Quasi-matter Bounce Cosmology in Light of Planck

Abstract

Abstract We study quasi-matter bounce cosmology in light of Planck cosmic microwave background angular anisotropy measurements along with the BICEP2/Keck Array data. We propose a new primordial scalar power spectrum by considering a linear approximation of the equation of state w ≅ w 0 + κ(η − η 0) for quasi-matter field in the contracting phase of the universe. Using this new primordial scalar power spectrum, we constrain the zeroth-order approximation of the equation of state w 0 = −0.00340 ± 0.00044 and first-order correction 10 4 ζ = − 1.67 − 0.83 + 1.50 at the 1σ confidence level by Planck temperature and polarization in combination with the BICEP2/Keck Array data in which ζ = 12κ/k * with pivot scale k *. The spectral index of scalar perturbations is determined to be n Bs = 0.9623 ± 0.0055, which lies 7σ away from the scale-invariant primordial spectrum. We find scale dependency for n s at the 1σ confidence level and a tighter constraint on the running of the spectral index compared to ΛCDM+α s cosmology. The running of the spectral index in quasi-matter bounce cosmology is α Bs = π ζ/2c s = −0.0021 ± 0.0016, which is nonzero at the 1.3σ level, whereas in ΛCDM+α s it is nonzero at the 0.8σ level for Planck temperature and polarization data. The sound speed of density fluctuations of the quasi-matter field at the crossing time is c s = 0.097 − 0.023 + 0.037 , which is not a very small value in the contracting phase.