3,245 research outputs found
Symmetric Vacua in Heterotic M-Theory
Symmetric vacua of heterotic M-theory, characterized by vanishing cohomology
classes of individual sources in the three-form Bianchi identity, are analyzed
on smooth Calabi-Yau three-folds. We show that such vacua do not exist for
elliptically fibered Calabi-Yau spaces. However, explicit examples are found
for Calabi-Yau three-folds arising as intersections in both unweighted and
weighted projective space. We show that such symmetric vacua can be combined
with attractive phenomenological features such as three generations of quarks
and leptons. Properties of the low energy effective actions associated with
symmetric vacua are discussed. In particular, the gauge kinetic functions
receive no perturbative threshold corrections, there are no corrections to the
matter field Kahler metric and the associated five-dimensional effective theory
admits flat space as its vacuum.Comment: 22 pages, Late
Flux, Gaugino Condensation and Anti-Branes in Heterotic M-theory
We present the potential energy due to flux and gaugino condensation in
heterotic M-theory compactifications with anti-branes in the vacuum. For
reasons which we explain in detail, the contributions to the potential due to
flux are not modified from those in supersymmetric contexts. The discussion of
gaugino condensation is, however, changed by the presence of anti-branes. We
show how a careful microscopic analysis of the system allows us to use standard
results in supersymmetric gauge theory in describing such effects - despite the
explicit supersymmetry breaking which is present. Not surprisingly, the
significant effect of anti-branes on the threshold corrections to the gauge
kinetic functions greatly alters the potential energy terms arising from
gaugino condensation.Comment: 40 pages, 1 figur
Algorithmic Algebraic Geometry and Flux Vacua
We develop a new and efficient method to systematically analyse four
dimensional effective supergravities which descend from flux compactifications.
The issue of finding vacua of such systems, both supersymmetric and
non-supersymmetric, is mapped into a problem in computational algebraic
geometry. Using recent developments in computer algebra, the problem can then
be rapidly dealt with in a completely algorithmic fashion. Two main results are
(1) a procedure for calculating constraints which the flux parameters must
satisfy in these models if any given type of vacuum is to exist; (2) a stepwise
process for finding all of the isolated vacua of such systems and their
physical properties. We illustrate our discussion with several concrete
examples, some of which have eluded conventional methods so far.Comment: 41 pages, 4 figure
U-duality Covariant M-theory Cosmology
A manifestly U-duality covariant approach to M-theory cosmology is developed
and applied to cosmologies in dimensions D=4,5. Cosmological properties such as
expansion powers and Hubble parameters turn out to be U-duality invariant in
certain asymptotic regions. U-duality transformations acting on cosmological
solutions, on the other hand, shift the transition time between two asymptotic
regions and determine the details of the transition. Moreover, in D=5, we show
that U-duality can map expanding negative and positive branch solutions into
each other.Comment: 18 pages, LATEX, 1 Postscript figure include
Monitoring Radiation Damage in the ATLAS Pixel Detector
Radiation hardness is one of the most important features of the ATLAS pixel detector in order to ensure a good performance and a long lifetime. Monitoring of radiation damage is crucial in order to assess and predict the expected performance of the detector. Key values for the assessment of radiation damage in silicon, such as the depletion voltage and depletion depth in the sensors, are measured on a regular basis during operations. This thesis summarises the monitoring program that is conducted in order to assess the impact of radiation damage and compares it to model predictions.
In addition, the physics performance of the ATLAS detector highly depends on the amount of disabled modules in the ATLAS pixel detector. A worrying amount of module failures was observed during run I. Thus it was decided to recover repairable modules during the long shutdown (LS1) by extracting the pixel detector. The impact of the module repairs and module failures on the detector performance is analysed in this thesis
magnum.fe: A micromagnetic finite-element simulation code based on FEniCS
We have developed a finite-element micromagnetic simulation code based on the
FEniCS package called magnum.fe. Here we describe the numerical methods that
are applied as well as their implementation with FEniCS. We apply a
transformation method for the solution of the demagnetization-field problem. A
semi-implicit weak formulation is used for the integration of the
Landau-Lifshitz-Gilbert equation. Numerical experiments show the validity of
simulation results. magnum.fe is open source and well documented. The broad
feature range of the FEniCS package makes magnum.fe a good choice for the
implementation of novel micromagnetic finite-element algorithms
The Isometries of Low-Energy Heterotic M-Theory
We study the effective D=4, N=1 supergravity description of five-dimensional
heterotic M-theory in the presence of an M5 brane, and derive the Killing
vectors and isometry group for the Kahler moduli-space metric. The group is
found to be a non-semisimple maximal parabolic subgroup of Sp(4,R), containing
a non-trivial SL(2,R) factor. The underlying moduli-space is then naturally
realised as the group space Sp(4,R)/U(2), but equipped with a nonhomogeneous
metric that is invariant only under that maximal parabolic group. This
nonhomogeneous metric space can also be derived via field truncations and
identifications performed on Sp(8,R)/U(4) with its standard homogeneous metric.
In a companion paper we use these symmetries to derive new cosmological
solutions from known ones.Comment: 11 pages, 1 table; two foonotes added, minor corrections to conten
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