694 research outputs found
Covariant And Local Field Theory On The World Sheet
In earlier work, using the light cone picture, a world sheet field theory
that sums planar phi^3 graphs was constructed and developed. Since this theory
is both non-local and not explicitly Lorentz invariant, it is desirable to have
a covariant and local alternative. In this paper, we construct such a covariant
and local world sheet theory, and show that it is equivalent to the original
non-covariant version.Comment: 22 pages,3 figures, typos and eqs.(11) and (63) are correcte
Mean Field Method Applied To The New World Sheet Field Theory: String Formation
The present article is based on a previous one, where a second quantized
field theory on the world sheet for summing the planar graphs of phi^3 theory
was developed. In this earlier work, the ground state of the model was
determined using a variational approximation. Here, starting with the same
world sheet theory, we instead use the mean field method to compute the ground
state, and find results in agreement with the variational calculation. Apart
from serving as a check on the variational calculation, the mean field method
enables us to go beyond the ground state to compute the excited states of the
model. The spectrum of these states is that of a string with linear
trajectories, plus a continuum that starts at higher energy. We show that, by
appropriately tuning the parameters of the model, the string spectrum can be
cleanly seperated from the continuum.Comment: 27 pages, 5 figures, typos correcte
Self Consistent Field Method for Planar phi^3 Theory
We continue and extend earlier work on the summation of planar graphs in
phi^3 field theory, based on a local action on the world sheet. The present
work employs a somewhat different version of the self consistent field
(meanfield) approximation compared to the previous work on the same subject.
Using this new approach, we are able to determine in general the asymptotic
forms of the solutions, and in the case of one solution, even its exact form.
This solution leads to formation of an unstable string, in agreement with the
previous work. We also investigate and clarify questions related to Lorentz
invariance and the renormalization of the solution.Comment: Latex, no other macros neede
Further Results about Field Theory on the World Sheet and String Formation
The present article is the continuation of the earlier work, which used the
world sheet representation and the mean field approximation to sum planar
graphs in massless phi^3 field theory. We improve on the previous work in two
respects: A prefactor in the world sheet propagator that had been neglected is
now taken into account. In addition, we introduce a non-zero bare mass for the
field phi. Working with a theory with cutoff, and using the mean field
approximation, we find that, depending on the range of values of the mass and
coupling constant, the model has two phases: A string forming phase and a
perturbative field theory phase. We also find the generation of a new degree of
freedom, which was not in the model originally. The new degree of freedom can
be thought of as the string slope, which is now promoted into a fluctuating
dynamical variable. Finally, we show that the introduction of the bare mass
makes it possible to renormalize the model.Comment: 39 pages, 10 figures, typos corrected and one equation simplifie
Meanfield Approximation For Field Theories On The Worldsheet Revisited
This work is the continuation of the earlier efforts to apply the mean field
approximation to the world sheet formulation of planar phi^3 theory. The
previous attempts were either simple but without solid foundation or well
founded but excessively complicated. In this article, we present an approach
both simple, and also systematic and well founded. We are able to carry through
the leading order mean field calculation analytically, and with a suitable
tuning of the coupling constant, we find string formation.Comment: 38 pages, 8 figures, late
Planar Graphs On The World Sheet: The Hamiltonian Approach
The present work continues the program of summing planar Feynman graphs on
the world sheet. Although it is based on the same classical action introduced
in the earlier work, there are important new features: Instead of the path
integral used in the earlier work, the model is quantized using the canonical
algebra and the Hamiltonian picture. The new approach has an important
advantage over the old one: The ultraviolet divergence that plagued the earlier
work is absent. Using a family of projection operators, we are able to give an
exact representation on the world sheet of the planar graphs of both the phi^3
theory, on which most of the previous work was based, and also of the phi^4
theory. We then apply the mean field approximation to determine the structure
of the ground state. In agreement with the earlier work, we find that the
graphs of phi^3 theory form a dense network (condensate) on the world sheet. In
the case of the phi^4 theory, graphs condense for the unphysical (attractive)
sign of the coupling, whereas there is no condensation for the physical
(repulsive) sign.Comment: 32 pages, 6 figures, typos corrected and some minor clarifications
adde
- …