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| Mohapatra–Senjanović | |
|---|---|
| Name | Mohapatra–Senjanović |
| Discoverer | Rao Mohapatra; Goran Senjanović |
| Year | 1975 |
| Field | Particle physics |
| Related | Seesaw mechanism, Left–right symmetry, Grand Unified Theory, Neutrino mass |
Mohapatra–Senjanović is a theoretical framework in Particle physics proposing a mechanism for small neutrino masses via restoration of Left–right symmetry and the introduction of heavy right-handed Majorana fermions. Developed by Rao Mohapatra and Goran Senjanović in the mid-1970s, it links ideas from the Seesaw mechanism, parity restoration, and extensions of the Standard Model to explain observed anomalies in solar neutrino problem, atmospheric neutrino anomaly, and neutrinoless double beta decay searches.
The proposal emerged in the context of attempts to extend the Standard Model after discoveries at the Fermilab, CERN, and results from Homestake experiment and Super-Kamiokande that suggested nonzero neutrino oscillation. Early precursors include the original Seesaw mechanism papers and models invoking heavy gauge bosons such as the W′ boson and Z′ boson. Mohapatra and Senjanović combined insights from Pati–Salam model, Grand Unified Theory scenarios like SO(10), and earlier work by Wolfenstein to craft a minimal left-right symmetric theory with heavy right-handed neutrinos. Subsequent developments connected the framework to leptogenesis, constraints from LEP, and searches at Large Hadron Collider.
The framework is built on an extension of the Standard Model gauge group to include SU(2)_R in addition to SU(2)_L and U(1)_{B-L} charge, inspired by the Pati–Salam model and embedding possibilities within SO(10). It introduces right-handed neutrino states analogous to left-handed counterparts present in Electroweak theory, and scalar sectors including bidoublet and triplet Higgs fields similar to those in Georgi–Glashow model. Spontaneous breaking of SU(2)_R leads to heavy gauge bosons like W_R and Z_R, and generates large Majorana masses for right-handed neutrinos through triplet vacuum expectation values as in the Type I seesaw and Type II seesaw contexts. The model naturally accommodates CP violation sources relevant for baryogenesis via leptogenesis and links to flavor physics anomalies studied at BaBar, Belle, and LHCb.
Phenomenology predicts heavy resonances accessible to high-energy colliders such as the Large Hadron Collider and potential future machines like the Future Circular Collider or International Linear Collider. Observable signatures include production of W_R and subsequent decay chains yielding same-sign dileptons, displaced vertices from heavy neutrino decay, and resonant peaks in dijet or dilepton spectra searched for by ATLAS and CMS. Low-energy consequences appear in neutrinoless double beta decay experiments like GERDA, KamLAND-Zen, and EXO, where Majorana neutrino exchange can produce measurable rates. Flavor-changing processes constrained by MEG experiment and precision electroweak measurements from LEP and SLD further restrict parameter space. Cosmological implications link to Big Bang nucleosynthesis and cosmic microwave background observations by Planck through effects on effective neutrino number and lepton asymmetries.
Collider searches at ATLAS and CMS provide direct limits on masses of W_R and heavy neutrinos, with complementary bounds from Tevatron and fixed-target experiments. Neutrinoless double beta decay searches by GERDA, KamLAND-Zen, and CUORE set upper bounds on effective Majorana mass parameters. Constraints from lepton flavor violation come from MEG (mu -> e gamma), SINDRUM (mu -> e conversion), and Belle II limits on rare tau decays. Cosmology-derived limits use Planck data and large-scale structure surveys including SDSS to bound light sterile states and extra relativistic degrees of freedom. Global fits combining NuFIT oscillation data, KATRIN beta-decay bounds, and collider limits map allowed regions for heavy-neutrino masses, mixing angles, and scalar sector parameters. Proposed future probes include displaced-vertex searches at the High-Luminosity LHC and intensity-frontier experiments like DUNE and Hyper-Kamiokande.
Many variants embed the core idea into larger frameworks: left-right symmetric SO(10) grand unification ties the model to Pati–Salam model and SU(5) extensions; inverse seesaw and linear seesaw variants introduce extra singlet fermions inspired by E6 constructions; supersymmetric left-right models incorporate Supersymmetry and address hierarchy problems with connections to MSSM and NMSSM. Other extensions consider gauged B-L scenarios, embedding in extra dimensions models influenced by Randall–Sundrum model, or coupling to dark-sector candidates studied in XENON1T and LUX experiments. Leptogenesis mechanisms vary between high-scale thermal leptogenesis and low-scale resonant leptogenesis linking to Affleck–Dine scenarios.
The gauge symmetry is typically written as SU(3)_C × SU(2)_L × SU(2)_R × U(1)_{B-L}, with fermion representations mirroring those in SO(10) 16-plets. Yukawa Lagrangians couple bidoublet Higgs fields Φ to left- and right-handed doublets, yielding Dirac mass matrices post-electroweak breaking analogous to those in Yukawa coupling sectors of the Standard Model. Triplet scalar fields Δ_L and Δ_R produce Majorana mass terms M_R ∼ f v_R for right-handed neutrinos; integrating out heavy M_R leads to effective light neutrino mass matrices m_ν ≈ −m_D M_R^{-1} m_D^T (Type I) and direct triplet contribution m_ν ≈ f v_L (Type II), combining in general to m_ν = m_ν^{I} + m_ν^{II}. Gauge boson mass matrices arise from Higgs kinetic terms generating mass eigenstates W_L, W_R and Z, Z′ after spontaneous symmetry breaking, with mixing angles constrained by electroweak precision observables measured at LEP. Flavor mixing matrices extend the PMNS matrix and introduce right-handed analogs affecting charged-current interactions; diagonalization involves biunitary transformations familiar from Cabibbo–Kobayashi–Maskawa matrix derivations. Detailed radiative corrections and renormalization group evolution connect high-scale parameters to low-energy observables similarly to analyses in Grand Unified Theory renormalization studies.
Category:Particle physics theories