
Sign problems are an important stumbling block in applying the Monte Carlo method to solve QCD at finite densities and understand nuclear matter. Sign problems also haunt several other research areas that deal with quantum many body physics, including strongly correlated electronic systems away from half filling and frustrated quantum spin models. This international conference brought together 71 physicists (45 senior researchers, 17 posdoctoral associates, 9 graduate students), interested in this broad area of research. This was the fifth in a series of conferences and the first one organized in the US.
Highlights of the conference:
The conference brought together physicists from particle, nuclear and condensed matter communities since the topic of the conference is of broad interest.
There were five review talks that covered important progress over the past few years in various fields. The topics of these reviews were: (1) problems with signal to noise ratios in baryon correlation functions, (2) complex Langevin and Lefshitz thimble approach to QCD, (3) sign problems and its relation to universality, entanglement and dynamics from a condensed matter (CM) perspective, (4) progress in QMC methods from the perspective of nuclear physics and (5) machine learning applied to quantum many body physics.
Some of the other main results presented at the conference included:
 A new local factorization of the fermion determinant in lattice gauge theories that may help in developing multilevel algorithms with a variety of applications.
 Progress in understanding the applicability of the complex Langevin and Lefshitz thimble approaches for solving sign problems through studies of toy models that have features in common with QCD.
 New solutions to sign problems in a variety of frustrated quantum spin systems (see figure below from Fabien Alet's talk).
 New solutions to sign problems in a variety of designer Hamiltonian models with gauge field interactions. Some of these are being applied to study Z2 gauge theories that show new quantum critical points (Figure below is taken from Snir Gazit's talk).
 New ideas were presented to alleviate bottlenecks in fermion QMC methods to explore large lattices.
 New progress in applications of world line methods to lattice gauge theories were proposed.
 New ideas to solve interesting sign problems in the context of applications to nuclear physics and new algorithms to compute entanglement entropies and nuclear wave functions were presented.
The interdisciplinary nature of the conference was interesting to many participants and the hope was that future SIGN conferences would continue this tradition.
