Does Palatini Higgs Inflation Conserve Unitarity?

Abstract

In the conventional metric formulation of gravity, the Higgs Inflation model violates unitarity in the electroweak vacuum in Higgs scattering at the energy scale $\Lambda \sim M_{Pl}/\xi$, where $\xi \sim 10^4$ is the non-minimal coupling of the Higgs to the Ricci scalar. In the Palatini formulation it is commonly believed that $\Lambda \sim M_{Pl}/\sqrt{\xi }$, where $\xi \sim 10^9$. Here we reconsider unitarity violation in the electroweak vacuum in the Palatini formulation. We argue that there is no unitarity violation in Higgs scattering in the Palatini non-minimally coupled Standard Model in the electroweak vacuum at energies below the Planck scale. In this case Palatini Higgs Inflation completely conserves unitarity and is consistent at all energies up to those at which quantum gravity becomes important. If true, this would imply that Palatini Higgs Inflation has a significant advantage over metric Higgs Inflation.

8 pages. Additional reference. Published in JCAP

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• On the number of $e$-folds in the Jordan and Einstein frames
• Multiple point criticality principle and Coleman-Weinberg inflation
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• Ultraviolet behaviour of Higgs inflation models
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• Observable Primordial Gravitational Waves from Non-minimally Coupled $R^2$ Palatini Modified Gravity
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• Ultraviolet Unitarity Violations in Non-minimally Coupled Scalar-Starobinsky Inflation
• Beyond (and back to) Palatini quadratic gravity and inflation
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• $\tilde{\xi }$-attractors in metric-affine gravity
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• Induced-Gravity Palatini-Like Higgs Inflation in Supergravity Confronts ACT DR6
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• Scalar-Induced Gravitational Waves in Palatini $f(R)$ Gravity