arXiv subjects

Anupam Ghosh

Publications and source records attributed to Anupam Ghosh.

At least 19 recordsLinked to original sources

arXiv2026

From WIMP to FIMP during reheating: collider vs non-collider probes for p-wave annihilation

By examining the transition from freeze-out to freeze-in dark matter (DM) production within the framework of perturbative reheating, where DM interacts with the visible sector through effective operators of dimension six, we have investigated how a broad range of new physics probes can reveal the nature of the pre-BBN Universe. Incorporating constraints from direct and indirect DM searches, invisible decay measurements, collider experiments, and gravitational wave observations, our analysis demonstrates that both current and forthcoming experimental sensitivities can serve as powerful tools for probing as well as constraining the post-inflationary era, together with new physics beyond the SM. Our analysis demonstrates that collider experiments at both the intensity and energy frontiers can impose strong bounds on derivative operators whose interactions are typically {\it p-wave suppressed}, and therefore only weakly constrained by astrophysical observations. In particular, these complementary searches can significantly restrict the allowed reheating temperature, DM mass and effective interaction scale required to reproduce the observed DM abundance for DM produced during the epoch of reheating.

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arXiv2026

The force of attraction between nucleons due to vacuum fluctuation

We investigate quantum vacuum interactions arising from the zero-point fluctuations of a spatially confined massive scalar field. Deriving analytical expressions for the planar interaction energy and vacuum pressure, we identify a fundamental transition from the canonical power-law scaling of massless fields to a distinct quantum saturation regime. We prove that in the macroscopic limit, where the boundary separation far exceeds the field's Compton wavelength ($a \gg \lambda_c$), the interaction energy does not vanish; instead, it asymptotes to a persistent constant, $-\hbar c / (24\pi \lambda_c^3)$. This reveals a cohesive zero-point energy reservoir inherent to massive vacua. Applying this formalism to the femtometer scale of the deuteron ($^2$H) nuclei, we demonstrate that confining massive pion fluctuations generates an attractive force between nucleons.

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arXiv2025

Lepton Collider as a Window to Reheating via Freezing Out Dark Matter Detection

We investigate a particle dark matter (DM) scenario where the DM interaction with the Standard Model are mediated by a leptophilic effective operator. Unlike conventional WIMP scenarios where thermal freeze-out occurs in a radiation-dominated Universe, we consider DM freeze-out during a prolonged reheating epoch driven by inflaton decay. The resulting departure from standard cosmology alters the thermal evolution of the dark matter abundance, making it sensitive to the reheating temperature and the history of entropy injection. The leptophilic nature of the interaction, motivated by the absence of DM signals in the current LHC searches, suppresses couplings to quarks and gluons and instead enables viable DM-lepton interactions that remain largely unconstrained. Within this setup, we analyze the mono-Higgs plus missing energy channel at future lepton colliders where the same operator responsible for setting the relic abundance can be directly probed. We perform a detailed signal-background analysis using both polarized and unpolarized beams. Additionally, our results illustrate how collider experiments, when interpreted jointly with relic density constraints, can provide indirect hints of the Universe's thermal history, offering potential insights into the reheating temperature and the dynamics preceding Big Bang Nucleosynthesis.

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arXiv2025

Conditional mutual information: A generalization of causal inference in quantum systems

The concept of causality is fundamental to numerous scientific explanations; however, its extension to the quantum regime has yet to be rigorously explored. This letter introduces the development of a quantum causal index, a novel extension of the classical causal inference framework, tailored to learn the causal relationships inherent in quantum systems. Our study focuses on the asymmetric quantum conditional mutual information (QCMI), incorporating the von Neumann entropy, as a directional metric of causal influence in quantum many-body systems. We analyze spin chains using the QCMI, implementing a projective measurement on one site as the intervention and monitoring its effect on a distant site conditioned on intermediate spins. Additionally, we study the effective causal propagation velocity, which is the speed at which QCMI becomes significant at distant sites. These findings indicate the presence of finite-speed propagation of causal influence, along with the emergence of coherent oscillations.

