Nikita Blinov Fermi National Accelerator Laboratory June 4, 2019 Freeze-in, Misalignment, and Non-Standard Thermal Histories . . . . . .. . . . . . . .. . . . . . . .. . . . . . . .. . . .. . . . . .
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2/17 Outline Non-thermal Thermal-ish Thermal coupling to SM relic abundance DM mass
. . . . . . . . . . . . Interactions probed by DD lead . Qualitatively difgerent cosmo/astro if DM/mediator effjciently produced in thermal environments Green and Rajendran (2017) Knapen, Lin and Zurek (2017) DM/mediator attains equilibrium at some point if Scattering Emission/Absorption . . . . . . . . . . . . . . . . . . . . . . . . . . . 3/17 Thermal Equilibrium to SM ↔ DM energy transfer DM DM SM SM DM SM SM Γ/ H > 1
. . . . . . . . . . . . . . . . . Reaction rates at fjnite temperature have the form light mediator heavy mediator . . . . . . . . . . . . . . . . . . . . . . 4/17 . Cosmology with Light Particles { λ 2 / T n Γ/ H ∝ λ 2 T n / m 4 Equilibration Equilibration reaction rate per Hubble reaction rate per Hubble Decreasing Coupling Decreasing Mediator Mass time (or 1 /T ) time (or 1 /T )
. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4/17 . . . . Cosmology with Light Particles If equilibrium attained before BBN (i.e. at T ≳ 5 MeV ) and m ≲ 10 MeV : ρ χ ∼ ρ γ modifjes the expansion rate Heat injection from decay/freeze-out dilutes T ν / T γ , baryon density η b Equilibration Equilibration reaction rate per Hubble reaction rate per Hubble Decreasing Coupling Decreasing Mediator Mass time (or 1 /T ) time (or 1 /T )
. . . . . . . . . . . . . . Aver, Olive & Skillman (2013); Cooke, Pettini & Steidel (2017) with standard BBN Light thermal DM particles can modify 1. Expansion rate: see, e.g., Nollett and Steigman (2013) SM-like N eff b . . . . . . . . . . . . . . 5/17 . . . . . . . . . . . . Constraints from BBN Primordial 4 He and D yields measured precisely ( ≲ 2 % ) 2.6 2.4 2.2 These are in ∼ 1 σ agreement 2.0 1.8 1.6 N eff ∝ ( T ν / T γ ) 4 2. Baryon density η b Success of standard BBN ⇒ thermal, EM-coupled relics have m ≳ few MeV
. . . . . . . . . . . . . . Aver, Olive & Skillman (2013); Cooke, Pettini & Steidel (2017) with standard BBN Light thermal DM particles can modify 1. Expansion rate: see, e.g., Nollett and Steigman (2013) SM-like b . . . . . . . . . . . . . . . . . . . . . . . 5/17 . . . Constraints from BBN Primordial 4 He and D yields measured precisely ( ≲ 2 % ) 2.6 2.4 2.2 N eff ↓ These are in ∼ 1 σ agreement 2.0 1.8 1.6 N eff ∝ ( T ν / T γ ) 4 2. Baryon density η b Success of standard BBN ⇒ thermal, EM-coupled relics have m ≳ few MeV
. . . . . . . . . . . . . . Aver, Olive & Skillman (2013); Cooke, Pettini & Steidel (2017) with standard BBN Light thermal DM particles can modify 1. Expansion rate: see, e.g., Nollett and Steigman (2013) SM-like N eff . . . . . . . . . . . . . . . . . . . . . . . 5/17 . . . Constraints from BBN Primordial 4 He and D yields measured precisely ( ≲ 2 % ) 2.6 2.4 2.2 η b ↑ These are in ∼ 1 σ agreement 2.0 1.8 1.6 N eff ∝ ( T ν / T γ ) 4 2. Baryon density η b Success of standard BBN ⇒ thermal, EM-coupled relics have m ≳ few MeV
. . . . . . . . . . . . . . . CMB sensitive to energy density in free-streaming species ( N eff ) Photon difgusion exponentially damps density perturbations for H Planck constraint on N eff translates into weaken CMB and BBN bounds. Hu, Fukugita, Zaldarriaga and Tegmark (2001) . . . . . . . . . . . . . . . . . . . . . 6/17 . . . . Constraints from the CMB 10 radiation √ n e σ T driving ℓ ≳ ℓ D ∼ ℓ A ( ∆ T l ) 2 damping 1 transfer function x baryon = modulation 0.1 l eq l A l D m χ ≳ few MeV ∗ 10 100 1000 l EM-coupled scalar. ∗ Extra “dark radiation” can ofg-set N eff decrease and
. . . . . . . . . . . . . . . CMB sensitive to energy density in free-streaming species ( N eff ) Photon difgusion exponentially damps density perturbations for H Planck constraint on N eff translates into weaken CMB and BBN bounds. Bashinsky and Seljak (2004), Hou et al (2011) . . . . . . . . . . . . . . 6/17 . . . . . . . . . . . Constraints from the CMB Fixed θ s , z eq 1 . 10 ( N eff = 3 . 046) √ n e σ T 1 . 05 ℓ ≳ ℓ D ∼ ℓ A 1 . 00 ∆ N eff = − 1 /C TT ∆ N eff = − 0 . 5 ℓ 0 . 95 ∆ N eff = 0 . 5 C TT ∆ N eff = 1 ℓ 0 . 90 m χ ≳ few MeV ∗ 10 1 10 2 10 3 Multipole ℓ EM-coupled scalar. ∗ Extra “dark radiation” can ofg-set N eff decrease and
