@article{chattopadhyay_heinz_schafer_2024, title={Far-off-equilibrium early-stage dynamics in high-energy nuclear collisions}, volume={296}, ISBN={["*****************"]}, ISSN={["2100-014X"]}, DOI={10.1051/epjconf/202429613009}, abstractNote={We explore the far-off-equilibrium aspects of the (1+1)-dimensional early-stage evolution of a weakly-coupled quark-gluon plasma using kinetic theory and hydrodynamics. For a large set of far-off-equilibrium initial conditions the system exhibits a peculiar phenomenon where its total equilibrium entropy decreases with time. Using a non-equilibrium definition of entropy based on Boltzmann’s H-function, we demonstrate how this apparently anomalous behavior is consistent with the second law of thermodynamics. We also use the H-function to formulate ‘maximum-entropy’ hydrodynamics, a far-offequilibrium macroscopic theory that can describe both free-streaming and nearequilibrium regimes of quark-gluon plasma in a single framework.}, journal={30TH INTERNATIONAL CONFERENCE ON ULTRA-RELATIVISTIC NUCLEUS-NUCLEUS COLLISIONS, QUARK MATTER 2023}, author={Chattopadhyay, Chandrodoy and Heinz, Ulrich and Schafer, Thomas}, year={2024} }
 @article{chattopadhyay_ott_schaefer_v. skokov_2024, title={Simulations of Stochastic Fluid Dynamics near a Critical Point in the Phase Diagram}, volume={133}, ISSN={["1079-7114"]}, url={https://doi.org/10.1103/PhysRevLett.133.032301}, DOI={10.1103/PhysRevLett.133.032301}, abstractNote={We present simulations of stochastic fluid dynamics in the vicinity of a critical endpoint belonging to the universality class of the Ising model.This study is motivated by the challenge of modeling the dynamics of critical fluctuations near a conjectured critical endpoint in the phase diagram of Quantum Chromodynamics (QCD).We focus on the interaction of shear modes with a conserved scalar density, which is known as model H.We show that the observed dynamical scaling behavior depends on the correlation length and the shear viscosity of the fluid.As the correlation length is increased or the viscosity is decreased we observe a cross-over from the dynamical exponent of critical diffusion, z ≃ 4, to the expected scaling exponent of model H, z ≃ 3. We use our method to investigate time-dependent correlation function of non-Gaussian moments M n (t) of the order parameter.We find that the relaxation time depends in non-trivial manner on the power n.}, number={3}, journal={PHYSICAL REVIEW LETTERS}, author={Chattopadhyay, Chandrodoy and Ott, Josh and Schaefer, Thomas and V. Skokov, Vladimir}, year={2024}, month={Jul} }
 @article{chattopadhyay_ott_schafer_skokov_2023, title={Dynamic scaling of order parameter fluctuations in model B}, volume={108}, ISSN={["2470-0029"]}, url={https://doi.org/10.1103/PhysRevD.108.074004}, DOI={10.1103/PhysRevD.108.074004}, abstractNote={We describe numerical simulations of the stochastic diffusion equation with a conserved charge. We focus on the dynamics in the vicinity of a critical point in the Ising universality class. The model we consider is expected to describe the critical dynamics near a possible QCD critical point if the coupling of the order parameter to the momentum density of the fluid can be neglected. The simulations are performed on a spatial lattice, and the time evolution is performed using a Metropolis algorithm. We determine the dynamical critical exponent $z\simeq 3.972(2)$, which agrees with predictions of the epsilon expansion. We also study non-equilibrium sweeps of the reduced temperature and observe approximate Kibble-Zurek scaling.}, number={7}, journal={PHYSICAL REVIEW D}, author={Chattopadhyay, Chandrodoy and Ott, Josh and Schafer, Thomas and Skokov, Vladimir}, year={2023}, month={Oct} }
