1,381 research outputs found
On Witten's global anomaly for higher SU(2) representations
The spectral flow of the overlap operator is computed numerically along a
particular path in gauge field space. The path connects two gauge equivalent
configurations which differ by a gauge transformation in the non-trivial class
of pi_4(SU(2)). The computation is done with the SU(2) gauge field in the
fundamental, the 3/2, and the 5/2 representation. The number of eigenvalue
pairs that change places along this path is established for these three
representations and an even-odd pattern predicted by Witten is verified.Comment: 24 pages, 12 eps figure
Effective Lagrangian for strongly coupled domain wall fermions
We derive the effective Lagrangian for mesons in lattice gauge theory with
domain-wall fermions in the strong-coupling and large-N_c limits. We use the
formalism of supergroups to deal with the Pauli-Villars fields, needed to
regulate the contributions of the heavy fermions. We calculate the spectrum of
pseudo-Goldstone bosons and show that domain wall fermions are doubled and
massive in this regime. Since we take the extent and lattice spacing of the
fifth dimension to infinity and zero respectively, our conclusions apply also
to overlap fermions.Comment: 26 pp. RevTeX and 3 figures; corrected error in symmetry breaking
scheme and added comments to discussio
Chiral perturbation theory at O(a^2) for lattice QCD
We construct the chiral effective Lagrangian for two lattice theories: one
with Wilson fermions and the other with Wilson sea fermions and Ginsparg-Wilson
valence fermions. For each of these theories we construct the Symanzik action
through order . The chiral Lagrangian is then derived, including terms of
order , which have not been calculated before. We find that there are only
few new terms at this order. Corrections to existing coefficients in the
continuum chiral Lagrangian are proportional to , and appear in the
Lagrangian at order or higher. Similarly, O(4) symmetry breaking
terms enter the Symanzik action at order , but contribute to the chiral
Lagrangian at order or higher. We calculate the light meson masses in
chiral perturbation theory for both lattice theories. At next-to-leading order,
we find that there are no order corrections to the valence-valence meson
mass in the mixed theory due to the enhanced chiral symmetry of the valence
sector.Comment: 25 pages, LaTeX2e; references adde
Quark propagator and vertex: systematic corrections of hypercubic artifacts from lattice simulations
This is the first part of a study of the quark propagator and the vertex
function of the vector current on the lattice in the Landau gauge and using
both Wilson-clover and overlap actions. In order to be able to identify lattice
artifacts and to reach large momenta we use a range of lattice spacings. The
lattice artifacts turn out to be exceedingly large in this study. We present a
new and very efficient method to eliminate the hypercubic (anisotropy)
artifacts based on a systematic expansion on hypercubic invariants which are
not SO(4) invariant. A simpler version of this method has been used in previous
works. This method is shown to be significantly more efficient than the popular
``democratic'' methods. It can of course be applied to the lattice simulations
of many other physical quantities. The analysis indicates a hierarchy in the
size of hypercubic artifacts: overlap larger than clover and propagator larger
than vertex function. This pleads for the combined study of propagators and
vertex functions via Ward identities.Comment: 14 pags., 9 fig
On the presence of mid-gap states in CaV4O9
Using exact diagonalizations of finite clusters with up to 32 sites, we study
the model on the 1/5 depleted square lattice. Spin-spin correlation
functions are consistent with plaquette order in the spin gap phase which
exists for intermediate values of . Besides, we show that singlet
states will be present in the singlet-triplet gap if is not too small
(). We argue that this property should play a central
role in determining the exchange integrals in Comment: 4 pages, 5 postscript figure
Long Range Dynamics Related to Magnetic Impurity in the 2D Heisenberg Antiferromagnet
We consider a magnetic impurity in the two-dimensional Heisenberg
antifferomagnet with long range antiferromagnetic order. At low temperature the
impurity magnetic susceptibility has a Curie term () and a
logarithmic correction (). We calculate the correction and
