arXiv subjects

A. Ghose-Choudhury

Publications and source records attributed to A. Ghose-Choudhury.

6 recordsLinked to original sources

arXiv2025

Quasi-harmonic spectra from branched Hamiltonians

We revisit the canonical quantization to assess the spectrum of the modified Emden equation $\ddot{x} + kx\dot{x} + ω^2 x + \frac{k^2}{9}x^3 = 0$, which is an isochronous case of the Liénard-Kukles equation. While its classical isochronicity and canonical quantization, leading to polynomial solutions with an exactly-equispaced spectrum have been discussed earlier, including in the recent paper [Int. J. Theor. Phys. 64, 212 (2025)], the present study focuses on the quantization of its branched Hamiltonians. For small $k$, we show numerically that the resulting energy spectrum is no longer perfectly harmonic but only approximately equispaced, exhibiting quasi-harmonic behavior characterized by deviations from uniform spacing. Our numerical results are precisely validated by analytical calculations based on perturbation theory.

quant-ph↗

arXiv2025

Generalized Liénard systems and isochronous connections

In this paper, we explore some classical and quantum aspects of the nonlinear Liénard equation $\ddot{x} + k x \dot{x} + ω^2 x + (k^2/9) x^3 = 0$, where $x=x(t)$ is a real variable and $k, ω\in \mathbb{R}$. We demonstrate that such an equation could be derived from an equation of the Levinson-Smith kind which is of the form $\ddot{z} + J(z) \dot{z}^2 + F(z) \dot{z} + G(z) = 0$, where $z=z(t)$ is a real variable and $\{J(z), F(z), G(z)\}$ are suitable functions to be specified. It can further be mapped to the harmonic oscillator by making use of a nonlocal transformation, establishing its isochronicity. Computations employing the Jacobi last multiplier reveal that the system exhibits a bi-Hamiltonian character, i.e., there are two distinct types of Hamiltonians describing the system. For each of these, we perform a canonical quantization in the momentum representation and explore the possibility of bound states. While one of the Hamiltonians is seen to exhibit an equispaced spectrum with an infinite tower of states, the other one exhibits branching but can be solved exactly in closed form for certain choices of the parameters.

quant-ph↗

arXiv2019

On purely nonlinear oscillators generalizing an isotonic potential

In this paper we consider a nonlinear generalization of the isotonic oscillator in the same spirit as one considers the generalization of the harmonic oscillator with a truly nonlinear restoring force. The corresponding potential being asymmetric we invoke the symmetrization principle and construct a symmetric potential in which the period function has the same value as in the original asymmetric potential. The period function is amplitude dependent and expressible in terms of the hypergeometric function and reduces to $2π$ when $α=1$, i.e., corresponding to the special case of an isotonic oscillator.

physics.class-ph↗

arXiv2018

Superintegrable systems with position dependent mass: master symmetry and action-angle methods

We consider the issue of deriving superintegrable systems with position dependent mass (PDM) in two dimensions from certain known superintegrable systems using the recently introduced method of master symmetries and complex factorization by M. Ranada \cite{Rana1,Rana2,Rana3,Rana4}. We introduce a noncanonical transformation to map the Hamiltonian of the PDM systems to that of ordinary unit mass systems. We observe a duality between these systems. We also study Tsiganov's method \cite{Tsiganov1,Tsiganov2,Tsiganov3,Tsiganov4} to derive polynomial integrals of motion using addition theorems for the action-angle variables using famous Chebyshev's theorem on binomial differentials. We compare Tsiganov's method of generating an additional integral of motion with that of Ranada's master symmetry method.

nlin.SI↗

arXiv2017

Jacobi-Maupertuis metric of Lienard type equations and Jacobi Last Multiplier

We present a construction of the Jacobi-Maupertuis (JM) principle for an equation of the Lienard type, viz \ddot{x} + f(x)x^2 + g(x) = 0 using Jacobi's last multiplier. The JM metric allows us to reformulate the Newtonian equation of motion for a variable mass as a geodesic equation for a Riemannian metric. We illustrate the procedure with examples of Painleve-Gambier XXI, the Jacobi equation and the Henon-Heiles system.

nlin.SI↗

arXiv2016

Noetherian symmetries of noncentral forces with drag term

We consider the Noetherian symmetries of second-order ODEs subjected to forces with nonzero curl. Both position and velocity dependent forces are considered. In the former case the first integrals are shown to follow from the symmetries of the celebrated Emden-Fowler equation.

math-ph↗