23,793 research outputs found
Theory for Gossamer and Resonating Valence Bond Superconductivity
We use an effective Hamiltonian for two-dimensional Hubbard model including
an antiferromagnetic spin-spin coupling term to study recently proposed
gossamer superconductivity. We formulate a renormalized mean field theory to
approximately take into account the strong correlation effect in the partially
projected Gutzwiller wavefucntions. At the half filled, there is a first order
phase transition to separate a Mott insulator at large Coulomb repulsion U from
a gossamer superconductor at small U. Away from the half filled,the Mott
insulator is evolved into an resonating valence bond state, which is
adiabatically connected to the gossamer superconductor.Comment: 10 pages, 13 figure
A longitudinal study of team-fan role identity on self-reported attendance behavior and future intentions
Attendance at college sporting events generates billions of dollars annually for athletic departments at the college level in the United States. Based on Identity Theory and prior research, we developed and tested two models that were successful in predicting actual attendance, attendance intentions (conative loyalty), and support for the team across time. Respondents (N = 165; 60% female, 59% Caucasian) filled out three surveys across the year. In Model A (RMSEA = .066, χ2/df = 50.02/29 = 1.73), prior season attendance, number of games intending to attend, and preseason team-fan role identity (Time 1) explained 63% of self-reported attendance behavior (Time 2). Those variables and postseason role identity (Time 2) explained 48.5% of attendance intentions (Time 3; Model A) and 43% of supporting the team in the future (Time 3; Model B, RMSEA = .060, χ2/df = 46.16/29 = 1.59). Sports marketers need to take into account both the impact of role identity as a fan of the team and attendance intentions, not just prior attendance behavior when predicting future attendance behavior and support for the tea
A rotating molecular jet from a Perseus protostar
We present CO(2-1) line and 1.4 mm continuum archival observations,
made with the Submillimeter Array, of the outflow HH 797 located in the IC 348
cluster in Perseus. The continuum emission is associated with a circumstellar
disk surrounding the class 0 object IC 348-MMS/SMM2, a very young solar analog.
The line emission, on the other hand, delineates a collimated outflow, and
reveals velocity asymmetries about the flow axis over the entire length of the
flow. The amplitude of velocity differences is of order 2 km s over
distances of about 1000 AU, and we interpret them as evidence for jet rotation
--although we also discuss alternative possibilities. A comparison with
theoretical models suggests that the magnetic field lines threading the
protostellar jet might be anchored to the disk of a radius of about 20 AU.Comment: Accepted for publication in Ap
Kondo lattice model: Unitary transformations, spin dynamics, strongly correlated charged modes, and vacuum instability
Using unitary transformations, we express the Kondo lattice Hamiltonian in
terms of fermionic operators that annihilate the ground state of the
interacting system and that represent the best possible approximations to the
actual charged excitations. In this way, we obtain an effective Hamiltonian
which, for small couplings, consists in a kinetic term for conduction electrons
and holes, an RKKY-like term, and a renormalized Kondo interaction. The
physical picture of the system implied by this formalism is that of a vacuum
state consisting in a background of RKKY-induced spin correlations, where two
kinds of elementary modes can be excited: Soft neutral modes associated with
deformations of the spin liquid, which lead to very large low-temperature
values of the heat capacity and magnetic susceptibility, and charged modes
corresponding to the excitation of electrons and holes in the system. Using the
translational and spin rotational symmetries, we construct a simple ansatz to
determine the charged excitations neglecting the effects of the spin
correlations. Apart from the `normal', uncorrelated states, we find strongly
correlated charged modes involving soft electrons (or holes) and spin
fluctuations, which strongly renormalize the low-energy charged spectrum, and
whose energy becomes negative beyond a critical coupling, signaling a vacuum
instability and a transition to a new phase.Comment: 35 pages, revtex 3.
