arXiv subjects

S. Sakai

Publications and source records attributed to S. Sakai.

72 records · Page 4Linked to original sources

arXiv2000

Improved Gauge Actions on Anisotropic Lattices I

On anisotropic lattices with the anisotropy $ξ=a_σ/a_τ$ the following basic parameters are calculated by perturbative method: (1) the renormalization of the gauge coupling in spatial and temporal directions, $g_σ$ and $g_τ$, (2) the $Λ$ parameter, (3) the ratio of the renormalized and bare anisotropy $η=ξ/ξ_B$ and (4) the derivatives of the coupling constants with respect to $ξ$, $\partial g_σ^{-2}/\partial ξ$ and $\partial g_τ^{-2}/\partial ξ$. We employ the improved gauge actions which consist of plaquette and six-link rectangular loops, $c_0 P(1 \times 1)_{μν} + c_1 P(1 \times 2)_{μν}$. This class of actions covers Symanzik, Iwasaki and DBW2 actions. The ratio $η$ shows an impressive behavior as a function of $c_{1}$, i.e.,$η>1$ for the standard Wilson and Symanzik actions, while $η<1$ for Iwasaki and DBW2 actions. This is confirmed non-perturbatively by numerical simulations in weak coupling regions. The derivatives $\partial g^{-2}_τ/\partial ξ$ and $\partial g^{-2}_σ/\partial ξ$ also changes sign as $-c_{1}$ increases. For Iwasaki and DBW2 actions they become opposite sign to those for standard and Symanzik actions. However, their sum is independent of the type of actions due to Karsch's sum rule.

hep-lat↗

arXiv2000

Large-Flavor QCD on the Lattice

We study the nature of the QCD vacuum at general number of flavors $N_F$ by numerical simulations on the lattice. Combining the results with those of the perturbation theory, we propose the following picture: 1) For $N_F \ge 17$, there exists only one IR fixed point at vanishing gauge coupling, i.e., the theory in the continuum limit is trivial. 2) For $16 \ge N_F \ge 7$, there is a non-trivial fixed point. Therefore, the theory is non-trivial with anomalous dimensions, however, without quark confinement. 3) For $N_F \le 6$, theories satisfy both quark confinement and spontaneous chiral symmetry breaking in the continuum limit.

hep-lat↗

arXiv1999

The Extragalactic Distance Scale Key Project XVIII. The Discovery of Cepheids and a New Distance to NGC 4535 Using the Hubble Space Telescope

We report on the discovery of Cepheids in the Virgo spiral galaxy NGC 4535, based on observations made with the Wide Field and Planetary Camera 2 on board the Hubble Space Telescope. NGC 4535 is one of 18 galaxies observed as a part of The HST Key Project on the Extragalactic Distance Scale which aims to measure the Hubble constant to 10% accuracy. NGC 4535 was observed over 13 epochs using the F555W filter, and over 9 epochs using the F814W filter. The HST F555W and F814W data were transformed to the Johnson V and Kron-Cousins I magnitude systems, respectively. Photometry was performed using two independent programs, DoPHOT and DAOPHOT II/ALLFRAME. Period-luminosity relations in the V and I bands were constructed using 39 high-quality Cepheids present in our set of 50 variable candidates. We obtain a distance modulus of 31.02+/-0.26 mag, corresponding to a distance of 16.0+/-1.9 Mpc. Our distance estimate is based on values of mu = 18.50 +/- 0.10 mag and E(V-I) = 0.13 mag for the distance modulus and reddening of the LMC, respectively.

astro-ph↗

arXiv1998

A Cepheid Distance to the Fornax Cluster

The Hubble Space Telescope is being used to measure accurate Cepheid distances to nearby galaxies with the ultimate aim of determining the Hubble constant, H_0. For the first time, it has become feasible to use Cepheid variables to derive a distance to a galaxy in the southern hemisphere cluster of Fornax. Based on the discovery of 37 Cepheids in the Fornax galaxy NGC 1365, a distance to this galaxy of 18.6 +/- 0.6 Mpc (statistical error only) is obtained. This distance leads to a value of H_0 = 70 +/- 7 (random) +/- 18 (systematic) km/sec/Mpc in good agreement with estimates of the Hubble constant further afield.

astro-ph↗

arXiv1998

The HST Key Project on the Extragalactic Distance Scale XIV. The Cepheids in NGC 1365

We report the detection of Cepheid variable stars in the barred spiral galaxy NGC 1365, located in the Fornax cluster, using the Hubble Space Telescope Wide Field and Planetary Camera 2. Twelve V (F555W) and four I (F814W) epochs of observation were obtained. The two photometry packages, ALLFRAME and DoPHOT, were separately used to obtain profile-fitting photometry of all the stars in the HST field. The search for Cepheid variable stars resulted in a sample of 52 variables, with periods between 14 and 60 days, in common with both datasets. ALLFRAME photometry and light curves of the Cepheids are presented. A subset of 34 Cepheids were selected on the basis of period, light curve shape, similar ALLFRAME and DoPHOT periods, color, and relative crowding, to fit the Cepheid period-luminosity relations in V and I for both ALLFRAME and DoPHOT. The measured distance modulus to NGC 1365 from the ALLFRAME photometry is 31.31 +/- 0.20 (random) +/- 0.18 (systematic) mag, corresponding to a distance of 18.3 +/- 1.7 (random) +/- 1.6 (systematic) Mpc. The reddening is measured to be E(V-I) = 0.16 +/- 0.08 mag. These values are in excellent agreement with those obtained using the DoPHOT photometry, namely a distance modulus of 31.26 +/- 0.10 mag, and a reddening of 0.15 +/- 0.10 mag (internal errors only).

