Antonio Carlos Baptista Antunes

Efimov effect and higher bound states in a three-particle system☆

Abstract We study the J = 0 bound states for a system of three identical spinless particles interacting in pairs through delta-shell potentials. The Efimov states are identified, and their wave functions obtained. We have found a new family of bound states, which occur for higher values of the attractive coupling strength.

Controlling nonholonomic Chaplygin systems

In this paper we deal with the problem of controlling some Chaplygin systems in the framework of the vakonomic approach for nonholonomic systems. Equations of motion for these systems are obtained which contain a free parameter that permits to control the system. It is show that given a prescribed path it is possible to determine the parameter of control which inserted in the equations of motion compel the trajectory of the system to follow the input function.

ABSENCE OF DIQUARKS IN S-WAVE BARYONS

We analyze the dynamics of diquark formation in baryons containing one light and two heavy quarks. Due to the slower motion of the heavy quarks, we consider the motion of the light quark in a reference frame fixed in the two heavy ones. The potential of the light quark interacting with the two heavy quarks is derived from the quark–antiquark potential in mesons. This potential has a repulsive barrier between the two heavy quarks. A variational approach similar to that used in the study of the hydrogen molecule is applied to determine the two lowest energy eigenvalues and eigenfunctions of the light quark. The time-dependent wave function obtained describes the oscillation of the light quark along the direction defined by the two heavy quarks. We observe that the energy of this oscillating state is higher than the repulsive barrier between the two heavy quarks. There is no tunneling in the oscillation of the light quark, so we conclude that there is not formation of clusters or metastable states of a heavy and a light quark in this kind of baryons.

The cold dark matter model with cosmological constant and the flatness constraint

The Hubble parameter, a function of the cosmological redshift, is derived from the Friedmann-Robertson-Walker equation. The three physical parameters H0, Ω0m and ΩΛ are determined fitting the Hubble parameter to the data from measurements of redshift and luminosity distances of type-Ia supernovae. The best fit is not consistent with the flatness constraint (k = 0). On the other hand, the flatness constraint is imposed on the Hubble parameter and the physical parameters used are the published values of the standard model of cosmology. The result is shown to be inconsistent with the data from type-Ia supernovae.

DIQUARK FORMATION IN ANGULAR-MOMENTUM-EXCITED BARYONS

Diquarks, or metastable clusters of two quarks inside baryons, are shown to be produced by angular momentum excitation. In baryons with a light quark and two heavy quarks with large angular momentum (L>2), the centrifugal barrier that appears in the rotation frame of the two heavy quarks prevents the light quark from passing freely between the two heavy quarks. The light quark must tunnelize through this potential barrier, which gives rise to the clusters of a light and a heavy quark.

A model for slope-mass correlation in nuclear diffraction dissociation

Abstract The increase of the slope of nuclear diffraction with the dissociated mass is described by a model of multiple incoherent inelastic diffraction of nucleons. The results obtained are in good agreement compared with experimental data.