67,458 research outputs found
Dilaton Stabilization in Brane Gas Cosmology
Brane Gas Cosmology is an M-theory motivated attempt to reconcile aspects of
the standard cosmology based on Einstein's theory of general relativity.
Dilaton gravity, when incorporating winding p-brane states, has verified the
Brandenberger--Vafa mechanism --a string-motivated conjecture which explains
why only three of the nine spatial dimensions predicted by string theory grow
large. Further investigation of this mechanism has argued for a hierarchy of
subspaces, and has shown the internal directions to be stable to initial
perturbations. These results, however, are dependent on a rolling dilaton, or
varying strength of Newton's gravitational constant. In these proceedings we
show that it is not possible to stabilize the dilaton and maintain the
stability of the internal directions within the standard Brane Gas Cosmology
setup.Comment: 6 pages, no figures. To appear in the Proceedings of MRST 2004, held
at Concordia University, Montreal, QC, 12-14 May 200
Probing the gluon self-interaction in light mesons
We investigate masses and decay constants of light mesons from a coupled
system of Dyson--Schwinger and Bethe--Salpeter equations. We explicitly take
into account dominant non-Abelian contributions to the dressed quark-gluon
vertex stemming from the gluon self-interaction. We construct the corresponding
Bethe-Salpeter kernel that satisfies the axial-vector Ward-Takahashi identity.
Our numerical treatment fully includes all momentum dependencies with all
equations solved completely in the complex plane. This approach goes well
beyond the rainbow-ladder approximation and permits us to investigate the
influence of the gluon self-interaction on the properties of mesons. As a first
result we find indications of a nonperturbative cancellation of the gluon
self-interaction contributions and pion cloud effects in the mass of the
rho-meson.Comment: 4 pages, 5 figures. Matches published version in PR
Beyond the rainbow: effects from pion back-coupling
We investigate hadronic unquenching effects in light quarks and mesons. To
this end we take into account the back-coupling of the pion onto the quark
propagator within the non-perturbative continuum framework of Schwinger-Dyson
equations (SDE) and Bethe-Salpeter equations (BSE). We improve on a previous
approach by explicitly solving both the coupled system of DSEs and BSEs in the
complex plane and the normalisation problem for Bethe-Salpeter kernels
depending on the total momentum of the meson. As a result of our study we find
considerable unquenching effects in the spectrum of light pseudoscalar, vector
and axial-vector mesons.Comment: 9 pages, 5 figures. Minor typos corrected. Version to appear in PR
Productivity of Federally Financed Research and Development Final Report, May 15, 1963 - May 14, 1966
Research project on federal and industrial patent acquisition and economic implications - NASA PROGRA
Effective Field Theory Approach to String Gas Cosmology
We derive the 4D low energy effective field theory for a closed string gas on
a time dependent FRW background. We examine the solutions and find that
although the Brandenberger-Vafa mechanism at late times no longer leads to
radion stabilization, the radion rolls slowly enough that the scenario is still
of interest. In particular, we find a simple example of the string inspired
dark matter recently proposed by Gubser and Peebles.Comment: 19 pages, 2 figures, comments adde
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