Left–right symmetric model

Left–right symmetric model
Name	Left–right symmetric model
Other names	LRSM
Introduced	1974
Proponents	Mohapatra, Senjanović
Field	Particle physics, Theoretical physics
Related	Standard Model, Grand Unified Theory, Neutrino oscillation

Left–right symmetric model The left–right symmetric model is an extension of the Standard Model of particle physics that restores parity symmetry at high energies by introducing right-handed weak interactions and new gauge bosons. It was developed to address the origin of parity violation observed in Weak interaction experiments and to provide natural mechanisms for small neutrino masses, linking to ideas in Grand Unified Theory and Electroweak symmetry breaking. The framework predicts distinctive signatures at colliders and in low-energy processes, relating to experiments at facilities such as the Large Hadron Collider, Super-Kamiokande, and Sudbury Neutrino Observatory.

Introduction

The model was formulated by researchers including Rabindra Mohapatra and Goran Senjanović to extend the Electroweak interaction gauge group of the Standard Model to a left–right symmetric gauge group, motivated by parity restoration similar to proposals in early work by T. D. Lee and C. N. Yang. Early phenomenological and model-building studies connected LRSM ideas to Pati–Salam model, SO(10), and Left-handedness in weak interactions puzzles, while experimental implications were discussed in the context of facilities such as the CERN collider programs and Fermilab experiments.

Gauge Structure and Particle Content

The canonical gauge structure enlarges the SU(2)subscript::L × U(1)subscript::Y of the Standard Model to SU(2)subscript::L × SU(2)subscript::R × U(1)subscript::B−L, incorporating right-handed gauge symmetry analogous to left-handed Weak isospin. The particle content adds right-handed neutrinos often embedded in multiplets similar to those in SO(10), and predicts new gauge bosons W_R and Z' that parallel the W boson and Z boson of the Electroweak theory. Quark and lepton representations echo chiral assignments studied in Cabibbo–Kobayashi–Maskawa matrix analyses and in extensions considered by Georgi–Glashow unified schemes. Scalar multiplets include bidoublets and triplets used to break the enlarged symmetry, analogously to fields considered in Higgs mechanism discussions linked to Peter Higgs and François Englert.

Symmetry Breaking and Higgs Sector

Symmetry breaking proceeds in stages: first SU(2)_R × U(1)_{B−L} → U(1)_Y at a high scale, then the usual electroweak breaking SU(2)_L × U(1)_Y → U(1)_{EM}. The Higgs sector includes an SU(2)_L × SU(2)_R bidoublet and SU(2)_R (and sometimes SU(2)_L) triplets, echoing scalar choices in analyses by Deshpande, Gunion, and others. Vacuum expectation values of triplet scalars can induce Majorana masses for neutrinos via seesaw mechanisms connected to classic papers by Minkowski, Yanagida, Gell-Mann, and Ramond. The Higgs spectrum yields charged and neutral scalars whose properties are constrained by searches at ATLAS and CMS as well as precision measurements by experiments like LEP.

Neutrino Masses and Seesaw Mechanisms

LRSM naturally accommodates heavy right-handed neutrinos leading to Type I and Type II seesaw mechanisms, building on proposals by Mohapatra–Senjanović and by authors such as Schechter–Valle. In Type I, heavy singlet neutrinos analogous to particles in SO(10) generate light masses via mass matrix diagonalization procedures used in Pontecorvo–Maki–Nakagawa–Sakata matrix studies. In Type II, triplet scalar VEVs contribute directly to Majorana masses, connecting to lepton-number-violating processes explored in Neutrinoless double beta decay searches conducted by collaborations like GERDA and KamLAND-Zen. These mechanisms intertwine with oscillation results from Super-Kamiokande, SNO, and Daya Bay.

Phenomenology and Experimental Signatures

Signatures include right-handed charged currents mediated by W_R, heavy neutral gauge bosons Z', heavy neutrinos N, and scalar triplets producing doubly charged Higgs bosons often sought in LHC searches by ATLAS and CMS. Collider signals include same-sign dilepton plus jets channels studied in analyses influenced by search strategies at Tevatron and CERN. Low-energy observables include contributions to Electric dipole moment measurements pursued at institutions like PSI and limits from flavor-changing processes constrained by Belle II and BaBar. Cosmological and astrophysical implications connect to leptogenesis scenarios first proposed by Fukugita–Yanagida and to constraints from Big Bang nucleosynthesis and Planck (spacecraft) data.

Constraints and Experimental Tests

Bounds on W_R and Z' masses derive from direct searches at ATLAS and CMS and from indirect limits in precision electroweak fits by groups associated with LEP and SLAC. Neutrinoless double beta decay experiments such as EXO-200 impose constraints on Majorana mass parameters and on triplet VEVs. Flavor observables from LHCb, Belle, and Kaon experiments restrict mixing matrices analogous to the CKM matrix while electric-dipole and rare-decay searches by collaborations at J-PARC and ISIS Neutron and Muon Source further limit CP-violating phases. Global fits often reference theoretical frameworks developed in Effective field theory and by collaborations at CERN Theory Division.

Variants and Extensions

Variants include models with manifest left–right symmetry, models embedded in SO(10) or E6 unified groups, supersymmetric LRSM studied with techniques from Minimal Supersymmetric Standard Model literature, and inverse-seesaw or linear-seesaw versions connected to work by Mohapatra–Valle and Gonzalez-Garcia. Other extensions relate LRSM to Dark matter candidates explored in collaborations such as XENON and LUX, and to flavor model-building by groups working on Froggatt–Nielsen mechanisms. Embeddings in higher-dimensional theories echo constructions considered in Randall–Sundrum model and string-inspired scenarios developed by researchers at institutions like CERN and Caltech.

Category:Particle physics