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arXiv2025

Illuminating Degenerate Dark Sector of Inert Doublet Model at Muon Collider

The Inert scalar Doublet Model (IDM) presents a simple yet elegant framework for a scalar dark sector where the lightest mode functions as a viable dark matter candidate under a $\mathbb{Z}_2$ symmetry. With TeV-scale particles accessible to the Large Hadron Collider (LHC) or future colliders, probing different dark matter scenarios within IDM provides an exciting opportunity. While the Higgs portal dark matter scenario is extensively well-studied at the LHC, probing the degenerate scalar dark sector presents some unique challenges, not only in detecting excessively soft decay products and the tiny production cross-section expected at the higher masses. The present study explores the potential of a forward muon facility at a future muon collider to uncover this elusive degenerate dark sector.

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arXiv2025

Electroweak Phase Transition, Gravitational Waves and Collider Probes in Multi-Scalar Dark Matter Scenarios

We study scalar singlet extensions of the Standard Model (SM), focusing on scenarios where dark matter (DM) is stabilized by a $\mathbb{Z}_2$ symmetry. In the minimal single-scalar extension of the SM, only a narrow region near the Higgs resonance remains viable, requiring small portal couplings in order to simultaneously satisfy the observed relic abundance and comply with the most recent direct detection limits from the LUX-ZEPLIN (LZ-2024) and XENON1T experiments. To address this limitation, we extend the dark sector by introducing additional real singlet scalars. In both two- and three-singlet extensions, we demonstrate that the observed dark matter relic density can be accommodated with larger Higgs portal couplings. These couplings significantly impact early-Universe dynamics by enhancing the strength of the electroweak phase transition. Both the two- and three-singlet scalar extensions can induce a strong first-order electroweak phase transition, generating stochastic gravitational waves potentially observable at future space-based detectors such as LISA and DECIGO. Notably, the three-singlet scenario induce an even stronger transition compared to the two-singlet case, enhancing the gravitational wave signal strength. Our results highlight the potential of extended scalar sectors as testable frameworks connecting dark matter and gravitational wave signals.

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arXiv2025

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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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 $5.3\,\sigma$ 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 $3.2\,\sigma$, outperforming traditional variables such as $E_b/E_t$ and $\cos\theta_b$.

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arXiv2025

Identifying the net information flow direction pattern in mutually coupled non-identical chaotic oscillators

This paper focuses on a fundamental inquiry in a coupled oscillator model framework. It specifically addresses the direction of net information flow in mutually coupled non-identical chaotic oscillators. Adopting a specific form of conditional mutual information as a model-free and asymmetric index, we establish that if the magnitude of the maximum Lyapunov exponent can be defined as the 'degree of chaos' of a given isolated chaotic system, a predominant net information transfer exists from the oscillator exhibiting a higher degree of chaos to the other while they are coupled. We incorporate two distinct categories of coupled 'non-identical' oscillators to strengthen our claim. In the first category, both oscillators share identical functional forms, differing solely in one parameter value. We also adopt another measure, the Liang-Kleeman information flow, to support the generality of our results. The functional forms of the interacting oscillators are entirely different in the second category. We further extend our study to the coupled oscillator models, where the interacting oscillators possess different dimensions in phase space. These comprehensive analyses support the broad applicability of our results.

nlin.CD↗

arXiv2024

Collider fingerprints of freeze-in dark matter produced during the fast expansion phase of Universe

We examine a simple dark sector extension where the observed dark matter (DM) abundance arises from a freeze-in process through the decay of heavy vector-like quarks into a scalar dark matter candidate. The detection prospects of such DM are challenging due to the feeble nature of the interactions, but these vector-like quarks can be produced copiously at the LHC, where they decay to Standard Model quarks along with DM. Depending on the decay rate, this scenario is typically probed through long-lived particle or displaced vertex signatures, assuming a radiation-dominated background. An alternative hypothesis suggests that the Universe may have experienced a rapid expansion phase instead of the standard radiation-dominated one during freeze-in. This would significantly alter the dark matter phenomenology, requiring a substantial increase in the interaction rate to match the observed relic density, resulting in the rapid decay of the parent particle. As a result, much of the parameter space for this scenario is beyond the reach of traditional long-lived particle and displaced vertex searches. Due to this non-standard cosmic evolution, existing constraints do not cover the expanded dark matter parameter space. We propose a complementary search strategy to explore this scenario, offering additional limits alongside searches for long-lived particles and displaced vertices. In our search, we investigate the FIMP dark matter model at the LHC using boosted fatjets and significant missing transverse momentum. To improve precision, we include one-loop QCD corrections for LHC production processes and employ a boosted decision tree multivariate analysis, leveraging jet substructure variables to explore a vast parameter space for this minimally extended FIMP dark matter model at the 14 TeV LHC.

