5,927 research outputs found
Pion-Pion Phase-Shifts and the Value of Quark-Antiquark Condensate in the Chiral Limit
We use low energy pion-pion phase-shifts in order to make distinction between
the alternatives for the value of the quark-antiquark condensate in the
chiral limit. We will consider the amplitude up to and including contributions within the Standard and Generalized Chiral Perturbation
Theory frameworks. They are unitarized by means of Pad\'e approximants in order
to fit experimental phase-shifts in the resonance region. As the best fits
correspond to , we conclude that pion-pion phase-shift
analysis favors the standard ChPT scenario, which assumes just one, large
leading order parameter .Comment: 5 pages, 3 figures and 1 tabl
Diffraction and an infrared finite gluon propagator
We discuss some phenomenological applications of an infrared finite gluon
propagator characterized by a dynamically generated gluon mass. In particular
we compute the effect of the dynamical gluon mass on and
diffractive scattering. We also show how the data on photoproduction
and hadronic reactions can be derived from the and
forward scattering amplitudes by assuming vector meson dominance and
the additive quark model.Comment: 4 pages, 7 figures, added references and figures, changed structure.
Contribution to Proceedings of XVIIIth Reuniao de Trabalho sobre Interacoes
Hadronicas, Sao Paulo, Brazil, 22-24 May, 200
Experimental Observation of Quantum Correlations in Modular Variables
We experimentally detect entanglement in modular position and momentum
variables of photon pairs which have passed through -slit apertures. We
first employ an entanglement criteria recently proposed in [Phys. Rev. Lett.
{\bf 106}, 210501 (2011)], using variances of the modular variables. We then
propose an entanglement witness for modular variables based on the Shannon
entropy, and test it experimentally. Finally, we derive criteria for
Einstein-Podolsky-Rosen-Steering correlations using variances and entropy
functions. In both cases, the entropic criteria are more successful at
identifying quantum correlations in our data.Comment: 7 pages, 4 figures, comments welcom
Two Superconducting Phases in CeRh_1-xIr_xIn_5
Pressure studies of CeRh_1-xIr_xIn_5 indicate two superconducting phases as a
function of x, one with T_c >= 2 K for x < 0.9 and the other with T_c < 1.2 K
for x > 0.9. The higher T_c phase, phase-1, emerges in proximity to an
antiferromagnetic quantum-critical point; whereas, Cooper pairing in the lower
T_c phase-2 is inferred to arise from fluctuations of a yet to be found
magnetic state. The T-x-P phase diagram of CeRh_1-xIr_xIn_5, though
qualitatively similar, is distinctly different from that of
CeCu_2(Si_1-xGe_x)_2.Comment: 5 pages, 3 figure
Mapping dynamical systems onto complex networks
A procedure to characterize chaotic dynamical systems with concepts of
complex networks is pursued, in which a dynamical system is mapped onto a
network. The nodes represent the regions of space visited by the system, while
edges represent the transitions between these regions. Parameters used to
quantify the properties of complex networks, including those related to higher
order neighborhoods, are used in the analysis. The methodology is tested for
the logistic map, focusing the onset of chaos and chaotic regimes. It is found
that the corresponding networks show distinct features, which are associated to
the particular type of dynamics that have generated them.Comment: 13 pages, 8 eps files in 5 figure
Semigroup analysis of structured parasite populations
Motivated by structured parasite populations in aquaculture we consider a
class of size-structured population models, where individuals may be recruited
into the population with distributed states at birth. The mathematical model
which describes the evolution of such a population is a first-order nonlinear
partial integro-differential equation of hyperbolic type. First, we use
positive perturbation arguments and utilise results from the spectral theory of
semigroups to establish conditions for the existence of a positive equilibrium
solution of our model. Then, we formulate conditions that guarantee that the
linearised system is governed by a positive quasicontraction semigroup on the
biologically relevant state space. We also show that the governing linear
semigroup is eventually compact, hence growth properties of the semigroup are
determined by the spectrum of its generator. In the case of a separable
fertility function, we deduce a characteristic equation, and investigate the
stability of equilibrium solutions in the general case using positive
perturbation arguments.Comment: to appear in Mathematical Modelling of Natural Phenomen
Scattering and Bound State Green's Functions on a Plane via so(2,1) Lie Algebra
We calculate the Green's functions for the particle-vortex system, for two
anyons on a plane with and without a harmonic regulator and in a uniform
magnetic field. These Green's functions which describe scattering or bound
states (depending on the specific potential in each case) are obtained exactly
using an algebraic method related to the SO(2,1) Lie group. From these Green's
functions we obtain the corresponding wave functions and for the bound states
we also find the energy spectra.Comment: 21 Latex pages. Typos corrected. Results unchanged. Version to appear
in JM
- …