[Paper Review] An NMSSM Without Domain Walls

Tao Han, Paul Langacker+1 more|ArXiv.org|Feb 6, 2004

Particle physics theoretical and experimental studies3 citations

TL;DR

This paper proposes an extended NMSSM with a U(1)' gauge symmetry and multiple singlet scalars to solve the μ problem without generating domain walls. By decoupling the effective μ parameter from the Z′ mass via distinct singlet fields, the model allows light Higgs bosons (down to 20 GeV) with significant doublet components, enabling detection at linear colliders despite suppressed couplings to Z and W bosons.

ABSTRACT

We consider the Higgs sector in an extension of the MSSM involving an extra U(1)' gauge symmetry and SM singlet U(1)' charged scalars, in which the effective $μ$ parameter is decoupled from the Z' mass. There are large mixings between Higgs doublets and singlets, significantly affecting the Higgs spectrum, production cross sections, decay modes, exclusion limits, and allowed parameters ranges. Scalars considerably lighter than 114 GeV are allowed, and the range $ an β\sim 1$ is both allowed and theoretically favored. We concentrate on the lighter (least model dependent) Higgs particles with significant SU(2)-doublet components to their wave functions, for the case of no explicit CP violation in the Higgs sector. We consider their spectra, including the dominant radiative corrections to their masses in the large $ ilde t$ mass limit; production cross sections and exclusion limits at LEP and a future linear collider; and decay properties.

Motivation & Objective

• To resolve the μ problem in the MSSM without introducing domain walls, which plague simpler NMSSM models.
• To construct a UV-compliant model based on a non-anomalous U(1)' gauge symmetry that naturally suppresses dangerous terms like μS and S³.
• To decouple the effective μ parameter from the Z′ gauge boson mass, enabling a heavy Z′ while allowing light Higgs states.
• To explore the phenomenology of light CP-even and CP-odd Higgs bosons with significant doublet components, focusing on LEP and linear collider constraints.
• To analyze Higgs production, decay modes, and exclusion limits in the absence of explicit CP violation.

Proposed method

• Introduce a superpotential with three singlet fields (S, S₁, S₂, S₃) and a U(1)' gauge symmetry to forbid μ and S³ terms via gauge invariance.
• Use F-term and D-term potentials from the superpotential and U(1)' charges to stabilize the scalar potential and generate mass splittings.
• Implement soft SUSY-breaking terms including trilinear A-terms and bilinear mass terms to break global symmetries and lift degeneracies.
• Compute one-loop radiative corrections to Higgs masses using the top/stop loop in the large stop mass limit.
• Perform a parameter scan over vacuum expectation values to identify viable minima with light Higgs states.
• Calculate Higgsstrahlung cross sections (e⁺e⁻ → ZH) and ZZH couplings relative to the SM for the lightest and heaviest CP-even states.

Experimental results

Research questions

• RQ1 Can a U(1)'-extended NMSSM avoid domain wall formation while solving the μ problem through a dynamically generated μ term?
• RQ2 What is the impact of decoupling the effective μ parameter from the Z′ mass on the Higgs spectrum and phenomenology?
• RQ3 How light can the lightest CP-even Higgs boson be while remaining consistent with LEP2 and future linear collider constraints?
• RQ4 What are the dominant decay modes of the light Higgs bosons, especially when kinematically allowed via new D-terms and singlet couplings?
• RQ5 How do the production cross sections and ZZH couplings of the heavier Higgs states compare to the Standard Model?

Key findings

• The model allows light CP-even Higgs bosons with masses as low as 20 GeV, escaping detection at LEP2 due to suppressed couplings to Z and W bosons.
• The lightest Higgs state (H₁) has a Higgsstrahlung cross section at a 500 GeV linear collider that remains measurable, indicating potential discovery at future colliders.
• The heaviest CP-even Higgs states have ZZH couplings suppressed relative to the Standard Model, indicating decoupling from the Z boson.
• New decay modes such as H → A₁A₁ and H → χ⁰χ⁰ dominate when kinematically allowed, due to D-term and F-term contributions from the U(1)' sector.
• The model supports a wide range of tanβ ∼ 1, which is both theoretically favored and consistent with experimental constraints.
• The parameter space includes viable vacuum configurations free of runaway directions, with the three singlets S₁, S₂, S₃ acquiring large vacuum expectation values compared to H₁, H₂, and S.