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M. Fukugita

Publications and source records attributed to M. Fukugita.

At least 55 records · Page 3Linked to original sources
arXiv2003

A Gravitationally Lensed Quasar with Quadruple Images Separated by 14.62 Arcseconds

Gravitational lensing is a powerful tool for the study of the distribution of dark matter in the Universe. The cold-dark-matter model of the formation of large-scale structures predicts the existence of quasars gravitationally lensed by concentrations of dark matter so massive that the quasar images would be split by over 7 arcsec. Numerous searches for large-separation lensed quasars have, however, been unsuccessful. All of the roughly 70 lensed quasars known, including the first lensed quasar discovered, have smaller separations that can be explained in terms of galaxy-scale concentrations of baryonic matter. Although gravitationally lensed galaxies with large separations are known, quasars are more useful cosmological probes because of the simplicity of the resulting lens systems. Here we report the discovery of a lensed quasar, SDSS J1004+4112, which has a maximum separation between the components of 14.62 arcsec. Such a large separation means that the lensing object must be dominated by dark matter. Our results are fully consistent with theoretical expectations based on the cold-dark-matter model.

astro-ph↗
arXiv2003

Non-perturbative calculation of $Z_V$ and $Z_A$ in domain-wall QCD on a finite box

We report on a non-perturbative evaluation of the renormalization factors for the vector and axial-vector currents, $Z_V$ and $Z_A$, in the quenched domain-wall QCD (DWQCD) with plaquette and renormalization group improved gauge actions. We take the Dirichlet boundary condition for both gauge and domain-wall fermion fields on the finite box, and introduce the flavor-chiral Ward-Takahashi identities to calculate the renormalization factors. As a test of the method, we numerically confirm the expected relation that $Z_V \simeq Z_A$ in DWQCD. Employing two different box sizes for the numerical simulations at several values of the gauge coupling constant $g^2$ and the domain-wall height $M$, we extrapolate $Z_V$ to the infinite volume to remove $a/L$ errors. We finally give the interpolation formula of $Z_V$ in the infinite volume as a function of $g^2$ and $M$.

hep-lat↗
arXiv2003

B-Bbar mixing in unquenched lattice QCD

We present an unquenched lattice calculation for the $B^0-\bar{B}^0$ transition amplitude. The calculation, carried out at an inverse lattice spacing $1/a$ = 2.22(4) GeV, incorporates two flavors of dynamical quarks described by the fully $O(a)$-improved Wilson fermion action and heavy quarks described by NRQCD. A particular attention is paid to the uncertainty that arises from the chiral extrapolation, especially the effect of pion loops, for light quarks, which we find could be sizable for the leptonic decay of the $B_d$ meson, whereas it is small for the $B_s$ meson and the $B$ parameters. We obtain $f_{B_d}=191(10)(^{+12}_{-22})$ MeV, $f_{B_s}/f_{B_d}=1.13(3)(^{+13}_{-\ 2})$, $B_{B_d}(m_b)=0.836(27)(^{+56}_{-62})$, $B_{B_s}/B_{B_d}=1.017(16)(^{+56}_{-17})$, $ξ=1.14(3)(^{+13}_{- 2})$, where the first error is statistical, and the second is systematic, including uncertainties due to chiral extrapolation, finite lattice spacing, heavy quark expansion and perturbative operator matching.

hep-ph↗
arXiv2003

Non-perturbative renormalization of vector and axial vector currents in quenched QCD for a renormalization group improved gauge action

Renormalization constants of vector ($Z_V$) and axial-vector ($Z_A$) currents are determined non-perturbatively in quenched QCD for an RG-improved gauge action and a tadpole-improved clover quark action using the Schrödinger functional method. Meson decay constants $f_ρ$ and $f_π$ show much better scaling when $Z_V$ and $Z_A$ estimated for infinite physical volume are used instead of $Z$-factors from tadpole-improved one-loop perturbation theory.

