1,010 research outputs found
Toxin production in nodularia spumigena : effects of salinity, phosphorus, nitrate and light
Point-Like Graviton Scattering in Plane-Wave Matrix Model
In a plane-wave matrix model we discuss a two-body scattering of gravitons in
the SO(3) symmetric space. In this case the graviton solutions are point-like
in contrast to the scattering in the SO(6) symmetric space where spherical
membranes are interpreted as gravitons. We concentrate on a configuration in
the 1-2 plane where a graviton rotates with a constant radius and the other one
elliptically rotates. Then the one-loop effective action is computed by using
the background field method. As the result, we obtain the 1/r^7-type
interaction potential, which strongly suggests that the scattering in the
matrix model would be closely related to that in the light-front
eleven-dimensional supergravity.Comment: 17 pages, 1 figure, LaTeX, v2) references adde
Analytical solution of generalized Burton--Cabrera--Frank equations for growth and post--growth equilibration on vicinal surfaces
We investigate growth on vicinal surfaces by molecular beam epitaxy making
use of a generalized Burton--Cabrera--Frank model. Our primary aim is to
propose and implement a novel analytical program based on a perturbative
solution of the non--linear equations describing the coupled adatom and dimer
kinetics. These equations are considered as originating from a fully
microscopic description that allows the step boundary conditions to be directly
formulated in terms of the sticking coefficients at each step. As an example,
we study the importance of diffusion barriers for adatoms hopping down
descending steps (Schwoebel effect) during growth and post-growth equilibration
of the surface.Comment: 16 pages, REVTeX 3.0, IC-DDV-94-00
A Charged Rotating Black Ring
We construct a supergravity solution describing a charged rotating black ring
with S^2xS^1 horizon in a five dimensional asymptotically flat spacetime. In
the neutral limit the solution is the rotating black ring recently found by
Emparan and Reall. We determine the exact value of the lower bound on J^2/M^3,
where J is the angular momentum and M the mass; the black ring saturating this
bound has maximum entropy for the given mass. The charged black ring is
characterized by mass M, angular momentum J, and electric charge Q, and it also
carries local fundamental string charge. The electric charge distributed
uniformly along the ring helps support the ring against its gravitational
self-attraction, so that J^2/M^3 can be made arbitrarily small while Q/M
remains finite. The charged black ring has an extremal limit in which the
horizon coincides with the singularity.Comment: 25 pages, 1 figur
Quadrupole Instabilities of Relativistic Rotating Membranes
We generalize recent study of the stability of isotropic (spherical) rotating
membranes to the anisotropic ellipsoidal membrane. We find that while the
stability persists for deformations of spin , the quadrupole and higher
spin deformations () lead to instabilities. We find the relevant
instability modes and the corresponding eigenvalues. These indicate that the
ellipsoidal rotating membranes generically decay into finger-like
configurations.Comment: 5 pages, 1 figur
Orbit spaces of free involutions on the product of two projective spaces
Let be a finitistic space having the mod 2 cohomology algebra of the
product of two projective spaces. We study free involutions on and
determine the possible mod 2 cohomology algebra of orbit space of any free
involution, using the Leray spectral sequence associated to the Borel fibration
. We also
give an application of our result to show that if has the mod 2 cohomology
algebra of the product of two real projective spaces (respectively complex
projective spaces), then there does not exist any -equivariant
map from for (respectively ), where
is equipped with the antipodal involution.Comment: 14 pages, to appear in Results in Mathematic
D-Brane Chemistry
We study several different kinds of bound states built from D-branes and
orientifolds. These states are to atoms what branonium - the bound state of a
brane and its anti-brane - is to positronium, inasmuch as they typically
involve a light brane bound to a much heavier object with conserved charges
which forbid the system's decay. We find the fully relativistic motion of a
probe Dp'-brane in the presence of source Dp-branes is integrable by
quadratures. Keplerian conic sections are obtained for special choices for p
and p' and the systems are shown to be equivalent to nonrelativistic systems.
Their quantum behaviour is also equivalent to the corresponding
non-relativistic limit. In particular the p=6, p'=0 case is equivalent to a
non-relativistic dyon in a magnetic monopole background, with the trajectories
in the surface of a cone. We also show that the motion of the probe branes
about D6-branes in IIA theory is equivalent to the motion of the corresponding
probes in the uplift to M-theory in 11 dimensions, for which there are no
D6-branes but their fields are replaced by a particular Taub-NUT geometry. We
further discuss the interactions of D-branes and orientifold planes having the
same dimension. this system behaves at large distances as a brane-brane system
but at shorter distances it does not have the tachyon instability.Comment: ref. added and typos correcte
Relating branes and matrices
We construct a general map between a Dp-brane with magnetic flux and a matrix
configuration of D0-branes, by showing how one can rewrite the boundary state
of the Dp-brane in terms of its D0-brane constituents. This map gives a simple
prescription for constructing the matrices of fuzzy spaces corresponding to
branes of arbitrary shape and topology. Since we explicitly identify the
D0-brane degrees of freedom on the brane, we also derive the D0-brane charge of
the brane in a very direct way including the A-genus term. As a check on our
formalism, we use our map to derive the abelian-Born-Infeld equations of motion
from the action of the D0-brane matrices.Comment: 28 pages, Late
Black Rings, Supertubes, and a Stringy Resolution of Black Hole Non-Uniqueness
In order to address the issues raised by the recent discovery of
non-uniqueness of black holes in five dimensions, we construct a solution of
string theory at low energies describing a five-dimensional spinning black ring
with three charges that can be interpreted as D1-brane, D5-brane, and momentum
charges. The solution possesses closed timelike curves (CTCs) and other
pathologies, whose origin we clarify. These pathologies can be avoided by
setting any one of the charges, e.g. the momentum, to zero. We argue that the
D1-D5-charged black ring, lifted to six dimensions, describes the thermal
excitation of a supersymmetric D1-D5 supertube, which is in the same U-duality
class as the D0-F1 supertube. We explain how the stringy microscopic
description of the D1-D5 system distinguishes between a spherical black hole
and a black ring with the same asymptotic charges, and therefore provides a
(partial) resolution of the non-uniqueness of black holes in five dimensions.Comment: 33 pages, 1 figur
Fuzzy Sphere Dynamics and Non-Abelian DBI in Curved Backgrounds
We consider the non-Abelian action for the dynamics of -branes in the
background of -branes, which parameterises a fuzzy sphere using the SU(2)
algebra. We find that the curved background leads to collapsing solutions for
the fuzzy sphere except when we have branes in the background, which
is a realisation of the gravitational Myers effect. Furthermore we find the
equations of motion in the Abelian and non-Abelian theories are identical in
the large limit. By picking a specific ansatz we find that we can
incorporate angular momentum into the action, although this imposes restriction
upon the dimensionality of the background solutions. We also consider the case
of non-Abelian non-BPS branes, and examine the resultant dynamics using
world-volume symmetry transformations. We find that the fuzzy sphere always
collapses but the solutions are sensitive to the combination of the two
conserved charges and we can find expanding solutions with turning points. We
go on to consider the coincident 5-brane background, and again construct
the non-Abelian theory for both BPS and non-BPS branes. In the latter case we
must use symmetry arguments to find additional conserved charges on the
world-volumes to solve the equations of motion. We find that in the Non-BPS
case there is a turning solution for specific regions of the tachyon and radion
fields. Finally we investigate the more general dynamics of fuzzy
in the -brane background, and find collapsing solutions
in all cases.Comment: 49 pages, 3 figures, Latex; Version to appear in JHE
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