5,892 research outputs found
Staggered Heavy Baryon Chiral Perturbation Theory
Although taste violations significantly affect the results of staggered
calculations of pseudoscalar and heavy-light mesonic quantities, those entering
staggered calculations of baryonic quantities have not been quantified. Here I
develop staggered chiral perturbation theory in the light-quark baryon sector
by mapping the Symanzik action into heavy baryon chiral perturbation theory.
For 2+1 dynamical quark flavors, the masses of flavor-symmetric nucleons are
calculated to third order in partially quenched and fully dynamical staggered
chiral perturbation theory. To this order the expansion includes the leading
chiral logarithms, which come from loops with virtual decuplet-like states, as
well as terms the order of the cubed pion mass, which come from loops with
virtual octet-like states. Taste violations enter through the meson propagators
in loops and tree-level terms the order of the squared lattice spacing. The
pattern of taste symmetry breaking and the resulting degeneracies and mixings
are discussed in detail. The resulting chiral forms are appropriate to lattice
results obtained with operators already in use and could be used to study the
restoration of taste symmetry in the continuum limit. I assume that the fourth
root of the fermion determinant can be incorporated in staggered chiral
perturbation theory using the replica method.Comment: 54 pages; v2: corrected discussion in Sec. III.C, conclusions
unchange
On N-wave type systems and their gauge equivalent
The class of nonlinear evolution equations - gauge equivalent to the N-wave
equations related to the simple Lie algebra g are derived and analyzed. They
are written in terms of the functions S(x,t) satisfying r= rank g nonlinear
constraints. The corresponding Lax pairs and the time evolution of the
scattering data are found. The Zakharov-Shabat dressing method is appropriately
modified to construct their soliton solutions.Comment: 5 pages, LaTeX 2e, revised versio
A flexible polymer chain in a critical solvent: Coil or globule?
We study the behavior of a flexible polymer chain in the presence of a
low-molecular weight solvent in the vicinity of a liquid-gas critical point
within the framework of a self-consistent field theory. The total free energy
of the dilute polymer solution is expressed as a function of the radius of
gyration of the polymer and the average solvent number density within the
gyration volume at the level of the mean-field approximation. Varying the
strength of attraction between polymer and solvent we show that two
qualitatively different regimes occur at the liquid-gas critical point. In case
of weak polymer-solvent interactions the polymer chain is in a globular state.
On the contrary, in case of strong polymer-solvent interactions the polymer
chain attains an expanded conformation. We discuss the influence of the
critical solvent density fluctuations on the polymer conformation. The reported
effect could be used to excert control on the polymer conformation by changing
the thermodynamic state of the solvent. It could also be helpful to estimate
the solvent density within the gyration volume of the polymer for drug delivery
and molecular imprinting applications
Goldstone boson counting in linear sigma models with chemical potential
We analyze the effects of finite chemical potential on spontaneous breaking
of internal symmetries within the class of relativistic field theories
described by the linear sigma model. Special attention is paid to the emergence
of ``abnormal'' Goldstone bosons with quadratic dispersion relation. We show
that their presence is tightly connected to nonzero density of the Noether
charges, and formulate a general counting rule. The general results are
demonstrated on an SU(3)xU(1) invariant model with an SU(3)-sextet scalar
field, which describes one of the color-superconducting phases of QCD.Comment: 10 pages, REVTeX4, 4 eps figures, v2: general discussion in Sec. IV
expanded and improved, references added, other minor corrections throughout
the tex
Probing Exciton Localization in Single-Walled Carbon Nanotubes Using High-Resolution Near-Field Microscopy
We observe localization of excitons in semiconducting single-walled carbon nanotubes at room temperature using high-resolution near-field photoluminescence (PL) microscopy. Localization is the result of spatially confined exciton energy minima with depths of more than 15 meV connected to lateral energy gradients exceeding 2 meV/nm as evidenced by energy-resolved PL imaging. Simulations of exciton diffusion in the presence of energy variations support this interpretation predicting strongly enhanced PL at local energy minima
Comparison of 1/mQ^2 Corrections in Mesons and Baryons
We extend our relativistic quark model to the study of the decay Lambda_b ->
Lambda_c ell nu and verify that the model satisfies the heavy-quark symmetry
constraints at order 1/mQ^2. We isolate a strong dependence on a parameter
which measures the relative distortion in the light-quark wave functions of the
Lambda_b and Lambda_c. This parameter and the 1/mQ^2 corrections turn out to be
small. The dependence on a corresponding parameter in the meson case leads to
large 1/mQ^2 corrections.Comment: 9 pages, LaTeX, 3 self-contained LaTeX figures in separate fil
Chaos at the border of criticality
The present paper points out to a novel scenario for formation of chaotic
attractors in a class of models of excitable cell membranes near an
Andronov-Hopf bifurcation (AHB). The mechanism underlying chaotic dynamics
admits a simple and visual description in terms of the families of
one-dimensional first-return maps, which are constructed using the combination
of asymptotic and numerical techniques. The bifurcation structure of the
continuous system (specifically, the proximity to a degenerate AHB) endows the
Poincare map with distinct qualitative features such as unimodality and the
presence of the boundary layer, where the map is strongly expanding. This
structure of the map in turn explains the bifurcation scenarios in the
continuous system including chaotic mixed-mode oscillations near the border
between the regions of sub- and supercritical AHB. The proposed mechanism
yields the statistical properties of the mixed-mode oscillations in this
regime. The statistics predicted by the analysis of the Poincare map and those
observed in the numerical experiments of the continuous system show a very good
agreement.Comment: Chaos: An Interdisciplinary Journal of Nonlinear Science
(tentatively, Sept 2008
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