astro-ph↗

arXiv1998

Quantum Chromodynamics with Many Flavors

We investigate the phase structure of lattice QCD for general number of flavors $N_F$. Based on numerical data combined with the results of the perturbation theory we propose the following picture: When $N_F \ge 17$, there is only one IR fixed point at vanishing gauge coupling, i.e., the theory in the continuum limit is trivial. On the other hand, when $16 \ge N_F \ge 7$, there is a non-trivial fixed point. Therefore, the theory is non-trivial with anomalous dimensions, however, without quark confinement. Theories which satisfy both quark confinement and spontaneous chiral symmetry breaking in the continuum limit exist only for $N_F \le 6$.

hep-lat↗

arXiv1997

The HST Key Project on the Extragalactic Distance Scale XIII. The Metallicity Dependence of the Cepheid Distance Scale

Uncertainty in the metal abundance dependence of the Cepheid variable period- luminosity (PL) relation remains one of the outstanding sources of systematic error in the extragalactic distance scale and Hubble constant. To test for such a metallicity dependence, we have used the WFPC2 camera on the Hubble Space Telescope (HST) to observe Cepheids in two fields in the nearby spiral galaxy M101, which span a range in oxygen abundance of 0.7+-0.15 dex. A differential analysis of the PL relations in V and I in the two fields yields a marginally significant change in the inferred distance modulus on metal abundance, with d(m-M)/d[O/H] = -0.24+-0.16 mag/dex. The trend is in the theoretically predicted sense that metal-rich Cepheids appear brighter and closer than metal-poor stars. External comparisons of Cepheid distances with those derived from three other distance indicators, in particular the tip of the red giant branch method, further constrain the magnitude of any Z-dependence of the PL relation at V and I. The overall effects of any metallicity dependence on the distance scale derived with HST will be of the order of a few percent or less for most applications, though distances to individual galaxies at the extremes of the metal abundance range may be affected at the 10% level.

astro-ph↗

arXiv1996

Phase structure of QCD for general number of flavors

We investigate and elucidate the phase structure of QCD for general number of flavors $N_F$ with Wilson quarks, varying $N_F$ from 2 up to 300. Based on numerical results combined with the result of the perturbation theory we propose the following picture: When $N_F \ge 17$, there is only a trivial fixed point and therefore the theory in the continuum limit is trivial. On the other hand, when $16 \ge N_F \ge 7$, there is a non-trivial fixed point and therefore the theory is non-trivial with anomalous dimensions, however, without quark confinement. Theories which satisfy both quark confinement and spontaneous chiral symmetry breaking in the continuum limit exist only for $N_F \le 6$. We also discuss the structure of the deconfining phase at finite temperatures for the small number of flavors such as $N_F=2$ and 3, through a systematic study of it for general number of flavors.

hep-lat↗

arXiv1996

Finite Temperature Transitions in Lattice QCD with Wilson Quarks --- Chiral Transitions and the Influence of the Strange Quark ---

The nature of finite temperature transitions in lattice QCD with Wilson quarks is studied near the chiral limit for the cases of 2, 3, and 6 flavors of degenerate quarks ($N_F=2$, 3, and 6) and also for the case of massless up and down quarks and a light strange quark ($N_F=2+1$). Our simulations mainly performed on lattices with the temporal direction extension $N_t=4$ indicate that the finite temperature transition in the chiral limit (chiral transition) is continuous for $N_F=2$, while it is of first order for $N_F=3$ and 6. We find that the transition is of first order for the case of massless up and down quarks and the physical strange quark where we obtain a value of $m_ϕ/m_ρ$ consistent with the physical value. We also discuss the phase structure at zero temperature as well as that at finite temperatures.

hep-lat↗

arXiv1995

Finite Temperature QCD with Wilson Quarks: A Study with a Renormalization Group Improved Gauge Action

Finite temperature transition in lattice QCD with degenerate Wilson quarks is investigated on an $N_t=4$ lattice, using a renormalization group improved gauge action. We find the following for the $N_F=2$ case: 1) The transition is smooth for a wide range of the quark mass. 2) The chiral transition is continuous. 3) The chiral condensation well satisfies a scaling relation with the critical exponents of the 3 dimensional $O(4)$ spin model. For $N_F=3$, we find that the chiral transition is of first order.

