Searcharxiv⌕ Search

arXiv subjects

Biswarup Mukhopadhyaya

Publications and source records attributed to Biswarup Mukhopadhyaya.

At least 19 recordsLinked to original sources
arXiv2026

Prospects of measuring the atmospheric muon neutrino and anti-neutrino flux ratio with the ATLAS detector

There is a significant uncertainty in the prediction of atmospheric muon neutrino and anti-neutrino flux ratio using different flux models, especially at higher energies. We study the prospects of experimentally measuring this flux ratio as a function of energy with the ATLAS detector at the LHC. To this end, we compute the contained-vertex and external upward going charged current event rates induced by atmospheric muon (anti-)neutrinos through deep inelastic scattering at the 4 kiloton hadron calorimeter (HCAL) component of ATLAS. We illustrate the event selection criteria necessary to eliminate the cosmic ray muon background for the above event classes. While the contained vertex events have a striking topology with a muon being created inside the HCAL and then travelling to the muon chamber possibly through the tracker, for muons with energy larger than 3 GeV, nearly 10 times more events are obtained for the external upward going muons created in the rock column below the detector. Our estimates show that the energy dependence of the ratio of negative and positively charged muons induced by atmospheric muon neutrino and anti-neutrino fluxes can be measured by ATLAS upto a muon energy of 100 GeV, with 1000-live days of neutrino physics exposure over a period of several years, considering only the period with the LHC beams not in circulation, but the detector and magnetic fields of ATLAS in operation. With this exposure, we expect to obtain 60 $μ^-$ and 30 $μ^+$ contained vertex events, and $599~μ^-$ and $292~μ^+$ external upward-going events, after imposing the necessary selection criteria. For the latter class of events, this corresponds to an expected ratio of negative to positive charged muon events averaged over all energies, $R_{μ^-/ μ^+}=2.05^{+0.15}_{-0.14}$, at $68\%$ C.L. (Abridged)

hep-ph↗
arXiv2026

LHC signatures of a light pseudoscalar in a flipped two-Higgs scenario: the usefulness of boosted $b{\bar b}$ pairs

Similar to some other two-Higgs doublet models (2HDM), the flipped 2HDM admits of a light pseudoscalar physical state whose mass can be well below 50 GeV. The fact that the pseudoscalar decays dominantly into a $b{\bar b}$ pair makes its identification at the Large Hadron Collider (LHC) difficult. Moreover, the regions of the parameter space corresponding to a light pseudoscalar tend to jeopardize perturbativity at a rather low scale. One possibility that ameliorates this problem is to postulate that the light physical state has the admixture of an SU(2) singlet field. In such a situation, however, the production mode of the pseudoscalar along with a $Z$ (which provides a useful tag) gets suppressed. We have here chosen to fall back on the QCD-driven final state, namely, one or two jets, together with an energetic squeezed $b{\bar b}$-pair. We utilize boosted di-b-jet tagging techniques and a strategy based on boosted decision trees (BDT) to analyze the signals, considering all backgrounds and likely fakes (mostly from charmed quarks). We find that, including 10\% systematics, one can expect signal significance of 5-10$σ$ with an integrated luminosity of 3 $ab^{-1}$.

hep-ph↗
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.

hep-ph↗
arXiv2025

Probing the low mass pseudoscalar in flipped Two Higgs Doublet Model

The phenomenology of the flipped two-Higgs-doublet model (2HDM) is relatively less explored so far, as compared to the other, commonly discussed, types. It is found that this scenario, like several others, admits of a light neutral pseudoscalar $A$ in the mass range 20 - 60 GeV, consistently with all current experimental data and theoretical constraints. However, the fact that such a pseudoscalar decays overwhelmingly into a $b\bar{b}$ pair makes its identification at the Large Hadron Collider (LHC) a challenging task. After identifying the region of the flipped 2HDM parameter space yielding a light pseudoscalar, we identify a useful search channel in the process $pp \rightarrow A Z(Z^{*}) \rightarrow b\bar{b} \ell^+ \ell^-$. A cut-based analysis, followed by one based on Boosted Decision Trees, shows that the light-$A$ scenario in flipped 2HDM should be detectable with rather high statistical significance at the high-luminosity LHC run, even after including systematic uncertainties. Furthermore, part of the parameter space, especially around $m_A = 30 - 40$ GeV is amenable to detection at the discovery level within Run-2 itself.

