arXiv subjects

Sanjoy Biswas

Publications and source records attributed to Sanjoy Biswas.

At least 19 recordsLinked to original sources

arXiv2026

Implications of portal vector-like lepton on associated Higgs production at a multi-TeV muon collider

We have explore a portal vector-like lepton (pVLL) extension of the Standard Model (SM) and study its implications for Higgs and vector-boson associated production ($hV$, with $~V = Z$-boson or dark photon) at a future muon collider facility. We show that while the $~μ^+ μ^- \to hZ~$ production rate remains close to its SM prediction in a wide range of parameter space, the rate for $~μ^+ μ^- \to hγ_d~$ can be substantially enhanced owing to the non-decoupling nature of the interaction involving the heavy lepton, the muon and the dark photon. We demonstrate that the $hγ_d$ production rate can exceed the corresponding $hZ$ rate by a factor of $1$-$100$ within the perturbative unitarity limit, making it a promising channel for probing Higgs interactions and potential new physics effects. We also examine the role of the pVLL state in the context of dark matter (DM) phenomenology and identify regions of parameter space consistent with the observed relic abundance by extending the simplified setup with a viable DM candidate. The $hγ_d$ production can also be used to constrain the dark photon mass ($m_{γ_d}$) and/or the dark gauge coupling ($g_d$) consistent with various constraints including the current muon $g-2$ measurements within the pVLL framework. We perform a detailed collider analysis of the $hγ_d$ process in the $b\bar{b}~+$ missing energy final state. A $2σ$ exclusion limit for $m_{γ_d}$ up to $80$ GeV is obtained assuming $~g_d=0.05$, $~\sinθ_L=4\times10^{-5}$, $~\sinθ_s=0.05$, for a heavy lepton mass $~\sim 3$ TeV at a $3$ TeV muon collider with an integrated luminosity of $1$ ab$^{-1}$.

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arXiv2026

Electroweak phase transitions in a $U(1)_D$ extension of the standard model with dimension-six operators: Gravitational waves and LHC signatures

We investigate the possibility of realizing strong first-order electroweak phase transition (SFOEWPT) in an effective field theory framework where the Standard Model is extended with a complex scalar singlet ($ϕ$) charged under a local $U(1)_D$ gauge group. The tree-level scalar potential contains a dimension-six term of the form $|H|^2|ϕ|^4$. We show that this higher-dimensional operator plays a crucial role in the phase transition dynamics by weakening the correlation between the Higgs-singlet portal coupling and the scalar mixing angle that typically constrains singlet-extended models. Consequently, SFOEWPT can be achieved over a significantly extended region of parameter space. The strength of the phase transition is primarily driven by the vacuum expectation value (VEV) of the singlet scalar which plays a central role in this analysis. We analyze the phase transition in this model and identify regions of parameter space consistent with SFOEWPT. The resulting phase transition can generate stochastic gravitational-wave signals potentially observable at future interferometers. The extended scalar sector in presence of the dimension-six operator also leads to distinctive multi-scalar production signatures at the LHC, intimately correlated with the singlet scalar VEV.

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arXiv2025

Machine learning tagged boosted dark photon: A signature of fermionic portal matter at the LHC

We use a Hybrid Deep Neural Network (HDNN) to identify a boosted dark photon jet as a signature of a heavy vector-like fermionic portal matter (PM) connecting the visible and the dark sectors. In this work, the fermionic PM, which mixes only with the Standard Model (SM) third-generation up-type quark, predominantly decays into a top quark and a dark photon pair. The dark photon then promptly decays to a pair of standard model fermions via the gauge kinetic mixing. We have analyzed two different final states, namely, (i) exactly one tagged dark photon and exactly one tagged top quark jet, and (ii) at least two tagged dark photons and at least one tagged top quark jet at the 13 and 14 TeV LHC center of mass energies. Both these final states receive significant contributions from the pair and single production processes of the top partner. The rich event topology of the signal processes, i.e., the presence of a boosted dark photon and top quark jet pair, along with the fact that the invariant mass of the system corresponds to the mass of the top partner, help us to significantly suppress potential SM backgrounds. We have shown that one can set a $2σ$ exclusion limit of $\sim 2.3$ TeV on the top partner mass with $\sinθ_L=0.1$ and assuming $100\%$ branching ratio of the top partner in the final state with exactly one tagged dark photon and exactly one tagged top quark jet at the 14 TeV LHC center of mass energy assuming 300 fb$^{-1}$ of integrated luminosity.

