Gravitational waves from bubble collisions: analytic derivation

Understand

We consider gravitational wave production by bubble collisions during a cosmological first-order phase transition.

• In the literature, such spectra have been estimated by simulating the bubble dynamics, under so-called thin-wall and envelope approximations in a flat background metric.
• However, we show that, within these assumptions, the gravitational wave spectrum can be estimated in an analytic way.
• Our estimation is based on the observation that the two-point correlator of the energy-momentum tensor $\langle T(x)T(y)\rangle$ can be expressed analytically under these assumptions.