638 research outputs found
Singularities in the Fermi liquid description of a partially filled Landau level and the energy gaps of fractional quantum Hall states
We consider a two dimensional electron system in an external magnetic field
at and near an even denominator Landau level filling fraction. Using a
fermionic Chern--Simons approach we study the description of the system's low
energy excitations within an extension of Landau's Fermi liquid theory. We
calculate perturbatively the effective mass and the quasi--particle interaction
function characterizing this description. We find that at an even denominator
filling fraction the fermion's effective mass diverges logarithmically at the
Fermi level, and argue that this divergence allows for an {\it exact}
calculation of the energy gaps of the fractional quantized Hall states
asymptotically approaching these filling fractions. We find that the
quasi--particle interaction function approaches a delta function. This singular
behavior leads to a cancelation of the diverging effective mass from the long
wavelength low frequency linear response functions at even denominator filling
fractions.Comment: 46 pages, RevTeX, 5 figures included in a uuencoded postscript file.
Minor revisions relative to the original version. The paper will be published
in the Physical Review B, and can be retrieved from the World Wide Web, in
http://cmtw.harvard.edu/~ster
Brain Structural Networks Associated with Intelligence and Visuomotor Ability
Increasing evidence indicates that multiple structures in the brain are associated with intelligence
and cognitive function at the network level. The association between the grey matter (GM) structural
network and intelligence and cognition is not well understood. We applied a multivariate approach
to identify the pattern of GM and link the structural network to intelligence and cognitive functions.
Structural magnetic resonance imaging was acquired from 92 healthy individuals. Source-based
morphometry analysis was applied to the imaging data to extract GM structural covariance. We
assessed the intelligence, verbal fluency, processing speed, and executive functioning of the
participants and further investigated the correlations of the GM structural networks with intelligence
and cognitive functions. Six GM structural networks were identified. The cerebello-parietal component
and the frontal component were significantly associated with intelligence. The parietal and frontal
regions were each distinctively associated with intelligence by maintaining structural networks with
the cerebellum and the temporal region, respectively. The cerebellar component was associated
with visuomotor ability. Our results support the parieto-frontal integration theory of intelligence by
demonstrating how each core region for intelligence works in concert with other regions. In addition,
we revealed how the cerebellum is associated with intelligence and cognitive functions
Goldfish geodesics and Hamiltonian reduction of matrix dynamics
We relate free vector dynamics to the eigenvalue motion of a time-dependent
real-symmetric NxN matrix, and give a geodesic interpretation to Ruijsenaars
Schneider models.Comment: 8 page
Magnetoresistance of Two-Dimensional Fermions in a Random Magnetic Field
We perform a semiclassical calculation of the magnetoresistance of spinless
two-dimensional fermions in a long-range correlated random magnetic field. In
the regime relevant for the problem of the half filled Landau level the
perturbative Born approximation fails and we develop a new method of solving
the Boltzmann equation beyond the relaxation time approximation. In absence of
interactions, electron density modulations, in-plane fields, and Fermi surface
anisotropy we obtain a quadratic negative magnetoresistance in the weak field
limit.Comment: 12 pages, Latex, no figures, Nordita repor
Non-Abelian, Self-Dual Chern-Simons Vortices Coupled to Gravity
In this article we consider Chern-Simons/Higgs theory coupled to
gravity in three-dimensions. It is shown that for a cylindrically symmetric
vortex both the Einstein equations and the field equations can be reduced to a
set of first-order Bogomol'nyi equations provided that we choose a specific
eighth-order potential.Comment: 21 pages, LATEX, no figure
Applicability of perturbative QCD to decays
We develop perturbative QCD factorization theorem for the semileptonic heavy
baryon decay , whose form factors are
expressed as the convolutions of hard quark decay amplitudes with universal
and baryon wave functions. Large logarithmic
corrections are organized to all orders by the Sudakov resummation, which
renders perturbative expansions more reliable. It is observed that perturbative
QCD is applicable to decays for velocity transfer
greater than 1.2. Under requirement of heavy quark symmetry, we predict the
branching ratio , and determine
the and baryon wave functions.Comment: 12 pages in Latex file, 3 figures in postscript files, some results
are changed, but the conclusion is the sam
An Extended Zel'dovich Model for the Halo Mass Function
A new way to construct a fitting formula for the halo mass function is
presented. Our formula is expressed as a solution to the modified Jedamzik
matrix equation that automatically satisfies the normalization constraint. The
characteristic parameters expressed in terms of the linear shear eigenvalues
are empirically determined by fitting the analytic formula to the numerical
results from the high-resolution N-body simulation and found to be independent
of scale, redshift and background cosmology. Our fitting formula with the
best-fit parameters is shown to work excellently in the wide mass-range at
various redshifts: The ratio of the analytic formula to the N-body results
departs from unity by up to 10% and 5% over 10^{11}<= M/(M_sun/h)<= 5x10^{15}
at z=0,\ 0.5 and 1 for the FoF-halo and SO-halo cases, respectively.Comment: Accepted for publication in JCAP; 19pages, 9 figures, significantly
revised, discussion on the limitation of our model adde
Chiral Baryon Fields in the QCD Sum Rule
We study the structure of local baryon fields using the method of QCD sum
rule. We only consider the single baryon fields and calculate their operator
product expansions. We find that the octet baryon fields belonging to the
chiral representations [(3,3*)+(3*,3)] and [(8,1)+(1,8)] and the decuplet
baryon fields belonging to the chiral representations [(3,6)+(6,3)] lead to the
baryon masses which are consistent with the experimental data of ground baryon
masses. We also calculate their decay constants, check our normalizations for
baryon fields in PRD81:054002(2010) and find that they are well-defined.Comment: 12 pages, 6 figure, 1 table, accepted by EPJ
The Spectrum of Electromagnetic Jets from Kerr Black Holes and Naked Singularities in the Teukolsky Perturbation Theory
We give a new theoretical basis for examination of the presence of the Kerr
black hole (KBH) or the Kerr naked singularity (KNS) in the central engine of
different astrophysical objects around which astrophysical jets are typically
formed: X-ray binary systems, gamma ray bursts (GRBs), active galactic nuclei
(AGN), etc. Our method is based on the study of the exact solutions of the
Teukolsky master equation for electromagnetic perturbations of the Kerr metric.
By imposing original boundary conditions on the solutions so that they describe
a collimated electromagnetic outflow, we obtain the spectra of possible {\em
primary jets} of radiation, introduced here for the first time. The theoretical
spectra of primary electromagnetic jets are calculated numerically. Our main
result is a detailed description of the qualitative change of the behavior of
primary electromagnetic jet frequencies under the transition from the KBH to
the KNS, considered here as a bifurcation of the Kerr metric. We show that
quite surprisingly the novel spectra describe linearly stable primary
electromagnetic jets from both the KBH and the KNS. Numerical investigation of
the dependence of these primary jet spectra on the rotation of the Kerr metric
is presented and discussed.Comment: 18 pages, 35 figures, LaTeX file. Final version. Accepted for
publication in Astrophysics and Space Science. Amendments. Typos corrected.
Novel notion -"primary jet" is introduced. New references and comments adde
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