98,716 research outputs found
Renormalization of
We derive the vertices of five-meson and seven-meson anomaly processes from
the four dimensional expansion form of Wess-Zumino term. Using these vertices
we calculate the amplitude, both the finite part and divergent part, of {} to one loop and renormalize the lagrangian.
The divergent part agrees with the result derived from path integral approach.
Contribution from counter terms is estimated by using the vector meson
dominance model. Test of the vertex in the -channel of near the threshold is discussed. We find
that the amplitudes arising from chiral loop and counter terms are of opposite
sign and the counter term amplitude is about twice the loop amplitude.Comment: 13 pages, latex, 7 figures unencoded and can be obtained by reques
Magnetoelectronic states of a monolayer graphite
The Peierl's tight-binding model, with the band Hamiltonian matrix, is used
to calculate the magnetoelectronic structure of a monolayergraphite. There are
many flat Landau levels and some oscillatory Landau levels. The low
Landau-level energies are characterized by a simple relation, not for others.
State degeneracy is, respectively, fourfold degenerate and doubly degenerate at
low and high energies. The level spacing declines quickly and then grows
gradually in the increase of state energy. The main features of electronic
properties are directly reflected in density of states. The predicted results
could be verified by the optical spectroscopy.Comment: 9 pages and 4 figure
Modulation effects on Landau levels in a monolayer graphene
A monolayer graphene exists in an environment where a uniform magnetic field
interacts a spatially modulated magnetic field. The spatially modulated
magnetic field could affect Landau levels due to a uniform magnetic field. The
modulation effects on Landau levels are investigated through the Peierl's
tight-binding model. The magneto-electronic properties are dominated by the
period, the strength, and the direction of a spatially modulated magnetic
field. Such a field could induce the growth in dimensionality, the change of
energy dispersions, the destroy of state degeneracy, and the creation of
band-edge states. There are a robust Landau level at Fermi level and 1D
parabolic subbands located around the original Landau levels, which make
density of states exhibit a delta-function-like structure and many pairs of
asymmetric peak structure, respectively. The density of states and the energies
of band-edge states strongly depend on the strength, but not on the period and
the direction.Comment: 11 pages,4 figure
Dynamic response of some tentative compliant wall structures to convected turbulence fields
Some tentative compliant wall structures designed for possible skin friction drag reduction are investigated. Among the structural models considered is a ribbed membrane backed by polyurethane or PVS plastisol. This model is simplified as a beam placed on a viscoelastic foundation as well as on a set of evenly spaced supports. The total length of the beam may be either finite or infinite, and the supports may be either rigid or elastic. Another structural model considered is a membrane mounted over a series of pretensioned wires, also evenly spaced, and the entire membrane is backed by an air cavity. The forcing pressure field is idealized as a frozen random pattern convected downstream at a characteristic velocity. The results are given in terms of the frequency response functions of the system, the spectral density of the structural motion, and the spectral density of the boundary layer pressure including the effect of structural motion. These results are used in a parametric study of structural configurations capable of generating favorable wave lengths, wave amplitudes, and wave speeds in the structural motion for potential drag reduction
Superconducting Resonance and paring symmetry in electron-doped cuprates
The magnetic excitations in the superconducting electron-doped cuprates are
studied in the framework of spin-density-wave description. The superconducting
resonance is a natural product of the superconductivity due to the opening of
d-wave gap. Its resonance energy exhibits well linear scaling with
superconducting gap as , quantitatively consisting
with the experimental discovery. This ratio is insensitive to the selected
parameters, manifesting its universality. Another lower-energy peak below
resonance energy is predicted when the hole pocket emerges due to suppression
of spin-density wave. We further verify that the ratio of linear scales is
intimately related to the pairing symmetry. Distinct ratio can be found with
respective pairing symmetry. In comparison with the inelastic neutron
scattering data, the monotonic d-wave superconductivity is the most likely
candidate in the electron-doped cuprates. Furthermore, we proposed a new method
to check the pairing symmetry by the inelastic neutron scattering measurements.Comment: 4 Pages, 4 Figure
The commensurate magnetic excitations induced by band-splitting and Fermi surface topology in n-type Cuprates
The antiferromagnetic correlation plays an important role in high-T
superconductors. Considering this effect, the magnetic excitations in n-type
cuprates near the optimal doping are studied within the spin density wave
