arXiv subjects

Biswajit Das

Publications and source records attributed to Biswajit Das.

At least 19 recordsLinked to original sources

arXiv2026

Impact of the Infrared Cutoff on Structure Formation in Tsallis Holographic Dark Energy

We investigate the viability of Tsallis holographic dark energy (THDE) models, focusing on the role of the infrared (IR) cutoff in the growth of cosmic structures. Considering two commonly used choices of the cutoff, the particle horizon and the future event horizon, we analyze the evolution of linear matter perturbations and compute the growth factor, growth rate, and the observable $f\sigma_8(z)$. These predictions are compared with observational data from redshift-space distortion measurements. We find that the growth history is highly sensitive to the choice of IR cutoff. Models based on the future event horizon are consistent with observational data and can provide a fit comparable to, or slightly better than, the $\Lambda$CDM model for suitable values of the Tsallis parameter $\delta$. In contrast, models constructed using the particle horizon generally fail to reproduce the observed growth of structure. These results demonstrate that the viability of THDE models depends crucially on the choice of IR cutoff and highlight the importance of structure formation as a stringent test of generalized holographic dark energy scenarios.

astro-ph.CO↗

arXiv2026

Localizing entropy production along non-equilibrium trajectories

Entropy production is a universal measure of irreversibility and energy dissipation in physical, chemical, and biological systems operating far from equilibrium. However, quantifying and spatiotemporally localising it in complex processes directly from experimental data remains a major open challenge. Here we address this issue through a data-driven approach that combines the recently developed short-time thermodynamic uncertainty relation based inference scheme with machine learning techniques. Our approach leverages the flexible function representation provided by deep neural networks to achieve accurate reconstruction of high-dimensional, potentially time-dependent dissipative force fields as well as the localization of fluctuating entropy production in both space and time along nonequilibrium trajectories. We demonstrate the versatility of the framework through applications to diverse systems of fundamental interest and experimental significance, where it successfully addresses distinct challenges in localising entropy production.

cond-mat.stat-mech↗

arXiv2026

Tunable Optical Torque by Asymmetry-Induced Spin-Hall Effect in Tightly Focused Spinless Gaussian Beams

A linearly polarized Gaussian beam, carrying zero net spin angular momentum, is conventionally not expected to exert optical torque or induce rotational motion in birefringent microparticles. When such a beam is tightly focused, the constituent left- and right-circular polarization components separate spatially due to spin-orbit interaction, commonly known as the spin Hall effect of light. However, this separation is at wavelength scales and is also axially symmetric, resulting in zero net spin angular momentum, and concomitantly no optical torque near the focal plane. Here, we demonstrate that this limitation can be overcome using several commonly encountered asymmetric illumination modalities that break the axial symmetry of the focusing system, thereby disrupting the symmetric separation of the spin components for the same linearly polarized Gaussian beam. As a consequence, trapped microparticles experience a tunable optical torque and exhibit rotational motion with distinct rotational frequencies at the same input power. The particles also undergo controlled reversal of the rotation direction simply by rotating the incident plane of polarization using a half-wave plate. Despite their apparent diversity, all these methods share the same physical origin rooted in asymmetric illumination. These results establish an experimentally accessible and minimal strategy for realizing controllable optical rotation devices exploiting spin-orbit optomechanics without requiring intrinsic angular momentum in the light.

physics.optics↗

arXiv2026

Associated Higgs production in lepton-photon collisions at FCC-ee

Following the HL-LHC era, proposed lepton colliders highlight the need to study various important Higgs boson production mechanisms to precisely probe the Standard Model Higgs sector. We propose a novel mechanism $e^\pm γ\rightarrow {\bar ν}_e (ν_e) H W^\pm$, which can be useful to study Higgs boson properties. This channel is relatively free from the background and can be used to measure the Higgs boson properties, in particular $WWH$ coupling. We examine the viability of this production mechanism. We show that the process can be observed at the planned FCC-ee with the center-of-mass energy of 365 GeV. At the center-of-mass energy of 500 GeV, the process can be observed within a few months of the operation. We use an in-house Monte Carlo event generator that simultaneously incorporates the photon distribution and electron/positron distribution. Our work is also a step towards realistic simulations of lepton- and photon-initiated processes at lepton colliders.

