arXiv subjects

Agnivo Sarkar

Publications and source records attributed to Agnivo Sarkar.

17 recordsLinked to original sources

arXiv2026

Explaining 650 GeV and 95 GeV Anomalies in the 2-Higgs Doublet Model Type-I

We propose an interpretation of a rather significant 650 GeV excess emerged at the Large Hadron Collider (LHC) from CMS Collaboration data in the $γγb\bar b$ final state, accompanied by further clusters at 125(90-100) GeV in the $γγ(b\bar b)$ system, within the 2-Higgs Doublet Model Type-I (2HDM-I) in presence of a softly broken $\mathcal{Z}_{2}$ symmetry. The underlying process that we probe is $gg$-initiated production of a CP-odd (or pseudoscalar) Higgs boson $A$, with mass around 650 GeV, decaying into the Standard Model (SM)-like Higgs state $H$ (decaying into $γγ$) and a $Z$ boson (decaying into $b\bar b$). We configure this theoretical framework so as to also have in the spectrum a light CP-even (or scalar) Higgs state $h$ with mass around 95 GeV, which is included for the purpose of simultaneously explaining additional data anomalies seen in the $b\bar b$, $γγ$ and $τ^+τ^-$ final states while searching for light Higgs states at the Large Electron-Positron (LEP) collider (the first one) and LHC (the last two). By accounting for both experimental and theoretical constraints, our results show that the 2HDM-I can explain all aforementioned anomalies at a significance level of $2.5 σ$.

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arXiv2026

Optimizing The Cut And Count Method In Phenomenological Studies

We introduce an optimization technique to discriminate signal and background in any phenomeno- logical study based on the cut and count-based method. The core ideas behind this technique are the introduction of a ranking scheme that can quantitatively assess the relative importance of var- ious observables involved in a new physics process, and a more methodical way of choosing what cuts to impose. The technique is an iterative process that works with the help of the MadAnalysis5 interface. Working in the context of a BSM (Beyond Standard Model) scenario where we carry out a signal search of singly charged Higgs in the context of the Two Higgs Doublet Model (2HDM), we demonstrate how automating the cut and count process in this specific way results in an enhanced discovery potential compared with the more traditional way of imposing cuts.

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arXiv2026

Probing compressed triplet scalars with ISR jets and soft leptons at the LHC

The Type-II seesaw model predicts doubly and singly charged scalars along with neutral Higgs states originating from an $SU(2)$ triplet. Current LHC searches by the ATLAS and CMS collaborations constrain these particles mainly under the assumption that the doubly charged scalar decays dominantly into same-sign dileptons or dibosons. However, when moderate mass splittings exist among the triplet scalars, cascade decays can dominate, suppressing these conventional search channels and leaving sizeable regions of parameter space weakly constrained. We study this compressed region characterized by $1~\text{GeV} \lesssim ΔM \lesssim 30~\text{GeV}$ and triplet vev $v_t \sim 10^{-7} - 10^{-3}$ GeV. In this scenario, charged scalars predominantly undergo cascade decays, while neutral scalars decay invisibly into neutrinos, leading to final states with soft leptons and missing transverse energy. We propose a dedicated search strategy at the 14 TeV LHC exploiting a hard initial-state radiation jet to boost the scalar system. Using a cut-and-count analysis, we show that discovery-level sensitivity can be achieved in this previously unexplored region with an integrated luminosity of $3000~\mathrm{fb}^{-1}$. Our results signify the importance of dedicated searches targeting cascade-dominated and compressed mass spectrum for beyond the standard model scenarios with an $SU(2)$ multiplet.

