Spinodal Gravitational Waves

Abstract

We uncover a new gravitational-wave production mechanism in cosmological, first-order, thermal phase transitions. These are usually assumed to proceed via the nucleationof bubbles of the stable phase inside the metastable phase. However, if the nucleationrate is sufficiently suppressed, then the Universe may supercool all the way down themetastable branch and enter the spinodal region. In this case the transition proceeds via theexponential growth of unstable modes and the subsequent formation, merging and relaxationof phase domains. We use holography to follow the real-time evolution of this process in astrongly coupled, four-dimensional gauge theory and compute the resulting gravitational-wavespectrum. We discuss the possibility that the spinodal dynamics may be preceded by aperiod of thermal inflation.