Probing decoupling in dark sectors with the cosmic microwave background

Journal Article · Fri Jun 29 00:00:00 EDT 2018 · Journal of Cosmology and Astroparticle Physics

DOI:https://doi.org/10.1088/1475-7516/2018/06/044· OSTI ID:1984851

Choi, Gongjun ^[1]; Chiang, Chi-Ting ^[1]; LoVerde, Marilena ^[1]

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1. Stony Brook University, NY (United States)

The acoustic peaks in the angular power spectrum of cosmic microwave background (CMB) temperature and polarization anisotropies play an important role as a probe of the nature of new relativistic particles contributing to the radiation density in the early universe, parametrized by Δ N_eff. Here, the amplitude and phase of the acoustic oscillations provide information about whether the extra species are free-streaming particles, like neutrinos, or tightly-coupled, like the photons, during eras probed by the CMB. On the other hand, some extensions of the Standard Model produce new relativistic particles that decouple from their own non-gravitational interactions after neutrinos, but prior to photons. We study the signature of new relativistic species that decouple during this intermediate epoch. We argue that the decoupling species will cause a scale-dependent change in the amplitude and phase shift of the acoustic oscillations, different from the usual constant shifts on small scales. For intermediate decoupling times, the phase and amplitude shifts depend not only on Δ N_eff but the redshift z_dec,X at which the new species decoupled. For Δ N_eff > 0.334, a Stage IV CMB experiment could determine N_eff at the percent level and z_dec,X at the ~ 10% level. For smaller values, Δ N_eff ~ 0.1, constraints on z_dec,X weaken but remain ~ 20–50% for z_dec,X ~ Script O(10³–10⁴). As an application, we study the contributions to Δ N_eff and determine the z_dec,X values for simple implementations of the so-called Nnaturalness model.

• Research Organization: State University of New York (SUNY), Stony Brook, NY (United States)
• Sponsoring Organization: USDOE Office of Science (SC), Fusion Energy Sciences (FES); USDOE Office of Science (SC), High Energy Physics (HEP); National Science Foundation (NSF)
• Grant/Contract Number: SC0017848; PHY-1620628
• OSTI ID: 1984851
• Journal Information: Journal of Cosmology and Astroparticle Physics, Vol. 2018, Issue 06; ISSN 1475-7516
• Publisher: Institute of Physics (IOP)
• Country of Publication: United States
• Language: English

Related Subjects

72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS
particle physics - cosmology connection
CMBR theory
cosmological parameters from CMBR