arXiv subjects

Kirtiman Ghosh

Publications and source records attributed to Kirtiman Ghosh.

At least 19 recordsLinked to original sources

arXiv2026

Light Leptoquarks in a Dark Sector: Scalar Dark Matter, Neutrino Mass, and Collider Signatures

We investigate the dark matter (DM) phenomenology and subsequent collider signatures of a dark leptoquark (LQ) model containing dark vector-like quarks (VLQs) and a scalar singlet. The dark LQs and VLQs participate in the radiative generation of Majorana neutrino masses at one loop. Since the coloured LQs and VLQs cannot serve as viable DM candidates, a $\mathbb{Z}_2$-odd singlet scalar is introduced as the DM candidate. The $\mathbb{Z}_2$-odd nature of the LQs forbids their conventional decays into a quark and a lepton, allowing them to evade the standard LHC constraints that apply to visible LQ signatures. This framework therefore offers the distinctive possibility of sub-TeV dark LQs coexisting with TeV-scale dark VLQs. These sub-TeV dark LQs help in achieving the observed relic abundance of the singlet through co-annihilation. We analyse the resulting DM phenomenology and assess the prospects for probing this scenario at a future muon collider.

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arXiv2026

Revised exclusion limits on doubly charged Higgs bosons from a reanalysis of the ATLAS multi-lepton search at $\sqrt{s} = 13$,TeV

The ATLAS search for pair-produced doubly charged Higgs bosons in multi-lepton final states using the full Run 2 dataset [Eur. Phys. J. C 83 (2023) 605] reports the strongest limits to date on the mass of doubly charged scalars, driven by an essentially background-free four-lepton channel. We show that the four-lepton signal efficiency implied by the auxiliary cutflow of that analysis exceeds a strict, mass-independent upper bound derived from the equal-branching-ratio assumption of the search, the leptonic $τ$ branching fractions, and the ATLAS lepton reconstruction efficiencies. We show that this excess cannot be explained by hadronic $τ$ or jet misidentification without invoking fake rates far above realistic values. We regenerate the signal independently and recompute the exclusion limit, using the corrected signal yields, the ATLAS background predictions and uncertainties, and the same $CL_s$ procedure implemented in pyhf. The resulting expected limit lies systematically above the ATLAS expected limit, by roughly a factor of two or more. This shifts the expected lower mass bound from $1065$ GeV to $\sim950$ GeV in the left-right symmetric type-II seesaw model, and from $880$ GeV to $\sim770$ GeV in the Zee--Babu model.

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arXiv2026

Resurrecting Kaluza-Klein Dark Matter with Low-Temperature Reheating

In Universal Extra Dimension (UED) scenarios, the lightest Kaluza-Klein (KK) particle is naturally stable due to a remnant discrete symmetry, KK parity, arising from extra-dimensional compactification. This stability requires no ad hoc symmetry and renders Kaluza-Klein dark matter a well-motivated candidate, provided it reproduces the observed relic abundance. The minimal UED (mUED) framework being highly predictive is strongly constrained by the combined requirements of relic density and collider searches under standard cosmological assumptions. We revisit the dark matter phenomenology of mUED in the presence of a nonstandard cosmological history featuring a low reheating temperature driven by prolonged inflaton decay. Solving the coupled Boltzmann equations for dark matter, radiation, and inflaton energy densities, we show that entropy injection during reheating can dilute the relic abundance by orders of magnitude, reopening large regions of parameter space previously ruled out. We further demonstrate that the revived parameter space is consistent with current collider, direct-detection, and indirect-detection constraints, while remaining testable by upcoming experiments.

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arXiv2025

Reinterpretation and preservation of data and analyses in HEP

Data from particle physics experiments are unique and are often the result of a very large investment of resources. Given the potential scientific impact of these data, which goes far beyond the immediate priorities of the experimental collaborations that obtain them, it is imperative that the collaborations and the wider particle physics community publish and preserve sufficient information to ensure that this impact can be realised, now and into the future. The information to be published and preserved includes the algorithms, statistical information, simulations and the recorded data. This publication and preservation requires significant resources, and should be a strategic priority with commensurate planning and resource allocation from the earliest stages of future facilities and experiments.

