Abnormal dilepton yield from parity breaking in dense nuclear matter

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 ρ spectral function and resulting in a potentially large excess of dileptons with respect to the predictions based in a ‘cocktail’ of known processes.