hep-ph↗

arXiv2026

On Patterns and Languages in 1-11-Representations of Graphs

A 1-11-representation of a graph $G(V,E)$ is a word over the alphabet $V$ such that two distinct vertices $x$ and $y$ are adjacent if and only if the restricted word $w{x,y}$ (obtained from $w$ by deleting all letters except $x$ and $y$) contains at most one occurrence of $xx$ or $yy$. Although every graph admits a 1-11-representation, the repetition patterns that may or must appear in such representations have not been fully studied. In this paper, we study cube-free and square-free 1-11-representations of graphs. We first show that cubes cannot always be avoided in 1-11-representations of minimum length by providing a graph for which every minimum-length 1-11-representation necessarily contains a cube. We then focus on permutational 1-11-representations, where the representing word is a concatenation of permutations of the vertex set. In this setting, we prove that any cube appearing in a permutational 1-11-representation can be removed without changing the represented graph. As a consequence, every permutational 1-11-representation attaining the permutational 1-11-representation number is cube-free. We further show that this behaviour does not extend to squares by providing a graph for which every permutational 1-11-representation with the minimum number of permutations necessarily contains a square. Finally, we prove that the language of all 1-11-representations of a given graph is regular. Moreover, we show that the language of all permutational 1-11-representations of a graph is also regular.

math.CO↗

arXiv2025

p-complete square-free Word-representation of Word-representable Graphs

A graph G(V, E) is word-representable if there exists a word w over V such that distinct letters x and y alternate in w iff $xy \in E$. We introduce p-complete squares and p-complete square-free word-representable graphs. A word is p-complete square-free if no induced subword over any subset of letters contains a square XX with $|X| \ge p$. A graph is p-complete square-free if it admits such a representation. We define p-complete square-free uniform word-representations and study their properties. We show that any graph admitting such a representation forbids Kp as an induced subgraph and that the recognition problem is NP-hard for arbitrary p. For p=1 and 2, we give complete characterisations. We prove that every $K_p$-free circle graph admits a p-complete square-free uniform representation and that any 3-complete square-free uniform word-representable graph has representation number at most three. We present a constructive method for generating new examples for p=3.

cs.DM↗

arXiv2025

Design and Evaluation of CZT-based Micro-activity Dose Calibrator for TAT Application using Monte Carlo Simulation

A novel CZT-based micro-activity dose calibrator has been designed via Monte Carlo simulation (GATE) to accurately measure low-level activity 225Ac for targeted alpha therapy (TAT) application. Because even small overdoses in TAT can induce severe local toxicity, activities in the microcurie down to nanocurie regime are often required, and accurate activity measurement by dose calibrators is a priori to safe and effective treatment. Standard dose calibrators, or high-pressurized gas-filled ionization chambers, are not suitable in this range due to limited sensitivity and lack of energy discrimination. To address this, we designed a CZT-based micro-activity calibrator that (i) adopts a box-shaped well geometry to obtain higher solid-angle coverage and (ii) applies time-coincident pixel-level clustering to recover full-energy-peak net counts otherwise lost to multi-site Compton scattering. Using GATE, serial dilutions from 1.0 uCi down to 1e-6 uCi were simulated, activities were reconstructed from the 218 and 440 keV gamma peaks and performance was compared against a NaI(Tl) well counter, which serves as an alternative to standard dose calibrator. Across six orders of magnitude, the CZT-based micro-activity dose calibrator exhibited near-unity linearity (slope m=0.9934) with percent-level bias, whereas the NaI(Tl) counter showed systematic under-response under identical conditions. These results indicate that a CZT-based approach can provide accurate low-activity quantification for TAT, motivating forthcoming hardware validation.

