Forecasting constraints on nonthermal light massive relics from future CMB experiments (CMB-S4/Simons Observatory)

Physical review. D/Physical review. D., vol. 113

Abstract

In this work we present Fisher forecasts on \textit{non-thermal LiMR} models for a CMB Stage IV-like experiment and the Simons Observatory -- particularly focusing on a model of inflaton/moduli decay giving rise to non-thermally distributed dark sector particles, and also comparing our results with those for sterile particles following the Dodelson-Widrow distribution. Two independent parameters, $ΔN_\mathrm{eff}$ and $M_\mathrm{sp}^\mathrm{eff}$, influence linear cosmological observables. We find $ΔN_\mathrm{eff}$ to be more tightly constrained (by a factor of $10$) for a less abundant, heavier LiMR which becomes fully non-relativistic around matter-radiation equality than a more abundant, lighter LiMR which becomes fully non-relativistic just after recombination. The uncertainties on $M_\mathrm{sp}^\mathrm{eff}$ differ by a factor of $\sim3$ between the two cases. Our analysis also reveals distinct parameter correlations: the phenomenological parameters $\{ΔN_\mathrm{eff},M_\mathrm{sp}^\mathrm{eff}\}$ are found to be negatively correlated for the former case and positively correlated for the latter. We obtain similar projected uncertainties on the cosmological parameters (in either case) for both the inflaton/moduli decay and the Dodelson-Widrow models when the first two moments of the LiMR distribution function, related to the phenomenological parameters, are matched. Finally, by constructing a modified distribution that matches the first two moments of the Dodelson-Widrow but deviates maximally in the third moment, we demonstrate that CMB Stage IV data is not expected to be sensitive to higher moments of the distribution.

Authors 4

1. Arka Banerjee
   Affiliation as printed

   Indian Institute of Science Education and Research

2. Subinoy Das

   Indian Institute of Astrophysics

   Affiliation as printed

   Indian Institute of Astrophysics

3. Anshuman Maharana

   Harish-Chandra Research Institute

   Affiliation as printed

   Harish-Chandra Research Institute

4. Ravi Kumar Sharma Aachen

   RWTH Aachen University

   Affiliation as printed

   RWTH Aachen University