[Paper Review] What tell us LHC data about Higgs boson parity

I. F. Ginzburg|arXiv (Cornell University)|Oct 26, 2016

Particle physics theoretical and experimental studies13 references3 citations

TL;DR

This paper argues that the LHC experiments CMS and ATLAS cannot definitively determine the Higgs boson's parity without assuming it has definite parity, a condition not guaranteed in BSM physics. The analysis shows that in CP-violating models like the 2HDM, significant P-odd components in the 125 GeV Higgs can still yield SM-like Higgs signal strengths, rendering the experiments' conclusions model-dependent and their titles misleading if not qualified.

ABSTRACT

Recently CMS and ATLAS announced that they had measured the Higgs boson parity. Here we note that their approach can determine this parity only under the additional assumption that this particle has a definite parity. If parity conservation is violated in the Higgs sector, the parity of observed "Higgs" boson does not exist. The approach used in the mentioned experiments does not allow to observe such opportunity. In this sense titles of mentioned CMS and ATLAS publications are misleading.

Motivation & Objective

• To challenge the validity of claiming Higgs boson parity measurement from LHC data without assuming definite parity.
• To demonstrate that CP-violating models, such as the 2HDM, can produce Higgs boson states with large P-odd components.
• To show that observed Higgs signal strengths (e.g., γγ, ZZ, tt̄h) remain SM-like even with significant P-odd admixtures.
• To argue that current LHC analyses cannot rule out parity non-conservation in the Higgs sector.
• To advocate for more accurate titles in CMS and ATLAS publications to reflect the model-dependent nature of parity determination.

Proposed method

• Analyzes the effective Lagrangian for Higgs-gauge boson interactions under CP-conserving and CP-violating scenarios.
• Compares the momentum correlations in H→ZZ* and H→WW* decays for P-even (SM-like) and P-odd (dimension-5 operator) interactions.
• Applies the 2HDM framework to model mixing between P-even and P-odd Higgs states, showing that the ZZZ coupling remains P-even-dominated in the leading approximation.
• Uses parameter sets for Higgs couplings (χaV, χa±, χt) to reproduce SM-like signal strengths in γγ and ZZ final states.
• Derives benchmark parameter sets (I and II) that satisfy σ(gg→h→γγ)/σSM = 1 and σ(gg→h→ZZ)/σSM = 1 with significant P-odd admixtures.
• Considers the role of Yukawa couplings and complex phases in probing CP violation, noting that no universal measure of parity non-conservation exists.

Experimental results

Research questions

• RQ1 Can the LHC experiments CMS and ATLAS definitively determine the Higgs boson's parity without assuming it has definite parity?
• RQ2 To what extent can a CP-violating Higgs sector in the 2HDM lead to a Higgs boson with significant P-odd component while preserving SM-like signal strengths?
• RQ3 Why are the titles of CMS and ATLAS papers claiming 'parity measurement' potentially misleading?
• RQ4 What constraints do current LHC data place on the admixture of P-odd components in the 125 GeV Higgs boson?
• RQ5 Are there viable BSM scenarios where the observed Higgs boson is not a pure P-even state but still reproduces SM Higgs signal strengths?

Key findings

• The LHC experiments' method for determining Higgs parity is only valid under the assumption of definite parity, which is not guaranteed in BSM physics.
• In CP-violating 2HDM, the observed Higgs boson can have a P-odd admixture of up to 30% (case I) or 50% (case II) while preserving SM-like signal strengths in γγ and ZZ decay channels.
• Benchmark set (I) allows a P-odd admixture of approximately 30%, with χ1V = 0.9 and (χ2V)² + (χ3V)² = 0.19.
• Benchmark set (II) allows a P-odd admixture of approximately 50%, with χ1V = 0.8 and (χ2V)² + (χ3V)² = 0.36.
• The same SM-like signal strengths in γγ and ZZ final states can be reproduced in both SM and strongly CP-violating 2HDM scenarios.
• No universal measure of parity non-conservation exists for the Higgs boson, as the P-odd admixture and Yukawa phase are independent parameters.