hep-ph↗
arXiv2025

Diphoton signals for the Georgi-Machacek scenario at the Large Hadron Collider

The diphoton channel for exploring the Georgi-Machacek (GM) scenario containing scalar triplets at the Large Hadron Collider (LHC) has been identified as germane, and subjected to a detailed study. The scalar spectrum of the model, which imposes a custodial SU(2) on the potential, gets classified into a 5-plet, a 3-plet and two singlets under the custodial symmetry. While most attempts to probe or constrain the scenario at the LHC depend largely on signals of charged scalars, we point out that the custodial SU(2) singlet state H can have a substantial branching ratio (amounting to a few percent) into two photons. We carry out a detailed simulation of the resulting signal and the standard model backgrounds, obtaining the signal significance in different regions of the parameter space using the profile likelihood ratio method. Substantial regions of the GM parameter space is thus shown to be accessible to LHC studies, both at the high-luminosity run with $\int {\cal L} dt = 3000 fb^{-1}$, and also in Run-3 with $\int {\cal L} dt = 300 fb^{-1}$, even after folding in systematic errors. We have also demonstrated that a rather subtantial improvement in the signal significance is achieved by switching over from a cut-based analysis to one based on neural network.

hep-ph↗
arXiv2025

Leptogenesis with triplet scalars at electroweak scale

Up until now the works regarding leptogenesis have discussed different mechanisms to explain the observed baryon asymmetry of the universe (BAU). The type-$II$ seesaw mechanism employing triplet scalars has been well studied in this context and the triplet vacuum expectation value (VEV) answering to the observed BAU is $(< 10^{-2} ~ GeV)$. On the contrary we are invoking an extended Georgi-Machacek type scenario, capable of generating BAU through leptogenesis while keeping the triplet VEV at a moderate range where it plays a nontrivial role in electroweak symmetry breaking (EWSB). In this study we have also considered the decaying scalar mass responsible for leptogenesis to be within a TeV and hence one can probe this possibility at the Large Hadron Collider (LHC) itself via different kinds of signature corresponding to different triplet VEV region.

hep-ph↗
arXiv2025

Neutrino Theory in the Precision Era

This document summarises discussions on future directions in theoretical neutrino physics, which are the outcome of a neutrino theory workshop held at CERN in February 2025. The starting point is the realisation that neutrino physics offers unique opportunities to address some of the most fundamental questions in physics. This motivates a vigorous experimental programme which the theory community fully supports. \textbf{A strong effort in theoretical neutrino physics is paramount to optimally take advantage of upcoming neutrino experiments and to explore the synergies with other areas of particle, astroparticle, and nuclear physics, as well as cosmology.} Progress on the theory side has the potential to significantly boost the physics reach of experiments, as well as go well beyond their original scope. Strong collaboration between theory and experiment is essential in the precision era. To foster such collaboration, \textbf{we propose to establish a CERN Neutrino Physics Centre.} Taking inspiration from the highly successful LHC Physics Center at Fermilab, the CERN Neutrino Physics Centre would be the European hub of the neutrino community, covering experimental and theoretical activities.

hep-ph↗
arXiv2024

Improved Treatment of Bosonic Dark Matter Dynamics in Neutron Stars: Consequences and Constraints

It is conceivable that a bosonic dark matter (DM) with non-gravitational interactions with SM particles will be accumulated at the center of a neutron star (NS) and can lead to black hole formation. In contrast to previous works with a fixed NS temperature, we dynamically determine the formation of Bose-Einstein condensate (BEC) for a given set of DM parameters, namely the DM-neutron scattering cross-section ($σ_{χn}$), the thermal average of DM annihilation cross-section ($\langleσv\rangle$) and the DM mass ($m_χ$). For both non-annihilating and annihilating DM with $\langleσv \rangle \lesssim 10^{-26}{~\rm cm^3~ s^{-1}}$, the BEC forms for $m_χ\lesssim 10$ TeV. In case of non-annihilating DM, observations of old NS allows $σ_{χn}\lesssim 10^{-52}~{\rm cm^2}$ for $10 {~\rm MeV} \leq m_χ \lesssim 10 {~\rm GeV}$ (with BEC) and $σ_{χn}\lesssim 10^{-47}~{\rm cm^2}$ for $5 {~\rm TeV} \lesssim m_χ\lesssim 30 {~\rm PeV} $ (without BEC). This analysis shows that the electroweak mass window, $10 {~\rm GeV} \lesssim m_χ\lesssim 5 {~\rm TeV}$ is essentially unconstrained by NS observations and therefore is subject only to direct detection experiments. In the annihilating DM scenario, the exclusion limits on DM parameters become weaker and even vanish for typical WIMP annihilation cross-section. However, the late-time heating of the NS enables us to probe the region with $σ_{χn}\gtrsim 10^{-47}~{\rm cm^2}$, using the James Webb Space Telescope in the foreseeable future. When our results are viewed in the context of indirect searches of DM, it provides a lower limit on the $\langleσv\rangle$, which is sensitive to the DM thermal state.

hep-ph↗
arXiv2024

Can leptophilic-ALP be a solution to the muon $(g-2)$ anomaly?