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arXiv2025

Multipartite dark matter in a gauge theory of leptons

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 $Z_2$ symmetry remains, which ensures the stability of the light $Z_2$ 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 constrain the parameter space from the indirect dark matter detection experiments like FermiLAT and CTA.

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arXiv2025

Advancing Higgsino Searches by Integrating ML for Boosted Object Tagging and Event Selection

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 W/Z/h 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.

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arXiv2025

A Comprehensive Search for Leptoquarks Decaying into Top-$τ$ Final States at the Future LHC

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.

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arXiv2024

Probing sub-TeV Higgsinos aided by a ML-based top tagger in the context of Trilinear RPV SUSY

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 R-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 BDT classifier to discriminate signal over SM backgrounds. We construct two signal regions characterized by at least one top jet and different multiplicities of $b$-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 high luminosity LHC.

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arXiv2024

Revisiting Universal Extra-Dimension Model with Gravity Mediated Decays

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.

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arXiv2024

Revisiting the LHC Constraints on Gauge-Mediated Supersymmetry Breaking Scenarios

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 mono-photon 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.

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arXiv2024

Unveiling the Secrets of New Physics Through Top Quark Tagging

The ubiquity of top-rich final states in the context of beyond the Standard Model (BSM) searches has led to their status as extensively studied signatures at the LHC. Over the past decade, numerous endeavours have been undertaken in the literature to develop methods for efficiently distinguishing boosted top quark jets from QCD jets. Although cut-based strategies for boosted top tagging, which rely on substructure information from fat jets resulting from the hadronic decay of boosted top quarks, were introduced in the literature as early as 2008, recent years have witnessed a surge in the utilization of machine learning-based approaches for the classification of top-jets from QCD jets. The review focuses on the present status of boosted top tagging and its application for BSM searchers.

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arXiv2024

Singlet-Doublet Fermionic Dark Matter in Gauge Theory of Baryons

We are considering a minimal $U(1)_B$ 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 $S$ spontaneously breaks the $U(1)_B$ symmetry, leaving behind a discrete $Z_2$ symmetry that ensures the stability of the lightest exotic fermion was 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 singlet-doublet mixing. We show that the model offers a viable parameter space for a cosmologically consistent DM candidate that can be probed through direct and indirect searches, collider experiments, and gravitational wave (GW) experiments.

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arXiv2023

ML-Based Top Taggers: Performance, Uncertainty and Impact of Tower & Tracker Data Integration

Machine learning algorithms have the capacity to discern intricate features directly from raw data. We demonstrated the performance of top taggers built upon three machine learning architectures: a BDT that uses jet-level variables (high-level features, HLF) as input, while a CNN trained on the jet image, and a GNN trained on the particle cloud representation of a jet utilizing the 4-momentum (low-level features, LLF) of the jet constituents as input. We found significant performance enhancement for all three classes of classifiers when trained on combined data from calorimeter towers and tracker detectors. The high resolution of the tracking data not only improved the classifier performance in the high transverse momentum region, but the information about the distribution and composition of charged and neutral constituents of the fat jets and subjets helped identify the quark/gluon origin of sub-jets and hence enhances top tagging efficiency. The LLF-based classifiers, such as CNN and GNN, exhibit significantly better performance when compared to HLF-based classifiers like BDT, especially in the high transverse momentum region. Nevertheless, the LLF-based classifiers trained on constituents' 4-momentum data exhibit substantial dependency on the jet modeling within Monte Carlo generators. The composite classifiers, formed by stacking a BDT on top of a GNN/CNN, not only enhance the performance of LLF-based classifiers but also mitigate the uncertainties stemming from the showering and hadronization model of the event generator. We have conducted a comprehensive study on the influence of the fat jet's reconstruction and labeling procedure on the efficiency of the classifiers. We have shown the variation of the classifier's performance with the transverse momentum of the fat jet.

