10,375 research outputs found
Non-Commutative Geometry from Strings
To appear in Encyclopedia of Mathematical Physics, J.-P. Fran\c{c}oise, G.
Naber and T.S. Tsou, eds., Elsevier, 2006. The article surveys the modern
developments of noncommutative geometry in string theory.Comment: 26 pages, no figures. To appear in the Elsevier Encyclopedia of
Mathematical Physics. This web version has a more comprehensive list of
references. Comments and corrections welcome. v2: Typos corrected, references
and some comments added. v3: 27 pages. more references and Comments added.
v4: references added. Final versio
On Non-Abelian Structure From Matrix Coordinates
We consider the matrix quantum mechanics of N D0-branes in the background of
the 1-form RR field. It is observed that the transformations of matrix
coordinates of D0-branes induce on the Abelian RR field symmetry
transformations that are like those of non-Abelian gauge fields. The
Lorentz-like equations of motion for matrix coordinates are derived. The field
strengths appearing in the Lorentz-like equations transform in the adjoint
representation of U(N) under symmetry transformations. A possible relation
between D0-brane dynamics in RR background, and the semi-classical dynamics of
charged particles in Yang-Mills background is mentioned.Comment: 12 pages, no figures, LaTeX. v2: typos fixed, to appear in Phys.
Lett.
Matrix Strings in Weakly Curved Background Fields
We investigate further the recent proposal for the form of the Matrix theory
action in weak background fields. We perform DVV reduction to the multiple
D0-brane action in order to find the Matrix string theory action for multiple
fundamental strings in curved but weak NS-NS and R-R backgrounds. This matrix
sigma model gives a definite prescription on how to deal with R-R fields with
an explicit spacetime dependence in Type II string theory. We do this both via
the 9-11 flip and the chain of T and S dualities, and further check on their
equivalence explicitly. In order to do so, we also discuss the implementation
of S-duality in the operators of the 2-dimensional world-volume supersymmetric
gauge theory describing the Type IIB D-string. We compare the result to the
known Green-Schwarz sigma model action (for one string), and use this
comparison in order to discuss about possible, non-linear background curvature
corrections to the Matrix string action (involving many strings), and therefore
to the Matrix theory action. We illustrate the nonabelian character of our
action with an example involving multiple fundamental strings in a non-trivial
R-R flux, where the strings are polarized into a noncommutative configuration.
This corresponds to a dielectric type of effect on fundamental strings.Comment: 46 pages, Latex; v2: added 3 refs and 1 commen
Evidence for a gravitational Myers effect
An indication for the existence of a collective Myers solution in the
non-abelian D0-brane Born-Infeld action is the presence of a tachyonic mode in
fluctuations around the standard diagonal background. We show that this
computation for non-abelian D0-branes in curved space has the geometric
interpretation of computing the eigenvalues of the geodesic deviation operator
for U(N)-valued coordinates. On general grounds one therefore expects a
geometric Myers effect in regions of sufficiently negative curvature. We
confirm this by explicit computations for non-abelian D0-branes on a sphere and
a hyperboloid. For the former the diagonal solution is stable, but not so for
the latter. We conclude by showing that near the horizon of a Schwarzschild
black hole one also finds a tachyonic mode in the fluctuation spectrum,
signaling the possibility of a near-horizon gravitationally induced Myers
effect.Comment: LaTeX, 23 page
THE INFLUENCE OF TECHNOLOGICAL PROGRESS ON THE LONG RUN FARM LEVEL ECONOMICS OF SOIL CONSERVATION
The complementary interaction between topsoil depth and technical progress for winter wheat in the Palouse region was found to strengthen the long run payoff to conservation tillage. Nonetheless, conservation tillage was found to be competitive with conventional tillage only if its current yield disadvantages were eliminated. Conservation tillage was relatively more competitive on shallower topsoils and for longer planning horizons. Short-term subsidies coupled with research directed towards reducing the cost and yield disadvantages of conservation tillage in the Palouse were advocated to maintain long-term soil productivity.Land Economics/Use, Research and Development/Tech Change/Emerging Technologies,
Issues in M(atrix) Theory Compactification
We discuss issues concerning M(atrix) theory compactifications on curved
spaces. We argue from the form of the graviton propagator on curved space that
excited string states do not decouple from the annulus D0-brane
amplitude, unlike the flat space case. This argument shows that a large class
of quantum mechanical systems with a finite number of degrees of freedom cannot
reproduce supergravity answers. We discuss the specific example of an ALE space
and suggest sources of possible higher derivative terms that might help
reproduce supergravity results.Comment: title modified, references corrected, 11 pages, harvma
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