Thermal Dark Matter Below an MeV ASHER BERLIN TeVPA, Ohio State University August 9, 2017 Collaboration with Nikita Blinov, arxiv: 1706.07046
Dark Matter Mass dwarf galaxies MACHO 10-31 GeV 10 58 GeV
Dark Matter Mass dwarf galaxies QCD axion WIMP MACHO 10-31 GeV 100 GeV 10 58 GeV
Dark Matter Mass dwarf galaxies QCD axion WIMP MACHO 10-31 GeV 100 GeV 10 58 GeV
Dark Matter Mass dwarf galaxies QCD axion? WIMP MACHO 10-31 GeV 100 GeV 10 58 GeV
Dark Matter Mass dwarf galaxies QCD axion WIMP MACHO 10-31 GeV 100 GeV 10 58 GeV Thermal Contact
Dark Matter Mass dwarf galaxies QCD axion WIMP MACHO 10-31 GeV 100 GeV 10 58 GeV Thermal Contact BBN Light DM WIMPs Ω > 1 10-3 GeV 10 GeV 10 5 GeV
Dark Matter Mass dwarf galaxies QCD axion WIMP MACHO 10-31 GeV 100 GeV 10 58 GeV Thermal Contact BBN Light DM WIMPs Ω > 1 10-3 GeV 10 GeV 10 5 GeV
thermal dark matter noun Definition of THERMAL DARK MATTER : dark matter that acquired its cosmological abundance through thermal contact with the Standard Model bath at large temperatures. First Known Use: 1970s
Neff
Neff (standard assumption) DM-SM Equilibration > MeV Neutrino-Photon Decoupling ~ MeV T ~ mχ
Neff (standard assumption) DM-SM Equilibration > MeV Neutrino-Photon Decoupling ~ MeV T ~ mχ DM-Neutrino Equilibration N e ' 3 1+ 4 4/3 21 g & 3.78 &.
Sub-MeV: BBN + CMB
Sub-MeV: BBN + CMB. N e (BBN) ' 2.85 ± 0.28 ' ± K. Nollett, G. Steigman, arxiv:1411.6005
inos at T & 2 MeV and T. 2 MeV N e ' 3 1+ 4 (7) /41/3 21 g & 3.18 N e ' 3 1+ 4 / 41/3 21 g & 3.18 (8) L ' 2 + 2 L ' Sub-MeV: 2 + 2 BBN + CMB (9) m. m m. m N e (BBN) (10) ' 2.85 ± 0.28 N e (BBN) ' 2.85 ± 0.28 N e (CMB) (11) ' 3.15 ± 0.23 N e (CMB) ' 3.15 ± 0.23 N e (CMB-S4) (12) ' ±0.027 N e (CMB-S4) ' ±0.027 (13) K. Nollett, G. Steigman, arxiv:1411.6005 Z. Hou, et al., arxiv:1104.2333
inos at T & 2 MeV and T. 2 MeV N e ' 3 1+ 4 (7) /41/3 21 g & 3.18 N e ' 3 1+ 4 / 41/3 21 g & 3.18 (8) L ' 2 + 2 L ' Sub-MeV: 2 + 2 BBN + CMB (9) m. m m. m N e (BBN) (10) ' 2.85 ± 0.28 N e (BBN) ' 2.85 ± 0.28 N e (CMB) (11) ' 3.15 ± 0.23 N e (CMB) ' 3.15 ± 0.23 N e (CMB-S4) (12) ' ±0.027 N e (CMB-S4) ' ±0.027 (13) Thermal DM should be heavier than an MeV K. Nollett, G. Steigman, arxiv:1411.6005 Z. Hou, et al., arxiv:1104.2333
How ubiquitous is DM-SM Equilibration Before Neutrino-Photon Decoupling?
How ubiquitous is DM-SM Equilibration Before Neutrino-Photon Decoupling? DM-Neutrino Equilibration N e ' 3 1+ 4 4/3 21 g & 3.78 &.
Dark Matter Mass Lee-Weinberg MeV GeV TeV χ SM Z m & m 2 Z GeV (T eq m pl ) 1/2 χ SM Sub-GeV thermal DM requires light mediators: m ' m B. Lee and S. Weinberg, Phys.Rev.Lett. 39 (1977) 165-168
Equilibration Light Mediator T,m 2 '/T Expansion H T 2 Heavy Mediator T ~ m j Heavy Mediator ' T 3 / 2 G H Light Mediator G = H ~ 1 ê T Æ
Equilibration Light Mediator T,m 2 '/T Expansion H T 2 Heavy Mediator T ~ m j Heavy Mediator ' T 3 / 2 G H Light Mediator G = H ~ 1 ê T Æ Light thermal DM naturally enters equilibrium (for high enough TRH)
Neff Neutrino-Photon Decoupling ~ MeV DM-SM Equilibration < MeV T ~ mχ DM-Neutrino & Equilibration. N e ' 3 1+ 4 / 41/3 21 g & 3.18 L
Neff Neutrino-Photon Decoupling ~ MeV DM-SM Equilibration < MeV T ~ mχ DM-Neutrino & Equilibration. N e ' 3 1+ 4 / 41/3 21 g & 3.18 L ' ± g. few
Neff i = Ti/T 1.0 0.9 0.8 0.7 0.6 equil./e ± SM freeze-out 0.5 10 0 10 1 10 2 10 3 T [MeV] ' decay 10 4 10 5
Thermal History Y DM WIMP ~ 1 ê T
Thermal History Light ''WIMP'' Y DM WIMP ~ 1 ê T
Thermal History Light ''WIMP'' Y DM Freeze-In WIMP ~ 1 ê T
A Toy Model ' L ' 2 + 2 m. m χ ϕ ν ϕ ν χ ϕ (Freeze-Out) (Equilibration and Decay)
A Toy Model ' L ' 2 + 2 10 2 Thermal Dark Matter Clusters l n = 10-8 mc ê m j 10 1 Ly-a l n = 10-9 Neff l n = 10-10 10 10 2 10 3 m c @kevd
Summary Sub-MeV DM that freezes-out thermally with the SM is possible. Equilibration predicts a limited range for DM-SM coupling. CMB-S4 and 21 cm observations will be sensitive to the entire parameter space.
Back Up Slides
Neff DM-SM Equilibration? Neutrino-Photon Decoupling ~ MeV End of BBN ~ 100 kev T Recombination ~ ev
Neff DM-SM Equilibration? Neutrino-Photon Decoupling ~ MeV End of BBN ~ 100 kev T Recombination ~ ev
Neff γ ν γ γ ν DM ν DM ν DM DM N e ' 3 1+ 4 4/3 21 g & 3.78 &.
Neff γ ν γ γ DM ν ν DM ν DM DM &. N e ' 3 1+ 4 / 41/3 21 g L & 3.18
Neff γ ν γ γ DM ν ν DM ν DM DM &. N e ' 3 1+ 4 / 41/3 21 g L & 3.18 (~ cyclic, but ds > 0)
Neff 5.5 Ne 5.0 4.5 4.0 T eq >T dec 3.5 b 3.0 T eq <T dec a 10 0 10 1 10 2 10 3 T [MeV] 10 4 10 5