Subdegree Cosmic Microwave Background Anisotropies from Inflationary Bubbles

It is well known that processes of first-order phase transitions may have occurred in the inflationary era. If one or more occurred well before the end of inflation, the nucleated bubbles would have been stretched to large scales and the primordial power spectrum would contain a scale-dependent non-Gaussian component provided by the remnants of the bubbles. We predict the anisotropies in the cosmic microwave background (CMB) induced by inflationary bubbles. We build a general analytic model for describing a bubbly perturbation, evolve each Fourier mode using the linear theory of perturbations from reheating until decoupling, and get the CMB anisotropies by considering the bubbly perturbation intersecting the last scattering surface. The CMB image of an inflationary bubble is a series of concentric isothermal rings of different color (sign of δT/T) on the scale of the sound horizon at decoupling (≤1° in the sky); the resulting anisotropy is therefore strongly non-Gaussian. The mean amplitude of δT/T for a bubble of size L follows the known estimates for linear perturbations, δT/T ≃ δρ/ρ(L/H^-1)². In particular, bubbles with size corresponding to the seeds of the observed large-scale voids (tens of comoving Mpc) induce an interesting pattern of CMB anisotropies on the subdegree angular scale, to be further investigated and compared with the forthcoming high-resolution CMB maps provided by the Microwave Anisotropy Probe (MAP) and the Planck experiments.