Journal Article

FZJ-2026-03093

http://join2-wiki.gsi.de/foswiki/pub/Main/Artwork/join2_logo100x88.png Can rooted staggered fermions describe nonzero baryon density at low temperatures?

Borsányi, S. ; Fodor, Z.FZJ* ; Giordano, M. ; Guenther, J. N. ; Katz, S. D. ; Pásztor, A. (Corresponding author) ; Wong, C. H.

2024
American Physical Society Ridge, NY

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Please use a persistent id in citations: doi:10.1103/PhysRevD.109.054509  doi:10.34734/FZJ-2026-03093

Abstract: Research on the quantum chromodynamics (QCD) phase diagram with lattice field theory methods is dominated by the use of rooted staggered fermions, as they are the computationally cheapest discretization available. We show that rooted staggered fermions at a nonzero baryochemical potential $𝜇_𝐵$ predict a sharp rise in the baryon density at low temperatures and $𝜇_𝐵 ≳3⁢𝑚_𝜋/2$, where $𝑚_𝜋$ is the Goldstone pion mass. We elucidate the nature of the nonanalyticity behind this sharp rise in the density by a comparison of reweighting results with a Taylor expansion of high order. While at first sight this nonanalytic behavior becomes apparent at the same position where the pion condensation transition takes place in the phase-quenched theory, the nature of the nonanalyticity in the two theories appears to be quite different: While at nonzero isospin density the data are consistent with a genuine thermodynamic (branch-point) singularity, the results at nonzero baryon density point to an essential singularity at $𝜇_𝐵 =0$. The effect is absent for four flavors of degenerate quarks, where rooting is not used. For the two-flavor case, we show numerical evidence that the magnitude of the effect diminishes on finer lattices. We discuss the implications of this technical complication on future studies of the QCD phase diagram.

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Contributing Institute(s):

1. Jülich Supercomputing Center (JSC)

Research Program(s):

1. 5111 - Domain-Specific Simulation & Data Life Cycle Labs (SDLs) and Research Groups (POF4-511) (POF4-511)
2. 05P21PXFCA - Verbundprojekt 05P2021 (ErUM-FSP T06) - Aufbau von CBM bei FAIR: Compressed-Baryonic-Matter-Physik an FAIR: Gittersimulationen zur starken Wechselwirkung mit endlicher Baryonendichte (BMBF-05P21PXFCA) (BMBF-05P21PXFCA)
3. NRW-FAIR (NW21-024-A) (NW21-024-A)
4. DFG project G:(GEPRIS)496127839 - Phasendiagramm und Phenomenologie des QCD Übergangs (496127839) (496127839)

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