Speaker
Dr
Marek Lewicki
Description
We derive efficiency factors for the production of
gravitational waves through bubble collisions and
plasma-related sources in strong phase transitions, and find
the conditions under which the bubble collisions can
contribute significantly to the signal. We illustrate our
findings in two examples, the Standard Model with an extra
$|H|^6$ interaction and a classically scale-invariant
$U(1)_{\rm B-L}$ extension of the Standard Model. The
contribution to the GW spectrum from bubble collisions is
found to be negligible in the $|H|^6$ model, whereas it can
play an important role in parts of the parameter space in
the scale-invariant $U(1)_{\rm B-L}$ model. In both cases
the sound-wave period is much shorter than a Hubble time,
suggesting a significant amplification of the
turbulence-sourced signal. We find, however, that the peak
of the plasma-sourced spectrum is still produced by sound
waves with the slower-falling turbulence contribution
becoming important off-peak.
