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Title: When the universe expands too fast: relentless dark matter

Abstract

We consider a modification to the standard cosmological history consisting of introducing a new species φ whose energy density red-shifts with the scale factor a like ρ{sub φ} ∝ a {sup −(4+} {sup n} {sup )}. For 0 n >, such a red-shift is faster than radiation, hence the new species dominates the energy budget of the universe at early times while it is completely negligible at late times. If equality with the radiation energy density is achieved at low enough temperatures, dark matter can be produced as a thermal relic during the new cosmological phase. Dark matter freeze-out then occurs at higher temperatures compared to the standard case, implying that reproducing the observed abundance requires significantly larger annihilation rates. Here, we point out a completely new phenomenon, which we refer to as relentless dark matter: for large enough n , unlike the standard case where annihilation ends shortly after the departure from thermal equilibrium, dark matter particles keep annihilating long after leaving chemical equilibrium, with a significant depletion of the final relic abundance. Relentless annihilation occurs for n ≥ 2 and n ≥ 4 for s -wave and p -wave annihilation, respectively, and it thus occurs in well motivatedmore » scenarios such as a quintessence with a kination phase. We discuss a few microscopic realizations for the new cosmological component and highlight the phenomenological consequences of our calculations for dark matter searches.« less

Authors:
; ;  [1]
  1. Department of Physics, University of California Santa Cruz, 1156 High St., Santa Cruz, CA 95064 (United States)
Publication Date:
OSTI Identifier:
22676226
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2017; Journal Issue: 05; Other Information: Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
79 ASTROPHYSICS, COSMOLOGY AND ASTRONOMY; ABUNDANCE; ANNIHILATION; COMPARATIVE EVALUATIONS; COSMOLOGICAL MODELS; ENERGY DENSITY; MODIFICATIONS; NONLUMINOUS MATTER; P WAVES; RED SHIFT; S WAVES; THERMAL EQUILIBRIUM; UNIVERSE

Citation Formats

D'Eramo, Francesco, Fernandez, Nicolas, and Profumo, Stefano, E-mail: fderamo@ucsc.edu, E-mail: nfernan2@ucsc.edu, E-mail: profumo@ucsc.edu. When the universe expands too fast: relentless dark matter. United States: N. p., 2017. Web. doi:10.1088/1475-7516/2017/05/012.
D'Eramo, Francesco, Fernandez, Nicolas, & Profumo, Stefano, E-mail: fderamo@ucsc.edu, E-mail: nfernan2@ucsc.edu, E-mail: profumo@ucsc.edu. When the universe expands too fast: relentless dark matter. United States. doi:10.1088/1475-7516/2017/05/012.
D'Eramo, Francesco, Fernandez, Nicolas, and Profumo, Stefano, E-mail: fderamo@ucsc.edu, E-mail: nfernan2@ucsc.edu, E-mail: profumo@ucsc.edu. Mon . "When the universe expands too fast: relentless dark matter". United States. doi:10.1088/1475-7516/2017/05/012.
@article{osti_22676226,
title = {When the universe expands too fast: relentless dark matter},
author = {D'Eramo, Francesco and Fernandez, Nicolas and Profumo, Stefano, E-mail: fderamo@ucsc.edu, E-mail: nfernan2@ucsc.edu, E-mail: profumo@ucsc.edu},
abstractNote = {We consider a modification to the standard cosmological history consisting of introducing a new species φ whose energy density red-shifts with the scale factor a like ρ{sub φ} ∝ a {sup −(4+} {sup n} {sup )}. For 0 n >, such a red-shift is faster than radiation, hence the new species dominates the energy budget of the universe at early times while it is completely negligible at late times. If equality with the radiation energy density is achieved at low enough temperatures, dark matter can be produced as a thermal relic during the new cosmological phase. Dark matter freeze-out then occurs at higher temperatures compared to the standard case, implying that reproducing the observed abundance requires significantly larger annihilation rates. Here, we point out a completely new phenomenon, which we refer to as relentless dark matter: for large enough n , unlike the standard case where annihilation ends shortly after the departure from thermal equilibrium, dark matter particles keep annihilating long after leaving chemical equilibrium, with a significant depletion of the final relic abundance. Relentless annihilation occurs for n ≥ 2 and n ≥ 4 for s -wave and p -wave annihilation, respectively, and it thus occurs in well motivated scenarios such as a quintessence with a kination phase. We discuss a few microscopic realizations for the new cosmological component and highlight the phenomenological consequences of our calculations for dark matter searches.},
doi = {10.1088/1475-7516/2017/05/012},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 05,
volume = 2017,
place = {United States},
year = {Mon May 01 00:00:00 EDT 2017},
month = {Mon May 01 00:00:00 EDT 2017}
}
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