Gluon-Photon mixing in dense QCD

Abstract

At high baryonic density with the formation of a diquark condensate $\Delta \neq 0$, the QCD color symmetry is spontaneously broken. Being massive by the Anderson-Higgs mechanism, gluon and photon should mix together within two linear combinations due to the color non-conservation. Consequently a gluon $\widetilde{G}$ could decay into an $e^- e^+$ pair via its photon component. With a low invariant mass (about a few ten MeV) and an extremely narrow width peaking above the continuum background, the purely leptonic decay of a strongly-interacting gluon $\widetilde{G} \to e^- + e^+$ constitutes a very distinctive signature of the color superconductivity phase. By a similar scenario of gluon-$Z$ mixing, another "missing-energy" decay into invisible neutrinos $\widetilde{G} \to \nu +\bar{\nu}$ could arise, its amplitude is however $(\Delta/M_Z)^2$ power-suppressed.