. . . . . . . . . . . . . . cannot be thermal? If equilibration occurs after neutrino-photon decoupling Energy conservation ensures Thermal neurtrino-coupled relics avoid BBN + CMB bounds EM-coupled relics still constrained by BBN (large Bartlett & Hall (1991); Chacko et al (2003, 2004); Berlin & NB (2017); Berlin, NB & Li (2019) . . . . . . . . . . . . . . . . . . . . . . . . . . 7/17 Late equilibration Do the CMB+BBN constraints imply that DM with m ≲ few MeV Late Equilibration of Dark Sector Particles reaction rate per Hubble γ, ν ( T ∼ 2 MeV ), coupled Γ /H = 1 N eff is close to SM value γ, ν decoupled time (or 1 /T ) modifjcations of η b )
. . . . . . . . . . . . . . . . . Equilibrium never achieved, density builds up gradually Generic and predicive, but hidden assumption: initial abundance tiny Dodelson and Widrow (1993); Hall, Jedamzik, March-Russell and West (2009) 8/17 . . . . . . . . . . . . . production rate always sub-Hubble . . . . . . . . . . Freeze-in ⇒ non-trivial constraint on cosmology, see Adshead, Cui & Shelton (2016) DD-accessible models feature light m φ < α m e mediator Freeze-In Freeze-in Abundance Evolution Equilibrium reaction rate per Hubble Γ /H = 1 log(abundance) correct relic abundance for λ ∼ 10 − 12 log( m/T ) time (or 1 /T )
. . . . . . . . . . . . . . Mediators other than (dark) photon too constrained Arises as fundamental Plasmon decay contribution previously missed; lowers preferred coupling by a factor of Annihilation Plasmon decay Dvorkin, Lin and Schutz (2019) . . . . . . . . . . . . . . 9/17 . . . . . . . . . . . . Freeze-in Through Dark Photon/Millicharge Portal e χ χγ µ χ A µ , Q χ ≪ 1 L ⊃ eQ χ ¯ χ e millicharge or via A ′ - γ mixing χ γ ∗ χ ≳ 3 for
. . . . . . . . . . . . . . . . . . Dvorkin, Lin and Schutz (2019) . . . . . . . . . . . . 9/17 . . . . . . . . . . Freeze-in Through Dark Photon/Millicharge Portal 10 − 9 Al SC CDMS G2 Super- Millicharge, Q = κg χ /e 10 − 10 Freeze-in 10 − 11 10 − 12 Stellar Emission GaAs ZrTe 5 10 − 13 Al 2 O 3 10 − 14 10 − 3 10 − 2 10 − 1 10 0 m χ [MeV]
. . . . . . . . . . . . . . . . BSM cooling mechanisms change distribution of stars Rafgelt (1996)++; Hardy and Lasenby (2016) constraints on detectable models Green and Rajendran (2017) , Knapen, Lin and Zurek (2017) Dvorkin, Lin and Schutz (In progress) Fully non-thermal production mechanisms are required for . . . . . . . . . . . . . . . . . . . . . 10/17 . . . Additional Constraints DM still produced from thermal SM particles ⇒ additional constraints Brighter Red Giants (later 4 He ignition), fewer Horizontal Branch stars (faster 4 He burn) For m ≲ 100 keV , these forbid thermal contact and put severe Frozen-in DM is produced with v χ ≲ 1 (similar to warm DM) m χ ≳ 20 keV m χ ≲ 100 keV
. . . . . . . . . . . . . . . Generic mechanism for light bosonic DM, a (axions, ALPs, moduli,…) Scalar displaced from the origin Oscillations about origin begin when Energy density redshifts as matter: . . . . . . . . . . . . . . 11/17 . . . . . . . . . . . Misalignment 1.0 0.8 0.6 0.4 0.2 0.0 of its potential with a i = θ 0 f a - 0.2 0.1 1 10 100 1 m a ∼ H 0.100 0.010 0.001 ρ a ∝ 1/ a 3 0.1 1 10 100
. Evolution before nucleosynthesis . . . . . . . . Final abundance depends on evolution of the total energy density . . m a a 12/17 radiation NB, Dolan, Draper & Kozaczuk (2019) matter Visinelli & Gondolo (2009)+ kination correct abundance obtained for difgerent values of m a , f a depending on cosmology . . . . . . . . . . . . . . . . . . . . . . . . . . . . . Sensitivity to Early Cosmology Fractional ALP Density Evolution 10 − 4 10 − 6 Early Matter Domination Radiation 10 − 8 ρ a /ρ tot T ≳ 5 MeV unknown: T RH , T kin 10 − 10 Kination ( ) 2 ( ) 1/2 a − 4 10 − 12 h 2 = 0 . 12 f a θ 0 Ω RD 10 13 GeV µ eV a − 3 ρ tot ∝ 10 − 14 10 0 10 1 10 2 10 3 10 4 a − 6 R/R osc Smaller f a ⇒ larger coupling to SM g a γγ ∝ 1/ f a
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