Probing Pre-BBN Cosmology with Primordial Gravitational Waves
Fazlollah Hajkarim (Frankfurt University)

Using the quantum chromodynamics (QCD) equation of state (EoS) from lattice calculations we investigated QCD effects on the first order primordial gravitational waves (PGWs) produced during the inflationary era. We also considered the cases for vanishing and nonvanishing lepton asymmetry where the latter one is constrained by cosmic microwave background experiments. Also, we investigated scenarios that inflation is succeeded by a phase where the energy density of the Universe was dominated by a scalar component with a general equation of state. Then we evaluated the spectrum of primordial gravitational waves induced in the post-inflationary Universe. We showed that if the energy density of the Universe was dominated by some specific fluid 𝜙 before Big Bang Nucleosynthesis (BBN), its equation of state could be constrained by gravitational wave experiments. Moreover, we studied the effect of QCD and electroweak transitions on the induced (or second order) PGW from scalar perturbations which is different from the first order PGW spectrum. Finally, I briefly discuss the production of dark matter (DM) in an early matter era dominated by a heavy long lived scalar field.