arXiv subjects

Ritesh K. Singh

Publications and source records attributed to Ritesh K. Singh.

At least 19 recordsLinked to original sources

arXiv2026

Generalised Dynamic Radius Jets for Robust Collider Analyses

Jets and their reconstructions play a central role in precision measurements and searches for new physics at hadron colliders. Conventional jet clustering algorithms employ a fixed radius parameter, which may not optimally describe events containing jets of varying characteristic sizes. Building on the recently proposed dynamic radius jet clustering framework, we construct several substructure-inspired dynamic radius prescriptions based on jet angularities and energy correlation functions. A detailed study of these algorithms is performed, including detector effects within the Delphes framework and in the presence of high pileup corresponding to an average of 150 interactions per event, with pileup contamination mitigated using the PUPPI algorithm. The performance of the proposed algorithms is compared with that of the standard anti-$k_t$ algorithm in boosted $Vj$ ($V=W^\pm,Z$) and $tj$ events against dijet backgrounds. Using jet substructure observables and multivariate analysis based on boosted decision trees, we find that the dynamic radius algorithms lead to improved reconstruction of boosted heavy-particle jets and achieve better signal-background discrimination compared to the conventional fixed radius anti-$k_t$ clustering.

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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

Probing the robustness of various self-testing protocols for multipartite entangled states

Device-independent certification of multipartite entangled states plays a central role in a wide range of practical applications, including quantum networks, conference key agreement, and verifiable distributed quantum computation. A particularly important class of multipartite entangled states is the class of Greenberger-Horne-Zeilinger (GHZ) states. Many Bell operators have been proposed to self-test GHZ states. However, in practical scenarios, due to imperfections and the finite collection of statistics, the observed statistics do not satisfy the ideal self-testing relations. Hence, it becomes essential to investigate and compare the robustness of the different self-testing protocols. In this work, we investigate the robustness of self-testing schemes constructed from Bell operators due to Svetlichny and Mermin--Ardehali--Belinskii--Klyshko (MABK), using the analytic operator-inequality framework developed by Kaniewski [\href{https://doi.org/10.1103/PhysRevLett.117.070402}{Phys. Rev. Lett. 117, 070402 (2016)}]. We derive lower bounds on the extractable fidelity as a function of the observed value of these Bell operators. Although these protocols self-test the same underlying state, they exhibit markedly different levels of robustness. By comparing the resulting fidelity bounds, we demonstrate that the self-testing scheme based on the Svetlichny's Bell operator is the more robust among the two. Our results thus identify the Svetlichny operator based self-testing protocol as the most favorable candidate for device-independent certification of GHZ states in realistic, noisy experimental scenarios.

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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 $ab^{-1}$.

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arXiv2026

Improving sensitivity of vectorlike top partner searches with jet substructure

Vectorlike quark partners appear in many BSM models and remain an important area of research, as they can offer insights into the electroweak symmetry breaking mechanism. In this work, we have focused on studying the production of a heavy vectorlike top partner in association with a SM top quark via chromomagnetic coupling and the four decay modes of the top partner, namely, $bW$, $tZ$, $th$, and $tg$. The signal has been studied in final states with one fat jet, at least one $b$-tagged jet, one lepton, and missing energy. This study focuses on the extensive use of jet substructure techniques in jets clustered with fixed and dynamically varying radius to deal with events containing differently sized jets. Important kinematic information, along with jet substructure and event shape observables, has been used in a multivariate analysis to extract signal with high significance. A comparative study between fixed and dynamically varying radius clustering of jets is also presented, leading to an improvement in signal sensitivity in the highly boosted scenario.

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arXiv2026

Scalable Self-Testing of Mutually Anticommuting Observables and Maximally Entangled Two-Qudits

