Improved supernova bounds on CP-even scalars: cooling and decay constraints

TL;DR

This paper enhances supernova-based constraints on CP-even scalars mixing with the Higgs, significantly improving sensitivity to tiny couplings and extending bounds to hadrophilic models, thus probing a wide parameter space relevant for dark matter.

Contribution

It provides the most stringent supernova constraints to date on CP-even scalars, combining updated production, decay, and astrophysical data to explore new parameter regions.

Findings

Cooling bounds improved by over an order of magnitude

Constraints on mixing angles as small as 10^{-9}

Yukawa couplings constrained down to 10^{-10}

Abstract

Supernovae provide among the most powerful probes of weakly-coupled new particles in the MeV mass range, where laboratory experiments lose sensitivity. In this work, we derive improved supernova constraints on CP-even scalars mixing with the Higgs boson, combining an updated production rate calculation, which improves the cooling bound by more than an order of magnitude, with new decay-based constraints from the galactic 511~keV positron flux and energy deposition in low-energy Type~II-P supernovae. Together, these constraints probe mixing angles as small as $\sin\theta \sim 10^{-9}$, more than five orders of magnitude below existing collider bounds. We also extend our analysis to a hadrophilic scalar model, constraining Yukawa couplings down to $y_N \sim 10^{-10}$. Our results demonstrate that the combination of astrophysical and collider probes covers over nine orders of magnitude in coupling for these classes of models, probing a large region of parameter space motivated by dark matter considerations.