In a broad class of theories, the relic abundance of dark matter is determined by interactions internal to a thermalized dark sector, with no direct involvement of the Standard Model (SM). We point out that these theories raise an immediate cosmological question: how was the dark sector initially populated in the early universe? Motivated in part by the difficulty of accommodating large amounts of entropy carried in dark radiation with cosmic microwave background measurements of the effective number of relativistic species at recombination, Neff , we aim to establish which admissible cosmological histories can populate a thermal dark sector that never reaches thermal equilibrium with the SM. The minimal cosmological origin for such a dark sector is asymmetric reheating, when the same mechanism that populates the SM in the early universe also populates the dark sector at a lower temperature. Here we demonstrate that the resulting inevitable inflaton-mediated scattering between the dark sector and the SM can wash out a would-be temperature asymmetry, and establish the regions of parameter space where temperature asymmetries can be generated in minimal reheating scenarios. Thus obtaining a temperature asymmetry of a given size either restricts possible inflaton masses and couplings or necessitates a non-minimal cosmology for one or both sectors. As a side benefit, we develop techniques for evaluating collision terms in the relativistic Boltzmann equation when the full dependence on Bose-Einstein or Fermi-Dirac phase space distributions must be retained, and present several new results on relativistic thermal averages in an appendix.
Cosmology of Theories beyond the SM Thermal Field Theory
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M. Khlopov, B.A. Malomed and I.B. Zeldovich, Gravitational instability of scalar fields and formation of primordial black holes, Mon. Not. Roy. Astron. Soc.215 (1985) 575 [INSPIRE].ADSCrossRefGoogle Scholar
T. Hahn, CUBA: A library for multidimensional numerical integration, Comput. Phys. Commun.168 (2005) 78 [hep-ph/0404043] [INSPIRE].
B.A. Bassett, S. Tsujikawa and D. Wands, Inflation dynamics and reheating, Rev. Mod. Phys.78 (2006) 537 [astro-ph/0507632] [INSPIRE].
R. Allahverdi, R. Brandenberger, F.-Y. Cyr-Racine and A. Mazumdar, Reheating in Inflationary Cosmology: Theory and Applications, Ann. Rev. Nucl. Part. Sci.60 (2010) 27 [arXiv:1001.2600].ADSCrossRefGoogle Scholar
J.F. Dufaux, G.N. Felder, L. Kofman, M. Peloso and D. Podolsky, Preheating with trilinear interactions: Tachyonic resonance, JCAP07 (2006) 006 [hep-ph/0602144] [INSPIRE].
N. Barnaby, E. Pajer and M. Peloso, Gauge Field Production in Axion Inflation: Consequences for Monodromy, non-Gaussianity in the CMB and Gravitational Waves at Interferometers, Phys. Rev.D 85 (2012) 023525 [arXiv:1110.3327] [INSPIRE].ADSGoogle Scholar
A. Linde, S. Mooij and E. Pajer, Gauge field production in supergravity inflation: Local non-Gaussianity and primordial black holes, Phys. Rev.D 87 (2013) 103506 [arXiv:1212.1693] [INSPIRE].ADSGoogle Scholar
Planck collaboration, P.A.R. Ade et al., Planck 2015 results. XVII. Constraints on primordial non-Gaussianity, arXiv:1502.01592 [INSPIRE].
BICEP2 and Keck Array collaborations, P.A.R. Ade et al., Improved Constraints on Cosmology and Foregrounds from BICEP2 and Keck Array Cosmic Microwave Background Data with Inclusion of 95 GHz Band, Phys. Rev. Lett.116 (2016) 031302 [arXiv:1510.09217] [INSPIRE].
P.B. Greene and L. Kofman, On the theory of fermionic preheating, Phys. Rev.D 62 (2000) 123516 [hep-ph/0003018] [INSPIRE].