193 research outputs found

### Solution of Two-Body Bound State Problems with Confining Potentials

The homogeneous Lippmann-Schwinger integral equation is solved in momentum
space by using confining potentials. Since the confining potentials are
unbounded at large distances, they lead to a singularity at small momentum. In
order to remove the singularity of the kernel of the integral equation, a
regularized form of the potentials is used. As an application of the method,
the mass spectra of heavy quarkonia, mesons consisting from heavy quark and
antiquark $(\Upsilon(b\bar{b}), \psi(c\bar{c}))$, are calculated for linear and
quadratic confining potentials. The results are in good agreement with
configuration space and experimental results.Comment: 6 pages, 5 table

### Relativistic three-particle dynamical equations: II. Application to the trinucleon system

We calculate the contribution of relativistic dynamics on the
neutron-deuteron scattering length and triton binding energy employing five
sets trinucleon potential models and four types of three-dimensional
relativistic three-body equations suggested in the preceding paper. The
relativistic correction to binding energy may vary a lot and even change sign
depending on the relativistic formulation employed. The deviations of these
observables from those obtained in nonrelativistic models follow the general
universal trend of deviations introduced by off- and on-shell variations of
two- and three-nucleon potentials in a nonrelativistic model calculation.
Consequently, it will be difficult to separate unambiguously the effect of off-
and on-shell variations of two- and three- nucleon potentials on low-energy
three-nucleon observables from the effect of relativistic dynamics.Comment: 15 pages, [Text and one postscript figure included, e-mail:
[email protected]; Fax: 55-11-288 8224] Report # IFT P.069/9

### Charged three-body system with arbitrary masses near conformal invariance

Within an adiabatic approximation to the three-body Coulomb system, we study
the strength of the leading order conformaly invariant attractive dipole
interaction produced when a slow charged particle $q_3$ (with mass $m_3$) is
captured by the first excited state of a dimer [with individual masses and
charges $(m_1,q_1$) and ($m_2,q_2=-q_1$)]. The approach leads to a universal
mass-charge critical condition for the existence of three-body level
condensation, ${(m_1^{-1}+m_2^{-1})}/ {[(m_1+m_2)^{-1}+m_3^{-1}]}>|{q_1}/(24
q_3)|$, as well as the ratio between the geometrically scaled energy levels.
The resulting expressions can be relevant in the analysis of recent
experimental setups with charged three-body systems, such as the interactions
of excitons, or other matter-antimatter dimers, with a slow charged particle.Comment: 5 pages, 1 figure, to appear in Physical Review

### Problem of Statistical Model in Deep Inelastic Scattering Phenomenology

Recent Deep Inelastic data leads to an up-down quark asymmetry of the nucleon
sea. Explanations of the flavour asymmetry and the di-lepton production in
proton-nucleus collisions call for a temperature $T \approx 100$ MeV in a
statistical model. This T may be conjectured as being due to the
Fulling-Davies-Unruh effect. But it is not possible to fit the structure
function itself.Comment: 8 pages, 2 figures, figures on request to [email protected],
IFT preprint-IFT P-050/93, Late

### Radii in weakly-bound light halo nuclei

A systematic study of the root-mean-square distance between the constituents
of weakly-bound nuclei consisting of two halo neutrons and a core is performed
using a renormalized zero-range model. The radii are obtained from a universal
scaling function that depends on the mass ratio of the neutron and the core, as
well as on the nature of the subsystems, bound or virtual. Our calculations are
qualitatively consistent with recent data for the neutron-neutron
root-mean-square distance in the halo of $^{11}$Li and $^{14}$Be nuclei

### Relativistic three-particle dynamical equations: I. Theoretical development

Starting from the two-particle Bethe-Salpeter equation in the ladder
approximation and integrating over the time component of momentum, we rederive
three dimensional scattering integral equations satisfying constraints of
relativistic unitarity and covariance, first derived by Weinberg and by
Blankenbecler and Sugar. These two-particle equations are shown to be related
by a transformation of variables. Hence we show how to perform and relate
identical dynamical calculation using these two equations. Similarly, starting
from the Bethe-Salpeter-Faddeev equation for the three-particle system and
integrating over the time component of momentum, we derive several three
dimensional three-particle scattering equations satisfying constraints of
relativistic unitarity and covariance. We relate two of these three-particle
equations by a transformation of variables as in the two-particle case. The
three-particle equations we derive are very practical and suitable for
performing relativistic scattering calculations.Comment: 30 pages, Report # IFT P.070/93, [Text in Latex, e-mail:
[email protected] ; FAX: 55-11-288-8224

### Path Dependence of the Quark Nonlocal Condensate within the Instanton Model

Within the instanton liquid model, we study the dependence of the gauge
invariant two--point quark correlator on the path used to perform the color
parallel transport between two points in the Euclidean space.Comment: 4 pages, 5 figure

### Two definitions of the electric polarizability of a bound system in relativistic quantum theory

For the electric polarizability of a bound system in relativistic quantum
theory, there are two definitions that have appeared in the literature. They
differ depending on whether or not the vacuum background is included in the
system. A recent confusion in this connection is clarified

### Liquid-Gas phase transition in Bose-Einstein Condensates with time evolution

We study the effects of a repulsive three-body interaction on a system of
trapped ultra-cold atoms in Bose-Einstein condensed state. The stationary
solutions of the corresponding $s-$wave non-linear Schr\"{o}dinger equation
suggest a scenario of first-order liquid-gas phase transition in the condensed
state up to a critical strength of the effective three-body force. The time
evolution of the condensate with feeding process and three-body recombination
losses has a new characteristic pattern. Also, the decay time of the dense
(liquid) phase is longer than expected due to strong oscillations of the
mean-square-radius.Comment: 4 eps-figure

### Validity of Feynman's prescription of disregarding the Pauli principle in intermediate states

Regarding the Pauli principle in quantum field theory and in many-body
quantum mechanics, Feynman advocated that Pauli's exclusion principle can be
completely ignored in intermediate states of perturbation theory. He observed
that all virtual processes (of the same order) that violate the Pauli principle
cancel out. Feynman accordingly introduced a prescription, which is to
disregard the Pauli principle in all intermediate processes. This ingeneous
trick is of crucial importance in the Feynman diagram technique. We show,
however, an example in which Feynman's prescription fails. This casts doubts on
the general validity of Feynman's prescription

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