[Paper Review] Sphaleron And Critical bubble in a scale invariant model : ReAnalysis

Kaori Fuyuto, Eibun Senaha|arXiv (Cornell University)|Apr 16, 2015

Oceanographic and Atmospheric Processes3 citations

TL;DR

This paper reanalyzes the electroweak phase transition (EWPT) in a scale-invariant two Higgs doublet model (SI-2HDM) using a resumed finite-temperature one-loop effective potential with thermal resummation. It demonstrates that the 125 GeV Higgs boson mass mandates a strong first-order EWPT, ensuring sphaleron decoupling (v_N/T_N > 1.2) and leading to a 10% reduction in Higgs signal strength to diphotons and an 82% enhancement in the triple Higgs coupling, both detectable in future LHC and ILC experiments.

ABSTRACT

We revisit the electroweak phase transition and the critical bubble in the scale invariant two Higgs doublet model in the light of recent LHC data. Moreover, the sphaleron decoupling condition is newly evaluated in this model. The analysis is done by using the resumed finite-temperature one-loop effective potential. It is found that the 125 GeV Higgs boson inevitably leads to the strong first-order electroweak phase transition, and the strength of which is always large enough to satisfy the sphaleron decoupling condition, $v_N/T_N > 1.2$, where $T_N$ denotes a nucleation temperature and $v_N$ is the Higgs vacuum expectation value at $T_N$. In this model, even if the Higgs boson couplings to gauge bosons and fermions are similar to the standard model values, the signal strength of the Higgs decay to two photons is reduced by 10% and the triple Higgs boson coupling is enhanced by 82% compared to the standard model prediction.

Motivation & Objective

• To reevaluate the electroweak phase transition (EWPT) in the scale-invariant two Higgs doublet model (SI-2HDM) using updated LHC data.
• To assess whether the 125 GeV Higgs boson mass leads to a strong first-order EWPT capable of supporting electroweak baryogenesis.
• To compute the sphaleron decoupling condition (v_N/T_N > 1.2) and critical bubble properties using a resumed finite-temperature effective potential.
• To quantify deviations in Higgs couplings—particularly γγ and triple Higgs coupling—from the Standard Model predictions.
• To evaluate the UV cutoff scale of the model and assess its phenomenological viability for future collider experiments.

Proposed method

• Uses the resumed finite-temperature one-loop effective potential with daisy resummation to account for thermal corrections in the SI-2HDM.
• Applies renormalization group equations (RGEs) at one-loop order to determine the UV cutoff scale (Λ) of the model.
• Imposes the condition that the Higgs boson mass is fixed at 125.09 GeV to constrain the parameter space.
• Evaluates the sphaleron decoupling condition via the ratio v_N/T_N at the nucleation temperature T_N.
• Computes Higgs boson couplings (κ_V, κ_f, μ_γγ, Δλ_hhh) relative to the Standard Model using loop corrections from heavy Higgs states.
• Analyzes bubble wall profiles and critical bubble energy to assess supercooling and phase transition strength.

Experimental results

Research questions

• RQ1 Does the 125 GeV Higgs boson mass in the SI-2HDM lead to a strong first-order electroweak phase transition?
• RQ2 Is the sphaleron decoupling condition (v_N/T_N > 1.2) satisfied in this model, ensuring baryon number violation suppression?
• RQ3 How do the Higgs boson couplings to photons and the triple Higgs coupling deviate from Standard Model predictions?
• RQ4 What is the UV cutoff scale (Λ) of the SI-2HDM, and does it allow for a consistent effective field theory description?
• RQ5 How do the critical bubble properties (e.g., energy, wall width) compare to those in the MSSM, and what are the implications for baryogenesis?

Key findings

• The 125 GeV Higgs boson mass in the SI-2HDM inevitably leads to a strong first-order electroweak phase transition.
• The sphaleron decoupling condition is satisfied with v_N/T_N = 2.94 at the nucleation temperature, well above the 1.2 threshold.
• The Higgs signal strength for the γγ decay mode is reduced by 10% compared to the Standard Model prediction.
• The triple Higgs boson coupling is enhanced by 82.1% relative to the Standard Model due to non-decoupling effects of heavy Higgs loops.
• The critical bubble energy per temperature is E_cb(T_N)/T_N = 151.7, indicating significant supercooling of about 15%.
• The UV cutoff scale is found to be Λ = 6.3 TeV for tanβ = 1, indicating a relatively low energy scale of validity, requiring UV completion.