New HST WFC3/UVIS observations augment the stellar-population complexity of omega Centauri
We used archival multi-band Hubble Space Telescope observations obtained with
the Wide-Field Camera 3 in the UV-optical channel to present new important
observational findings on the color-magnitude diagram (CMD) of the Galactic
globular cluster omega Centauri. The ultraviolet WFC3 data have been coupled
with available WFC/ACS optical-band data. The new CMDs, obtained from the
combination of colors coming from eight different bands, disclose an even more
complex stellar population than previously identified. This paper discusses the
detailed morphology of the CMDs.Comment: 17 pages, 14 figures (11 in low res), 3 tables. Accepted for
publication in AJ on June 19, 201
Quiver Structure of Heterotic Moduli
We analyse the vector bundle moduli arising from generic heterotic
compactifications from the point of view of quiver representations. Phenomena
such as stability walls, crossing between chambers of supersymmetry, splitting
of non-Abelian bundles and dynamic generation of D-terms are succinctly encoded
into finite quivers. By studying the Poincar\'e polynomial of the quiver moduli
space using the Reineke formula, we can learn about such useful concepts as
Donaldson-Thomas invariants, instanton transitions and supersymmetry breaking.Comment: 38 pages, 5 figures, 1 tabl
Thermodynamics of a weakly interacting Bose-Einstein gas
The one-loop effective potential for non-relativistic bosons with a delta
function repulsive potential is calculated for a given chemical potential using
functional methods. After renormalization and at zero temperature it reproduces
the standard ground state energy and pressureas function of the particle
density. At finite temperatures it is found necessary to include ring
corrections to the one-loop result in order to satisfy the Goldstone theorem.
It is natural to introduce an effective chemical potential directly related to
the order parameter and which uniformly decreases with increasing temperatures.
This is in contrast to the the ordinary chemical potential which peaks at the
critical temperature. The resulting thermodynamics in the condensed phase at
very low temperatures is found to be the same as in the Bogoliubov
approximation where the degrees of freedom are given by the Goldstone bosons.
At higher temperatures the ring corrections dominate and result in a critical
temperature unaffected by the interaction.Comment: 39 pages, 9 figures, picTex, submitted to Annals of Physics.
Discussions on renormalization and off-diagonal self energies are made
clearer in this version. A short derivation of the non-relativistic limit is
adde
Is there spin-charge separation in the 2D Hubbard and t-J models at low electronic densities?
The spin and density correlation functions of the two-dimensional Hubbard
model at low electronic density are calculated in the ground state by
using the power method, and at finite temperatures by using the quantum Monte
Carlo technique. Both approaches produce similar results, which are in close
agreement with numerical and high temperature expansion results for the
two-dimensional model. Using perturbative approximations, we show
that the examination of the density correlation function alone is not enough to
support recent claims in the literature that suggested spin and charge
separation in the low electronic density regime of the model.Comment: 11 pages, tex, 3 figures upon request, NTHU - preprin
Gossamer Superconductor, Mott Insulator, and Resonating Valence Bond State in Correlated Electron Systems
Gutzwiller variational method is applied to an effective two-dimensional
Hubbard model to examine the recently proposed gossamer superconductor by
Laughlin. The ground state at half filled electron density is a gossamer
superconductor for smaller intra-site Coulomb repulsion U and a Mott insulator
for larger U. The gossamer superconducting state is similar to the resonant
valence bond superconducting state, except that the chemical potential is
approximately pinned at the mid of the two Hubbard bands away from the half
filled
Structural Polymorphism of the Cytoskeleton: A Model of Linker-Assisted Filament Aggregation
The phase behavior of charged rods in the presence of inter-rod linkers is
studied theoretically as a model for the equilibrium behavior underlying the
organization of actin filaments by linker proteins in the cytoskeleton. The
presence of linkers in the solution modifies the effective inter-rod
interaction and can lead to inter-filament attraction. Depending on the
system's composition and physical properties such as linker binding energies,
filaments will either orient perpendicular or parallel to each other, leading
to network-like or bundled structures. We show that such a system can have one
of three generic phase diagrams, one dominated by bundles, another by networks,
and the third containing both bundle and network-like phases. The first two
diagrams can be found over a wide range of interaction energies, while the
third occurs only for a narrow range. These results provide theoretical
understanding of the classification of linker proteins as bundling proteins or
crosslinking proteins. In addition, they suggest possible mechanisms by which
the cell may control cytoskeletal morphology.Comment: 17 pages, 3 figure
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