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arXiv2024

Unveiling desert region in inert doublet model assisted by Peccei-Quinn symmetry

The Inert Higgs Doublet model (IDM), assisted by Peccei-Quinn (PQ) symmetry, offers a simple but natural framework of a dark sector that accommodates Weakly Interacting Massive Particle (WIMP) and axion as dark matter components. Spontaneous breaking of $U(1)_{PQ}$ symmetry, which was originally proposed as an elegant solution to the strong charge-parity (CP) problem, also ensures the stability of WIMP through a residual $\mathbb{Z}_2$ symmetry. Interestingly, additional fields necessitated by PQ symmetry further enrich the dark sector. These include a scalar field proprietor for axion DM and a vector-like quark (VLQ) that acts as a portal for the dark sector through Yukawa interactions. Moreover, this combination of the axion and WIMP components satisfies the observed DM relic density and reopens the phenomenologically exciting region of the IDM parameter space where the WIMP mass falls between 100 - 550 GeV. We investigate the model-independent pair production of VLQs exploring this region at the Large Hadron Collider (LHC), incorporating the effects of next-to-leading order (NLO) QCD corrections. After production, each VLQ decays into a top or bottom quark accompanied by an inert scalar, a consequence of the residual $\mathbb{Z}_2$ symmetry. Utilising relevant observables with a leptonic search channel and employing multivariate analysis, we demonstrate the ability of this analysis to exclude a significant portion of the parameter space with an integrated luminosity of 300 $\text{fb}^{-1}$.

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arXiv2023

Measure synchronization in interacting Hamiltonian systems: A brief review

This paper aims to review the measure synchronization, a weak form of synchronization observed in coupled Hamiltonian systems, briefly. This synchronization is characterized by a Hamiltonian system that displays either quasiperiodic or chaotic dynamics. Each system, in the presence of either linear or nonlinear coupling, shares a phase space domain with an identical invariant measure in the measure synchronized state. It is important to note that while the trajectories are identical in measure, they do not necessarily exhibit complete temporal synchrony. This synchronization has been observed in various physical systems, such as coupled pendulums, Josephson junctions, and lasers.

nlin.CD↗

arXiv2023

Precision prediction of a democratic up-family philic KSVZ axion model at the LHC

In this work, we study the $SU(2)_L$ singlet complex scalar extended KSVZ model that, in addition to providing a natural solution to the strong-CP problem, furnishes two components of dark matter that satisfy observer relic density without fine-tuning the model's parameters. A colored vector-like quark (VLQ) is naturally present in the KSVZ axion model, providing a rich dark matter and collider phenomenology. In this extended model, scalar dark matter interacts with the Standard Model up-type quarks (up, charm, top) through VLQ. We explore the possibility of democratic Yukawa interaction of the VLQ with all up-type quarks and scalar dark matter candidate. We also employ next-to-leading order NLO-QCD correction on dominant production channels for VLQ pair production to study a unique search at the LHC, generating a pair of boosted tops with sizeable missing transverse momentum. Such corrections are significant and reduce factorization and renormalization scale uncertainties substantially. The NLO fixed order results are matched with the Pythia8 parton shower. After being pair-produced, each VLQ decays into a dark matter and a top quark. We conducted a multivariate analysis using jet substructure variables of boosted top fatjets with a significant missing transverse momentum signal. This analysis allows us to explore a substantial parameter space of this model at the 14 TeV LHC.

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arXiv2023

Precise probing and discrimination of third-generation scalar leptoquarks

We explore the pair production of third-generation scalar leptoquark at the Large Hadron Collider to next-to-leading order accuracy in QCD, matched to parton shower for a precise probing of the stemming model. We propose to tag two boosted top-like fatjets produced from the decay of heavy leptoquarks in association with notably large missing transverse momentum and consider them as the potential signal. Such a signal demonstrates the capability of a robust discovery prospect in the multivariate analysis with different high-level observables, including jet substructure variables. Various scalar leptoquark models predict different chirality of the top quark appearing from the decay of the leptoquark carrying same electromagnetic charge. We make use of the polarization variables sensitive to the top quark polarization in order to identify the underlying theory.

