Kavli Affiliate: Gordan Krnjaic
| First 5 Authors: Kylar Greene, Aurora Ireland, Gordan Krnjaic, Yuhsin Tsai,
| Summary:
A B-mode polarization signal in the cosmic microwave background (CMB) is
widely regarded as smoking gun evidence for gravitational waves produced during
inflation. Here we demonstrate that tensor perturbations from a cosmological
phase transition can produce a B-mode signal whose strength rivals that of
testable inflationary predictions across a range of observable scales. Although
phase transitions arise from causal sub-horizon physics, they nevertheless
exhibit a white noise power spectrum on super-horizon scales. Power is
suppressed on the large scales relevant for CMB B-mode polarization, but it is
not necessarily negligible. For appropriately chosen phase transition
parameters, the maximal B-mode amplitude can compete with inflationary
predictions that can be tested with current and future experiments. These
scenarios can be differentiated by performing measurements on multiple angular
scales, since the phase transition signal predicts peak power on smaller
scales.
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