21,406 research outputs found
Gauged Fermionic Q-balls
We present a new model for a non-topological soliton (NTS) that contains
interacting fermions, scalar particles and a gauge field. Using a variational
approach, we estimate the energy of the localized configuration, showing that
it can be the lowest energy state of the system for a wide range of parameters.Comment: 5 pages, 2 figures; revised version to appear in Phys. Rev.
The Kaon B-parameter in Mixed Action Chiral Perturbation Theory
We calculate the kaon B-parameter, B_K, in chiral perturbation theory for a
partially quenched, mixed action theory with Ginsparg-Wilson valence quarks and
staggered sea quarks. We find that the resulting expression is similar to that
in the continuum, and in fact has only two additional unknown parameters. At
one-loop order, taste-symmetry violations in the staggered sea sector only
contribute to flavor-disconnected diagrams by generating an O(a^2) shift to the
masses of taste-singlet sea-sea mesons. Lattice discretization errors also give
rise to an analytic term which shifts the tree-level value of B_K by an amount
of O(a^2). This term, however, is not strictly due to taste-breaking, and is
therefore also present in the expression for B_K for pure G-W lattice fermions.
We also present a numerical study of the mixed B_K expression in order to
demonstrate that both discretization errors and finite volume effects are small
and under control on the MILC improved staggered lattices.Comment: 29 pages, 4 figures; Expanded spurion discussion, other discussions
clarified, version to appear in PR
Porosity Variations Between Fine Grained Rims and Matrix in a CM Chondrite by 3D Serial Sectioning
No abstract available
Evolution of scale-free random graphs: Potts model formulation
We study the bond percolation problem in random graphs of weighted
vertices, where each vertex has a prescribed weight and an edge can
connect vertices and with rate . The problem is solved by the
limit of the -state Potts model with inhomogeneous interactions for
all pairs of spins. We apply this approach to the static model having
so that the resulting graph is scale-free with
the degree exponent . The number of loops as well as the giant
cluster size and the mean cluster size are obtained in the thermodynamic limit
as a function of the edge density, and their associated critical exponents are
also obtained. Finite-size scaling behaviors are derived using the largest
cluster size in the critical regime, which is calculated from the cluster size
distribution, and checked against numerical simulation results. We find that
the process of forming the giant cluster is qualitatively different between the
cases of and . While for the former, the giant
cluster forms abruptly at the percolation transition, for the latter, however,
the formation of the giant cluster is gradual and the mean cluster size for
finite shows double peaks.Comment: 34 pages, 9 figures, elsart.cls, final version appeared in NP
Electrical Switching in Metallic Carbon Nanotubes
We present first-principles calculations of quantum transport which show that
the resistance of metallic carbon nanotubes can be changed dramatically with
homogeneous transverse electric fields if the nanotubes have impurities or
defects. The change of the resistance is predicted to range over more than two
orders of magnitude with experimentally attainable electric fields. This novel
property has its origin that backscattering of conduction electrons by
impurities or defects in the nanotubes is strongly dependent on the strength
and/or direction of the applied electric fields. We expect this property to
open a path to new device applications of metallic carbon nanotubes.Comment: 4 pages and 4 figure
A Solvable Model for Many Quark Systems in QCD Hamiltonians
Motivated by a canonical, QCD Hamiltonian we propose an effective Hamiltonian
to represent an arbitrary number of quarks in hadronic bags. The structure of
the effective Hamiltonian is discussed and the BCS-type solutions that may
represent constituent quarks are presented. The single particle orbitals are
chosen as 3-dimensional harmonic oscillators and we discuss a class of exact
solutions that can be obtained when a subset of single-particle basis states is
restricted to include a certain number of orbital excitations. The general
problem, which includes all possible orbital states, can also be solved by
combining analytical and numerical methods.Comment: 24 pages, 2 figures, research articl
Chemical abundance anticorrelations in globular cluster stars: The effect on cluster integrated spectra
It is widely accepted that individual Galactic globular clusters harbor two
coeval generations of stars, the first one born with the `standard'
-enhanced metal mixture observed in field Halo objects, the second one
characterized by an anticorrelated CN-ONa abundance pattern overimposed on the
first generation, -enhanced metal mixture. We have investigated with
appropriate stellar population synthesis models how this second generation of
stars affects the integrated spectrum of a typical metal rich Galactic globular
cluster, like 47\,Tuc, focusing our analysis on the widely used Lick-type
indices. We find that the only indices appreciably affected by the abundance
anticorrelations are Ca4227, G4300, , and NaD. The
age-sensitive Balmer line, Fe line and the [MgFe] indices widely used to
determine age, Fe and total metallicity of extragalactic systems are largely
insensitive to the second generation population. Enhanced He in second
generation stars affects also the Balmer line indices of the integrated
spectra, through the change of the turn off temperature and -- in the
assumption that the mass loss history of both stellar generations is the same
-- the horizontal branch morphology of the underlying isochrones.Comment: Accepted for publication in Ap
Quantum Monte Carlo Calculations of Pion Scattering from Li
We show that the neutron and proton transition densities predicted by recent
quantum Monte Carlo calculations for A=6,7 nuclei are consistent with pion
scattering from 6Li and 7Li at energies near the Delta resonance. This has
provided a microscopic understanding of the enhancement factors for quadrople
excitations, which were needed to describe pion inelastic scattering within the
nuclear shell model of Cohen and Kurath.Comment: 10 pages, REVTeX, 3 postscript figures; added calculation of elastic
and inelastic pion scattering from 6Li at multiple energie
Fermion and Anti-Fermion Effective Masses in High Temperature Gauge Theories in -Asymmetric Background
We calculate the splitting between fermion and anti-fermion effective masses
in high temperature gauge theories in the presence of a non-vanishing chemical
potential due to the -asymmetric fermionic background. In particular we
consider the case of left-handed leptons in the theory when
the temperature is above GeV and the gauge symmetry is restored.Comment: 13 pages, TIPAC-93001
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