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arXiv2025

Higgs couplings in SMEFT via Zh production at the HL-LHC

We study the Higgs couplings involved in the $Zh$ associated production mode at the Large Hadron Collider (LHC) in presence of Higgs-gauge boson coupling modifiers via $κ$ framework, and dimension 6 Standard Model Effective Theory (SMEFT) operators. The analysis is performed mainly in context of the HL-LHC (with $\sqrt{s}=$14 TeV and luminosity 3000 $fb^{-1}$) setup using cut based as well as machine learning techniques. The analysis shows significant betterment in the signal significance by using the machine learning technique. We also do a $χ^2$ analysis, which reveals an appreciable change in the sensitivity of the coupling modifiers due to the presence of effective operators, in particular due to the $qqZh$ Higgs-current interactions. The dipole operators concerning the same vertex, combine quarks of different chiralities and does not interfere with the SM diagrams, hence contributing only at $\mathcal{O} (Λ^{-4})$. In order to observe better sensitivity for this class of operators, we need to move to higher center-of-mass energy, where the effects of both Higgs-current and dipole 4-point interactions are more prominent.

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arXiv2023

Associated production of Higgs and single top at the LHC in presence of the SMEFT operators

We analyse the single top production in association with the Higgs at the Large Hadron Collider (LHC) using Standard Model (SM) effective operators upto dimension six. We show that the presence of effective operators can significantly alter the existing bound on the top-Higgs Yukawa coupling. We analyse events at the LHC with 35.9 and 137(140) fb$^{-1}$ integrated luminosities using both cut-based and machine learning techniques to probe new physics (NP) scale and operator coefficients addressing relevant SM background reduction. The four fermi effective operator(s) that contributes to the signal, turns out to be crucial and a bound on the operator coefficient is obtained from the present data and for future sensitivities.

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arXiv2023

Exploring maverick top partner decays at the LHC

In this work, we have considered an extension of the standard model (SM) with a $SU(2)_L$ singlet vectorlike quark (VLQ) with electric charge $Q=+2/3$. The model also contains an additional local $U(1)_d$ symmetry group and the corresponding gauge boson is the dark photon. The VLQ is charged while all the SM particles are neutral under the new $U(1)_d$ gauge group. Even though in this model the VLQ possesses many properties qualitatively similar to that of the traditional top partner ($T_p$), there are some compelling differences as well. In particular, its branching ratio to the traditional modes ($T_p \to bW, tZ, th$) are suppressed which in turn helps to evade many of the existing bound, mainly coming from the LHC experiments. In an earlier work, such a VLQ is referred to as ``maverick top partner". It has been shown that the top partner in this model predominantly decays to a top quark and a dark photon/dark higgs pair ($T_p \to tγ_d ,~th_d$) over a large region of the parameter space. The dark photon can be made invisible and consequently, it gives rise to the missing transverse energy ($\not\!\!{E} _{T}$) signature at the LHC detector. We have mainly focused on the LHC signatures and future prospects of such top partners. In particular, we have studied the $t\bar{t}+\not\!\!{E}_{T}$ and $t+\not\!\!{E}_{T}$ signatures in the context of the LHC via pair and single productions of the top partner, respectively at 13 and 14 TeV LHC center of mass energies assuming that the dark photon either decays into an invisible mode or it is invisible at the length scale of the detector. We have shown that one can exclude $\sinθ_L \sim 0.025$ (0.05) for $m_{_{T_p}} \leq $ 2.0 (2.6) TeV at $\sqrt{s}=14$ TeV with an integrated luminosity of 3 ab$^{-1}$ using the single top partner production channel.

