arXiv subjects

Sankarshan Sahu

Publications and source records attributed to Sankarshan Sahu.

8 recordsLinked to original sources

arXiv2026

Supersymmetry Without Time-Reversal Invariance in Model A: A FRG perspective

We show that, contrary to common belief, supersymmetry alone is not sufficient in Model A dynamics to ensure relaxation toward a stationary state satisfying time-reversal invariance (TRI). An additional condition on top of supersymmetry is required for TRI, which we analyze in detail. We explicitly construct a model that is supersymmetric but violates TRI, and argue that, at least perturbatively, TRI nevertheless emerges as an effective large-scale symmetry. Using the functional renormalization group (FRG), we further show that the dynamical effective action, $\Gamma[\varphi,\tilde\varphi]$, contains the derivative of the equilibrium effective action, $\Gamma^{\mathrm{eq}}[\varphi]$, whose renormalization-group flow is identical to that of the equilibrium theory order by order in the derivative expansion. Finally, extending the same line of reasoning, we show that the probability distribution of the total magnetization in the Ising model can be recovered within the Model A framework.

cond-mat.stat-mech↗

arXiv2026

State-Selective Signatures of Quantum and Classical Gravitational Environments

A unified framework is developed for determining whether a gravitational-wave (GW) background behaves as a classical field or as a genuinely quantum environment. Unified here means that both descriptions originate from the same tidal coupling derived from geodesic deviation, which yields an identical quadratic interaction Hamiltonian for the detector; the only distinction lies in whether the GW degrees of freedom are modeled as classical phase-randomized coherent states or as quantized graviton modes. Within this common framework, the reduced dynamics of a quantum harmonic oscillator exhibit a sharp structural contrast: a quantized graviton bath preserves coherence within the lowest phonon-number manifold, forming a protected sector at leading order, whereas a classical stochastic GW field inevitably induces decoherence even inside this subspace. This difference provides an operational criterion for diagnosing the classical or quantum nature of gravitational waves using mesoscopic optomechanical systems. Our results establish decoherence structure - not merely its magnitude - as a sensitive probe of gravitational quantumness and delineate the experimental regimes under which such tests may become feasible.

gr-qc↗

arXiv2025

Critical Probability Distributions of the order parameter at two loops II: $O(n)$ universality class

We show how to compute the probability distributions of the order parameter of the $O(n)$ model at two-loop order of perturbation theory generalizing the methods developed for computing the same in case of the Ising model \cite{Sahu:2025bkp}. We show that even for the $O(n)$ model, there exists not one but a family of these probability distribution functions indexed by $\zeta$ which is the ratio of system size $L$ to the bulk correlation length $\xi_{\infty}$. We also compare these PDFs to the Monte-Carlo simulations and the existing FRG results for the $O(2)$ and $O(3)$ models.

cond-mat.stat-mech↗

arXiv2025

Critical Probability Distributions of the order parameter at two loops I: Ising universality class

There exists an entire family of universal PDFs of the magnetization mode of the three dimensional Ising model parameterized by $\zeta = \lim_{L,\xi_{\infty}}L/\xi_{\infty}$ which is the ratio of the system size $L$ to the bulk correlation length $\xi_{\infty}$ with both the thermodynamic limit and the critical limit being taken simultaneously at fixed $\zeta$. Recently, the probability distribution functions (PDFs) of the magnetization mode of the three-dimensional Ising model has been computed at one-loop in the $\epsilon=4-d$ expansion [arXiv preprint arXiv:2407.12603 (2024)]. We show how these PDFs or, equivalently, the rate functions which are their logarithm, can be systematically computed at second order of the perturbative expansion. We compute the whole family of universal rate-functions and show that their agreement with the Monte Carlo data improves significantly at this order when compared to their one-loop counterpart.

cond-mat.stat-mech↗

arXiv2024

Generalization of the Central Limit Theorem to Critical Systems: Revisiting Perturbation Theory

