3,373 research outputs found
Chiral sedimentation of extended objects in viscous media
We study theoretically the chirality of a generic rigid object's
sedimentation in a fluid under gravity in the low Reynolds number regime. We
represent the object as a collection of small Stokes spheres or stokeslets, and
the gravitational force as a constant point force applied at an arbitrary point
of the object. For a generic configuration of stokeslets and forcing point, the
motion takes a simple form in the nearly free draining limit where the
stokeslet radius is arbitrarily small. In this case, the internal hydrodynamic
interactions between stokeslets are weak, and the object follows a helical path
while rotating at a constant angular velocity about a fixed axis. This
is independent of initial orientation, and thus constitutes a chiral
response for the object. Even though there can be no such chiral response in
the absence of hydrodynamic interactions between the stokeslets, the angular
velocity obtains a fixed, nonzero limit as the stokeslet radius approaches
zero. We characterize empirically how depends on the placement of the
stokeslets, concentrating on three-stokeslet objects with the external force
applied far from the stokeslets. Objects with the largest are aligned
along the forcing direction. In this case, the limiting varies as the
inverse square of the minimum distance between stokeslets. We illustrate the
prevalence of this robust chiral motion with experiments on small macroscopic
objects of arbitrary shape.Comment: 35 pages, 10 figures; Section VII.A redone and other edits made for
clarity. Accepted by Phys. Rev.
Stress condensation in crushed elastic manifolds
We discuss an M-dimensional phantom elastic manifold of linear size L crushed
into a small sphere of radius R << L in N-dimensional space. We investigate the
low elastic energy states of 2-sheets (M=2) and 3-sheets (M=3) using analytic
methods and lattice simulations. When N \geq 2M the curvature energy is
uniformly distributed in the sheet and the strain energy is negligible. But
when N=M+1 and M>1, both energies appear to be condensed into a network of
narrow M-1 dimensional ridges. The ridges appear straight over distances
comparable to the confining radius R.Comment: 4 pages, RevTeX + epsf, 4 figures, Submitted to Phys. Rev. Let
String splitting and strong coupling meson decay
We study the decay of high spin mesons using the gauge/string theory
correspondence. The rate of the process is calculated by studying the splitting
of a macroscopic string intersecting a D-brane. The result is applied to the
decay of mesons in N=4 SYM with a small number of flavors and in a gravity dual
of large N QCD. In QCD the decay of high spin mesons is found to be heavily
suppressed in the regime of validity of the supergravity description.Comment: 17 pages, 2 figures. V2: References added. V3: Minor correction
Low Energy Skyrmion-Skyrmion Scattering
We study the scattering of Skyrmions at low energy and large separation using
the method proposed by Manton of truncation to a finite number of degrees
freedom. We calculate the induced metric on the manifold of the union of
gradient flow curves, which for large separation, to first non-trivial order is
parametrized by the variables of the product ansatz. (presented at the Lake
Louise Winter Institute, 1994)Comment: 6 page
The Semiclassical Limit for and Gauge Theory on the Torus
We prove that for and quantum gauge theory on a torus,
holonomy expectation values with respect to the Yang-Mills measure d\mu_T(\o)
=N_T^{-1}e^{-S_{YM}(\o)/T}[{\cal D}\o] converge, as , to
integrals with respect to a symplectic volume measure on the moduli
space of flat connections on the bundle. These moduli spaces and the symplectic
structures are described explicitly.Comment: 18 page
A class of six-dimensional conformal field theories
We describe a class of six-dimensional conformal field theories that have
some properties in common with and possibly are related to a subsector of the
tensionless string theories. The latter theories can for example give rise to
four-dimensional superconformal Yang-Mills theories upon
compactification on a two-torus. Just like the tensionless string theories, our
theories have an -classification, but no other discrete or continuous
parameters. The Hilbert space carries an irreducible representation of the same
Heisenberg group that appears in the tensionless string theories, and the
`Wilson surface' observables obey the same superselection rules. When
compactified on a two-torus, they have the same behaviour under -duality as
super Yang-Mills theory. Our theories are natural generalizations of the
two-form with self-dual field strength that is part of the world-volume theory
of a single five-brane in -theory, and the theory can in fact be
seen as arising from non-interacting chiral two-forms by factoring out the
collective `center of mass' degrees of freedom.Comment: 8 pages. More pedagogical presentation, added section on relationship
to d = 4 Yang-Mills theor
Lineal gravity from planar gravity
We show how to obtain the two-dimensional black hole action by dimensional
reduction of the three-dimensional Einstein action with a non-zero cosmological
constant. Starting from the Chern-Simons formulation of 2+1 gravity, we obtain
the 1+1 dimensional gauge formulation given by Verlinde. Remarkably, the
proposed reduction shares the relevant features of the formulation of Cangemi
and Jackiw, without the need for a central charge in the algebra. We show how
the Lagrange multipliersin these formulations appear naturally as the remnants
of the three dimensional connection associated to symmetries that have been
lostin the dimensional reduction. The proposed dimensional reduction involves a
shift in the three dimensional connection whose effect is to make the length of
the extra dimension infinite.Comment: 13 pages, plain Te
A note on M(atrix) theory in seven dimensions with eight supercharges
We consider M(atrix) theory compactifications to seven dimensions with eight
unbroken supersymmetries. We conjecture that both M(atrix) theory on K3 and
Heterotic M(atrix) theory on T^3 are described by the same 5+1 dimensional
theory with N=2 supersymmetry which is broken to N=1 by the base space. The
emergence of the extra dimension follows from a recent result of
Rozali[hep-th/9702136]. We show that the seven dimensional duality between
M-theory on K3 and Heterotic string theory on T^3 is realised in M(atrix)
theory as the exchange of one of the dimensions with this new dimension.Comment: RevTeX, 8 pages, version to appear in journa
Non-Renormalization Theorems in Non-Renormalizable Theories
A perturbative non-renormalization theorem is presented that applies to
general supersymmetric theories, including non-renormalizable theories in which
the integrand is an arbitrary gauge-invariant function
of the chiral superfields and gauge field-strength
superfields , and the -integrand is restricted only by gauge
invariance. In the Wilsonian Lagrangian, is unrenormalized except
for the one-loop renormalization of the gauge coupling parameter, and
Fayet-Iliopoulos terms can be renormalized only by one-loop graphs, which
cancel if the sum of the U(1) charges of the chiral superfields vanishes. One
consequence of this theorem is that in non-renormalizable as well as
renormalizable theories, in the absence of Fayet-Iliopoulos terms supersymmetry
will be unbroken to all orders if the bare superpotential has a stationary
point.Comment: 13 pages (including title page), no figures. Vanilla LaTe
On a Modification of the Boundary State Formalism in Off-shell String Theory
We examine the application of boundary states in computing amplitudes in
off-shell open string theory. We find a straightforward generalization of
boundary state which produces the correct matrix elements with on-shell closed
string states.Comment: Latex, 10 pages, refs added, minor typos correcte
- …