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arXiv2022

Occasional coupling enhances amplitude death in delay-coupled oscillators

This paper aims to study amplitude death in time delay coupled oscillators using the occasional coupling scheme that implies the intermittent interaction among the oscillators. An enhancement of amplitude death regions (i.e., an increment of the width of the amplitude death regions along the control parameter axis) can be possible using the occasional coupling in a pair of delay-coupled oscillators. Our study starts with coupled limit cycle oscillators (Stuart-Landau) and coupled chaotic oscillators (Rössler). We further examine coupled horizontal Rijke tubes, a prototypical model of thermoacoustic systems. Oscillatory states are highly detrimental to thermoacoustic systems such as combustors. Consequently, a state of amplitude death is always preferred. We employ the on-off coupling (i.e., a square wave function), as an occasional coupling scheme, to these coupled oscillators. On monotonically varying the coupling strength (as a control parameter), we observe an enhancement of amplitude death regions using the occasional coupling scheme compared to the continuous coupling scheme. In order to study the contribution of the occasional coupling scheme, we perform a detailed linear stability analysis and analytically explain this enhancement of the amplitude death region for coupled limit cycle oscillators. We also adopt the frequency ratio of the oscillators and the time delay between the oscillators as the control parameters. Intriguingly, we obtain a similar enhancement of the amplitude death regions using frequency ratio and time delay as the control parameters in the presence of the occasional coupling. Finally, we use a half-wave rectified sinusoidal wave function (motivated by practical reality) to introduce the occasional coupling in time-delay coupled oscillators and get similar results.

nlin.AO↗

arXiv2022

Early detection of synchrony in coupled oscillator model

In this paper, we study the applicability of an early warning index while studying the transitions to complete and generalized synchronizations in the coupled oscillator models using an unconventional system parameter and the coupling strength as the required control parameters. The coupled oscillator models are widely used and well-documented for studying various aspects of nature. However, the early warning index used in this paper is an explicit function of the mutual information of the coupled oscillators and reaches two different values before the interacting oscillators yield complete and generalized synchronizations. The transitions to synchrony using the unconventional control parameter are associated with a transition to periodic dynamics of the individual oscillators from their initial chaotic dynamics. Besides, when we use the coupling strength as a control parameter, the interacting oscillator exhibits chaotic dynamics during the synchronizations. Our analysis mainly involves different examples of two low-dimensional oscillators. Finally, we extend our study to a network of interacting oscillators. The applicability of the early detection index is verified in all cases.

nlin.AO↗

arXiv2022

Top-philic Dark Matter in a Hybrid KSVZ axion framework

We explore a two-component dark matter scenario in an extended Kim-Shifman-Vainshtein-Zakharov (KSVZ) axion framework. This hybrid setup incorporates an extra $SU(2)_L$ complex singlet scalar whose lightest component plays the role of one of the dark matter, while the QCD axion of the KSVZ model acts as a second dark matter candidate. In this work, we focus on accentuating the role of vector-like quark that naturally emerges in the KSVZ extension on the dark matter and collider phenomenology. Here, we demonstrate that the presence of this colored particle can significantly affect the allowed dark matter parameter space of the scalar dark matter by opening up additional co-annihilation as well as the direct detection channels. Moreover, the interaction between the color particle with the top quark and scalar dark matter provides a unique topology to generate a boosted-top pair with considerable missing transverse momentum at the LHC. Using jet substructure variables and multivariate analysis, here we show that one can already exclude a vast region of parameter space with 139 $\text{fb}^{-1}$ integrated luminosity at 14 TeV LHC.

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arXiv2021

Precise probing of the inert Higgs-doublet model at the LHC

The inert Higgs-doublet model provides a simple framework to accommodate a viable Higgs portal scalar dark matter candidate, together with other heavier scalars of mass 100 GeV or more. We study the effect of next-to-leading order (NLO) QCD corrections in this scenario in the context of the Large Hadron Collider. ${\cal{O}}(\alpha_s)$ corrections to the gluon-gluon-Higgs effective coupling have been taken into account in this study wherever appropriate. We find such corrections have a significant impact on various kinematic distributions and reduce scale uncertainties substantially. Fixed order NLO results are matched to the {\sc Pythia8} parton shower (PS) and the di-fatjet signal associated with the missing transverse momentum is analyzed, as this channel has the ability to explore its entire parameter space during the next phase of the LHC run. A closer look at the NLO+PS computation indicates a sizable NLO effect together with a subdued contribution from associated production of the heavy scalar compared to the pair production, thereby leading to a refined analysis strategy during the multivariate analysis of this signal.

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