arXiv subjects

Benjamin Fuks

Publications and source records attributed to Benjamin Fuks.

At least 19 recordsLinked to original sources

arXiv2026

Multiboson Signatures of Doubly Charged Scalars at a Same-Sign Muon Collider

We investigate the sensitivity of a same-sign $\mu^+\mu^+$ collider to doubly charged scalars in the Type-II seesaw framework, focusing on the regime in which the doubly charged scalar decays dominantly into same-sign $W$-boson pairs. Motivated by the $\mu$TRISTAN proposal, for a benchmark we consider a degenerate triplet spectrum at a center-of-mass energy of $2~{\rm TeV}$ and an integrated luminosity of $1~{\rm ab}^{-1}$. The signal process is studied in the fully hadronic $W$-decay mode, leading to a characteristic $\mu^+\mu^+ + 8j$ final state. We develop a cut-based analysis based on high jet multiplicity and global hadronic $W$ reconstruction, and then improve its sensitivity with a multivariate strategy exploiting reconstructed $W$ observables, global event kinematics, multi-boson variables and spectator-muon information. The best-performing setup reaches a $2\sigma$ sensitivity level for doubly charged scalar masses up to $425-430~{\rm GeV}$, extending the cut-based reach by a few tens of GeV. This indicates an improvement over the current LHC coverage, while also providing an independent probe based on a qualitatively different production mode and collider environment.

hep-ph↗

arXiv2026

Searching for charged Higgs bosons in top decays via the $t^*b$ channel

Rare top-quark decays offer a sensitive probe of charged Higgs bosons with masses below the top mass, owing to the large $t\bar t$ production rate at the LHC and the distinctive final states involving leptons and $b$-jets. While existing searches target the $H^\pm\to \tau\nu$, $cs$, and $cb$ modes, the decay $H^\pm\to tb$ has been studied only for heavier charged Higgs bosons with an on-shell top quark in the final state. The low-mass off-shell channel $H^\pm\to t^*b$ therefore remains essentially unconstrained, even though it can become the dominant decay mode below the top-quark threshold owing to the large top Yukawa coupling. We study charged-Higgs production from the rare top decay $t\to H^\pm b$, followed by the decay $H^\pm\to t^*b$. Top-antitop production and decay hence give rise to a $t\bar t b\bar b$-like final state, which we constrain by reinterpreting recent ATLAS fiducial measurements in dileptonic events. We obtain model-independent limits of 1.9%-2.9% on the product of branching ratios ${\rm Br}(t\to H^\pm b)\times{\rm Br}(H^\pm\to t^*b)$ for charged-Higgs masses between 110 and 165 GeV, and interpret these bounds in several two-Higgs-doublet scenarios. While dedicated searches for conventional charged-Higgs decays dominate for canonical $Z_2$-symmetric models, the $t^*b$ reinterpretation becomes competitive near the top-quark threshold in the up-type aligned limit and provides relevant direct constraint in a top-philic scenario. In the top-specific Two-Higgs-Doublet Model, it additionally excludes a low-$\tan\beta$ region not covered by conventional searches. These results thus establish $t\bar t$ production with additional $b$-jets as a complementary probe of light charged Higgs bosons and nonstandard top-quark decays, and motivate dedicated analyses by the LHC collaborations.

hep-ph↗

arXiv2026

Photons, jets and missing momentum from a two-vector dark sector

We investigate the LHC phenomenology of a vector dark-sector effective theory containing two neutral massive vector states, both odd under a dark-parity symmetry. The lightest state is stable and provides a dark-matter candidate, while the leading interactions with the Standard Model arise from dimension-six operators involving the hypercharge field strength. In the prompt-decay regime considered in this work, the heavier state can decay radiatively, leading to a $\gamma+\text{jets}+E_T^{\text{miss}}$ signature when the two dark vectors are produced in association with QCD radiation. We study this topology at the LHC through a cut-based analysis, comparing an inclusive missing-transverse-momentum selection with a three-bin strategy that retains coarse shape information. The binned analysis is found to substantially improve the expected reach and probes regions of the parameter space compatible with the observed relic abundance in the standard freeze-out scenario. We also discuss the freeze-in interpretation and the limitations associated with the EFT description at high masses.

