arXiv subjects

Nivedita Ghosh

Publications and source records attributed to Nivedita Ghosh.

At least 19 recordsLinked to original sources

arXiv2026

Chasing Long-Lived Doubly Charged Scalars at Future Lepton Colliders

We come up with a novel search strategy for long-lived doubly charged scalars at future proposed lepton colliders. The doubly charged scalar studied in this work belongs to an $SU(2)_L$ complex scalar triplet that accounts for tiny neutrino masses via the Type-II Seesaw mechanism. For scalar masses $\lesssim 200 $ GeV and appropriate values of the triplet vacuum expectation value, this state can be long-lived and decay predominantly into like-sign muon pairs (e.g. $μ^+μ^+ $ or $μ^-μ^-$), producing distinctive displaced-vertex signals. We investigate the pair production of these scalars at the International Linear Collider (ILC) and a prospective muon collider, considering their planned center-of-mass energies. Incorporating theoretical and experimental constraints, we study the resulting signature of four leptons accompanied by missing transverse energy. Displaced vertices offer direct evidence of the scalar's long lifetime, while we further show that the invariant mass distribution of same-sign dilepton pairs serves as a powerful complementary probe for discovering doubly charged Higgs bosons at both the ILC and muon collider.

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arXiv2026

Proposal for a shared transverse LLP detector for FCC-ee and FCC-hh and a forward LLP detector for FCC-hh

As the particle physics community has explored most of the conventional avenues for new physics, the more elusive areas are becoming increasingly appealing. One such potential region, where new physics might be hiding, involves light and weakly interacting long-lived particles (LLPs). To probe deeper into this region, where the possibility of highly displaced scenarios weakens the role of general-purpose collider detectors, dedicated LLP detectors are our best option. However, their potential can only be fully realized if we optimize their position and dimensions to suit our physics goals. This is possible at the upcoming Future Circular Collider (FCC) facility, where the feasibility and design studies are still ongoing and can accommodate new proposals focused specifically on LLP searches. We propose optimized dedicated detectors in both the transverse and forward directions, DELIGHT and FOREHUNT, significantly enhancing the sensitivity to previously uncharted regions of the new physics parameter space. Our proposed DELIGHT detector can additionally serve as a shared transverse detector during both the FCC-ee and FCC-hh runs. The concept of a shared transverse detector is novel and sustainable, utilizing the same interaction points of the lepton and hadron colliders at the FCC. This minimizes costs and boosts the LLP physics case at the FCC.

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arXiv2026

Long-lived Light Mediators in a Higgs Portal Model at the FCC-ee

In the search for beyond the Standard Model (SM) physics, long-lived particles (LLPs) have emerged as potential candidates and are being explored in various ongoing experiments. Future lepton colliders, such as the FCC-ee, shall provide an excellent opportunity to probe LLPs, owing to their clean environment and improved particle identification. This study investigates the potential of the proposed \textbf{I}nnovative \textbf{D}etector for an \textbf{E}lectron-Positron \textbf{A}ccelerator (IDEA) detector at FCC-ee in the detection of LLPs produced from $B$-meson and Higgs boson decays. We explore benchmark scenarios for different final states resulting from LLP decays, including a detailed analysis of the SM long-lived hadronic background. Additionally, we propose dedicated LLP detectors with different configurations, dimensions, and locations with respect to the IDEA detector. DELIGHT B, originally proposed as a dedicated LLP detector for the FCC-hh, stands out as the detector with the maximum efficiency for detecting LLPs produced at FCC-ee. We find that cylindrical detector configurations, if feasible to construct around the IDEA detector, would also enhance sensitivity for LLPs mostly decaying outside it.

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arXiv2026

Investigating the leptonic couplings of doubly charged scalars at the muon collider

We study the lepton flavour conserving and violating couplings of a doubly charged scalar at a 3 TeV muon collider. Using a model independent Lagrangian, we analyse the electron electron, muon muon, and tau tau final states mediated by the doubly charged scalar to probe individual couplings to mu e, mu mu, and mu tau. We find that for a doubly charged scalar of mass greater than 1 TeV and order one couplings, we achieve high signal significance in these channels. We delineate the collider s sensitivity in the mass vs coupling plane, highlighting the extensive reach of the muon collider in probing these couplings far beyond the current experimental limits. We also propose an angular distribution variable to discriminate the exchange of a doubly charged scalar from that of a neutral scalar, which give identical signals.

