Refined bounds on MeV-scale thermal dark sectors from BBN and the CMB

Sabti, Nashwan; Alvey, James; Escudero, Miguel; Fairbairn, Malcolm; Blas, Diego

doi:10.1088/1475-7516/2020/01/004

Cited by 187 publications

(181 citation statements)

References 188 publications

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“…Finally, while we do not focus explicitly on this case in this work, very strong additional limits from the CMB arise when one of the dark sector fermion is lighter than around 5 MeV (see e.g. [116] for an up-to-date estimate). For dark fermions light enough to behave as radiation at neutrino decoupling, the strongest limits come from the effective number of relativistic degrees of freedom N eff in the early universe.…”

Section: Early Universe and Relic Density Boundsmentioning

confidence: 99%

Light dark sectors through the Fermion portal

Ellis

You

2020

J. High Energ. Phys.

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Pairs of Standard Model fermions form dimension-3 singlet operators that can couple to new dark sector states. This "fermion portal" is to be contrasted with the lower-dimensional Higgs, vector and neutrino singlet portals. We characterise its distinct phenomenology and place effective field theory bounds on this framework, focusing on the case of fermion portals to a pair of light dark sector fermions. We obtain current and projected limits on the dimension-6 effective operator scale from a variety of meson decay experiments, missing energy and long-lived particle searches at colliders, as well as astrophysical and cosmological bounds. The DarkEFT public code is made available for recasting these limits, which we illustrate with various examples including an integratedout heavy dark photon.

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Section: Early Universe and Relic Density Boundsmentioning

confidence: 99%

Light dark sectors through the Fermion portal

Ellis

You

2020

J. High Energ. Phys.

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“…We do this by i) using up-to-date measurements of the primordial element abundances reported in the PDG [37], ii) including a weak determination of the baryon density [16] to alleviate the degeneracy between Ω b h 2 and G in the deuterium abundance, iii) accurately accounting for incomplete neutrino decoupling following [38,39], and iv) making use of the state-of-theart BBN code PRIMAT [40] which has updated nuclear reaction rates and accounts for many corrections to the weak reaction rates. The methodology applied here follows that in [41].…”

mentioning

confidence: 99%

“…Methodology.-To derive the bounds on the variation of the gravitational constant, we follow the approach presented in [41]. We make use of the publicly available code NUDEC BSM [38,39] to compute the background cosmology, including the effects of non-instantaneous neutrino decoupling.…”

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confidence: 99%

Improved BBN constraints on the variation of the gravitational constant

et al. 2020

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Big Bang Nucleosynthesis (BBN) is very sensitive to the cosmological expansion rate. If the gravitational constant G took a different value during the nucleosynthesis epoch than today, the primordial abundances of light elements would be affected. In this work, we improve the bounds on this variation using recent determinations of the primordial element abundances, updated nuclear and weak reaction rates and observations of the Cosmic Microwave Background (CMB). When combining the measured abundances and the baryon density from CMB observations by Planck, we find GBBN/G0 = 1.02 +0.03 −0.03 at 2σ confidence level. If the variation of G is linear in time, we finḋ G/G0 = −1.4 +2.2 −2.3 × 10 −12 yr −1 , again at 2σ. These bounds are significantly stronger than those from previous primordial nucleosynthesis studies, and are comparable and complementary to CMB, stellar, solar system, lunar laser ranging, pulsar timing and gravitational wave constraints.

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“…The constraints are especially severe in the case of light DM. Thermal relic DM with a mass below an MeV is essentially ruled out [3][4][5][6][7][8][9], although a few exceptions do exist [8,[10][11][12]. These constraints are almost completely relaxed for DM that is a diluted hot relic.…”

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confidence: 99%

Light Dark Matter from Entropy Dilution

Evans

Ghalsasi

Gori

et al. 2020

J. High Energ. Phys.

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We show that a thermal relic which decouples from the standard model (SM) plasma while relativistic can be a viable dark matter (DM) candidate, if the decoupling is followed by a period of entropy dilution that heats up the SM, but not the dark sector. Such diluted hot relics can be as light as a keV, while accounting for the entirety of the DM, and not conflicting with cosmological and astrophysical measurements. The requisite dilution can be achieved via decays of a heavy state that dominates the energy budget of the universe in the early matter dominated era. The heavy state decays into the SM particles, heats up the SM plasma, and dilutes the hidden sector. The interaction required to equilibrate the two sectors in the early universe places a bound on the maximum possible dilution as a function of the decoupling temperature. As an example of diluted hot relic DM we consider a light Dirac fermion with a heavy dark photon mediator. We present constraints on the model from terrestrial experiments (current and future), astrophysics, and cosmology.ArXiv ePrint: nnnn.nnnnn

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Refined bounds on MeV-scale thermal dark sectors from BBN and the CMB

Cited by 187 publications

References 188 publications

Light dark sectors through the Fermion portal

Light dark sectors through the Fermion portal

Improved BBN constraints on the variation of the gravitational constant

Light Dark Matter from Entropy Dilution

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