We study observational viability of Natural Inflation with a tachyon field as inflaton .
By obtaining the main perturbation parameters in this model , we perform a numerical analysis on the parameter space of the model and in confrontation with 68 \% and 95 \% CL regions of Planck2015 data .
By adopting a warped background geometry , we find some new constraints on the width of the potential in terms of its height and the warp factor .
We show that the Tachyon Natural Inflation in the large width limit recovers the tachyon model with a \phi ^ { 2 } potential which is consistent with Planck2015 observational data .
Then we focus on the reheating era after inflation by treating the number of e-folds , temperature and the effective equation of state parameter in this era .
Since it is likely that the value of the effective equation of state parameter during the reheating era to be in the range 0 \leq \omega _ { eff } \leq \frac { 1 } { 3 } , we obtain some new constraints on the tensor to scalar ratio , r , as well as the e-folds number and reheating temperature in this Tachyon Natural Inflation model .
In particular , we show that a prediction of this model is r \leq \frac { 8 } { 3 } \delta _ { ns } , where \delta _ { ns } is the scalar spectral tilt , \delta _ { ns } = 1 - n _ { s } .
In this regard , given that from the Planck2015 data we have \delta _ { ns } = 0.032 ( corresponding to n _ { s } = 0.968 ) , we get r \leq 0.085 . PACS : 98.80.Bp , 98.80.Cq , 98.80.Es Key Words : Natural Inflation , Tachyon Field , Reheating , Observational Constraints