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 is widely
regarded as smoking gun evidence for gravitational waves produced during
inflation. Here we demonstrate that tensor perturbations from a cosmological
phase transition in the post-inflationary universe can nearly mimic the
characteristic shape and power of inflationary predictions across a range of
observable angular scales. Although phase transitions arise from subhorizon
physics, they nevertheless exhibit a white noise power spectrum on superhorizon
scales. Thus, while B-mode power is suppressed on these large scales, it is not
necessarily negligible. For viable phase transition parameters, the maximal
B-mode amplitude at multipole moments around the recombination peak can be
comparable to nearly all single-field inflationary predictions that can be
tested with current and future experiments. This approximate degeneracy can be
broken if a signal is measured at different angular scales, since the
inflationary power spectrum is nearly scale invariant while the phase
transition predicts a distinct suppression of power on large scales.
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