We investigate a novel collider signature within the minimal Left-Right Symmetric Model, featuring a Higgs sector composed of a bi-doublet and two triplets. Our study focuses on a region of the parameter space where the SU(2) charged gauge boson $\textit{W}$ lies in the multi-TeV regime (3–100 TeV) and the additional Higgs states play a significant role. In this scenario, a heavy neutral Higgs boson ∆ with a dominant SU(2) triplet component can be produced in association with either a Standard Model Higgs boson or a massive weak boson. The subsequent decay of the heavy Higgs into Majorana neutrinos $\textit{N}$ results in displaced lepton signatures, providing a striking manifestation of lepton number violation. Additionally, we explore how the production of $\textit{b}$-jets in these processes can enhance hadron-collider sensitivity to such signals. A particularly compelling channel, $$ pp\to b\overline{b} NN $$ , offers the exciting possibility of simultaneously probing the spontaneous mass origin of both Dirac fermions and Majorana states. Based on an optimised event selection strategy and state-of-the-art Monte Carlo simulations, we outline the expected reach at the HL-LHC and future colliders. Our findings demonstrate that this channel probes a region of parameter space where the neutral Higgs triplet and heavy neutrino masses are relatively light ($\textit{m}$ ≲ 250 GeV, $\textit{m}$ ≲ 80 GeV), indirectly constraining the $\textit{W}$ boson to the deep multi-TeV domain, with sensitivity extending up to 70–80 TeV, effectively turning the LHC into a precision machine.

France

Benjamin Fuks

Slovenia

Jonathan Kriewald

Miha Nemevšek

Italy

Fabrizio Nesti

Beautiful Majorana Higgses at colliders

<p>We examine the prospect of observing genuine lepton-number-violating (LNV) signals at hadron colliders in the context of the type II seesaw mechanism. The model features smoking gun signals involving same-sign di-leptons and jets that may be the primary observable channel in certain regions of the parameter space. The flavor composition of final-state charged leptons is related to the origin of neutrino masses and is correlated with other rare processes, such as neutrinoless double-beta decay. We review existing collider limits and provide sensitivity estimates from LNV signals at upcoming Large Hadron Collider runs, including nonzero mass splittings between triplet components.</p>

Patrick D. Bolton

United States

Juan Carlos Vasquez

Hadron colliders signatures of lepton number violation in the type II seesaw model

Axion-mediated forces are enhanced by the presence of <math><mi>C</mi><mi>P</mi></math>-violating axion couplings, which are however tightly constrained by electric dipole moment (EDM) searches. We discuss the underlying hypotheses behind different sources of <math><mi>C</mi><mi>P</mi></math> violation at high energies and the interplay between axion-mediated force experiments and EDM observables. Specifically, we identify various mechanisms, based on new sources of <math><mi>C</mi><mi>P</mi></math> violation or Peccei-Quinn symmetry breaking, that can significantly relax EDM constraints, leading to a substantial redefinition of the QCD axion window for axion-mediated forces. By considerably enlarging the QCD axion parameter space, our results provide a well-motivated target for experiments probing scalar axion couplings to matter fields. These include fifth-force tests of gravity, as well as searches for spin-dependent forces via precision magnetometry, proton storage rings and ultracold molecules.

Luca Di Luzio

Spain

Hector Gisbert

Philip Sørensen

Axion window on new macroscopic forces

We investigate the structure of the minimal left-right symmetric model that enables precise predictions in the gauge, scalar and neutrino sector. We revisit the complete set of mass spectra and mixings for the charged and neutral gauge bosons, would-be-Goldstones and gauge fixing, together with the ghost Lagrangian. In the scalar sector, we analytically re-derive all the massive states with mixings and devise a non-trivial physical input scheme, expressing the model couplings in terms of masses and mixing angles. Fermion couplings are also determined in closed form, including the Dirac mixing in the neutrino sector, evaluated explicitly using the Cayley–Hamilton theorem. These analytic developments are implemented in a comprehensive FeynRules model file. We calculate the one loop QCD corrections and provide a complete UFO file for NLO studies, demonstrated on relevant hadron-collider benchmarks. We provide various restricted variants of the model file with different gauges, massless states, neutrino hierarchies and parity violating $$g_L \ne g_R$$ gauge couplings.

Enabling precise predictions for left-right symmetry at colliders

We study the production of right-handed bosons <math><msub><mi>W</mi><mi>R</mi></msub></math> and heavy neutrinos <math><mi>N</mi></math> at a future 100 TeV high-energy hadron collider in the context of left-right symmetry, including the effects of <math><mrow><msub><mrow><mi>W</mi></mrow><mrow><mi>L</mi></mrow></msub><mtext>−</mtext><msub><mrow><mi>W</mi></mrow><mrow><mi>R</mi></mrow></msub></mrow></math> gauge boson mixing. We estimate the collider reach for up to <math><mrow><mn>3</mn><mo>/</mo><mi>ab</mi></mrow></math> integrated luminosity using a multibinned sensitivity measure. In the Keung-Senjanović and missing-energy channels, the <math><mrow><mn>3</mn><mi>σ</mi></mrow></math> sensitivity extends up to <math><msub><mi>M</mi><msub><mi>W</mi><mi>R</mi></msub></msub><mo>=</mo><mn>35</mn></math> and 37 TeV, respectively. We further clarify the interplay between the missing-energy channel and the (expected) limits from neutrinoless double beta decay searches and big bang nucleosynthesis (and dark matter).

