arXiv subjects

Benoy Talukdar

Publications and source records attributed to Benoy Talukdar.

At least 19 recordsLinked to original sources

arXiv2025

Travelling wave solutions of equations in the Burgers Hierarchy

We emphasize that construction of travelling wave solutions for partial differential equations is a problem of considerable interest and thus introduce a simple algebraic method to generate such solutions for equations in the Burgers hierarchy. Our method based on a judicious use of the well known Cole-Hopf transformation is found to work satisfactorily for higher Burgers equations for which the direct method of integration is inapplicable. For Burgers equation we clearly demonstrate how does the diffusion term in the equation counteract the nonlinearity to result in a smooth wave. We envisage a similar study for higher equations in the Buggers hierarchy and establish that (i) as opposed to the solution of the Burgers equation, the purely nonlinear terms of these equations support smooth solutions and more interestingly (ii) the complete solutions of all higher-order equations are identical.

nlin.SI↗

arXiv2025

Travelling-wave solutions and solitons of KdV, mKdV and NLS equations

We introduce the concept of soliton solutions of integrable nonlinear partial differential equations and point out that the inverse spectral method represents the rigorous mathematical formalism to construct such solutions. We work with the travelling waves of the KdV, mKdV and nonlinear Schr\"{o}dinger (NLS) equations and derive a pedagogic method to find their soliton solutions. The travelling wave of the KdV equation leads directly to the well known bell type KdV soliton while the mKdV equation needs some additional consideration in respect of this. The travelling waves of a generalized mKdV and NLS equations are obtained in terms of $sn(u,m)$, the so called Jacobi elliptic sine function. The choice $m=1$ provides a constraint on the parameters of the equations and gives their kink and anti-kink soliton solutions. We further show that by expressing the travelling waves of these equations in terms of Jacobi elliptic cosine functions, $cn(u,m)$, it is possible to construct bell-type soliton solutions.

math-ph↗

arXiv2025

On the solution and Lagrangian representation of Duffing oscillator with damping

We construct the equation of Duffing oscillator in a dissipative medium using certain concepts from elementary mechanics. The Duffing equation (DE) without damping can be solved analytically. This is not true for a DE that involves a damping term. We remove the damping term from a linearly damped DE and thus obtain a simple analytical solution x(t) of the damped Duffing equation in the weak damping limit. The constructed solution allows us to examine the effect of damping on the phase path of the oscillator. The phase path is a parametric plot of x(t) and x = dxdt on the plane (x, x). While the phase path of the un-damped Duffing oscillator is an isolated limit cycle, the corresponding phase path for the Duffing oscillator with damping is a distorted one. We confirm our observation on the effect of dissipation by numerical simulation. We point out that it is often of interest to study dissipative systems at the quantum level and construct Lagrangian representations for both un-damped and damped Duffing oscillators. These results are expected to play a role to quantize the systems. We make some additional comments in respect of this.

physics.class-ph↗

arXiv2024

Inverse variational problem for equations in the Riccati chain

The nonstandard Lagrangian representations of Ricatti and Riccati-type equations that exist in the literature cannot be obtained using Helmholtz solution of the inverse problem. In this work we consider Riccati and higher-order Riccati equations and construct their standard Lagrangian representation by using a simple variant of the Helmholtz theory. We make use of the self-adjoint form of the linear equations corresponding to odd-order equations in the Riccati chain to provide a symmetry-based approach for the solution of inverse problem. Explicit results presented for Lagrangians of the first and third-order Riccati equations show that one cannot Hamiltonize the Riccati family of equations by the traditional method used in classical mechanics.

math-ph↗

arXiv2024

Null Lagrangians in Schwarzian mechanics

In addition to standard and non-standard Lagrangians of classical mechanics, we consider, in this work, null Lagrangians that (i) identically satisfy the Euler-Lagrange equation and at the same time can be expressed as (ii) the total derivative of some scalar function. As an addendum to the properties in (i) and (ii) we find that null Lagrangians are also characterized by (iii) vanishing energy functions or Jacobi integrals. By working with higher-order SL(2;R) invariant Schwarzian derivatives introduced recently by Krivonos we demonstrate that these Schwarzians, especially the even-order ones, provide a natural basis to introduce higher-order null Lagrangians in Schwarzian mechanics.

math-ph↗

arXiv2023

Compressing the atomic cloud in a matter-wave stripe soliton

We consider an attractive quasi-one dimensional spin-orbit coupled Bose-Einstein condensate (SOC BEC) confined in a periodic potential produced by the combination of linear and nonlinear optical lattices, and study the effects of squeezing a stripe soliton by varying the inter-atomic interaction in the nonlinear lattice. It is observed that the nodes on the soliton arising entirely due to the effect of spin-orbit coupling tend to disappear as we increase the squeezing effect to finally get a stable fundamental soliton. This leads us to conclude that external pressure can reduce the effect of spin-orbit coupling in the SOC BEC and even convert the system to a traditional BEC without spin-orbit coupling. We make use of an information theoretic measure to visualize how does the atomic density distribution in the condensate respond to continual reduction in the spin-orbit coupling effect.

