Speaker
Description
The order of the phase transition in QCD is known to depend on the quark masses and the baryon chemical potential $\mu$. In the heavy-quark limit and at $\mu/T=i\pi/3$, the first-order Roberge-Weiss transition line terminates at a triple first-order point where three first-order lines merge. As the quark mass decreases, this triple point is expected to terminate at a tricritical point. Determining the location of this tricritical point is therefore an important subject for understanding the phase structure of heavy-quark QCD at imaginary chemical potential.
In this study, we investigate the location of the Roberge-Weiss tricritical point in the heavy-quark region in lattice QCD simulations. The simulations are performed using the hopping-parameter expansion, which enables high-statistical analyses over a wide range of heavy-quark masses. We use the Binder cumulant and related observables to analyze the finite-size scaling behavior and identify the change in the order of the transition. We also investigate the Lee-Yang zeros in the complex $\mu$ plane. Their approach to the imaginary axis in the thermodynamic limit provides information on the order of the transition and the associated critical behavior. Using these numerical results, we constrain the location of the tricritical point with significantly improved precision compared with previous studies and discuss the associated critical exponents.