derive related Ward identity for the impurity-spin-wave vertex.Comment: 5 pages, 6 figure
Schwinger-boson approach to quantum spin systems: Gaussian fluctuactions in the "natural" gauge
We compute the Gaussian-fluctuation corrections to the saddle-point
Schwinger-boson results using collective coordinate methods. Concrete
application to investigate the frustrated J1-J2 antiferromagnet on the square
lattice shows that, unlike the saddle-point predictions, there is a quantum
nonmagnetic phase for 0.53 < J2/J1 < 0.64. This result is obtained by
considering the corrections to the spin stiffness on large lattices and
extrapolating to the thermodynamic limit, which avoids the infinite-lattice
infrared divergencies associated to Bose condensation. The very good agreement
of our results with exact numerical values on finite clusters lends support to
the calculational scheme employed.Comment: 4 pages, Latex, 3 figures included as eps files,minor correction
Indications for liver transplantation in the cyclosporine era
One hundred seventy orthotopic liver transplants were performed under conventional immunosuppression with azathioprine and steroids with 1- and 5-year survivals of 32.9% and 20.0%, respectively. Since the introduction of cyclosporine-prednisone therapy in March 1980, 313 primary orthotopic liver transplants have been performed. Actuarial survivals at 1 and 5 years have improved to 69.7% and 62.8%, respectively. Biliary atresia is now the most common indication for liver replacement. In adults, primary biliary cirrhosis and sclerosing cholangitis have become more common indications for transplantation, and alcoholic cirrhosis and primary liver malignancy as indications have declined. Early enthusiasm for liver transplantation in patients with hepatic cancer has been tempered by the finding that recurrence is both common and rapid. An increasing number of patients with inborn errors of metabolism originating in the liver are receiving transplants, including patients with Wilson's disease, tyrosinemia, alpha-1-antitrypsin deficiency, glycogen storage disease, familial hypercholesterolemia, and hemochromatosis. Survival in this group of patients has been excellent (74.4% at 1 and 5 years). A hemophiliac who received a transplant for postnecrotic cirrhosis has survived and may have been cured of his hemophilia. About 20% of patients require retransplantation for rejection, technical failure, or primary graft failure. Only 4 of the patients receiving retransplants under conventional immunosuppression survived beyond 6 months, and all died within 14 months of retransplantation. Sixty-eight patients have received retransplants under cyclosporine-prednisone. Thirty-one patients are surviving, all for at least 1 year. Six of the 12 patients requiring a third transplant are alive 2 to 3 years after the primary operation. An aggressive approach to retransplantation in the patient with a failed graft is justified
Numerical study of lattice index theorem usingimproved cooling and overlap fermions
We investigate topological charge and the index theorem on finite lattices
numerically. Using mean field improved gauge field configurations we calculate
the topological charge Q using the gluon field definition with -improved cooling and an -improved field strength tensor
. We also calculate the index of the massless overlap fermion
operator by directly measuring the differences of the numbers of zero modes
with left- and right--handed chiralities. For sufficiently smooth field
configurations we find that the gluon field definition of the topological
charge is integer to better than 1% and furthermore that this agrees with the
index of the overlap Dirac operator, i.e., the Atiyah-Singer index theorem is
satisfied. This establishes a benchmark for reliability when calculating
lattice quantities which are very sensitive to topology.Comment: 15 pages, 1 figure
Atributos de cor em filés de peixes capturados no reservatório da Usina Hidrelétrica do Lageado, estado do Tocantins.
Objetivando caracterizar colorimetricamente os filĂ©s de quatro espĂ©cies de peixe capturadas no reservatĂłrio da Usina HidrelĂ©trica do Lageado, estado do Tocantins, foram selecionadas, ao todo, 47 amostras de peixes identificados como mandi-moela (Pimelodina flavipinnis), cuiĂș-cuiĂș (Oxydoras niger), maparĂĄ (Hypophthalmus edentatus) e corvina (Plagioscion squamosissimus).Organizado por: SĂlvio Ricardo Maurano; AQUACIĂNCIA 2012
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