In the light of recent measurement of muon $(g-2)$, we investigate the phenomenological implications of an axion-like particle (ALP) which only couples to the standard model charged leptons. We find that in a narrow mass range of ALP, it can alleviate the tension between the theoretical prediction and experimental observation of $(g-2)_μ$ once we consider all possible one and two-loop diagrams. In particular, ALP can either explain the muon $(g-2)$ anomaly for $5\,{\rm GeV} \lesssim m_a \lesssim 6 \,{\rm GeV}$ while satisfying the other experimental constraints, or be restricted by it.

hep-ph↗
arXiv2024

Improving probes of $hAA$ coupling in the Type-X two Higgs Doublet Model scenario: the crucial role of $τ$-jet charge identification

The exotic decay modes of the already discovered 125-GeV scalar into a pair of light pseudoscalars is a good probe of those new physics scenarios where such pseudoscalars exist. Searches in the mass region where the pseudoscalar ($A$) is lighter than 62.5 GeV have yielded null findings so far. No search has yet examined $m_A > 62.5$ GeV where the cross section is suppressed by the off-shell pseudoscalar. We point out a possible enhancement of the sensitivity of probing $hAA$ coupling in the context of a Type-X two Higgs doublet model. We focus on $h\to A A^{(*)} \to 4τ$, and select events with two same-sign $τ$-jets along with a pair of same-sign leptons. This enables much more effective background elimination than in the erstwhile proposed channels. Taking two values of the $ττA$ coupling into account, we obtain limits on the $hAA$ coupling that can be probed at 2$σ$ and 3$σ$ significance, for $m_A$ ranging up to 85 GeV. For $m_A < 62.5$ GeV, too, we find the probe through our suggested channel exhibits considerable improvement upon the usual $2μ2τ$-based searches conducted at the LHC. Within this region, achieving the reach of $λ_{hAA}$ coupling at 3000 fb$^{-1}$ luminosity using our strategy would require approximately $\sim$ 3.6$\times 10^{5}$ fb$^{-1}$ luminosity using conventional $2μ2τ$-based searches.

hep-ph↗
arXiv2023

Two-component dark matter : How to get the hint at collider?

We investigate ways of identifying two kinds of dark matter (DM) component particles at high-energy colliders. The strategy is to notice and distinguish double-peaks(humps) in the missing energy/transverse energy distribution. The relative advantage of looking for {\em missing energy} is pointed out, in view of the fact that the longitudinal component of the momentum imbalance becomes an added input. It thus turns out that an electron-positron collider is better suited for discovering a two-component DM scenario. Furthermore, using Gaussian fits of the distribution histograms, we develop a set of criteria to evaluate the distinguishability of the two-peaks quantitatively.

hep-ph↗
arXiv2023

Mono-X signal and two component dark matter: new distinction criteria

The identification and isolation of two WIMP dark matter (DM) components at colliders is of wide interest on the one hand but extremely challenging on the other, especially when the dominant signal of both DM components is of the mono-X type ($X=γ, Z, H$). After emphasizing that an $e^+e^-$ collider is more suitable for this goal, we first identify the theoretical principles that govern the occurrence of two peaks in missing energy (ME) distribution, in a double-DM scenario. We then identify a variable that rather spectacularly elicits the double-peaking behaviour, namely, the plot of bin-wise statistical significance ($S/\sqrt{B}$) against ME. Using Gaussian fits of the histograms, we apply a set of criteria developed by us, to illustrate the above points numerically for suitable benchmarks.

hep-ph↗
arXiv2023

Loop-induced Higgs decays in two Higgs doublet scenarios: some observations

We study the decay of three neutral Higgs bosons into γγ and Zγ in the four major types of two Higgs doublet models with CP conserved. Particular focus is made on the possibility of the width of the latter decay dominating over the former. For the 125-GeV scalar, such a possibility is mostly excluded when one imposes all theoretical and experimental constraints, other than the Higgs data at the Large Hadron Collider. For the other CP-even neutral scalar, there remain regions in each kind of model where the Zγ mode dominates. For the CP-odd state, this possibility is restricted to only the models of Types II and Y, in certain regions of the parameter space.

hep-ph↗
arXiv2023

MeV to multi-TeV thermal WIMPs: most conservative limits

We consider a weakly interacting massive particle (WIMP) dark matter (DM) annihilating into all possible Standard Model (SM) particle pairs, including the SM neutrinos, via $s$-wave processes and derive the branching ratio independent upper limit on the total annihilation cross-section $\langle σv \rangle$ using the data of CMB, gamma-ray, cosmic-ray and several neutrino observations. For conservative choices of all relevant astrophysical parameters, we obtain upper limits of $10^{-23}-10^{-25}\,{\rm cm}^3{\rm s}^{-1}$ on the total $\langle σv \rangle$ for the WIMP mass range $10\,{\rm MeV}-100\,{\rm TeV}$, thus making the entire mass range consistent with the observed relic density. An important input that goes into our analysis is the assumption that thermal WIMPs can have significant coupling to the SM neutrinos.

