Vacuum popcorn: ultra-high-energy particles from collapsing false-vacuum pockets

First-order phase transitions in the early universe can leave behind pockets of false vacuum that trap a gas of particles. Inside a pocketthe particles are light, and they lack the energy to take on their larger mass outside it. If such a pocket collapses today (a “pop”), its wallbecomes ultra-relativistic and throws the trapped particles out, much as fingers pinched together shoot out a pip. I followed tens of thousandsof them through such collapses with exact relativistic kinematics. A particle that meets the fast-moving wall with energy E leaves with aboutm2out /4E, where mout is its mass outside. For a gas at rest and mass ratios up to a million, the median escapee carries 0.1 to 1.6 per cent ofm2out /min. At larger ratios most escapees leave with less, but the most energetic tenth still carry 0.05 to 0.5 per cent of m2out /min . A particleof 107 GeV outside and 10 GeV inside has a median escape energy near 1020 eV, and one of 1 TeV outside and 10 eV inside sends a tenthor more of its escapees above that. If the escapees decay to photons, Auger’s photon limit caps pops in the Galaxy at about three events ayear in a 3000 km2 array. The nearest pops would arrive as several air showers at the same instant from one direction. No experiment hasyet searched for such groups at these energies.