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Inflation and Dark Matter in the Higgs Portal of Classically Scale Invariant Standard Model

Valentin V. Khoze

TL;DR

This paper develops a minimal classically scale-invariant extension of the Standard Model that includes a Coleman-Weinberg sector and an additional real singlet s. The singlet is non-minimally coupled to gravity and drives single-field slow-roll inflation in the Einstein frame with a plateau-like potential $V(\sigma) \approx (\lambda_s M^4)/(4 \xi_s^2) [1 - \exp(-2\sigma/(\sqrt{6}M))]^2$, yielding Planck-compatible predictions when $\xi_s \approx 4.7\times 10^4 \sqrt{\lambda_s}$. The singlet also serves as a dark matter candidate via a $Z_2$ symmetry, with DM phenomenology identical to the standard scalar singlet DM and constrained by relic density, invisible Higgs decays, and direct-detection bounds; viable regions exist for $m_s > m_h/2$, and upcoming experiments like XENON1T can probe much of the parameter space. The work further discusses the relation between classical scale invariance and potential local scale invariance in gravity, arguing that the electroweak scale can remain natural within this framework while inflation and DM arise without spoiling SM physics.

Abstract

We consider a minimal classically scale-invariant extension of the Standard Model. In this theory, the Higgs mechanism is triggered and the electroweak symmetry breaking is generated radiatively by the Coleman-Weinberg sector which is coupled to the SM Higgs. We extend the Higgs portal interactions of the theory to include an additional singlet which is also non-minimally coupled to gravity. This generates a single-field slow-roll inflation mechanism in the effective field theory formulation which is robust up to Planck scales. Our approach does not require integrating in any additional new physics degrees of freedom to unitarise the theory in the sub-Planckian regime where inflation happens. As a result, no large threshold corrections appear in our approach to inflation so that the electroweak scale and the SM Higgs mass are not affected. The singlet field responsible for inflation also gives a viable dark matter candidate in our model. We also discuss the relation between classical scale-invariance of the effective theory and the possible local scale invariance of the full theory and comment on the naturalness of the electroweak scale.

Inflation and Dark Matter in the Higgs Portal of Classically Scale Invariant Standard Model

TL;DR

This paper develops a minimal classically scale-invariant extension of the Standard Model that includes a Coleman-Weinberg sector and an additional real singlet s. The singlet is non-minimally coupled to gravity and drives single-field slow-roll inflation in the Einstein frame with a plateau-like potential , yielding Planck-compatible predictions when . The singlet also serves as a dark matter candidate via a symmetry, with DM phenomenology identical to the standard scalar singlet DM and constrained by relic density, invisible Higgs decays, and direct-detection bounds; viable regions exist for , and upcoming experiments like XENON1T can probe much of the parameter space. The work further discusses the relation between classical scale invariance and potential local scale invariance in gravity, arguing that the electroweak scale can remain natural within this framework while inflation and DM arise without spoiling SM physics.

Abstract

We consider a minimal classically scale-invariant extension of the Standard Model. In this theory, the Higgs mechanism is triggered and the electroweak symmetry breaking is generated radiatively by the Coleman-Weinberg sector which is coupled to the SM Higgs. We extend the Higgs portal interactions of the theory to include an additional singlet which is also non-minimally coupled to gravity. This generates a single-field slow-roll inflation mechanism in the effective field theory formulation which is robust up to Planck scales. Our approach does not require integrating in any additional new physics degrees of freedom to unitarise the theory in the sub-Planckian regime where inflation happens. As a result, no large threshold corrections appear in our approach to inflation so that the electroweak scale and the SM Higgs mass are not affected. The singlet field responsible for inflation also gives a viable dark matter candidate in our model. We also discuss the relation between classical scale-invariance of the effective theory and the possible local scale invariance of the full theory and comment on the naturalness of the electroweak scale.

Paper Structure

This paper contains 4 sections, 60 equations, 1 figure.

Table of Contents

  1. Introduction
  2. Singlet-field slow-roll inflation in the Higgs portal
  3. Dark matter
  4. Conclusions

Figures (1)

  • Figure 1: DM exclusion contours from Ref. Cline:2013gha on the $\lambda_{hs}$, $m_s$ plane. Left plot is a close-up on the region $m_s \lesssim m_h/2$. The dark-shaded lower region is ruled out by the upper bound on the singlet DM relic density, $\Omega_S/\Omega_{\rm DM} \le 1$. The region in the upper-left corner is ruled out by constraints on invisible Higgs decays. Right plot is over a wide mass range $45\,{\rm\,GeV} \le m_s \le 5\,{\rm TeV}$. The DM relic density exclusion is shown superimposed with the current bound from XENON100 and bounds from future direct detection experiments (in lighter shades of blue).