Tatsuhiro Misumi

Finite-temperature spectral function of the vector mesons in a holographic QCD model

We use the soft-wall anti-de Sitter/QCD model to investigate the finite-temperature effects on the spectral function in the vector channel. The dissociation of the vector meson tower onto the anti-de Sitter black hole leads to the in-medium mass shift and the width broadening in a way similar to the lattice QCD results for the heavy quarkonium at finite temperature. We also show the momentum dependence of the spectral function and find it consistent with screening in a hot wind.

Adjoint QCD on ℝ3 × S1 with twisted fermionic boundary conditions

A bstractWe investigate QCD with adjoint Dirac fermions on ℝ3 × S1 with generic boundary conditions for fermions along S1. By means of perturbation theory, semiclassical methods and a chiral effective model, we elucidate a rich phase structure in the space spanned by the S1 compactification scale L, twisted fermionic boundary condition ϕ and the fermion mass m. We found various phases with or without chiral and center symmetry breaking, separated by first- and second-order phase transitions, which in specific limits (ϕ = 0, ϕ = π, L → 0 and m → ∞) reproduce known results in the literature. In the center- symmetric phase at small L, we show that Ünsal’s bion-induced confinement mechanism is at work but is substantially weakened at ϕ = 0 by a linear potential between monopoles. Through an analytic and numerical study of the PNJL model, we show that the order parameters for center and chiral symmetries (i.e., Polyakov loop and chiral condensate) are strongly intertwined at ϕ = 0. Due to this correlation, a deconfined phase can intervene between a weak-coupling center-symmetric phase at small L and a strong-coupling one at large L. Whether this happens or not depends on the ratio of the dynamical fermion mass to the energy scale of the Yang-Mills theory. Implication of this possibility for resurgence in gauge theories is briefly discussed. In an appendix, we study the index of the adjoint Dirac operator on ℝ3 × S1 with twisted boundary conditions, which is important for semiclassical analysis of monopoles.

Aoki phases in the lattice Gross-Neveu model with flavored mass terms

We investigate the parity-broken phase structure for staggered and naive fermions in the Gross-Neveu model as a toy model of QCD. We consider a generalized staggered Gross-Neveu model including two types of four-point interactions. We use generalized mass terms to split the doublers for both staggered and naive fermions. The phase boundaries derived from the gap equations show that the mass splitting of tastes results in an Aoki phase both in the staggered and naive cases. We also discuss the continuum limit of these models and explore taking the chirally symmetric limit by fine-tuning a mass parameter and two-coupling constants. This supports the idea that in lattice QCD we can derive one- or two-flavor staggered fermions by tuning the mass parameter, which are likely to be less expensive than Wilson fermions in QCD simulation.

Melting spectral functions of the scalar and vector mesons in a holographic QCD model

We investigate the finite-temperature spectral functions of heavy quarkonia by using the soft-wall anti-de Sitter/QCD model. We discuss the scalar, the pseudoscalar, the vector, and the axial-vector mesons and compare their qualitative features of the melting temperature and growing width. We find that the axial-vector meson melts earlier than the vector meson, while there appears only a slight difference between the scalar and pseudoscalar mesons, which also melt earlier than the vector meson.

Neutral bions in the

A bstractWe study classical configurations in the ℂ

model

\mathbb{C}

Resurgence in sine-Gordon quantum mechanics: exact agreement between multi-instantons and uniform WKB

PN −1 model on ℝ