arXiv subjects

Indranil Mukherjee

Publications and source records attributed to Indranil Mukherjee.

18 recordsLinked to original sources

arXiv2026

Quasiparticle Diffusion for the Toda Fluid in Equilibrium

Many-body integrable systems can be understood as a gas of quasiparticles. They propagate ballistically and drive large-scale transport. However, with the exception of the hard rods system, no tools have been available to numerically track such quasiparticles. Focusing on the Toda fluid, whose integrability relies on the availability of a Lax pair, we present a numerical scheme to track quasiparticle trajectories as determined by the time-dependent eigenvectors of the Lax matrix. Simulating the Toda fluid in thermal equilibrium, this tracking scheme is used to numerical confirm Brownian motion of a quasiparticle. Simulated is also the motion of a tagged particle. Our numerical results for the diffusion constant matches with a novel TBA prediction. We believe our numerical scheme can be extended to other classical many-particle models possessing a Lax matrix.

cond-mat.stat-mech↗

arXiv2026

Microscopic and hydrodynamic correlation in 1d hard rod gas

We compute mass density correlations of a one-dimensional gas of hard rods at both microscopic and macroscopic scales. We provide exact analytical calculations of the microscopic correlation. For the correlation at macroscopic scale, we utilize Ballistic Macroscopic Fluctuation Theory (BMFT) to derive an explicit expression for the correlations of a coarse-grained mass density, which reveals the emergence of long-range correlations on the Euler space-time scale. By performing a systematic coarse-graining of our exact microscopic results, we establish a micro-macro correspondence and demonstrate that the resulting macroscopic correlations agree precisely with the predictions of BMFT. This analytical verification provides a concrete validation of the underlying assumptions of hydrodynamic theory in the context of hard rod gas.

cond-mat.stat-mech↗

arXiv2025

Stochastic dynamics of quasiparticles in the hard rod gas

We consider a one-dimensional gas of hard rods, one of the simplest examples of an interacting integrable model. It is well known that the hydrodynamics of such integrable models can be understood by viewing the system as a gas of quasiparticles. Here, we explore the dynamics of individual quasiparticles for a variety of initial conditions of the background gas. The mean, variance, and two-time correlations are computed exactly and lead to a picture of quasiparticles as drifting Brownian particles. For the case of a homogeneous background, we show that the motion of two tagged quasiparticles is strongly correlated, and they move like a rigid rod at late times. Apart from a microscopic derivation based on the mapping to point particles, we provide an alternate derivation which emphasizes that quasiparticle fluctuations are related to initial phase-space fluctuations, which are carried over in time by Euler scale dynamics. For the homogeneous state, we use the Brownian motion picture to develop a Dean-Kawasaki-type fluctuating hydrodynamic theory, formally having the same structure as that derived recently by Ferrari and Olla. We discuss differences with existing proposals on the hydrodynamics of hard rods and some puzzles.

cond-mat.stat-mech↗

arXiv2025

Quasi-integrability from PT-symmetry

Parity and time-reversal (PT ) symmetry is shown as the natural cause of quasi-integrability of deformed integrable models, crucial to represent real physical systems as they posses various irregularities. The condition for asymptotic conservation of quasi-conserved charges appear as a direct consequence of the PT -symmetric phase of the system, ensuring definite PT -properties of the corresponding Lax pair as well as that of the anomalous contribution, consistent with the Wilson-loop criterion for integrability-like behavior. As a result, the quasi-deformed charge densities always acquire definite PT -properties suitable for the asymptotic conservation, as the Abelianization approach to construct them also preserves the definite PT -behavior of the Lax pair. This PT -symmetry based origin of quasi-conservation is general and has been demonstrated for quasi-deformations of multiple systems such as KdV, NLSE and non-local NLSE.

nlin.SI↗

arXiv2025

Spectra of T-vertex and T-edge neighbourhood corona of Two Graphs

The $T$-graph $T(G)$ of a graph $G$ is the graph whose vertices are the vertices and edges of $G$, with two vertices of $T(G)$ are adjacent if and only if the corresponding elements of $G$ are adjacent or incident. In this paper, we determine the adjacency and Laplacian spectra of $T$-vertex neighborhood corona and $T$-edge neighborhood corona of a connected regular graph with an arbitrary regular graph in terms of their eigenvalues. Moreover, applying these results we construct some non-regular $A$-cospectral and $L$-cospectral graphs.

