Quasi-matter Bounce Cosmology in Light of Planck
  We study quasi-matter bounce cosmology in light of Planck cosmic microwave
background (CMB) 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 $w\cong w_0+\kappa(\eta-\eta_0)$
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 $w_0= -\,0.00340\pm 0.00044$ and first-order
correction $10^{4} \zeta= -1.67^{+1.50}_{-0.83}$ at the $1\sigma$ confidence
level by Planck temperature and polarization in combination with the
BICEP2/Keck Array data in which $\zeta = 12\kappa/k_*$ with pivot scale $k_*$.
The spectral index of scalar perturbations is determined to be $n_{\rm
Bs}=0.9623\pm0.0055$ which lies 7$\sigma$ away from the scale-invariant
primordial spectrum. We find scale dependency for $n_{\rm s}$ at the $1\sigma$
confidence level and a tighter constraint on the running of the spectral index
compared to $\Lambda$CDM+$\alpha_s$ cosmology. The running of the spectral
index in quasi-matter bounce cosmology is $\alpha_{\rm Bs}= \pi \zeta /2 c_{\rm
s} = -\hspace{.5mm}0.0021 \pm 0.0016$ which is nonzero at the $1.3\sigma$
level, whereas in $\Lambda$CDM+$\alpha_{\rm s}$ it is nonzero at the
$0.8\sigma$ level for Planck temperature and polarization data. The sound speed
of density fluctuations of the quasi-matter field at the crossing time is
$c_{\rm s} = 0.097^{+0.037}_{-0.023}$, which is not a very small value in the
contracting phase.
