Hosted by: Morgan May

An intriguing possibility that can address pathologies in both early universe cosmology (i.e. the horizon problem) and quantum gravity (i.e. non-renormalizability), is that particles at very high energies and/or temperatures could propagate arbitrarily fast. In this talk, I introduce Thermal Tachyacoustic Cosmology (TTC), i.e. this scenario with thermal initial conditions. We find that a phase transition in the early universe, around the scale of Grand Unified Theories (GUT scale; T∼10^{15} GeV), during which the speed of sound drops by several orders of magnitude within a Hubble time, can fit current CMB observations. However, I will then argue that cosmological bounds on the density of primordial black holes suggest that Lorentz invariance in the primordial thermal plasma may not recover until much lower temperatures, close to the QCD phase transition. This presents the exciting possibility of testing this scenario in the thermal plasma produced in relativistic heavy ion collisions.