arXiv subjects

S. Das Adhikary

Publications and source records attributed to S. Das Adhikary.

3 recordsLinked to original sources

arXiv2026

Chaos in the dynamics of electromagnetic solitons in relativistic degenerate plasmas

We propose a coupled system for the nonlinear interaction between high-frequency, circularly polarized, intense electromagnetic (EM) waves and low-frequency electron-density perturbations, driven by the EM-wave ponderomotive force, in an unmagnetized plasma composed of fully degenerate relativistic electrons and stationary positive ions, including a higher-order correction to the nonlocal nonlinearity. We show that the modulational instability (MI) growth rate associated with the generation of EM envelope solitons gets significantly reduced with a slight increase in either the nonlocal nonlinear correction or the degeneracy parameter. Furthermore, a three-wave temporal model predicts the existence of quasiperiodic and chaotic states of EM solitons while interacting with longitudinal electron density perturbations. We show that the greater the degeneracy (or the higher the contribution from the nonlocal correction), the smaller the instability domain of modulation wave numbers; thus, degeneracy favors the stability of EM soliton evolution. The existence of temporal chaos in a low-dimensional model could be a signature of the development of spatiotemporal chaos in the complete nonlinear model, in which many electromagnetic solitons can be excited and saturated as they interact with electron plasma waves.

physics.plasm-ph↗

arXiv2026

Pattern formation and spatiotemporal chaos in relativistic degenerate plasmas

We numerically study the nonlinear interactions of high-frequency circularly polarized electromagnetic (EM) waves and low-frequency electron-acoustic (EA) density perturbations driven by the EM wave ponderomotive force in relativistic plasmas {(moderate, strong, and ultra-relativistic)} with two groups of electrons--the population of relativistic degenerate dense electrons (bulk plasma) and the sparse relativistic nondegenerate (classical) electrons, and immobile singly charged positive ions. By pattern selection, we show that many solitary patterns can be generated and drenched through modulational instability of EM waves at different spatial length scales and that the EM wave radiation spectra emanating from compact astrophysical objects may not settle into stable envelope solitons but into different incoherent states, including the emergence of temporal and spatiotemporal chaos due to collisions and fusions among the patterns with strong EA wave emission. The appearance of these states is confirmed by analyzing the Lyapunov exponent spectra, correlation function, and mutual information {as quantitative evidence}. As a result, the redistribution of wave energy from initially exciting many solitary patterns at large scales to a few new incoherent patterns with small wavelengths in the system occurs, leading to the onset of turbulence in astrophysical plasmas.

physics.plasm-ph↗

arXiv2025

Thermoacoustic internal gravity wave turbulence in the Earth's lower atmosphere

We propose, for the first time, a two-dimensional model for the nonlinear coupling of internal gravity and thermal waves in the presence of temperature-dependent density inhomogeneity due to thermal expansion and thermal feedback in stratified fluids of the Earth's lower atmosphere ($0-50$ km). Such a coupling gives rise to the evolution of thermoacoustic internal gravity waves (IGWs), which are distinctive from the known IGWs in the literature. We perform numerical simulations to study the nonlinear interactions of velocity and density perturbations associated with the IGWs and thermal fluctuations corresponding to the thermal mode. We show that solitary vortices of IGWs coupled to the thermal wave can lead to thermoacoustic turbulence. We observe the formation of large-scale velocity potential flows and small-scale structures in the density and temperature profiles. Interestingly, while the wave energy spectra exhibit power laws: $ k_x^{-1.67}$ and $ k_z^{-2.89}$, respectively, for horizontal and vertical wave numbers, in the troposphere ($0-15$ km) with negative temperature gradient, the same in the stratosphere ($15-50$ km) with positive temperature gradient tend to relax toward $k_x^{-1.83}$-horizontal and $k_z^{-1.03}$-vertical spectra. We find that while the energy spectra in the tropospheric turbulence are consistent with the observed phenomena without temperature gradients, those in the stratosphere differ.

physics.ao-ph↗