hep-ph↗

arXiv2026

Composite top partners in exotic colour representations

Composite Higgs models with partial compositeness generically predict coloured fermionic resonances associated with the strong dynamics responsible for electroweak symmetry breaking. While most phenomenological studies have focused on colour-triplet and colour-octet top partners, several UV-complete hypercolour constructions also contain fermionic colour sextets. We present a systematic study of these states in the minimal model classes where they arise, constructing the relevant low-energy interactions and deriving their characteristic decay patterns. The sextets predominantly decay through coloured pseudo-Nambu-Goldstone bosons, leading to top-rich final states, while additional channels with $b$-jets and missing transverse energy can be important. We reinterpret existing ATLAS and CMS searches for high-multiplicity final states to derive the dedicated constraints on these resonances. For the benchmark spectra considered, current LHC data exclude individual sextet components up to masses in the $2-2.5$ TeV regime, with stronger bounds when the full sextet multiplet is included, while conservative extrapolations to the HL-LHC indicate a reach close to $3$ TeV. Our results therefore show that colour-sextet fermions provide a powerful and largely unexplored probe of composite Higgs models with partial compositeness.

hep-ph↗

arXiv2026

Extracting a Toponium Signal at the LHC with Spin and Quantum Information Tools

We investigate near-threshold top-antitop production at the LHC, focusing on the impact of toponium formation on spin correlations and quantum information properties of the final state. Considering the top-antitop system as a mixed two-qubit state, we reconstruct spin density matrices via quantum tomography and evaluate several observables including some inspired by quantum information. We then compare their sensitivity in discriminating toponium effects from top-antitop production without these effects. Our results demonstrate that combining these variables is expected to significantly enhance sensitivity to toponium effects, bringing new ways to explore these subtle features.

hep-ph↗

arXiv2026

Long-lived Left-Right signals at the FCC-ee

We give an extensive discussion of the displaced signals of heavy Majorana neutrino production at future electron-positron colliders operating at various proposed energies in the context of the Left-Right symmetric model. A comprehensive collection of channels is taken into account, ranging from those featuring $W$ and $W_R$ mediation to those induced by scalar mixing and gauge/scalar boson fusion, with connections to the mechanism of neutrino mass origin. The emerging signatures feature possibly multiple displaced heavy neutrinos that are in some cases accompanied by prompt activity and forward leptons. We derive the corresponding total production rates and differential distributions, which allow us to differentiate the channels and have analytical estimates of the signal yield. We then develop realistic estimates of the selection efficiencies using a dedicated vertexing algorithm which establishes the displaced decay positions and supplies a reliable proxy for reconstructing the full four-momenta of long-lived particles. This allows to determine the realistic reaches in the parameter space of the Left-Right symmetric model across the various channels, and we show that these can strongly surpass the LHC ones, demonstrating that future lepton colliders are sensitive to left-right symmetry breaking scales in the deep multi-TeV regime.

hep-ph↗

arXiv2026

Flavour-Changing Neutral Current Top Decays in the Three Higgs Doublet Model

We study flavour-changing neutral current decays of the top quark in the democratic Three Higgs Doublet Model featuring a $Z_3$-symmetric scalar potential and Natural Flavour Conservation. In this framework, while such processes are absent at tree-level, the extended scalar sector induces new one-loop contributions to rare top decays. We compute the branching ratios for processes of the form $t \to q X$ (with $q = u, c$ and $X$ denoting a boson of the model), and explore the viable regions of the parameter space under theoretical consistency conditions and current experimental constraints. Several alignment-limit scenarios corresponding to different hierarchies among the CP-even Higgs states are analysed, and we find that the predicted branching ratios can significantly exceed their Standard Model expectations while remaining consistent with existing limits. In particular, we identify scenarios with light non-standard scalars that can lead to rates within the projected sensitivity of the High-Luminosity LHC. Our results therefore highlight rare top decays as a promising probe of the extended scalar sector of the Three Higgs Doublet Model.

hep-ph↗

arXiv2025

New physics in toponium's shadow?

