A bstract Cosmological phase transitions in the primordial universe can produce anisotropic stochastic gravitational wave backgrounds (GWB), similar to the cosmic microwave background (CMB). For adiabatic perturbations, the fluctuations in GWB follow those in the CMB, but if primordial fluctuations carry an isocurvature component, this need no longer be true. It is shown that in non-minimal inflationary and reheating settings, primordial isocurvature can survive in GWB and exhibit significant non-Gaussianity (NG) in contrast to the CMB, while obeying current observational bounds. While probing such NG GWB is at best a marginal possibility at LISA, there is much greater scope at future proposed detectors such as DECIGO and BBO. It is even possible that the first observations of inflation-era NG could be made with gravitational wave detectors as opposed to the CMB or Large-Scale Structure surveys.
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Large primordial fluctuations in gravitational waves from phase transitions
A bstract It is well-known that first-order phase transitions in the early universe can be a powerful source of observable stochastic gravitational wave backgrounds. Any such gravitational wave background must exhibit large-scale anisotropies at least as large as those seen in the CMB 10 − 5 , providing a valuable new window onto the (inflationary) origins of primordial fluctuations. While significantly larger fractional anisotropies are possible (for example, in multi-field inflation) and would be easier to interpret, it has been argued that these can only be consistent with CMB bounds if the gravitational wave signal is correspondingly smaller. In this paper, we show that this argument, which relies on assuming radiation dominance of the very early universe, can be evaded if there is an era of early matter dominance of a certain robust type. This allows large gravitational wave anisotropies to be consistent with observable signals at proposed future gravitational wave detectors. Constraints from the CMB on large scales, as well as primordial black hole and mini-cluster formation on small scales, and secondary scalar-induced gravitational waves are all taken into account.
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- Award ID(s):
- 2210361
- PAR ID:
- 10421665
- Date Published:
- Journal Name:
- Journal of High Energy Physics
- Volume:
- 2023
- Issue:
- 6
- ISSN:
- 1029-8479
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1007/JHEP06(2023)029
