Four-boson scale near a Feshbach resonance

We show that an independent four-body momentum scale mu((4)) drives the tetramer binding energy for fixed trimer energy (or three-body scale mu((3))) and large scattering length (a). The three- and four-body forces from the one-channel reduction of the atomic interaction near a Feshbach resonance disentangle mu((4)) and mu((3)). The four-body independent scale is also manifested through a family of Tjon lines, with slope given by mu((4))/mu((3)) for a(-1) = 0. There is the possibility of a new renormalization group limit cycle due to the new scale.

Dissipation-managed soliton in a quasi-one-dimensional Bose-Einstein condensate

We use the time-dependent mean-field Cross-Pitaevskii equation to study the formation of a dynamically-stabilized dissipation managed bright soliton in a quasi-one dimensional Bose-Einstein condensate (BEC). Because of three-body recombination of bosonic atoms to molecules, atoms are lost (dissipated) from a BEC. Such dissipation leads to the decay of a BEC soliton. We demonstrate by a perturbation procedure that an alimentation of atoms from an external source to the BEC may compensate for the dissipation loss and lead to a dynamically-stabilized soliton. The result of the analytical perturbation method is in excellent agreement with mean-field numerics. It seems possible to obtain such a dynamically stabilized BEC soliton without dissipation in laboratory.

Low-energy direct muon transfer from H to Ne10+, S16+ and Ar18+ using the two-state close-coupling approximation to the Faddeev-Hahn-type equation

We perform a three-body calculation of direct muon-transfer rates from thermalized muonic hydrogen isotopes to bare nuclei Ne10+, S16+ and Ar18+ employing integro-differential Faddeev-Hahn-type equations in configuration space with a two-state close-coupling approximation scheme. All Coulomb potentials including the strong final-state Coulomb repulsion are treated exactly. A long-range polarization potential is included in the elastic channel to take into account the high polarizability of the muonic hydrogen. The transfer rates so-calculated are in good agreement with recent experiments. We find that the muon is captured predominantly in the n = 6, 9 and 10 states of muonic Ne10+, S16+ and Ar18+, respectively.

Stability and collapse of a coupled Bose-Einstein condensate

The dynamics of a coupled Bose-Einstein condensate involving trapped atoms in two quantum states is studied using the time-dependent Gross-Pitaevskii equation including an interaction which can transform atoms from one state to the other. We find interesting oscillation of the number of atoms in each of the states. For all repulsive interactions, stable condensates are formed. When some of the atomic interactions are attractive, the possibility of collapse is studied by including an absorptive contact interaction and a quartic three-body recombination term. One or both components of the condensate may undergo collapse when one or more of the nonlinear terms are attractive in nature. (C) 2001 Elsevier B.V. B.V. All rights reserved.

Triatomic states in ultracold gases

We study the trajectory of Efimov states for a trapped three-boson system when the two-body scattering length a is changed. We show that these states follow the route virtual-bound-continuum resonance state when a is varied, respectively, from large positive to negative values. For a < 0, we include the triatomic continuum resonance effect to extend the three-body recombination length for trap temperatures greater than zero. For a > 0, we predict trimer binding energies based on the recombination length and the two-body scattering length.

The pion electromagnetic form factor in a QCD-inspired model

We present detailed numerical results for the pion space-like electromagnetic form factor obtained within a recently proposed model of the pion electromagnetic current in a confining light-front QCD-inspired model. The model incorporates the vector meson dominance mechanism at the quark level, where the dressed photon with q(+) > 0 decays in an interacting quark-antiquark pair, which absorbs the initial pion and produces the pion in the final state.

