Supernova bounds on new scalars from resonant and soft emission

TL;DR

This paper investigates how supernova observations constrain the properties of hypothetical light scalar particles, focusing on their production mechanisms and the resulting bounds on their interactions with standard particles.

Contribution

It provides a comprehensive analysis of supernova cooling bounds on light scalars with various couplings, including resonant mixing and nucleon bremsstrahlung, reducing uncertainties in these constraints.

Findings

Scalars with masses below the plasma frequency are efficiently produced via resonant mixing.

Heavier scalars are mainly produced by nucleon bremsstrahlung, with conservative rate estimates.

Supernova profile variations and scalar decay effects significantly influence the bounds.

Abstract

We study supernova cooling constraints on new light scalars that mix with the Higgs, couple only to nucleons, or couple only to leptons. We show that in all these cases scalars with masses smaller than the plasma frequency in the supernova core are efficiently produced by resonant mixing with the in-medium longitudinal degree of freedom of the photon. The resulting bounds are free from uncertainties associated to the rate of emission of the scalar in nucleon-nucleon scatterings, which would otherwise badly affect the Higgs-mixed and nucleophilic scenarios. Heavier scalars that mix with the Higgs or couple only to nucleons are mostly produced by nucleon bremsstrahlung, and we obtain a conservative approximation for the corresponding rate using a soft theorem. We also analyse the impact of different supernova profiles, nucleon degeneracy, trapping and scalar decays on the constraints.