9,672 research outputs found
Mass Uncertainties of f0(600) and f0(1370) and their Effects on Determination of the Quark and Glueball Admixtures of the I=0 Scalar Mesons
Within a nonlinear chiral Lagrangian framework the correlations between the
quark and glueball admixtures of the isosinglet scalar mesons below 2 GeV and
the current large uncertainties on the mass of the f0(600) and the f0(1370) are
studied. The framework is formulated in terms of two scalar meson nonets (a
two-quark nonet and a four-quark nonet) together with a scalar glueball. It is
shown that while some properties of these states are sensitive to the mass of
f0(600) and f0(1370), several relatively robust conclusions can be made: The
f0(600), the f0(980), and the f0(1370) are admixtures of two and four quark
components, with f0(600) being dominantly a non-strange four-quark state, and
f0(980) and f0(1370) having a dominant two-quark component. Similarly, the
f0(1500) and the f0(1710) have considerable two and four quark admixtures, but
in addition have a large glueball component. For each state, a detailed
analysis providing the numerical estimates of all components is given. It is
also shown that this framework clearly favors the experimental values:
m[f0(600)] < 700 MeV and m[f0(1370)] = 1300-1450 MeV. Moreover, an overall fit
to the available data shows a reciprocal substructure for the f0(600) and the
f0(1370), and a linear correlation between their masses of the form m
[f0(1370)] = 0.29 m[f0(600)] + 1.22 GeV. The scalar glueball mass of 1.5-1.7
GeV is found in this analysis.Comment: placement of figures inside text improved. Content unchange
Coulomb blockade and Kondo effect in the electronic structure of Hubbard molecules connected to metallic leads: a finite-temperature exact-diagonalization study
The electronic structure of small Hubbard molecules coupled between two
non-interacting semi-infinite leads is studied in the low bias-voltage limit.
To calculate the finite-temperature Green's function of the system, each lead
is simulated by a small cluster, so that the problem is reduced to that of a
finite-size system comprising the molecule and clusters on both sides. The
Hamiltonian parameters of the lead clusters are chosen such that their
embedding potentials coincide with those of the semi-infinite leads on
Matsubara frequencies. Exact diagonalization is used to evaluate the effect of
Coulomb correlations on the electronic properties of the molecule at finite
temperature. Depending on key Hamiltonian parameters, such as Coulomb
repulsion, one-electron hopping within the molecule, and hybridization between
molecule and leads, the molecular self-energy is shown to exhibit Fermi-liquid
behavior or deviations associated with finite low-energy scattering rates. The
method is shown to be sufficiently accurate to describe the formation of Kondo
resonances inside the correlation-induced pseudogaps, except in the limit of
extremely low temperatures. These results demonstrate how the system can be
tuned between the Coulomb blockade and Kondo regimes.Comment: 14 pages; 14 figure
Exact Diagonalization Dynamical Mean Field Theory for Multi-Band Materials: Effect of Coulomb correlations on the Fermi surface of Na_0.3CoO_2
Dynamical mean field theory combined with finite-temperature exact
diagonalization is shown to be a suitable method to study local Coulomb
correlations in realistic multi-band materials. By making use of the sparseness
of the impurity Hamiltonian, exact eigenstates can be evaluated for
significantly larger clusters than in schemes based on full diagonalization.
Since finite-size effects are greatly reduced this approach allows the study of
three-band systems down to very low temperatures, for strong local Coulomb
interactions and full Hund exchange. It is also shown that exact
diagonalization yields smooth subband quasi-particle spectra and self-energies
at real frequencies. As a first application the correlation induced charge
transfer between t2g bands in Na_0.3CoO_2 is investigated. For both Hund and
Ising exchange the small eg' Fermi surface hole pockets are found to be
slightly enlarged compared to the non-interacting limit, in agreement with
previous Quantum Monte Carlo dynamical mean field calculations for Ising
exchange, but in conflict with photoemission data.Comment: 9 pages, 7 figure
Superconducting anisotropy and evidence for intrinsic pinning in single crystalline MgB
We examine the superconducting anisotropy
of a metallic high- superconductor MgB by measuring the magnetic
torque of a single crystal. The anisotropy does not depend
sensitively on the applied magnetic field at 10 K. We obtain the anisotropy
parameter . The torque curve shows the sharp
hysteresis peak when the field is applied parallel to the boron layers. This
comes from the intrinsic pinning and is experimental evidence for the
occurrence of superconductivity in the boron layers.Comment: REVTeX 4, To be published in Physical Review
Evidence for Strong-coupling S-wave Superconductivity in MgB2 :11B NMR Study
We have investigated a gap structure in a newly-discovered superconductor,
MgB2 through the measurement of 11B nuclear spin-lattice relaxation rate,
^{11}(1/T_1). ^{11}(1/T_1) is proportional to the temperature (T) in the normal
state, and decreases exponentially in the superconducting (SC) state, revealing
a tiny coherence peak just below T_c. The T dependence of 1/T_1 in the SC state
can be accounted for by an s-wave SC model with a large gap size of 2\Delta
/k_BT_c \sim 5 which suggests to be in a strong-coupling regime.Comment: 2 pages with 1 figur
A chiral model for bar{q}q and bar{q}bar{q}qq$ mesons
We point out that the spectrum of pseudoscalar and scalar mesons exhibits a
cuasi-degenerate chiral nonet in the energy region around 1.4 GeV whose scalar
component has a slightly inverted spectrum. Based on the empirical linear
rising of the mass of a hadron with the number of constituent quarks which
yields a mass around GeV for tetraquarks, we conjecture that this
cuasi-chiral nonet arises from the mixing of a chiral nonet composed of
tetraquarks with conventional bar{q}q states. We explore this possibility in
the framework of a chiral model assuming a tetraquark chiral nonet around 1.4
GeV with chiral symmetry realized directly. We stress that U_{A}(1)
transformations can distinguish bar{q}q from tetraquark states, although it
cannot distinguish specific dynamics in the later case. We find that the
measured spectrum is consistent with this picture. In general, pseudoscalar
states arise as mainly bar{q}q states but scalar states turn out to be strong
admixtures of bar{q}q and tetraquark states. We work out also the model
predictions for the most relevant couplings and calculate explicitly the strong
decays of the a_{0}(1450) and K_{0}^*(1430) mesons. From the comparison of some
of the predicted couplings with the experimental ones we conclude that
observable for the isovector and isospinor sectors are consistently described
within the model. The proper description of couplings in the isoscalar sectors
would require the introduction of glueball fields which is an important missing
piece in the present model.Comment: 20 pages, 3 figure
ALMA Observations of the Gravitational Lens SDP.9
We present long-baseline ALMA observations of the strong gravitational lens
H-ATLAS J090740.0-004200 (SDP.9), which consists of an elliptical galaxy at
lensing a background submillimeter galaxy into two
extended arcs. The data include Band 6 continuum observations, as well as CO
=65 molecular line observations, from which we measure an updated source
redshift of . The image morphology in the ALMA data is
different from that of the HST data, indicating a spatial offset between the
stellar, gas, and dust component of the source galaxy. We model the lens as an
elliptical power law density profile with external shear using a combination of
archival HST data and conjugate points identified in the ALMA data. Our best
model has an Einstein radius of and a
slightly steeper than isothermal mass profile slope. We search for the central
image of the lens, which can be used constrain the inner mass distribution of
the lens galaxy including the central supermassive black hole, but do not
detect it in the integrated CO image at a 3 rms level of 0.0471 Jy km
s.Comment: Accepted for publication in ApJL; 6 pages, 2 figures, 3 table
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