QFTcore Seminar
2 events

Localization and universality in nonHermitian manybody systems
May 29 (Fri) at 15:00  16:30, 2020
Ryusuke Hamazaki (Senior Research Scientist, iTHEMS / RIKEN Hakubi Team Leader, Nonequilibrium Quantum Statistical Mechanics RIKEN Hakubi Research Team, RIKEN Cluster for Pioneering Research (CPR))
Recent study on isolated quantum manybody systems have revealed two different phases distinguished by their dynamics and spectral statistics. One is an ergodic phase whose spectral statistics exhibit universality of random matrices, and the other is a manybody localized phase where dynamics is constrained due to strong disorder. In this talk, we show that novel and rich physics concerning such localization and universality appears in nonHermitian manybody systems, which have been utilized in diverse scientific disciplines from open quantum systems to biology. As a first topic, we analyze nonHermitian quantum manybody systems in the presence of interaction and disorder [1]. We demonstrate that a novel realcomplex transition occurs upon manybody localization of nonHermitian interacting systems with asymmetric hopping that respect timereversal symmetry. As a second topic, we show that “Dyson’s threefold way,” a threefold symmetry classification of universal spectral statistics of random matrices, is nontrivially extended to nonHermitian random matrices [2]. We report our discovery of two distinct universality classes characterized by transposition symmetry, which is distinct from timereversal symmetry due to nonHermiticity. We show that the newly found universality classes indeed manifest themselves in dissipative quantum manybody ergodic systems described by Lindblad equations.
Venue: via Zoom
Event Official Language: English

Gradient Flow Equation and Its Applications
May 15 (Fri) at 13:30  15:00, 2020
Kengo Kikuchi (Special Postdoctoral Researcher, iTHEMS)
Gradient flow is the one of the methods to suppress the ultraviolet divergence in gauge theories. The any correlation functions in terms of the flowed field, which is defined by the gradient flow equation, are finite without additional renormalizations. Because of this surprising property, the methods has been studied widely, especially in the lattice field theory. In this seminar, we introduce what the gradient flow is briefly. And we show our work, “generalized gradient flow equation”, which is the gradient flow equation for field theories with nonlinearly realized symmetry. Applying the formalism to a supersymmetric theory and O(N) non linear sigma model, we obtain the SUSY gradient flow and the Large N gradient flow. We also refer to the current research, the gradient flow of the supersymmetric theory with the nonrenormalization theorem and the new formalism to obtain the sphalerons, which is one of the static classical solutions, using gradient flow methods, if time allows.
Venue: via Zoom
Event Official Language: English
2 events