The Central Limit Theorem does not hold for strongly correlated stochastic variables, as is the case for statistical systems close to criticality. Recently, the calculation of the probability distribution function (PDF) of the magnetization mode has been performed with the functional renormalization group in the case of the three-dimensional Ising model [Balog et al., Phys. Rev. Lett. {\bf 129}, 210602 (2022)]. It has been shown in that article that there exists an entire family of universal PDFs parameterized by $\zeta=\lim_{L,\xi_\infty\rightarrow\infty} L/\xi_\infty$ which is the ratio of the system size $L$ to the bulk correlation length $\xi_{\infty}$ with both the thermodynamic limit and the critical limit being taken simultaneously. We show how these PDFs or, equivalently, the rate functions which are their logarithm, can be systematically computed perturbatively in the $\epsilon=4-d$ expansion. We determine the whole family of universal PDFs and show that they are in good qualitative agreement with Monte Carlo data. Finally, we conjecture on how to significantly improve the quantitative agreement between the one-loop and the numerical results.

cond-mat.stat-mech↗

arXiv2021

A note on broken dilatation symmetry in planar noncommutative theory

A study of a riveting connection between noncommutativity and the anomalous dilatation (scale) symmetry is presented for a generalized quantum Hall system due to time dilatation transformations. On using the "Peierls substitution" scheme, it is shown that noncommutativity between spatial coordinates emerges naturally at a large magnetic field limit. Thereafter, we derive a path-integral action for the corresponding noncommutative quantum system and discuss the equivalence between the considered noncommutative system and the generalized Landau problem thus rendering an effective commmutative description. By exploiting the path-integral method due to Fujikawa, we derive an expression for the unintegrated scale or dilatation anomaly for the generalized Landau system, wherein the anomalies are identified with Jacobian factors arising from measure change under scale transformation and is subsequently renormalised. In fact, we derive exact expressions of anomalous Ward identities from which one may point out the existence of scale anomaly which is a purely quantum effect induced from the noncommutative structure between spatial coordinates.

hep-th↗

arXiv2020

On the collapse of states and the uncertainty principle

There had been previous successful explanations of Quantum Mechanics using the popular Copenhagen interpretation. In this paper,we build an equivalent mathematical structure of Copenhagen Interpretation from the Electromagnetic Field Theory and show how un-certainty principle is associated with the collapse of states. We also try to provide a more intuitive method towards our understanding of Quantum Mechanics.

physics.gen-ph↗

arXiv2019

Perturbation of Quantum Harmonic oscillator and its effect on the Quantum Field Theory

Here a special case of perturbation in quantum harmonic oscillator is studied. Here we assume the perturbed potential to be a Harmonic Oscillator that has been shifted in the position space.We construct the new creation and annihilation operators for the new Hamiltonian to find out its energy eigenstates. What is interesting about the solution of this system is that we find out that the ground state of this system is a coherent state of the ground state of the original harmonic oscillator. We know that the Hamiltonian of electromagnetic field is similar to that of the harmonic oscillator where the electric field and magnetic field are expressed in terms of time evolution of annihilation and creation operators. According to the quantum electromagnetic field theory, photon states are expressed as the coherent states of the ground states of the unperturbed harmonic oscillator.In the previous research works,it has been established how coherent states provide a better picture of Electric field compared to the energy eigenstates. This paper mainly deals with why the coherent states provide a more complete picture of electric and magnetic field theory compared to just energy eigenstates. Here we find how our perturbation act as a coherent state generator and adds a new term in the Hamiltonian. The Perturbation is thought to arise from the only available interaction i.e. observation. The perturbation also explains how observation leads to coherence of photon states. We will find out how the new perturbation affects the time evolution of electromagnetic field. This also explains how the classical electromagnetic field theory takes into account the factor of observation, due to which the classical laws are in perfect agreement with the quantum laws.

quant-ph↗