1,355 research outputs found
Spin-charge separation and simultaneous spin and charge Kondo effect
We study the spin-charge separation in a Kondo-like model for an impurity
with a spin and a charge (isospin) degree of freedom coupled to a single
conduction channel (the ``spin-charge'' Kondo model). We show that the spin and
charge Kondo effects can occur simultaneously at any coupling strength. In the
continuum (wide-band or weak coupling) limit, the Kondo screening in each
sector is independent, while at finite bandwidth and strong coupling the
lattice effects lead to a renormalization of the effective Kondo exchange
constants; nevertheless, universal spin and charge Kondo effects still occur.
We find similar behavior in the two-impurity Anderson model with positive and
negative electron-electron interaction and in the two-impurity
Anderson-Holstein model with a single phonon mode. We comment on the
applicability of such models to describe the conductance of deformable
molecules with a local magnetic moment.Comment: 13 pages, 11 figure
A General Precipitation-Limited L_X-T-R Relation Among Early-Type Galaxies
The relation between X-ray luminosity (L_X) and ambient gas temperature (T)
among massive galactic systems is an important cornerstone of both
observational cosmology and galaxy-evolution modeling. In the most massive
galaxy clusters, the relation is determined primarily by cosmological structure
formation. In less massive systems, it primarily reflects the feedback response
to radiative cooling of circumgalactic gas. Here we present a simple but
powerful model for the L_X-T relation as a function of physical aperture R
within which those measurements are made. The model is based on the
precipitation framework for AGN feedback and assumes that the circumgalactic
medium is precipitation-regulated at small radii and limited by cosmological
structure formation at large radii. We compare this model with many different
data sets and show that it successfully reproduces the slope and upper envelope
of the L_X-T-R relation over the temperature range from ~0.2 keV through >10
keV. Our findings strongly suggest that the feedback mechanisms responsible for
regulating star formation in individual massive galaxies have much in common
with the precipitation-triggered feedback that appears to regulate
galaxy-cluster cores.Comment: Submitted to ApJ, 9 pages, 3 figures (v2 fixes a few small typos
Galaxy cluster outskirts: a universal entropy profile for relaxed clusters?
We fit a functional form for a universal ICM entropy profile to the scaled
entropy profiles of a catalogue of X-ray galaxy cluster outskirts results,
which are all relaxed cool core clusters at redshift below 0.25. We also
investigate the functional form suggested by Lapi et al. and Cavaliere et al.
for the behaviour of the entropy profile in the outskirts and find it to fit
the data well outside 0.3r200 . We highlight the discrepancy in the entropy
profile behaviour in the outskirts between observations and the numerical
simulations of Burns et al., and show that the entropy profile flattening due
to gas clumping calculated by Nagai & Lau is insufficient to match
observations, suggesting that gas clumping alone cannot be responsible for all
of the entropy profile flattening in the cluster outskirts. The entropy
profiles found with Suzaku are found to be consistent with ROSAT, XMM-Newton
and Planck results.Comment: 5 pages, 5 figures. Accepted for publication in MNRA
Phase diagram of an asymmetric spin ladder
We investigate an asymmetric zig-zag spin ladder with different exchange
integrals on both legs using bosonization and renormalization group. When the
leg exchange integrals and frustration both are sufficiently small,
renormalization group analysis shows that the Heisenberg critical point flows
to an intermediate-coupling fixed point with gapless excitations and a
vanishing spin velocity. When they are large, a spin gap opens and a dimer
liquid is realized. Here, we find a continuous manifold of Hamiltonians with
dimer product ground states, interpolating between the Majumdar-Ghosh and
sawtooth spin-chain model.Comment: 4 pages, 2 EPS figures, to be published in PR
An Exactly Solvable Kondo Problem for Interacting One-Dimensional Fermions
The single impurity Kondo problem in the one-dimensional -potential
Fermi gas is exactly solved for two sets of special coupling constants via
Bethe ansatz. It is found that ferromagnetic Kondo screening does occur in one
case which confirms the Furusaki-Nagaosa conjecture while in the other case it
does not, which we explain in a simple physical picture. The surface energy,
the low temperature specific heat and the Pauli susceptibility induced by the
impurity and thereby the Kondo temperature are derived explicitly.Comment: 8 pages, LATEX, REVTE
One dimensional strongly interacting Luttinger liquid of lattice spinless fermions
The spinless fermion model with hard core repulsive potential extended on a
few lattice sites is considered.The Luttinger liquid behaviour is studied for
the different values of a hard core radius. A critical exponent of the one
particle correlation function for arbitrary electron density and coupling
constant are obtained.Comment: 4 pages, 4 figures, Late
Unusual electronic ground state of a prototype cuprate: band splitting of single CuO_2-plane Bi_2 Sr_(2-x) La_x CuO_(6+delta)
By in-situ change of polarization a small splitting of the Zhang-Rice singlet
state band near the Fermi level has been resolved for optimum doped (x=0.4)
BiSrLaCuO at the (pi,0)-point (R.Manzke et al.
