Supergravity corrections due to the energy density of a right-handed sneutrino can generate a negative mass squared for the inflaton , flattening the inflaton potential and reducing the spectral index and inflaton energy density .
For the case of D-term hybrid inflation , we show that the spectral index can be lowered from the conventional value n = 0.98 to a value within the range favoured by the latest WMAP analysis , n = 0.951 ^ { +0.015 } _ { -0.019 } .
The modified energy density is consistent with non-observation of cosmic strings in the CMB if n < 0.946 .
The WMAP lower bound on the spectral index implies that the D-term cosmic string contribution may be very close present CMB limits , contributing at least 5 % to the CMB multipoles .