Mayukh Bandyopadhyay | Searcharxiv

arXiv2026

Effective and Floquet Hamiltonians for High Frequency Driving and Floquet-induced Heating in Quantum Spin Chains

We study the non-equilibrium dynamics of a disordered periodically driven quantum spin chain, with the competition between the interaction, disorder, and Floquet driving being of particular interest. We study dynamics of entanglement entropy, energy absorption to characterize dynamical regimes of the system whether it stays in the Floquet-MBL(many-body localization) region or thermalized region. Starting with a product state in the computational basis, followed by reduced density matrix which in turn gives rise to the entanglement entropy density. With the strength of the interaction, the transverse field, the parallel field, the disorder strength W and the driving frequency, we discover the distinct behaviors of fast delocalization and logarithmic entanglement growth and long-lasting memory of the initial state, indicative of localized or prethermal Floquet regimes. We observe that strong disorder arrests transport and enables slow entanglement dynamics, whereas strong driving frequency arrests energy absorption and creates a long-lived non-equilibrium state. Conversely, weak disorder or low driving frequency leads to delocalization. The outcomes show strong support for non-equilibrium phases in driven many-body systems.

cond-mat.other↗

arXiv2020

Generalized Model of Interacting Dark Energy and Dark Matter : Phase Portrait Analysis of Evolving Universe

Main aim of this work is to give a suitable explanation of present accelerating universe through an acceptable interactive dynamical cosmological model. A three-fluid cosmological model is introduced in the background of Friedmann-Lemaître-Robertson-Walker asymptotically flat spacetime. This model consists of interactive dark matter and dark energy with baryonic matter taken as perfect fluid satisfying barotropic equation of state. We consider dust as the candidate of dark matter. A scalar field $ϕ$ represents dark energy with potential $V(ϕ)$. Einstein's field equations are utilised to construct a three-dimensional interactive autonomous system by choosing suitable interaction between dark energy and dark matter. We take the interaction kernel as $Q = 3β^{2γ} Hρ_d$. In order to explain the stability of this system, we obtained some suitable critical points. We analyse stability of obtained critical points to show the different phases of universe and cosmological implications. Surprisingly, we find some stable critical points which represent late time dark energy dominated era when a model parameter $α=-5.05$. In order to explain both the energy dominated era as well as the late-time acceleration of the universe at same time, we introduce a two-dimensional interactive autonomous system. After graphical analysis of two-dimensional system, we get several stable points which represent dark energy dominated era and the late-time cosmic acceleration both at the same time. We also show the variation in interaction at vicinity of phantom barrier ($ω_{eff}=-1$). From our work we can also predict the future phase evolution of the universe. No tendency for future deceleration is detected so far.

gr-qc↗