403 research outputs found
Flowing with Eight Supersymmetries in M-Theory and F-theory
We consider holographic RG flow solutions with eight supersymmetries and
study the geometry transverse to the brane. For both M2-branes and for
D3-branes in F-theory this leads to an eight-manifold with only a four-form
flux. In both settings there is a natural four-dimensional hyper-Kahler slice
that appears on the Coulomb branch. In the IIB theory this hyper-Kahler
manifold encodes the Seiberg-Witten coupling over the Coulomb branch of a U(1)
probe theory. We focus primarily upon a new flow solution in M-theory. This
solution is first obtained using gauged supergravity and then lifted to eleven
dimensions. In this new solution, the brane probes have an Eguchi-Hanson moduli
space with the M2-branes spread over the non-trivial 2-sphere. It is also shown
that the new solution is valid for a class of orbifold theories. We discuss how
the hyper-Kahler structure on the slice extends to some form of G-structure in
the eight-manifold, and describe how this can be computed.Comment: 29 pages, 1 figure, harvma
Higher Dimensional Classical W-Algebras
Classical -algebras in higher dimensions are constructed. This is achieved
by generalizing the classical Gel'fand-Dickey brackets to the commutative limit
of the ring of classical pseudodifferential operators in arbitrary dimension.
These -algebras are the Poisson structures associated with a higher
dimensional version of the Khokhlov-Zabolotskaya hierarchy (dispersionless
KP-hierarchy). The two dimensional case is worked out explicitly and it is
shown that the role of Diff is taken by the algebra of generators of
local diffeomorphisms in two dimensions.Comment: 22 pages, Plain TeX, KUL-TF-92/19, US-FT/6-9
Dynamics of the self-interacting chameleon cosmology
In this article we study the properties of the flat FRW chameleon cosmology
in which the cosmic expansion of the Universe is affected by the chameleon
field and dark energy. In particular, we perform a detailed examination of the
model in the light of numerical analysis. The results illustrate that the
interacting chameleon filed plays an important role in late time universe
acceleration and phantom crossing.Comment: 13 pages, 8 figures, to appear in Astrophysics and Space Sc
Geometric and thermodynamic properties in Gauss-Bonnet gravity
In this paper, the generalized second law (GSL) of thermodynamics and entropy
is revisited in the context of cosmological models in Gauss-Bonnet gravity with
the boundary of the universe is assumed to be enclosed by the dynamical
apparent horizon. The model is best fitted with the observational data for
distance modulus. The best fitted geometric and thermodynamic parameters such
as equation of state parameter, deceleration parameter and entropy are derived.
To link between thermodynamic and geometric parameters, the "entropy rate of
change multiplied by the temperature" as a model independent thermodynamic
state parameter is also derived. The results show that the model is in good
agreement with the observational analysis.Comment: 13 pages, 13 figures, to be published in Astrophysics and Space Sc
Dynamics of Warped Flux Compactifications
We discuss the four dimensional effective action for type IIB flux
compactifications, and obtain the quadratic terms taking warp effects into
account. The analysis includes both the 4-d zero modes and their KK
excitations, which become light at large warping. We identify an `axial' type
gauge for the supergravity fluctuations, which makes the four dimensional
degrees of freedom manifest. The other key ingredient is the existence of
constraints coming from the ten dimensional equations of motion. Applying these
conditions leads to considerable simplifications, enabling us to obtain the low
energy lagrangian explicitly. In particular, the warped K\"ahler potential for
metric moduli is computed and it is shown that there are no mixings with the KK
fluctuations and the result differs from previous proposals. The four
dimensional potential contains a generalization of the Gukov-Vafa-Witten term,
plus usual mass terms for KK modes.Comment: 37 pages. v2. References added, typos corrected. v3. Matches JHEP
versio
Observational constraint on generalized Chaplygin gas model
We investigate observational constraints on the generalized Chaplygin gas
(GCG) model as the unification of dark matter and dark energy from the latest
observational data: the Union SNe Ia data, the observational Hubble data, the
SDSS baryon acoustic peak and the five-year WMAP shift parameter. It is
obtained that the best fit values of the GCG model parameters with their
confidence level are ()
, ()
. Furthermore in this model, we can see that the
evolution of equation of state (EOS) for dark energy is similar to quiessence,
and its current best-fit value is with the confidence
level .Comment: 9 pages, 5 figure
Intersection rules, dynamics and symmetries
We consider theories containing gravity, at most one dilaton and form field
strengths. We show that the existence of particular BPS solutions of
intersecting extremal closed branes select the theories, which upon dimensional
reduction to three dimensions possess a simple simply laced Lie group symmetry
G. Furthermore these theories can be fully reconstructed from the dynamics of
such branes and of their openings. Amongst such theories are the effective
actions of the bosonic sector of M-theory and of the bosonic string. The BPS
intersecting brane solutions form representations of a subgroup of the group of
Weyl reflections and outer automorphisms of the triple Kac-Moody extension G+++
of the G algebra, which cannot be embedded in the overextended Kac-Moody
subalgebra G++ characterising the cosmological Kasner solutions.Comment: Latex 30 pages, 3 figure
Constraints on accelerating universe using ESSENCE and Gold supernovae data combined with other cosmological probes
We use recently observed data: the 192 ESSENCE type Ia supernovae (SNe Ia),
the 182 Gold SNe Ia, the 3-year WMAP, the SDSS baryon acoustic peak, the X-ray
gas mass fraction in clusters and the observational data to constrain
models of the accelerating universe. Combining the 192 ESSENCE data with the
observational data to constrain a parameterized deceleration parameter,
we obtain the best fit values of transition redshift and current deceleration
parameter , .
Furthermore, using CDM model and two model-independent equation of
state of dark energy, we find that the combined constraint from the 192 ESSENCE
data and other four cosmological observations gives smaller values of
and , but a larger value of than the combined
constraint from the 182 Gold data with other four observations. Finally,
according to the Akaike information criterion it is shown that the recently
observed data equally supports three dark energy models: CDM,
and .Comment: 18 pages, 8 figure
Scintillation Counters for the D0 Muon Upgrade
We present the results of an upgrade to the D0 muon system. Scintillating
counters have been added to the existing central D0 muon system to provide
rejection for cosmic ray muons and out-of-time background, and to provide
additional fast timing information for muons in an upgraded Tevatron.
Performance and results from the 1994-1996 Tevatron run are presented.Comment: 30 pages, 25 postscript figure
Teleparallel Gravity and Dimensional Reductions of Noncommutative Gauge Theory
We study dimensional reductions of noncommutative electrodynamics on flat
space which lead to gauge theories of gravitation. For a general class of such
reductions, we show that the noncommutative gauge fields naturally yield a
Weitzenbock geometry on spacetime and that the induced diffeomorphism invariant
field theory can be made equivalent to a teleparallel formulation of gravity
which macroscopically describes general relativity. The Planck length is
determined in this setting by the Yang-Mills coupling constant and the
noncommutativity scale. The effective field theory can also contain
higher-curvature and non-local terms which are characteristic of string theory.
Some applications to D-brane dynamics and generalizations to include the
coupling of ordinary Yang-Mills theory to gravity are also described.Comment: 31 pages LaTeX; References adde
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