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arXiv2026

Soft Symmetry Breaking as a Nonstandard Source of Mass: Phenomenological Insights from the Two-Higgs-Doublet Model

The soft-breaking parameter, $m_{12}^2$, frequently appearing in the 2HDM scalar potential is much more remarkable than being just a nonstandard parameter that helps make the BSM scalars super heavy. In fact, as we show through explicit calculations, it should be treated as the direct but concise embodiment of new non-electroweak spontaneous symmetry breaking effects at very high energy scales, wherein lies its quiddities. Consequently, it is argued that $m_{12}^2$ and the electroweak VEV serve as two distinct sources for the nonstandard scalar masses, which are completely unrelated to each other. Such distinctions allow us to define parameters that conveniently capture the fraction of the nonstandard scalar masses derived from the electroweak VEV. Finally, we demonstrate that constraints can already be placed on such fractions from the current measurements of the diphoton signal strength and from direct searches of new nonstandard scalar resonances in the diphoton channel.

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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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arXiv2026

LHC Signatures of Neutral Scalar Cascades in the $Z_3$ symmetric 3HDM

Extending the scalar sector is one of the standard approaches to exploring scenarios beyond the Standard Model. In this work, we examine the collider phenomenology of the Three Higgs Doublet Model (3HDM) in the Type-Z or the democratic Yukawa interaction setup at the LHC. The scalar spectrum of the 3HDM includes three CP-even scalars, two CP-odd scalars, and four charged Higgs bosons. Focusing on cascade decay topologies, we investigate the collider signatures of the neutral scalars through the process $pp \rightarrow SV$, where $S$ is a neutral scalar and $V$ is a vector boson. We perform a cross-section analysis across multiple benchmark points that satisfy both theoretical and experimental constraints, considering two mass hierarchy scenarios: (i) Regular Hierarchy, where the SM-like Higgs is the lightest CP-even scalar, and (ii) Medial Hierarchy, featuring one Higgs boson lighter than the SM Higgs and one heavier. For both scenarios, we study the specific process $pp \rightarrow A \rightarrow HZ \rightarrow b \bar{b} l^+l^-$, performing a cut and count analysis at $\sqrt{s}=14$ TeV. Our results demonstrate that while the Medial Hierarchy scenario allows discovery-level sensitivity for both the CP-even and CP-odd scalars, achieving the same sensitivity in the Regular Hierarchy setup necessitates substantially higher luminosity.

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arXiv2025

Explaining 95 GeV Anomalies in the 2-Higgs Doublet Model Type-I

We show how the 2-Higgs Doublet Model (2HDM) Type-I can explain some excesses recently seen at the Large Hadron Collider (LHC) in $γγ$ and $τ^+τ^-$ final states in turn matching Large Electron Positron (LEP) data in $b\bar b$ signatures, all anomalies residing around 95 GeV. The explanation to such anomalous data is found in the aforementioned scenario when in inverted mass hierarchy, in two configurations: i) when the lightest CP-even Higgs state is alone capable of reproducing the excesses; ii) when a combination of such a state and the CP-odd Higgs boson is able to do so. To test further this scenario, we present some Benchmark Points (BPs) of it amenable to phenomenological investigation.

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arXiv2025

Constraining the 3HDM Parameter Space using Active Learning

One of the standard ways to study scenarios beyond the Standard Model involves extending the Higgs Sector. This work examines the Three Higgs Doublet Model (3HDM) in a Type-Z or democratic setup, where each Higgs doublet couples exclusively to a specific type of fermion. The particle spectrum of the 3HDM includes four charged Higgs bosons, two CP-odd scalars, and three CP-even scalars. This work investigates the allowed mass and coupling parameter space in the Type-Z 3HDM after imposing all theoretical and experimental constraints. We extract the allowed parameter space under three distinct alignment-limit conditions or mass hierarchies leveraging machine learning techniques. Specifically, we analyze scenarios where the 125 GeV Higgs is the lightest, an intermediary, or the heaviest CP-even Higgs boson. Our findings indicate that while a single lighter CP-even Higgs boson below 125 GeV still remains a possibility, the presence of two lighter Higgses is ruled out.