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arXiv2022

Dark photon searches via Higgs boson production at the LHC and beyond

Many scenarios beyond the standard model, aiming to solve long-standing cosmological and particle physics problems, suggest that dark matter might experience long-distance interactions mediated by an unbroken dark $U(1)$ gauge symmetry, hence foreseeing the existence of a massless dark photon. Contrary to the massive dark photon, a massless dark photon can only couple to the standard model sector by means of effective higher dimensional operators. Massless dark-photon production at colliders will then in general be suppressed at low energy by a UV energy scale, which is of the order of the masses of portal (messenger) fields connecting the dark and the observable sectors. A violation of this expectation is provided by dark-photon production mediated by the Higgs boson, thanks to the non-decoupling Higgs properties. Higgs-boson production at colliders, followed by the Higgs decay into a photon and a dark photon, provides then a very promising production mechanism for the dark photon discovery, being insensitive in particular regimes to the UV scale of the new physics. This decay channel gives rise to a peculiar signature characterized by a monochromatic photon with energy half the Higgs mass (in the Higgs rest frame) plus missing energy. We show how such resonant photon-plus-missing-energy signature can uniquely be connected to a dark photon production. Higgs boson production and decay into a photon and a dark photon as a source of dark photons is reviewed at the Large Hadron Collider, in the light of the present bounds on the corresponding signature by the CMS and ATLAS collaborations. Perspectives for the dark-photon production in Higgs-mediated processes at future $e^+e^-$ colliders are also discussed.

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arXiv2019

Probing Dark-ALP Portals at Future $e^+e^-$ Colliders

We study portal interactions connecting visible and dark sectors, and involving local interactions of a photon, a dark photon and a axion-like particle (ALP) at future $e^+e^-$ colliders. These interactions, mediated by higher-dimensional effective operators, may arise at one-loop by kinetic mixing between dark and ordinary photons, or, for massless dark photons, by direct short-distance contributions. We explore these portal interactions for a heavy ALP with masses between about 10 GeV and 230 GeV by investigating the sensitivity of the production $e^+e^- \to γγ\barγ$ to the effective couplings, where the dark photon $\barγ$ gives rise to missing momentum in the final state. We will show how an appropriate choice of missing-energy and missing-mass cuts can optimize the signal to standard-model background ratio. Exclusion regions for the effective photon-dark-photon-ALP couplings versus the ALP mass are worked out for a few representative values of the collision energy and integrated luminosity, as presently envisaged by future $e^+e^-$ projects.

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arXiv2017

Dark-photon searches via $ZH$ production at $e^+e^-$ colliders

We study the $ZH$ associated production followed by the Higgs $H\to γ\barγ$ decay into a photon plus an invisible and massless dark photon, at future high-energy $e^+e^-$ facilities. Large $H\to γ\barγ$ decay rates (with branching ratios up to a few percent) are allowed, thanks to possible non-decoupling properties of the Higgs boson under specific conditions, and unsuppressed dark-photon couplings in the dark sector. Such large decay rates can be obtained in the framework of recent flavor models that aim to naturally explain the observed spread in the fermion mass spectrum. We analyze the experimental prospects for observing the $e^+e^-\rightarrow ZH$ process followed by the semi invisible Higgs decay into a photon plus a massless invisible system. Search strategies for both the leptonic and the hadronic final states (arising from $Z\rightarrow μ^+μ^-$ and $Z\rightarrow q\bar{q}$, respectively) are outlined. We find that a $5σ$ sensitivity to a branching fraction $BR_{γ\barγ}\sim 3\times 10^{-4}$ can be achieved by combining the two channels with an integrated luminosity of 10 ab$^{-1}$ at a c.m. energy of 240 GeV. This is considerably better than the corresponding sensitivity in alternative channels previously studied at lepton colliders. The analysis is model independent, and its results can be straightforwardly applied to the search of any Higgs two-body decay into a photon plus an undetected light particle.

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arXiv2016

Higgs-boson production in association with a Dark Photon in $e^+ e^-$ collisions

We study the production of a Higgs boson recoiling from a massless invisible system in $e^ + e^ -$ collisions. This is a quite distinctive signature that can arise when the Higgs boson is produced in association with a massless dark photon, which can happen in BSM scenarios foreseeing an extra unbroken $U(1)$ gauge group. Dark photons can indeed acquire effective couplings to the Higgs boson as occurs in models recently proposed to generate exponentially-spread Yukawa couplings. We analyze the signal and corresponding backgrounds for $H\to b\bar{b}$, and estimate ILC and FCC-ee sensitivities in a model-independent way.

