1,381 research outputs found
Selected topics on Low Energy Antiproton Physics
Some of the last results on low energy antiproton physics are reviewed. First
Faddeev calculations for \={n}d scattering length are presented.Comment: 10 pages, 11 figures Invited talk to the Biennial Conference on Low
Energy Antiproton Physics (LEAP 2000), Venice 20-26 August (2000). To appear
in Nuclear Physics
Relativistic wave functions and energies for nonzero angular momentum states in light-front dynamics
Light-front dynamics (LFD) is a powerful approach to the theory of
relativistic composite systems (hadrons in the quark models and relativistic
nucleons in nuclei). Its explicitly covariant version has been recently applied
with success to describe the new CEBAF/TJNAF data on the deuteron
electromagnetic form factors. The solutions used in were however not obtained
from solving exactly the LFD equations but by means of a perturbative
calculation with respect to the non relativistic wave function. Since, a
consequent effort has been made to obtain exact solutions of LFD equations. The
first results concerning J=0 states in a scalar model have been published in
nucl-th/9912050. The construction of states in LFD is complicated by
the two following facts. First, the generators of the spatial rotations contain
interaction and are thus difficult to handle. Second, one is always forced to
work in a truncated Fock space, and consequently, the Poincar\'e group
commutation relations between the generators -- ensuring the correct properties
of the state vector under rotation -- are in practice destroyed. In the
standard approach, with the light-front plane defined as , this
violation of rotational invariance manifests by the fact that the energy
depends on the angular momentum projection on -axis.
We present here a method to construct states in the explicitly
covariant formulation of LFD and show how it leads to a restoration of
rotational invariance.Comment: To appear in Nucl.Phys.B, 3 pages, 2 figures, .tar.gz fil
Stability of bound states in the light-front Yukawa model
We show that in the system of two fermions interacting by scalar exchange,
the solutions for J= bound states are stable without any cutoff
regularization for coupling constant below some critical value.Comment: 5 pages, 2 figures, submitted to publicatio
Two-Body Bound States in Light-Front Dynamics
We present the main features of the explicitly covariant Light-Front Dynamics
formalism and a summary of our recent works on this topic. They concern the
bound states of two scalar particles in the Wick-Cutkosky model and of two
fermions interacting via the usual OBEP ladder kernels.Comment: Invited contribution to the XIVth International School on Nuclear
Physics, Varna, Bulgaria, Sept 25-30. 20 pages, 23 figure
Electromagnetic form factor via Bethe-Salpeter amplitude in Minkowski space
For a relativistic system of two scalar particles, we find the Bethe-Salpeter
amplitude in Minkowski space and use it to compute the electromagnetic form
factor. The comparison with Euclidean space calculation shows that the Wick
rotation in the form factor integral induces errors which increase with the
momentum transfer Q^2. At JLab domain (Q^2=10 GeV^2/c^2), they are about 30%.
Static approximation results in an additional and more significant error. On
the contrary, the form factor calculated in light-front dynamics is almost
indistinguishable from the Minkowski space one.Comment: 8 pages, 7 figures, to be published in Eur. Phys. J. A; Reference
[15] is adde
Stability of two-fermion bound states in the explicitly covariant Light-Front Dynamics
The covariant light-front equations have been solved exactly for a two
fermion system with different boson exchange ladder kernels. We present a
method to study the cutoff dependence of these equations and to determine
whether they need to be regularized or not. Results are presented for scalar
and pseudo-scalar exchange. This latter furthermore exhibits some strange
particularities which will be discussed.Comment: 5 pages, 8 figures, to be published in Nucl. Phys. B (Proc. Suppl.),
contribution to the XIth Light-cone Meeting at ECT* in Trento, Sep 3-11, 200
Relativistic bound states in Yukawa model
The bound state solutions of two fermions interacting by a scalar exchange
are obtained in the framework of the explicitly covariant light-front dynamics.
The stability with respect to cutoff of the J= and J=
states is studied. The solutions for J= are found to be stable for
coupling constants below the critical value
and unstable above it. The asymptotic behavior of the
wave functions is found to follow a law. The coefficient
and the critical coupling constant are calculated from an
eigenvalue equation. The binding energies for the J= solutions
diverge logarithmically with the cutoff for any value of the coupling constant.
For a wide range of cutoff, the states with different angular momentum
projections are weakly split.Comment: 22 pages, 13 figures, .tar.gz fil
Distortion of the Stoner-Wohlfarth astroid by a spin-polarized current
The Stoner-Wohlfarth astroid is a fundamental object in magnetism. It
separates regions of the magnetic field space with two stable magnetization
equilibria from those with only one stable equilibrium and it characterizes the
magnetization reversal of nano-magnets induced by applied magnetic fields. On
the other hand, it was recently demonstrated that transfer of spin angular
momentum from a spin-polarized current provides an alternative way of switching
the magnetization. Here, we examine the astroid of a nano-magnet with uniaxial
magnetic anisotropy under the combined influence of applied fields and
spin-transfer torques. We find that spin-transfer is most efficient at
modifying the astroid when the external field is applied along the easy-axis of
magnetization. On departing from this situation, a threshold current appears
below which spin-transfer becomes ineffective yielding a current-induced dip in
the astroid along the easy-axis direction. An extension of the Stoner-Wohlfarth
model is outlined which accounts for this phenomenon.Comment: 8 pages, 6 figure
Two-fermion bound states in the explicitly covariant Light-Front Dynamics
We develop a general method to construct two relativistic fermions bound states with a given , in the framework of the explicitly covariant light-front dynamics
Electromagnetic form factor via Minkowski and Euclidean Bethe-Salpeter amplitudes
The electromagnetic form factors calculated through Euclidean Bethe-Salpeter
amplitude and through the light-front wave function are compared with the one
found using the Bethe-Salpeter amplitude in Minkowski space. The form factor
expressed through the Euclidean Bethe-Salpeter amplitude (both within and
without static approximation) considerably differs from the Minkowski one,
whereas form factor found in the light-front approach is almost
indistinguishable from it.Comment: 3 pages, 2 figures. Contribution to the proceedings of the 20th
International Conference on Few-Body Problems in Physics (FB20), Pisa, Italy,
September 10-14, 2007. To be published in "Few-Body Systems
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