9,777 research outputs found
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
STRINGVACUA: A Mathematica Package for Studying Vacuum Configurations in String Phenomenology
We give a simple tutorial introduction to the Mathematica package
STRINGVACUA, which is designed to find vacua of string-derived or inspired
four-dimensional N=1 supergravities. The package uses powerful
algebro-geometric methods, as implemented in the free computer algebra system
Singular, but requires no knowledge of the mathematics upon which it is based.
A series of easy-to-use Mathematica modules are provided which can be used both
in string theory and in more general applications requiring fast polynomial
computations. The use of these modules is illustrated throughout with simple
examples.Comment: 21 pages, 9 figure
Exploring the Vacuum Geometry of N=1 Gauge Theories
Using techniques of algorithmic algebraic geometry, we present a new and
efficient method for explicitly computing the vacuum space of N=1 gauge
theories. We emphasize the importance of finding special geometric properties
of these spaces in connecting phenomenology to guiding principles descending
from high-energy physics. We exemplify the method by addressing various
subsectors of the MSSM. In particular the geometry of the vacuum space of
electroweak theory is described in detail, with and without right-handed
neutrinos. We discuss the impact of our method on the search for evidence of
underlying physics at a higher energy. Finally we describe how our results can
be used to rule out certain top-down constructions of electroweak physics.Comment: 35 pages, 2 figures, LaTe
Exploring Positive Monad Bundles And A New Heterotic Standard Model
A complete analysis of all heterotic Calabi-Yau compactifications based on
positive two-term monad bundles over favourable complete intersection
Calabi-Yau threefolds is performed. We show that the original data set of about
7000 models contains 91 standard-like models which we describe in detail. A
closer analysis of Wilson-line breaking for these models reveals that none of
them gives rise to precisely the matter field content of the standard model. We
conclude that the entire set of positive two-term monads on complete
intersection Calabi-Yau manifolds is ruled out on phenomenological grounds. We
also take a first step in analyzing the larger class of non-positive monads. In
particular, we construct a supersymmetric heterotic standard model within this
class. This model has the standard model gauge group and an additional
U(1)_{B-L} symmetry, precisely three families of quarks and leptons, one pair
of Higgs doublets and no anti-families or exotics of any kind.Comment: 48 page
Vacuum Geometry and the Search for New Physics
We propose a new guiding principle for phenomenology: special geometry in the
vacuum space. New algorithmic methods which efficiently compute geometric
properties of the vacuum space of N=1 supersymmetric gauge theories are
described. We illustrate the technique on subsectors of the MSSM. The fragility
of geometric structure that we find in the moduli space motivates
phenomenologically realistic deformations of the superpotential, while arguing
against others. Special geometry in the vacuum may therefore signal the
presence of string physics underlying the low-energy effective theory.Comment: 8 pages, LaTeX; v2: revised title, minor changes in wording,
reference adde
Dietary nitrate reduces skeletal muscle oxygenation response to physical exercise : a quantitative muscle functional MRI study
© 2014 The Authors. Physiological Reports published by Wiley Periodicals, Inc. on behalf of the American Physiological Society and The Physiological Society.Peer reviewedPublisher PD
Robust Estimator-Based Safety Verification: A Vector Norm Approach
In this paper, we consider the problem of verifying safety constraint
satisfaction for single-input single-output systems with uncertain transfer
function coefficients. We propose a new type of barrier function based on a
vector norm. This type of barrier function has a measurable upper bound without
full state availability. An identifier-based estimator allows an exact bound
for the uncertainty-based component of the barrier function estimate. Assuming
that the system is safe initially allows an exponentially decreasing bound on
the error due to the estimator transient. Barrier function and estimator
synthesis is proposed as two convex sub-problems, exploiting linear matrix
inequalities. The barrier function controller combination is then used to
construct a safety backup controller. And we demonstrate the system in a
simulation of a 1 degree-of-freedom human-exoskeleton interaction.Comment: 6 pages, 5 figures. Accepted for publication at the 2020 American
Control Conference. Copyright IEEE 202
- …