We study gravitational-wave production from bubble collisions in a cosmic first-order phase transition, focusing on the possibility of model separation by the bubble nucleation rate dependence of the resulting gravitational-wave spectrum. By using the method of relating the spectrum with the two-point correlator of the energy-momentum tensor $\left< T(x)T(y) \right>$, we first write down analytic expressions for the spectrum with a Gaussian correction to the commonly used nucleation rate, $\Gamma \propto e^{ \beta t}\rightarrow e^{ \beta t-\gamma^2t^2}$, under the thin-wall and envelope approximations. Then we quantitatively investigate how the spectrum changes with the size of the Gaussian correction. It is found that the spectral shape shows ${ \mathcal O}(10)\%$ deviation from $\Gamma \propto e^{ \beta t}$ case for some physically motivated scenarios. We also briefly discuss detector sensitivities required to distinguish different spectral shapes.
Categories: hep-ph astro-ph.CO gr-qc hep-th