Single field inflation in the light of Pulsar Timing Array Data: Quintessential interpretation of blue tilted tensor spectrum through Non-Bunch Davies initial condition

Understand

In this work, we present a quintessential interpretation of having a blue-tilted tensor power spectrum for canonical single-field slow-roll inflation to explain the recently observed Pulsar Timing Array (NANOGrav 15-year and EPTA) signal of Gravitational Waves (GW).

• We formulate the complete semi-classical description of cosmological perturbation theory in terms of scalar and tensor modes using the Non-Bunch Davies initial condition.
• We found that the existence of the blue tilt ($n_t$) within the favoured range $1.2<n_t<2.5$ can be explained in terms of a newly derived consistency relation.
• Further, we compute a new field excursion formula using the Non-Bunch Davies initial condition, that validates the requirement of Effective Field Theory in the sub-Planckian regime, $|\Delta\phi|\ll M_{\rm pl}$ for the allowed value of the tensor-to-scalar ratio, $r<0.06$ from CMB observations.