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arXiv2016

Di-Higgs signatures from R-parity violating supersymmetry as the origin of neutrino mass

Motivated by the naturalness and neutrino mass generation, we study a bilinear R-parity violating supersymmetric scenario with a light Higgsino-like lightest supersymmetric particle (LSP). We observe that the LSP dominantly decays to $νh$ in a large part of the parameter space, and thus study the pair production of electroweakinos followed by the decays $\tildeχ^\pm_1\to \tildeχ^0_1 W^{\pm*}$ and $\tildeχ^0_1\to νh$. This leads to an interesting signature of Higgs boson pair production associated with significantly large missing transverse energy which is grossly distinct from the di-Higgs production in the Standard Model. We investigate the perspective of probing such signatures by performing a realistic detector level simulation of both the signal and corresponding backgrounds for the high-luminosity high energy phase of the Large Hadron Collider (LHC). We also advocate some observables based on kinematical features to provide an excellent handle to suppress the backgrounds.

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arXiv2016

Dark-Photon searches via Higgs-boson production at the LHC

Dark photons $\bar γ$ mediating long-range forces in a dark sector are predicted by various new physics scenarios, and are being intensively searched for in experiments. We extend a previous study of a new discovery process for dark photons proceedings via Higgs-boson production at the LHC. Thanks to the non-decoupling properties of the Higgs boson, BR($H\to γ\bar γ$) values up to a few percent are possible for a massless dark photon, even for heavy dark-sector scenarios. The corresponding signature consists (for a Higgs boson at rest) of a striking monochromatic photon with energy $E_γ= m_H/2$, and similar amount of missing energy. We perform a model independent analysis at the LHC of both the gluon-fusion and VBF Higgs production mechanisms at 14 TeV, including parton-shower effects, and updating our previous parton-level analysis at 8 TeV in the gluon-fusion channel by a more realistic background modeling. We find that a $5σ$ sensitivity can be reached in the gluon-fusion channel for BR($H\to γ\bar γ)\simeq\,$0.1% with an integrated luminosity of $L\simeq 300\, {\rm fb}^{-1}$. The corresponding VBF reach is instead restricted to 1%. Such decay rates can be naturally obtained in dark-photon scenarios arising from unbroken $U(1)_F$ models explaining the origin and hierarchy of the Yukawa couplings, strongly motivating the search for this exotic Higgs decay at the LHC.

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arXiv2015

Explaining the Lepton Non-universality at the LHCb and CMS from a Unified Framework

The recent results from the LHCb in the context of $(B^+ \rightarrow K^+ l l)$ decay and the CMS analysis in the context of right handed $W$-boson ($W_R$) search show a $2.6σ$ and a $2.8σ$ deviations from the Standard Model expectations respectively. In this work, we address these two seemingly uncorrelated results in the context of \R-parity violating supersymmetry. We found that a particular combination of $LQD^c$-type operators which successfully explain the LHCb result, can also accommodate the CMS excess in the $eejj$ channel of the $W_R$ search.

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arXiv2014

Explaining a CMS $eejj$ Excess With $\mathcal{R}-$parity Violating Supersymmetry and Implications for Neutrinoless Double Beta Decay

A recent CMS search for the right handed gauge boson $W_R$ reports an interesting deviation from the Standard Model. The search has been conducted in the $eejj$ channel and has shown a 2.8$σ$ excess around $m_{eejj} \sim 2$ TeV. In this work, we explain the reported CMS excess with R-parity violating supersymmetry (SUSY). We consider resonant selectron and sneutrino production, followed by the three body decays of the neutralino and chargino via an $\mathcal{R}-$parity violating coupling. We fit the excess for slepton masses around 2 TeV. The scenario can further be tested in neutrinoless double beta decay ($0νββ$) experiments. GERDA Phase-II will probe a significant portion of the good-fit parameter space.

