4,185 research outputs found
Universality of the Kondo Effect in a Quantum Dot out of Equilibrium
We study the Kondo effect in a quantum dot driven out of equilibrium by an
external ac field. The Kondo effect can be probed by measuring the dc current
induced by an auxiliary dc bias applied across the dot. In the absence
of ac perturbation, the corresponding differential conductance is
known to exhibit a sharp peak at , which is the manifestation of the
Kondo effect. In the equilibrium, there exists only one energy scale, the Kondo
temperature , which controls all the low-energy physics of the system;
is some universal function of . We demonstrate that the dot out of
equilibrium is also characterized by a universal behavior: conductance
depends on the ac field only through two dimensionless parameters, which are
the frequency and the amplitude of the ac perturbation, both divided
by . We find analytically the large- and small-frequency asymptotes of the
universal dependence of on these parameters. The obtained results allow us
to predict the behavior of the conductance in the crossover regime
.Comment: 18 pages, 5 figure
Towards a unitary Dalitz plot analysis of three-body hadronic B decays
A unitary model of the final state kaon pion interaction amplitudes in the B
--> K pi pi decays is constructed. The weak decay penguin amplitudes, derived
in QCD factorization, are supplemented by phenomenological contributions. The
strange kaon- pion scalar and vector form factors are used to calculate the
kaon pion effective mass and helicity angle distributions, branching ratios, CP
asymmetries and the phase difference between the B0 and anti B0 decay
amplitudes to K*(892) pi. The fit on the phenomenological parameters leads to a
good agreement with the experimental data, particularly for the
B --> K*(892) pi decays. However, our predicted B+- --> K*0(1430) pi+-,
K*0(1430)--> K+-pi-+ branching fraction is smaller than the results of the
Belle and BaBar collaborations, obtained from isobar model analyses. A new
parameterization of the S-wave kaon- pion effective mass distribution, which
can be used in future experimental Dalitz plot analyses, is proposed.Comment: 5 pages, 1 figure, contribution to Proc. Int. Europhysics Conference
on High Energy Physics (HEP2009), July 16-22, 2009, Krakow, Poland,
PoS(HEP2009)20
Final state interactions and CP violation in B decays to three pseudoscalars
We study CP violation and final state interactions between pions and kaons in
B+, B-, B0 and bar B0 decays into K pi pi. The weak transition amplitudes
consist of two terms: the first part is derived in QCD factorization approach
and the second one is a phenomenological long-distance charming penguin
contribution. The final state K pi interactions in S- and P-waves are described
by strange scalar and vector form factors, respectively. These are determined
using a unitary coupled channel model together with chiral symmetry and
asymptotic QCD constraints. The final state interactions are dominated by
presence of the scalar K*0(1430) and the vector K*(892) resonances. We show
that additional charming penguin amplitudes are needed to reproduce the latest
experimental K pi effective mass and helicity angle distributions, branching
fractions and asymmetries obtained by Belle and BaBar collaborations.Comment: Talk given at XIII International Conference on Hadron Spectroscopy
(Hadron 2009), Nov. 29 - Dec. 4 2009, Florida State Universit
CP violation and final state interactions in B --> K pi pi decays
Effects of CP violation and of final state interactions between pairs of
pseudoscalar mesons are studied in three-body B+, B-, B0 and antiB0 decays into
K pi pi. An alternative approach to the isobar model for three-body B decays is
proposed. It is based on the QCD factorization approximation and the knowledge
of the meson-meson form factors. Some phenomenological charming penguin
amplitudes are needed to describe the branching fractions, direct CP
asymmetries of the quasi-two-body B --> K*(892) pi and B --> K0*(1430) pi
decays as well as the K pi effective mass and the helicity angle distributions.
The experimental branching fractions for the B --> K0*(1430) pi decay, obtained
by the Belle and BaBar collaborations using the isobar model, are larger than
our predictions by about 52 per cent.Comment: 3 pages, contribution to International Europhysics Conference on High
Energy Physics HEP 2007, Manchester (England), July 19-25, 200
On knottings in the physical Hilbert space of LQG as given by the EPRL model
We consider the EPRL spin foam amplitude for arbitrary embedded
two-complexes. Choosing a definition of the face- and edge amplitudes which
lead to spin foam amplitudes invariant under trivial subdivisions, we
investigate invariance properties of the amplitude under consistent
deformations, which are deformations of the embedded two-complex where faces
are allowed to pass through each other in a controlled way. Using this
surprising invariance, we are able to show that in the physical Hilbert space
as defined by the sum over all spin foams contains no knotting classes of
graphs anymore.Comment: 22 pages, 14 figure
Griffiths phase in diluted magnetic semiconductors
We study the effects of disorder in the vicinity of the ferromagnetic
transition in a diluted magnetic semiconductor in the strongly localized
regime. We derive an effective polaron Hamiltonian, which leads to the
Griffiths phase above the ferromagnetic transition point. The Griffiths-McCoy
effects yield non-perturbative contributions to the dynamic susceptibility. We
explicitly derive the long-time susceptibility, which has a pseudo-scaling
form, with the dynamic critical exponent being expressed through the
percolation indices.Comment: 4 pages, final version as publishe
B decays into pion-pion-kaon and into kaon-antikaon-kaon: long distance and final-state effects
The interplay of strong and weak decay amplitudes for B -> pion-pion-kaon and
B -> kaon-antikaon-kaon, with the pion-pion and kaon-antikaon pairs interacting
in isospin-0 S-wave, is analyzed for pion-pion effective mass from threshold to
1.2 GeV. To improve agreement with experiment of a factorization approach with
some QCD corrections, addition of long-distance contributions, called charming
penguins is necessary.Comment: 5 pages, 1 figure, invited talk at the Third Asia-Pacific Conference
on Few-Body Problems in Physics (APFB05), Nakhon Ratchassima, Thailand, July
26-30, 2005, to be published by the Scientific World Publishing C
Coherency of the superconducting state: the muon spin rotation and ARPES studies of (BiPb)_2(SrLa)_2CuO_{6+\delta}
The superfluid density \rho_s in underdoped (T_c\simeq23K), optimally doped
(T_c\simeq35K) and overdoped (T_c\simeq29K) single crystalline
(BiPb)_2(SrLa)_2CuO_{6+\delta} samples was studied by means of muon-spin
rotation (\muSR). By combining the \muSR data with the results of ARPES
measurements on similar samples [Nature 457, 296 (2009)] good self-consistent
agreement is obtained between two techniques concerning the temperature and the
doping evolution of \rho_s.Comment: 4 pages, 3 figures
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