math.CO↗

arXiv2025

Percolation of systems having hyperuniformity or giant number-fluctuations

We generate point configurations (PCs) by thresholding the local energy of the Ashkin-Teller model in two dimensions (2D) and study the percolation transition at different values of $\lambda$ along the critical Baxter line by varying the threshold that controls the particle density $\rho$. For all values of $\lambda$, the PCs exhibit power-law correlations with a decay exponent $a$ that remains independent of $\rho$ and varies continuously with $\lambda$. For $\lambda < 0$, where the PCs are hyperuniform, the percolation critical behavior is identical to that of ordinary percolation. In contrast, for $\lambda > 0$, the configurations exhibit giant number fluctuations, and all critical exponents vary continuously, but form a superuniversality class of percolation transition in 2D.

cond-mat.stat-mech↗

arXiv2024

Hyperuniformity in Ashkin-Teller model

We show that equilibrium systems in $d$ dimension that obey the inequality $d\nu> 2,$ known as Harris criterion, exhibit suppressed energy fluctuation in their critical state. Ashkin-Teller model is an example in $d=2$ where the correlation length exponent $\nu$ varies continuously with the inter-spin interaction strength $\lambda$ and exceeds the value $\frac d2$ set by Harris criterion when $\lambda$ is negative; there, the variance of the subsystem energy across a length scale $l$ varies as $l^{d-\alpha}$ with hyperuniformity exponent $\alpha = 2(1-\nu^{-1}).$ Point configurations constructed by assigning unity to the sites which has coarse-grained energy beyond a threshold value also exhibit suppressed number fluctuation and hyperuniformiyty with same exponent $\alpha.$

cond-mat.stat-mech↗

arXiv2023

Hidden superuniversality in systems with continuous variation of critical exponents

Renormalization group theory allows continuous variation of critical exponents along a marginal direction (when there is one), keeping the scaling relations invariant. We propose a super universality hypothesis (SUH) suggesting that, up to constant scale factors, the scaling functions along the critical line must be identical to that of the base universality class even when all the critical exponents vary continuously. We demonstrate this in the Ashkin Teller (AT) model on a two-dimensional square lattice where two different phase transitions occur across the self-dual critical line: while magnetic transition obeys the weak-universality hypothesis where exponent ratios remain fixed, the polarization exhibits a continuous variation of all critical exponents. The SUH not only explains both kinds of variations observed in the AT model, it also provides a unified picture of continuous variation of critical exponents observed in several other contexts.

cond-mat.stat-mech↗

arXiv2023

How motility affects Ising transitions

We study a lattice gas model of hard-core particles on a square lattice experiencing nearest neighbour attraction $J$. Each particle has an internal orientation, independent of the others, that point towards one of the four nearest neighbour and it can move to the neighbouring site along that direction with the usual Metropolis rate if the target site is vacant. The internal orientation of the particle can also change to any of the other three with a constant rate $\omega.$ The dynamics of the model in $\omega\to \infty$ reduces to that of the Lattice Gas (LG) which exhibits a phase separation transition at particle density $\rho=\frac12$ and temperature $T=1,$ when the strength of attraction $J$ crosses a threshold value $\ln(1+ \sqrt{2}).$ This transition belongs to Ising universality class. For any finite $\omega>0,$ the particles can be considered as attractive run-and-tumble particles (RTPs) in two dimensions with motility $\omega^{-1}.$ We find that RTPs also exhibit a phase separation transition, but the critical interaction required is $J_c(\omega)$ which increases monotonically with increased motility $\omega^{-1}.$ It appears that the transition belongs to Ising universality class. Surprisingly, in these models, motility impedes cluster formation process necessitating higher interaction to stabilize microscopic clusters. Moreover, MIPS like phases are not found when $J=0.$

