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T. Takaishi

Publications and source records attributed to T. Takaishi.

At least 19 recordsLinked to original sources
arXiv2021

Power-Law Return-Volatility Cross Correlations of Bitcoin

This paper investigates the return-volatility asymmetry of Bitcoin. We find that the cross correlations between return and volatility (squared return) are mostly insignificant on a daily level. In the high-frequency region, we find thata power-law appears in negative cross correlation between returns and future volatilities, which suggests that the cross correlation is \revision{long ranged}. We also calculate a cross correlation between returns and the power of absolute returns, and we find that the strength of \revision{the cross correlations} depends on the value of the power.

q-fin.ST↗
arXiv2005

The 3-state Potts model as a heavy quark finite density laboratory

The 3-D Z(3) Potts model is a model for finite temperature QCD with heavy quarks. The chemical potential in QCD becomes an external magnetic field in the Potts model. Following Alford et al.\cite{Alford_et_al}, we revisit this mapping, and determine the phase diagram for an arbitrary chemical potential, real or imaginary. Analytic continuation of the phase transition line between real and imaginary chemical potential can be tested with precision. Our results show that the chemical potential weakens the heavy-quark deconfinement transition in QCD.

hep-lat↗
arXiv2005

Properties of hadron screening masses at small baryonic density

The properties of hadron screening masses around the deconfinement phase transition at finite baryonic density can be studied by evaluating the Taylor coefficients with respect to the iso-scalar and iso-vector chemical potentials. We simulate 2-flavour lattice QCD with staggered fermions on a 12*12*24*6 lattice with ma = 0.05 and 0.10 and report investigations of nucleon, pseudo-scalar and vector mesons. We present new, strong evidence that in the confining phase, the screening masses at vanishing chemical potential have significant temperature dependence, but the effect of the iso-scalar chemical potential is very small. Above the critical temperature, the second derivative terms of mesons rapidly increase as contrasted to the case of baryon. We also study the responses of the screening masses to an iso-vector chemical potential and discuss some of the issues related to the properties of hadron masses at finite density.

hep-lat↗
arXiv2003

Simulation of Wilson fermion at finite isospin density

For QCD with Wilson fermions at isospin chemical potential we study the finite phase transition on an $8^3\times4$ lattice at $κ=0.15$. We use two gauge actions: Wilson action and DBW2 action. Both actions give the same results. The phase diagram is qualitatively similar to the one obtained for QCD at small baryon chemical potential. We also calculate the number density for various isospin chemical potentials.

hep-lat↗
arXiv2003

Phase Fluctuation of Fermion Determinant in Lattice QCD at Finite Density

Once the quark chemical potential $μ$ is introduced in finite density QCD, the fermion determinant appeared in the path integral measure becomes complex. In order to investigate the phase effect of SU(3) lattice QCD (2-flavors), we calculated the fluctuation of the phase of $\detΔ(μ)$ on a $8^3\times4$ lattice at $μ= 0.1$ and 0.2. Then we calculated the chiral condensate and Polyakov line in the no phase and reweighted cases. There is little difference between these two cases at $μ= 0.1$ and 0.2. We consider a possible reason for this result below $μ\le 0.27$ in terms of $Z_3$ symmetry.

hep-lat↗
arXiv2003

Quenched charmonium spectrum

We study charmonium using the standard relativistic formalism in the quenched approximation, on a set of lattices with isotropic lattice spacings ranging from 0.1 to 0.04 fm. We concentrate on the calculation of the hyperfine splitting between eta_c and J/psi, aiming for a controlled continuum extrapolation of this quantity. The splitting extracted from the non-perturbatively improved clover Dirac operator shows very little dependence on the lattice spacing for $a \leq 0.1$ fm. The dependence is much stronger for Wilson and tree-level improved clover operators, but they still yield consistent extrapolations if sufficiently fine lattices, $a \leq 0.07$ fm ($a M(η_c) \leq 1$), are used. Our result for the hyperfine splitting is 77(2)(6) MeV (where Sommer's parameter, r_0, is used to fix the scale). This value remains about 30% below experiment. Dynamical fermions and OZI-forbidden diagrams both contribute to the remainder. Results for the eta_c and J/psi wave functions are also presented.

hep-lat↗
arXiv2002

QCD simulations at small chemical potential

Within the reweighting approach, one has the freedom to choose the Monte Carlo action so that it provides a good overlap with the finite-μmeasure but remains simple to simulate. We explore several choices of action in the regime of small μ. Simulating with a finite isospin chemical potential μ_I=μgives a better overlap than the standard choice μ=0, with no computational overhead.

hep-lat↗
arXiv2002

Responses of quark condensates to the chemical potential

The responses of quark condensates to the chemical potential, as a function of temperature T and chemical potential μ, are calculated within the Nambu--Jona-Lasinio (NJL) model. We compare our results with those from the recent lattice QCD simulations [QCD-TARO Collaboration, Nucl. Phys. B (Proc. Suppl.) 106, 462 (2002)]. The NJL model and lattice calculations show qualitatively similar behavior, and they will be complimentary ways to study hadrons at finite density. The behavior above T_c requires more elaborated analyses.

