Abstract
Spectra of stochastic gravitational waves (GW) generated in cosmological first-order phase transitions are computed within strongly correlated theories with a dual holographic description. The theories are mostly used as models of dark sectors. In particular, we consider the so-called Witten-Sakai-Sugimoto model, a SU(N) gauge theory coupled to different matter fields in both the fundamental and the adjoint representations. The model has a well-known top-down holographic dual description which allows us to perform reliable calculations in the strongly coupled regime. We consider the GW spectra from bubble collisions and sound waves arising from two different kinds of first-order phase transitions: a confinement/deconfinement one and a chiral symmetry breaking/restoration one. Depending on the model parameters, we find that the GW spectra may fall within the sensibility region of ground-based and space-based interferometers, as well as of Pulsar Timing Arrays. In the latter case, the signal could be compatible with the recent potential observation by NANOGrav. When the two phase transitions happen at different critical temperatures, characteristic spectra with double frequency peaks show up. Moreover, in this case we explicitly show how to correct the redshift factors appearing in the formulae for the GW power spectra to account for the fact that adiabatic expansion from the first transition to the present times cannot be assumed anymore.
Highlights
Two of them are dimensional quantities: MKK, which represents the dynamically generated scale providing the mass of the first glueball and that of the first KK field, and L which gives the scale of chiral symmetry breaking fχ,L, as we will discuss in a moment
Let us comment on the behavior of the spectra that we find in the scenarios where a chiral symmetry breaking/restoration transition occurs
11Indeed, we recall that the formulae for the spectra are affected by the incertitudes mentioned in the introduction, a big chiral symmetry signal is needed in order to be significant
Summary
We describe the features of the Witten-Sakai-Sugimoto model that are needed in order to understand the calculation of the GW spectra. Two of them are dimensional quantities: MKK, which represents the dynamically generated scale providing the mass of the first glueball and that of the first KK field, and L which gives the scale of chiral symmetry breaking fχ,L, as we will discuss in a moment. L is a free parameter of the model that can be used to separate the confinement scale from the chiral symmetry. When L > 0.97MK−K1 the confinement/deconfinement transition implies the chiral symmetry breaking/restoration one. When L < 0.97MK−K1 , the two transitions are independent, with the chiral symmetry breaking/restoration one occurring at the temperature. The parameter L has the maximal value L = πMK−K1 , when the scale of chiral symmetry breaking reads fχ.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have