physics.ins-det↗

arXiv2025

A stochastic heat engine driven using a nonlinear protocol

A colloidal particle confined in a time-dependent optical trap can function as a microscopic heat engine, with optimization strategies playing a crucial role in enhancing its performance. In this study, we numerically investigate a Stirling heat engine operating in both passive and active environments using a protocol inspired by the Engineered Swift Equilibration (ESE) method. This approach differs from the standard process and focuses on enhancing engine efficiency, particularly at short time scales. We analyze various fluctuating parameters throughout the cycle to validate the robustness of the engine, and demonstrate a significant enhancement in performance compared to conventional Stirling engines. Most crucially, we observe that the nonlinear protocol can even transform a heat-pump-like operation into a genuine heat engine under strong activity, thereby surpassing bounds imposed on efficiency by high-temperature and quasi-static conditions. Finally, the proposed protocol is designed with experimental feasibility in mind, making it a promising framework for the practical realization of efficient microscopic heat engines.

cond-mat.stat-mech↗

arXiv2025

NLO QCD effects on angular observables in $e^-p \to e^-(ν_e)Hj$ in presence of non-standard $HVV$ couplings

The single Higgs production in neutral-current (NC) and charged-current (CC) processes at an electron-proton ($ep$) collider is a useful channel to probe new physics effects in the Higgs coupling to vector boson ($HVV$). In this context, observables sensitive to non-standard couplings previously studied at leading order require improved theoretical precision through the inclusion of radiative corrections. In this work, we present a fully differential Higgs plus one jet production at next-to-leading-order (NLO) accuracy in QCD for both the NC and CC processes. For the proposed Large Hadron electron Collider (LHeC) configuration, with a 60~GeV electron beam and a 7~TeV proton beam, the total cross sections receive modest corrections with significantly reduced scale uncertainties. We find that in several kinematic distributions which are relevant to the analysis of $HVV$ couplings, the NLO K-factors are not flat. Within the Standard Model, the polar angle of the electron (for NC) and the azimuthal angular correlation (for both NC and CC processes) receive maximum corrections in the range of 8-10\% in certain bins. We also compute NLO QCD corrections in the presence of non-standard $HVV$ interactions. The corrections in the azimuthal angular correlations are similar to the standard model predictions. For the polar angle of the electron, the corrections are sensitive to the nature of the $HVV$ coupling.

hep-ph↗

arXiv2025

Word-Representable Co-Bipartite Graphs: Vertex Ordering, Representation Number, Speed, and Entropy

A graph $G(V, E)$ is word-representable if there exists a word $w$ over the alphabet $V$ such that for distinct letters $x,y\in V$, $x$ and $y$ alternate in $w$ if and only if they are adjacent in $G$. In general, determining whether a graph is word-representable is an NP-complete problem. A graph is co-bipartite if its complement is bipartite. Therefore, the vertex set of a co-bipartite graph can be partitioned into two disjoint subsets $X$ and $Y$ such that the subgraphs induced by $X$ and $Y$ are cliques. In this paper, we obtain necessary and sufficient conditions for a co-bipartite graph to be word-representable in terms of a vertex ordering. Based on this ordering, we study the representation number of word-representable co-bipartite graphs and analyse the speed and entropy of this graph class. We show that the representation number of any word-representable co-bipartite graph is at most $3$, and that permutation graphs are the only co-bipartite graphs with representation number $2$. We prove that the speed is $2^{O(n \log n)}$ and the entropy is $0$. This provides an asymptotic bound on the number of labelled graphs in this class, which is significantly smaller than the known bound for the class of all co-bipartite graphs. These results provide a better understanding of the structure and enumeration of word-representable co-bipartite graphs and show that vertex ordering is an effective tool for studying this class.

math.CO↗

arXiv2025

Effect of anomalous $HHH$ coupling on the decay $H\rightarrow Z\,Z^*\rightarrow$ 4 charged leptons

