Metastable pions in dense media

TL;DR

This paper investigates the conditions under which charged pions become metastable in dense stellar environments, affecting their decay processes and neutrino emission, especially relevant for protoneutron stars.

Contribution

It introduces a detailed analysis of pion metastability in dense media, considering thermal fluctuations and chemical equilibrium in compact star environments.

Findings

Pion decay is suppressed due to Pauli blocking in dense media.

Metastable pions can significantly influence neutrino emissivity in protoneutron stars.

Conditions for simultaneous thermal and chemical equilibrium are identified.

Abstract

We study the leptonic decay of charged pions in a compact star environment. Considering leptons as a degenerated Fermi system, pions are tightly constrained to decay into these particles because their Fermi levels are occupied. Thus, pion decay is only possible through thermal fluctuations. Under these circumstances, pion lifetime is larger and hence can be considered to reach a metastable state. We explore restrictions under which such a metastability is possible. We also study conditions under which pions and leptons already in chemical equilibrium can reach simultaneously the thermal equilibrium, and obtain the neutrino emissivity from metastable pions. Scenarios that favor this metastable state are protoneutron stars.