arXiv subjects

T. Doi

Publications and source records attributed to T. Doi.

36 records · Page 2Linked to original sources

arXiv2012

The United Nations Human Space Technology Initiative (HSTI)

The Human Space Technology Initiative (HSTI) has been launched under the framework of the United Nations Programme on Space Applications with its aims of promoting international cooperation in human spaceflight and space exploration-related activities; creating awareness among United Nations Member States on the benefits of utilizing human space technology and its applications; and building capacity in microgravity education and research. The International Space Station (ISS), being operational with a permanent crew of six (6), is an unprecedented facility for research on science and technology and can be regarded as one of the greatest resources for humankind to explore space. The HSTI seeks to promote human space technology and to expand ISS utilization. This report describes the background, objectives, and current three-year work plan of HSTI which is composed of organizing expert meetings, seminars, and workshops as well as building capacity by distributing educational materials and zero-gravity experiment instruments.

physics.space-ph↗

arXiv2010

Overlap Valence on 2+1 Flavor Domain Wall Fermion Configurations with Deflation and Low-mode Substitution

The overlap fermion propagator is calculated on 2+1 flavor domain wall fermion gauge configurations on 16^3 x 32, 24^3 x 64 and 32^3 x 64 lattices. With HYP smearing and low eigenmode deflation, it is shown that the inversion of the overlap operator can be expedited by ~ 20 times for the 16^3 x 32 lattice and ~ 80 times for the 32^3 x 64 lattice. Through the study of hyperfine splitting, we found that the O(m^2a^2) error is small and these dynamical fermion lattices can adequately accommodate quark mass up to the charm quark. The low energy constant Δ_{mix} which characterizes the discretization error of the pion made up of a pair of sea and valence quarks in this mixed action approach is calculated via the scalar correlator with periodic and anti-periodic boundary conditions. It is found to be small which shifts a 300 MeV pion mass by ~ 10 to 19 MeV on these sets of lattices. We have studied the signal-to-noise issue of the noise source for the meson and baryon. It is found that the many-to-all meson and baryon correlators with Z_3 grid source and low eigenmode substitution is efficient in reducing errors for the correlators of both mesons and baryons. With 64-point Z_3 grid source and low-mode substitution, it can reduce the statistical errors of the light quark (m_π ~ 200 - 300 MeV) meson and nucleon correlators by a factor of ~ 3-4 as compared to the point source. The Z_3 grid source itself can reduce the errors of the charmonium correlators by a factor of ~ 3.

hep-lat↗

arXiv2010

Meson spectra from overlap fermion on domain wall gauge configurations

We report meson spectra obtained by using valence overlap fermion propagators generated on a background of 2+1 flavor domain wall fermion gauge configurations on 16^3 X 32, 24^3 X 64 and 32^3 X 64 lattices. We use many-to-all correlators with Z3 grid source and low eigenmode substitution which is efficient in reducing errors for the hadron correlators. The preliminary results on meson spectrum, a0 correlators, and charmonium hyperfine splitting for three sea quark masses are reported here.

hep-lat↗

arXiv2010

The study of the Three Nucleon Force in full QCD Lattice calculations

We study the three nucleon force in the triton channel using dynamical clover fermion lattice QCD. The Nambu-Bethe-Salpeter wave function is utilized to obtain the potentials among three nucleons. Since the straightforward calculation is prohibitively expensive, two different frameworks are developed to meet the challenge. In the first method, we study the effective two nucleon potentials in the three nucleon system, where the differences between the effective two nucleon potentials and the genuine two nucleon potentials correspond to the three nucleon system effect, part of which is originated from the three nucleon force. The calculation is performed using Nf=2 clover fermion at m(π)= 1.13GeV generated by CP-PACS Collaboration, and Nf=2+1 clover fermion at m(π)= 0.70, 0.57GeV generated by PACS-CS Collaboration. In the second method, we study the three nucleon system with 3D-configuration of nucleons fixed. This enables us to extract the three nucleon force directly, if both of parity-even and parity-odd two nucleon potentials are provided. Since parity-odd two nucleon potentials are not available in lattice QCD at this moment, we propose a new general procedure to identify the three nucleon force using only parity-even two nucleon potentials. The calculation are performed with Nf=2 clover fermion at m(π)= 1.13GeV generated by CP-PACS Collaboration, employing the linear setup for the 3D-configuration. Preliminary results for the scalar/isoscalar three nucleon force are presented.

