Medium effects in supernovae constraints on light mediators

TL;DR

This paper reevaluates supernova constraints on light mediators by including medium effects in neutrino interactions, revealing significant impacts on neutrino mean free paths and tightening bounds on new physics models.

Contribution

It introduces a detailed calculation of medium effects on neutrino scattering in supernovae, refining constraints on light scalar and vector mediators beyond previous vacuum-based estimates.

Findings

Medium effects can increase neutrino mean free path by an order of magnitude.

SN constraints on neutrino diffusion are within already excluded parameter regions.

Refined bounds on $U(1)_{B-L}$ and scalar models improve previous limits.

Abstract

In this article, we reevaluate supernovae (SN) constraints on the diffusion time of neutrinos for a family of extensions of the Standard Model that incorporate new light scalar and vector mediators. We compute the neutrino mean free path, taking into account medium effects in the neutrino-nucleon scattering cross-section, and a radial dependence of the density, energy, and temperature inside the proto-neutron star to determine the coupling strengths compatible with SN1987A constraints on the time duration signal of diffusing neutrinos. We show that medium effects can induce an order of magnitude enhancement in the neutrino mean free path with respect to the vacuum calculation. The increase is more significant when new physics terms dominate over the Standard Model contribution (that is, for small mediator mass and large couplings). Finally, we interpret these results as bounds on the parameter space of a vector $U(1)_{B-L}$ model and scalar lepton number conserving and lepton number violating scenarios, improving on previous results in the literature where medium effects were ignored. We show that SN constraints on the neutrino diffusion time lie within regions of the parameter space that are already ruled out by other experimental constraints. We also comment on potential limits due to changes in the SN equation of state or right-handed neutrino free-streaming, but argue that detailed numerical simulations are needed to improve the reliability of these limits.