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Improved Naturalness with a Heavy Higgs: An Alternative Road to LHC Physics

Riccardo Barbieri, Lawrence J. Hall, Vyacheslav S. Rychkov

TL;DR

The paper argues that a heavy Higgs (400–600 GeV) can be compatible with electroweak precision data if naturalness is preserved up to about $1.5$ TeV by extending the SM with an inert second Higgs doublet. This Inert Doublet Model (IDM) introduces a parity-protected, non-VEV doublet whose inert spectrum (H^+, S, A) yields a stable lightest inert particle as a dark matter candidate and provides positive contributions to the $T$ parameter to offset the heavy Higgs effects. The authors analyze perturbativity, naturalness, and EWPT constraints, identifying broad regions of parameter space where the model is perturbative and natural up to 1.5 TeV, with DM phenomenology that can align with relic abundance in some mass ranges and predict testable collider and direct-detection signals. The IDM thus offers a concrete, self-consistent path to LHC physics distinct from SUSY, with characteristic multi-lepton + MET signals and potentially observable Higgs-width modifications. The framework links a heavy-Higgs solution to a viable DM candidate and distinctive LHC/DM phenomenology, providing concrete predictions for upcoming experiments.

Abstract

The quadratic divergences of the Higgs mass may be cancelled either accidentally or by the exchange of some new particles. Alternatively its impact on naturalness may be weakened by raising the Higgs mass, which requires changing the Standard Model below its natural cut-off. We show in detail how this can be achieved, while preserving perturbativity and consistency with the electroweak precision tests, by extending the Standard Model to include a second Higgs doublet that has neither a vev nor couplings to quarks and leptons. This Inert Doublet Model yields a perturbative and completely natural description of electroweak physics at all energies up to 1.5 TeV. The discrete symmetry that yields the Inert Doublet is unbroken, so that Dark Matter may be composed of neutral inert Higgs bosons, which may have escaped detection at LEP2. Predictions are given for multilepton events with missing transverse energy at the Large Hadron Collider, and for the direct detection of dark matter.

Improved Naturalness with a Heavy Higgs: An Alternative Road to LHC Physics

TL;DR

The paper argues that a heavy Higgs (400–600 GeV) can be compatible with electroweak precision data if naturalness is preserved up to about TeV by extending the SM with an inert second Higgs doublet. This Inert Doublet Model (IDM) introduces a parity-protected, non-VEV doublet whose inert spectrum (H^+, S, A) yields a stable lightest inert particle as a dark matter candidate and provides positive contributions to the parameter to offset the heavy Higgs effects. The authors analyze perturbativity, naturalness, and EWPT constraints, identifying broad regions of parameter space where the model is perturbative and natural up to 1.5 TeV, with DM phenomenology that can align with relic abundance in some mass ranges and predict testable collider and direct-detection signals. The IDM thus offers a concrete, self-consistent path to LHC physics distinct from SUSY, with characteristic multi-lepton + MET signals and potentially observable Higgs-width modifications. The framework links a heavy-Higgs solution to a viable DM candidate and distinctive LHC/DM phenomenology, providing concrete predictions for upcoming experiments.

Abstract

The quadratic divergences of the Higgs mass may be cancelled either accidentally or by the exchange of some new particles. Alternatively its impact on naturalness may be weakened by raising the Higgs mass, which requires changing the Standard Model below its natural cut-off. We show in detail how this can be achieved, while preserving perturbativity and consistency with the electroweak precision tests, by extending the Standard Model to include a second Higgs doublet that has neither a vev nor couplings to quarks and leptons. This Inert Doublet Model yields a perturbative and completely natural description of electroweak physics at all energies up to 1.5 TeV. The discrete symmetry that yields the Inert Doublet is unbroken, so that Dark Matter may be composed of neutral inert Higgs bosons, which may have escaped detection at LEP2. Predictions are given for multilepton events with missing transverse energy at the Large Hadron Collider, and for the direct detection of dark matter.

Paper Structure

This paper contains 25 sections, 67 equations, 7 figures, 1 table.

Table of Contents

  1. Introduction
  2. Standard Model with a Heavy Higgs
  3. Improved naturalness
  4. Perturbativity, or how heavy is heavy?
  5. ElectroWeak Precision Tests
  6. The Inert Doublet Model
  7. The Model
  8. Perturbativity
  9. Naturalness
  10. ElectroWeak Precision Tests
  11. Summary of constraints on the spectrum and couplings
  12. Dark Matter
  13. Relic abundance
  14. Direct detection
  15. Collider signals
  16. ...and 10 more sections

Figures (7)

  • Figure 1: (Adapted from Plot.) Dependence of the $S,T$ parameters on the Higgs mass. The thick black band marks $m_{h}=400-600$ GeV.
  • Figure 2: The maximal and minimal $\Delta T$ allowed by naturalness and perturbativity as a function of $m_{L}$. The horizontal grey band marks the range needed to compensate for the heavy Higgs.
  • Figure 3: The relation between the first and the second spacing in the inert particle spectrum following from the EWPT constraint (\ref{['pred']}).
  • Figure 4: $\lambda_{4,5}$ in the allowed region as functions of $m,\Delta m$ computed from (\ref{['l4']}), (\ref{['l5']}) with $M=120$ GeV.
  • Figure 5: $\lambda_{\text{L}}^{\min}$ and $\lambda_{\text{L}}^{\max}$ for $M=120$ GeV. Notice that $\lambda_{\text{L}}^{\min}$ depends only on $m_{\text{L}}$ and is constant for $m_{\text{L}}\gtrsim180$ GeV.
  • ...and 2 more figures