Girish Chakravarty, Subhendra Mohanty, Naveen K. Singh
We have generalized the curvature coupling models of Higgs inflation to study inflation with a scalar field coupling of the form $(\xi \Phi^a R^b)/(M_p^{a+2b-4})$ . Such higher order scalar and graviton terms can be expected from the renormalization close to Planck scale. We compute the amplitude and spectral index of curvature perturbations generated during inflation and fix the parameters of the model by comparing these with the WMAP9 data. We find that if the scalar self coupling $\lambda$ is in the range (10^{-5}-0.1), parameter a in the range (2.5 -3.6) and b in the range (0.86-0.20) at the Planck scale, one can have a viable inflation model even for $\xi \simeq 1$. The tensor to scalar ratio $r$ in this model is small and our model with scalar-curvature couplings is not ruled out by observational limits on $r$ unlike the pure $\lambda\Phi^4/4$ theory. By requiring the curvature coupling parameter to be of order unity, we have evaded the problem of unitarity violation in scalar-graviton scatterings which plague the $\xi \Phi^2 R$ Higgs inflation models. We conclude that the Higgs field may still be a good candidate for being the inflaton in the early universe if one considers higher dimensional curvature coupling.
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http://arxiv.org/abs/1303.3870
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