Arata Yamamoto

Charged vector mesons in a strong magnetic field

We show that charged vector mesons cannot be condensed by a magnetic field. Although some hadron models predict the charged vector meson condensation in a strong magnetic field, we prove, by means of the Vafa-Witten theorem, that this is not the case in QCD. We also perform the numerical analysis for the meson mass and condensation in lattice QCD. The lattice QCD data confirm no charged vector meson condensation in a magnetic field.

Chaotic behavior in classical Yang-Mills dynamics

Institut fu¨r Theoretische Physik, Universita¨t Regensburg, D-93040 Regensburg, Germany(Dated: August 9, 2010)Understanding the underlying mechanisms causing rapid thermalization deduced for high-energyheavy ion collissons is still a challenge. To estimate the thermalization time, entropy growth forclassical Yang-Mills theories is studied, based on the determination of Lyapunov exponents. Distinctregimes for short, medium and long sampling times are characterized by different properties of theirspectrum of Lyapunov exponents. Clarifying the existence of these regimes and their implications forgauge-field dynamics is one of the results of this contribution. As a phenomenological application weconclude that for pure gauge theories with random initial conditions thermalization occures withinfew fm/c, an estimate which can be reduced by the inclusion of fermions, specific initial conditionsetc.I. INTRODUCTION

Relevant energy scale of color confinement from lattice QCD

We propose a new lattice framework to extract the relevant gluonic energy scale of QCD phenomena which is based on a cut on link variables in momentum space. This framework is expected to be broadly applicable to all lattice QCD calculations. Using this framework, we quantitatively determine the relevant energy scale of color confinement, through the analyses of the quark-antiquark potential and meson masses. The relevant energy scale of color confinement is found to be below 1.5 GeV in the Landau gauge. In fact, the string tension is almost unchanged even after cutting off the high-momentum gluon component above 1.5 GeV. When the relevant low-energy region is cut, the quark-antiquark potential is approximately reduced to a Coulomb-like potential, and each meson becomes a quasifree quark pair. As an analytical model calculation, we also investigate the dependence of the Richardson potential on the cut, and find the consistent behavior with the lattice result.

Lattice QCD in rotating frames.

We formulate lattice QCD in rotating frames to study the physics of QCD matter under rotation. We construct the lattice QCD action with the rotational metric and apply it to the Monte Carlo simulation. As the first application, we calculate the angular momenta of gluons and quarks in the rotating QCD vacuum. This new framework is useful to analyze various rotation-related phenomena in QCD.

Lattice Analysis for the Energy Scale of QCD Phenomena

We formulate a new framework in lattice QCD to study the relevant energy scale of QCD phenomena. By considering the Fourier transformation of link variable, we can investigate the intrinsic energy scale of a physical quantity nonperturbatively. This framework is broadly available for all lattice QCD calculations. We apply this framework for the quark-antiquark potential and meson masses in quenched lattice QCD. The gluonic energy scale relevant for the confinement is found to be less than 1 GeV in the Landau or Coulomb gauge.

Complex Langevin simulation of quantum vortices in a Bose-Einstein condensate

The ab-initio simulation of quantum vortices in a Bose-Einstein condensate is performed by adopting the complex Langevin techniques. We simulate the nonrelativistic boson field theory at finite chemical potential under rotation. In the superfluid phase, vortices are generated above a critical angular velocity and the circulation is clearly quantized even in the presence of quantum fluctuations.

Lattice QCD with strong external electric fields.

We study particle generation by a strong electric field in lattice QCD. To avoid the sign problem of the Minkowskian electric field, we adopt the isospin electric charge. When a strong electric field is applied, the insulating vacuum is broken down and pairs of charged particles are produced by the Schwinger mechanism. The competition against the color confining force is also discussed.

Asymptotically free lattice gauge theory in five dimensions

A lattice formulation of Lifshitz-type gauge theories is presented. While the Lorentz-invariant Yang-Mills theory is not renormalizable in five dimensions, non-Abelian Lifshitz-type gauge theories are renormalizable and asymptotically free. We construct a lattice gauge action and numerically examine the continuum limit and the bulk phase structure.

Lattice QCD in curved spacetimes

We formulate the lattice QCD simulation with background classical gravitational fields. This formulation enables us to study nonperturbative aspects of quantum phenomena in curved spacetimes from the first principles. As the first application, we perform the simulation with the Friedmann-Lemaitre-Robertson-Walker metric and analyze particle production in the expanding universe.

Lattice QCD simulation at finite chiral chemical potential

Chiral chemical potential does not cause the sign problem in the Monte Carlo simulation of lattice QCD. Using the chiral chemical potential, we study the chiral magnetic effect in two-flavor full QCD. We show that a strong external magnetic field induces an electric current in a chirally imbalanced QCD matter. The qualitative feature of the induced current is consistent with an analytical prediction.