162 research outputs found
The spin and charge gaps of the half-filled N-leg Kondo ladders
In this work, we study N-leg Kondo ladders at half-filling through the
density matrix renormalization group. We found non-zero spin and charge gaps
for any finite number of legs and Kondo coupling . We also show evidence
of the existence of a quantum critical point in the two dimensional Kondo
lattice model, in agreement with previous works. Based on the binding energy of
two holes, we did not find evidence of superconductivity in the 2D Kondo
lattice model close to half-filling.Comment: 4 pages, 1 table, 3 fig
Open Cosmic Strings in Black Hole Space-Times
We construct open cosmic string solutions in Schwarzschild black hole and
non-dilatonic black p-brane backgrounds. These strings can be thought to
stretch between two D-branes or between a D-brane and the horizon in curved
space-time. We study small fluctuations around these solutions and discuss
their basic properties.Comment: 11 pages, REVTex, 5 figures, a reference adde
Scaling approach to itinerant quantum critical points
Based on phase space arguments, we develop a simple approach to metallic
quantum critical points, designed to study the problem without integrating the
fermions out of the partition function. The method is applied to the
spin-fermion model of a T=0 ferromagnetic transition. Stability criteria for
the conduction and the spin fluids are derived by scaling at the tree level. We
conclude that anomalous exponents may be generated for the fermion self-energy
and the spin-spin correlation functions below , in spite of the spin fluid
being above its upper critical dimension.Comment: 3 pages, 2 figures; discussion of the phase space restriction
modified and, for illustrative purposes, restricted to the tree-level
analysis of the ferromagnetic transitio
The nucleon's strange electromagnetic and scalar matrix elements
Quenched lattice QCD simulations and quenched chiral perturbation theory are
used together for this study of strangeness in the nucleon. Dependences of the
matrix elements on strange quark mass, valence quark mass and momentum transfer
are discussed in both the lattice and chiral frameworks. The combined results
of this study are in good agreement with existing experimental data and
predictions are made for upcoming experiments. Possible future refinements of
the theoretical method are suggested.Comment: 24 pages, 9 figure
Diamagnetic Persistent Currents and Spontaneous Time-Reversal Symmetry Breaking in Mesoscopic Structures
Recently, new strongly interacting phases have been uncovered in mesoscopic
systems with chaotic scattering at the boundaries by two of the present authors
and R. Shankar. This analysis is reliable when the dimensionless conductance of
the system is large, and is nonperturbative in both disorder and interactions.
The new phases are the mesoscopic analogue of spontaneous distortions of the
Fermi surface induced by interactions in bulk systems and can occur in any
Fermi liquid channel with angular momentum . Here we show that the phase
with even has a diamagnetic persistent current (seen experimentally but
mysterious theoretically), while that with odd can be driven through a
transition which spontaneously breaks time-reversal symmetry by increasing the
coupling to dissipative leads.Comment: 4 pages, three eps figure
Unitarized Chiral Perturbation Theory in a finite volume: scalar meson sector
We develop a scheme for the extraction of the properties of the scalar mesons
f0(600), f0(980), and a0(980) from lattice QCD data. This scheme is based on a
two-channel chiral unitary approach with fully relativistic propagators in a
finite volume. In order to discuss the feasibility of finding the mass and
width of the scalar resonances, we analyze synthetic lattice data with a fixed
error assigned, and show that the framework can be indeed used for an accurate
determination of resonance pole positions in the multi-channel scattering.Comment: 15 pages, 17 figure
Emission from the D1D5 CFT
It is believed that the D1D5 brane system is described by an 'orbifold CFT'
at a special point in moduli space. We first develop a general formulation
relating amplitudes in a d-dimensional CFT to absorption/emission of quanta
from flat infinity. We then construct the D1D5 vertex operators for minimally
coupled scalars in supergravity, and use these to compute the CFT amplitude for
emission from a state carrying a single excitation. Using spectral flow we
relate this process to one where we have emission from a highly excited initial
state. In each case the radiation rate is found to agree with the radiation
found in the gravity dual.Comment: 49 pages, latex, 6 figures; v2: reformatted for JHEP, corrected
typos, and added reference
Scalar mesons moving in a finite volume and the role of partial wave mixing
Phase shifts and resonance parameters can be obtained from finite-volume
lattice spectra for interacting pairs of particles, moving with nonzero total
momentum. We present a simple derivation of the method that is subsequently
applied to obtain the pi pi and pi K phase shifts in the sectors with total
isospin I=0 and I=1/2, respectively. Considering different total momenta, one
obtains extra data points for a given volume that allow for a very efficient
extraction of the resonance parameters in the infinite-volume limit.
Corrections due to the mixing of partial waves are provided. We expect that our
results will help to optimize the strategies in lattice simulations, which aim
at an accurate determination of the scattering and resonance properties.Comment: 19 pages, 12 figure
Superstrings on PP-Wave Backgrounds and Symmetric Orbifolds
We study the superstring theory on pp-wave background with NSNS-flux that is
realized as the Penrose limit of AdS_3 x S^3 x M^4, where M^4 is T^4 or
T^4/Z_2(~ K3). Quantizing this system in the covariant gauge, we explicitly
construct the space-time supersymmetry algebra and the complete set of DDF
operators. We analyse the spectrum of physical states by using the spectrally
flowed representations of current algebra. This spectrum is classified by the
``short string sectors'' and the ``long string sectors'' as in AdS_3 string
theory. The states of the latter propagate freely along the transverse plane of
pp-wave background, but the states of the former do not. We compare the short
string spectrum with the BPS and almost BPS states which have large R-charges
in the symmetric orbifold conformal theory, which is known as the candidate of
dual theory of superstrings on AdS_3 x S^3 x M^4. We show that every short
string states can be embedded successfully in the single particle Hilbert space
of symmetric orbifold conformal theory.Comment: Latex, 35 pages, minor change
Quark contributions to baryon magnetic moments in full, quenched, and partially quenched QCD
The chiral nonanalytic behavior of quark-flavor contributions to the magnetic moments of octet baryons is determined in full, quenched and partially quenched QCD, using an intuitive and efficient diagrammatic formulation of quenched and partially quenched chiral perturbation theory. The technique provides a separation of quark-sector magnetic-moment contributions into direct sea-quark loop, valence-quark, indirect sea-quark loop and quenched valence contributions, the latter being the conventional view of the quenched approximation. Both meson and baryon mass violations of SU(3)-flavor symmetry are accounted for. Following a comprehensive examination of the individual quark-sector contributions to octet baryon magnetic moments, numerous opportunities to observe and test the underlying structure of baryons and the nature of chiral nonanalytic behavior in QCD and its quenched variants are discussed. In particular, the valence u-quark contribution to the proton magnetic moment provides the optimal opportunity to directly view nonanalytic behavior associated with the meson cloud of full QCD and the quenched meson cloud of quenched QCD. The u quark in ÎŁ+ provides the best opportunity to display the artifacts of the quenched approximation.Derek B. Leinwebe
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