26,381 research outputs found
Exotic candidates with heavy quark(s)
In the last decades, the number of exotic candidates which are beyond the
conventional quark model has grown dramatically. At the same time, numerous
theoretical interpretations, such as tetraquark, hybrid, hadroquarkonium and
hadronic molecule, have been proposed to understand their nature. In principle,
all the configurations with the same quantum numbers can mix with each other.
Thus at present we aim at identifying the prominent component. As an extended
object, a hadronic molecule has some distinguishable features from other more
compact configurations. In the end, the two states are used to illustrate
some features of the molecular scenario.Comment: XVII International Conference on Hadron Spectroscopy and Structure -
Hadron201
Universal spectral statistics in Wigner-Dyson, chiral and Andreev star graphs I: construction and numerical results
In a series of two papers we investigate the universal spectral statistics of
chaotic quantum systems in the ten known symmetry classes of quantum mechanics.
In this first paper we focus on the construction of appropriate ensembles of
star graphs in the ten symmetry classes. A generalization of the
Bohigas-Giannoni-Schmit conjecture is given that covers all these symmetry
classes. The conjecture is supported by numerical results that demonstrate the
fidelity of the spectral statistics of star graphs to the corresponding
Gaussian random-matrix theories.Comment: 15 page
Orbitally excited and hybrid mesons from the lattice
We discuss in general the construction of gauge-invariant non-local meson
operators on the lattice. We use such operators to study the - and -wave
mesons as well as hybrid mesons in quenched QCD, with quark masses near the
strange quark mass. The resulting spectra are compared with experiment for the
orbital excitations. For the states produced by gluonic excitations (hybrid
mesons) we find evidence of mixing for non-exotic quantum numbers. We give
predictions for masses of the spin-exotic hybrid mesons with $J^{PC}=1^{-+},\
0^{+-}2^{+-}$.Comment: 31 pages, LATEX, 8 postscript figures. Reference adde
Entangled end states with fractionalized spin projection in a time-reversal-invariant topological superconducting wire
We study the ground state and low-energy subgap excitations of a finite wire
of a time-reversal-invariant topological superconductor (TRITOPS) with
spin-orbit coupling. We solve the problem analytically for a long chain of a
specific one-dimensional lattice model in the electron-hole symmetric
configuration and numerically for other cases of the same model. We present
results for the spin density of excitations in long chains with an odd number
of particles. The total spin projection along the axis of the spin-orbit
coupling is distributed with fractions localized at
both ends, and shows even-odd alternation along the sites of the chain. We
calculate the localization length of these excitations and find that it can be
well approximated by a simple analytical expression. We show that the energy
of the lowest subgap excitations of the finite chain defines tunneling and
entanglement between end states.We discuss the effect of a Zeeman coupling
on one of the ends of the chain only. For , the energy
difference of excitations with opposite spin orientation is ,
consistent with a spin projection . We argue that these physical
features are not model dependent and can be experimentally observed in TRITOPS
wires under appropriate conditions.Comment: 14 pages, 8 Figure
Boundary Conditions and Unitarity: the Maxwell-Chern-Simons System in AdS_3/CFT_2
We consider the holography of the Abelian Maxwell-Chern-Simons (MCS) system
in Lorentzian three-dimensional asymptotically-AdS spacetimes, and discuss a
broad class of boundary conditions consistent with conservation of the
symplectic structure. As is well-known, the MCS theory contains a massive
sector dual to a vector operator in the boundary theory, and a topological
sector consisting of flat connections dual to U(1) chiral currents; the
boundary conditions we examine include double-trace deformations in these two
sectors, as well as a class of boundary conditions that mix the vector
operators with the chiral currents. We carefully study the symplectic product
of bulk modes and show that almost all such boundary conditions induce
instabilities and/or ghost excitations, consistent with violations of unitarity
bounds in the dual theory.Comment: 50+1 pages, 6 figures, PDFLaTeX; v2: added references, corrected
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Adaptive Embedded LES of the NASA Hump
A scheme for adaptive embedded LES is proposed which automatically determines boundaries for LES regions in a hybrid LES-RANS computation, with the goal of minimizing the LES part of the computation for maximum accuracy with minimum cost. The model-invariant hybrid formulation enables this scheme through greater flexibility in the placement of RANS-LES transitions. An adaptive embedded large-eddy simulation is carried out for the NASA hump test case and adaptive meshing is added to show how additional adaptive features may be controlled by the adaptive hybrid scheme
Model-Invariant Hybrid RANS-LES Computations on Unstructured Meshes
Hybrid RANS-LES computations combine the bene ts of RANS and LES so that LES is used in regions where the accuracy of RANS deteriorates. The numerous hybrid approaches are limited by the speci cation of the LES-RANS interface, which can cause nonphysical results such as log-layer mismatch and low shear stress. The hybrid RANS-LES approach based on the concept of model invariance, mitigates these problems, enabling seamless blending of the RANS and LES regions while forming the basis for interpreting the results in the interface region. This hybrid formulation was implemented in the NASA FUN3D unstructured code and computations for ow in a channel at Reynolds number of 3300 (based on the channel half width h and the bulk in ow velocity u(infinity) were carried out. An isotropic stochastic turbulence generator was implemented to generate in ow turbulence. The present approach was able to eliminate the log-layer mismatch and predict the shear stress fairly well. Thus, the model-invariant hybrid formulation coupled with the isotropic turbulence in ow generation serves as a physically meaningful way of performing hybrid RANS-LES computations
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