Viability of post-inflationary freeze-in with precision cosmology

TL;DR

This paper explores how inflationary observables, especially the spectral index, can constrain post-inflationary dark matter production via UV freeze-in, providing novel bounds on the cutoff scale of the effective operator.

Contribution

It introduces a new method linking inflationary parameters to dark matter relic density, constraining the UV cutoff scale using cosmological data.

Findings

Planck data excludes cutoff scale $\\\Lambda \lesssim 10^{12}$ GeV for DM masses 1 MeV to 1 TeV.

Combined Planck and ACT data can exclude cutoff scales up to the Planck scale for TeV-scale DM.

The approach provides stronger constraints than previous terrestrial experiments.

Abstract

Prediction of inflationary observables from the temperature fluctuation of Cosmic Microwave Background (CMB) can play a pivotal role in predicting the reheating dynamics in the early universe. In this work, we highlight how the inflationary observables, in particular the spectral index $n_s$, can play a potential role in constraining the post-inflationary dark matter (DM) production. We demonstrate a novel way of constraining the non-thermal production of DM via UV freeze-in which is otherwise elusive in terrestrial experiments. We consider a scenario in which DM is produced from this thermal plasma via a dimension-five operator. The mutual connection between $n_s$ and relic density of DM via the reheating temperature, $T_{\rm RH}$, enables us to put constraints on the DM parameter space. For the minimal choice of the inflationary model parameters and DM mass between $1\,\rm MeV$ to $1\,\rm TeV$, we found that Planck alone can exclude the cut-off scale of the dimension-five operator $\Lambda \lesssim 10^{12}\,\rm GeV$ which is significantly stronger than any other existing constraints on such minimal scenario. If we impose the combined prediction form Planck and recently released data by ACT, the exclusion limit can reach up to the Planck scale for TeV-scale dark matter.