We studied the collider phenomenology of third-generation scalar leptoquarks at the Large Hadron Collider (LHC) with a 14 TeV center-of-mass energy. The analysis focuses on leptoquarks decaying exclusively into top quarks and tau leptons, employing machine learning-based tagging techniques for identifying hadronically decaying boosted top quarks, W/Z, and Higgs bosons, as well as a multivariate classifier to distinguish signal events from Standard Model (SM) backgrounds. The expected 95% confidence level (CL) upper limits on the leptoquark production cross-section are computed assuming integrated luminosities of 200 and 500 inverse femtobarns at the 14 TeV LHC. The results demonstrate significant sensitivity improvements for detecting leptoquarks at masses beyond the current experimental limits.

India

Debabrata Sahoo

Rameswar Sahu

Kirtiman Ghosh

A comprehensive search for leptoquarks decaying into top- <italic>&#964;</italic> final states at the future LHC

Higgsinos near the TeV mass range are highly motivated as they offer an elegant solution to the naturalness problem in the Standard Model. Extensive searches for such higgsinos within the framework of General Gauge Mediation (GGM) have been conducted by both the ATLAS and CMS collaborations. However, the sensitivity of these searches in the hadronic channel remains limited, primarily due to the reliance on traditional substructure-based techniques for fat jet identification. In this work, we present a novel search strategy that leverages graph neural networks (GNNs) to improve the characterization of fat jets originating from <italic>W</italic>/ <italic>Z</italic>/ <italic>h</italic> bosons, top quarks, and QCD-initiated light quarks and gluons. The GNN scores, combined with a boosted decision tree (BDT) classifier, enhance signal-background discrimination, offering a significant improvement in sensitivity for higgsino searches at the LHC.

Advancing higgsino searches by integrating ML for boosted object tagging and event selection

<p>Probing Higgsinos remains a challenge at the LHC owing to their small production cross sections and the complexity of the decay modes of the nearly mass degenerate Higgsino states. The existing limits on Higgsino mass are much weaker compared to its bino and wino counterparts. This leaves a large chunk of sub-TeV supersymmetric parameter space unexplored so far. In this work, we explore the possibility of probing Higgsino masses in the 400–1000 GeV range. We consider a simplified supersymmetric scenario where <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>R</mi></math>-parity is violated through a baryon number violating trilinear coupling. We adopt a machine-learning-based top tagger to tag the boosted top jets originating from Higgsinos, and for our collider analysis, we use a boosted decision tree classifier to discriminate signal over SM backgrounds. We construct two signal regions characterized by at least one top jet and different multiplicities of <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>b</mi></math>-jets and light jets. Combining the statistical significance obtained from the two signal regions, we show that Higgsino mass as high as 925 GeV can be probed at the HL-LHC.</p>

Rajneil Baruah

Arghya Choudhury

Subhadeep Mondal

Probing sub-TeV Higgsinos aided by a machine-learning-based top tagger in the context of trilinear <math xmlns="http://www.w3.org/1998/Math/MathML" display="inline"><mi>R</mi></math>-parity violating SUSY

The classical conservation of the lepton number is an accidental symmetry present in the Standard Model (SM). Thus, we consider here a scenario where the SM is extended with a U(1) gauge group, promoting the lepton number to a local symmetry. The gauge anomaly cancellations necessitate the extension of the particle spectrum with several beyond the SM (BSM) particle fields. The extended lepton gauge group breaks around the TeV scale via spontaneous symmetry breaking, and a $\textit{Z}$ symmetry remains, which ensures the stability of the light $\textit{Z}$ odd BSM particles. Interestingly, the particle spectrum of the model has two distinct dark sectors with one having a Dirac type DM and the other one containing a Majorana type DM, thus resulting in a multipartite dark matter scenario. We have explored the available parameter space consistent with the observed dark matter relic density and direct detection measurements for both of the DM particles. Having a Majorana dark matter, we have also studied for the gamma line signatures to constraint the parameter space from the indirect dark matter detection experiments like FermiLAT and CTA.

