1,266 research outputs found
A Class of Distal Functions on Semitopological Semigroups
The norm closure of the algebra generated by the set and of
functions on was studied in \cite{S} (and was named as the
Weyl algebra). In this paper, by a fruitful result of Namioka, this algebra is
generalized for a general semitopological semigroup and, among other things, it
is shown that the elements of the involved algebra are distal. In particular,
we examine this algebra for and (more generally) for the
discrete (additive) group of any countable ring. Finally, our results are
treated for a bicyclic semigroup.Comment: To appear in Methods Funct. Anal. Topolog
Different D-brane Interactions
We use rotation of one D-brane with respect to the other to reveal the hidden
structure of D-branes in type-II theories. This is done by calculation of the
interaction amplitude for two different parallel and angled branes. The
analysis of strings with different boundary conditions at the ends is also
given. The stable configuration for two similar branes occurs when they are
anti-parallel. For branes of different dimensions stability is attained for
either parallel or anti-parallel configurations and when dimensions differ by
four the amplitude vanishes at the stable point. The results serve as more
evidence that D-branes are stringy descriptions of non-perturbative extended
solutions of SUGRA theories, as low energy approximation of superstrings.Comment: Tex, 12 pages. Typographical errors are corrected, minor changes
done, acknowledgements adde
Horizon fluff, semi-classical black hole microstates - Log-corrections to BTZ entropy and black hole/particle correspondence
According to the horizon fluff proposal microstates of a generic black hole
belong to a certain subset of near horizon soft hairs that cannot be extended
beyond the near horizon region. In [1,2] it was shown how the horizon fluff
proposal works for AdS3 black holes. In this work we clarify further this
picture by showing that BTZ black hole microstates are in general among the
coherent states in the Hilbert space associated with conic spaces or their
Virasoro descendants, provided we impose a (Bohr-type) quantization condition
on the angular deficit. Thus BTZ black holes may be viewed as condensates (or
solitonic states) of AdS3 particles. We provide canonical and microcanonical
descriptions of the statistical mechanical system associated with BTZ black
holes and their microstates, and relate them. As a further non-trivial check we
show the horizon fluff proposal correctly reproduces the expected logarithmic
corrections to the BTZ entropy.Comment: 47pp, v2: added references, minor correction in section 6.1, results
unchanged, v3: 51pp, added figures, references and clarifications, to appear
in JHE
On Classification of Geometries with SO(2,2) Symmetry
Motivated by the Extremal Vanishing Horizon (EVH) black holes, their near
horizon geometry and the EVH/CFT proposal, we construct and classify solutions
with (local) SO(2,2) symmetry to four and five dimensional
Einstein-Maxwell-Dilaton (EMD) theory with positive, zero or negative
cosmological constant Lambda, the EMD- theory, and also
gauged supergravity in four dimensions and gauged supergravity in five
dimensions. In four dimensions the geometries are warped product of AdS3 with
an interval or a circle. In five dimensions the geometries are of the form of
warped product of AdS3 and a 2d surface . For the
Einsten-Maxwell- theory we prove that should have a U(1)
isometry, a rigidity theorem in this class of solutions. We also construct all
d dimensional Einstein vacuum solutions with or
isometry.Comment: 26 pages, updated to published versio
- …