1,903 research outputs found
Decays rates for S- and P-wave bottomonium
We use the Bodwin-Braaten-Lepage factorization scheme to separate the long-
and short-distance factors that contribute to the decay rates of ,
(S-wave) and , (P-wave). The long distance matrix
elements are calculated on the lattice in the quenched approximation using a
non-relativistic formulation of the quark dynamics.Comment: 3 pages Latex using espcrc2.sty and epsf.sty + 2 postscript figure
Mesons and nucleons from holographic QCD in a unified approach
We investigate masses and coupling constants of mesons and nucleons within a
hard wall model of holographic QCD in a unified approach. We first examine an
appropriate form of fermionic solutions by restricting the mass coupling for
the five dimensional bulk fermions and bosons. We then derive approximated
analytic solutions for the nucleons and the corresponding masses in a small
mass coupling region. In order to treat meson and nucleon properties on the
same footing, we introduce the same infrared (IR) cut in such a way that the
meson-nucleon coupling constants, i.e., g_{pi NN} and g_{rho NN} are uniquely
determined. The first order approximation with respect to a dimensionless
expansion parameter, which is valid in the small mass coupling region,
explicitly shows difficulties to avoid the IR scale problem of the hard wall
model. We discuss possible ways of circumventing these problems.Comment: 15 pages, No figure. Several typos have been remove
Spatial Compactification and Decay-Rate Behavior
The pahse transition from instanton-dominated quantum tunneling regime to
sphaleron-dominated classical crossover regime is explored in (1+1)-dimensional
scalar field theory when spatial coordinate is compactified. It is shown that
the type of sphaleron transition is critically dependent on the circumference
of the spatial coordinate.Comment: 12 pages, 6 postscript figures included, accepted version in PL
Hysteresis in an Ising model with mobile bonds
Hysteresis is studied in a disordered Ising model in which diffusion of
antiferromagnetic bonds is allowed in addition to spin flips. Saturation
behavior changes to a figure-eight loop when diffusion is introduced. The upper
and lower fields delimiting the figure-eight are determined by the Hamiltonian,
while its surface and the crossing point depend on the temperature and details
of the dynamics. The main avalanche is associated with the disappearance of
hidden order. Some experimental observations of figure-eight anomalies are
discussed. It is argued they are a signal of a transient rearrangement of
domain couplings, characteristic of amorphous and/or magnetically soft samples,
and similar to evolution of kinetic glasses.Comment: 7 pages, 7 figure
Nonvanishing Cosmological Constant of Flat Universe in Brane-World Scenario
The finite temperature effect is examined in Randall-Sundrum brane-world
scenario with inclusion of the matter fields on the brane. At zero temperature
it is found that the theory on the brane is conformally invariant, which
guarantees /CFT. At 4d effective action we derived a temperature-dependent
nonvanishing cosmological constant at the flat spacetime limit of brane
worldvolume. At the cosmological temperature the cosmological
constant is roughly which is within the upper bound of the
recent experimental value Comment: 10 pages, 1 figure; V2 12 pages, figure removed, the contribution of
matter to the cosmological constant is added, will appear in PL
The Chiral Model of Sakai-Sugimoto at Finite Baryon Density
In the context of holographic QCD we analyze Sakai-Sugimoto's chiral model at
finite baryon density and zero temperature. The baryon number density is
introduced through compact D4 wrapping S^4 at the tip of D8-\bar{D8}. Each
baryon acts as a chiral point-like source distributed uniformly over R^3, and
leads a non-vanishing U(1)_V potential on the brane. For fixed baryon charge
density n_B we analyze the bulk energy density and pressure using the canonical
formalism. The baryonic matter with point like sources is always in the
spontaneously broken phase of chiral symmetry, whatever the density. The
point-like nature of the sources and large N_c cause the matter to be repulsive
as all baryon interactions are omega mediated. Through the induced DBI action
on D8-\bar{D8}, we study the effects of the fixed baryon charge density n_B on
the pion and vector meson masses and couplings. Issues related to vector
dominance in matter in the context of holographic QCD are also discussed.Comment: V3: 39 pages, 16 figures, minor corrections, version to appear in
JHEP. V2: references added, typos correcte
Winding Number Transitions in the Mottola-Wipf Model on a Circle
Winding number transitions from quantum to classical behavior are studied in
the case of the {1+1} dimensional Mottola-Wipf model with the space coordinate
on a circle for exploring the possibility of obtaining transitions of second
order. The model is also studied as a prototype theory which demonstrates the
procedure of such investigations. In the model at hand we find that even on a
circle the transitions remain those of first order.Comment: 17pages + 5 ps figures, final version to appear in Nucl. Phys.
Compromise of Localized Graviton with a Small Cosmological Constant in Randall-Sundrum Scenario
A new mechanism which leads to a linearized massless graviton localized on
the brane is found in the /CFT setting, {\it i.e.} in a single copy of
spacetime with a singular brane on the boundary, within the
Randall-Sundrum brane-world scenario. With an help of a recent development in
path-integral techniques, a one-parameter family of propagators for linearized
gravity is obtained analytically, in which a parameter reflects various
kinds of boundary conditions that arise as a result of the half-line
constraint. In the case of a Dirichlet boundary condition () the
graviton localized on the brane can be massless {\it via} coupling constant
renormalization. Our result supports a conjecture that the usual
Randall-Sundrum scenario is a regularized version of a certain underlying
theory.Comment: 6 pages, no figure, V2 12 pages, one more author added, will appear
in PL
Fuzzy BIon
We construct a solution of the BFSS matrix theory, which is a counterpart of
the BIon solution representing a fundamental string ending on a bound state of
a D2-brane and D0-branes. We call this solution the `fuzzy BIon' and show that
this configuration preserves 1/4 supersymmetry of type IIA superstring theory.
We also construct an effective action for the fuzzy BIon by analyzing the
nonabelian Born-Infeld action for D0-branes. When we take the continuous limit,
with some conditions, this action coincides with the effective action for the
BIon configuration.Comment: 11 pages, 1 figure, reference and note adde
Baryonic Response of Dense Holographic QCD
The response function of a homogeneous and dense hadronic system to a
time-dependent (baryon) vector potential is discussed for holographic dense QCD
(D4/D8 embedding) both in the confined and deconfined phases. Confined
holographic QCD is an uncompressible and static baryonic insulator at large N_c
and large \lambda, with a gapped vector spectrum and a massless pion.
Deconfined holographic QCD is a diffusive conductor with restored chiral
symmetry and a gapped transverse baryonic current. Similarly, dense D3/D7 is
diffusive for any non-zero temperature at large N_c and large \lambda. At zero
temperature dense D3/D7 exhibits a baryonic longitudinal visco-elastic mode
with a first sound speed \lambda/\sqrt{3} and a small width due to a shear
viscosity to baryon ratio \eta/n_B=\hbar/4. This mode is turned diffusive by
arbitrarily small temperatures, a hallmark of holography.Comment: V2: 47 pages, 7 figures, references added, typos correcte
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