cond-mat.quant-gas↗

arXiv2022

Satyendra Nath Bose: Quantum statistics to Bose-Einstein condensation

Satyendra Nath Bose is one of the great Indian scientists. His remarkable work on the black body radiation or derivation of Planck's law led to quantum statistics, in particular, the statistics of photon. Albert Einstein applied Bose's idea to a gas made of atoms and predicted a new state of matter now called Bose-Einstein condensate. It took 70 years to observe the predicted condensation phenomenon in the laboratory. With a brief introduction to the formative period of Professor Bose, this research survey begins with the founding works on quantum statistics and, subsequently, provides a brief account of the series of events terminating in the experimental realization of Bose-Einstein condensation. We also provide two simple examples to visualize the role of synthetic spin-orbit coupling in a quasi-one-dimensional condensate with attractive atom-atom interaction.

physics.hist-ph↗

arXiv2022

Schwarzian derivative in higher-order Riccati equations

The Sturm-Liouville equation represents the linearized form of the first-order Riccati equation. This provides an evidence for the connection between Schwarzian derivative and this first-order nonlinear differential equation. Similar connection is not obvious for higher-order equations in the Riccati chain because the corresponding linear equations are of order greater than two. With special attention to the second- and third-order Riccati equations we demonstrate that Schwarzian derivative has a natural space in higher Riccati equations. There exist higher-order analogues of the Schwarztan derivative. We demonstrate that equations in the Riccati hierarchy are embedded in these higher-order derivatives.

math-ph↗

arXiv2021

Information theoretic approach to effects of spin-orbit coupling in Bose-Einstein condensates

We make use of Shannon entropy ($S$) and Fisher information ($I$) to study the response of atomic density profiles of a spin-orbit coupled Bose-Einstein condensate to changes in the wave number ($κ_L$) of the Raman laser that couples two hyperfine states of atoms in the condensate. The choice for values of $κ_L$, the so-called spin-orbit parameter, and Rabi frequency ($Ω$) leads to two distinct regions in the system's energy spectrum with different order parameters and/or probability densities. In addition, we can have a spatially modulated density profile, reminiscent of the so called stripe phase. Our numbers for $S$ and $I$ demonstrate that for $κ_L^2<Ω$ (region 1) the density profile becomes localized as $κ_L$ increases while we observe delocalization in the density distribution for $κ_L^2>Ω$ (region 2) for increasing values of $κ_L$. In the stripe phase the nature of $S$ and $I$ to changes in $κ_L$ is similar to that found for the condensate in region 2. The results for information theoretic quantities in the stripe phase are, in general, augmented compared to those of region 2. In particular, the highly enhanced values of position-space Fisher information imply an extremely concentrated atomic density distribution to provide an evidence for supersolid properties of Bose-Einstein condensates in the presence of spin-orbit coupling.

cond-mat.quant-gas↗

arXiv2021

Effects of optical lattices on bright solitons in spin-orbit coupled Bose-Einstein condensates

The stationary bright solitons that appear in the ground state of the spin-orbit coupled Bose-Einstein condensate (SOC-BEC) exhibit nodes. We consider SOC-BEC in combined linear and nonlinear optical lattices and study their effects on the matter-wave bright soliton and find that the parameters of the nonlinear lattice or atomic scattering length can be judiciously manipulated to have useful control over the nodes of the soliton. It is seen that the soliton with large number of nodes is less stable compared to one having fewer number of nodes. We infer that that the synthetic spin-orbit coupling induces instability in the ordinary matter-wave soliton.

physics.atom-ph↗

arXiv2020

Integrable systems: From the inverse spectral transform to zero curvature condition

This \textquoteleft research-survey' is meant for beginners in the studies of integrable systems. Here we outline some analytical methods for dealing with a class of nonlinear partial differential equations. We pay special attention to \textquoteleft inverse spectral transform', \textquoteleft Lax pair representation', and \textquoteleft zero-curvature condition' as applied to these equations. We provide a number of interesting examples to gain some physico-mathematical feeling for the methods presented.

nlin.SI↗

arXiv2020

Inverse variational problem for nonlinear dynamical systems

In this paper we have chosen to work with two different approaches to solving the inverse problem of the calculus of variation. The first approach is based on an integral representation of the Lagrangian function that uses the first integral of the equation of motion while the second one relies on a generalization of the well known Noether's theorem and constructs the Lagrangian directly from the equation of motion. As an application of the integral representation of the Lagrangian function we first provide some useful remarks for the Lagrangian of the modified Emden-type equation and then obtain results for Lagrangian functions of (i) cubic-quintic Duffing oscillator, (ii) Liénard-type oscillator and (iii) Mathews-Lakshmanan oscillator. As with the modified Emden-type equation these oscillators were found to be characterized by nonstandard Lagrangians except that one could also assign a standard Lagrangian to the Duffing oscillator. We used the second approach to find indirect analytic (Lagrangian) representation for three velocity-dependent equations for (iv) Abraham-Lorentz oscillator, (v) Lorentz oscillator and (vi) Van der Pol oscillator. For each of the dynamical systems from (i)-(vi) we calculated the result for Jacobi integral and thereby provided a method to obtain the Hamiltonian function without taking recourse to the use of the so-called Legendre transformation.

