Periodic Reporting for period 1 - NonEqbSK (Effective field theories for non-equilibrium many-body systems)
Période du rapport: 2021-09-01 au 2023-08-31
The overarching goal of this research project was to develop new effective field theories with non-equilibrium systems accounting for the effects of dissipation and stochastic fluctuations. Macroscopic processes that we see around us typically involve a very large number of constituents and feature dissipation and loss of tractable information. Reconciling these characteristics with a formally consistent mathematical framework has been an open challenge in physics and is what this project aimed to make progress towards. The new effective field theories developed in this research project will help us make better or more predictable models of nonequilibrium systems that we see around us in nature and will have far-reaching consequences for various areas of physics and engineering. The concrete objectives of the project were to develop effective field theories for systems nearing a phase transition, for active systems with an intrinsic source of heat and broken symmetries, and for fluids confined between physical boundaries.
New hydrodynamic effective field theories for systems operating far from equilibrium have been obtained. A complete hydrodynamic classification of various phases of matter based on higher-form symmetry was carried out. These results were utilised to understand the solid/liquid phase transition in electronic crystals mediated by topological defects and plasticity. An effective field theory for relativistic fluids with gapped degrees of freedom was developed to address causality and stability issues. A hydrodynamic theory for critical phenomena in relativistic hydrodynamics has also been developed. A hydrodynamic effective field theory for systems with approximate spacetime and internal symmetries was developed. An extension of these results to account for violations of the second law of thermodynamics, including novel non-unitarity aspects of the effective field theory framework, has been performed. Related results for field theoretic and hydrodynamic description of systems with fracton excitations were also obtained. A hydrodynamic theory for a stochastic fluid in confined volume was investigated for signatures of the stochastic Casimir effect. The simplest such model did not exhibit such an effect, but further extensions are being currently investigated. New hydrodynamic effective field theory models for fluids with dynamical boundaries have been obtained. 4 research paper from this research project have been published in open-access peer-reviewed journals; 2 research papers are under peer-review and are available on online preprint repositories; 2 research papers are under preparation.
Our results show, for the first time, how to use continuous higher-form symmetries to characterise the dynamical aspects of topological phase transitions. The applications of these results range from plasma phase transition in electromagnetism, QCD phase transition in quark-gluon plasma, superfluid phase transition, superconducting phase transition, solid/liquid phase transition etc. We addressed the potential causality and stability issues in the EFT framework of relativistic hydrodynamics, which are crucial for any practical application of the EFT technology to real world scenarios. Our results also show for the first time how to systematically use approximate symmetries to constraint the dynamics of hydrodynamic systems. Using our results, we were able to derive certain phenomenological constraints on transport coefficients in systems with approximate symmetries that were empirically discovered in the literature using holographic modelling. We also discovered entirely new transport coefficients pertaining to the modification of thermodynamic susceptibilities in the presence of explicit symmetry breaking that were previously overlooked in the literature. We have developed novel field theoretic understanding of fractons by systematically coupling these systems to spacetime backgrounds without boost symmetry. We have developed the requisite technology to apply the non-equilibrium effective field theory technology to real world scenarios where the fluid is confined within a finite box, with far-reaching consequences in various physical systems in condensed-matter physics and biophysics.