At the end of inflation the Bunch-Davies vacuum of de Sitter space changes to a different asymptotic vacuum. The two-point correlation of the gravitons will be affected by the mode mixing between the Bunch-Davies de Sitter modes and the eigenmodes of the ‘out’ vacuum. The Bogoliuobov coefficients of this mixing are expected to be a thermal distribution with a Gibbons-Hawking temperature $T=H/2\pi$. We show that the resulting two-point function of the tensor perturbations shows a blue tilt with spectral index $n_T\sim 1$ even in the standard slow-roll inflation. The blue tilted spectrum of tensor perturbation due to Gibbons-Hawking temperature can reconcile the tension between BICEP2 measurement of B-mode polarization with the upper bound from PLANCK.
S. Mohanty and A. Nautiyal
Wed, 9 Apr 14