4 research outputs found
Stringy Instantons and Quiver Gauge Theories
We explore contributions to the 4D effective superpotential which arise from
Euclidean D3 branes (``instantons'') that intersect space-filling D-branes.
These effects can perturb the effective field theory on the space-filling
branes by nontrivial operators composed of charged matter fields, changing the
vacuum structure in a qualitative way in some examples. Our considerations are
exemplified throughout by a careful study of a fractional brane configuration
on a del Pezzo surface.Comment: 30 pages, 4 figures; v2: reference added; v3: confusing minor error
in axion charges fixed (thanks to D. Green for pointing it out
Sigma-model for Generalized Composite p-branes
A multidimensional gravitational model containing several dilatonic scalar
fields and antisymmetric forms is considered. The manifold is chosen in the
form M = M_0 x M_1 x ... x M_n, where M_i are Einstein spaces (i > 0). The
block-diagonal metric is chosen and all fields and scale factors of the metric
are functions on M_0. For the forms composite (electro-magnetic) p-brane ansatz
is adopted. The model is reduced to gravitating self-interacting sigma-model
with certain constraints. In pure electric and magnetic cases the number of
these constraints is m(m - 1)/2 where m is number of 1-dimensional manifolds
among M_i. In the "electro-magnetic" case for dim M_0 = 1, 3 additional m
constraints appear. A family of "Majumdar-Papapetrou type" solutions governed
by a set of harmonic functions is obtained, when all factor-spaces M_k are
Ricci-flat. These solutions are generalized to the case of non-Ricci-flat M_0
when also some additional "internal" Einstein spaces of non-zero curvature are
added to M. As an example exact solutions for D = 11 supergravity and related
12-dimensional theory are presented.Comment: 33 pages, Latex. Some corrections and rearrangements are mad
The Bekenstein Formula and String Theory (N-brane Theory)
A review of recent progress in string theory concerning the Bekenstein
formula for black hole entropy is given. Topics discussed include p-branes,
D-branes and supersymmetry; the correspondence principle; the D- and M-brane
approach to black hole entropy; the D-brane analogue of Hawking radiation, and
information loss; D-branes as probes of black holes; and the Matrix theory
approach to charged and neutral black holes. Some introductory material is
included.Comment: 53 pages, LaTeX. v3: Typos fixed, minor updates, references added,
brief Note Added on AdS/CF
Global RNA Structure Analysis of Poliovirus Identifies a Conserved RNA Structure Involved in Viral Replication and Infectivity
The genomes of RNA viruses often contain RNA structures that are crucial for translation and RNA replication and may play additional, uncharacterized roles during the viral replication cycle. For the picornavirus family member poliovirus, a number of functional RNA structures have been identified, but much of its genome, especially the open reading frame, has remained uncharacterized. We have now generated a global RNA structure map of the poliovirus genome using a chemical probing approach that interrogates RNA structure with single-nucleotide resolution. In combination with orthogonal evolutionary analyses, we uncover several conserved RNA structures in the open reading frame of the viral genome. To validate the ability of our global analyses to identify functionally important RNA structures, we further characterized one of the newly identified structures, located in the region encoding the RNA-dependent RNA polymerase, 3D(pol), by site-directed mutagenesis. Our results reveal that the structure is required for viral replication and infectivity, since synonymous mutants are defective in these processes. Furthermore, these defects can be partially suppressed by mutations in the viral protein 3C(pro), which suggests the existence of a novel functional interaction between an RNA structure in the 3D(pol)-coding region and the viral protein(s) 3C(pro) and/or its precursor 3CD(pro)