Seminars

Fri. Dec 15th 2025

Title: Classification of color superconductivity revisited

Yuki Fujimoto (Niigata University)

abstract: The dense region of the QCD phase diagram, particularly concerning the ground state of color superconductor at densities below the onset of

color-flavor locking (CFL), remains unsettled to date. This uncertainty stems from various complexities, including the effect of strange quark mass, which splits apart the Fermi surfaces and breaks the pairing.

In this seminar, I revisit the classification of color superconductivity based on the one-gluon exchange helicity amplitude at weak coupling, focusing solely on homogeneous pairing. This framework was initially explored in the seminal work of Bailin and Love but has since been largely overlooked within the community.

I will begin the talk by outlining the importance of this somewhat abandoned research field, especially as interest in the dense region of the phase diagram continues to rise and the relevance of color superconductivity becomes increasingly apparent. I will demonstrate that the loss of Lorentz invariance in the dense medium, together with the decoupling of renormalization group equations, enables us to categorize the possible pairing pattern in color superconductivity in a manner analogous to the nonrelativistic case.

The talk is based on my recent papers, arXiv:2508.19222; 2508.19728

Fri. Dec 20th 2024

Title: 't Hooft loop in SU(2) Yang-Mills Theory Revisited

Hiromasa Watanabe (YITP)

abstract: The ’t Hooft loop is the important line operator as well as the Wilson loop to distinguish phases of Yang-Mills (YM) theory in four dimensions. For YM with the theta term, there are nontrivial confining phases where the dyons condensate instead of magnetic monopoles, which is known as the oblique confinement. These phases can be distinguished by the above line operators according to the Wilson-’t Hooft classification. The generalized notion of symmetries and anomalies enables us in deeper understanding of this classification. In this study, we revisit SU(2) pure YM at $theta \simeq 0, 2\pi$ by the lattice Monte Carlo simulation, where we can tame the sign problem using the reweighting method, and discuss the characterization of phases in the language of line operators.