Higgs Inflation and the Electroweak Gauge Sector

Abstract

We introduce a new method that allows for the Higgs to be the inflaton. That is, we let the Higgs be a pseudo-Nambu-Goldstone (pNG) boson of a global coset symmetry $G/H$ that spontaneously breaks at an energy scale $\sim 4\pi f$ and give it a suitable $SU(2) \subset G$ Chern-Simons interaction, with $\beta$ the dimensionless Chern-Simons coupling strength and $f$ an $SU(2)$ decay constant. As a result, slow-roll inflation occurs via $SU(2)$-induced friction down a steep sinusoidal potential. In order to obey electroweak $SU(2)_{\rm L}\times U(1)_Y$ symmetry, the lowest-order Chern-Simons interaction is required to be quadratic in the Higgs with coupling strength $\propto \beta^2/f^2$. Higher-order interaction terms keep the full Lagrangian nearly invariant under the approximate pNG shift symmetry. Employing the simplest symmetry coset $SU(5)/SO(5)$, $N$ $e$-folds of inflation occur when $N \approx 60 \left(g/0.64\right)^2\left[\beta/\left(3\times 10^6\right)\right]^{8/3}\left[f/\left(5\times 10^{11}\ {\rm GeV}\right)\right]^{2/3}$, with $g$ the weak isospin gauge coupling constant. Small values of the decay constant, $f \lesssim 5 \times 10^{11} {\rm GeV}$, which are needed to address the Higgs hierarchy problem, are ruled out by electric dipole measurements and so successfully explaining inflation requires large $\beta$. We discuss possible methods to achieve such large couplings and other alternative Higgs inflation scenarios outside the standard modified-gravity framework.