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arXiv2014

Enhancing the ttH signal through top-quark spin polarization effects at the LHC

We compare the impact of top-quark spin polarization effects in Higgs boson production in association with top-quark pairs and in corresponding backgrounds at the LHC. Because of the spin-zero nature of the Higgs boson, one expects, in the chiral limit for the top quarks, a substantial complementarity in $t\bar t$ spin correlations for a Higgs decaying into fermions/gauge-bosons and $t\bar{t}$ spin correlations for the corresponding irreducible $t\bar t f\bar f/VV$ backgrounds. Although top mass effects in $t\bar t H$ production are in general dominant, and seriously spoil the chiral-limit expectations, one can find observables that capture the $t \bar t$ angular spin correlations and can help in separating the signal from irreducible backgrounds. In particular, we show that, for both $H\to b\bar b$ and $H\to γγ$, taking into account $t\bar{t}$ spin correlations in $t\bar t H$ production and irreducible backgrounds could appreciably improve the LHC sensitivity to the $t\bar t H$ channel.

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arXiv2014

Multi-leptons and Top-jets in the Hunt for Gluinos in R-parity Violating Supersymmetry

The presence of R-parity ($\mathcal{R}_p$) violation offers intersting decay channels for the gluinos. In this work we present a new search strategy for the gluinos in the presence of semileptonic $\mathcal{R}_p$ violating couplings $λ^{'}_{133}$ and $λ^{'}_{233}$. We consider two scenarios (i) $λ^{'}$ induced 3-body decay of gluinos to a top quark ($t$), a bottom quark ($b$) and a light lepton ($\ell$) (ii) cascade decay of gluinos to top quarks and neutralinos ($\widetildeχ_1^0$) followed by the decay of $\widetildeχ_1^0$ to $t$, $b$ and $\ell$ through $λ^{'}$ couplings. We present two different search procedures which are common to both the scenarios. While the first one involves the traditional approach with multi-leptons and $b$-tagged jets, the second one employs the more recent technique to reconstruct highly energetic hadronically decaying top quarks. We perform a detailed simulation of the signal as well as all the relevant Standard Model backgrounds to show that the second procedure offers slightly better sensitivity for gluino discovery. In both the procedures, a $\geq$ 5$σ$ discovery is possible for the gluino mass in the range 1.5 -1.7 TeV at 14 TeV LHC with 50 fb$^{-1}$ integrated luminosity.

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arXiv2013

Direct constraints on the top-Higgs coupling from the 8 TeV LHC data

The LHC experiments have analyzed the 7 and 8 TeV LHC data in the main Higgs production and decay modes. Current analyses only loosely constrain an anomalous top-Higgs coupling in a direct way. In order to strongly constrain this coupling, the Higgs-top associated production is reanalyzed. Thanks to the strong destructive interference in the t-channel for standard model couplings, this process can be very sensitive to both the magnitude and the sign of a non-standard top-Higgs coupling. We project the sensitivity to anomalous couplings to the integrated luminosity of 50 fb^{-1}, corresponding to the data collected by the ATLAS and CMS experiments in 7 and 8 TeV collisions, as of 2012. We show that the combination of di-photon and multi-lepton signatures, originating from different combinations of the top and Higgs decay modes, can be a potential probe to constrain a large portion of the negative top-Higgs coupling space presently allowed by the ATLAS and CMS global fits.

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arXiv2012

Single top and Higgs associated production as a probe of the Htt coupling sign at the LHC

The LHC sensitivity to an anomalous Higgs coupling to the top quark in the Higgs-top associated production is analyzed. Thanks to the strong destructive interference in the t-channel for standard model couplings, this process can be very sensitive to both the magnitude and the sign of a nonstandard top-Higgs coupling. We analyze cross sections and the main irreducible backgrounds for the $H \to γγ$ decay channel. Sensitivities to an anomalous sign for the top Yukawa coupling are found to be large. In particular, at \sqrt{s}=14 TeV, assuming a universal rescaling in the Yukawa sector, a parton-level analysis with realistic selection cuts gives a signal-to-background ratio S/B ~ 5, for -1.5 < Y_t/Y_t^{SM} < 0. A number of events S ~ 10 (with corresponding significances ~ 3 σ) are expected for 60 fb^{-1}, to be compared with the standard-model expectation S ~ 0.3.

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