52 research outputs found
Equivalence of renormalized covariant and light-front perturbation theory: I. Longitudinal divergences in the Yukawa model
Light-front perturbation theory has been proposed as an alternative to
covariant perturbation theory. Light-front perturbation theory is only
acceptable if it produces invariant S-matrix elements. Doubts have been raised
concerning the equivalence of light-front and covariant perturbation theory.
One of the obstacles to a rigorous proof of equivalence is the occurrence of
longitudinal divergences not present in covariant perturbation theory. We show
in the case of the Yukawa model of fermions interacting with scalar bosons at
the one-loop level how to deal with the longitudinal divergences. Invariant
S-matrix elements are obtained using our method.Comment: 11 pages, epsf, revtex, contains more elaborate explanation of Forced
Instantaneous Loops (FILs
On two dimensional coupled bosons and fermions
We study complex bosons and fermions coupled through a generalized Yukawa
type coupling in the large-N_c limit following ideas of Rajeev [Int. Jour. Mod.
Phys. A 9 (1994) 5583]. We study a linear approximation to this model. We show
that in this approximation we do not have boson-antiboson and
fermion-antifermion bound states occuring together. There is a possibility of
having only fermion-antifermion bound states. We support this claim by finding
distributional solutions with energies lower than the two mass treshold in the
fermion sector. This also has implications from the point of view of scattering
theory to this model. We discuss some aspects of the scattering above the two
mass treshold of boson pairs and fermion pairs. We also briefly present a
gauged version of the same model and write down the linearized equations of
motion.Comment: 25 pages, no figure
Compactification near and on the light front
We address problems associated with compactification near and on the light
front. In perturbative scalar field theory we illustrate and clarify the
relationships among three approaches: (1) quantization on a space-like surface
close to a light front; (2) infinite momentum frame calculations; and (3)
quantization on the light front. Our examples emphasize the difference between
zero modes in space-like quantization and those in light front quantization. In
particular, in perturbative calculations of scalar field theory using
discretized light cone quantization there are well-known ``zero-mode induced''
interaction terms. However, we show that they decouple in the continuum limit
and covariant answers are reproduced. Thus compactification of a light-like
surface is feasible and defines a consistent field theory.Comment: 24 pages, 4 figure
The Rotation Average in Lightcone Time-Ordered Perturbation Theory
We present a rotation average of the two-body scattering amplitude in the
lightcone time()-ordered perturbation theory. Using a rotation average
procedure, we show that the contribution of individual time-ordered diagram can
be quantified in a Lorentz invariant way. The number of time-ordered diagrams
can also be reduced by half if the masses of two bodies are same. In the
numerical example of theory, we find that the higher Fock-state
contribution is quite small in the lightcone quantization.Comment: 25 pages, REVTeX, epsf.sty, 69 eps file
Teleparallel formalism of galilean gravity
A pseudo-Riemannian manifold is introduced, with light-cone coordinates in
(4+1) dimensional space-time, to describe a Galilei covariant gravity. The
notion of 5-bein and torsion are developed and a galilean version of
teleparallelism is constructed in this manifold. The formalism is applied to
two spherically symmetric configurations. The first one is an ansatz which is
inferred by following the Schwarzschild solution in general relativity. The
second one is a solution of galilean covariant equations. In addition, this
Galilei teleparallel approach provides a prescription to couple the 5-bein
field to the galilean covariant Dirac field.Comment: 10 page
Restoration of rotational invariance of bound states on the light front
We study bound states in a model with scalar nucleons interacting via an
exchanged scalar meson using the Hamiltonian formalism on the light front. In
this approach manifest rotational invariance is broken when the Fock space is
truncated. By considering an effective Hamiltonian that takes into account two
meson exchanges, we find that this breaking of rotational invariance is
decreased from that which occurs when only one meson exchange is included. The
best improvement occurs when the states are weakly bound.Comment: 20 pages, 6 figures, uses feynMF; changed typos, clarified use of
angular momentu
Infinite Nuclear Matter on the Light Front: Nucleon-Nucleon Correlations
A relativistic light front formulation of nuclear dynamics is developed and
applied to treating infinite nuclear matter in a method which includes the
correlations of pairs of nucleons: this is light front Brueckner theory. We
start with a hadronic meson-baryon Lagrangian that is consistent with chiral
symmetry. This is used to obtain a light front version of a one-boson-exchange
nucleon-nucleon potential (OBEP). The accuracy of our description of the
nucleon-nucleon (NN) data is good, and similar to that of other relativistic
OBEP models. We derive, within the light front formalism, the Hartree-Fock and
Brueckner Hartree-Fock equations. Applying our light front OBEP, the nuclear
matter saturation properties are reasonably well reproduced. We obtain a value
of the compressibility, 180 MeV, that is smaller than that of alternative
relativistic approaches to nuclear matter in which the compressibility usually
comes out too large. Because the derivation starts from a meson-baryon
Lagrangian, we are able to show that replacing the meson degrees of freedom by
a NN interaction is a consistent approximation, and the formalism allows one to
calculate corrections to this approximation in a well-organized manner. The
simplicity of the vacuum in our light front approach is an important feature in
allowing the derivations to proceed. The mesonic Fock space components of the
nuclear wave function are obtained also, and aspects of the meson and nucleon
plus-momentum distribution functions are computed. We find that there are about
0.05 excess pions per nucleon.Comment: 39 pages, RevTex, two figure
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