cond-mat.stat-mech↗

arXiv2023

Nonexistence of motility induced phase separation transition in one dimension

We introduce and study a model of hardcore particles obeying run-and-tumble dynamics on a one-dimensional lattice, where particles run in either +ve or -ve $x$-direction with an effective speed $v$ and tumble (change their direction of motion) with a constant rate $ω.$ We show that the coarse-grained dynamics of the system can be mapped to a beads-in-urn model called misanthrope process where particles are identified as urns and vacancies as beads that hop to a neighbouring urn situated in the direction opposite to the current. The hop rate, same as the magnitude of the current, depends on the total number of beads present in the departure and the arrival urn; we calculate it analytically and show that it does not satisfy the criteria required for a phase separation transition. Tumbling is generally detrimental to the stability of jamming; thus, our results for this restricted tumbling model strongly suggest that motility induced phase separation transition can not occur in one dimension.

cond-mat.stat-mech↗

arXiv2022

Describing the effect of influential spreaders on the different sectors of Indian market: a complex networks perspective

Market competition has a role which is directly or indirectly associated with influential effects of individual sectors on other sectors of the economy. The present work studies the relative position of a product in the market through the identification of influential spreaders and its corresponding effect on the other sectors of the market using complex network analysis during the pre-, in-, and post-crisis induced lockdown periods using daily data of NSE from December, 2019 to June, 2021. The existing approaches using different centrality measures failed to distinguish between the positive and negative influences of the different sectors in the market which act as spreaders. To obviate this problem, this paper presents an effective measure called LIEST (Local Influential Effects for Specific Target) that can examine the positive and negative influences separately with respect to any crisis period. LIEST considers the combined impact of all possible nodes which are at most three steps away from the specific targets for the networks. The essence of non-linearity in the network dynamics without considering single node effect becomes visible particularly in the proposed network.

physics.soc-ph↗

arXiv2022

Non-holonomic and Quasi-integrable deformations of the AB Equations

For the first time, both non-holonomic and quasi-integrable deformations are obtained for the AB system of coupled equations. The AB system models geophysical and atmospheric fluid motion along with ultra-short pulse propagation in nonlinear optics and serves as a generalization of the well-known sine-Gordon equation. The non-holonomic deformation retains integrability subjected to higher-order differential constraints whereas the quasi-AB system, which is partially deviated from integrability, is characterized by an infinite subset of quantities (charges) that are conserved only asymptotically given the solution possesses definite space-time parity properties. Particular localized solutions to both these deformations of the AB system are obtained, some of which are qualitatively unique to the corresponding deformation, displaying similarities with physically observed excitations.

math-ph↗

arXiv2021

Particle hopping on a ladder: exact solution using multibalance

We study particle hopping on a two-leg ladder where a particle can jump to their immediate neighbours, one at a time, with rates that depend on the occupation of the departure site and a neighbouring site on the other leg. For specific choices of rates, the model can be solved using pairwise balance known earlier. For the other regimes, we introduce a new balance condition called multibalance which helps us in obtaining the exact steady state. The direction of the total current in these models does not necessarily decide the direction of the currents in individual legs; we find the regions in the parameter space where the currents in individual legs alter their direction. In some parameter regime, the total current exhibits the re-entrance phenomena, in the sense that the total current flips its direction with increase of certain parameter and flips it again when the parameter is increased further. It turns out that the multibalance condition we introduce here is very useful and it can be applied generically to several other models. We discuss some of these models in short.

cond-mat.stat-mech↗

arXiv2021

Multibalance conditions in nonequilibrium steady states

We study a new balance condition multibalance to obtain the nonequilibrium steady states of a class of nonequilibrium lattice models on a ring where a particle hops from a particular site to its nearest and next nearest neighbours. For the well-known zero range process (ZRP) with asymmetric hop rates, with this balance condition, we obtain the conditions on hop rates that lead to a factorized steady state (FSS). We show that this balance condition gives the cluster-factorized steady state (CFSS) for finite range process (FRP) and other models. We also discuss the application of multibalance condition to two species FRP model with hop rates ranging up to K nearest neighbours.

cond-mat.stat-mech↗

arXiv2019

Analysis and comparative study of non-holonomic and quasi-integrable deformations of the Nonlinear Schrödinger Equation

