18 research outputs found
Qualitative solution of QCD sum rules
We show how such important features of QCD as chiral symmetry breaking or the
formation of a mass-gap can be directly traced from QCD sum rules for two point
functions assuming, in the large number of colors limit, exact duality between
the operator product expansion and the spectrum described by linearly (or
nearly linear) rising Regge trajectories as predicted by string theory. We see
how the presence of chiral symmetry breaking is intimately related to
confinement in this scenario, as expected from general arguments, and how Regge
trajectories change when chiral symmetry is broken. As a result the whole meson
mass spectrum can be parametrized with a good accuracy by the constant
only, thus realizing the program proposed by Migdal some time ago.Comment: Version published in JHE
Matching Regge Theory to the OPE
The spectra of masses and decay constants for non-strange meson resonances in
the energy range 0--2.5 GeV is analyzed. It is known from meson phenomenology
that for given quantum numbers these spectra approximately follow linear
trajectories with a universal slope. These facts can be understood in terms of
an effective string description for QCD. For light meson states the
trajectories deviate noticeably from the linear behavior. We investigate the
possible corrections to the linear trajectories by matching two-point
correlators of quark currents to the Operator Product Expansion (OPE). We find
that the allowed modifications to the linear Regge behavior must decrease
rapidly with the principal quantum number. After fitting the lightest states in
each channel and certain low-energy constants the whole spectrum for meson
masses and residues is obtained in a satisfactory agreement with phenomenology.
We briefly speculate on possible implications for the QCD effective string.Comment: 24 pages, Latex, significant changes in discussion of fits, more refs
adde
Bouncing and Accelerating Solutions in Nonlocal Stringy Models
A general class of cosmological models driven by a non-local scalar field
inspired by string field theories is studied. In particular cases the scalar
field is a string dilaton or a string tachyon. A distinguished feature of these
models is a crossing of the phantom divide. We reveal the nature of this
phenomena showing that it is caused by an equivalence of the initial non-local
model to a model with an infinite number of local fields some of which are
ghosts. Deformations of the model that admit exact solutions are constructed.
These deformations contain locking potentials that stabilize solutions.
Bouncing and accelerating solutions are presented.Comment: Minor corrections, references added, published in JHE