 @article{chattopadhyay_heinz_schaefer_2023, title={Far-off-equilibrium expansion trajectories in the QCD phase diagram}, volume={107}, ISSN={["2469-9993"]}, url={https://doi.org/10.1103/PhysRevC.107.044905}, DOI={10.1103/PhysRevC.107.044905}, abstractNote={We consider the hydrodynamic evolution of a quark-gluon gas with non-zero quark masses and net baryon number in its phase diagram. For far-off-equilibrium initial conditions the expansion trajectories appear to violate simple rules based on the second law of thermodynamics that were previously established for ideal or weakly dissipative fluids. For Bjorken flow we present a detailed analysis within kinetic theory that provides a full microscopic understanding of these macroscopic phenomena and establishes their thermodynamic consistency. We point out that, for certain far-off-equilibrium initial conditions, the well-known phenomenon of"viscous heating"turns into"viscous cooling"where, driven by dissipative effects, the temperature decreases faster than in adiabatic expansion.}, number={4}, journal={PHYSICAL REVIEW C}, author={Chattopadhyay, Chandrodoy and Heinz, Ulrich and Schaefer, Thomas}, year={2023}, month={Apr} }
 @article{chattopadhyay_heinz_schafer_2023, title={Fluid dynamics from the Boltzmann equation using a maximum entropy distribution}, volume={108}, ISSN={["2469-9993"]}, url={https://doi.org/10.1103/PhysRevC.108.034907}, DOI={10.1103/PhysRevC.108.034907}, abstractNote={Using the recently developed ``Maximum Entropy'' (or ``least biased'') distribution function to truncate the moment hierarchy arising from kinetic theory, we formulate a far-from-equilibrium macroscopic theory that provides the possibility of describing both free-streaming and hydrodynamic regimes of heavy-ion collisions within a single framework. Unlike traditional hydrodynamic theories that include viscous corrections to finite order, the present formulation incorporates contributions to all orders in shear and bulk inverse Reynolds numbers, allowing it to handle large dissipative fluxes. By considering flow profiles relevant for heavy-ion collisions (Bjorken and Gubser flows), we demonstrate that the present approach provides excellent agreement with underlying kinetic theory throughout the fluid's evolution and, especially, in far-off-equilibrium regimes where traditional hydrodynamics breaks down.}, number={3}, journal={PHYSICAL REVIEW C}, author={Chattopadhyay, Chandrodoy and Heinz, Ulrich and Schafer, Thomas}, year={2023}, month={Sep} }
 @article{jaiswal_pal_chattopadhyay_du_heinz_2023, title={FAR-FROM-EQUILIBRIUM ATTRACTOR IN NON-CONFORMAL PLASMAS}, volume={16}, ISSN={["2082-7865"]}, DOI={10.5506/APhysPolBSupp.16.1-A119}, abstractNote={We study the far-off-equilibrium dynamics of a Bjorken expanding non-conformal system within kinetic theory and hydrodynamics. We show that, in contrast to the conformal case, neither shear nor bulk viscous pressure re-lax quickly to a non-equilibrium attractor. In kinetic theory an early-time, far-from-equilibrium attractor exists for the scaled longitudinal pressure, driven by the rapid longitudinal expansion of the medium. Second-order dissipative hydrodynamics fails to accurately describe this attractor, but a modified anisotropic hydrodynamic formulation reproduces it and provides excellent agreement with kinetic theory.}, number={1}, journal={ACTA PHYSICA POLONICA B PROCEEDINGS SUPPLEMENT}, author={Jaiswal, Sunil and Pal, Subrata and Chattopadhyay, Chandrodoy and Du, Lipei and Heinz, Ulrich}, year={2023} }
