Messengers from the Early Universe: Cosmic Neutrinos and Other Light Relics

Green, Daniel

Title: Messengers from the Early Universe: Cosmic Neutrinos and Other Light Relics

Abstract

The hot dense environment of the early universe is known to have produced large numbers of baryons, photons, and neutrinos. These extreme conditions may have also produced other long-lived species, including new light particles (such as axions or sterile neutrinos) or gravitational waves. The gravitational effects of any such light relics can be observed through their unique imprint in the cosmic microwave background (CMB), the large-scale structure, and the primordial light element abundances, and are important in determining the initial conditions of the universe. We argue that future cosmological observations, in particular improved maps of the CMB on small angular scales, can be orders of magnitude more sensitive for probing the thermal history of the early universe than current experiments. These observations offer a unique and broad discovery space for new physics in the dark sector and beyond, even when its effects would not be visible in terrestrial experiments or in astrophysical environments. A detection of an excess light relic abundance would be a clear indication of new physics and would provide the first direct information about the universe between the times of reheating and neutrino decoupling one second later.

Authors:

Green, Daniel ^[1]

Univ. of California, San Diego, CA (United States)

Publication Date:: Tue Mar 12 00:00:00 EDT 2019

Research Org.:: Brookhaven National Lab. (BNL), Upton, NY (United States); Fermi National Accelerator Lab. (FNAL), Batavia, IL (United States); Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States); Lawrence Berkeley National Lab. (LBNL), Berkeley, CA (United States); SLAC National Accelerator Lab., Menlo Park, CA (United States); Argonne National Lab. (ANL), Argonne, IL (United States)

Sponsoring Org.:: USDOE Office of Science (SC), High Energy Physics (HEP)

OSTI Identifier:: 1542185

Report Number(s):: arXiv:1903.04763; FERMILAB-PUB-19-099-A-AE-CD
Journal ID: ISSN 0002-7537; 1724727

Grant/Contract Number:: AC02-07CH11359

Resource Type:: Accepted Manuscript

Journal Name:: Bulletin of the American Astronomical Society

Additional Journal Information:: Journal Volume: 51; Journal Issue: 7; Journal ID: ISSN 0002-7537

Publisher:: American Astronomical Society

Country of Publication:: United States

Language:: English

Subject:: 79 ASTRONOMY AND ASTROPHYSICS; 72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS

Citation Formats


                    Green, Daniel. Messengers from the Early Universe: Cosmic Neutrinos and Other Light Relics.  United States: N. p., 2019. 
Web.

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                    Green, Daniel. Messengers from the Early Universe: Cosmic Neutrinos and Other Light Relics.  United States.

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                    Green, Daniel. Tue .  
"Messengers from the Early Universe: Cosmic Neutrinos and Other Light Relics".  United States.  https://www.osti.gov/servlets/purl/1542185.

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@article{osti_1542185,

  title        = {Messengers from the Early Universe: Cosmic Neutrinos and Other Light Relics},

  author       = {Green, Daniel},

  abstractNote = {The hot dense environment of the early universe is known to have produced large numbers of baryons, photons, and neutrinos. These extreme conditions may have also produced other long-lived species, including new light particles (such as axions or sterile neutrinos) or gravitational waves. The gravitational effects of any such light relics can be observed through their unique imprint in the cosmic microwave background (CMB), the large-scale structure, and the primordial light element abundances, and are important in determining the initial conditions of the universe. We argue that future cosmological observations, in particular improved maps of the CMB on small angular scales, can be orders of magnitude more sensitive for probing the thermal history of the early universe than current experiments. These observations offer a unique and broad discovery space for new physics in the dark sector and beyond, even when its effects would not be visible in terrestrial experiments or in astrophysical environments. A detection of an excess light relic abundance would be a clear indication of new physics and would provide the first direct information about the universe between the times of reheating and neutrino decoupling one second later.},

  doi          = {},

  journal      = {Bulletin of the American Astronomical Society},

  number       = 7,

  volume       = 51,

  place        = {United States},

  year         = {Tue Mar 12 00:00:00 EDT 2019},

  month        = {Tue Mar 12 00:00:00 EDT 2019}

}

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Figure 1: Left: Limits on the dark matter-baryon cross section σ_bDM for a Yukawa potential. Future cosmological constraints will restrict ∆N_eff < 0.09 and, therefore, exclude cross sections large enough to thermalize the (200 keV-mass) particle mediating the force [55]. This limit is compared to the direct bound on baryon-darkmore »

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