4,300 research outputs found
Electromagnetic splitting for mesons and baryons using dressed constituent quarks
Electromagnetic splittings for mesons and baryons are calculated in a
formalism where the constituent quarks are considered as dressed
quasiparticles. The electromagnetic interaction, which contains coulomb,
contact, and hyperfine terms, is folded with the quark electrical density. Two
different types of strong potentials are considered. Numerical treatment is
done very carefully and several approximations are discussed in detail. Our
model contains only one free parameter and the agreement with experimental data
is reasonable although it seems very difficult to obtain a perfect description
in any case.Comment: 14 pages, Revised published versio
Towers of hybrid mesons
A hybrid meson is a quark-antiquark pair in which, contrary to ordinary
mesons, the gluon field is in an excited state. In the framework of constituent
models, the interaction potential is assumed to be the energy of an excited
string. An approximate, but accurate, analytical solution of the
Schr\"{o}dinger equation with such a potential is presented. When applied to
hybrid charmonia and bottomonia, towers of states are predicted in which the
masses are a linear function of a harmonic oscillator band number for the
quark-antiquark pair. Such a formula could be a reliable guide for the
experimental detection of heavy hybrid mesons.Comment: 3 figure
Radiative transitions in mesons in a non relativistic quark model
In the framework of the non relativistic quark model, an exhaustive study of
radiative transitions in mesons is performed. The emphasis is put on several
points. Some traditional approximations (long wave length limit, non
relativistic phase space, dipole approximation for E1 transitions, gaussian
wave functions) are analyzed in detail and their effects commented. A complete
treatment using three different types of realistic quark-antiquark potential is
made. The overall agreement with experimental data is quite good, but some
improvements are suggested.Comment: 42 pages, 2 figure
Further developments for the auxiliary field method
The auxiliary field method is a technique to obtain approximate closed
formulae for the solutions of both nonrelativistic and semirelativistic
eigenequations in quantum mechanics. For a many-body Hamiltonian describing
identical particles, it is shown that the approximate eigenvalues can be
written as the sum of the kinetic operator evaluated at a mean momentum
and of the potential energy computed at a mean distance . The quantities
and are linked by a simple relation depending on the quantum
numbers of the state considered and are determined by an equation which is
linked to the generalized virial theorem. The (anti)variational character of
the method is discussed, as well as its connection with the perturbation
theory. For a nonrelativistic kinematics, general results are obtained for the
structure of critical coupling constants for potentials with a finite number of
bound states.Comment: New improved presentatio
Average consensus and gossip algorithms in networks with stochastic asymmetric communications
We consider that a set of distributed agents desire to reach consensus on the average of their initial state values, while communicating with neighboring agents through a shared medium. This communication medium allows only one agent to transmit unidirectionally at a given time, which is true, e.g., in wireless networks. We address scenarios where the choice of agents that transmit and receive messages at each transmission time follows a stochastic characterization, and we model the topology of allowable transmissions with asymmetric graphs. In particular, we consider: (i) randomized gossip algorithms in wireless networks, where each agent becomes active at randomly chosen times, transmitting its data to a single neighbor; (ii) broadcast wireless networks, where each agent transmits to all the other agents, and access to the network occurs with the same probability for every node. We propose a solution in terms of a linear distributed algorithm based on a state augmentation technique, and prove that this solution achieves average consensus in a stochastic sense, for the special cases (i) and (ii). Expressions for absolute time convergence rates at which average consensus is achieved are also given
Synthesis and properties of Co-doped titanate nanotubes and their optical sensitization with methylene blue
Here we report on a novel chemical route to synthesize homogenous cobalt
doped titanate nanotubes (CoTNT), using an amorphous Co-doped precursor. The
influence of the synthesis temperature, autoclave dwell time and metal doping
on the structural and microstructural as well as on the optical properties of
the synthesized titanate nanotubes is studied and discussed. The optical band
gaps of the CoTNT samples are red shifted in comparison with the values
determined for the undoped samples, such red shifts bringing the absorption
edge of the CoTNT samples into the visible region. CoTNT materials also
demonstrate particular high adsorption ability for methylene blue, the amount
of the adsorbed dye being higher than the one predictable for a monolayer
formation. This suggests the possibility of intercalation of the dye molecule
between the TiO6 layers of the TNT structure. It is also shown that the
methylene blue sensitized Co-doped nanostructures are highly stable under UV
radiation and present a strong and broad absorption in the visible region.Comment: 31 pages, 3 tables, 7 figure
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