638 research outputs found
Heavy Quarks on the Lattice
Lattice quantum chromodynamics provides first principles calculations for
hadrons containing heavy quarks -- charm and bottom quarks. Their mass spectra,
decay rates, and some hadronic matrix elements can be calculated on the lattice
in a model independent manner. In this review, we introduce the effective
theories that treat heavy quarks on the lattice. We summarize results on the
heavy quarkonium spectrum, which verify the validity of the effective theory
approach. We then discuss applications to physics, which is the main target
of the lattice theory of heavy quarks. We review progress in lattice
calculations of the meson decay constant, the parameter, semi-leptonic
decay form factors, and other important quantities.)Comment: 38 pages, Latex, ar.sty, 7 figures. A review based on the work until
February 2004. To appear in the Annual Review of Nuclear & Particle Science,
Vol. 5
Surface density: a new parameter in the fundamental metallicity relation of star-forming galaxies
Star-forming galaxies display a close relation among stellar mass,
metallicity and star-formation rate (or molecular-gas mass). This is known as
the fundamental metallicity relation (FMR) (or molecular-gas FMR), and it has a
profound implication on models of galaxy evolution. However, there still
remains a significant residual scatter around the FMR. We show here that a
fourth parameter, the surface density of stellar mass, reduces the dispersion
around the molecular-gas FMR. In a principal component analysis of 29 physical
parameters of 41,338 star-forming galaxies, the surface density of stellar mass
is found to be the fourth most important parameter. The new four-dimensional
(4D) fundamental relation forms a tighter hypersurface that reduces the
metallicity dispersion to 50% of that of the molecular-gas FMR. We suggest that
future analyses and models of galaxy evolution should consider the FMR in a 4D
space that includes surface density. The dilution time scale of gas inflow and
the star-formation efficiency could explain the observational dependence on
surface density of stellar mass. AKARI is expected to play an important role in
shedding light on the infrared properties of the new 4D FMR.Comment: Proceedings of the "The Cosmic Wheel and the Legacy of the AKARI
archive: from galaxies and stars to planets and life", held from October 17 -
20, 2017, Tokyo, Japa
Phase diagram of QCD chaos in linear sigma models and holography
Measuring chaos of QCD-like theories is a challenge for formulating a novel
characterization of quantum gauge theories. We define a chaos phase diagram of
QCD allowing us to locate chaos in the parameter space of energy of homogeneous
meson condensates and the QCD parameters such as pion/quark mass. We draw the
chaos phase diagrams obtained in two ways: first, by using a linear sigma
model, varying parameters of the potential, and second, by using the D4/D6
holographic QCD, varying the number of colors and the 't Hooft coupling
constant . A scaling law drastically simplifies our analyses, and we
discovered that the chaos originates in the maximum of the potential, and
larger or larger diminishes the chaos.Comment: 25 pages, 7 figure
Theta vacuum physics from QCD at fixed topology
We propose a method to obtain physical quantities in the theta vacuum from
those at fixed topology, which are different by finite size effects. Extending
the work by Brower et al., we derive the formula to estimate these finite size
corrections for arbitrary correlators in terms of the topological
susceptibility and the theta dependence. Applying this formula, we show that
topological susceptibility can be measured through two-point functions of
pseudoscalar operator.Comment: 7 pages, 2 figures, talk presented at the XXV International Symposium
on Lattice Field Theory, July 30 - August 4, 2007, Regensburg, German
Chaos of QCD string from holography
It is challenging to quantify chaos of QCD, because non-perturbative QCD
accompanies non-local observables. By using holography, we find that QCD
strings at large and strong coupling limit exhibit chaos, and measure
their Lyapunov exponent at zero temperature. A pair of a quark and an antiquark
separated by in the large QCD is dual to a Nambu-Goto string
hanging from the spatial boundary of the D4-soliton geometry. We numerically
solve the motion of the string after putting a pulse force on its boundaries.