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arXiv2025

Signals for a 2HDM with $Z'$ at the LHC

We consider a neutrinophilic $U(1)$ extension of the Standard Model (SM) under which only a second Higgs doublet and SM singlet scalars and fermions are charged. The new gauge boson $Z'$ couples to SM minimally, generated by $Z-Z'$ mixing. As the $Z'$ is very weakly coupled, it can mostly be produced through the decay of the scalars from the second Higgs doublet at the Large Hadron Collider (LHC). We discuss the scalar sector of the model in detail and consider decay modes such as $(H^{\pm} \to W^\pm Z', h_2 \to VV, (V = W^\pm, Z, Z'), A_2 \to h_1 Z'(Z))$ that lead to multilepton signals at the LHC from the pair production of the scalars. We analyze the signal with a representative value of the $Z'$ mass to show the discovery potential of the 2HDM scalars at the LHC.

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arXiv2024

Sign of the $hZZ$ coupling and implication for new physics

The magnitudes of the couplings of the scalar resonance at 125 GeV with the SM particles are found to be consistent with those of the SM Higgs boson. However, the signs are not experimentally determined in most of the cases, a prime example being that with the $Z$-boson pair. In other words, $κ_Z^h$, the ratio of the couplings of the actual 125 GeV resonance with $ZZ$ and that of the SM Higgs boson with the same, is consistent with both $+1$ and $-1$, the latter being the `wrong-sign'. We argue that the wrong-sign $hZZ$ coupling will necessitate the intervention of new physics below $\mathcal{O}\left(620\right)$ GeV to safeguard the underlying theory from unitarity violation. The strength of the new nonstandard couplings can be derived from the unitarity sum rules, which are comparable to the SM-Higgs couplings in magnitude. Thus the strong limits from the direct searches at the LHC can help us rule out the existence of such nonstandard particles with unusually large couplings thereby disfavoring the possibility of a wrong-sign $hZZ$ coupling.

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arXiv2024

Multicomponent Scalar Dark Matter with an Extended Gauge Sector

We consider an extension of the Standard Model of particle physics with an additional $SU(2)$ gauge sector along with an additional scalar bidoublet and a non-linear sigma field. The neutral components of the bidoublet serve as dark matter candidates by virtue of the bidoublet being odd under a $Z_2$ symmetry. Generic beyond Standard Model constraints like vacuum stability, invisible decay of higgs, Higgs alignment limit and collider constraints on heavy gauge bosons restrict the parameter space of this model. In this multicomponent dark matter scenario, we investigate the interplay between the annihilation and co-annihilation channels originating from the new gauge sector as those contribute to the relic abundance. We also inspect the direct detection constraints on scattering cross-sections of the dark matter particles with the detector nucleons and present our observations.

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arXiv2022

An Alternate Left-Right Symmetric Model with Dirac Neutrinos

We study a different variant of Left-Right Symmetric Model, incorporating Dirac type neutrinos. In the absence of the bi-doublet scalars, the possibility of a universal seesaw type of mass generation mechanism for all the Standard Model charged fermions have been discussed. The model has been constructed by extending the Standard Model particle spectrum with heavy vector-like fermions as well as different scalar multiplets. We have shown that this model can generate non zero neutrino mass through loop mediated processes. The parameters which are involved in neutrino mass generation mechanism can satisfy the neutrino oscillation data for both normal and inverted hierarchy. The lightest charged Higgs plays a crucial role in neutrino mass generation mechanism and can have mass of $\mathcal{O}[\text{GeV}]$. We have systematically studied different constraints which are relevant for the charged Higgs phenomenology. In addition to that we also briefly discuss discovery prospects of the charged Higgs at different colliders.

