37,346 research outputs found
The observed by the BES Collaboration
In the framework of the meson decay model, the strong decays of the
and states are investigated. It is found that in
the presence of the initial state mass being 2.24 GeV, the total widths of the
and states are about 438 MeV and 125 MeV,
respectively. Also, when the initial state mass varies from 2220 to 2400 MeV,
the total width of the state varies from about 100 to 132
MeV, while the total width of the state varies from about
400 to 594 MeV. A comparison of the predicted widths and the experimental
result of GeV, the width of the
with a mass of GeV recently observed by the
BES Collaboration in the radiative decay , suggests that it would be very difficult to identify the
as the state, and the seams a
good candidate for the state.Comment: 14 pages, 3 figures, typos corrected, Accepted by Physical Review
Charge and spin Hall effect in graphene with magnetic impurities
We point out the existence of finite charge and spin Hall conductivities of
graphene in the presence of a spin orbit interaction (SOI) and localized
magnetic impurities. The SOI in graphene results in different transverse forces
on the two spin channels yielding the spin Hall current. The magnetic
scatterers act as spin-dependent barriers, and in combination with the SOI
effect lead to a charge imbalance at the boundaries. As indicated here, the
charge and spin Hall effects should be observable in graphene by changing the
chemical potential close to the gap.Comment: 7 page
Three realizations of quantum affine algebra
In this article we establish explicit isomorphisms between three realizations
of quantum twisted affine algebra : the Drinfeld ("current")
realization, the Chevalley realization and the so-called realization,
investigated by Faddeev, Reshetikhin and Takhtajan.Comment: 15 page
Heavy Quark diffusion from lattice QCD spectral functions
We analyze the low frequency part of charmonium spectral functions on large
lattices close to the continuum limit in the temperature region as well as for . We present evidence for the
existence of a transport peak above and its absence below . The
heavy quark diffusion constant is then estimated using the Kubo formula. As
part of the calculation we also determine the temperature dependence of the
signature for the charmonium bound state in the spectral function and discuss
the fate of charmonium states in the hot medium.Comment: 4 pages, Proceedings for Quark Matter 2011 Conference, May 23-28,
2011, Annecy, Franc
Extraction of the Electron Self-Energy from Angle Resolved Photoemission Data: Application to Bi2212
The self-energy , the fundamental function which
describes the effects of many-body interactions on an electron in a solid, is
usually difficult to obtain directly from experimental data. In this paper, we
show that by making certain reasonable assumptions, the self-energy can be
directly determined from angle resolved photoemission data. We demonstrate this
method on data for the high temperature superconductor
(Bi2212) in the normal, superconducting, and pseudogap phases.Comment: expanded version (6 pages), to be published, Phys Rev B (1 Sept 99
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Evolving graphs: dynamical models, inverse problems and propagation
Applications such as neuroscience, telecommunication, online social networking,
transport and retail trading give rise to connectivity patterns that change over time.
In this work, we address the resulting need for network models and computational
algorithms that deal with dynamic links. We introduce a new class of evolving
range-dependent random graphs that gives a tractable framework for modelling and
simulation. We develop a spectral algorithm for calibrating a set of edge ranges from
a sequence of network snapshots and give a proof of principle illustration on some
neuroscience data. We also show how the model can be used computationally and
analytically to investigate the scenario where an evolutionary process, such as an
epidemic, takes place on an evolving network. This allows us to study the cumulative
effect of two distinct types of dynamics
Coherent quasiparticle weight and its connection to high-T_c superconductivity from angle-resolved photoemission
In conventional superconductors, the pairing energy gap (\Delta) and
superconducting phase coherence go hand-in-hand. As the temperature is lowered,
both the energy gap and phase coherence appear at the transition temperature
T_c. In contrast, in underdoped high-T_c superconductors (HTSCs), a pseudogap
appears at a much higher temperature T^*, smoothly evolving into the
superconducting gap at T_c. Phase coherence on the other hand is only
established at T_c, signaled by the appearance of a sharp quasiparticle (QP)
peak in the excitation spectrum. Another important difference between the two
types of superconductors is in the ratio of 2\Delta / T_c=R. In BCS theory,
R~3.5, is constant. In the HTSCs this ratio varies widely, continuing to
increase in the underdoped region, where the gap increases while T_c decreases.
Here we report that in HTSCs it is the ratio z_A\Delta_m/T_c which is
approximately constant, where \Delta_m is the maximum value of the d-wave gap,
and z_A is the weight of the coherent excitations in the spectral function.
This is highly unusual, since in nearly all phase transitions, T_c is
determined by an energy scale alone. We further show that in the
low-temperature limit, z_{\it A} increases monotonically with increasing doping
x. The growth is linear, i.e. z_A(x)\propto x, in the underdoped to optimally
doped regimes, and slows down in overdoped samples. The reduction of z_A with
increasing temperature resembles that of the c-axis superfluid density.Comment: 11 pages, 5 figures, revised versio
Fermi Surface Evolution, Pseudo Gap and Stagger Gauge Field Fluctuation in Underdoped Cuprates
In the context of t-J model we show that in underdoped regime,beside the
usual long wave length gauge field fluctuation, an additional low energy
fluctuation, staggered gauge field fluctuation plays a crucial role in the
evolution of Fermi surface(FS) as well as the line shape of spectral function
for the cuprates. By including the staggered gauge field fluctuation we
calculate the spectral function of the electrons by RPA(random phase
approximation). The line shape of the spectral function near is very
broad in underdoped case and is quite sharp in overdoped case. For the spectral
function near , the quasiparticle peaks are always very sharp
in both underdoped and overdoped case. The temperature dependence of the
spectral function is also discussed in our present calculation. These results
fit well with the recent ARPES experiments. We also calculate the FS crossover
from a small four segment like FS to a large continuous FS. The reason of such
kind of FS crossover is ascribed to the staggered gauge field fluctuation which
is strong in underdoped regime and becomes much weaker in overdoped regime. The
pseudo gap extracted from the ARPES data can be also interpreted by the
calculation.Comment: 4 pages,6 eps figures include
Phenomenology of Photoemission Lineshapes of High Tc Superconductors
We introduce a simple phenomenological form for the self-energy which allows
us to extract important information from angle resolved photoemission data on
the high Tc superconductor Bi2212. First, we find a rapid suppression of the
single particle scattering rate below Tc for all doping levels. Second, we find
that in the overdoped materials the gap Delta at all k-points on the Fermi
surface has significant temperature dependence and vanishes near Tc. In
contrast, in the underdoped samples such behavior is found only at k-points
close to the diagonal. Near (pi,0), Delta is essentially T-independent in the
underdoped samples. The filling-in of the pseudogap with increasing T is
described by a broadening proportional to T-Tc, which is naturally explained by
pairing correlations above Tc.Comment: 4 pages, revtex, 3 encapsulated postscript figure
On the \phi(1020)f_0(980) S-wave scattering and the Y(2175) resonance
We have studied the \phi(1020)f_0(980) S-wave scattering at energies around
threshold employing chiral Lagrangians coupled to vector mesons through minimal
coupling. The interaction kernel is obtained by considering the f_0(980) as a
K\bar{K} bound state. The Y(2175) resonance is generated in this approach by
the self-interactions between the \phi(1020) and the f_0(980) resonances. We
are able to describe the e^+e^-\to \phi(1020)f_0(980) recent scattering data to
test experimentally our scattering amplitudes, concluding that the Y(2175)
resonance has a large \phi(1020)f_0(980) meson-meson component.Comment: 20 pages, 8 figure
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