arXiv subjects

Yoshimasa Hidaka

Publications and source records attributed to Yoshimasa Hidaka.

At least 73 records · Page 4Linked to original sources

arXiv2018

Diffusive Nambu-Goldstone modes in quantum time-crystals

We study the Nambu-Goldstone (NG) modes associated with spontaneous breaking of the continuous time-translation symmetry. To discuss a quantum time-crystal with the spontaneously-broken continuous time-translation symmetry, we introduce the van der Pol type nonlinear-friction to open quantum systems. By considering small fluctuations around a time-periodic mean-field solution, we show that a gapless collective mode necessarily appears; this is nothing but the NG mode associated with a time crystal. We show that its dispersion relation becomes $ω=-iC\bm p^2$. We also show that noncommutative breaking of the time-translation and U(1) symmetries results in mixing of the NG modes, and the (typically) propagating NG mode appears, whose dispersion relation becomes $ω=(\pm C_1-iC_2)\bm p^2$.

hep-th↗

arXiv2018

Non-Equilibrium Quantum Transport of Chiral Fluids from Kinetic Theory

We introduce the quantum-field-theory (QFT) derivation of chiral kinetic theory (CKT) from the Wigner-function approach, which manifests side jumps and non-scalar distribution functions associated with Lorentz covariance and incorporates both background fields and collisions. The formalism is utilized to investigate second-order responses of chiral fluids near local equilibrium. Such non-equilibrium anomalous transport is dissipative and affected by interactions. Contributions from both quantum corrections in anomalous hydrodynamic equations (EOM) of motion and those from the CKT and Wigner functions (WF) are considered in a relaxation-time approximation (RTA). Anomalous charged Hall currents engendered by background electric fields and temperature/chemical-potential gradients are obtained. Furthermore, chiral magnetic/vortical effects (CME/CVE) receive viscous corrections as non-equilibrium modifications stemming from the interplay between side jumps, magnetic-moment coupling, and chiral anomaly.

nucl-th↗

arXiv2018

Non-equilibrium Chiral Magnetic/Vortical Effects in Viscous Fluids

We utilize the chiral kinetic theory in a relaxation-time approximation to investigate the nonlinear anomalous responses of chiral fluids with viscous effects. Unlike the cases in equilibrium, it is found that the chiral magnetic effect and chiral vortical effect are modified by the shear and bulk strengths. Particularly, the shear strength could result in charged Hall currents for chiral magnetic and chiral vortical effects, which propagate perpendicular to applied magnetic fields and vorticity. These quantum corrections stemming from side jumps and anomalies are dissipative and pertinent to interactions. Although the non-equilibrium effects upon charge currents are dissipative, the second law of thermodynamics is still satisfied.

hep-th↗

arXiv2018

Nonlinear Responses of Chiral Fluids from Kinetic Theory

The second-order nonlinear responses of inviscid chiral fluids near local equilibrium are investigated by applying the chiral kinetic theory (CKT) incorporating side-jump effects. It is shown that the local equilibrium distribution function can be non-trivially introduced in a co-moving frame with respect to the fluid velocity when the quantum corrections in collisions are involved. For the study of anomalous transport, contributions from both quantum corrections in anomalous hydrodynamic equations of motion and those from the CKT and Wigner functions are considered under the relaxation-time (RT) approximation, which result in anomalous charge Hall currents propagating along the cross product of the background electric field and the temperature (or chemical-potential) gradient and of the temperature and chemical-potential gradients. On the other hand, the nonlinear quantum correction on the charge density vanishes in the classical RT approximation, which in fact satisfies the matching condition given by the anomalous equation obtained from the CKT.

hep-th↗

arXiv2018

Relativistic hydrodynamics from projection operator method

We study relativistic hydrodynamics in the linear regime, based on Mori's projection operator method. In relativistic hydrodynamics, it is considered that ambiguity about the fluid velocity occurs from a choice of a local rest frame: the Landau and Eckart frames. We find that the difference of the frames is not the choice of the local rest frame, but rather that of dynamic variables in the linear regime. We derive hydrodynamic equations in the both frames by the projection operator method. We show that natural derivation gives the linearized Landau equation. Also, we find that, even for the Eckart frame, the slow dynamics is actually described by the dynamic variables for the Landau frame.

hep-ph↗

arXiv2018

Spontaneous symmetry breaking and Nambu-Goldstone modes in dissipative systems

We discuss spontaneous breaking of internal symmetry and its Nambu-Goldstone (NG) modes in dissipative systems. We find that there exist two types of NG modes in dissipative systems corresponding to type-A and type-B NG modes in Hamiltonian systems. To demonstrate the symmetry breaking, we consider a $O(N)$ scalar model obeying a Fokker-Planck equation. We show that the type-A NG modes in the dissipative system are diffusive modes, while they are propagating modes in Hamiltonian systems. We point out that this difference is caused by the existence of two types of Noether charges, $Q_R^α$ and $Q_A^α$: $Q_R^α$ are symmetry generators of Hamiltonian systems, which are not conserved in dissipative systems. $Q_A^α$ are symmetry generators of dissipative systems described by the Fokker-Planck equation, which are conserved. We find that the NG modes are propagating modes if $Q_R^α$ are conserved, while those are diffusive modes if they are not conserved. We also consider a $SU(2)\times U(1)$ scalar model with a chemical potential to discuss the type-B NG modes. We show that the type-B NG modes have a different dispersion relation from those in the Hamiltonian systems.