ATLAS and CMS have recently reported enhancements in the top-antitop production rate near threshold, a region where non-perturbative QCD dynamics associated with toponium formation become relevant. We investigate how this behaviour is modified in the presence of a neutral pseudoscalar that couples to gluons and top quarks, using an effective description that consistently incorporates perturbative Standard Model and new physics contributions, their interference and non-perturbative threshold effects. We show that the combined effect of those ingredients markedly shapes the viable region of the pseudoscalar parameter space, particularly for narrow resonances with masses close to twice the top mass. While Standard Model threshold effects could explain a sizeable part of the measured enhancements, the current data remain compatible with additional contributions from pseudoscalar interactions.

hep-ph↗

arXiv2025

Statistical Indications of Toponium Formation in Top Quark Pair Production

We present an analysis of six differential cross-section measurements of top-quark pair production in the dilepton channel from the ATLAS and CMS experiments. The data are compared to state-of-the-art QCD predictions with and without the inclusion of toponium formation effects. This contribution is modelled via a re-weighting of fixed-order matrix elements using the Green's function of the non-relativistic QCD Hamiltonian, and we employ a statistical model to quantify the preference of the data for the toponium hypothesis. All observables yield Bayes factors larger than unity, with two exceeding 20, yielding strong evidence for the toponium hypothesis in top-quark pair production at the LHC.

hep-ph↗

arXiv2025

Extracting Higgs Self-Coupling Constraints through Triple Higgs Boson Production at Future Hadron Colliders

We present a systematic study of triple Higgs boson production at future high-energy hadron colliders, using the six-$b$-jet final state as a probe of the Higgs self-interactions. We conduct, under realistic detector smearing assumptions, both a traditional cut-based analysis, and a multivariate one using gradient boosting. The multivariate strategy is found to enhance sensitivity to beyond the Standard Model effects on the Higgs boson's self-couplings, while preserving large signal event yields, thus enabling more robust statistical inference. This allows us to assess the impact of detector effects, systematic uncertainties, background normalisation, as well as different truncation choices in an effective-field-theory description of the new physics effects possibly affecting the Higgs boson's self-interactions. Our results demonstrate that statistically-meaningful and perturbative-unitarity-compatible constraints on the trilinear and quartic Higgs boson self-couplings can be achieved, provided that systematic uncertainties are controlled at the few-percent level. Finally, we extrapolate our results to various collider energies and luminosities, demonstrating in particular that an 85 TeV proton-proton collider performs comparably to a 100 TeV machine. Altogether, our findings therefore establish the six-$b$ channel as a viable probe of the Higgs self-interactions at most future hadron collider options currently being examined by the high-energy physics community.

hep-ph↗

arXiv2025

Prospects for toponium formation at the LHC in the single-lepton mode

We investigate the formation of toponium in the single-leptonic final state at the LHC. Our study builds on our recently proposed framework that incorporates the associated non-perturbative effects into Monte Carlo simulations through the Green's function of the non-relativistic QCD Hamiltonian and the re-weighting of hard-scattering matrix elements. This allows us to perform a phenomenological analysis that demonstrates that a statistically significant excess from toponium formation could already be accessible in Run~2 data. Moreover, our results highlight observables that provide handles for signal characterisation and establish the single-leptonic channel as a competitive and complementary avenue for the ongoing exploration of toponium signatures at colliders.

hep-ph↗

arXiv2025

Deep learning approaches to top FCNC couplings to photons at the LHC

We investigate the sensitivity of the LHC to flavour-changing neutral current interactions involving the top quark and a photon using a model-independent effective field theory framework, focusing on two complementary processes: single top production via $qg \to t\gamma$ and the rare decay $t \to q\gamma$ in top pair events. To enhance signal discrimination, we employ a range of deep learning classifiers, including multi-layer perceptrons, graph attention networks and transformers, and compare them against a traditional cut-based analysis. Our results demonstrate that attention-based architectures, in particular transformer networks, significantly outperform other strategies, yielding up to a factor of five improvement in the expected exclusion limits. In particular, we show that at the high-luminosity LHC, rare top branching ratios can be probed down to values as low as $10^{-6}$. Our results thus highlight the significant potential of attention-based architectures for improving the sensitivity to new physics signatures in top quark processes at colliders.

hep-ph↗

arXiv2025

Deciphering compressed electroweakino excesses with MadAnalysis 5

We present version 1.11 of MadAnalysis 5, which extends the software package in several major ways to improve the handling of efficiency tables, the computation of observables in different reference frames and the calculation of statistical limits and/or significance. We detail how these improvements, whose development was motivated by the desire to implement two Run 2 LHC analyses targeting signatures with soft leptons and missing energy and exhibiting mild excesses (ATLAS-SUSY-2018-16 and ATLAS-SUSY-2019-09), have been implemented by both direct extensions of the code and integrations with third-party software. We then document the implementation and validation of these analyses, demonstrating their utility along with the improved statistics capabilities of MadAnalysis 5 through an investigation of the Next-to-Minimal Supersymmetric Standard Model in the context of a larger set of overlapping excesses in channels with soft leptons/jets and missing transverse energy.

