possible contributions of $R$ like $R^2$ and $R^2~\ln [R]$ which also have importance in the inflationary scenario. We should also mention here that in the latter case one needs not only quasi-exponential expansion but a metastable (i.e. slowly rolling) one. In $f(R)$ gravity this may occur only if $f(R)$ is close to $R^2$ over some range of $R$ [@refsug].

Acknowledgements {#acknowledgements .unnumbered}
================

The author was partly supported by the Excellence-in-Research Fellowship of IIT Gandhinagar. The author would like to thank an anonymous referee for enlightening comments which immensely helped in improving the manuscript.

[100]{}

Supernova Search Team collaboration, A. G. Riess [*et al.*]{}, Astron. J. [**116**]{} (1998) 1009. Supernova Cosmology Project collaboration, S. Perlmutter [*et al.*]{}, Astrophys. J. [**517**]{} (1999) 565. Boomerang collaboration, P. de Bernardis [*et al.*]{}, Nature 404 (2000) 955. Supernova Cosmology Project collaboration, R. A. Knop [*et al.*]{}, Astrophys. J. 598 (2003) 102.

V. Sahni and A. A. Starobinsky, Int. J. Mod. Phys. D [**9**]{} (2000) 373. T. Padmanabhan, Phys. Rept. [**380**]{} (2003) 235. P. J. E. Peebles and B. Ratra, Rev. Mod. Phys. [**75**]{} (2003) 559. E. J. Copeland, M. Sami and S. Tsujikawa, Int. J. Mod. Phys. D [**15**]{} (2006) 1753. V. Sahni and 