Abstract
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.
Highlights
Map, we can obtain a complementary insight into the nature of inflationary fluctuations relative to the Cosmic Microwave Background (CMB) and Large-Scale Structure (LSS)
Just as primordial non-Gaussianity (NG) in the cosmic microwave background (CMB) or LSS can arise as reflections of interactions of the inflationary fields, and is being actively searched for, it is possible for the gravitational wave backgrounds (GWB) fluctuations to exhibit NG
We find that for the latter case, provided the astrophysical GW “foreground” from binary mergers can be subtracted, future GW detectors would be able to probe primordial NG in a stronger way compared to the CMB and especially, LSS
Summary
GW from first order PT get generated due to three processes: collisions of nucleating bubble walls, magnetohydrodynamic (MHD) turbulence and sound waves in the plasma (for recent discussions see [40, 41] and references therein). We note that while the more recently considered “bulk-flow approximation” [49, 50] can change the frequency dependence of GW away from the peak, the peak amplitude roughly matches the one from the envelope approximation for some models, as seen in [51]. This conclusion regarding the peak amplitude remains true for the new estimates of GW obtained in [51, 52] as well.
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call