論文 - 早田　智也

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

Tomoya Hayata, Arata Yamamoto

Physical Review A - Atomic, Molecular, and Optical Physics （American Physical Society）  92 （ 4 ）  2015年10月

筆頭著者, 責任著者, 査読有り,  ISSN  1094-1622

　概要を見る

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.

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Relativistic hydrodynamics from quantum field theory on the basis of the generalized Gibbs ensemble method

Tomoya Hayata, Yoshimasa Hidaka, Toshifumi Noumi, Masaru Hongo

Physical Review D - Particles, Fields, Gravitation and Cosmology （American Physical Society）  92 （ 6 ）  2015年09月

査読有り,  ISSN  1550-2368

　概要を見る

We derive relativistic hydrodynamics from quantum field theories by assuming that the density operator is given by a local Gibbs distribution at initial time. We decompose the energy-momentum tensor and particle current into nondissipative and dissipative parts, and analyze their time evolution in detail. Performing the path-integral formulation of the local Gibbs distribution, we microscopically derive the generating functional for the nondissipative hydrodynamics. We also construct a basis to study dissipative corrections. In particular, we derive the first-order dissipative hydrodynamic equations without a choice of frame such as the Landau-Lifshitz or Eckart frame.

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Inhomogeneous Polyakov loop induced by inhomogeneous chiral condensates

Tomoya Hayata, Arata Yamamoto

PHYSICS LETTERS B （ELSEVIER SCIENCE BV）  744   401 - 405 2015年05月

筆頭著者, 責任著者, 査読有り,  ISSN  0370-2693

　概要を見る

We study the spatial inhomogeneity of the Polyakov loop induced by inhomogeneous chiral condensates. We formulate an effective model of gluons on the background fields of chiral condensates, and perform its lattice simulation. On the background of inhomogeneous chiral condensates, the Polyakov loop exhibits an in-phase spatial oscillation with the chiral condensates. We also analyze the heavy quark potential and show that the inhomogeneous Polyakov loop indicates the inhomogeneous confinement of heavy quarks. (C) 2015 The Authors. Published by Elsevier B.V.

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Dispersion relations of Nambu-Goldstone modes at finite temperature and density

Tomoya Hayata, Yoshimasa Hidaka

Physical Review D - Particles, Fields, Gravitation and Cosmology （American Physical Society）  91 （ 5 ）  2015年03月

査読有り,  ISSN  1550-2368

　概要を見る

We discuss the dispersion relations of Nambu-Goldstone (NG) modes associated with spontaneous breaking of internal symmetries at finite temperature and/or density. We show that the dispersion relations of type-A (I) and type-B (II) NG modes are linear and quadratic in momentum, whose imaginary parts are quadratic and quartic, respectively. In both cases, the real parts of the dispersion relations are larger than the imaginary parts when the momentum is small, so that the NG modes can propagate far away. We derive the gap formula for NG modes in the presence of a small explicit breaking term. We also discuss the gapped partners of type-B NG modes, when the expectation values of a charge density and a local operator that break the same symmetry coexist.

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Complex langevin simulation in condensed matter physics

Yamamoto A, Hayata T

Proceedings of Science 14-18-July-2015 2015年

査読有り

　概要を見る

The complex Langevin method is one hopeful candidate to tackle the sign
problem. This method is applicable not only to QCD but also to nonrelativistic
field theory, such as condensed matter physics. We present the simulation
results of a rotating Bose gas and an imbalanced Fermi-Hubbard model.

Broken spacetime symmetries and elastic variables

Tomoya Hayata, Yoshimasa Hidaka

PHYSICS LETTERS B （ELSEVIER SCIENCE BV）  735   195 - 199 2014年07月

査読有り,  ISSN  0370-2693

　概要を見る

We discuss spontaneous breaking of continuum symmetries, whose generators do explicitly depend on the spacetime coordinates. We clarify the relation between broken symmetries and elastic variables at both zero and finite temperatures, and/or finite densities, and show the general counting rule that is model-independently determined by the symmetry breaking pattern. We apply it to three intriguing examples: rotational, conformal, and gauge symmetries. (C) 2014 The Authors. Published by Elsevier B. V.

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Schwinger mechanism with stochastic quantization

Kenji Fukushima, Tomoya Hayata

PHYSICS LETTERS B （ELSEVIER SCIENCE BV）  735   371 - 375 2014年07月

査読有り,  ISSN  0370-2693

　概要を見る

We prescribe a formulation of the particle production with real-time Stochastic Quantization. To construct the retarded and the time-ordered propagators we decompose the stochastic variables into positive- and negative-energy parts. In this way we demonstrate how to derive a standard formula for the Schwinger mechanism under time-dependent electric fields. We discuss a mapping to the Schwinger-Keldysh formalism and a relation to the classical statistical simulation. (C) 2014 The Authors. Published by Elsevier B.V.

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Temporal chiral spiral in QCD in the presence of strong magnetic fields

Tomoya Hayata, Yoshimasa Hidaka, Arata Yamamoto

PHYSICAL REVIEW D （AMER PHYSICAL SOC）  89 （ 8 ）  2014年04月

筆頭著者, 責任著者, 査読有り,  ISSN  1550-7998

　概要を見る

Vacuum properties of quantum chromodynamics in strong magnetic and finite electric fields are investigated. We show that when a uniform electric field is instantaneously applied in the parallel direction to a strong magnetic field, it induces temporal oscillation of the scalar and pseudoscalar condensates. This is a temporal analog to the chiral spiral. The oscillation originates with the propagation of the collective mode, which is protected by the axial anomaly and thus is nondissipative.

