Implementation of the manifest left–right symmetric model in FeynRules

Abstract

We present an implementation of the manifest left-right symmetric model in FeynRules. The different aspects of the model are briefly described alongside the corresponding elements of the model file. The model file is validated and can be easily translated to matrix element generators such as MadGraph5_aMC@NLO, CalcHEP, Sherpa, etc. The implementation of the left-right symmetric model is a useful step for studying new physics signals with the data generated at the LHC.Keywords: left-right model; Feynman diagrams; CalcHEP model; MadGraph model; introductonThe main goal of the LHC is to search for signals of new physics beyond the Standard Model (SM), motivated by the shortcomings of the SM. In particular, the SM is incapable of explaining a number of fundamental issues, such as the hierarchy problem (resulting from the large difference between the weak force and the gravitational force), dark matter, the number of families in the quark and lepton sector. It is, therefore, widely believed that new physics beyond the SM will be discovered in the coming years. Among the possible attractive platforms for new physics are left-right symmetric models (LRSM) [1,2], on which we focus in this paper. In particular, we describe here a LRSM with no explicit CP violation in the Higgs potential, the manifest (or quasi-manifest) left-right symmetric model (MLRSM or QMLRSM, respectively), and its implementation in matrix element generators through FeynRules 2.0 [3].The LRSM address two specific difficulties of the SM: (i) Parity violation in the weak interactions, and (ii) non-zero neutrino masses implied by the experimental evidence of neutrino oscillation [4]. In particular, the left-right symmetry which underlies LRSM restores Parity symmetry at energies appreciably higher than the electroweak (EW) scale, resulting in the addition of three new heavy gauge bosons, W Early constructions of the LRSM comprise a Higgs sector with a Higgs bidoublet and two Higgs doublets [1]. In such a setup, the neutrinos are of Dirac type and no natural explanation for their small masses is provided. A later version, the above mentioned MLRSM, incorporates a Higgs bidoublet and two Higgs triplets, which leads to Majorana type neutrinos [2]. In particular, the MLRSM provides a natural setup for the smallness of neutrino masses, relating their mass scale to the large left-right symmetry breaking scale through the see-saw mechanism [5].This work includes the following:• An implementation of the MLRSM carrying an identical structure to the Lagrangian of [6] (i.e. identical parametrization and definitions of the Lagrangian terms). As such, it features the following elements in particular:1. The use of alternative empirical parameters (i.e. fermion mass matrices, CKM-type mixing matrices and Higgs VEVs) to indirectly set values to the Yukawa matrices, 2. Majorana type neutrinos (for a Dirac type see the Left-Right model based on [7]), 3. Directly controlling the QMLRSM diagonal matrices described in Refs. [5] and [6].• As a result, this is the fi...

Unified Explanation of theeejj, Diboson, and Dijet Resonances at the LHC

“…We calculate the W R -production cross section at NLO using the FeynRules [35] implementation of the LRSM [36] in MadGraph [37] with NNPDF2.3 PDF sets [38]. We find σ(pp → W R ) = 223.4 fb for M W R = 1.9 TeV and g R = 0.51.…”

Right-handed lepton mixings at the LHC

“…Instead it is minimal when the relation In order to see how the above results are affected once hadronization effects are taken into account, we extent the Feynrules implementation of the mLRSM in [46] to include leptonic mixing in the type II see-saw dominance for C as the LR symmetry, where it can be shown that V R = K e V * L . The events at the parton level are simulated with Madgraph 5 [47] and hadronization effects with Pythia 6 [48].…”

Probing left-right seesaw models using beam polarization at an e+e− collider

“…In addition, for the heavy Majorana neutrino coupling to the electron flavor, there are stringent constraints from non-observation of the rare LNV process of neutrinoless double beta decay (0νββ) [88]. Assuming that the purely RH current contribution to 0νββ is the dominant one and using the latest limit from GERDA phase-II on the half-life of 76 Ge, T 0ν 1/2 ≥ 5.3×10…”

“…(4), calculated using a FeynRules [75] implementation of the L-R seesaw model [76] in MadGraph5 [77], are shown in Fig. 2 for a modest value of center of mass energy √ s = 500 GeV.…”