29,553 research outputs found
The Gauge/Gravity Correspondence for Non-Supersymmetric Theories
We review the string construction of the ``orientifold field theories'' and
we show that for these theories the gauge/gravity correspondence is only valid
for a large number of colours.Comment: 7 pages, Latex, Talk given at 37. International Symposium Ahrenshoop,
Berlin, August 2004. Added references and acknowledgements; corrected typo
One-neutron halo structure by the ratio method
We present a new observable to study halo nuclei. This new observable is a
particular ratio of angular distributions for elastic breakup and scattering.
For one-neutron halo nuclei, it is shown to be independent of the reaction
mechanism and to provide significant information about the structure of the
projectile, including binding energy, partial-wave configuration, and radial
wave function of the halo. This observable offers new capabilities for the
study of nuclear structure far from stability.Comment: 9 pages, 4 figure
Crowd-Anticrowd Theory of Multi-Agent Market Games
We present a dynamical theory of a multi-agent market game, the so-called
Minority Game (MG), based on crowds and anticrowds. The time-averaged version
of the dynamical equations provides a quantitatively accurate, yet intuitively
simple, explanation for the variation of the standard deviation (`volatility')
in MG-like games. We demonstrate this for the basic MG, and the MG with
stochastic strategies. The time-dependent equations themselves reproduce the
essential dynamics of the MG.Comment: Presented at APFA2 (Liege) July 2000. Proceedings: Eur.Phys.J. B
[email protected]
Control of DNA minor groove width and Fis protein binding by the purine 2-amino group.
The width of the DNA minor groove varies with sequence and can be a major determinant of DNA shape recognition by proteins. For example, the minor groove within the center of the Fis-DNA complex narrows to about half the mean minor groove width of canonical B-form DNA to fit onto the protein surface. G/C base pairs within this segment, which is not contacted by the Fis protein, reduce binding affinities up to 2000-fold over A/T-rich sequences. We show here through multiple X-ray structures and binding properties of Fis-DNA complexes containing base analogs that the 2-amino group on guanine is the primary molecular determinant controlling minor groove widths. Molecular dynamics simulations of free-DNA targets with canonical and modified bases further demonstrate that sequence-dependent narrowing of minor groove widths is modulated almost entirely by the presence of purine 2-amino groups. We also provide evidence that protein-mediated phosphate neutralization facilitates minor groove compression and is particularly important for binding to non-optimally shaped DNA duplexes
More Anomalies from Fractional Branes
In this note we show how the anomalies of both pure and matter coupled N=1,2
supersymmetric gauge theories describing the low energy dynamics of fractional
branes on orbifolds can be derived from supergravity.Comment: 11 pages, latex; v2: minor typos fixe
Is a classical description of stable non-BPS D-branes possible?
We study the classical geometry produced by a stack of stable (i.e. tachyon
free) non-BPS D-branes present in K3 compactifications of type II string
theory. This classical representation is derived by solving the equations of
motion describing the low-energy dynamics of the supergravity fields which
couple to the non-BPS state. Differently from what expected, this configuration
displays a singular behaviour: the space-time geometry has a repulson-like
singularity. This fact suggests that the simplest setting, namely a set of
coinciding non-interacting D-branes, is not acceptable. We finally discuss the
possible existence of other acceptable configurations corresponding to more
complicated bound states of these non-BPS branes.Comment: Latex file: 41 pages, 5 figures; some minor corrections and
references adde
Gauge theories from wrapped and fractional branes
We compare two applications of the gauge/gravity correspondence to a non
conformal gauge theory, based respectively on the study of D-branes wrapped on
supersymmetric cycles and of fractional D-branes on orbifolds. We study two
brane systems whose geometry is dual to N=4, D=2+1 super Yang-Mills theory, the
first one describing D4-branes wrapped on a two-sphere inside a Calabi-Yau
two-fold and the second one corresponding to a system of fractional
D2/D6-branes on the orbifold R^4/Z_2. By probing both geometries we recover the
exact perturbative running coupling constant and metric on the moduli space of
the gauge theory. We also find a general expression for the running coupling
constant of the gauge theory in terms of the "stringy volume" of the two-cycle
which is involved in both types of brane systems.Comment: AMS-LaTeX, 35 pages, no figures. Minor typos corrected, version to
appear in NP
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