenerate DM particles, and DM particles can only annihilate. annihilation The subsequent evolution of the dark matter number density depends crucially on the fact that our Universe is expanding. Dark matter population in a static Universe Dark matter population in a static Universe Dark matter population in a static Universe Dark matter population in a static Universe Dark matter population in a static Universe Dark matter population in a static Universe Dark matter population in a static Universe No DM particles at present times! Dark matter population in an expanding Universe Dark matter particles can no longer annihilate. The number of dark matter particles “freezes-out” The “relic abundance” of dark matter particles depends on their annihilation cross section and on their relative velocity The “relic abundance” of dark matter particles depends on their annihilation cross section and on their relative velocity The “relic abundance” of dark matter particles depends on their annihilation cross section and on their relative velocity Large annihilation cross section → Small relic abundance Small annihilation cross section → Large relic abundance The “relic abundance” of dark matter particles depends on their annihilation cross section and on their relative velocity The “relic abundance” of dark matter particles depends on their annihilation cross section and on their relative velocity The “relic abundance” of dark matter particles depends on their annihilation cross section and on their relative velocity Small velocity → Large relic abundance Large velocity → Small relic abundance Fraction of the total energy of the Universe in the form of DM Correct DM abundance (25% of the total energy of the Universe), if Fraction of the total energy of the Universe in the form of DM Correct DM abundance (25% of the total energy of the Universe), if 1 pb = 10-36 cm2. Speed of light Typical strength of the weak interactions Fraction of the total energy of the Universe in the form of DM Correct DM abundance (25% of the total energy of the Universe), if production 1 pb = 10-36 cm2. Speed of light DM SM Typical strength of g n i the weak interactions r e t t a DM c SM s annihilation ~ weak interaction Fraction of the total energy of the Universe in the form of DM Correct DM abundance (25% of the total energy of the Universe), if production The dark matter is a Weakly Interacting Massive Particle (WIMP) DM SM g n i r e t t a DM c SM s annihilation ~ weak interaction Fraction of the total energy of the Universe in the form of DM Correct DM abundance (25% of the total energy of the Universe), if The dark matter is a Weakly Interacting Massive Particle (WIMP) SM DM More numerology: DM SM The freeze-out mechanism suggests that the WIMP has mass ~ a few GeV – a few TeV and a coupling with ordinary matter ~ 0.1 – 0.01 DM DM SM SM scattering production DM SM DM SM DM SM DM SM annihilation Indirect Dark Matter Searches Indirect dark matter searches DM e n p DM g The dark matter annihilates into ordinary particles, such as electrons and positrons, antiprotons, neutrinos, photons... Indirect dark matter searches DM e n p DM g Neutral particles propagate in straight lines practically without losing energy. Charged particles, on the other hand, propagate in a complicated way through the tangled magnetic field of our Galaxy. Indirect dark matter searches DM e n p DM g The fluxes at Earth can be calculated and depend on: The dark matter mass (mDM) The annihilation cross section times the velocity (sv) Indirect dark matter searches DM e n p DM g The fluxes at Earth can be calculated and depend on: The dark matter mass (mDM) The annihilation cross section times the velocity (sv) Which (s v)? A well motivated choice: “Canonical” annihilation cross section for WIMP dark matter First milestone for experimental searches. Indirect dark matter searches DM e n p DM g The annihilation products arrive to Earth, along with gamma-rays and cosmic rays produced in astrophysical processes. 105 1 r 6 s 10 1 s 2 m 7 c 10 V bb e G m =500 GeV 8 DM 10 2 E 109 20 30 50 70 100 150 200 300 E GeV Where to look for dark matter annihilations Where to look for dark matter annihilations Galactic center Where to look for dark matter annihilations Satellites Where to look for dark matter annihilations Galactic halo Where to look for dark matter annihilations Extragalactic background Where to look for dark matter annihilations Galaxy clusters Where to look for dark matter annihilations Features in the energy spectrum A promising target for detection: dwarf galaxies Segue 1: Optical image A promising target for detection: dwarf galaxies Segue 1: Optical image A promising target for detection: dwarf galaxies Segue 1: Optical image A promising target for detection: dwarf galaxies Mass-to-light ratio ~ 3400 Msun/Lsun Most DM-dominated object known so far! Segue 1: Optical image A promising target for detection: dwarf galaxies Segue 1: Gamma-ray image (simulated!) A promising target for detection: dwarf galaxies Gamma-ray image taken with the MAGIC telescopes A promising target for detection: dwarf galaxies MAGIC coll.
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