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Title: Long-lived light mediator to dark matter and primordial small scale spectrum

Abstract

We calculate the early universe evolution of perturbations in the dark matter energy density in the context of simple dark sector models containing a GeV scale light mediator. We consider the case that the mediator is long-lived, with lifetime up to a second, and before decaying it temporarily dominates the energy density of the universe. We show that for primordial perturbations that enter the horizon around this period, the interplay between linear growth during matter domination and collisional damping can generically lead to a sharp peak in the spectrum of dark matter density perturbation. As a result, the population of the smallest DM halos gets enhanced. Possible implications of this scenario are discussed.

Authors:
 [1]
  1. Walter Burke Institute for Theoretical Physics,California Institute of Technology, Pasadena, CA 91125 (United States)
Publication Date:
Sponsoring Org.:
SCOAP3, CERN, Geneva (Switzerland)
OSTI Identifier:
22458434
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Cosmology and Astroparticle Physics; Journal Volume: 2015; Journal Issue: 05; Other Information: PUBLISHER-ID: JCAP05(2015)008; OAI: oai:repo.scoap3.org:10207; cc-by Article funded by SCOAP3. Content from this work may be used under the terms of the Creative Commons Attribution 3.0 License. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; DISTURBANCES; ENERGY DENSITY; GALACTIC EVOLUTION; GEV RANGE; NONLUMINOUS MATTER; SPECTRA; UNIVERSE; VISIBLE RADIATION

Citation Formats

Zhang, Yue. Long-lived light mediator to dark matter and primordial small scale spectrum. United States: N. p., 2015. Web. doi:10.1088/1475-7516/2015/05/008.
Zhang, Yue. Long-lived light mediator to dark matter and primordial small scale spectrum. United States. doi:10.1088/1475-7516/2015/05/008.
Zhang, Yue. 2015. "Long-lived light mediator to dark matter and primordial small scale spectrum". United States. doi:10.1088/1475-7516/2015/05/008.
@article{osti_22458434,
title = {Long-lived light mediator to dark matter and primordial small scale spectrum},
author = {Zhang, Yue},
abstractNote = {We calculate the early universe evolution of perturbations in the dark matter energy density in the context of simple dark sector models containing a GeV scale light mediator. We consider the case that the mediator is long-lived, with lifetime up to a second, and before decaying it temporarily dominates the energy density of the universe. We show that for primordial perturbations that enter the horizon around this period, the interplay between linear growth during matter domination and collisional damping can generically lead to a sharp peak in the spectrum of dark matter density perturbation. As a result, the population of the smallest DM halos gets enhanced. Possible implications of this scenario are discussed.},
doi = {10.1088/1475-7516/2015/05/008},
journal = {Journal of Cosmology and Astroparticle Physics},
number = 05,
volume = 2015,
place = {United States},
year = 2015,
month = 5
}
  • We calculate the early universe evolution of perturbations in the dark matter energy density in the context of simple dark sector models containing a GeV scale light mediator. We consider the case that the mediator is long-lived, with lifetime up to a second, and before decaying it temporarily dominates the energy density of the universe. We show that for primordial perturbations that enter the horizon around this period, the interplay between linear growth during matter domination and collisional damping can generically lead to a sharp peak in the spectrum of dark matter density perturbation. As a result, the population ofmore » the smallest DM halos gets enhanced. Possible implications of this scenario are discussed.« less
  • One of the best motivated hypotheses in cosmology states that most of the matter in the universe is in the form of weakly-interacting massive particles that decoupled early in the history of the universe and cooled adiabatically to an extremely low temperature. Nevertheless, the finite temperature and horizon scales at which these particles decoupled imprint generic signatures on their small-scale density fluctuations. We show that the previously recognized cut-off in the fluctuation power-spectrum due to free-streaming of particles at the thermal speed of decoupling, is supplemented by acoustic oscillations owing to the initial coupling between the cold dark matter (CDM)more » and the radiation field. The power-spectrum oscillations appear on the scale of the horizon at kinematic decoupling which corresponds to a mass scale of {approx}10{sup -4}(T{sub d}/10 MeV){sup -3}M{sub {center_dot}} for a CDM decoupling temperature T{sub d}. The suppression of the power-spectrum on smaller scales by the acoustic oscillations is physically independent from the free-streaming effect, although the two cut-off scales are coincidentally comparable for T{sub d}{approx}10 MeV and a particle mass of M{approx}100 GeV. The initial conditions for recent numerical simulations of the earliest and smallest objects to have formed in the universe, need to be modified accordingly. The smallest dark-matter clumps may be detectable through {gamma}-ray production from particle annihilation, through fluctuations in the event rate of direct detection experiments, or through their tidal gravitational effect on wide orbits of objects near the outer edge of the solar system.« less
  • We systematically study light (
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  • Self-interacting dark matter (SIDM) is a simple and well-motivated scenario that could explain long-standing puzzles in structure formation on small scales. If the required self-interaction arises through a light mediator (with mass ∼10 MeV) in the dark sector, this new particle must be unstable to avoid overclosing the universe. The decay of the light mediator could happen due to a weak coupling of the hidden and visible sectors, providing new signatures for direct detection experiments. The SIDM nuclear recoil spectrum is more peaked towards low energies compared to the usual case of contact interactions, because the mediator mass is comparablemore » to the momentum transfer of nuclear recoils. We show that the SIDM signal could be distinguished from that of DM particles with contact interactions by considering the time-average energy spectrum in experiments employing different target materials, or the average and modulated spectra in a single experiment. Using current limits from LUX and SuperCDMS, we also derive strong bounds on the mixing parameter between hidden and visible sector.« less