Seminars

ハドロン物理セミナーでは、気鋭の研究者に最近の研究のお話をしていただきます。

We invite spirited researchers as speakers of the Hadron Physics Seminar.

*  以下の時間は、UTC + 9である日本標準時（JST）です。

*  The schedule below is in terms of Japan Standard Time (JST), namely UTC +9.

Mon. Oct. 5th

Exploring the QCD Phase Diagram with Lee-Yang Zeros and Edge

Singularities

Tatsuya Wada (Kyoto U.)
Room 907 (16:00-18:00)

Abstract: In QCD at finite temperature and density, a first-order phase transition line terminating at a critical point is conjectured to exist. The location of this critical point, however, remains undetermined from first principles, as lattice QCD suffers from the sign problem at finite baryon density. Recently, approaches to exploring the QCD phase diagram using Lee-Yang zeros (LYZ), the zeros of the partition function in complex parameter space, and Lee-Yang edge singularities (LYES), which emerge as accumulation points of these zeros in the thermodynamic limit, have attracted considerable attention. However, extracting LYES from LYZ obtained at finite volumes requires careful control of finite-volume effects.

To address this issue, we have introduced the Lee-Yang zero ratio (LYZR), defined as the ratio of the imaginary parts of two LYZ, and proposed a method for locating critical points based on finite-size scaling. At a critical point, the LYZR approaches a universal value in the large-volume limit. Its finite-size scaling can therefore be used to locate the critical point and identify its universality class without explicitly extrapolating the zero locations to infinite volume. In this talk, I first review the current status of QCD phase-diagram studies using LYZ and LYES and introduce the LYZR method. I then discuss (i) its applications to lattice QCD in the heavy-quark region and the three-dimensional Ising model, (ii) the qualitative relation between LYZ and LYES investigated within a mean-field approach, and (iii) prospects for applications to QCD with physical quark masses.

This talk is based on the following papers:

[1] T. Wada, M. Kitazawa, and K. Kanaya, “Locating Critical Points Using Ratios of Lee-Yang Zeros,” Phys. Rev. Lett. 134, 162302 (2025) [arXiv:2410.19345].

[2] T. Wada, M. Kitazawa, and K. Kanaya, “Lee-Yang-zero Ratio Method in Three-dimensional Ising Model,” J. Phys. Soc. Jpn. 95, 024002 (2026) [arXiv:2508.20422].

[3] T. Wada, G. Kovács, M. Kitazawa, and T. M. Doi, “Lee-Yang zeros and edge singularity in a mean-field approach,” Phys. Rev. D 114, 036013 (2026) [arXiv:2605.19964].