Left-right symmetry at an FCC-hh

We argue that Left-Right parity symmetry  $${\mathcal {P}}$$  <math> <mi>P</mi> </math>   can arise as a discrete remnant of a unified gauge symmetry. The high-energy unification necessarily includes the gauging of the Lorentz symmetry, bringing into the game gravitational interactions, and leading to a gravi-GUT scheme. Parity emerges unbroken below the Planck scale, and can be broken spontaneously at lower energies making contact with the Standard Model. This framework motivates the spontaneous origin of parity violation as in Left-Right symmetric theories with  $${\mathcal {P}}$$  <math> <mi>P</mi> </math>  . The possible unifying gauge groups are identified as  $$\mathrm{SO}(1,7)$$  <math> <mrow> <mi>SO</mi> <mo>(</mo> <mn>1</mn> <mo>,</mo> <mn>7</mn> <mo>)</mo> </mrow> </math>   for gravitational and weak interactions, or  $$\mathrm{SO}(7,7)$$  <math> <mrow> <mi>SO</mi> <mo>(</mo> <mn>7</mn> <mo>,</mo> <mn>7</mn> <mo>)</mo> </mrow> </math>   for a complete unification.

Croatia

Alessio Maiezza

Parity from gauge symmetry

We compute the <math><mi>C</mi><mi>P</mi></math>-violating scalar axion coupling to nucleons in the framework of baryon chiral perturbation theory and we apply the results to the case of left-right symmetry. The correlated constraints with other <math><mi>C</mi><mi>P</mi></math>-violating observables show that the predicted axion nucleon coupling is within the reach of present axion-mediated force experiments for <math><msub><mi>M</mi><msub><mi>W</mi><mi>R</mi></msub></msub></math> up to 1000 TeV.

Stefano Bertolini

Germany

Axion-Mediated Forces, <math><mi>C</mi><mi>P</mi></math> Violation, and Left-Right Interactions

Within the minimal left-right (LR) symmetric model we revisit the predictions for the kaon <math><mi>C</mi><mi>P</mi></math> violating observables <math><mi>ϵ</mi></math> and <math><msup><mi>ϵ</mi><mo>′</mo></msup></math> in correlation with the neutron electric dipole moment. We perform a complete study of the cross constraints on the model parameters, phases and the <math><msub><mi>M</mi><msub><mi>W</mi><mi>R</mi></msub></msub></math> scale, considering the two cases of extended parity or charge conjugation as LR discrete symmetries, together with the possible presence of a Peccei-Quinn symmetry. We discuss in particular two scenarios: whether the Standard Model saturates the experimental value of <math><msup><mi>ϵ</mi><mo>′</mo></msup><mo>/</mo><mi>ϵ</mi></math> or whether new physics is needed, still an open issue after the recent lattice results on the QCD penguin matrix elements. Within the first scenario, we find no constraints on the LR scale in the charge-conjugation case while in the parity case we show that <math><msub><mi>M</mi><msub><mi>W</mi><mi>R</mi></msub></msub></math> can be as low as 13 TeV. On the other side, the request that new physics contributes dominantly to <math><msup><mi>ϵ</mi><mo>′</mo></msup></math> implies strong correlations among the model parameters, with an upper bound of <math><mrow><msub><mrow><mi>M</mi></mrow><mrow><msub><mrow><mi>W</mi></mrow><mrow><mi>R</mi></mrow></msub></mrow></msub><mo>&lt;</mo><mn>8</mn><mi>–</mi><mn>100</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></mrow></math> depending on <math><mi>tan</mi><mi>β</mi></math> in the case of charge conjugation and a range of <math><mrow><msub><mrow><mi>M</mi></mrow><mrow><msub><mrow><mi>W</mi></mrow><mrow><mi>R</mi></mrow></msub></mrow></msub><mo>≃</mo><mn>7</mn><mi>–</mi><mn>45</mn><mtext> </mtext><mtext> </mtext><mi>TeV</mi></mrow></math> in the parity setup. Both scenarios may be probed directly at future colliders and only indirectly at the LHC.

Kaon <math><mi>C</mi><mi>P</mi></math> violation and neutron EDM in the minimal left-right symmetric model

In the context of left-right symmetry, we revisit the Keung-Senjanović production of right-handed <math><mrow><msub><mrow><mi>W</mi></mrow><mrow><mi>R</mi></mrow></msub></mrow></math> bosons and heavy neutrinos <math><mi>N</mi></math> at high energy colliders. We develop a multibinned sensitivity measure and use it to estimate the sensitivity for the entire range of <math><mi>N</mi></math> masses, spanning the standard and merged prompt signals, displaced vertices and the invisible <math><mi>N</mi></math> region. The estimated sensitivity of the LHC with 300/fb integrated luminosity ranges from 5 to beyond 7 TeV, while the future 33(100) TeV collider’s reach with 3/ab extends to 12(26) TeV.

Goran Popara

Keung-Senjanović process at the LHC: From lepton number violation to displaced vertices to invisible decays

Collider signals of heavy Majorana neutrino mass origin are studied in the minimal Left-Right symmetric model, where their mass is generated spontaneously together with the breaking of lepton number. The right-handed triplet Higgs boson Δ, responsible for such breaking, can be copiously produced at the LHC through the Higgs portal in the gluon fusion and less so in gauge mediated channels. At Δ masses below the opening of the V V decay channel, the two observable modes are pair-production of heavy neutrinos via the triplet gluon fusion gg → Δ → NN and pair production of triplets from the Higgs h → ΔΔ → 4 N decay. The latter features tri- and quad same-sign lepton final states that break lepton number by four units and have no significant background. In both cases up to four displaced vertices may be present and their displacement may serve as a discriminating variable. The backgrounds at the LHC, including the jet fake rate, are estimated and the resulting sensitivity to the Left-Right breaking scale extends well beyond 10 TeV. In addition, sub-dominant radiative modes are surveyed: the γγ , Zγ and lepton flavour violating ones. Finally, prospects for Δ signals at future e + e − colliders are presented.