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arXiv2025

Unveiling the CP-odd Higgs in a Generalized 2HDM at a Muon Collider

We revisit the generalized two-Higgs-doublet model (2HDM) with a minimally perturbed lepton specific (Type-X) Yukawa sector in context of the muon collider. The model offers a large region of parameter space where it can provide a solution to the observed muon ($g-2$) excess. Specifically the low mass CP odd scalar of this model plays an important role to fit this anomaly. Interestingly, the coupling of the pseudo scalar with the muons is proportional to $\tan β$ (the ratio of VEVs of the Higgs doublets) which dominantly controls the one loop and two loop contributions of the muon magnetic moment, therefore it can be probed directly at a muon collider with greater sensitivity in comparison to Large Hadron Collider (LHC). Primarily focusing on a parameter space where muon $g-2$ anomaly is satisfied, we explore the available theoretical and experimental constraints arising from vacuum stability, unitarity, lepton falvour violation (LFV), electroweak precision constraint, B-meson decay and collider experiments on the model. In the parameter space where all these constraints are satisfied, we propose to study the production of the light pseudo-scalar $A$ in association with a photon at a $3$ TeV muon collider. Subsequent decay of $A$ into a $τ$ pair will produce a striking $l^+ l^- γ$ plus missing energy signature.

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arXiv2024

Light long-lived particles at the FCC-hh with the proposal for a dedicated forward detector FOREHUNT and a transverse detector DELIGHT

In this paper, we propose a dedicated forward detector, FOREHUNT (FORward~Experiment~for~HUNdred~TeV), for 100 TeV FCC-hh for the detection of light long-lived particles (LLP) coming from $B$-meson decay. We calculate the signal acceptance as a function of mass and proper decay length of the LLP for 100 TeV and interpret our result in terms of model parameters for models of dark Higgs scalar and heavy neutral leptons. We also compare the sensitivity with proposed transverse detectors like MATHUSLA, CODEX-b for HL-LHC, and DELIGHT (Detector for long-lived particles at high energy of 100 TeV) for FCC-hh. Our analysis reveals that if the LLP is light ($\lesssim 4.4$ GeV) and has a low proper decay length ($<10$ m), a forward detector like FOREHUNT is the best option to look for the decaying LLP, while DELIGHT is preferable for higher proper decay lengths.

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arXiv2024

Search For a Leptoquark and Vector-like Lepton in a Muon Collider

The proposal for a high-energy muon collider offers many opportunities in the search for physics beyond the Standard Model (BSM). The collider by construction is likely to be more sensitive to the muon-philic models, primarily motivated by the BSM explanation of muon $(g-2)$ excess and quark flavor anomalies. In this work, we explore the potential of the proposed muon collider in the context of such models and focus on one such model that extends the Standard Model (SM) with a leptoquark, a vector-like lepton, and a real scalar. In this model, we propose searches for TeV scale leptoquarks in $2μ+2b+mET$ channel. Notably, the leptoquark can be produced singly at the muon collider with a large cross-section. We have shown that a significant signal in this channel can be detected at a 3~TeV muon collider even with an integrated luminosity as low as $\sim 10$~fb$^{-1}$

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arXiv2023

New physics implications of VBF searches exemplified through the Georgi-Machacek model

LHC searches for nonstandard scalars in vector boson fusion (VBF) production processes can be particularly efficient in probing scalars belonging to triplet or higher multiplet representations of the Standard Model $SU(2)_L$ gauge group. They can be especially relevant for models where the additional scalars do not have any tree-level couplings to the Standard Model fermions, rendering VBF as their primary production mode at the LHC. In this work, we employ the latest LHC data from VBF resonance searches to constrain the properties of nonstandard scalars, taking the Georgi-Machacek model as a prototypical example. We take into account the theoretical constraints on the potential from unitarity and boundedness-from-below as well as indirect constraints coming from the signal strength measurements of the 125 GeV Higgs boson at the LHC. To facilitate the phenomenological analysis we advocate a convenient reparametrization of the trilinear couplings in the scalar potential. We derive simple correlations among the model parameters corresponding to the decoupling limit of the model. We explicitly demonstrate how a combination of theoretical and phenomenological constraints can push the GM model towards the decoupling limit. Our analysis suggests that the VBF searches can provide key insights into the composition of the electroweak vacuum expectation value.

