386 research outputs found
Self Consistent Expansion In The Presence Of Electroweak Interactions
In the conventional approach to the expansion, electroweak
interactions are switched off and large QCD is treated in isolation. We
study the self-consistency of taking the large limit in the presence of
electroweak interaction. If the electroweak coupling constants are held
constant, the large counting rules are violated by processes involving
internal photon or weak boson lines. Anomaly cancellations, however, fix the
ratio of electric charges of different fermions. This allows a self-consistent
way to scale down the electronic charge in the large limit and hence
restoring the validity of the large counting rules.Comment: 9 pages in REVTeX, no figure
Circulating Levels of Adipocyte and Epidermal Fatty Acid–Binding Proteins in Relation to Nephropathy Staging and Macrovascular Complications in Type 2 Diabetic Patients
OBJECTIVE—To investigate the relationships of serum adipocyte fatty acid–binding protein (A-FABP) and epidermal fatty acid–binding protein (E-FABP) with renal dysfunction and macrovascular complications in type 2 diabetic patients
Dirichlet sigma models and mean curvature flow
The mean curvature flow describes the parabolic deformation of embedded
branes in Riemannian geometry driven by their extrinsic mean curvature vector,
which is typically associated to surface tension forces. It is the gradient
flow of the area functional, and, as such, it is naturally identified with the
boundary renormalization group equation of Dirichlet sigma models away from
conformality, to lowest order in perturbation theory. D-branes appear as fixed
points of this flow having conformally invariant boundary conditions. Simple
running solutions include the paper-clip and the hair-pin (or grim-reaper)
models on the plane, as well as scaling solutions associated to rational (p, q)
closed curves and the decay of two intersecting lines. Stability analysis is
performed in several cases while searching for transitions among different
brane configurations. The combination of Ricci with the mean curvature flow is
examined in detail together with several explicit examples of deforming curves
on curved backgrounds. Some general aspects of the mean curvature flow in
higher dimensional ambient spaces are also discussed and obtain consistent
truncations to lower dimensional systems. Selected physical applications are
mentioned in the text, including tachyon condensation in open string theory and
the resistive diffusion of force-free fields in magneto-hydrodynamics.Comment: 77 pages, 21 figure
Short-Range Interactions and Scaling Near Integer Quantum Hall Transitions
We study the influence of short-range electron-electron interactions on
scaling behavior near the integer quantum Hall plateau transitions. Short-range
interactions are known to be irrelevant at the renormalization group fixed
point which represents the transition in the non-interacting system. We find,
nevertheless, that transport properties change discontinuously when
interactions are introduced. Most importantly, in the thermodynamic limit the
conductivity at finite temperature is zero without interactions, but non-zero
in the presence of arbitrarily weak interactions. In addition, scaling as a
function of frequency, , and temperature, , is determined by the
scaling variable (where is the exponent for the temperature
dependence of the inelastic scattering rate) and not by , as it would
be at a conventional quantum phase transition described by an interacting fixed
point. We express the inelastic exponent, , and the thermal exponent, ,
in terms of the scaling dimension, , of the interaction strength
and the dynamical exponent (which has the value ), obtaining
and .Comment: 9 pages, 4 figures, submitted to Physical Review
Four-fermion heavy quark operators and light current amplitudes in heavy flavor hadrons
We introduce and study the properties of the "color-straight" four-quark
operators containing heavy and light quark fields. They are of the form (\bar
b\Gamma_b b)(\bar q\Gamma_q q) where both brackets are color singlets. Their
expectation values include the bulk of the nonfactorizable contributions to the
nonleptonic decay widths of heavy hadrons. The expectation values of the
color-straight operators in the heavy hadrons are related to the momentum
integrals of the elastic light-quark formfactors of the respective heavy
hadron. We calculate the asymptotic behavior of the light-current formfactors
of heavy hadrons and show that the actual decrease is 1/(q^2)^3/2 rather than
1/q^4. The two-loop hybrid anomalous dimensions of the four-quark operators and
their mixing (absent in the first loop) are obtained. Using plausible models
for the elastic formfactors, we estimate the expectation values of the
color-straight operators in the heavy mesons and baryons. Improved estimates
will be possible in the future with new data on the radiative decays of heavy
hadrons. We give the Wilson coefficients of the four-fermion operators in the
1/m_b expansion of the inclusive widths and discuss the numerical predictions.
Estimates of the nonfactorizable expectation values are given.Comment: 51 pages. The case of flavor-singlet operators is added for the
two-loop anomalous dimension
Baryonium, tetra-quark state and glue-ball in large N_c QCD
From the large-N_c QCD point of view, baryonia, tetra-quark states, hybrids,
and glueballs are studied. The existence of these states is argued for. They
are constructed from baryons. In N_f=1 large N_c QCD, a baryonium is always
identical to a glueball with N_c valence gluons. The ground state 0^{-+}
glueball has a mass about 2450 MeV. f_0(1710) is identified as the lowest
0^{++} glueball. The lowest four-quark nonet should be f_0(1370), a_0(1450),
K^*_0(1430) and f_0(1500). Combining with the heavy quark effective theory,
spectra of heavy baryonia and heavy tetra-quark states are predicted. 1/N_c
corrections are discussed.Comment: 16 pages, 3 figure
Characterization of Avian Influenza Viruses A (H5N1) from Wild Birds, Hong Kong, 2004–2008
Repeated detection of subclade 2.3.2 viruses in nonpasserine birds from different regions suggests possible establishment of this lineage in wild bird species
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