77 research outputs found
Equation of state of hadronic matter with dibaryons in an effective quark model
The equation of state of symmetric nuclear matter with the inclusion of
non-strange dibaryons is studied. We pay special attention to the existence of
a dibaryon condensate at zero temperature. These calculations have been
performed in an extended quark-meson coupling model with density-dependent
parameters, which takes into account the finite size of nucleons and dibaryons.
A first-order phase-transition to pure dibaryon matter has been found. The
corresponding critical density is strongly dependent on the value of the
dibaryon mass. The density behavior of the nucleon and dibaryon effective
masses and confining volumes have also been discussed.Comment: 9 pages, LaTex, 3 Postscript figures, a misprint correcte
Nonabelian solutions in N=4, D=5 gauged supergravity
We consider static, nonabelian solutions in N=4, D=5 Romans' gauged
supergravity model. Numerical arguments are presented for the existence of
asymptotically anti-de Sitter configurations in the version of the
theory, with a dilaton potential presenting a stationary point. Considering the
version of the theory with a Liouville dilaton potential, we look for
configurations with unusual topology. A new exact solution is presented, and a
counterterm method is proposed to compute the mass and action.Comment: 15 pages, 4 figure
Rotating strings and D2-branes in type IIA reduction of M-theory on G2 manifold and their semiclassical limits
We consider rotating strings and D2-branes on type IIA background, which
arises as dimensional reduction of M-theory on manifold of G2 holonomy, dual to
N=1 gauge theory in four dimensions. We obtain exact solutions and explicit
expressions for the conserved charges. By taking the semiclassical limit, we
show that the rotating strings can reproduce only one type of semiclassical
behavior, exhibited by rotating M2-branes on G2 manifolds. Our further
investigation leads to the conclusion that the rotating D2-branes reproduce two
types of the semiclassical energy-charge relations known for membranes in
eleven dimensions.Comment: LaTeX, 29 pages, no figures; V2:comments added; V3:no changes, to
appear in JHE
Duality symmetric massive type II theories in D=8 and D=6
We study compactification of massive type IIA supergravity in presence
of possible Ramond-Ramond (RR) background fluxes. The resulting theory in D=8
is shown to possess full T-duality symmetry similar to
the massless case. It is shown that elements of duality symmetry interpolate
between massive type IIA compactified on and ordinary type IIA
compactified on with RR 2-form flux. We also discuss relationship between
M-theory vacua and massive type IIA vacua. The D8-brane is found to correspond
to M-theory `pure gravity' solution which is a direct product of 7-dimensional
Minkowski space and a 4-dimensional instanton. We also construct D6-D8 bound
state which preserves 1/2 supersymmetries. We then discuss massive IIA
compactification on and point out that when all possible RR fluxes on
are turned on the six-dimensional theory appears to assume a nice SO(4,4)
invariant form.Comment: 19 pages, JHEP3, typos fixed, references added; v2: small correction
in eq.(5.3), published in JHE
Four-point functions and kaon decays in a minimal AdS/QCD model
We study the predictions of holographic QCD for various observable four-point
quark flavour current-current correlators. The dual 5-dimensional bulk theory
we consider is a Yang Mills theory in a slice of
spacetime with boundaries. Particular UV and IR boundary conditions
encode the spontaneous breaking of the dual 4D global chiral symmetry down to
the subgroup. We explain in detail how to calculate the 4D four-point
quark flavour current-current correlators using the 5D holographic theory,
including interactions. We use these results to investigate predictions of
holographic QCD for the rule for kaon decays and the
parameter. The results agree well in comparison with experimental data, with an
accuracy of 25% or better. The holographic theory automatically includes the
contributions of the meson resonances to the four-point correlators. The
correlators agree well in the low-momentum and high-momentum limit, in
comparison with chiral perturbation theory and perturbative QCD results,
respectively.Comment: Published version, title changed to conform with Journal format,
references and clarifying remarks added, 40 pages, 5 figure
Branes with fluxes wrapped on spheres
Following an eight-dimensional gauged supergravity approach we construct the
most general solution describing D6-branes wrapped on a Kahler four-cycle taken
to be the product of two spheres of different radii. Our solution interpolates
between a Calabi-Yau four-fold and the spaces S^2xS^2xS^2xR^2 or S^2xS^2xR^4,
depending on generic choices for the parameters. Then we turn on a background
four-form field strength, corresponding to D2-branes, and show explicitly how
our solution is deformed. For a particular choice of parameters it represents a
flow from a Calabi-Yau four-fold times the three-dimensional Minkowski
space-time in the ultraviolet, to the space-time AdS_4xQ^{1,1,1} in the
infrared. In general, the solution in the infrared has a singularity which
within type-IIA supergravity corresponds to the near horizon geometry of the
solution for the D2-D6 system. Finally, we uncover the relation with work done
in the eighties on Freund-Rubin type compactifications.Comment: 15 pages, Late
Brane Worlds, String Cosmology, and AdS/CFT
Using the thin-shell formalism we discuss the motion of domain walls in de Sitter and anti-de Sitter (AdS) time-dependent bulks. This motion results in a dynamics for the brane scale factor. We show that in the case of a clean brane the scale factor describes both singular and non-singular universes, with phases of contraction and expansion. These phases can be understood as quotients of AdS spacetime by a discrete symmetry group. We discuss this effect in some detail, and suggest how the AdS/CFT correspondence could be applied to obtain a non perturbative description of brane-world string cosmology
- …