New one-parametric extension of the Starobinsky inflationary model

We propose a one-parametric extension of the Starobinsky $R+R^2$ model by adding the $(R+m^2{\beta }^2{)}^{3\mathrm{/}2}$ term. The parameter $m$ is the inflaton mass, which is determined in the same way as in the Starobinsky model, and $\beta$ is a dimensionless constant. Using the Einstein frame and the scalar field potential, we get the inflationary parameters of the model proposed. The value of the tensor-to-scalar ratio $r$ can be significantly larger than in the Starobinsky model. The considered inflationary model is in a good agreement with the current observational data. The corresponding scalar field potential is a polynomial of the exponential function.