The next frontier in device-independent quantum information lies in the certification of scalable and parallel quantum resources, which underpin advanced quantum technologies. We put forth a simultaneous self-testing framework for maximally entangled two-qudit state of local dimension $m_*=2^{\lfloor n/2 \rfloor}$ (equivalently $\lfloor n/2 \rfloor$ copies of maximally entangled two-qubit pairs), together with $n$ numbers of anti-commuting observables on one side. To this end, we employ an $n$-settings Bell inequality comprising two space-like separated observers, Alice and Bob, having $2^{n-1}$ and $n$ number of measurement settings, respectively. We derive the local ontic bound of this inequality and, crucially, employ the Sum-of-Squares decomposition to determine the optimal quantum bound without presupposing the dimension of the state or observables. We then establish that any physical realisation achieving the maximal quantum violation must, up to local isometries and complex conjugation, correspond to a reference strategy consisting of a maximally entangled state of local dimension of at least $2^{\lfloor n/2 \rfloor}$ and local observables forming an irreducible representation of the Clifford algebra. This construction thereby demonstrates that the minimal dimension compatible with $n$ mutually anticommuting observables is naturally self-tested by the maximal violation of the proposed Bell functional. Finally, we analyse the robustness of the protocol by establishing quantitative bounds relating deviations in the observed Bell value to the fidelity between the realised and the ideal strategies. Our results thus provide a scalable, dimension-independent route for the certification of high-dimensional entanglement and Clifford measurements in a fully device-independent framework.

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arXiv2025

Probing anomalous $W^-W^+γ/Z$ couplings in the SMEFT with $e^-e^+ \to W^-W^+ \to 4j/\ell^-\ell^+\slashed{E}$ channel

We investigate anomalous charged triple gauge boson couplings induced by $SU(2)_L \times U(1)_Y$ gauge-invariant dimension-6 operators in the HISZ basis through the processes $e^-e^+ \to 4j$ and $e^-e^+ \to \ell^-\ell^+ + \text{missing energy}$ at $\sqrt{s}=250\,$GeV with longitudinally polarized beams. The analysis includes three CP-even operators $(O_{WWW}, O_W, O_B)$ and two CP-odd operators $(\tilde O_{WWW}, \tilde O_W)$, which parameterize deviations in the $W^-W^+γ/Z$ vertex. All leading-order contributions are included, including interference between $W^-W^+$ production and non-resonant amplitudes. In the $e^-e^+ \to 4j$ channel, $W^-W^+$ candidates are selected using boosted decision trees. The $W$-boson charges are reconstructed using a jet-charge observable, and jet flavors from $W$ decays are identified with a dedicated classifier, enabling measurements of vector polarization and correlation asymmetries. In the $e^-e^+ \to \ell^-\ell^+ + \text{missing energy}$ channel, events are selected with cuts on lepton transverse momentum and dilepton mass, and the two neutrino momenta are reconstructed using neural-network regression. Combining total cross sections with spin asymmetries allows constraints on anomalous gauge couplings. The fully hadronic channel provides the strongest sensitivity to $O_B$ and $\tilde O_W$, while the semi-leptonic channel yields tighter limits on $O_{WWW}$, $O_W$, and $\tilde O_{WWW}$. The fully leptonic channel adds complementary sensitivity. Finally, we derive marginalized limits on all five operators using a Markov Chain Monte Carlo analysis for several choices of systematic uncertainties and integrated luminosities.

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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.

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arXiv2025

Bounds on SMEFT affecting multi gauge and Higgs-gauge couplings using two and three body spin correlations in $e^-e^+\to 3l2j\slashed{E}$ process

The upcoming electron-positron collider provides an ideal place to probe deviation from the Standard Model predictions with its clean environment, beam polarization and significant luminosity. We studied anomalous quartic gauge boson couplings~($VVW^-W^+, V\in\{γ,Z\}$), triple gauge couplings~($W^-W^+γ/Z)$, and Higgs-gauge couplings $(HVV, V\in\{W^\pm,Z,γ\}$) induced by $SU(2)_L \times U(1)_Y$ gauge invariant dimension-6 operators in $3l2j\slashed{E}$ final events with initial beam polarization. The phase space of two prominent amplitudes i.e, triple gauge boson production $(WWV)$ and vector boson scattering sub-processes, are selected with boosted decision trees. We employ the asymmetries related to polarization and spin correlation observables along with cross~section to constrain the anomalous couplings. The parity odd polarizations and spin correlations of jets from $W$ boson require flavor tagging which is done using artificial neural networks. We provide one parameter limits at $95\%$ confidence level combining cross~section and spin related observables. Finally, marginalized limits on all nine anomalous couplings are obtained with MCMC analysis. The limits are found to be insensitive to systematic errors and dominated by statistics. We find that the VBS-like events provides a tighter constraints to $c_W$ and $c_B$ Wilson coefficients (WCs) in comparison to limits from WWZ phase space. For the remaining $7$ WCs, WWZ contribute significantly to the overall limits.