The chaos is observed for the amplitude of the force larger than a certain
lower bound. The bound increases as grows, and its dependence is well
approximated by a hypothesis that the chaos originates in the endpoints of the
QCD string.Comment: 12 pages, 13 figure
Perturbative calculation of O(a) improvement coefficients
We compute several coefficients needed for O(a) improvement of currents in
perturbation theory, using the Brodsky-Lepage-Mackenzie prescription for
choosing an optimal scale q*. We then compare the results to non-perturbative
calculations. Normalization factors of the vector and axial vector currents
show good agreement, especially when allowing for small two-loop effects. On
the other hand, there are large discrepancies in the coefficients of O(a)
improvement terms. We suspect that they arise primarily from power corrections
inherent in the non-perturbative methods.Comment: 14pp, 3 figs (8 plots
Formation of the Pd atomic chain in hydrogen atmosphere
The formation of a Pd atomic chain in a hydrogen atmosphere was investigated
by measurements of conductance and vibrational spectroscopy of a single
molecular junction, and the theoretical calculation. While atomic chains were
not formed for clean 3d and 4d metals, in the case of Pd (a 4d metal) atomic
chains could be formed in the presence of hydrogen. Stable atomic chains with
two different atomic configurations were formed when the Pd atomic contact was
stretched in a H atmosphere; highly conductive short hydrogen adsorbed
atomic chain and low conductive long hydrogen incorporated atomic chain.Comment: 11pages, 4 figures, to be appear in Phys. Rev.
A filtering technique for the temporally reduced matrix of the Wilson fermion determinant
The Wilson fermion determinant can be written in the form of a series
expansion in fugacity , provided that the eigenmodes of the
temporally reduced operator are obtained. Since the calculation of all
eigenmodes rapidly becomes prohibitive for larger volumes, we develop a method
to calculate only the low-energy eigenmodes of the reduced matrix using a
matrix filetering technique. This provides a basis for an approximation to
neglect uninteresting ultraviolet contributions.Comment: 7 pages, 2figures. Proceedings of The 32nd International Symposium on
Lattice Field Theory, 23-28 June, 2014 Columbia University New York, N
An extinction free AGN selection by 18-band SED fitting in mid-infrared in the AKARI NEP deep field
We have developed an efficient Active Galactic Nucleus (AGN) selection method
using 18-band Spectral Energy Distribution (SED) fitting in mid-infrared
(mid-IR). AGNs are often obscured by gas and dust, and those obscured AGNs tend
to be missed in optical, UV and soft X-ray observations. Mid-IR light can help
us to recover them in an obscuration free way using their thermal emission. On
the other hand, Star-Forming Galaxies (SFG) also have strong PAH emission
features in mid-IR. Hence, establishing an accurate method to separate
populations of AGN and SFG is important. However, in previous mid-IR surveys,
only 3 or 4 filters were available, and thus the selection was limited. We
combined AKARI's continuous 9 mid-IR bands with WISE and Spitzer data to create
18 mid-IR bands for AGN selection. Among 4682 galaxies in the AKARI NEP deep
field, 1388 are selected to be AGN hosts, which implies an AGN fraction of
29.60.8 (among them 47 are Seyfert 1.8 and 2). Comparing the
result from SED fitting into WISE and Spitzer colour-colour diagram reveals
that Seyferts are often missed by previous studies. Our result has been tested
by stacking median magnitude for each sample. Using X-ray data from Chandra, we
compared the result of our SED fitting with WISE's colour box selection. We
recovered more X-ray detected AGN than previous methods by 20.Comment: 11 pages, 13 figures; accepted for publication in MNRAS; A video
summary: https://www.youtube.com/watch?v=gMfH0vkStq
AGN selection by 18-band SED fitting in mid-infrared in the AKARI NEP deep field
In this research, we provide a new, efficient method to select infrared (IR)
active galatic nucleus (AGN). In the past, AGN selection in IR had been
established by many studies using color-color diagrams. However, those methods
have a problem in common that the number of bands is limited. The AKARI North
Ecliptic Pole (NEP) survey was carried out by the AKARI Infrared Camera (IRC),
which has 9 filters in mid-IR with a continuous wavelength coverage from 2 to
24m. Based on the intrinsic different mid-IR features of AGN and
star-forming galaxies (SFGs), we performed SED fitting to separate these two
populations by the best-fitting model. In the X-ray AGN sample, our method by
SED fitting selects 50 AGNs, while the previous method by colour criteria
recovers only 30 of them, which is a significant improvement. Furthermore,
in the whole NEP deep sample, SED fitting selects two times more AGNs than the
color selection. This may imply that the black hole accretion history could be
more stronger than people expected before.Comment: Proceedings of the "The Cosmic Wheel and the Legacy of the AKARI
archive: from galaxies and stars to planets and life", held from October 17 -
20, 2017, Tokyo, Japa
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