9,061 research outputs found
Competitive interference of plant species in monocultures and mixed stands
A dynamic model is presented for calculating the dry matter yields of individual plant species in a mixed stand by means of parameters derived from a spacing experiment with species grown at 2 densities and harvested at regular intervals. Results are given of trials with different crops, including tall and dwarf peas. The model is intended for use under conditions of near-optimum supply of water and nutrients, where the principal competition is for light. A simple method for measuring relative light interception by species in mixed stands is also described
Principles of measuring crop losses in competitive situations with particular reference to weeds
On BPS bounds in D=4 N=2 gauged supergravity II: general matter couplings and black hole masses
We continue the analysis of BPS bounds started in arXiv:1110.2688, extending
it to the full class of N=2 gauged supergravity theories with arbitrary vector
and hypermultiplets. We derive the general form of the asymptotic charges for
asymptotically flat (M_4), anti-de Sitter (AdS_4), and magnetic anti-de Sitter
(mAdS_4) spacetimes. Some particular examples from black hole physics are given
to explicitly demonstrate how AdS and mAdS masses differ when solutions with
non-trivial scalar profiles are considered.Comment: 21 pages; v2 added reference, published version; v3 minor correction
The Gaugings of Maximal D=6 Supergravity
We construct the most general gaugings of the maximal D=6 supergravity. The
theory is (2,2) supersymmetric, and possesses an on-shell SO(5,5) duality
symmetry which plays a key role in determining its couplings. The field content
includes 16 vector fields that carry a chiral spinor representation of the
duality group. We utilize the embedding tensor method which determines the
appropriate combinations of these vectors that participate in gauging of a
suitable subgroup of SO(5,5). The construction also introduces the magnetic
duals of the 5 two-form potentials and 16 vector fields.Comment: 34 pages, latex, reference added, typo's corrected and minor
improvements mad
Consistent truncation of d = 11 supergravity on AdS_4 x S^7
We study the system of equations derived twenty five years ago by B. de Wit
and the first author [Nucl. Phys. B281 (1987) 211] as conditions for the
consistent truncation of eleven-dimensional supergravity on AdS_4 x S^7 to
gauged N = 8 supergravity in four dimensions. By exploiting the E_7(7)
symmetry, we determine the most general solution to this system at each point
on the coset space E_7(7)/SU(8). We show that invariants of the general
solution are given by the fluxes in eleven-dimensional supergravity. This
allows us to both clarify the explicit non-linear ansatze for the fluxes given
previously and to fill a gap in the original proof of the consistent
truncation. These results are illustrated with several examples.Comment: 41 pages, typos corrected, published versio
String Amplitudes and N=2, d=4 Prepotential in Heterotic K3 x T^2 Compactifications
For the gauge couplings, which arise after toroidal compactification of
six-dimensional heterotic N=1 string theories from the T^2 torus, we calculate
their one-loop corrections. This is performed by considering string amplitudes
involving two gauge fields and moduli fields. We compare our results with the
equations following from N=2 special geometry and the underlying prepotential
of the theory. Moreover we find relations between derivatives of the N=2, d=4
prepotential and world-sheet tau-integrals which appear in various string
amplitudes of any T^2-compactification.Comment: 28 TeX pages, uses harvmac, Final Version to appear in NP
A dynamical symmetry for supermembranes
A dynamical symmetry for supersymmetric extended objects is given.Comment: 3 page
M Theory As A Matrix Model: A Conjecture
We suggest and motivate a precise equivalence between uncompactified eleven
dimensional M-theory and the N = infinity limit of the supersymmetric matrix
quantum mechanics describing D0-branes. The evidence for the conjecture
consists of several correspondences between the two theories. As a consequence
of supersymmetry the simple matrix model is rich enough to describe the
properties of the entire Fock space of massless well separated particles of the
supergravity theory. In one particular kinematic situation the leading large
distance interaction of these particles is exactly described by supergravity .
The model appears to be a nonperturbative realization of the holographic
principle. The membrane states required by M-theory are contained as
excitations of the matrix model. The membrane world volume is a noncommutative
geometry embedded in a noncommutative spacetime.Comment: Typo and tex error corrected. 41 pages, harvma
The Hypermultiplet with Heisenberg Isometry in N=2 Global and Local Supersymmetry
The string coupling of N=2 supersymmetric compactifications of type II string
theory on a Calabi-Yau manifold belongs to the so-called universal dilaton
hypermultiplet, that has four real scalars living on a quaternion-Kaehler
manifold. Requiring Heisenberg symmetry, which is a maximal subgroup of
perturbative isometries, reduces the possible manifolds to a one-parameter
family that describes the tree-level effective action deformed by the only
possible perturbative correction arising at one-loop level. A similar argument
can be made at the level of global supersymmetry where the scalar manifold is
hyper-Kaehler. In this work, the connection between global and local
supersymmetry is explicitly constructed, providing a non-trivial gravity
decoupled limit of type II strings already in perturbation theory.Comment: 24 page
Electric and magnetic charges in N=2 conformal supergravity theories
General Lagrangians are constructed for N=2 conformal supergravity theories
in four space-time dimensions involving gauge groups with abelian and/or
non-abelian electric and magnetic charges. The charges are encoded in the gauge
group embedding tensor. The scalar potential induced by the gauge interactions
is quadratic in this tensor, and, when the embedding tensor is treated as a
spurionic quantity, it is formally covariant with respect to electric/magnetic
duality. This work establishes a general framework for studying any deformation
induced by gauge interactions of matter-coupled N=2 supergravity theories. As
an application, full and residual supersymmetry realizations in maximally
symmetric space-times are reviewed. Furthermore, a general classification is
presented of supersymmetric solutions in
space-times. As it turns out, these solutions allow either eight or four
supersymmetries. With four supersymmetries, the spinorial parameters are
Killing spinors of that are constant on , so that they
carry no spin, while the bosonic background is rotationally invariant.Comment: 49 pages, typos correcte
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