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arXiv2025

Jet Substructure Probe on Scalar Leptoquark Models via Top Polarization

The study of leptoquarks and their couplings to fermions with different chiralities provides a powerful tool for distinguishing among different leptoquark models. As a case study, we focus on two specific third-generation scalar leptoquark models, $S_3$ and $R_2$, which differ in their electroweak quantum numbers and chiral structures of couplings to the top quark, leading to distinct top-quark polarization states. To enhance the efficacy of the analysis, we employ jet substructure techniques like Soft Drop, $N$-subjettiness, and our custom $b$-tagging method, along with other event variables. The analysis has been performed using both fixed radius and dynamic radius jet clustering algorithms. A multivariate analysis using a boosted decision tree (BDT) is performed to isolate signal from the Standard Model background. For a leptoquark mass of 1250 GeV, the analysis achieves a signal significance of up to $5.3\,σ$ at the 14 TeV HL-LHC. Furthermore, a $CL_s$-based profile likelihood estimator is applied to polarization-sensitive variables to discriminate between the two models. To enhance separation between the two models, an additional BDT classifier score is obtained by training a BDT network to distinguish between the $S_3$ and $R_2$ models. In the chosen signal region, the BDT classifier score provides a separation score of up to $3.2\,σ$, outperforming traditional variables such as $E_b/E_t$ and $\cosθ_b$.

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arXiv2025

Self-testing in a constrained prepare-measure scenario sans assuming quantum dimension

We present a device-independent (DI) self-testing protocol in a constrained prepare-measure scenario, based on the $n-$bit parity-oblivious multiplexing (POM) task. In this scenario, a parity-oblivious constraint is imposed on the preparations, allowing us to define a classical bound derived from a preparation noncontextual ontological model. We derive the optimal quantum success probability in the POM task devoid of assuming the dimension of the quantum system, an essential step towards DI self-testing, which has hitherto not been demonstrated in prepare-measure scenario. We demonstrate that the optimal quantum value exceeds preparation noncontextual bound and, as a result, this establishes DI self-testing of the preparations and the measurement devices. Furthermore, by explicitly constructing the required unitaries, we show that the optimal preparations and measurements in an unknown but finite dimensional Hilbert space, responsible for the observed input-output correlations, can be mapped, via an unitary, onto a known finite-dimensional quantum system. Our results thus pave the way for scalable, single system based DI certification protocols in the prepare-measure scenario.

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arXiv2024

Looking into the quantum entanglement in $H\to ZZ^\star$ at LHC within SMEFT framework

We study $H\to ZZ^\star$ production process in final four lepton states at $13$ TeV LHC in SMEFT framework. The anomalous $HZZ$ couplings are parameterized with dimension-6 $SU(2)_L\times U(1)_Y$ gauge invariant operators. We compute the eight polarizations of each $Z$ boson and $64$ spin-correlations as asymmetries in angular functions of final decayed leptons in the rest frame of the $Z$ boson. These asymmetries are further used to construct the joint density matrix (DM) for $ZZ^\star$ system. However, such DM suffers from negative probability and eigenvalues. To alleviate the negativity issues, we reconstruct the DM using asymmetries of symmetrized angular functions owing to the indistinguishability of two $Z$ bosons. The symmetrized DM is further employed to compute lower bound for concurrence as a witness of entanglement measurable at the collider experiments. The $ZZ^\star$ system is found to be in an entangled state for all values of the anomalous couplings. Notably, while the lower bound exhibits poorer sensitivity to anomalous couplings compared to asymmetries, it demonstrates distinct behavior for CP-even and odd couplings.

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arXiv2024

Robust self-testing of the $m-$partite maximally entangled state and observables

As quantum technologies continue to advance rapidly, the device-independent testing of the functioning of a quantum device has become increasingly important. Self-testing, a correlation based protocol, enables such certification of a promised quantum state as well as measurements performed on it without requiring knowledge of the device's internal workings. This approach typically relies on achieving the optimal quantum violation of a suitable Bell inequality. Self-testing has been extensively investigated in the context of bipartite Bell experiments. However, its extension to multipartite scenarios remains largely unexplored, owing to the intricate nature of multipartite quantum correlations. In this work, we propose a simple and efficient self-testing protocol that certifies the state and observables based on the optimal quantum violation of the Svetlichny inequality involving an arbitrary number of parties, each with two inputs. Our method leverages an elegant sum-of-squares approach to derive the optimal quantum value of the Svetlichny functional, devoid of assuming the dimension of the quantum system. This enables the self-testing of the $m-$partite maximally entangled state and local anti-commuting observables for each party. Moreover, we develop a swap circuit isometry to assess the proximity of reference states and measurements to their ideal counterparts in the presence of noise and imperfections in real experiments, thereby demonstrating the robustness of our self-testing protocol. Finally, we illustrate how our self-testing protocol facilitates the generation of certified genuine randomness from correlations that enable the optimal violation of the Svetlichny inequality.