hep-lat↗

arXiv2010

Electromagnetic mass splittings of the low lying hadrons and quark masses from 2+1 flavor lattice QCD+QED

Results are presented for the electromagnetic mass splittings of the low lying hadrons. These are used to determine the non-degenerate light quark masses. It is found that m_u=2.24(10)(34), m_d=4.65(15)(32), and $m_s=97.6(2.9)(5.5)$ MeV (MSbar scheme, 2 GeV scale). The first error is statistical and the second systematic. We find the lowest order electromagnetic splitting (m_pi+-m_pi0)_QED=3.38(23) MeV, the splittings including next-to-leading order, (m_pi+-m_pi0)_QED=4.50(23) MeV, (m_K+-m_K0)_QED=1.87(10) MeV, and the m_u != m_d contribution to the kaon mass difference, (m_K+-m_K0)_(m_u-m_d)=-5.840(96) MeV. All errors are statistical only, and the next-to-leading order pion splitting is only approximate; it does not contain all next-to-leading order contributions. We also computed the proton-neutron mass difference, including for the first time, QED interactions in a realistic 2+1 flavor calculation. We find $(m_p-m_n)_{\rm QED}=0.383(68)$ MeV, (m_p-m_n)_(m_u-m_d)=-2.51(14) MeV, and the total m_p-m_n=-2.13(16)(70) MeV, where the first error is statistical, and the second, part of the systematic error. We use domain wall fermions and the Iwasaki gauge action (gauge coupling beta=2.13). We use two lattice sizes, 16^3 and 24^3, to address finite volume effects. Non-compact QED is treated in the quenched approximation. We present new results for the electromagnetic low energy constants in SU(3) and SU(2) partially-quenched chiral perturbation theory to the next-to-leading order, obtained from fits to our data. Detailed analysis of systematic errors in our results and methods for improving them are discussed. Finally, new analytic results for SU(2)_L x SU(2)_R-plus-kaon chiral perturbation theory, including the one-loop logs proportional to alpha_em*m, are given.

hep-lat↗

arXiv2010

Kaon-Nucleon potential from lattice QCD

We study the KN interactions in the I(J^π)=0(1/2^-) and 1(1/2^-) channels and associated exotic state Θ^+ from 2+1 flavor full lattice QCD simulation for relatively heavy quark mass corresponding to m_π=871 MeV. The s-wave KN potentials are obtained from the Bethe-Salpeter wave function by using the method recently developed by HAL QCD (Hadrons to Atomic nuclei from Lattice QCD) Collaboration. Potentials in both channels reveal short range repulsions: Strength of the repulsion is stronger in the I=1 potential, which is consistent with the prediction of the Tomozawa-Weinberg term. The I=0 potential is found to have attractive well at mid range. From these potentials, the $KN$ scattering phase shifts are calculated and compared with the experimental data.

hep-lat↗

arXiv2008

Moments of Nucleon's Parton Distribution for the Sea and Valence Quarks from Lattice QCD

We extend the study of lowest moments, $ $ and $ $, of the parton distribution function of the nucleon to include those of the sea quarks; this entails a disconnected insertion calculation in lattice QCD. This is carried out on a $16^3 \times 24$ quenched lattice with Wilson fermion. The quark loops are calculated with $Z_2$ noise vectors and unbiased subtractions, and multiple nucleon sources are employed to reduce the statistical errors. We obtain 5$σ$ signals for $ $ for the $u,d,$ and $s$ quarks, but $ $ is consistent with zero within errors. We provide results for both the connected and disconnected insertions. The perturbatively renormalized $ $ for the strange quark at $μ= 2$ GeV is $ _{s+\bar{s}} = 0.027 \pm 0.006$ which is consistent with the experimental result. The ratio of $ $ for $s$ vs. $u/d$ in the disconnected insertion with quark loops is calculated to be $0.88 \pm 0.07$. This is about twice as large as the phenomenologically fitted $\displaystyle\frac{< x>_{s+\bar{s}}}{< x>_{\bar{u}}+< x>_{\bar{d}}}$ from experiments where $\bar{u}$ and $\bar{d}$ include both the connected and disconnected insertion parts. We discuss the source and implication of this difference.

