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- W4288727994 abstract "We present new Big Bang Nucleosynthesis (BBN) limits on the cosmic expansion rate or relativistic energy density, quantified via the number $N_nu$ of equivalent neutrino species. We use the latest light element observations, neutron mean lifetime, and update our evaluation for the nuclear rates $d+d rightarrow He3 + n$ and $d+d rightarrow H3 + p$. Combining this result with the independent constraints from the cosmic microwave background (CMB) yields tight limits on new physics that perturbs $N_nu$ and $eta$ prior to cosmic nucleosynthesis: a joint BBN+CMB analysis gives $N_nu = 2.898 pm 0.141$, resulting in $N_nu < 3.180$ at $2sigma$. We apply these limits to a wide variety of new physics scenarios including right-handed neutrinos, dark radiation, and a stochastic gravitational wave background. We also search for limits on potential {em changes} in $N_nu$ and/or the baryon-to-photon ratio $eta$ between the two epochs. The present data place strong constraints on the allowed changes in $N_nu$ between BBN and CMB decoupling; for example, we find $-0.708 < N_nu^{rm CMB}-N_nu^{rm BBN} < 0.328$ in the case where $eta$ and the primordial helium mass fraction $Y_p$ are unchanged between the two epochs; we also give limits on the allowed variations in $eta$ or in $(eta,N_nu)$ jointly. Looking to the future, we forecast the tightened precision for $N_nu$ arising from both CMB Stage 4 measurements as well as improvements in astronomical he4 measurements. We find that CMB-S4 combined with present BBN and light element observation precision can give $sigma(N_nu) simeq 0.03$. Such future precision would reveal the expected effect of neutrino heating ($N_{rm eff}-3=0.044$) of the CMB during BBN, and would be near the level to reveal any particle species ever in thermal equilibrium with the standard model." @default.
- W4288727994 created "2022-07-30" @default.
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- W4288727994 date "2022-07-26" @default.
- W4288727994 modified "2023-09-30" @default.
- W4288727994 title "Probing Physics Beyond the Standard Model: Limits from BBN and the CMB Independently and Combined" @default.
- W4288727994 doi "https://doi.org/10.48550/arxiv.2207.13133" @default.
- W4288727994 hasPublicationYear "2022" @default.
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