547 research outputs found
Conformal Invariance and Duality in Self-Dual Gravity and (2,1) Heterotic String Theory
A system of gravity coupled to a 2-form gauge field, a dilaton and Yang-Mills
fields in dimensions arises from the (2,1) sigma model or string. The
field equations imply that the curvature with torsion and Yang-Mills field
strength are self-dual in four dimensions, or satisfy generalised self-duality
equations in dimensions. The Born-Infeld-type action describing this
system is simplified using an auxiliary metric and shown to be classically Weyl
invariant only in four dimensions. A dual form of the action is found (no
isometries are required). In four dimensions, the dual geometry is self-dual
gravity without torsion coupled to a scalar field. In dimensions, the
dual geometry is hermitian and determined by a form potential ,
generalising the K\"{a}hler potential of the four dimensional case, with the
fundamental 2-form given by . The
coupling to Yang-Mills is through a term and leads to
a Uhlenbeck-Yau field equation .Comment: LaTeX, 14 pages, no figures. One reference added and interpretation
revised; version to appear in Physics Letters
Einstein Supergravity and New Twistor String Theories
A family of new twistor string theories is constructed and shown to be free
from world-sheet anomalies. The spectra in space-time are calculated and shown
to give Einstein supergravities with second order field equations instead of
the higher derivative conformal supergravities that arose from earlier twistor
strings. The theories include one with the spectrum of N=8 supergravity,
another with the spectrum of N=4 supergravity coupled to N=4 super-Yang-Mills,
and a family with supersymmetries with the spectra of self-dual
supergravity coupled to self-dual super-Yang-Mills. The non-supersymmetric
string with N=0 gives self-dual gravity coupled to self-dual Yang-Mills and a
scalar. A three-graviton amplitude is calculated for the N=8 and N=4 theories
and shown to give a result consistent with the cubic interaction of Einstein
supergravity.Comment: LaTeX, 69 pages, no figures; v2: minor corrections made, footnotes
and references adde
Application of olive mill waste-based biochar for improving wheat response to salt stress
The production of olive mill solid waste (OMSW) raises concerns due to its toxicity and negative environmental impact. However, by utilizing pyrolysis, OMSW can be converted into biochar, a carbon-rich material that detoxifies the waste and preserves its nutrient content. The OMSW-based biochar possesses alkaline properties (pH 9.6), low electrical conductivity (EC), high cation exchange capacity (CEC), a porous surface morphology, various surface functional groups, and high mineral content. This study assessed the influence of two concentrations (5% and 10%) of OMSW-based biochar on wheat plants' growth biomarkers and physiological characteristics subjected to salt stress conditions (150 mM NaCl). Findings of the study revealed that salt stress had deleterious effects on various parameters, including shoot height, fresh and dry weights of shoots and roots, relative water content (RWC%), membrane stability index (MSI%), photosynthetic pigments, and photosynthetic parameters such as the coefficient of the effective quantum yield of photochemical energy conversion of PSII (ĂPSII), photochemical quenching (qP), and photochemical efficiency of PSII (Fo, Fm, Fv/Fo, and Fv/Fm). Furthermore, the levels of lipid peroxidation (MDA), hydrogen peroxide (H2O2), superoxide dismutase (SOD), and peroxidase (POD) activities significantly increased in stressed plants. On the other hand, applying both concentrations of OMSW-based biochar effectively improved the overall performance of wheat plants, irrespective of the presence of salinity. OMSW-based biochar is a promising strategy for promoting wheat growth in salt-stressed soil by improving various growth parameters and mitigating plant oxidative stress
Sigma models with non-commuting complex structures and extended supersymmetry
We discuss additional supersymmetries for N = (2, 2) supersymmetric
non-linear sigma models described by left and right semichiral superfields.Comment: 11 pages. Talk presented by U.L. at "30th Winter School on Geometry
and Physics" Srni, Czech Republic January 2010
The Wall Properties Effect on Peristaltic Transport of Micropolar Non-Newtonian Fluid with Heat and Mass Transfer
The problem of the unsteady peristaltic mechanism with heat and mass transfer of an incompressible micropolar non-Newtonian fluid in a two-dimensional channel. The flow includes the viscoelastic wall properties and micropolar fluid parameters using the equations of the fluid as well as of the deformable boundaries. A perturbation solution is obtained, which satisfies the momentum, angular momentum, energy, and concentration equations for case of free pumping (original stationary fluid). Numerical results for the stream function, temperature, and concentration distributions are obtained. Several graphs of physical interest are displayed and discussed
The Gauged (2,1) Heterotic Sigma-Model
The geometry of (2,1) supersymmetric sigma-models with isometry symmetries is
discussed. The gauging of such symmetries in superspace is then studied. We
find that the coupling to the (2,1) Yang-Mills supermultiplet can be achieved
provided certain geometric conditions are satisfied. We construct the general
gauged action, using an auxiliary vector to generate the full non-polynomial
structure.Comment: LaTeX, 25 pages, no figures; version to appear in Nuclear Physics
Geometric Actions for D-Branes and M-Branes
New forms of Born-Infeld, D-brane and M theory five-brane actions are found
which are quadratic in the abelian field strength. The gauge fields couple both
to a background or induced metric and a new auxiliary metric, whose elimination
reproduces the non-polynomial Born-Infeld action. This is similar to the
introduction of an auxiliary metric to simplify the Nambu-Goto string action.
This simplifies the quantisation and dualisation of the gauge fields.Comment: LaTeX, 9 pages, no figures. Minor corrections; version to appear in
Physics Letters
T-Duality in Superspace
We find the T-duality transformation rules for 2-dimensional (2,1)
supersymmetric sigma-models in (2,1) superspace. Our results clarify certain
aspects of the (2,1) sigma model geometry relevant to the discussion of
T-duality. The complexified duality transformations we find are equivalent to
the usual Buscher duality transformations (including an important refinement)
together with diffeomorphisms. We use the gauging of sigma-models in (2,1)
superspace, which we review and develop, finding a manifestly real and
geometric expression for the gauged action. We discuss the obstructions to
gauging (2,1) sigma-models, and find that the obstructions to (2,1) T-duality
are considerably weaker.Comment: 45 pages, Minor Correction
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