hep-lat↗
arXiv2002

Renormalization group flow of SU(3) lattice gauge theory - Numerical studies in a two coupling space

We investigate the renormalization group (RG) flow of SU(3) lattice gauge theory in a two coupling space with couplings $β_{11}$ and $β_{12}$ corresponding to $1\times 1$ and $1\times 2$ loops respectively. Extensive numerical calculations of the RG flow are made in the fourth quadrant of this coupling space, i.e., $β_{11}>0$ and $β_{12}<0$. Swendsen's factor two blocking and the Schwinger-Dyson method are used to find an effective action for the blocked gauge field. The resulting renormalization group flow runs quickly towards an attractive stream which has an approximate line shape. This is numerical evidence of a renormalized trajectory which locates close to the two coupling space. A model flow equation which incorporates a marginal coupling (asymptotic scaling term), an irrelevant coupling and a non-perturbative attraction towards the strong coupling limit reproduces qualitatively the observed features. We further examine the scaling properties of an action which is closer to the attractive stream than the currently used improved actions. It is found that this action shows excellent restoration of rotational symmetry even for coarse lattices with $a \sim 0.3$ fm.

hep-lat↗
arXiv2001

Screening mass responses to the chemical potential at finite temperature

Responses to chemical potential of the pseudoscalar meson screening mass and the chiral condensate in lattice QCD are investigated. On a $16 \times 8^2 \times \4$ lattice with two flavors of staggered quarks the first and second responses below and above $T_c$ are evaluated. Different behavior in the low and the high temperature phases are observed, which may be explained as a consequence of the chiral symmetry breaking and restoration.

hep-lat↗
arXiv2001

Responses of hadrons to chemical potential at finite temperature

We present a framework to compute the responses of hadron masses to the chemical potential in lattice QCD simulations. As a first trial, the screening mass of the pseudoscalar meson and its first and second responses are evaluated. We present results on a $16\times 8^2\times 4$ lattice with two flavors of staggered quarks below and above $T_c$. The responses to both the isoscalar and isovector chemical potentials are obtained. They show different behavior in the low and the high temperature phases, which may be explained as a consequence of chiral symmetry breaking and restoration, respectively.

hep-lat↗
arXiv2001

Quenched charmonium near the continuum limit

We study relativistic charmonium on very fine quenched lattices (beta=6.4 and 6.6). We concentrate on the calculation of the hyperfine splitting between eta_c and J/psi, aiming for a controlled continuum extrapolation of this quantity. Results for the eta_c and J/psi wave functions are also presented.

hep-lat↗
arXiv2000

Chemical potential response of meson masses at finite temperature

We study the response of meson masses to the chemical potential ($\partial{m}/\partialμ$) at high temperature and at zero chemical potential on $N_f=2$ lattice with staggered fermions. Preliminary results for the meson composed of different quarks show that $\partial{m}/\partialμ|_{μ=0}$ is negative in the confinement phase and positive in the deconfinement phase.

hep-lat↗
arXiv2000

Simulation of n_f =3 QCD by Hybrid Monte Carlo

Simulations of odd flavors QCD can be performed in the framework of the hybrid Monte Carlo algorithm where the inverse of the fermion matrix is approximated by a polynomial. In this exploratory study we perform three flavors QCD simulations. We make a comparison of the hybrid Monte Carlo algorithm and the R-algorithm which also simulates odd flavors systems but has step-size errors. We find that results from our hybrid Monte Carlo algorithm are in agreement with those from the R-algorithm obtained at very small step-size.

hep-lat↗
arXiv2000

Simulation of SU(2) Dynamical Fermion at Finite Chemical Potential and at Finite Temperature

SU(2) lattice gauge theory with dynamical fermion at non-zero chemical potential and at finite temperature is studied. We focus on the influence of chemical potential for quark condensate and mass of pseudoscalar meson at finite temperature. Hybrid Monte Carlo simulations with $N_f=8$ staggered fermions are carried out on $12 \times 12\times 24 \times 4$ lattice. At $β=1.1$ and $m_{q}=$0.05,0.07,0.1, we calculate the quark condensate and masses of pseudoscalar meson consisting of light and heavier quarks for chemical potential $μ=$ 0.0,0.02,0.05,0.1,0.2.

hep-lat↗
arXiv2000

Meson Correlators in Finite Temperature Lattice QCD

We analyze temporal and spatial meson correlators in quenched lattice QCD at T>0. Below T_c we observe little change in the meson properties as compared with T=0. Above T_c we observe new features: chiral symmetry restoration and signals of plasma formation, but also indication of persisting mesonic (metastable) states and different temporal and spatial masses in the mesonic channels. This suggests a complex picture of QGP in the region 1 - 1.5 T_c.

hep-lat↗
arXiv1999

A Study of Meson Correlators at Finite Temperature

We present results for mesonic propagators in temporal and spatial directions at T below and above the deconfining transition in quenched QCD. Anisotropic lattices are used to get enough information in the temporal direction. We use the Wilson fermion action for light quarks and Fermilab action for heavy quarks.

hep-lat↗