3,726 research outputs found
M-theory from the superpoint
The “brane scan” classifies consistent Green–Schwarz strings and membranes in terms of the invariant cocycles on super Minkowski spacetimes. The “brane bouquet” generalizes this by consecutively forming the invariant higher central extensions induced by these cocycles, which yields the complete fundamental brane content of string/M-theory, including the D-branes and the M5-brane, as well as the various duality relations between these. This raises the question whether the super Minkowski spacetimes themselves arise as maximal invariant central extensions. Here, we prove that they do. Starting from the simplest possible super Minkowski spacetime, the superpoint, which has no Lorentz structure and no spinorial structure, we give a systematic process of consecutive “maximal invariant central extensions” and show that it discovers the super Minkowski spacetimes that contain superstrings, culminating in the 10- and 11-dimensional super Minkowski spacetimes of string/M-theory and leading directly to the brane bouquet
DDF and Pohlmeyer invariants of (super)string
We show how the Pohlmeyer invariants of the bosonic string are expressible in
terms of DDF invariants. Quantization of the DDF observables in the usual way
yields a consistent quantization of the algebra of Pohlmeyer invariants.
Furthermore it becomes straightforward to generalize the Pohlmeyer invariants
to the superstring as well as to all backgrounds which allow a free field
realization of the worldsheet theory.Comment: 17 pp, minor typos corrected, references to papers by Isaev and
Borodulin added, which contain essentially the same results as reported her
A laser gyroscope system to detect the Gravito-Magnetic effect on Earth
Large scale square ring laser gyros with a length of four meters on each side
are approaching a sensitivity of 1x10^-11 rad/s/sqrt(Hz). This is about the
regime required to measure the gravitomagnetic effect (Lense Thirring) of the
Earth. For an ensemble of linearly independent gyros each measurement signal
depends upon the orientation of each single axis gyro with respect to the
rotational axis of the Earth. Therefore at least 3 gyros are necessary to
reconstruct the complete angular orientation of the apparatus. In general, the
setup consists of several laser gyroscopes (we would prefer more than 3 for
sufficient redundancy), rigidly referenced to each other. Adding more gyros for
one plane of observation provides a cross-check against intra-system biases and
furthermore has the advantage of improving the signal to noise ratio by the
square root of the number of gyros. In this paper we analyze a system of two
pairs of identical gyros (twins) with a slightly different orientation with
respect to the Earth axis. The twin gyro configuration has several interesting
properties. The relative angle can be controlled and provides a useful null
measurement. A quadruple twin system could reach a 1% sensitivity after 3:2
years of data, provided each square ring has 6 m length on a side, the system
is shot noise limited and there is no source for 1/f- noise.Comment: 9 pages, 6 figures. 2010 Honourable mention of the Gravity Research
Foundation; to be published on J. Mod. Phys.
Temperature-Dependent Cathodoluminescence Spectroscopy and Microscopy as a Tool for Defect Identification in Semiconducting Ceramics: Application to BaTiO3 Ceramics
Cathodoluminescence (CL) spectroscopy and microscopy were applied to investigate the characteristic grain-boundary contrast in semiconducting ferroelectric BaTiO3 ceramics. It was shown, that chemically clean grain boundaries do not reveal any specific CL components neither in the visible nor in the infrared part of the spectrum. Instead, the contrast arises from at least two different non-radiative recombination centers present in the grain and the grain-boundary zones, respectively. Activation thresholds for these centers were determined from the temperature dependence of the integral CL signal down to 30K. The different values found explain the contrast reversal observed in BaTiO3 ceramics upon cooling. Starting from a consideration of the defect equilibria present in the samples after selected treatment cycles, we could attribute the non-radiative recombination centers to oxygen vacancies
A 1.82 m^2 ring laser gyroscope for nano-rotational motion sensing
We present a fully active-controlled He-Ne ring laser gyroscope, operating in
square cavity 1.35 m in side. The apparatus is designed to provide a very low
mechanical and thermal drift of the ring cavity geometry and is conceived to be
operative in two different orientations of the laser plane, in order to detect
rotations around the vertical or the horizontal direction. Since June 2010 the
system is active inside the Virgo interferometer central area with the aim of
performing high sensitivity measurements of environmental rotational noise. So
far, continuous not attempted operation of the gyroscope has been longer than
30 days. The main characteristics of the laser, the active remote-controlled
stabilization systems and the data acquisition techniques are presented. An
off-line data processing, supported by a simple model of the sensor, is shown
to improve the effective long term stability. A rotational sensitivity at the
level of ten nanoradiants per squareroot of Hz below 1 Hz, very close to the
required specification for the improvement of the Virgo suspension control
system, is demonstrated for the configuration where the laser plane is
horizontal
Principal 2-bundles and their gauge 2-groups
In this paper we introduce principal 2-bundles and show how they are
classified by non-abelian Cech cohomology. Moreover, we show that their gauge
2-groups can be described by 2-group-valued functors, much like in classical
bundle theory. Using this, we show that, under some mild requirements, these
gauge 2-groups possess a natural smooth structure. In the last section we
provide some explicit examples.Comment: 40 pages; v3: completely revised and extended, classification
corrected, name changed, to appear in Forum Mat
Selfdual strings and loop space Nahm equations
We give two independent arguments why the classical membrane fields should be
loops. The first argument comes from how we may construct selfdual strings in
the M5 brane from a loop space version of the Nahm equations. The second
argument is that there appears to be no infinite set of finite-dimensional Lie
algebras (such as for any ) that satisfies the algebraic structure
of the membrane theory.Comment: 28 pages, various additional comment
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