hep-ph↗

arXiv2008

Survival of charmonia above Tc in anisotropic lattice QCD

We find a strong evidence for the survival of $J/Ψ$ and $η_c$ as spatially-localized $c\bar c$ (quasi-)bound states above the QCD critical temperature $T_c$, by investigating the boundary-condition dependence of their energies and spectral functions. In a finite-volume box, there arises a boundary-condition dependence for spatially spread states, while no such dependence appears for spatially compact states. In lattice QCD, we find almost {\it no} spatial boundary-condition dependence for the energy of the $c\bar c$ system in $J/Ψ$ and $η_c$ channels for $T\simeq(1.11-2.07)T_c$. We also investigate the spectral function of charmonia above $T_c$ in lattice QCD using the maximum entropy method (MEM) in terms of the boundary-condition dependence. There is {\it no} spatial boundary-condition dependence for the low-lying peaks corresponding to $J/Ψ$ and $η_c$ around 3GeV at $1.62T_c$. These facts indicate the survival of $J/Ψ$ and $η_c$ as compact $c\bar c$ (quasi-)bound states for $T_c < T < 2T_c$.

hep-lat↗

arXiv2008

Velocity Structure in the Orion Nebula. II. Emission Line Atlas of Partially Ionized to Fully Ionized Gas

We present an atlas of three-dimensional (position-position-velocity) spectra of the Orion Nebula in optical emission lines from a variety of different ionization stages: [O I] 6300, [S II] 6716,6731, [N II] 6584, [S III] 6312, H alpha 6563, and [O III] 5007. These transitions provide point to point information about the physical structure and kinematics of the nebula at an effective resolution of 3'' x 2'' x 10 km/s, clearly showing the large scale behavior of the ionized gas and the presence of localized phenomena such as Herbig-Haro outflows. As an example application of the atlas, we present a statistical analysis of the widths of the H alpha, [O III], and [N II] lines that permits a determination of the mean electron temperature in the nebula of (9200 +/- 400) K. We also find, in contradiction to previous claims, that the non-thermal line broadening is not significantly different between recombination lines and collisional lines.

astro-ph↗

arXiv2006

Charmonium properties in deconfinement phase in anisotropic lattice QCD

J/Psi and eta_c above the QCD critical temperature T_c are studied in anisotropic quenched lattice QCD, considering whether the c\bar c systems above T_c are spatially compact (quasi-)bound states or scattering states. We adopt the standard Wilson gauge action and O(a)-improved Wilson quark action with renormalized anisotropy a_s/a_t =4.0 at β=6.10 on 16^3\times (14-26) lattices, which correspond to the spatial lattice volume V\equiv L^3\simeq(1.55{\rm fm})^3 and temperatures T\simeq(1.11-2.07)T_c. We investigate the c\bar c system above T_c from the temporal correlators with spatially-extended operators, where the overlap with the ground state is enhanced. To clarify whether compact charmonia survive in the deconfinement phase, we investigate spatial boundary-condition dependence of the energy of c\bar c systems above T_c. In fact, for low-lying S-wave c \bar c scattering states, it is expected that there appears a significant energy difference ΔE \equiv E{\rm (APBC)}-E{\rm (PBC)}\simeq2\sqrt{m_c^2+3π^2/L^2}-2m_c (m_c: charm quark mass) between periodic and anti-periodic boundary conditions on the finite-volume lattice. In contrast, for compact charmonia, there is no significant energy difference between periodic and anti-periodic boundary conditions. As a lattice QCD result, almost no spatial boundary-condition dependence is observed for the energy of the c\bar c system in J/Ψand η_c channels for T\simeq(1.11-2.07)T_c. This fact indicates that J/Ψand η_c would survive as spatially compact c\bar c (quasi-)bound states below 2T_c. We also investigate a $P$-wave channel at high temperature with maximally entropy method (MEM) and find no low-lying peak structure corresponding to χ_{c1} at 1.62T_c.