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arXiv2023

Collider Signatures of a Scalar Leptoquark and Vector-like Lepton in Light of Muon Anomaly

Despite the immense success of the Standard Model, the hunt for physics beyond the Standard Model has continued. Extension of the SM gauge group or the particle content of the SM remains a viable solution to many observed anomalies, such as the anomalous magnetic moment of muon, flavor violation, dark matter, etc. In this work, we consider a BSM model which includes a leptoquark, a vector-like lepton, and a real scalar singlet. The model accounts for a dark matter candidate through a $\mathbb{Z}_2$ symmetry in addition to predicting the muon $(g-2)$ in agreement with the experimental measurement. We also show that the experimental measurements of the lepton flavor violation are satisfied in a wide range of parameter space. The viable parameter space of the model is used to study the collider signatures arising from the pair production of the leptoquark in the $2μ+2b+MET$ channel at the 14 TeV LHC run.

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arXiv2022

Signals for vector-like leptons in an $S_3$-symmetric 2HDM at ILC

In this work, we explore the signals of an $S_3$-symmetric two Higgs doublet model with two generations of vector-like leptons (VLLs) at the proposed International Linear Collider (ILC). The lightest neutral component of the VLL in this model provides a viable dark matter (DM) candidate satisfying the current relic density data as well as circumventing all direct and indirect DM search constraints. Some representative benchmark points have been selected with low, medium and high DM masses, satisfying all theoretical and experimental constraints of the model and constraints coming from the DM sector. The VLLs (both neutral and charged) will be produced in pair leading to multi-lepton and multi-jet final states. We show that the ILC will prove to be a much more efficient and useful machine to hunt for such signals compared to LHC. Using traditional cut-based analysis as well as sophisticated multivariate analysis, we perform a detailed analysis of some promising channels containing mono-lepton plus di-jet, di-lepton, four-lepton and four jets along with missing transverse energy in the final state at 1 TeV ILC.

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arXiv2021

Generalized 2HDM with wrong-sign lepton Yukawa coupling, in light of $g_μ-2$ and lepton flavor violation at the future LHC

To explain the observed muon anomaly and simultaneously evade bounds from lepton flavor violation in the same model parameter space is a long cherished dream. In view of a generalized Two Higgs Doublet Model, with a Yukawa structure as a perturbation of Type-X, we are able to get substantial parameter space satisfying this criteria. We are focusing on a region with "{\bf wrong-sign}" lepton-Yukawa coupling which gives rise to an interesting phenomenological consequences. We found that in the "wrong-sign" region, it is possible to probe the low-mass pseudoscalar in flavor-violating decay mode with considerably better significance compared to the "right-sign" region. Performing a simple cut-based analysis we show that at 14 TeV run of the LHC with $300 fb^{-1}$ integrated luminosity, part of the model parameter space can be probed with significance $\geq 5σ$ which further improves with Artificial Neural Network analysis.

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arXiv2021

Dark Matter and Collider Searches in $S_3$-Symmetric 2HDM with Vector Like Leptons

We study the $S_3$-symmetric two Higgs doublet model by adding two generations of vector like leptons (VLL) which are odd under a discrete $Z_2$ symmetry. The lightest neutral component of the VLL acts as a dark matter (DM) whereas the full VLL set belongs to a dark sector with no mixings allowed with the standard model fermions. We analyse the model in light of dark matter and collider searches. We show that the DM is compatible with the current relic density data as well as satisfying all direct and indirect dark matter search constraints. We choose some representative points in the model parameter space allowed by all aforementioned dark matter constraints and present a detailed collider analysis of multi-lepton signal viz. the mono-lepton, di-lepton, tri-lepton and four-lepton along with missing transverse energy in the final state using both the cut-based analysis and multivariate analysis respectively at the high luminosity 14 TeV LHC run.

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arXiv2021

Revisiting Generalized Two Higgs Doublet Model in the Light of Muon Anomaly and Lepton Flavor Violating Decays at HL-LHC

One of the main motivations to look beyond the SM is the discrepancy between the theoretical prediction and observation of anomalous magnetic moment of muon. Alleviating this tension between theory and experiment and satisfying the bounds from lepton flavor violation data simultaneously is a challenging task. In this paper, we consider generalised Two Higgs Doublet Model, with a Yukawa structure as a perturbation of Type X Two Higgs Doublet Model. In view of this model, we explore muon anomaly and lepton flavor violation along with constraints coming from B-physics, theoretical constraints, electroweak observables and collider data which can restrict the model parameter space significantly. We find that within the framework of this model it is possible to obtain regions allowed by all constraints, that can provide an explanation for the observed muon anomaly and at the same time predicts interesting signatures of lepton flavor violation. Furthermore, we consider the flavor violating decay of low-mass CP-odd scalar to probe the allowed parameter space at future runs of the LHC. With simple cut-based analysis we show that part of that parameter space can be probed with significance $> 5 σ$. We also provide Artificial Neural Network analysis which definitely improves our cut-based results significantly.

