Constraints on the generalized natural inflation after Planck 2018

Based on the dynamics of single scalar field slow-roll inflation and the theory of reheating,we investigate the generalized natural inflationary(GNI)model.We introduce constraints on the scalar spectral index ns and the tensor-to scalar ratio r for theΛCDM+r model,according to the latest data from Planck 2018 TT,TE,EE+low E+lensing(P18)and BICEP2/Keck 2015 season(BK15),i.e.,with ns=0.9659±0.0044 at 68%confidence level(CL),and r<0.0623 at 95%CL.We find that the GNI model is favored by P18 and BK15 in the ranges log10(f/Mp)=0.62^+0.17−0.18 and m=0.35^+0.13−0.23 at 68%CL.In addition,the corresponding predictions of generalized and two-phase reheating are discussed.It follows that the parameter m has significant effect on the model behavior.