Utkarsh Patel

 Avnish

Sudhanwa Patra

Multipartite dark matter in a gauge theory of leptons

<p>Supersymmetry (SUSY) addresses several problems of the Standard Model, such as the naturalness problem and gauge coupling unification, and can provide cosmologically viable dark matter candidates. SUSY must be broken at high energy scales with mechanisms like gravity, anomaly, gauge mediation, etc. This paper revisits the gauge mediated SUSY breaking (GMSB) scenarios in the context of data from the Large Hadron Collider (LHC) experiment. The ATLAS monophoton search at 139 inverse femtobarn integrated luminosity at the 13 TeV LHC, in the context of a simplified general gauge mediation (GGM) scenario (which is a phenomenological version of GMSB with an agnostic approach to the nature of the hidden sector), relies on assumptions that do not hold across the entire parameter space. We identify a few crucial assumptions regarding the decay widths of SUSY particles into final states with gravitinos that affect the LHC limits on the masses of the SUSY particles. Our study aims to reinterpret the ATLAS constraints on the gluino-NLSP mass plane, considering all possible decay modes of SUSY particles in a realistic GGM model.</p>

Finland

Katri Huitu

Revisiting the LHC constraints on gauge-mediated supersymmetry breaking scenarios

We explore the collider phenomenology of the fat-brane realization of the Minimal Universal Extra Dimension (mUED) model, where Standard Model (SM) fields propagate in a small extra dimension while gravity accesses additional large extra dimensions. This configuration allows for gravity-mediated decay (GMD) of Kaluza-Klein (KK) particles, resulting in unique final states with hard photons, jets, massive SM bosons, and large missing transverse energy due to invisible KK gravitons. We derive updated constraints on the model’s parameter space by recasting ATLAS mono-photon, di-photon, and multi-jet search results using 139 inverse femtobern of integrated luminosity data. Recognizing that current LHC search strategies are tailored for supersymmetric scenarios and may not fully capture the distinct signatures, we propose optimized strategies using machine learning algorithms to tag boosted SM bosons and enhance signal discrimination against SM backgrounds. These methods improve sensitivity to fat-brane mUED signatures and offer promising prospects for probing this model in future LHC runs.

Revisiting universal extra-dimension model with gravity mediated decays

We are considering a minimal U(1) extension of the Standard Model (SM) by promoting the baryon number as a local gauge symmetry to accommodate a stable dark matter (DM) candidate. The gauge theory of baryons induces non-trivial triangle gauge anomalies, and we provide a simple anomaly-free solution by adding three exotic fermions. A scalar $\textit{S}$ spontaneously breaks the U(1) symmetry, leaving behind a discrete $\textit{Z}$ symmetry that ensures the stability of the lightest exotic fermion originally introduced to cancel the triangle gauge anomalies. Scenarios with weakly interacting DM candidates having non-zero hypercharge usually face stringent constraints from experimental bounds on the DM spin-independent direct-detection (SIDD) cross-section. In this work, we consider a two-component singlet-doublet fermionic dark matter scenario, which significantly relaxes the constraints from bounds on the DM SIDD cross-section for suppressed single-doublet mixing. We show that the model offers a viable parameter space for a cosmologically consistent DM candidate that can be probed through direct detection searches, collider experiments, and gravitational wave (GW) experiments.

