Kalb-Ramond axion production in anisotropic string cosmologies
  We compute the energy spectra for massless Kalb-Ramond axions in four-dimensional anisotropic string cosmological models. We show that, when integrated over directions, the four-dimensional anisotropic model leads to infra-red divergent spectra similar to the one found in the isotropic case. 
Ruth Durrer and Mairi Sakellariadou