 @article{jaiswal_chattopadhyay_du_heinz_pal_2022, title={Nonconformal kinetic theory and hydrodynamics for Bjorken flow}, volume={105}, ISSN={["2469-9993"]}, DOI={10.1103/PhysRevC.105.024911}, abstractNote={Using and comparing kinetic theory and second-order Chapman-Enskog hydrodynamics, we study the non-conformal dynamics of a system undergoing Bjorken expansion. We use the concept of ‘free-streaming fixed lines’ for scaled shear and bulk stresses in non-conformal kinetic theory and hydrodynamics, and show that these ‘fixed lines’ behave as early-time attractors and repellors of the evolution. In the conformal limit, the free-streaming fixed lines reduce to the well-known fixed points of conformal Bjorken dynamics. A new fixed point in the free streaming regime is identified which lies at the intersection of these fixed lines. Contrary to the conformal scenario, both kinetic theory and hydrodynamics predict the absence of attractor behavior in the normalised shear stress channel. In kinetic theory a far-off-equilibrium attractor is found for the normalised effective longitudinal pressure, driven by rapid longitudinal expansion. Second-order viscous hydrodynamics fails to accurately describe this attractor. From a thorough analysis of the free-streaming dynamics in Chapman-Enskog hydrodynamics we conclude that this failure results from an inaccurate approximation of the fixed lines and a related incorrect description of the nature of the fixed point. A modified anisotropic hydrodynamic description is presented that provides excellent agreement with kinetic theory results and reproduces the far-from-equilibrium attractor for the scaled longitudinal pressure.}, number={2}, journal={PHYSICAL REVIEW C}, author={Jaiswal, Sunil and Chattopadhyay, Chandrodoy and Du, Lipei and Heinz, Ulrich and Pal, Subrata}, year={2022}, month={Feb} }
 @article{liyanage_everett_chattopadhyay_heinz_2022, title={Prehydrodynamic evolution and its impact on quark-gluon plasma signatures}, volume={105}, ISSN={["2469-9993"]}, DOI={10.1103/PhysRevC.105.064908}, abstractNote={State-of-the-art hydrodynamic models of heavy-ion collisions have considerable theoretical model uncertainties in the description of the very early pre-hydrodynamic stage. We add a new computational module, K T Iso , that describes the pre-hydrodynamic evolution kinetically, based on the relativistic Boltzmann equation with collisions treated in the Isotropization Time Approximation. As a novelty, K T Iso allows for the inclusion and evolution of initial-state momentum anisotropies. To maintain computational efficiency K T Iso assumes strict longitudinal boost invariance and allows collisions to isotropize only the transverse momenta. We use it to explore the sensitivity of hadronic observables measured in relativistic heavy-ion collisions to initial-state momentum anisotropies and microscopic scattering during the pre-hydrodynamic stage.}, number={6}, journal={PHYSICAL REVIEW C}, author={Liyanage, Dananjaya and Everett, Derek and Chattopadhyay, Chandrodoy and Heinz, Ulrich}, year={2022}, month={Jun} }
 @article{chattopadhyay_jaiswal_du_heinz_pal_2022, title={Non-conformal attractor in boost-invariant plasmas}, volume={824}, ISSN={["1873-2445"]}, DOI={10.1016/j.physletb.2021.136820}, abstractNote={We study the dissipative evolution of (0+1)-dimensionally expanding media with Bjorken symmetry using the Boltzmann equation for massive particles in relaxation-time approximation. Breaking conformal symmetry by a mass induces a non-zero bulk viscous pressure in the medium. It is shown that even a small mass (in units of the local temperature) drastically modifies the well-known attractor for the shear Reynolds number previously observed in massless systems. For generic nonzero particle mass, neither the shear nor the bulk viscous pressure relax quickly to a non-equilibrium attractor; they approach the hydrodynamic limit only late, at small values of the inverse Reynolds numbers. Only the longitudinal pressure, which is a combination of thermal, shear and bulk viscous pressures, continues to show early approach to a far-off-equilibrium attractor, driven by the rapid longitudinal expansion at early times. Second-order dissipative hydrodynamics based on a gradient expansion around locally isotropic thermal equilibrium fails to reproduce this attractor.}, journal={PHYSICS LETTERS B}, author={Chattopadhyay, Chandrodoy and Jaiswal, Sunil and Du, Lipei and Heinz, Ulrich and Pal, Subrata}, year={2022}, month={Jan} }