hep-lat↗

arXiv1995

QCD Phase Transition with Strange Quark in Wilson Formalism for Fermions

The nature of QCD phase transition is studied with massless up and down quarks and a light strange quark, using the Wilson formalism for quarks on a lattice with the temporal direction extension $N_t=4$. We find that the phase transition is first order in the cases of both about 150 MeV and 400 MeV for the strange quark mass. These results together with those for three degenerate quarks suggest that QCD phase transition in nature is first order.

hep-lat↗

arXiv1995

Chiral Phase Transition in Lattice QCD with Wilson Quarks

The nature of the chiral phase transition in lattice QCD is studied for the cases of 2, 3 and 6 flavors with degenerate Wilson quarks, mainly on a lattice with the temporal direction extension $N_t=4$. We find that the chiral phase transition is continuous for the case of 2 flavors, while it is of first order for 3 and 6 flavors.

hep-lat↗

arXiv1994

Finite Temperature Transition in Two Flavor QCD with Renormalization Group Improved Action

The finite temperature transition or crossover in QCD with two degenerate Wilson quarks is investigated using a renormalization group improved action. At $β=2.0$ and 2.1 where $a^{-1} \sim 1.0-1.2$ GeV, the expectation value of the Polyakov loop and the pion screening mass on an $8^3 \times 4$ lattice vary smoothly with the hopping parameter through the transition/crossover. The quark screening mass in the high temperature phase agrees well with that in the low temperature phase calculated on an $8^4$ lattice. The smooth transition of the observables is totally different from the sharp transition found for the standard action at $β=5.0$ and 5.1 where $a^{-1}$ is also $1.0-1.2$ GeV.

hep-lat↗

arXiv1994

Nature of the finite temperature transition in QCD with strange quark

The finite temperature transition in QCD is studied using Wilson quarks for the cases of $N_F=2$, 3 and 2+1. For $N_F=2$ the transition is smooth in the chiral limit on both $\nt=4$ and 6 lattices. For $N_F=3$, clear two state signals are observed for $β\leq4.7$ on $8^2\times10 \times4$ and $12^3\times4$ lattices, which implies the transition is first order for $m_q \simm{<} 140$ MeV. For $N_F=2+1$ we study two cases of $m_s \simeq 150$ and 400 MeV with $m_u=m_d \simeq 0$. In contrast to a previous result with staggered quarks, two state signals are clearly observed for both cases, suggesting a first order QCD phase transition in the real world.

hep-lat↗

arXiv1993

High statistics calculations of quenched QCD spectrum using various quark sources

We present the results for the hadron spectrum calculated on 400 configurations using point source, wall source and 8-cubic sources, in quenched QCD with Wilson fermions at $β=6.0$ and $K=0.155$ on a $24^3 \times 54$ lattice. The results for the ground state masses obtained with three types of quark sources agree well with each other. Masses of the first excited states appear consistent with experimental values within large errors.

hep-lat↗

arXiv1993

Quantum chromodynamics with various number of flavors

The phase structure of QCD with various number of flavors is studied for Wilson quarks. For the case of $N_F=3$ we find that the finite temperature deconfining transition is of first order in the chiral limit on an $N_t=4$ lattice. Together with our previous results that the deconfining transition in the chiral limit is continuous for $N_F=2$ and is first order for $N_F=6$, the order of the transition is found to be consistent with a prediction of universality. The case of $SU(2)$ QCD is also studied in the strong coupling limit and the phase structure is found to be quite similar to the case of $SU(3)$: There exists a critical number of flavors $N_F^*$ and for $N_F \geq N_F^*$ the confinement is broken even in the strong coupling limit for light quarks. $N_F^*=3$ corresponding to 7 for $SU(3)$.

hep-lat↗

arXiv1992

Quark Confinement in Multi-Flavor Quantum Chromodynamics

It is investigated how quark confinement depends on the number of flavors, $N_f$, in QCD on the lattice with Wilson quarks. We strengthen and extend the conclusion reported at {\it Lattice 91}: (1) For $N_f \le 6$ the finite temperature deconfining transition/crossover line crosses the chiral limit at finite $β$. We identify the crossing point for $N_f=2$ and 6 on a $T=4$ lattice, where $T$ is the lattice size in the temporal direction. We find the phase transition at the crossing point is continuous for $N_f=2$, while it is of first order for $N_f=6$. (2) For $N_f \ge 7$, the $T$-independent deconfining transition observed at $β=0$ extends up to $β=4.5$ with the critical quark mass $m_{\rm quark} = O(a^{-1})$, where $a$ is the lattice spacing.

hep-lat↗

arXiv1992

Contamination of Excited States in Quenched QCD Hadron Propagators

Quenched QCD hadron spectrum is calculated with Wilson's quark action at $β=5.85$ and 6.0 on a $24^3 \times 54$ lattice. We discuss the problem of whether we have extracted the mass of the ground state at these $β$'s without contamination of the excited states. We show that the masses of the first excited states turn out to be consistent with experiment when we are able to obtain the propagators up to the large time slice region where the propagators take the asymptotic forms of the ground states.

hep-lat↗