PRB 63, R100504 (2001). Here we treat the momentum dependence and lineshape of
the split band by photoemission in the EDC-mode with very high angular and
energy resolution. The splitting into two destinct emissions could also be
observed over a large portion of the major symmetry line M, giving the
dispersion for the individual contributions. Since bi-layer effects can not be
present in this single-layer material the results have to be discussed in the
context of one-particle removal spectral functions derived from current
theoretical models. The most prominent are microscopic phase separation
including striped phase formation, coexisting antiferromagnetic and
incommensurate charge-density-wave critical fluctuations coupled to electrons
(hot spots) or even spin charge separation within the Luttinger liquid picture,
all leading to non-Fermi liquid like behavior in the normal state and having
severe consequences on the way the superconducting state forms. Especially the
possibilty of observing spinon and holon excitations is discussed.Comment: 5 pages, 4 figure
Bandpass Dependence of X-ray Temperatures in Galaxy Clusters
We explore the band dependence of the inferred X-ray temperature of the
intracluster medium (ICM) for 192 well-observed galaxy clusters selected from
the Chandra Data Archive. If the hot ICM is nearly isothermal in the projected
region of interest, the X-ray temperature inferred from a broad-band (0.7-7.0
keV) spectrum should be identical to the X-ray temperature inferred from a
hard-band (2.0-7.0 keV) spectrum. However, if unresolved cool lumps of gas are
contributing soft X-ray emission, the temperature of a best-fit
single-component thermal model will be cooler for the broad-band spectrum than
for the hard-band spectrum. Using this difference as a diagnostic, the ratio of
best-fitting hard-band and broad-band temperatures may indicate the presence of
cooler gas even when the X-ray spectrum itself may not have sufficient
signal-to-noise to resolve multiple temperature components. To test this
possible diagnostic, we extract X-ray spectra from core-excised annular regions
for each cluster in our archival sample. We compare the X-ray temperatures
inferred from single-temperature fits when the energy range of the fit is
0.7-7.0 keV (broad) and when the energy range is 2.0/(1+z)-7.0 keV (hard). We
find that the hard-band temperature is significantly higher, on average, than
the broad-band temperature. Upon further exploration, we find this temperature
ratio is enhanced preferentially for clusters which are known merging systems.
In addition, cool-core clusters tend to have best-fit hard-band temperatures
that are in closer agreement with their best-fit broad-band temperatures. We
show, using simulated spectra, that this diagnostic is sensitive to secondary
cool components (TX = 0.5-3.0 keV) with emission measures >10-30% of the
primary hot component.Comment: Accepted for publication in Ap
A Deoxyribonucleic Acid Decoy Trapping DUX4 for the Treatment of Facioscapulohumeral Muscular Dystrophy
Facioscapulohumeral dystrophy (FSHD) is characterized by a loss of repressive epigenetic marks leading to the aberrant expression of the DUX4 transcription factor. In muscle, DUX4 acts as a poison protein though the induction of multiple downstream genes. So far, there is no therapeutic solution for FSHD. Because DUX4 is a transcription factor, we developed an original therapeutic approach, based on a DNA decoy trapping the DUX4 protein, preventing its binding to genomic DNA and thereby blocking the aberrant activation of DUX4’s transcriptional network. In vitro, transfection of a DUX4 decoy into FSHD myotubes reduced the expression of the DUX4 network genes. In vivo, both double-stand DNA DUX4 decoys and adeno-associated viruses (AAVs) carrying DUX4 binding sites reduced transcriptional activation of genes downstream of DUX4 in a DUX4-expressing mouse model. Our study demonstrates, both in vitro and in vivo, the feasibility of the decoy strategy and opens new avenues of research
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