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arXiv2024

Anomalous triple gauge couplings in $e^-e^+\to 4j$: Role of polarizations, spin correlations and interference

We investigate the anomalous charged triple gauge boson couplings generated via $SU(2)_l\times U(1)_Y$ gauge invariant dimension-6 operators with final state four jet events in an $e^-e^+$ Collider at $\sqrt{s}=250$~GeV. We consider all the leading order contributions including the contribution from the interference of $W^-W^+$ diagrams with other possible diagrams. The tagging of two $W$ bosons with a pair of jets is done using the jet charge, while the decay products of $W^\prime$s are tagged as \emph{up/down}-type using boosted decision trees to construct polarizations and spin correlations. Marginalized limits on five anomalous couplings are obtained by Markov Chain Monte Carlo analysis using polarizations, spin correlations, and cross~section. We found that the full-hadronic channel provides tighter limits on anomalous couplings than compared to the usually sought-after clean semi-leptonic channel, owing to the large contribution from interference.

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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.

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arXiv2023

Sensitivity of polarizations and spin correlations of Z boson to anomalous neutral triple gauge couplings at lepton collider with polarized beams

We investigate the effects of anomalous neutral triple gauge couplings in $ZZ$ and $Zγ$ production processes, followed by the leptonic decay of the $Z$ boson, at a lepton collider with center-of-mass energy $\sqrt{s}=250$~GeV and polarized beams. We use an effective Lagrangian formalism to parameterize the anomalous couplings in terms of dimension-8 operators $c_{\widetilde{B}W}$, $c_{BW}$, $c_{WW}$, and $c_{BB}$, and study the sensitivity of observables such as cross~section, polarization, and spin correlation as functions of these couplings. We perform a Bayesian statistical analysis using Markov Chain Monte Carlo methods to determine simultaneous limits on the anomalous couplings, taking into account various luminosities $\mathcal{L} \in \{0.1~\text{ab}^{-1}, 0.3~\text{ab}^{-1}, 1~\text{ab}^{-1}, 3~\text{ab}^{-1}, 10~\text{ab}^{-1}\}$ and systematic uncertainties. We find that polarization and spin correlation observables significantly enhance the sensitivity to anomalous couplings, providing stringent constraints on these couplings.

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arXiv2023

Embedding of a non-Hermitian Hamiltonian to emulate the von Neumann measurement scheme

The problem of how measurement in quantum mechanics takes place has existed since its formulation. Von Neumann proposed a scheme where he treated measurement as a two-part process -- a unitary evolution in the full system-ancilla space and then a projection onto one of the pointer states of the ancilla (representing the "collapse" of the wavefunction). The Lindblad master equation, which has been extensively used to explain dissipative quantum phenomena in the presence of an environment, can effectively describe the first part of the von Neumann measurement scheme when the jump operators in the master equation are Hermitian. We have proposed a non-Hermitian Hamiltonian formalism to emulate the first part of the von Neumann measurement scheme. We have used the embedding protocol to dilate a non-Hermitian Hamiltonian that governs the dynamics in the system subspace into a higher-dimensional Hermitian Hamiltonian that evolves the full space unitarily. We have obtained the various constraints and the required dimensionality of the ancilla Hilbert space in order to achieve the required embedding. Using this particular embedding and a specific projection operator, one obtains non-Hermitian dynamics in the system subspace that closely follow the Lindblad master equation. This work lends a new perspective to the measurement problem by employing non-Hermitian Hamiltonians.

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arXiv2023

Measuring Electroweak Quantum Numbers of Color Sextet Resonances at the LHC

We study the prospect of measuring the electroweak quantum numbers of beyond the Standard Model (SM) color sextet particles that decay into same-sign top quark pairs. Among these particles, the color sextet scalars give rise to top quarks with the same chirality, while the top quarks coming from the color sextet vector would have opposite chirality. This difference gets encoded in the angular distributions of the bottom quarks and leptons originating from the decays of the top quarks. We utilize this feature and the energy distributions of the final state jets and leptons to distinguish among the three possible color sextet resonances, taking into account various SM background processes at the $13$ TeV LHC.

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