hep-lat↗
arXiv2003

Light hadron spectrum in three-flavor QCD with O(a)-improved Wilson quark action

We report on a calculation of the light hadron spectrum and quark masses in three-flavor dynamical QCD using the non-perturbatively O(a)-improved Wilson quark action and a renormalization-group improved gauge action. Simulations are carried out on a 16^3 \times 32 lattice at β=1.9, where a^{-1} \simeq 2GeV, with 6 ud quark masses corresponding to m_{pi}/m_{rho} \simeq 0.64-0.77 and 2 s quark masses close to the physical value. We observe that the inclusion of dynamical strange quark brings the lattice QCD meson spectrum to good agreement with experiment. Dynamical strange quarks also lead to a reduction of the uds quark masses by about 15%.

hep-lat↗
arXiv2003

Study of finite volume effects in the non-perturbative determination of $\csw$ with the SF method in full three-flavor lattice QCD

The non-perturbative $\csw$ determined by the Schrödinger functional (SF) method with the RG-improved gauge action in dynamical $N_f=3$ QCD shows a finite volume effect when the numerical simulations are carried out at a constant lattice size $L/a$. We remove the unwanted finite volume effect by keeping physical lattice extent $L$ at a constant. The details of the method and the result obtained for non-perturbative $\csw$ with a constant $L$ are reported.

hep-lat↗
arXiv2003

Continuum limit of proton decay matrix elements in quenched lattice QCD

We present a lattice QCD calculation of the parameters αand βwhich are necessary in the theoretical estimation of the proton lifetime in grand unified theories (GUTs) using chiral lagrangian approach. The simulation is carried out using the Wilson quark action at three gauge coupling constants in the quenched approximation. We obtain |α(2GeV)|=0.0091(08)(^{+10}_{-19})GeV^3 and |β(2GeV)|=0.0098(08)(^{+10}_{-20})GeV^3 in the continuum limit where the first error is statistical and the second one is due to scale setting.

hep-lat↗
arXiv2003

Light hadron spectroscopy with two flavors of $O(a)$-improved dynamical quarks

We present a high statistics study of the light hadron spectrum and quark masses in QCD with two flavors of dynamical quarks. Numerical simulations are carried out using the plaquette gauge action and the O(a)-improved Wilson quark action at β=5.2, where the lattice spacing is found to be a=0.0887(11)fm from ρmeson mass, on a 20^3\times 48 lattice. At each of five sea quark masses corresponding to m_{PS}/m_{V} \simeq 0.8-0.6, we generate 12000 trajectories using the symmetrically preconditioned Hybrid Monte Carlo algorithm. Finite spatial volume effects are investigated employing 12^3 \times 48, 16^3 \times 48 lattices. We also perform a set of simulations in quenched QCD with the same lattice actions at a similar lattice spacing to those for the full QCD runs. In the meson sector we find clear evidence of sea quark effects. The J parameter increases for lighter sea quark masses, and the full QCD meson masses are systematically closer to experiment than in quenched QCD. Careful finite-size studies are made to ascertain that these are not due to finite-size effects. Evidence of sea quark effects is less clear in the baryon sector due to larger finite-size effects. We also calculate light quark masses and find m_{ud}^{MS}(2GeV) =3.223(+0.046/-0.069)MeV and m_s^{MS}(2GeV)=84.5(+12.0/-1.7)MeV which are about 20% smaller than in quenched QCD.

hep-lat↗
arXiv2003

Two flavors of dynamical quarks on anisotropic lattices

We report on our study of two-flavor full QCD on anisotropic lattices using $O(a)$-improved Wilson quarks coupled with an RG-improved glue. The bare gauge and quark anisotropies corresponding to the renormalized anisotropy $ξ=a_s/a_t = 2$ are determined as functions of $β$ and $κ$, which covers the region of spatial lattice spacings $a_s\approx 0.28$--0.16 fm and $m_{PS}/m_V\approx 0.6$--0.9. The calibrations of the bare anisotropies are performed with the Wilson loop and the meson dispersion relation at 4 lattice cutoffs and 5--6 quark masses. Using the calibration results we calculate the meson mass spectrum and the Sommer scale $r_0$. We confirm that the values of $r_0$ calculated for the calibration using pseudo scalar and vector meson energy momentum dispersion relation coincide in the continuum limit within errors. This work serves to lay ground toward studies of heavy quark systems and thermodynamics of QCD including the extraction of the equation of state in the continuum limit using Wilson-type quark actions.

