Title: Higgs Inflation in Unimodular Gravity

Abstract: The discovery of Higgs mechanism within the context of spontaneous symmetry breaking has offered a new perspective on the early time cosmic inflation and also on the relationship between elementary particles and dark energy, believed to drive the universe's accelerating expansion. We suggest an inflation scenario driven by the Higgs boson within the framework of unimodular gravity, where the Higgs field acts as the inflaton and has a significant non-minimal coupling to the gravity. We present a detailed analysis of the problem in the Jordan and then Einstein frame for a unimodular Higgs inflation, followed by a comparison of our findings with the Cosmic Microwave Background observations made by the Planck Collaboration and other joint data sets. Therefore, new constraints are imposed on the non-minimal coupling parameter, $\xi$, by determining the magnitudes required for effective cosmic inflation. We demonstrate that a substantial non-minimal coupling of order $\xi\sim 10^{2}-10^{4}$ is required for this model to match with the observed primordial spectrum.