hep-lat↗

arXiv2006

Nuclear force in Lattice QCD

We perform the quenched lattice QCD analysis on the nuclear force (baryon-baryon interactions). We employ $20^3\times 24$ lattice at $β=5.7$ ($a\simeq 0.19$ fm) with the standard gauge action and the Wilson quark action with the hopping parameters $κ=0.1600, 0.1625, 0.1650$, and generate about 200 gauge configurations. We measure the temporal correlators of the two-baryon system which consists of heavy-light-light quarks. We extract the inter-baryon force as a function of the relative distance $r$. We also evaluate the contribution to the nuclear force from each ``Feynman diagram'' such as the quark-exchange diagram individually, and single out the roles of Pauli-blocking effects or quark exchanges in the inter-baryon interactions.

hep-lat↗

arXiv2006

Anisotropic lattice QCD studies of penta-quarks and tetra-quarks

Anisotropic lattice QCD studies of penta-quarks(5Q) with J^P=1/2^\pm and 3/2^{\pm} are presented at the quenched level together with tetra-quarks(4Q). The standard gauge action at β=5.75 and O(a) improved quark (clover) action with κ=0.1410(0.010)0.1440 are employed on the anisotropic lattice with the renormalized anisotropy a_s/a_t = 4. The ``hybrid boundary condition(HBC)'' is adopted to discriminate a compact resonance state from scattering states. Only massive 5Q states are found for J^P=1/2^+ and 3/2^{\pm}, which cannot be identified as Θ^+(1540). A low-lying 5Q state is found for J^P=1/2^- at m_{5Q}\simeq 1.75 GeV, which however turns out to be an NK scattering state through the HBC analysis. A preliminary result for 4Q states is presented suggesting an existence of a compact 4Q resonance at m_{4Q} \simeq 1.1 GeV in the idealized SU(4)_f chiral limit.

hep-lat↗

arXiv2005

Tetraquark and Pentaquark Systems in Lattice QCD

Motivated by the recent experimental discoveries of multi-quark candidates, e.g., the $Θ^+(1540)$, we study multi-quark systems in lattice QCD. First, we perform accurate mass measurements of low-lying 5Q states with $J=1/2$ and I=0 in both positive- and negative-parity channels in anisotropic lattice QCD. The lowest positive-parity 5Q state is found to have a large mass of about 2.24GeV after the chiral extrapolation. To single out the compact 5Q state from $NK$ scattering states, we develop a new method with the hybrid-boundary condition (HBC), and find no evidence of the compact 5Q state below 1.75GeV in the negative-parity channel. Second, we perform the first study of the multi-quark potential in lattice QCD to clarify the inter-quark interaction in multi-quark systems. The 5Q potential $V_{\rm 5Q}$ for the QQ-${\rm \bar{Q}}$-QQ system is found to be well described by the ``OGE Coulomb plus multi-Y Ansatz": the sum of the one-gluon-exchange (OGE) Coulomb term and the multi-Y-type linear term based on the flux-tube picture. The 4Q potential $V_{\rm 4Q}$ for the QQ-${\rm \bar{Q}\bar{Q}}$ system is also described by the OGE Coulomb plus multi-Y Ansatz, when QQ and $\rm \bar Q \bar Q$ are well separated. The 4Q system is described as a "two-meson" state with disconnected flux tubes, when the nearest quark and antiquark pair is spatially close. We observe a lattice-QCD evidence for the ``flip-flop'', i.e., the flux-tube recombination between the connected 4Q state and the ``two-meson'' state. On the confinement mechanism, the lattice QCD results indicate the flux-tube-type linear confinement in multi-quark hadrons.

hep-ph↗

arXiv2005

Spin 3/2 Penta-quarks in anisotropic lattice QCD

A high-precision mass measurement for the pentaquark (5Q) Theta^+ in J^P=3/2^{\pm} channel is performed in anisotropic quenched lattice QCD using a large number of gauge configurations as N_{conf}=1000. We employ the standard Wilson gauge action at beta=5.75 and the O(a) improved Wilson (clover) quark action with kappa=0.1210(0.0010)0.1240 on a 12^3 \times 96 lattice with the renormalized anisotropy as a_s/a_t = 4. The Rarita-Schwinger formalism is adopted for the interpolating fields. Several types of the interpolating fields with isospin I=0 are examined such as (a) the NK^*-type, (b) the (color-)twisted NK^*-type, (c) a diquark-type. The chiral extrapolation leads to only massive states, i.e., m_{5Q} \simeq 2.1-2.2 GeV in J^P=3/2^- channel, and m_{5Q} = 2.4-2.6 GeV in J^P=3/2^+ channel. The analysis with the hybrid boundary condition(HBC) is performed to investigate whether these states are compact 5Q resonances or not. No low-lying compact 5Q resonance states are found below 2.1GeV.