We have computed the electroweak corrections to $H\rightarrow Z\,Z^*\rightarrow$ 4 charged leptons, including the effect of anomalous $HHH$ coupling in the $κ$-framework. The results of this scaling are gauge invariant. We have computed the results for $ H \to e^+ e^- μ^+ μ^-$ and $ H \to e^+ e^- e^+ e^-$ processes. The corrections for the both processes depend on the input parameter scheme. In the $G_F$ scheme, the electroweak corrections are about $1.26\%$ for the $ H \to e^+ e^- μ^+ μ^-$ and about $0.25\%$ for the $ H \to e^+ e^- e^+ e^-$ process. However changing the $κ$ from $4$ to $-4$, the corrections vary from less than $1\%$ to about $-6\%$. We have plotted a number of kinematic distributions. The corrections over most of the phase space regions are similar. These large corrections can be used to put a bound on the $HHH$ coupling. This can help in determining the structure of the Higgs potential.

hep-ph↗

arXiv2025

Decoding active force fluctuations from spatial trajectories of active systems

Mesoscopic active systems exhibit various unique behaviours - absent in passive systems - due to the forces generated by the corresponding constituents by converting their available free energies. However, estimating these forces - which are also stochastic and remain intertwined with the thermal noise - is especially non-trivial. Here, we introduce a technique to extract such fluctuating active forces acting on a passive particle immersed in an active bath with high statistical accuracy by filtering out the related thermal noise. We first test the efficacy of our method under numerical scenarios with different types of activity, and then apply it to the experimental trajectories of a microscopic particle (optically) trapped inside an active bath consisting of motile \textit{E.Coli.} bacteria. We believe that our simple yet powerful approach, which appears agnostic to the nature of the active force, should enable accurate measurement of force dynamics in living matter and potentially allow direct but reliable estimation of key thermodynamic parameters such as heat, work, and entropy production.

cond-mat.soft↗

arXiv2025

Unravelling the Flow of Information in a Nonequilibrium Process in the Presence of Hydrodynamic Interactions

Identifying the origin of nonequilibrium characteristics in a generic interacting system having multiple degrees of freedom is a challenging task. In this context, information theoretic measures such as mutual information and related polymorphs offer valuable insights. Here, we explore these measures in a minimal experimental model consisting of two hydrodynamically coupled colloidal particles, where a nonequilibrium drive is introduced via an exponentially correlated noise acting on one of the particles. We show that the information-theoretic tools considered enable a systematic, data-driven dissection of information flow within the system. These measures allow us to identify the driving node and reconstruct the directional dependencies between particles. Notably, they help explain a recently observed, counterintuitive trend in the dependence of irreversibility on interaction strength under coarse-graining (B. Das et.al., arXiv:2405.00800 (2024)). Finally, our results demonstrate how directional information measures can uncover the hidden structure of nonequilibrium dynamics and provide a framework for studying similar effects in more complex systems.

cond-mat.stat-mech↗

arXiv2025

Simultaneous active and diffusive behaviour of asymmetric microclusters in a photophoretic trap

Active and diffusive motion in Brownian particles are regularly observed in fluidic environments, albeit at different time scales. Here, we experimentally study the dynamics of highly asymmetric microclusters trapped in air employing photophoretic forces generated from a loosely focused laser beam, where the trapped particles display active and diffusive dynamics simultaneously in orthogonal spatial directions. Thus, particle motion in the longitudinal direction ($z$) is enslaved to irregular kicks that naturally arise from an interplay of gravitational and photophoretic forces. This leads to a bimodal nature of the probability distribution function with a near-ballistic scaling of mean-squared displacement in the $z$ direction demonstrating active like dynamics, while the dynamics along the transverse ($x$) direction displays diffusive behaviour with a strong dependence on the motion along $z$. To explain these unique characteristics, we developed a 2D-Langevin model of a confined elliptic particle experiencing an additional stochastic force along $z$ to account for the arbitrary jumps. The numerical results show excellent qualitative agreement with the experimental observations. Our findings should pave the way for the design of high-efficiency Brownian engines in air, besides stimulating new research in the emerging field of photophoretic trapping.