The non-holonomic deformation of the nonlinear Schrödinger equation, uniquely obtained from both the Lax pair and Kupershmidt's bi-Hamiltonian [Phys. Lett. A 372, 2634 (2008)] approaches, is compared with the quasi-integrable deformation of the same system [Ferreira et. al. JHEP 2012, 103 (2012)]. It is found that these two deformations can locally coincide only when the phase of the corresponding solution is discontinuous in space, following a definite phase-modulus coupling of the non-holonomic inhomogeneity function. These two deformations are further found to be not gauge-equivalent in general, following the Lax formalism of the nonlinear Schrödinger equation. However, asymptotically they converge for localized solutions as expected. Similar conditional correspondence of nonholonomic deformation with a non-integrable deformation, namely, due to local scaling of the amplitude of the nonlinear Schrödinger equation is further obtained.

nlin.SI↗

arXiv2019

Study of Non-Holonomic Deformations of Non-local integrable systems belonging to the Nonlinear Schrodinger family

The non-holonomic deformations of non-local integrable systems belonging to the Nonlinear Schrodinger family are studied using the Bi-Hamiltonian formalism as well as the Lax pair method. The non-local equations are first obtained by symmetry reductions of the variables in the corresponding local systems. The bi-Hamiltonian structures of these equations are explicitly derived. The bi-Hamiltonian structures are used to obtain the non-holonomic deformation following the Kupershmidt ansatz. Further, the same deformation is studied using the Lax pair approach and several properties of the deformation discussed. The process is carried out for coupled non-local Nonlinear Schrodinger and Derivative Nonlinear Schrodinger (Kaup Newell) equations. In case of the former, an exact equivalence between the deformations obtained through the bi-Hamiltonian and Lax pair formalisms is indicated

nlin.SI↗

arXiv2017

Study of quasi-integrable and non-holonomic deformation of equations in the NLS and DNLS hierarchy

The hierarchy of equations belonging to two different but related integrable systems, the Nonlinear Schrödinger and its derivative variant, DNLS are subjected to two distinct deformation procedures, viz. quasi-integrable deformation (QID) that generally do not reserve the integrability, only asymptotically integrable, and non-holonomic deformation (N HD) that does. QID is carried out generically for the NLS hierarchy while for the DNLS hierarchy, it is first done on the Kaup-Newell system followed by other members of the family. No QI anomaly is observed at the level of EOMs which suggests that at that level the QID may be identified as some integrable deformation. NHD is applied to the NLS hierarchy generally as well as with the specific focus on the NLS equation itself and the coupled KdV type NLS equation. For the DNLS hierarchy, the Kaup-Newell(KN) and Chen-Lee-Liu (CLL) equations are deformed non-holonomically and subsequently, different aspects of the results are discussed.

math-ph↗

arXiv2014

Study of the family of Nonlinear Schrodinger equations by using the Adler-Kosant-Symes framework and the Tu methodology and their Non-holonomic deformation

The objective of this work is to explore the class of equations of the Non-linear Schrodinger type by employing the Adler-Kostant-Symes theorem and the Tu methodology.In the first part of the work, the AKS theory is discussed in detail showing how to obtain the non-linear equations starting from a suitably chosen spectral problem.Equations derived by this method include different members of the NLS family like the NLS, the coupled KdV type NLS, the generalized NLS, the vector NLS, the Derivative NLS, the Chen-Lee-Liu and the Kundu-Eckhaus equations. In the second part of the paper, the steps in the Tu methodology that are used to formulate the hierarchy of non-linear evolution equations starting from a spectral problem, are outlined. The AKNS, Kaup-Newell, and generalized DNLS hierarchies are obtained by using this algorithm. Several reductions of the hierarchies are illustrated. The famous trace identity is then applied to obtain the Hamiltonian structure of these hierarchies and establish their complete integrability. In the last part of the paper, the non-holonomic deformation of the class of integrable systems belonging to the NLS family is studied. Equations examined include the NLS, coupled KdV-type NLS and Derivative NLS (both Kaup-Newell and Chen-Lee-Liu equations). NHD is also applied to the hierarchy of equations in the AKNS system and the KN system obtained through application of the Tu methodology.Finally, we discuss the connection between the two formalisms and indicate the directions of our future endeavour in this area.

nlin.SI↗