Abnormal dilepton yield from parity breaking in dense nuclear matter

TL;DR

This paper proposes that local parity breaking in dense nuclear matter, caused by a time-dependent pseudoscalar condensate, can explain the observed excess of dileptons in heavy ion collisions by altering photon and vector meson dispersion relations.

Contribution

It introduces a novel mechanism involving parity breaking and a Chern-Simons term to explain dilepton excess in heavy ion collisions.

Findings

Parity breaking modifies photon and vector meson dispersion relations.

The $ ho$ spectral function is significantly altered.

Potentially large dilepton excess explained by the model.

Abstract

At finite density parity can be spontaneously broken in strong interactions with far reaching implications. In particular, a time-dependent pseudoscalar background would modify QED by adding a Chern-Simons term to the lagrangian. As a striking consequence we propose a novel explanation for the dilepton excess observed in heavy ion collisions at low invariant masses. The presence of local parity breaking due to a time-dependent pseudoscalar condensate substantially modifies the dispersion relation of photons and vector mesons propagating in such a medium, changing the $\rho$ spectral function and resulting in a potentially large excess of dileptons with respect to the predictions based in a `cocktail' of known processes.