cond-mat.stat-mech↗

arXiv2017

Goldstino in supersymmetric Bose-Fermi mixtures in the presence of Bose Einstein condensate

We analyze the spectral properties of the Goldstino excitation in a Bose-Fermi mixture of cold atoms, whose masses and interaction strengths are tuned so that the hamiltonian is supersymmetric. We consider systems at zero temperature and assume that, in the weak coupling regime, the fermions form a Fermi sea, while the bosons form a Bose-Einstein condensate. We study the excitation spectrum within a simple extension of the random phase approximation, taking into account the mixing between the supercharge and the fermion caused by the condensate. This mixing affects the fermion spectrum strongly. We argue that the corresponding modification of the fermion spectrum, and the associated fermion distribution in momentum space, could be accessible experimentally, and potentially allow for a determination of the Goldstino properties.

cond-mat.quant-gas↗

arXiv2017

Electric conductivity of hot and dense quark matter in a magnetic field with Landau level resummation via kinetic equations

We compute the electric conductivity of quark matter at finite temperature $T$ and quark chemical potential $μ$ under a magnetic field $B$ beyond the Lowest Landau level approximation. The electric conductivity transverse to $B$ is dominated by the Hall conductivity $σ_H$. For the longitudinal conductivity $σ_\parallel$, we need to solve kinetic equations. Then, we numerically find that $σ_\parallel$ has only mild dependence on $μ$ and the quark mass $m_q$. Moreover, $σ_\parallel$ first decreases and then linearly increases as a function of $B$, leading to an intermediate $B$ region which looks consistent with the experimental signature for the chiral magnetic effect. We also point out that $σ_\parallel$ at nonzero $B$ remains within the range of the lattice-QCD estimate at $B=0$.

hep-ph↗

arXiv2017

General formulae for dipole Wilson line correlators with the Color Glass Condensate

We present general formulae to compute Wilson line correlators with the Color Glass Condensate described by the McLerran-Venugopalan model. We explicitly construct a complete and non-orthogonal set of color-singlet bases and write matrix elements down, so that the exponential of the matrix leads to the Wilson line correlators. We further develop a systematic perturbative expansion of dipole Wilson line correlators in terms of $1/N_c$ where $N_c$ is the color number. As a phenomenological application we calculate the flow harmonics $v_n\{m\}$ in the dipole model and discuss the $N_c$ scaling.

hep-ph↗

arXiv2017

Relativistic Chiral Kinetic Theory from Quantum Field Theories

The chiral kinetic theory of Weyl fermions with collisions in the presence of weak electric and magnetic fields is derived from quantum field theories. It is found that the side-jump terms in the perturbative solution of Wigner functions play a significant role for the derivation. Moreover, such terms manifest the breaking of Lorentz symmetry for distribution functions. The Lorentz covariance of Wigner functions thus leads to modified Lorentz transformation associated with side-jump phenomena further influenced by background fields and collisions.

hep-th↗

arXiv2017

Kinetic derivation of generalized phase space Chern-Simons theory

We study anomalous transport phenomena induced by phase-space Berry curvature. For that purpose we construct a kinetic theory in $2d$ phase space when all abelian Berry curvatures are nonzero. We derive anomalous currents by calculating the complete form of the Poisson brackets of phase space coordinates. Then we construct the low-energy effective theory to reproduce the anomalous currents obtained from the kinetic theory. Such an effective theory is given by the Chern-Simons theory in $1+2d$ dimensions. Some implications of the Chern-Simons theory are also discussed.

cond-mat.mes-hall↗

arXiv2017

Complex saddle points and the sign problem in complex Langevin simulation

We show that complex Langevin simulation converges to a wrong result, by relating it to the Lefschetz-thimble path integral, when the path-integral weight has different phases among dominant complex saddle points. Equilibrium solution of the complex Langevin equation forms local distributions around complex saddle points. Its ensemble average approximately becomes a direct sum of the average in each local distribution, where relative phases among them are dropped. We propose that by taking these phases into account through reweighting, we can solve the wrong convergence problem. However, this prescription may lead to a recurrence of the sign problem in the complex Langevin method for quantum many-body systems.

hep-lat↗

arXiv2017

Kinetic Theory and Anomalous Transports in the Presence of Nonabelian Phase-Space Berry Curvatures

