Higgs Portal Inflation

TL;DR

Lebedev and Lee propose Higgs portal inflation with a real singlet coupled to gravity via large non-minimal terms, yielding a mixed Higgs-scalar inflaton that drives inflation and leaves testable low-energy signatures. The model provides universal inflationary predictions of $n_s \simeq 0.97$ and $r \simeq 0.0033$, while RG and stability conditions constrain the high-energy parameter space, notably preferring negative $\lambda_{hs}$ in the mixed-inflaton case. Phenomenologically, the framework predicts two Higgs-like states with universally suppressed couplings and potential invisible Higgs decays, subject to LEP/EW bounds and LHC searches; LHC measurements could, in favorable regions, reconstruct low-energy couplings and test inflationary consistency. Unitarity concerns are addressed by a UV completion with a heavy σ field, which unitarizes amplitudes without altering the inflationary predictions or low-energy phenomenology. The work links early-universe inflation to collider-scale Higgs portal physics, offering concrete signatures and a UV-consistent pathway to reconcile unitarity with inflation.

Abstract

The Higgs sector of the Standard Model offers a unique opportunity to probe the hidden sector. The Higgs squared operator is the only dimension two operator which is Lorentz and gauge invariant. It can therefore couple both to scalar curvature and the hidden sector at the dim--4 level. We consider the possibility that a combination of the Higgs and a singlet from the hidden sector plays the role of inflaton, due to their large couplings to gravity. This implies that the quartic couplings satisfy certain constraints which leads to distinct low energy phenomenology, including Higgs signals at the LHC. We also address the unitarity issues and show that our analysis survives the unitarization procedure.

Figures (4)

• Figure 1: Parameter space consistent with the mixed Higgs--singlet inflaton. $\lambda_i$ are given at the scale $m_t$, while $x$ is a high energy input.
• Figure 2: $\vert \sin\theta\vert$ and the Higgs masses as functions of $\lambda_{hs}$ and $r$ for $m_h^2 <0, m_s^2 <0$. (Here we redefine $\theta$ to be in the range $\vert\theta\vert < \pi/4$). The parameter range is consistent with the mixed Higgs--singlet inflaton at $x\sim 1$.
• Figure 3: Parameter space allowed by the LEP and electroweak constraints for $m_{s,h}^2 <0$. The region within the contour is allowed by the mixed Higgs-singlet inflaton; grey -- allowed by LEP (and automatically consistent with the 99.5% CL electroweak constraints); black -- preferred by the 95% CL electroweak constraints. $\lambda_i$ are given at the scale $m_t$.
• Figure 4: Constraints on pure singlet and Higgs inflation. The region within the contour is consistent with singlet (left, center) and Higgs (right) inflation; grey -- allowed by $\langle s \rangle \not= 0$ and LEP; black -- favored by the 95% CL electroweak constraints. Here $m_{s,h}^2 <0$ and $\lambda_i$ are given at the scale $m_t$.