Gluon-Photon mixing in dense QCD

Abstract

At high baryonic density with the formation of a diquark condensate $\Delta \ne 0$, 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 $\tilde{G}$ 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 $\tilde{G}\to e^{-}+e^{+}$ 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 $\tilde{G}\to \nu +\bar{\nu }$ could arise, its amplitude is however $(\Delta /M_Z{)}^2$ power-suppressed.

LaTeX, 8 pages + 1 postscript figure