hep-lat↗
arXiv2003

The Earliest Epoch of Reionisation in the Standard $Λ$CDM Model

We show that the earliest possible reionisation of the Universe is approximately at $z\simeq 13.5$ and the optical depth is $τ\simeq 0.17$ in the conventionally accepted $Λ$ cold dark matter ($Λ$CDM) model with adiabatic fluctuations of a flat spectrum normalised to the cosmic microwave background. This is consistent with the reionisation found by WMAP (the apparently earlier reionisation epoch of the WMAP is ascribed to the adoption of the instantaneous reionisation approximation), i.e., the WMAP result is realised only if reionisation of the universe takes place nearly at the maximal efficiency in the $Λ$CDM model.

astro-ph↗
arXiv2003

Stellar and Dynamical Masses of Ellipticals in the Sloan Digital Sky Survey

We study the variation of the dark matter mass fraction of elliptical galaxies as a function of their luminosity, stellar mass, and size using a sample of 29,469 elliptical galaxies culled from the Sloan Digital Sky Survey. We model ellipticals as a stellar Hernquist profile embedded in an adiabatically compressed dark matter halo. This model allows us to estimate a dynamical mass ($M_{dynm}$) at the half-light radius from the velocity dispersion of the spectra, and to compare these to the stellar mass estimates ($M_{*}$) from Kauffmann et al (2003). We find that $M_{*}/L$ is independent of luminosity, while $M_{dynm}/L$ increases with luminosity, implying that the dark matter fraction increases with luminosity. We also observe that at a fixed luminosity or stellar mass, the dark matter fraction increases with increasing galaxy size or, equivalently, increases with decreasing surface brightness: high surface brightness galaxies show almost no evidence for dark matter, while in low surface brightness galaxies, the dark matter exceeds the stellar mass at the half light radius. We relate this to the fundamental plane of elliptical galaxies, suggesting that the tilt of this plane from simple virial predictions is due to the dark matter in galaxies. We find that a simple model where galaxies are embedded in dark matter halos and have a star formation efficiency independent of their surface brightness explains these trends. We estimate the virial mass of ellipticals as being approximately 7-30 times their stellar mass, with the lower limit suggesting almost all of the gas within the virial radius is converted into stars.

astro-ph↗
arXiv2003

Non-Perturbative Determination of $c_{\rm SW}$ in Three-flavor Dynamical QCD

We present a fully non-perturbative determination of the $O(a)$ improvement coefficient $c_{\rm SW}$ in three-flavor dynamical QCD for the RG improved as well as the plaquette gauge actions, using the Schrödinger functional scheme. Results are compared with one-loop estimates at weak gauge coupling.

hep-lat↗
arXiv2003

An Exact Algorithm for Any-flavor Lattice QCD with Kogut-Susskind Fermion

We propose an exact simulation algorithm for lattice QCD with dynamical Kogut-Susskind fermion in which the N_f-flavor fermion operator is defined as the N_f/4-th root of the Kogut-Susskind (KS) fermion operator. The algorithm is an extension of the Polynomial Hybrid Monte Carlo (PHMC) algorithm to KS fermions. The fractional power of the KS fermion operator is approximated with a Hermitian Chebyshev polynomial, with which we can construct an algorithm for any number of flavors. The error which arises from the approximation is corrected by the Kennedy-Kuti noisy Metropolis test. Numerical simulations are performed for the two-flavor case for several lattice parameters in order to confirm the validity and the practical feasibility of the algorithm. In particular tests on a 16^4 lattice with a quark mass corresponding to m_{PS}/m_V ~ 0.68 are successfully accomplished. We conclude that our algorithm provides an attractive exact method for dynamical QCD simulations with KS fermions.