description. The magnetic excitations are commensurate in the low energy regime
and further develop into spin wave-like dispersion at higher energy, well
consistent with the inelastic neutron scattering measurements. We clearly
demonstrate that the commensurability originates from the band splitting and
Fermi surface topology. The commensurability is a normal state property, and
has nothing to do with d-wave superconductivity. The distinct behaviors of
magnetic excitation between the n-type and p-type cuprates are further
discussed. Our results strongly suggest the essential role of antiferromagnetic
correlations in the cuprates.Comment: 5 pages, 3 figure
MgCNi3: a conventional and yet puzzling superconductor
The newly discovered superconductivity in MgCNi3, though with Tc<8 K lower
than that of the celebrated MgB2, is probably even more interesting in its many
puzzling physical properties. MgCNi3 has been theoretically speculated to be
unstable towards ferromagnetism. However, there are numerous evidences from the
specific heat C(T), Tunneling spectroscopy and NMR experiments indicating
conventional s-wave superconductivity in MgCNi3. The Hall effect and the
thermoelectric power experiments suggest that the carriers responsible for the
transport properties are electrons, in obvious contrast to holes predicated by
the band structure calculations. In this article, we report the results of C(T)
experiments, upper critical field Hc2 measurements, and the pressure effects on
MgCNi3. These experimental evidences clearly demonstrate that superconductivity
in MgCNi3 is well explained within the conventional electron-phonon interaction
scenario, at most with minor modifications from the magnetic interaction. The
thermodynamic data C(T) is consistent with the conventional s-wave order
parameter. Hc2 of all samples follows a universal WHH relation . Surprisingly,
dTc/dP is positive which leaves room for further improvements in band structure
calculations. There are other serious discrepancies between experiments and
theory like in the transport properties and x-ray photoemission. The possible
reconciliation within the two-band model and the consequent difficulties are
discussed.Comment: 27 pages, 9 pages, tentatively to appear in ''Horizons in
Superconductivity'' by Nova Science Publishers, In
Heavy Quark and Chiral Symmetry Predictions for Semileptonic Decays B->D(D*),pi,l,nu
We study in detail the prediction for the semileptonic decays by heavy quark and chiral symmetry. The branching
ratio for is quite significant, as big as
. The branching ratio for is
only of order . Numerical results for various single particle
spectra and their dependence on the pion momentum cutoff schemes are presented
in a series of figures, as are the model independent ratios for differential
rates of and . We also study the parity-violation effects on the decay
rates for different polarization states of the . Figures may be obtained
by anonymous FTP from strange.tn.cornell.edu in the directory pub/CLNS931204,
or by email from the author.Comment: 28 pages, 23 figs (FTP from author), LaTeX, Typos corrected in Eq.
4.9c (factor of 2), Eq. A.4, and Tables II & III. No change in content,
results, or figures. CLNS93/1204, IP-ASTP-15-9
The selection rule of graphene in a composite magnetic field
The generalized tight-binding model with exact diagonalization method is
developed to calculate the optical properties of monolayer graphene in the
presence of composite magnetic fields. The ratio of the uniform magnetic field
and the modulated one accounts for a strong influence on the structure, number,
intensity and frequency of absorption peaks, and thus the extra selection rules
that are subsequently induced can be explained. When the modulated field
increases, each symmetric peak, under a uniform magnetic field, splits into a
pair of asymmetric peaks with lower intensities. The threshold absorption
frequency exhibits an obvious evolution in terms of a redshift. These
absorption peaks obey the same selection rule that is followed by Landau level
transitions. Moreover, at a sufficiently strong modulation strength, the extra
peaks in the absorption spectrum might arise from different selection rules
Optical Properties of Graphene in External Fields
The generalized tight-binding model, with the exact diagonalization method,
is developed to investigate optical properties of graphene in five kinds of
external fields. The quite large Hamiltonian matrix is transferred into the
band-like one by the rearrangement of many basis functions; furthermore, the
spatial distributions of wave functions on distinct sublattices are utilized to
largely reduce the numerical computation time. The external fields have a
strong influence on the number, intensity, frequency and structure of
absorption peaks, and the selection rules. The optical spectra in a uniform
magnetic field exhibit plentiful symmetric absorption peaks and obey a specific
selection rule. However, there are many asymmetric peaks and extra selection
rules under the modulated electric field, the modulated magnetic field, the
composite electric and magnetic fields, and the composite magnetic fields.Comment: 68 pages and 21 figure
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