We construct the kinetic theory in ($1+2d$)-dimensional phase space and time when all abelian and nonabelian phase-space Berry curvatures are nonzero. Then we calculate anomalous transports induced by the Berry curvatures on the basis of the kinetic theory. As an example, we study anomalous charge and spin transports induced by the SU($2$) Berry curvatures. We also derive the topological effective theory to reproduce the transports in insulators calculated from the kinetic theory. Such an effective theory is given by the nonabelian phase space Chern-Simons theory.

cond-mat.mes-hall↗

arXiv2016

Lefschetz-thimble approach to the Silver Blaze problem of one-site fermion model

The sign problem of finite-density QCD at the zero temperature becomes very severe if the quark chemical potential exceeds half of the pion mass. In order to understand its property, we consider the sign problem of the one-site fermion model appearing in its path-integral expression by using the Lefschetz-thimble method. We show that the original integration cycle becomes decomposed into multiple Lefschetz thimbles at a certain value of the fermion chemical potential, which would correspond to half of the pion mass of finite-density QCD. This triggers a fictitious phase transition on each Lefschetz thimble, and the interference of complex phases among them plays an important role for the correct description of the system. We also show that the complex Langevin method does not work in this situation.

hep-lat↗

arXiv2016

Tetrahedral shape and surface density wave of $^{16}$O caused by $α$-cluster correlations

$α$-cluster correlations in the $0^+_1$ and $3^-_1$ states of $^{12}$C and $^{16}$O are studied using the method of antisymmetrized molecular dynamics, with which nuclear structures are described from nucleon degrees of freedom without assuming existence of clusters. The intrinsic states of $^{12}$C and $^{16}$O have triangle and tetrahedral shapes, respectively, because of the $α$-cluster correlations. These shapes can be understood as spontaneous symmetry breaking of rotational invariance, and the resultant surface density oscillation is associated with density wave (DW) caused by the instability of Fermi surface with respect to particle-hole correlations with the wave number $λ=3$. $^{16}$O($0^+_1$) and $^{16}$O($3^-_1$) are regarded as a set of parity partners constructed from the rigid tetrahedral intrinsic state, whereas $^{12}$C($0^+_1$) and $^{12}$C($3^-_1$) are not good parity partners as they have triangle intrinsic states of different sizes with significant shape fluctuation because of softness of the $3α$ structure. $E3$ transition strengths from the $3^-_1$ to $0^+_1$ states in $^{12}$C and $^{16}$O are also discussed.

nucl-th↗

arXiv2016

Magnetic shift of the chemical freezeout and electric charge fluctuations

We discuss the effect of a strong magnetic field on the chemical freezeout points in the ultrarelativistic heavy-ion collision. As a result of the inverse magnetic catalysis or the magnetic inhibition, the crossover onset to hot and dense matter out of quarks and gluons should be shifted to a lower temperature. To quantify this shift we employ the hadron resonance gas model and an empirical condition for the chemical freezeout. We point out that the charged particle abundances are significantly affected by the magnetic field so that the electric charge fluctuation is largely enhanced especially at high baryon density. The charge conservation partially cancels the enhancement but our calculation shows that the electric charge fluctuation and the charge chemical potential could serve as a magnetometer. We find that the fluctuation exhibits a crossover behavior rapidly increased for eB >~ (0.4GeV)^2, while the charge chemical potential has better sensitivity to the magnetic field.

hep-ph↗

arXiv2016

Lefschetz-thimble analysis of the sign problem in one-site fermion model

The Lefschetz-thimble approach to path integrals is applied to a one-site model of electrons, i.e., the one-site Hubbard model. Since the one-site Hubbard model shows a non-analytic behavior at the zero temperature and its path integral expression has the sign problem, this toy model is a good testing ground for an idea or a technique to attack the sign problem. Semiclassical analysis using complex saddle points unveils the significance of interference among multiple Lefschetz thimbles to reproduce the non-analytic behavior by using the path integral. If the number of Lefschetz thimbles is insufficient, we found not only large discrepancies from the exact result, but also thermodynamic instabilities. Analyzing such singular behaviors semiclassically, we propose a criterion to identify the necessary number of Lefschetz thimbles. We argue that this interference of multiple saddle points is a key issue to understand the sign problem of the finite-density quantum chromodynamics.

hep-th↗

arXiv2015

Spectral properties of the Goldstino in supersymmetric Bose-Fermi mixtures

We evaluate the spectral properties of the Goldstino in a Bose-Fermi mixture of cold atoms and molecules whose dynamics is governed by a supersymmetric hamiltonian. Model independent results are obtained from sum rules obeyed by the spectral function. We carry out specific calculations, at zero and finite temperature, using the Random Phase Approximation, and obtain in particular analytic expressions for the dispersion relation at small momentum. These explicit calculations allow us to pin down more precisely the features of the Goldstino that can be attributed to the supersymmetry alone, together with its spontaneous breaking. The anomalous large effect of the Fermi sea at moderate and large momenta is emphasized.

cond-mat.quant-gas↗