Stability and collapse of a hybrid Bose-Einstein condensate of atoms and molecules

The dynamics of stability and collapse of a trapped atomic Bose-Einstein condensate (BEC) coupled to a molecular one is studied using the time-dependent Gross-Pitaevskii (GP) equation including a nonlinear interaction term which can transform two atoms into a molecule and vice versa. We find an interesting oscillation of the number of atoms and molecules for a BEC of fixed mass. This oscillation is a consequence of continuous transformation in the condensate of two atoms into a molecule and vice versa. For the study of collapse an absorptive contact interaction and an imaginary quartic three-body recombination term are included in the GP equation. It is possible to have a collapse of one or both components when one or more of the nonlinear terms in the GP equation are attractive in nature, respectively.

Dynamical mean-field study of strongly interacting Bose-Einstein condensate

The experimental results of Rb-85 Bose-Einstein condensates are analyzed within the mean-field approximation with time-dependent two-body interaction and dissipation due to three-body recombination. We found that the magnitude of the dissipation is consistent with the three-body theory for longer rise times. However, for shorter rise times, it occurs an enhancement of this parameter, consistent with a coherent dimer formation. (C) 2004 Elsevier B.V. All rights reserved.

Structure of large two-neutron halos in light exotic nuclei

The structure of three-body halo nuclei formed by two neutrons and a core (nnc) is studied using zero-range interactions. The halo wave function can be completely parameterized only by the s-wave scattering lengths and two-neutron separation energy. The sizes and the neutron-neutron correlation function of Li-11 and Be-14 are calculated and compared to experimental data. A general classification scheme for three-body halos with two identical particles is discussed as well as the critical conditions to allow excited Efimov states.

Constraints on two-neutron separation energy in the Borromean C-22 nucleus

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Charm Production in Antiproton-Proton Annihilation

We study the production of charmed mesons (D) and baryons (Lambda(c)) in antiproton- proton ((p) over barp) annihilation close to their respective production thresholds. The elementary charm production process is described by either baryon/ meson exchange or by quark/ gluon dynamics. Effects of the interactions in the initial and final states are taken into account rigorously. The calculations are performed in close analogy to our earlier study on (p) over bar -> (Lambda) over bar Lambda and (p) over barp (K) over bar K by connecting the processes via SU(4) flavor symmetry. Our predictions for the (Lambda) over bar (c)Lambda(c) production cross section are in the order of 1 to 7 mb, i. e. a factor of around 10-70 smaller than the corresponding cross sections for (Lambda) over bar Lambda However, they are 100 to 1000 times larger than predictions of other model calculations in the literature. on the other hand, the resulting cross sections for (D) over barD production are found to be in the order of 10(-2) - 10(-1)mu b and they turned out to be comparable to those obtained in other studies.

Dynamics of Bose-Einstein condensates with atomic pumping and dissipative processes

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Functional Analysis for Gauge Fields on the Front-Form and the Light-Cone Gauge

Constrained systems in quantum field theories call for a careful study of diverse classes of constraints and consistency checks over their temporal evolution. Here we study the functional structure of the free electromagnetic and pure Yang-Mills fields on the front-form coordinates with the null-plane gauge condition. It is seen that in this framework, we can deal with strictu sensu physical fields.

Low-Energy Scattering of Heavy-Light Mesons from Nucleons

We study the low-energy scattering of charmed (D) and strange (K) mesons by nucleons. The short-distance part of the interaction is due to quark-gluon interchanges derived from a model that realizes dynamical chiral symmetry breaking and confines color. The quark-gluon interaction incorporates a confining Coulomb-like potential extracted from lattice QCD simulations in Coulomb gauge and a transverse hyperfine interaction consistent with a finite gluon propagator in the infrared. The long-distance part of the interaction is due to single vector (rho, omega) and scalar (sigma) meson exchanges. We show results for scattering cross-sections for isospin I = 0 and I = 1.

Vacuum Polarization Tensor for QED in the Light Front Gauge

The use of light front coordinates in quantum field theories (QFT) always brought some problems and controversies. In this work we explore some aspects of its formalism with respect to the employment of dimensional regularization in the computation of the photon's self-energy at the one-loop level and how the fermion propagator has an important role in the outcoming results.