hep-lat↗

arXiv2005

Penta-quark in Anisotropic Lattice QCD

Penta-quark (5Q) baryons are studied using anisotropic lattice QCD for high-precision measurement of temporal correlators. A non-NK-type interpolating field is employed to study the 5Q states with J^P=1/2^{\pm} and I=0. In J^P=1/2^+ channel, the lowest-lying state is found at m_{5Q} \simeq 2.25 GeV, which is too massive to be identified as the Theta^+(1540). In J^P=1/2^- channel, the lowest-lying state is found at m_{5Q} \simeq 1.75 GeV. To distinguish a compact 5Q resonance state from an NK scattering state, a new method with ``hybrid boundary condition (HBC)'' is proposed. As a result of the HBC analysis, the observed state in the negative-parity channel turns out to be an $NK$ scattering state.

hep-lat↗

arXiv2004

Anisotropic Lattice QCD Studies of Penta-quark Anti-decuplet

Anti-decuplet penta-quark baryon is studied with the quenched anisotropic lattice QCD for accurate measurement of the correlator. Both the positive and negative parity states are studied using a non-NK type interpolating field with I=0 and J=1/2. After the chiral extrapolation, the lowest positive parity state is found at m_{Theta} \simeq 2.25 GeV, which is too massive to be identified with the experimentally observed Theta^+(1540). The lowest negative parity state is found at m_{Theta}\simeq 1.75 GeV, which is rather close to the empirical value. To confirm that this state is a compact 5Q resonance, a new method with ``hybrid boundary condition (HBC)'' is proposed. The HBC analysis shows that the observed state in the negative parity channel is an NK scattering state.

hep-lat↗

arXiv2004

Penta-Quark Anti-Decuplet in Anisotropic Lattice QCD

The penta-quark(5Q) Theta^+(1540) is studied in anisotropic lattice QCD with renormalized anisotropy a_s/a_t=4 for a high-precision measurement. Both the positive and the negative parity 5Q baryons are studied using a non-NK type interpolating field with I=0 and J=1/2. After the chiral extrapolation, the lowest positive parity state is found at m_{Theta}\simeq 2.25 GeV, which is too heavy to be identified with Theta^+(1540). In the negative parity channel, the lowest energy state is found at m_{Theta}\simeq 1.75 GeV. Although it is rather close to the empirical value, it is considered to be an NK scattering state rather than a localized resonance state.

hep-lat↗

arXiv2004

Penta-quark baryon in anisotropic lattice QCD

The penta-quark(5Q) baryon is studied in anisotropic quenched lattice QCD with renormalized anisotropy a_s/a_t=4 for a high-precision mass measurement. The standard Wilson action at beta=5.75 and the O(a) improved Wilson quark action with kappa=0.1210(0.0010)0.1240 are employed on a 12^3 \times 96 lattice. Contribution of excited states is suppressed by using a smeared source. We investigate both the positive- and negative-parity 5Q baryons with I=0 and spin J=1/2 using a non-NK-type interpolating field. After chiral extrapolation, the lowest positive-parity state is found to have a mass, m_{Theta}=2.25 GeV, which is much heavier than the experimentally observed Theta^+(1540). The lowest negative-parity 5Q appears at m_{Theta}=1.75 GeV, which is near the s-wave NK threshold. To distinguish spatially-localized 5Q resonances from NK scattering states, we propose a new general method imposing a ``Hybrid Boundary Condition (HBC)'', where the NK threshold is artificially raised without affecting compact five-quark states. The study using the HBC method shows that the negative-parity state observed on the lattice is not a compact 5Q but an s-wave NK-scattering state.

hep-lat↗