hep-lat↗
arXiv2003

Heavy quark expansion parameters from lattice NRQCD

We present a lattice QCD calculation of the heavy quark expansion parameters $μ_π^2$ and $μ_G^2$ for heavy-light mesons and heavy-light-light baryons. The calculation is carried out on a 20$^3\times$48 lattice at $β$ = 6.0 in the quenched approximation, using the lattice NRQCD action for heavy quarks. We obtain the parameters $μ_π^2$ and $μ_G^2$ in two different methods: a direct calculation of the matrix elements and an indirect calculation through the mass spectrum, and confirm that the both methods give consistent results. We also discuss an application to the lifetime ratios.

hep-lat↗
arXiv2003

Calculation of Non-Leptonic Kaon Decay Amplitudes from $K\toπ$ Matrix Elements in Quenched Domain-Wall QCD

We explore application of the domain wall fermion formalism of lattice QCD to calculate the $K\toππ$ decay amplitudes in terms of the $K\toπ$ and $K\to 0$ hadronic matrix elements through relations derived in chiral perturbation theory. Numerical simulations are carried out in quenched QCD using domain-wall fermion action for quarks and an RG-improved gauge action for gluons on a $16^3\times 32\times 16$ and $24^3\times 32\times 16$ lattice at $β=2.6$ corresponding to the lattice spacing $1/a\approx 2$GeV. Quark loop contractions which appear in Penguin diagrams are calculated by the random noise method, and the $ΔI=1/2$ matrix elements which require subtractions with the quark loop contractions are obtained with a statistical accuracy of about 10%. We confirm the chiral properties required of the $K\toπ$ matrix elements. Matching the lattice matrix elements to those in the continuum at $μ=1/a$ using the perturbative renormalization factor to one loop order, and running to the scale $μ=m_c=1.3$ GeV with the renormalization group for $N_f=3$ flavors, we calculate all the matrix elements needed for the decay amplitudes. With these matrix elements, the $ΔI=3/2$ decay amplitude shows a good agreement with experiment in the chiral limit. The $ΔI=1/2$ amplitude, on the other hand, is about 50--60% of the experimental one even after chiral extrapolation. In view ofthe insufficient enhancement of the $ΔI=1/2$ contribution, we employ the experimental values for the real parts of the decay amplitudes in our calculation of $ε'/ε$. We find that the $ΔI=3/2$ contribution is larger than the $ΔI=1/2$ contribution so that $ε'/ε$ is negative and has a magnitude of order $10^{-4}$. Possible reasons for these unsatisfactory results are discussed.

hep-lat↗
arXiv2003

Predictions from the Fritzsch-Type Lepton Mass Matrices

We revisit the Fritzsch-type lepton mass matrix models confronted with new experiments for neutrino mixings. It is shown that the model is viable and leads to a rather narrow range of free parameters. Using empirical mixing information between $ν_e$ and $ν_μ$, and between $ν_μ$ and $ν_τ$, it is predicted that the mixing angle between $nu_e$ and $ν_τ$ is in the range $0.04<|U_{13}|<0.20$, consistent with the CHOOZ experiment and the lightest neutrino mass is $0.0004 <0.007$ eV.

hep-ph↗
arXiv2003

Constraints on the Star Formation Rate from Supernova Relic Neutrino Observations

We discuss the implication of the observation of supernova relic neutrinos on the study of the star formation rate (SFR) in galaxies. The limit recently obtained at Super-Kamiokande (SK) is already marginally significant: The SFR we derived $ψ(t_0)<0.040M_{\odot}$yr$^{-1}$Mpc$^{-3}$(at a 90% CL) is about twice the SFR estimated from radio observations, and five times the rate from H$α$ allowing for uncertainties in the model supernova neutrino flux.

astro-ph↗