We study the Higgs inflation model realized in the supersymmetric $SU(5)$ grand unified theory (GUT), focusing on its multifield dynamics and prediction of cosmological observables. The requirement for GUT symmetry breaking during inflation imposes tight constraints on the model parameters. We find, nevertheless, that with an appropriately chosen noncanonical Kähler potential the model is in excellent agreement with the present cosmological observations. The effects from multifield dynamics are found to be minor and thus, unlike other similar supersymmetric implementations of nonminimally coupled Higgs inflation, the prediction of this model is robust against multifield ambiguities.

• Received 31 December 2015

DOI:https://doi.org/10.1103/PhysRevD.93.065023