The 38th International Symposium on Lattice Field Theory

New approach to lattice QCD at finite density: reweighting without an overlap problem

27 Jul 2021, 05:30

15m

Oral presentation QCD at nonzero Temperature and Density QCD at nonzero Temperature and Density

Speaker

Attila Pasztor (Eötvös University)

Description

All methods currently used to study finite baryon density lattice QCD suffer from uncontrolled systematic uncertainties in addition to the well-known sign problem. We formulate and test a method - sign reweighting - that works directly at finite chemical potential and is yet free from any such uncontrolled systematics: with this approach the only problem is the sign problem itself. In practice the approach involves the generation of configurations with the positive fermionic weights $|\mathrm{R}\mathrm{e}\mathrm{d}\mathrm{e}\mathrm{t}\mathrm{D}(\mu )|$ where $D(\mu )$ is the Dirac matrix and the signs $\mathrm{s}\mathrm{i}\mathrm{g}\mathrm{n}(\mathrm{R}\mathrm{e}\mathrm{d}\mathrm{e}\mathrm{t}\mathrm{D}(\mu ))=\pm 1$ are handled by a discrete reweighting. Hence there are only two sectors, $+1$ and $-1$ and as long as the average $⟨\pm 1⟩\hspace{0.17em}\ne 0$ (with respect to the positive weight) this discrete reweighting has no overlap problem - unlike other reweighting methods - and the results are reliable. We will also present results based on this algorithm on the phase diagram of lattice QCD with two different actions: as a first test, we apply the method to calculate the position of the critical endpoint with unimproved staggered fermions at $N_{\tau }=4$; as a second application, we study the phase diagram with 2stout improved staggered fermions at $N_{\tau }=6$. This second one is already a reasonably fine lattice - relevant for phenomenology.

Presentation materials

redet.pdf

Video