413 research outputs found
Minimal immersions of closed surfaces in hyperbolic three-manifolds
We study minimal immersions of closed surfaces (of genus ) in
hyperbolic 3-manifolds, with prescribed data , where
is a conformal structure on a topological surface , and is a holomorphic quadratic differential on the surface . We
show that, for each for some , depending only on
, there are at least two minimal immersions of closed surface
of prescribed second fundamental form in the conformal structure
. Moreover, for sufficiently large, there exists no such minimal
immersion. Asymptotically, as , the principal curvatures of one
minimal immersion tend to zero, while the intrinsic curvatures of the other
blow up in magnitude.Comment: 16 page
Holography and Defect Conformal Field Theories
We develop both the gravity and field theory sides of the Karch-Randall
conjecture that the near-horizon description of a certain D5-D3 brane
configuration in string theory, realized as AdS_5 x S^5 bisected by an AdS_4 x
S^2 "brane", is dual to N=4 Super Yang-Mills theory in R^4 coupled to an R^3
defect. We propose a complete Lagrangian for the field theory dual, a novel
"defect superconformal field theory" wherein a subset of the fields of N=4 SYM
interacts with a d=3 SU(N) fundamental hypermultiplet on the defect preserving
conformal invariance and 8 supercharges. The Kaluza-Klein reduction of wrapped
D5 modes on AdS_4 x S^2 leads to towers of short representations of OSp(4|4),
and we construct the map to a set of dual gauge-invariant defect operators O_3
possessing integer conformal dimensions. Gravity calculations of and
are given. Spacetime and N-dependence matches expectations from dCFT,
while the behavior as functions of lambda = g^2 N at strong and weak coupling
is generically different. We comment on a class of correlators for which a
non-renormalization theorem may still exist. Partial evidence for the
conformality of the quantum theory is given, including a complete argument for
the special case of a U(1) gauge group. Some weak coupling arguments which
illuminate the duality are presented.Comment: 47 pages, LaTeX, 2 figures, feynmf. v2: fixed minor errors, added
references. v3: fixed more typo
Optical Spectra of SNR Candidates in NGC 300
We present moderate-resolution (<5A) long-slit optical spectra of 51 nebular
objects in the nearby Sculptor Group galaxy NGC 300 obtained with the 2.3 meter
Advanced Technology Telescope at Siding Spring Observatory, Australia. Adopting
the criterion of [SII]/Ha>=0.4 to confirm supernova remnants (SNRs) from
optical spectra, we find that of 28 objects previously proposed as SNRs from
optical observations, 22 meet this criterion with six showing [SII]/Ha of less
than 0.4. Of 27 objects suggested as SNRs from radio data, four are associated
with the 28 previously proposed SNRs. Of these four, three (included in the 22
above) meet the criterion. In all, 22 of the 51 nebular objects meet the
[SII]/Ha criterion as SNRs while the nature of the remaining 29 objects remains
undetermined by these observations.Comment: Accepted for publication in Astrophysics & Space Scienc
On the equivalence between Implicit Regularization and Constrained Differential Renormalization
Constrained Differential Renormalization (CDR) and the constrained version of
Implicit Regularization (IR) are two regularization independent techniques that
do not rely on dimensional continuation of the space-time. These two methods
which have rather distinct basis have been successfully applied to several
calculations which show that they can be trusted as practical, symmetry
invariant frameworks (gauge and supersymmetry included) in perturbative
computations even beyond one-loop order.
In this paper, we show the equivalence between these two methods at one-loop
order. We show that the configuration space rules of CDR can be mapped into the
momentum space procedures of Implicit Regularization, the major principle
behind this equivalence being the extension of the properties of regular
distributions to the regularized ones.Comment: 16 page
The Local Velocity Anomaly
There is a velocity discontinuity at about 7 Mpc between the galaxies of the
Local Sheet that are moving together with low internal velocity dispersion and
the adjacent structures. The Local Sheet bounds the Local Void. The Local Sheet
is determined to have a peculiar velocity of 260 km/s away from the center of
the void. In order for this large velocity to be generated by an absence of
gravity, the Local Void must be at least 45 Mpc in diameter and be very empty.Comment: Invited review, "Galaxies in the Local Volume", Sydney, 8-13 July,
2007. eds. B. Koribalski & H. Jerjen, Astrophys. & Space Sci. Proceed. 10
pages with 7 figure
Linearized Treatment of Scalar perturbations in the Asymptotic Cosmological Model
In this paper the implications of a recently proposed phenomenological model
of cosmology, the Asymptotic Cosmological Model (ACM), on the behavior of
scalar perturbations are studied. Firstly we discuss new fits of the ACM at the
homogeneous level, including fits to the Type Ia Supernovae UNION dataset,
first CMB peak of WMAP5 and BAOs. The linearized equations of scalar
perturbations in the FRW metric are derived. A simple model is used to compute
the CMB temperature perturbation spectrum. The results are compared with the
treatment of perturbations in other approaches to the problem of the
accelerated expansion of the universe.Comment: 14 pages, 5 figures. Presentation in sections 2 and 3 clarified,
references added. Final version to appear in Astroparticle Physic
Restricting quark matter models by gravitational wave observation
We consider the possibilities for obtaining information about the equation of
state for quark matter by using future direct observational data on
gravitational waves. We study the nonradial oscillations of both fluid and
spacetime modes of pure quark stars. If we observe the and the lowest
modes from quark stars, by using the simultaneously obtained
radiation radius we can constrain the bag constant with reasonable
accuracy, independently of the quark mass.Comment: To appear in Phys. Rev.
An extension of the cosmological standard model with a bounded Hubble expansion rate
The possibility of having an extension of the cosmological standard model
with a Hubble expansion rate constrained to a finite interval is
considered. Two periods of accelerated expansion arise naturally when the
Hubble expansion rate approaches to the two limiting values. The new
description of the history of the universe is confronted with cosmological data
and with several theoretical ideas going beyond the standard cosmological
model.Comment: 10 pages, 4 figures. Minor revisio
Correlation Functions in 2-Dimensional Integrable Quantum Field Theories
In this talk I discuss the form factor approach used to compute correlation
functions of integrable models in two dimensions. The Sinh-Gordon model is our
basic example. Using Watson's and the recursive equations satisfied by matrix
elements of local operators, I present the computation of the form factors of
the elementary field and the stress-energy tensor of
the theory.Comment: 19pp, LATEX version, (talk at Como Conference on ``Integrable Quantum
Field Theories''
Tunneling and Metastability of continuous time Markov chains
We propose a new definition of metastability of Markov processes on countable
state spaces. We obtain sufficient conditions for a sequence of processes to be
metastable. In the reversible case these conditions are expressed in terms of
the capacity and of the stationary measure of the metastable states
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