Version 5 (modified by richardphysics, 4 years ago) (diff)

In-progress update of Lagrangian

Hello World - In Development - To be published Oct 30


  • Description
  • Files
  • Notes

Effective Left-Right Symmetric Model at NLO in QCD

Contact Author

Richard Ruiz

  • University of Durham (IPPP)
  • richard.ruiz AT

In collaboration with Olivier Mattelaer and Manimala Mitra [ 1 ], and Manimala Mitra, Darren Scott, and Michael Spannowsky [ 2 ].

Model Description

This effective model extends the Standard Model (SM) field content by introducing heavy Left-Right symmetric gauge bosons WR+/-, ZR with masses MWR and MZR, as well as three heavy Majorana neutrinos Ni with mass mNi. The Lagrangian is given by,

\mathcal{L} = \mathcal{L}_{\rm SM} + \mathcal{L}_{\rm LRSM~Kin.} + \mathcal{L}_{\rm LRSM~Int.}

The first term is the Standard Model Lagrangian. In the mass basis, i.e., after mixing with active neutrinos, the heavy Majorana neutrinos' kinetic and mass terms are

\mathcal{L}_{\rm LRSM~Kin.} \ni \frac{1}{2}\overline{N_k} i\!\not\!\partial N_k - \frac{1}{2}m_{N_k} \overline{N_k}N_k, \quad k=1,\dots,3,

The WR, ZR, couplings to fermions is separated into three pieces:

\mathcal{L}_{\rm LRSM~Int.} = \mathcal{L}_{W_R-q-q'} + \mathcal{L}_{W_R-\ell-\nu/N} + 

The WR chiral coupling to quarks are

 \mathcal{L}_{W_R-q-q'} = \frac{-\kappa_R^q g}{\sqrt{2}}\sum_{i,j=u,d,\dots}\overline{u}_i V_{ij}^{\rm CKM'}~W_{R \mu}^+ \gamma^\mu P_R~ d_j + \text{H.c.}

VCKM' is the RH Cabbibo-Kobayashi-Masakawa (CKM) matrix, which is related to the SM CKM matrix. g=\sqrt{4\pi\alpha_{\rm EM}(M_Z)}/\sin\theta_W is the SM Weak coupling constant and \kappa_{R}{q} is an overall real normalization for the WR interaction strength. For leptons, the WR coupling and leptonic mixing is parametrized by~\cite{Atre:2009rg,Han:2012vk}

 \mathcal{L}_{W_R-\ell-\nu/N} = \frac{-\kappa_R^\ell g}{\sqrt{2}}
 \sum_{m'=1}^3	\overline{N_{m'}} Y_{\ell m'}
~W_{R \mu}^+ \gamma^\mu P_R~ \ell^-+\text{H.c.}

For chiral fermion $f$, we parametrize the $\ZR$ neutral currents by

 \mathcal{L}_{Z_R-f-f} = \frac{-\kappa_{R}^f g}{\sqrt{1 - \left(1/\kappa_{R}^f\right)^2 \tan^2\theta_W}}\sum_{f=u,e,\dots}
 \overline{f} Z_{R \mu} \gamma^\mu \left(g_{L}^{Z_R,f}P_L + g_{R}^{Z_R,f}P_R\right)f.

$\kappa_{R}{f}$ are the same $\kappa_{R}{q,\ell}$ as for $\WR$. In terms of electric and isospin charges, the chiral coefficients are


QCD Corrections

The SM Lagrangian with Goldstone boson couplings in the Feynman Gauge and the above Lagrangian in the Unitary gauge was implemented into FeynRules 2.3.10. QCD renormalization and R2 rational counter terms were determined using NLOCT 1.02 and FeynArts? 3.8. Feynman rules were collected into a single UFO, available below. In the UFO file, five massless quarks are assumed as are zero off-diagonal SM CKM and RH CKM' matrix entries. For additional details, see [ 1 ]. These additions permit tree-level calculations at LO and NLO in QCD and loop-induced calculations at LO in QCD using MadGraph_aMC@NLO, HERWIG, and SHERPA.

Model Files

  • Main model file. Relies on (default FR model file) being declared elsewhere.
  • heavyN_NLO.nb: Mathematica notebook file that generates UFO file from FeynRules model files. Allows user to also run quick sanity checks (optional) on model.
  • SM_HeavyN_Files.tgz: Standalone package containing, heavyN_NLO.nb, massless.rst (default FR file), diagonalCKM.rst (default FR file), and (default FR file).


  • To download any of the packages and unpack via the terminal, use the commands:

~/Path $ wget

~/Path $ tar -zxvf SM_HeavyN_NLO_UFO.tgz

~/Path $ wget

~/Path $ tar -zxvf SM_HeavyN_FilesWithUFO.tgz

  • This model contains 15 free parameters:
    • Three masses: mN1, mN2, mN3. Defaults are 300 GeV, 500 GeV, and 1 TeV, respectively.
    • Three widths: WN1, WN2, WN3. Defaults are 0.303 GeV, 1.50 GeV, and 12.3 GeV, respectively.
    • Nine real (no CP violation) mixing parameters: Vlk for l = e, mu, tau and k = 1,2,3. Default values are Vlk = Identity(3x3), i.e., Ve1 = Vmu2 = Vta3 = 1 and all others zero.
    • Note: VlN are restricted to be real in the model file.
    • Note: Default parameters are set so "out-of-the-box" checks can be made with [ 1 ] and [ 2 ].


  • The model file was checked against exact NLO WR predictions from [ 2 ].
  • Partial and total widths for WR, ZR, and N1 are checked against exact analytic calculations. See [ 1 ] for more information.

List of studies that have used the model file

  • Please email to update this space.


  • Please cite [ 1 ] for the model file and [ 2 ] for neutrino jets.

[1] O. Mattelaer, M. Mitra, R. Ruiz, Automated Neutrino Jet and Top Jet Predictions at NLO+PS Matching in Effective Left-Right Symmetric Models, arXiv:1610.XXXXX [hep-ph]

[2] M. Mitra, D. Scott, and M. Spannowsky, Neutrino Jets from High-Mass WR Gauge Bosons in TeV-Scale Left-Right Symmetric Models, arXiv:1607.03504 [hep-ph]

[3] A. Atre, T. Han, S. Pascoli and B. Zhang, The Search for Heavy Majorana Neutrinos, JHEP 0905, 030 (2009), arXiv:0901.3589 [hep-ph]

[3] T. Han, I. Lewis, R. Ruiz, Z.-G. Si, Lepton Number Violation and W' Chiral Couplings at the LHC, PRD87, 035011 (2013)

Attachments (5)

  • (8.0 KB) - added by richardphysics 4 years ago. Main Effective LRSM model file. Relies on (default FR model file) being declared elsewhere.
  • effLRSMnlo.nb (27.3 KB) - added by richardphysics 4 years ago. Mathematica notebook file that generates UFO file from FeynRules model files. Allows user to also run quick sanity checks (optional) on model.
  • EffLRSM_NLO.tgz (22.3 KB) - added by richardphysics 4 years ago. Standalone NLO in QCD-accurate UFO folder.
  • EffLRSMnlo_Files.tgz (14.8 KB) - added by richardphysics 4 years ago. Standalone package containing, effLRSMnlo.nb, diagonalMixing.rst, massless.rst (default FR file), and (default FR file).
  • EffLRSMnlo_FilesWithUFO.tgz (36.8 KB) - added by richardphysics 4 years ago. Combination of EffLRSMnlo_Files.tgz and EffLRSM_NLO.tgz.

Download all attachments as: .zip