Watching Worlds Collide: Effects on the CMB from Cosmological Bubble Collisions

TL;DR

This paper models how collisions between cosmological bubbles could leave detectable anisotropic signatures in the cosmic microwave background, with effects varying based on collision parameters and inflation history.

Contribution

It extends previous models to calculate CMB effects from bubble collisions, showing these effects can persist through significant inflation periods.

Findings

Collision effects produce anisotropies in the CMB.

Effects can manifest as hot or cold spots and power asymmetries.

Effects can survive long inflation periods, depending on parameters.

Abstract

We extend our previous work on the cosmology of Coleman-de Luccia bubble collisions. Within a set of approximations we calculate the effects on the cosmic microwave background (CMB) as seen from inside a bubble which has undergone such a collision. We find that the effects are always qualitatively similar--an anisotropy that depends only on the angle to the collision direction--but can produce a cold or hot spot of varying size, as well as power asymmetries along the axis determined by the collision. With other parameters held fixed the effects weaken as the amount of inflation which took place inside our bubble grows, but generically survive order 10 efolds past what is required to solve the horizon and flatness problems. In some regions of parameter space the effects can survive arbitrarily long inflation.