43,086 research outputs found
A Laplace Transform Method for Molecular Mass Distribution Calculation from Rheometric Data
Polydisperse linear polymer melts can be microscopically described by the
tube model and fractal reptation dynamics, while on the macroscopic side the
generalized Maxwell model is capable of correctly displaying most of the
rheological behavior. In this paper, a Laplace transform method is derived and
different macroscopic starting points for molecular mass distribution
calculation are compared to a classical light scattering evaluation. The
underlying assumptions comprise the modern understanding on polymer dynamics in
entangled systems but can be stated in a mathematically generalized way. The
resulting method is very easy to use due to its mathematical structure and it
is capable of calculating multimodal molecular mass distributions of linear
polymer melts
Bipolaron-SO(5) Non-Fermi Liquid in a Two-channel Anderson Model with Phonon-assisted Hybridizations
We analyze non-Fermi liquid (NFL) properties along a line of critical points
in a two-channel Anderson model with phonon-assisted hybridizations. We succeed
in identifying hidden nonmagnetic SO(5) degrees of freedom for
valence-fluctuation regime and analyze the model on the basis of boundary
conformal field theory. We find that the NFL spectra along the critical line,
which is the same as those in the two-channel Kondo model, can be alternatively
derived by a fusion in the nonmagnetic SO(5) sector. The leading irrelevant
operators near the NFL fixed points vary as a function of Coulomb repulsion U;
operators in the spin sector dominate for large U, while those in the SO(5)
sector do for small U, and we confirm this variation in our numerical
renormalization group calculations. As a result, the thermodynamic singularity
for small U differs from that of the conventional two-channel Kondo problem.
Especially, the impurity contribution to specific heat is proportional to
temperature and bipolaron fluctuations, which are coupled electron-phonon
fluctuations, diverge logarithmically at low temperatures for small U.Comment: 16 pages, 4 figures, 3 table
Bound states for Overlap and Fixed Point Actions close to the chiral limit
We study the overlap and the fixed point Dirac operators for massive fermions
in the two-flavor lattice Schwinger model. The masses of the triplet (pion) and
singlet (eta) bound states are determined down to small fermion masses and the
mass dependence is compared with various continuum model approximations. Near
the chiral limit, at very small fermion masses the fixed point operator has
stability problems, which in this study are dominated by finite size effects,Comment: 13 pages, 2 figure
Nucleon excited states on the lattice
We study the pion-nucleon system in s-wave in the framework of lattice QCD in
order to gain new information on the nucleon excited states. We perform
simulations for mass degenerate light quarks at a pion mass of 266
MeV. The results show that including the two-particle states drastically
changes the energy levels. The variational analysis and the distillation
approach play an important role in the extraction of the energy levels. The
phase shift analysis allows to extract information on the resonance nature of
the observed states.Comment: 6 pages, 2 figures, talk presented at Excited QCD 2013, Bjelasnica
Mountain, Sarajev
Dirac zero-modes in compact U(1) gauge theory
We study properties of the zero and near-zero eigenmodes of the overlap Dirac
operator in compact U(1) gauge theory. In the confinement phase the exact
zero-modes are localized as found by studying the values of the inverse
participation ratio and other features. Non-zero-eigenmodes are less localized
in the confinement phase. In the Coulomb phase no zero-modes are observed and
the eigenmodes show no localization at all.Comment: Minor corrections, 15 pages, 5 figures, LaTeX styl
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