physics.class-ph↗

arXiv2020

On the analytic representation of Newtonian systems

We show that the theory of self-adjoint differential equations can be used to provide a satisfactory solution of the inverse variational problem in classical mechanics. A Newtonian equation when transformed to the self-adjoint form allows one to find an appropriate Lagrangian representation (direct analytic representation) for it. On the other hand, the same Newtonian equation in conjunction with its adjoint provides a basis to construct a different Lagrangian representation (indirect analytic representation) for the system. We obtain the time-dependent Lagrangian of the damped Harmonic oscillator from the self-adjoint form of the equation of motion and at the same time identify the adjoint of the equation with the so called Bateman image equation with a view to construct a time-independent indirect Lagrangian representation. We provide a number of case studies to demonstrate the usefulness of the approach derived by us. We also present similar results for a number of nonlinear differential equations by using an integral representation of the Lagrangian function and make some useful comments.

physics.class-ph↗

arXiv2020

Insights from intracules and Coulomb holes

We point out that a typical two-electron distribution function in atoms and molecules often called the intracule depends sensitively on the electron-electron repulsion which leads to the so-called Coulomb correlation. The difference between the intracule densities computed by using the correlated and uncorrelated wave functions has been given the name Coulomb hole. Studies in intracule densities and Coulomb holes form a subject of considerable current interest. We make use of a three-parameter correlated wave function and its uncorrelated limit to study the properties of intracules and Coulomb holes in $He$, $Li^+$, $Be^{2+}$ and $Ne^{8+}$ and thus provide a transparent physical picture for the interplay between the electron-nucleus attraction and electron-electron repulsion in forming Coulomb holes around electrons in atoms of different $Z$ values.

physics.atom-ph↗

arXiv2018

Analytic representation of discrete and continuous mechanical systems

We investigate how the theory of self-adjoint differential equations alone can be used to provide a satisfactory solution of the inverse vatiational problem. For the discrete system, the self-adjoint form of the Newtonian equation allows one to find an explicitly time-dependent Lagrangian representation. On the other hand, the same Newtonian equation in conjunction with its adjoint forms a natural basis to construct an explicitly time-independent analytic representation of the system. This approach when applied to the equation of damped harmonic oscillator help one disclose the mathematical origin of the Bateman image equation. We have made use of a continuum analog of the same approach to find the Lagrangian or analytic representation of nonlinear evolution equations.

physics.class-ph↗

arXiv2017

Shannon entropies and Fisher information of K-shell electrons of neutral atoms

We represent the two K-shell electrons of neutral atoms by Hylleraas-type wave function which fulfils the exact behavior at the electron-electron and electron-nucleus coalescence points and, derive a simple method to construct expressions for single-particle position- and momentum-space charge densities, $ρ(\vec{r})$ and $γ(\vec{p})$ respectively. We make use of the results for $ρ(\vec{r})$ and $γ(\vec{p})$ to critically examine the effect of correlation on bare (uncorrelated) values of Shannon information entropies ($S$) and of Fisher information ($F$) for the K-shell electrons of atoms from helium to neon. Due to inter-electronic repulsion the values of the uncorrelated Shannon position-space entropies are augmented while those of the momentum-space entropies are reduced. The corresponding Fisher information are found to exhibit opposite behavior in respect of this. Attempts are made to provide some plausible explanation for the observed response of $S$ and $F$ to electronic correlation.

cond-mat.quant-gas↗

arXiv2017

Bound-state momentum-space wave function of the quasi-one-dimensional hydrogen atom

We prove that the bound-state momentum-space wave function $ϕ(p)$ for the quasi-one-dimensional hydrogen atom as used by Olendski in two recent publications (Eur. J. Phys.38, 038001(2017), arXiv : 1703.10042v1, 26 Mar2017) is incorrect. Further, we reconfirm that the wave function used by us in Eur. J.. Phys. 38, 025103 is correct.

quant-ph↗

arXiv2017

Fisher information for quasi-one-dimensional hydrogen atom

The coordinate-space wave function $ψ(x)$ of quasi-one-dimensional atoms is defined in the $x\geq 0$ region only. This poses a typical problem to write a physically acceptable momentum-space wave function $ϕ(p)$ from the Fourier transform of $ψ(x)$. We resolve the problem with special attention to the behavior of real and imaginary parts of the complex-valued function $ϕ(p)$ as a function of $p$ and confirm that $ϕ_i(p)$ (the imaginary part of $ϕ(p)$) represents the correct momentum-space wave function. We make use of the results for $ψ(x)$ and $ϕ_i(p)$ to express the position- and momentum-space Fisher information in terms of the principal quantum number and energy eigen value of the system and provide some useful checks on the result presented with particular attention on the information theoretic uncertainty relation.

cond-mat.stat-mech↗