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arXiv2020

Associated $Z^\prime$ production in the flavorful $U(1)$ scenario for $R_{K^{(*)}}$

The flavorful $Z^\prime$ model with its couplings restricted to the left-handed second generation leptons and third generation quarks can potentially resolve the observed anomalies in $R_K$ and $R_{K^*}$. After examining the current limits on this model from various low-energy processes, we probe this scenario at 14 TeV high-luminosity run of the LHC using two complementary channels: one governed by the coupling of $Z'$ to $b$-quarks and the other to muons. We also discuss the implications of the latest LHC high mass resonance searches in the dimuon channel on the model parameter space of our interest.

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arXiv2020

Collider signature of $U_1$ Leptoquark and constraints from $b\to c$ observables

One of the most popular models that is known to be able to solve the lepton flavour universality violating charged ($b\to c$) and neutral current ($b\to s$) anomalies is the Leptoquark Model. In this work we examine the {\it multijet} + $\mET$ collider signature of a vector leptoquark ($U_1$) which has the potential to mediate both the charged and neutral current processes at tree level. From our collider analysis we derive the exclusion limits on mass for the $U_1$ leptoquark at 95\% C.L. at the current and future experiment of the Large Hadron Collider. We also calculate the effect of such a leptoquark in $b\to c$ observables.

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arXiv2020

Charged Higgs searches in the Georgi-Machacek model at the LHC

The Georgi-Machacek Model allows for a large triplet vacuum expectation value (vev) with a custodial symmetric scalar potential. This manifestly leads to large charged Higgs coupling to SM fermions thus enhancing the detection probability of the model at the Large hadron collider. We show that the latest bound from LHC searches on singly charged Higgs scalar decaying to top and bottom quark restricts the triplet vev from above. We demonstrate that the combined limit from theoretical constraints and the latest Higgs data together with this charged Higgs bound can already curb the model parameter space significantly. Further, we propose the charged Higgs decaying to $W^{\pm}$ boson and a SM-like Higgs as a prospective channel to probe the yet unbounded model parameter space at the future run of the LHC. A simple cut-based analysis for this channel has been made showing the parameter region that can be probed with $5σ$ significance at the high luminosity LHC run.

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arXiv2019

Distinctive Collider Signals for a Two Higgs Triplet Model

The extension of the Standard Model (SM) with two complex $SU(2)_{L}$ scalar triplets enables one to have the Type II seesaw mechanism operative consistently with texture-zero neutrino mass matrices. This framework predicts additional doubly charged, singly charged and neutral spinless states. We show that, for certain values of the model parameters, there is sufficient mass splitting between the two doubly charged states ( $H_1^{\pm\pm}, H_2^{\pm\pm}$) that allows the decay $H_1^{\pm\pm} \to H_2^{\pm\pm} h $, and thus leads to a unique signature of this scenario. We show that the final state $2(\ell^{\pm} \ell^{\pm}) + 4b + \mET~$ arising from this mode can be observed at the high energy, high luminosity (HE-HL) run of the 14 TeV Large Hadron Collider (LHC), and also at a 100 TeV Future Circular Collider (FCC-hh).

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arXiv2018

Revisiting the high-scale validity of Type-II seesaw model with novel LHC signature

The Type-II seesaw model is a well-motivated new physics scenario to address the origin of the neutrino mass issue. We show that this model can easily accommodate an absolutely stable vacuum until the Planck scale, however with strong limit on the exotic scalar masses and the corresponding mixing angle. We examine the model prediction at the current and future high luminosity run of the Large Hadron Collider (LHC) for the scalar masses and mixing angles fixed at such high-scale valid region. Specifically, we device the associated and pair production of the charged scalars as a new probe of the model at the LHC. We show that for a particular signal process the model can be tested with $5σ$ signal significance even at the present run of the LHC.

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