physics.optics↗

arXiv2025

Irreversibility of mesoscopic processes with hydrodynamic interactions

Optically confined colloidal particles, when placed in close proximity, form a dissipatively coupled system through hydrodynamic interactions. The role of such interactions influencing irreversibility and energy dissipation in out-of-equilibrium systems is often not well deciphered. Here, we demonstrate - through the estimation of the entropy production rate - that the nonequilibrium features of the system with such interactions vary depending on the nature of external driving, and importantly, on the level of coarse-graining. Crucially, we show that coarse-graining reverses the dependence of the measured entropy production rate on the strength of the hydrodynamic interactions. Furthermore, we clarify that such interactions do not violate energy balance at the level of individual trajectories, as was believed earlier. Our results highlight a previously unnoticed effect of coarse-graining in nonequilibrium systems, and have implications for the inference of entropy production in experimental contexts.

cond-mat.stat-mech↗

arXiv2025

NLO QCD effects on angular observables in single Higgs production at electron-proton collider

Properties of the Higgs boson ($H$) at current and future particle colliders are crucial to explore new physics beyond the standard model. In particular, experimental and theoretical outlooks at future colliders drive interest in Higgs to gauge boson couplings. Single Higgs production via vector-boson fusion allows probing Higgs couplings with massive vector bosons ($V = W, Z$). We consider electron-proton (eP) collider to study these couplings due to the low background. In a recent study, we considered the most general anomalous Higgs-vector boson ($HVV$) couplings and explored the potential of eP collider in constraining the parameters of $HVV$ couplings. Our results were based on leading order predictions in perturbation theory. We include further Next to Leading Order (NLO) corrections of Quantum Chromodynamic (QCD) in Standard Model signal to make precise predictions. In this talk, I will present the effect of NLO QCD corrections on the standard model and anomalous $HVV$ couplings.

hep-ph↗

arXiv2025

Word-representability of co-bipartite graph

A graph $G = (V, E)$ is word-representable, if there exists a word $w$ over the alphabet $V$ such that for letters $\{x,y\}\in V$, $x$ and $y$ alternate in $w$ if and only if $xy \in E$. A graph is co-bipartite if its complement is a bipartite graph. Therefore, the vertex set of a co-bipartite graph can be partitioned into two disjoint cliques. The concept of word-representability for co-bipartite graphs has not yet been fully studied. In the book Words and Graphs written by Sergey Kitaev and Vadim Lozin, examples of co-bipartite graphs that are not word-representable are provided. The authors have stated that it remains an open problem to characterize word-representable co-bipartite graphs. It is known that taking the complement of word-representable graphs does not preserve their word-representability. In this paper, we first identify certain classes of bipartite graphs for which word-representation is preserved after the complement operation. We found that the complement of the path graphs, even cycle graphs and generalized crown graphs are also word-representable. Next, we aim to find word-representable co-bipartite graphs in which the size of one clique partition is fixed while the other one can vary. We studied the word-representability of co-bipartite graphs where the sizes of one clique partition are $2$ and $3$. We found that any co-bipartite graphs where the size of the one clique partition is $2$ are word-representable. Also, when the size of the one clique partition is $3$, we found certain co-bipartite graphs are word-representable. Additionally, for word-representable graphs, it has been established that a graph is word-representable if and only if it can be oriented in a specific manner, known as semi-transitive orientation. We provide the necessary and sufficient conditions for a co-bipartite graph to have a semi-transitive orientation.

math.CO↗

arXiv2024

Next-to-leading order QCD corrections to $Z\to q\bar{q}γ$, $q\bar{q}γγ$

We consider the rare decay channels of the $Z$ boson: $Z \to \text{two}\ \textrm{jets} + γ$ and $Z \to \text{two}\ \textrm{jets} +2\, γ$. To obtain the widths and distributions for these processes, we compute the effect of NLO QCD corrections to the processes $Z \to q {\bar q}+ γ$ and $Z \to q {\bar q} +2\, γ$. We find that these corrections reduce the widths of these processes by about $6.03\%$ and $12.39\%$, respectively. The reduction in the partial widths is larger at the jet level. These NLO-improved decay observables may be tested in future runs of the LHC or at future $e^{+}e^{-}$ colliders.

hep-ph↗