Lecturer:  Dr. Yael Avni, University of Chicago, The James Franck Institute
 Abstract:
Non-reciprocal interactions, in which the effect of “A” on “B” differs from that of “B” on “A”, effectively emerge in complex systems such as macromolecules, cells, and humans. While a mean-field description of many-body systems with non-reciprocal interactions often predicts oscillatory states, it remains an open question whether such states are real ``phases of matter”, i.e., if they survive fluctuations in spatially-extended systems of arbitrary size. We address this question by studying a non-reciprocal generalization of the most paradigmatic statistical mechanical system: the Ising model. Our results show that an oscillatory phase is destroyed by fluctuations in two dimensions through the proliferation of discrete spiral defects, but is stabilized in three dimensions where non-reciprocity changes the critical exponents from Ising to XY. Finally, we demonstrate how non-reciprocity combined with agent motility leads to new inhomogeneous time-dependent states, that can emerge in models of social behavior.