Cosmic Microwave Background ( CMB ) is an important probe for understanding the inflationary era of the Universe .
We consider the Perturbed Power Law ( PPL ) model of inflation which is a soft deviation from Power Law ( PL ) inflationary model .
This model captures the effect of higher order derivative of Hubble parameter during inflation , which in turn leads to a non-zero effective mass m _ { eff } for the inflaton field .
The higher order derivatives of Hubble parameter at leading order sources constant difference in the spectral index for scalar and tensor perturbation going beyond PL model of inflation .
PPL model have two observable independent parameters , namely spectral index for tensor perturbation \nu _ { t } and change in spectral index for scalar perturbation \nu _ { st } to explain the observed features in the scalar and tensor power spectrum of perturbation .
From the recent measurements of CMB power spectra by WMAP , Planck and BICEP-2 for temperature and polarization , we estimate the feasibility of PPL model with standard \Lambda CDM model .
Although BICEP-2 claimed a detection of r = 0.2 , estimates of dust contamination provided by Planck have left open the possibility that only upper bound on r will be expected in a joint analysis .
As a result we consider different upper bounds on the value of r and show that PPL model can explain a lower value of tensor to scalar ratio ( r < 0.1 or r < 0.01 ) for a scalar spectral index of n _ { s } = 0.96 by having a non-zero value of effective mass of the inflaton field \frac { m ^ { 2 } _ { eff } } { H ^ { 2 } } .
The analysis with WP+ Planck likelihood shows a non-zero detection of \frac { m ^ { 2 } _ { eff } } { H ^ { 2 } } with 5.7 \sigma and 8.1 \sigma respectively for r < 0.1 and r < 0.01 .
Whereas , with BICEP-2 likelihood \frac { m ^ { 2 } _ { eff } } { H ^ { 2 } } = -0.0237 \pm 0.0135 which is consistent with zero .