Gravitational waves from the big bounce

Abstract

In this paper we investigate gravitational wave production during the big bounce phase,inspired by loop quantum cosmology. We consider the influence of the holonomy correctionsto the equation for tensor modes. We show that they act like additional effective gravitonmass, suppressing gravitational wave creation. However, such effects can be treatedperturbatively. We investigate a simplified model without holonomy corrections to theequation for modes and find its exact analytical solution. Assuming the form for matter we calculate the full spectrum of the gravitational waves from the big bounce phase. Thespectrum obtained decreases to zero for the low energy modes. On the basis of thisobservation we infer that this effect can lead to low cosmic microwave background (CMB)multipole suppression and gives a potential way for testing loop quantum cosmologymodels. We also consider a scenario with a post-bounce inflationary phase. The powerspectrum obtained gives a qualitative explanation of the CMB spectra, including lowmultipole suppression.