Scalar field models of inflation based on a large nonminimal coupling to gravity $\xi$, in particular, Higgs inflation, may violate unitarity at an energy scale $\Lambda \sim M_p/\xi \ll M_p$. In this case the model is incomplete at energy scales relevant to inflation. Here we propose a new unitarity-conserving model of Higgs inflation. The completion of the theory is achieved via additional interactions which are proportional to products of the derivatives of the Higgs doublet. The resulting model differs from the original version of Higgs inflation in its prediction for the spectral index, with a classical value $n=0.974$. In the case of a nonsupersymmetric model, quantum corrections are likely to strongly modify the tree-level potential, suggesting that supersymmetry or a gauge singlet scalar inflaton is necessary for a completely successful model.

• Received 10 June 2010

DOI:https://doi.org/10.1103/PhysRevD.82.103525