 Taramati

Singlet-doublet fermionic dark matter in gauge theory of baryons

Non-zero neutrino mass and dark matter (DM) overshadow the success of the Standard Model (SM) of particle physics. The most straightforward extension of the SM to explain these two issues is the Scotogenic model, where the SM particle spectrum extends with three isospin singlet right-handed neutrinos and one doublet scalar, all odd under a <math><msub><mrow><mi>Z</mi></mrow><mrow><mn>2</mn></mrow></msub></math> symmetry. The neutrino masses and mixings result from the Weinberg operator induced at one-loop level. The particle spectrum of this model contains a few weakly interacting stable massive particles, each of which can be a good candidate for DM. In this work, we have considered the lightest right-handed neutrino as DM candidate. The Yukawa couplings that give rise to the observed flavor mixings in the neutrino sector also lead to flavor violation in the SM charged lepton sector and hence, get tightly constrained from the charged lepton flavor violating (CLFV) observables. The same Yukawa couplings also contribute to the DM annihilation in the early universe and hence, determine the relic density of the DM. In this work, we address the tension between the constraints from CLFV observables and measured DM relic density to obtain the large Yukawa couplings with the help of a parameterization that reduces the phenomenology relevant parameters to merely three and enhances the detection prospect at the collider experiments. We have explored the parameter space consistent with current CLFV bounds, the observed DM relic density, and the absolute neutrino mass limit. To search for these scenarios, we have identified two promising signals at the proposed lepton colliders: the mono-photon plus missing energy and di-lepton plus missing energy signals. We have studied the collider phenomenology of these signatures and estimated the 5σ detection required luminosity for the center of mass energies at 500 GeV and 1 TeV.

Radiative neutrino mass with electroweak scale Majorana dark matter in the Scotogenic model

Search for light (within the mass range 84–200 GeV) doubly charged Higgs bosons decaying into a pair of <math><mi>W</mi></math> bosons has been deemed challenging using the conventional LHC searches with leptons, jets, and missing transverse momentum in the final state. Such Higgses, together with slightly heavier singly-charged and neutral Higgses, when arranged in an <math><mi>S</mi><mi>U</mi><mo>(</mo><mn>2</mn><msub><mo>)</mo><mi>L</mi></msub></math> triplet as in the type-II seesaw model, have been recently shown to accommodate the recent measurement of the <math><mi>W</mi></math>-boson mass by the CDF Collaboration. When produced in a highly Lorentz-boosted regime, these tend to manifest as a single fat jet or a pair of adjacent same-sign leptons plus missing transverse momentum. First, we perform a multivariate analysis to discern such exotic jets from the standard model jets. Then, we present a novel search in the final state with an exotic jet and two same-sign leptons plus missing transverse momentum. We find that such low-mass doubly charged Higgses could be directly probed with the already collected Run 2 LHC data.

Saiyad Ashanujjaman

Low-mass doubly charged Higgs bosons at the LHC

We study the phenomenology of a particular leptoquark extension of the Standard Model (SM), namely the doublet-singlet scalar leptoquark extension of the SM (DSL-SM). Besides generating Majorana mass for neutrinos, these leptoquarks contribute to muon and electron (<math><mrow><mi>g</mi><mo>−</mo><mn>2</mn></mrow></math>) and various lepton flavor violating processes. Collider signatures of the benchmark points (BPs), consistent with the neutrino oscillation data, anomalous muon/electron magnetic moments, experimental bounds on the charged lepton flavor violation observables, etc., are studied at the LHC/FCC with center-of-mass energies of 14, 27 and 100 TeV. While the two <math><mo>−</mo><mn>1</mn><mo>/</mo><mn>3</mn></math> charged colored scalars from the singlet and the doublet leptoquark mix with each other, the charge <math><mn>2</mn><mo>/</mo><mn>3</mn></math> colored scalar from the doublet leptoquark remains pure. With a near-degenerate mass spectrum, the pure and mixed leptoquark states are shown to be distinguishable from multiple final states, while discerning between the two mixed states remains very challenging.

Snehashis Parashar

Spain

Anirban Karan

Priyotosh Bandyopadhyay

Phenomenology of scalar leptoquarks at the LHC in explaining the radiative neutrino masses, muon <math><mi>g</mi><mo>−</mo><mn>2</mn></math>, and lepton flavor violating observables