Power law plateau inflation and primordial gravitational waves in the light of ACT

We investigate Power-Law Plateau (PLP) inflation in standard gravity and its consistency with ACT DR6 data. While many inflationary models, including the Starobinsky inflation, are disfavored by ACT observations, the PLP potential remains viable across a broad range of its parameters. Then, the dynamics of the reheating phase are investigated, with a primary focus on the reheating temperature and its relationship with the inflationary phase and primordial gravitational waves. Incorporating the overproduction of the primordial gravitational waves can affect the effective number of relativistic species during reheating. The constraint on Δ N eff can impose a lower bound on the reheating temperature. This constraint will be more efficient for a stiff equation of state. It is determined that for w re ≳ 0.58, this constraint would be efficient. Combining the result of the reheating temperature and the inflationary phase, it is concluded that to have both a viable result standing in 1 σ of ACT DR6 and also to satisfy the reheating lower bound, the number of remaining e-folds of inflation after the pivot scale exits the horizon should be N k ≲ 62. Higher e-folds of expansion result in a reheating temperature below the bound, which is disfavored. Finally, for the constraint values of the reheating temperature, the energy spectrum of the primordial gravitational waves (PGWs) has been explored. The results indicate that there is a higher chance of detection of PGWs for lower reheating temperatures and higher reheating equation of state. We also address the condensate fragmentation during reheating for stiff w re ≥ 0.58. It is discussed that for our model, the stiff phase could last for some e-folds before w re → 1/3. This leads to a larger reheating temperature T re , however, the resulting PGWs energy spectrum is suppressed and it is below the detectable level.