hep-ph↗

arXiv2025

Searching for top-philic heavy resonances in boosted four-top final states

New heavy resonances with sizeable couplings to top quarks can be probed through searches for beyond-the-Standard-Model effects in four-top production at the LHC. In this work, we present the first next-to-leading-order QCD predictions for the full on-shell and off-shell production of four-top events via new electroweak singlet states, along with dedicated analysis strategies based on the reconstruction and tagging of all final-state top quarks. We develop a detector-level simulation incorporating recent advances in top-tagging and boosted object reconstruction. Moreover, we demonstrate that searches at LHC Run 3 and high-luminosity phase in the zero-lepton, one-lepton and same-sign di-lepton channels can improve the sensitivity to the new physics cross sections by up to two orders of magnitude. In particular, colour-octet resonances with masses up to 2-2.5 TeV and colour-singlet states with masses up to 1-1.5 TeV are within reach for coupling values in the 0.1-1 range.

hep-ph↗

arXiv2025

A joint explanation for the soft lepton and monojet LHC excesses in the wino-bino model

We present new recasts of the CMS Run 2 soft-leptons + missing energy analysis and the ATLAS Run 2 multijet + missing energy analysis. These analyses are relevant for probing the parameter space of electroweak-charged particles with compressed spectra. We review these analyses and detail their implementation and validation in HackAnalysis (for CMS) and MadAnalysis 5 (ATLAS). We then use these new recasts to combine four LHC analyses to identify a region of parameter space of the "wino-bino" simplified model, which corresponds to a limit of the Minimal Supersymmetric Standard Model in which higgsinos are decoupled, that is preferred over the Standard Model by excesses in the data. We find that the favoured region is compatible with the observed dark matter relic density, assuming freeze out within a standard cosmology, and we comment on the importance of this result and on how the simplified model should be mapped onto a complete supersymmetric model.

hep-ph↗

arXiv2025

Vector Boson Fusion Signatures of Superheavy Majorana Neutrinos at Muon Colliders

We investigate the sensitivity of future high-energy muon colliders to heavy Majorana neutrinos, considering both opposite-sign ($\mu^+\mu^-$) and same-sign ($\mu^+\mu^+$) collision modes. We focus on $\mu^+\mu^-$ colliders operating at centre-of-mass energies of 1, 3 and 10 TeV, as well as the proposed $\mu$TRISTAN facility at 2 TeV, and we analyse the production of heavy neutrinos via vector boson fusion in the $t$-channel, a mechanism that becomes dominant in the multi-TeV regime. We evaluate its exclusion potential in terms of the heavy neutrino mass and the mixing of the heavy neutrino with its Standard Model counterparts, using both cut-based selections and boosted decision trees trained to exploit the distinct kinematic signatures of heavy Majorana neutrino exchanges. Our results demonstrate the complementarity between collider configurations, and show that active-sterile mixing angles as small as 0.001 could be probed for neutrino masses up to 100 TeV, an experimentally inaccessible region of the parameter space at current facilities. Altogether, this work establishes the discovery potential of muon colliders for testing super-heavy Majorana neutrinos, complementary to conventional probes, and provides compelling motivation for the next generation of high-energy lepton colliders.

hep-ph↗

arXiv2025

Toponium physics at the Large Hadron Collider

We examine toponium formation effects in top-antitop pair production at the LHC, focusing on the near-threshold region where non-relativistic corrections are relevant. We discuss their modelling using non-relativistic QCD Green's functions, and show that predictions reproduce features expected from bound-state dynamics, in contrast to pseudo-scalar toy models.

hep-ph↗

arXiv2025

t-channel dark matter at the LHC -- a whitepaper

This report, summarising work achieved in the context of the LHC Dark Matter Working Group, investigates the phenomenology of $t$-channel dark matter models, spanning minimal setups with a single dark matter candidate and mediator to more complex constructions closer to UV-complete models. For each considered class of models, we examine collider, cosmological and astrophysical implications. In addition, we explore scenarios with either promptly decaying or long-lived particles, as well as featuring diverse dark matter production mechanisms in the early universe. By providing a unified analysis framework, numerical tools and guidelines, this work aims to support future experimental and theoretical efforts in exploring $t$-channel dark matter models at colliders and in cosmology.

hep-ph↗