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Sign problem and the chiral spiral on the finite density lattice

Ryutaro Fukuda, Kenji Fukushima, Tomoya Hayata, Yoshimasa Hidaka

PHYSICAL REVIEW D （AMER PHYSICAL SOC）  89 （ 1 ）  2014年01月

査読有り,  ISSN  1550-7998

　概要を見る

We investigate the sign problem of the fermion determinant at finite baryon density in (1 + 1) dimensions, in which the ground state in the chiral limit should be free from the sign problem by forming a chiral spiral. To confirm it, we evaluate the fermion determinant in the continuum theory at the one-loop level and find that the determinant becomes real as expected. The conventional lattice formulation to implement a chemical potential is, however, not compatible with the spiral transformation. We discuss an alternative of the finite-density formulation and numerically verify the chiral spiral on the finite density lattice.

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Dynamical mass generation of vector mesons from QCD trace anomaly

Tomoya Hayata

PHYSICAL REVIEW D （AMER PHYSICAL SOC）  88 （ 3 ）  2013年08月

筆頭著者, 責任著者, 査読有り,  ISSN  1550-7998

　概要を見る

Mass formulas for the vector mesons written in terms of the gluon condensate, i.e., the trace anomaly in quantum chromodynamics (QCD), are derived on the basis of finite energy QCD sum rules. We utilize sum rules with s(n) and s(n+1/2) weights, which relate the energy-weighted spectral sums to the vacuum expectation values of certain commutation relations. After evaluating the commutation relations, the sum rules with s(n) weights are reduced to the familiar ones obtained from the operator product expansion (OPE). On the other hand, the sum rules with s(n+1/2) weights cannot be derived from OPE. They give new relations between the spectral sums and QCD vacuum fluctuations. To derive a simple mass formula, we adopt the pole + continuum ansatz for the spectral function, and we solve coupled equations given by the sum rules with s(0,1) weights and the new sum rule with s(1/2) weight. Application of our approach to the axial-vector meson is also discussed.

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Time-dependent heavy-quark potential at finite temperature from gauge-gravity duality

Tomoya Hayata, Kanabu Nawa, Tetsuo Hatsuda

Physical Review D - Particles, Fields, Gravitation and Cosmology （American Physical Society (APS)）  87 （ 10 ）  2013年05月

筆頭著者, 責任著者, 査読有り,  ISSN  1550-7998

　概要を見る

The potential between a heavy quark and an antiquark inside the quark-gluon plasma is studied on the basis of the gauge-gravity duality. A real-time complex potential VQQ̄(t,r) is derived from the Wilson loop, which is evaluated by its gravity dual in the Euclidean five-dimensional anti-de Sitter black hole metric. To make the analytic continuation from the imaginary time to the real time, specific variational configurations of the string world sheet in the Euclidean metric are introduced. A rapid approach of V QQ̄(t,r) to its stationary value is found at the time scale t (πT)-1, and the imaginary part of VQQ̄(r) becomes significant above the length scale r=1.72(πT)-1. Also, these scales are independent of the 't Hooft coupling λ. Implications of these results to the properties of heavy quarkonia in quark-gluon plasma are briefly discussed. © 2013 American Physical Society.

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New QCD sum rules based on canonical commutation relations

Tomoya Hayata

PROGRESS IN PARTICLE AND NUCLEAR PHYSICS （ELSEVIER SCIENCE BV）  67 （ 2 ） 136 - 139 2012年04月

筆頭著者, 責任著者, 査読有り,  ISSN  0146-6410

　概要を見る

New derivation of QCD sum rules by canonical commutators is developed. It is the simple and straightforward generalization of Thomas-Reiche-Kuhn sum rule on the basis of Kugo-Ojima operator formalism of a non-abelian gauge theory and a suitable subtraction of UV divergences. By applying the method to the vector and axial vector current in QCD, the exact Weinberg's sum rules are examined. Vector current sum rules and new fractional power sum rules are also discussed. (C) 2011 Elsevier B.V. All rights reserved.

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Resealed Perturbation Theory

Tomoya Hayata

PROGRESS OF THEORETICAL PHYSICS （PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE）  124 （ 6 ） 1097 - 1104 2010年12月

筆頭著者, 責任著者, 査読有り,  ISSN  0033-068X

　概要を見る

A nonperturbative method that can go beyond the weak coupling perturbation theory is introduced. The essential idea is to formulate a set of exact differential equations as a function of coupling strength g. Unlike other resummation methods in which information on higher-order terms is necessary, we only need a leading-order perturbative formula in every step to reach a large value of g. The method is applied to the quantum anharmonic oscillator and quantum double-well potential in one dimension. Both are known to have divergent series in the weak coupling perturbation and the latter is not Borel-summable. Our method is shown to work well from the weak coupling to the strong coupling for the energy eigenvalues and the wave functions. The method is also applied successfully to a system with a time-dependent external field.

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