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Alternative left-right scenario: Unitarity, vacuum stability, and RG evolution

Hrishikesh Deka1,*, Avnish2,†, Sumit K. Garg3,‡, and Poulose Poulose4,§

  • *Contact author: hrishikesh.deka@iitg.ac.in
  • †Contact author: avnishy@uohyd.ac.in
  • ‡Contact author: sumit.kumar@manipal.edu
  • §Contact author: poulose@sju.edu.in
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Phys. Rev. D 114, 055007 – Published 8 September, 2026

DOI: https://doi.org/10.1103/ygy3-n2zh

Abstract

We study the theoretical constraints on the scalar sector of the alternative left-right model (ALRM), an E6-motivated extension of the Standard Model based on the gauge group SU(3)c⊗SU(2)L⊗SU(2)R′⊗U(1)B−L, supplemented by a global U(1)S symmetry. We derive the complete set of tree-level perturbative unitarity constraints on the model, resulting in 14 independent conditions on the quartic scalar couplings. When combined with the boundedness-from-below conditions and the requirement of positive-definite scalar mass-squared eigenvalues, this yields significantly more stringent restrictions on the parameter space than either set alone. We then perform a one-loop renormalization group analysis, evolving the model parameters up to a high-energy cutoff scale, and requiring that the vacuum stability, the unitarity, and the perturbativity conditions are preserved throughout. The renormalization group evolution is found to restrict the allowed parameter space considerably beyond the tree-level bounds, with the constraints on the quartic couplings becoming more stringent as the cutoff scale is raised. Consequently, the physical scalar masses in the model acquire upper bounds. For the right-hand symmetry breaking scale, vR=10  TeV and requiring theoretical consistency up to 1016  GeV, we obtain mH1±≲6.5  TeV, mH2±≲1.5  TeV, and mH10≃mA1≲1.5  TeV, with all bounds scaling with vR. These findings offer a predictive and falsifiable framework for searches of the extended Higgs sector of the ALRM at the current and future collider experiments.

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Phys. Rev. D 114, 055007– Published 8 September, 2026
  • Received 28 May 2026
  • Accepted 31 July 2026
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Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI. Funded by SCOAP3.

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