Observational constraints on power law Starobinsky inflation

In this work we revisit power law, M12 RQ, inflation to find the deviations from R2 inflation allowed by current cosmic microwave background (CMB) and large-scale structure (LSS) observations. We compute the power spectra for scalar and tensor perturbations numerically and perform Markov chain Monte Carlo analysis to put constraints on parameters M and Q from Planck-2018, BICEP3 and other LSS observations. We consider general reheating scenario and also vary the number of e-foldings during inflation, Npivot, along with the other parameters. We find Q = 1.966 thorn 0.035 -0.042 , M = (3.31 thorn 5 -2 ) x 10-5 and Npivot = 41 thorn 10 -10 with 95% C.L. This indicates that the current observations allow deviation from Starobinsky inflation. The scalar spectral index, ris, and tensor-to-scalar ratio, r, derived from these parameters, are consistent with the Planck and BICEP3 observations.