Inflation in the Scale Symmetric Standard Model and Weyl geometry

TL;DR

This paper investigates inflation within a scale-symmetric extension of the Standard Model Higgs sector using Weyl geometry, analyzing quantum corrections and their implications for inflationary observables.

Contribution

It introduces a novel inflationary model based on Weyl geometry with quantum corrections, predicting a very small tensor-to-scalar ratio consistent with observations.

Findings

Spectral index and tensor-to-scalar ratio align with Planck 2018 constraints.

Predicted gravitational wave signal is too small to detect.

Unitarity cutoff is below inflation energy scales in certain parameter regimes.

Abstract

This work explores the possibility of inflation in a scale-symmetric extension of the Standard Model Higgs sector, where the Higgs field $\phi_1$ is coupled to a singlet scalar, the dilaton $\phi_0$. The two-scalar theory is formulated within Weyl geometry, which modifies the Einstein frame form of the resulting single-field inflationary potential. We extend the analysis to include quantum corrections, incorporating curvature effects in the one-loop effective potential. We find that the resulting spectral index $n_s$ and tensor-to-scalar ratio $r_{0.002}$ can be consistent with the Planck 2018 observational constraints. The predicted value $r_{0.002} \lesssim 10^{-6}$ remains too small to yield a detectable gravitational wave signal. In the regime with a strong hierarchy between the non-minimal couplings, $\xi_1\ll\xi_0$, the unitarity cutoff in the large-field background, $\Lambda_{UV}\sim M_P/\sqrt{\xi_1}$, lies below the energy scales relevant during inflation.