[Paper Review] New Physics Search via the Higgs Self-Coupling

Shinya Kanemura, Shingo Kiyoura+3 more|ArXiv.org|Sep 27, 2002

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper investigates quantum corrections to the Higgs self-coupling (λhhh) in the Two Higgs Doublet Model (THDM) and Minimal Supersymmetric Standard Model (MSSM), showing that non-decoupling quartic mass effects in the THDM can lead to O(100%) deviations from the Standard Model prediction—even when all other Higgs couplings are SM-like. In contrast, the MSSM exhibits standard decoupling behavior due to suppressed loop corrections.

ABSTRACT

We discuss quantum corrections of new physics to the triple coupling of the lightest CP-even Higgs boson in the Two Higgs Doublet Model (THDM) and also in the Minimal Supersymmetric Standard Model (MSSM). In the THDM, quartic contributions of the mass of heavy particles in the loop can appear, which are not absorbed by renormalization of the Higgs boson mass. Such non-decoupling effects on the self-coupling can give corrections of ${\cal O}(100%)$, even when all measured Higgs couplings with gauge bosons and fermions are consistent with the Standard Model prediction. In the MSSM, the loop-corrections decouple in such a scenario.

Motivation & Objective

• To investigate how new physics in the Two Higgs Doublet Model (THDM) affects the Higgs self-coupling λhhh through one-loop quantum corrections.
• To compare the decoupling behavior of heavy Higgs bosons in THDM versus the MSSM, especially regarding non-decoupling quartic mass contributions.
• To assess the detectability of new physics via precise measurements of λhhh at future linear colliders (LCs), given SM-like couplings for hVV and fermions.
• To determine the conditions under which large deviations in λhhh can occur in THDM despite consistency with SM predictions for other Higgs couplings.
• To evaluate the role of the soft-breaking scale M and heavy Higgs masses in determining the magnitude of non-decoupling effects on λhhh.

Proposed method

• Calculates the effective Higgs self-coupling λhhh^eff in the THDM using one-loop corrections involving heavy Higgs states (H, A, H±), with contributions scaled by mΦ⁴/v² and suppressed by (1 - M²/mΦ²)³.
• Applies the same framework to the MSSM, where the Higgs sector is a weakly coupled limit of THDM, and derives the stop-loop correction with suppression by mₜ⁴/Mₛ².
• Uses the condition sin²(α - β) ≈ 1 to enforce SM-like hVV couplings and fermion couplings, isolating the self-coupling as the key probe of new physics.
• Performs numerical analysis of λhhh^eff as a function of heavy Higgs masses (m_A, m_H, m_H±) and soft-breaking scale M, with constraints from perturbative unitarity and the ρ parameter.
• Evaluates momentum dependence of λhhh^eff(q²) for off-shell Higgs bosons, particularly in the M → 0 limit.
• Compares results across Model I and Model II of THDM, noting that differences appear only in charged Higgs contributions due to b → sγ constraints.

Experimental results

Research questions

• RQ1 Can large deviations in the Higgs self-coupling λhhh occur in the THDM even when all other Higgs couplings are consistent with the Standard Model?
• RQ2 What is the role of quartic mass dependence (mΦ⁴) in the loop corrections to λhhh in the THDM, and how does it lead to non-decoupling effects?
• RQ3 How does the decoupling behavior of heavy Higgs contributions in the MSSM differ from that in the general THDM, particularly in the limit of large M?
• RQ4 To what extent can the stop-loop contribution in the MSSM affect λhhh, and under what parameter choices does it exceed 5%?
• RQ5 What are the detectable signatures of new physics in λhhh at linear colliders, given integrated luminosities of 1 ab⁻¹ (500 GeV) and 5 ab⁻¹ (3 TeV)?

Key findings

• In the THDM, non-decoupling quartic contributions from heavy Higgs bosons (H, A, H±) can lead to corrections of up to 100% in λhhh, even when all other Higgs couplings are SM-like.
• The maximum non-decoupling effect occurs in the limit M → 0, where the suppression factor (1 - M²/mΦ²)³ vanishes, allowing large mΦ⁴ contributions.
• For m_A = 400 GeV, the deviation from the SM prediction reaches approximately 100%, constrained by perturbative unitarity (m_A < 600 GeV).
• At 500 GeV LC with 1 ab⁻¹ luminosity, λhhh can be measured with ~20% accuracy for m_h = 120 GeV, improving to ~7% at 3 TeV with 5 ab⁻¹.
• In the MSSM, loop corrections to λhhh are suppressed by mₜ⁴/Mₛ² and exhibit standard decoupling; the stop-loop correction exceeds 5% only in light stop scenarios with small Mₛ.
• The momentum dependence of λhhh^eff(q²) for off-shell Higgs bosons shows significant variation at M = 0, indicating strong sensitivity to new physics in the off-shell regime.