Cosmological signatures of late-time SU(3)_c symmetry breaking

The only two gauge symmetries which remain unbroken today are SU(3) _c and U(1)_EM. Both are crucial for our universe to appear the way it does and for our form of life to exist. Unless we are very special observers living at the very end of the cosmological symmetry-breaking chain, there is no reason to believe that these two symmetries will remain unbroken forever. In this paper, we investigate the cosmological observational signatures of a late-time SU(3) _c symmetry breaking. We introduce a model with a new colored scalar field whose potential supports a first-order phase transition through nucleation of true-vacuum bubbles. We analyze three physically distinct particle-production mechanisms associated with the expanding bubble wall. The first is direct nonthermal particle production from vacuum mismatch across the accelerating wall, including both the scalar and massive-gluon sectors. The second is particle production from frictional dissipation into a shocked layer. For this channel we include the finite-temperature effective potential and show that, for our benchmark, the critical temperature is below the massive-gluon and scalar masses; therefore an equilibrated relativistic thermal bath of broken-phase massive particles would restore SU(3) _c . We consequently formulate a subcritical thermal freeze-out estimate below T_c, where massive broken-phase particles can still be produced but only with Boltzmann suppression. The third is a non-equilibrium wall-matter transition-radiation channel, in which ambient baryonic matter crossing the relativistic SU(3) _c → U(2) wall can radiate broken-phase massive gluons and scalar excitations. This channel does not require a thermal bath above T_c and can continue after the wall reaches terminal velocity. We then study the decays of the physical color-octet scalar and the massive gluons, and use Pythia to hadronize their decay products and determine the resulting photon and neutrino spectra. If the wall reaches a subluminal terminal velocity, these photons and neutrinos can arrive before the wall itself. The resulting high-energy photon and neutrino spectra constitute a long-range observational signature which, if ever observed, could be interpreted as a signal of cosmic doomsday.