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arXiv2023

Radiative Neutrino Mass with Electroweak Scale Majorana Dark Matter in Scotogenic Model

Non-zero neutrino mass and dark matter cast a shadow over the success of the Standard Model (SM) of Particle Physics. The most straightforward extension of the SM to explain these two phenomena is the Scotogenic model, where the SM particle spectrum extends with three isospin singlet right-handed neutrinos and one doublet scalar while all of these being odd under $Z_2$ symmetry. In this work, we have considered the lightest right-handed neutrino as the dark matter candidate and freeze-out mechanism for producing observed dark matter relic density. The observed dark matter relic density, neutrino oscillation data and limits on the charged lepton flavor violation processes impose severe constraints on the model. After satisfying all the constraints, we study the collider signatures of the model at the proposed lepton collider experiments.

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arXiv2023

Phenomenology of Scalar Leptoquarks at the LHC in Explaining the Radiative Neutrino Mass, Muon $g-2$ and Lepton Flavour Violating Observables

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 $(g-2)$ and various lepton flavour 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 flavour violation observables, etc., are studied at the LHC/FCC with centre-of-mass energies of 14, 27 and 100 TeV. While the two $-1/3$ charged colored scalars from singlet and doublet leptoquark mix with each other, the charge $2/3$ 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 finalstates, while discerning between the two mixed states remain very challenging.

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arXiv2022

Low-mass doubly-charged Higgs bosons at LHC

Search for light (within the mass range 84-200 GeV) doubly-charged Higgs bosons decaying into a pair of W-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 $SU(2)_L$ triplet as in the type-II see-saw model, are lately shown to accommodate the recent measurement of the $W$-boson mass by the CDF collaboration. These, when produced in a highly Lorentz-boosted regime, tend to manifest themselves 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 SM 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 Higgsses could be directly probed with the already collected Run 2 LHC data.

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arXiv2022

Type-II see-saw: searching the LHC elusive low-mass triplet-like Higgses at $e^-e^+$ colliders

While the triplet-like Higgses up to a few hundred GeV masses are already excluded for a vast region of the model parameter space from the LHC searches, strikingly, there is a region of this parameter space that is beyond the reach of the existing LHC searches, and doubly/singly-charged and neutral Higgses as light as 200 GeV or even lighter are still allowed by the LHC data. We study several search strategies targeting different parts of this LHC elusive parameter space at two configurations of $e^-e^+$ colliders -- 500 GeV and 1 TeV centre of mass energies. We find that a vast region of this parameter space could be probed with 5$σ$ discovery with the early $e^-e^+$ colliders' data.

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arXiv2022

Search for exotic leptons in final states with two or three leptons and fat-jets at 13 TeV LHC

Exotic leptons in large gauge multiplets, appearing in many scenarios beyond the Standard Model (SM), can be produced at the LHC in pairs or association. Owing to their large masses, their eventual decay products -- SM leptons and bosons -- tend to be highly boosted, with the jets stemming from the SM bosons more likely to manifest themselves as a single fat-jet rather than two resolved ones. With the corresponding SM backgrounds being suppressed, final states with two or three leptons and one or two fat-jets are expected to be sensitive in probing exotic fermions much heavier than 1 TeV, and we propose and investigate an appropriate search strategy. To concentrate on the essential, we consider extensions of the SM by leptonic multiplets of a single kind (triplets, quadruplets or quintuplets), bearing in mind that such simplified models typically arise as low-energy limits of more ambitious scenarios addressing various lacunae of the SM. Performing a systematic and comprehensive study of nine such scenarios at the 13 TeV LHC, we find that the corresponding $5σ$ discovery reaches a range from 985 GeV to 1650 GeV (1345 GeV to 2020 GeV) for 300 (3000) fb$^{-1}$.

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