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arXiv2022

Re-examining $N_{R}$-EFT Upto Dimension Six

The gauge singlet right-handed neutrinos (RHNs) are essential fields in several neutrino mass models that explain the observed eV scale neutrino mass. We assume RHN field to be present in the vicinity of the electroweak scale and all the other possible beyond the standard model (BSM) fields arise at high energy scale $\geΛ$. In this scenario, the BSM physics can be described using effective field theory (EFT) where the set of canonical degrees of freedoms consists of both RHN and SM fields. EFT of this kind is usually dubbed as $N_{R}$-EFT. We systematically construct relevant operators that can arise at dimension five and six while respecting underlying symmetry. To quantify the phenomenological implication of these EFT operators we calculate different couplings that involve RHN fields. We discuss the constraints on these EFT operators coming from different energy and precision frontier experiments. For $pp$, $e^{-}p$ and $e^{+}e^{-}$ colliders, we identify various channels which crucially depends on these operators. We analytically evaluate the decay widths of RHN considering all relevant operators and highlight the differences that arise because of the EFT framework. Based upon the signal cross-section we propose different multi-lepton channels to search for the RHN at 14 TeV LHC as well as \emph{future} particle colliders.

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arXiv2021

Charged Higgs Prospects In Extended Gauge Models

In this paper, we explore the collider phenomenology of the charged Higgs boson in the context of a generic Beyond Standard Model scenario with extended gauge and scalar sectors. In such scenarios, the charged Higgs boson can decay via the $W^{'}Z/ WZ^{'}$ channels. We formulate a search strategy for the $H^{\pm}$ in the channel $σ(g b \rightarrow H^{\pm}t)\mathcal{BR}(H^{\pm} \rightarrow W' Z)$ considering the interesting cascade decay chain $H^{\pm} \rightarrow W^{'} Z \rightarrow W^{\pm} Z Z$. We find that the charged Higgs can be discovered in final states with multiple hard leptons and/ or b-quarks which future LHC experiments with sufficiently large luminosity ($\mathcal{L} = 1000 fb^{-1}$ and above) can probe.

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arXiv2020

The 2HDM Doppelganger

We discuss the structure of a model with an extended gauge symmetry group $SU(2)\times SU(2)\times U(1)$ with a correspondingly rich Electroweak Symmetry Breaking structure. In spite of the additional scalar degrees of freedom in the model, the presence of the extra gauge group $SU(2)$ and its associated heavy vector bosons ensures that the scalar spectrum of the model after symmetry breaking is identical to that of the Two Higgs Doublet Models. We construct the model and discuss its implications, specifically the phenomenology associated with this class of models in contrast to the 2HDM.

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arXiv2019

Charged Higgs Discovery Prospects

We study the discovery prospects of the charged Higgs boson in the context of multi Higgs models in certain BSM scenarios. We classify models into three categories based on the charged Higgs coupling properties: gaugophobic, fermiophobic, and chromophobic. In each case, we identify viable modes of discovery, and present LHC analysis for discovery. We find that extensions of the Standard Model in which the charged Higgs does not couple to colored particles offer the best possible avenues for discovery.

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arXiv2018

Fermiophobic gauge boson phenomenology in 221 Models

Models with extra gauge symmetry are well-motivated extensions of the Standard Model. In this paper, we study an extended gauge model with a heavy neutral gauge boson $Z'$ which is fermiophobic. Thus, the production of such particles can occur via vector boson fusion, with subsequent decays into $WW$ or $Zh$. We investigate the collider phenomenology of such $Z'$s in the context of both the 14 TeV LHC and the future CLIC. We find that looking at $\ell\ell b b$ final states provides a rich opportunity to discover such new vector bosons where conventional search strategies in the dilepton channel would fail. In particular, we optimize our analysis by putting in kinematic cuts deriving model-independent values of $σ\times$BR needed for a 5$σ$ discovery at the LHC. We then translate this into the parameter space of a specific model for illustration purpose -- our results show that fermiophobic $Z'$s are discoverable in the $\ell\ell b b$ channel for wide range of parameter values.

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