hep-ph↗
arXiv2023

High scale validity of two Higgs doublet scenarios with a real scalar singlet dark matter

We study the high-scale validity of two kinds of two Higgs doublet models (2HDM), namely, Type-II and Type-X, but with a scalar SU(2) singlet dark matter (DM) candidate in addition in each case. The additional quartic couplings involving the DM particle in the scalar potential in both the scenarios bring in additional constraints from the requirement of perturbative unitarity and vacuum stability. DM relic density and direct search constraints play a crucial role in this analysis as the perturbative unitarity of the DM-Higgs portal couplings primarily decide the high scale validity of the model. We find that, within the parameter regions thus restricted, the Type-II scenario must have a cut-off at around $10^6$ GeV, while the Type-X scenario admits of validity upto the Planck scale. However, only those regions which are valid upto about $10^8$ GeV in Type-X 2HDM is amenable to detection at the High-luminosity LHC (upto 3000 $fb^{-1}$), while most of the parameter space of the Type-II scenario mentioned above is likely to be detectable.

hep-ph↗
arXiv2023

Novel signals for the Type-X two Higgs doublet scenario at the Large Hadron Collider

We consider, in the context of the Large Hadron Collider, the signals of the Type-X two Higgs doublet model (2HDM) in the parameter region answering to the best possible solution to the muon $(g-2)$ data within this framework. The analysis takes into account all theoretical and observational constraints, and is based on the final state comprising a same-sign dilepton pair and a pair of same-sign $τ$ jets. The crucial ingredient in making the signal clean is the same-sign feature of both the dilepton and the $τ$-jet pair individually. After a detailed estimate of the signal and all noteworthy backgrounds, we show that this channel offers by far the best signal significance among those studied so far, predicting discovery with an integrated luminosity of 3000 fb$^{-1}$, and strong indications even with 1000 fb$^{-1}$ if systematic uncertainies do not exceed about 10%. We also demonstrate that the recently developed dynamic radius jet algorithm is effective in this connection.

hep-ph↗
arXiv2023

The $ρ$ parameter and the CDF W-mass anomaly: observations on the role of scalar triplets

The $ρ$-parameter, together with the W-and Z-masses, acts as Occam's razor on extensions of the electroweak symmetry breaking sectors. We apply this to non-doublet Higgs scenarios, by examining the CDF- $II$ claim on the W-boson mass. Suspending any judgement on the CDF claim, we show that in general, if one works at the tree level, theoretical models which predict $ρ=1$ at the tree-level are inconsistent with the CDF claims at 4-6 standard deviations if one confines oneself to the existing Z-boson mass, and the earlier $M_W$ value from either the global fit or the ATLAS data. We take some well-motivated scenarios containing one or more scalar SU(2) triplets in addition to the usual doublet, and show that, both a scenario including a complex scalar triplet and one with a complex as well as a real triplet (the Georgi-Machacek model) can be made consistent with the new data, where a small splitting between the complex and the real triplet vacuum expectation values is required in the second scenario. We will explore the consequences of this splitting, either at tree level or via incalculable new physics contribution to $M_W$, and indicate, as illustrations its implications in $H^{\pm}W^{\mp}Z$ type interaction vertices.

hep-ph↗
arXiv2023

Some new observations for the Georgi-Machacek scenario with triplet Higgs

The Georgi-Machacek model, introducing a complex and a real scalar triplet as additional components of the electroweak symmetry breaking sector, enables substantial triplet contributions to the weak gauge boson masses, subject to the equality of the complex and the real triplet vacuum expectation values (vev) via a custodial SU(2) symmetry. We present an updated set of constraints on this scenario, from collider data (including those from 137/139~fb$^{-1}$ of luminosity at the Large Hadron Collider), available data on the 125-GeV scalar, indirect limits and also theoretical restrictions from vacuum stability and unitarity. It is found that some bounds get relaxed, and the phenomenological potential of the scenario is more diverse, if the doubly charged scalar in the spectrum can decay not only into two like-sign $W$'s but also into one or two singly charged scalars. Other interesting features are noticed in a general approach, such as substantial $γγ$ and $Zγ$ branching ratios of the additional custodial singlet scalar, and appreciable strength of the trilinear interaction of a charged scalar, the $W$ and the $Z$. Finally,, we take into account the possibility of custodial SU(2) breaking, resulting in inequality of the real and the complex scalar vevs which too in principle may allow large triplet contribution to weak boson masses. Illustrative numerical results on the modified limits and predictions are presented, once more taking into account all the constraints mentioned above.

hep-ph↗