9,100 research outputs found
String Unification, Higher-Level Gauge Symmetries, and Exotic Hypercharge Normalizations
We explore the extent to which string theories with higher-level gauge
symmetries and non-standard hypercharge normalizations can reconcile the
discrepancy between the string unification scale and the GUT scale extrapolated
from the Minimal Supersymmetric Standard Model (MSSM). We determine the
phenomenologically allowed regions of (k_Y,k_2,k_3) parameter space, and
investigate the proposal that there might exist string models with exotic
hypercharge normalizations k_Y which are less than their usual value k_Y=5/3.
For a broad class of heterotic string models (encompassing most realistic
string models which have been constructed), we prove that k_Y >= 5/3. Beyond
this class, however, we show that there exist consistent MSSM embeddings which
lead to k_Y < 5/3. We also consider the constraints imposed on k_Y by demanding
charge integrality of all unconfined string states, and show that only a
limited set of hypercolor confining groups and corresponding values of k_Y are
possible.Comment: 59 pages, standard LaTeX, 4 figures (Encapsulated PostScript).
Expanded reference
String Theory on AdS3: Some Open Questions
String theory on curved backgrounds has received much attention on account of
both its own interest, and of its relation with gauge theories. Despite the
progress made in various directions, several quite elementary questions remain
unanswered, in particular in the very simple case of three-dimensional anti-de
Sitter space. I will very briefly review these problems, discuss in some detail
the important issue of constructing a consistent spectrum for a string
propagating on ADS3 plus torsion background, and comment on potential
solutions.Comment: 18 pages, latex. To appear in the proceedings of the TMR European
program meeting "Quantum aspects of gauge theories, supersymmetry and
unification", Paris, France, 1--7 September, 1999; v2: comments and
references adde
A Labelled Analytic Theorem Proving Environment for Categorial Grammar
We present a system for the investigation of computational properties of
categorial grammar parsing based on a labelled analytic tableaux theorem
prover. This proof method allows us to take a modular approach, in which the
basic grammar can be kept constant, while a range of categorial calculi can be
captured by assigning different properties to the labelling algebra. The
theorem proving strategy is particularly well suited to the treatment of
categorial grammar, because it allows us to distribute the computational cost
between the algorithm which deals with the grammatical types and the algebraic
checker which constrains the derivation.Comment: 11 pages, LaTeX2e, uses examples.sty and a4wide.st
String Consistency for Unified Model Building
We explore the use of real fermionization as a test case for understanding
how specific features of phenomenological interest in the low-energy effective
superpotential are realized in exact solutions to heterotic superstring theory.
We present pedagogic examples of models which realize SO(10) as a level two
current algebra on the world-sheet, and discuss in general how higher level
current algebras can be realized in the tensor product of simple constituent
conformal field theories. We describe formal developments necessary to compute
couplings in models built using real fermionization. This allows us to isolate
cases of spin structures where the standard prescription for real
fermionization may break down.Comment: harvmac (available from xxx.lanl.gov), 30 pages (reduced format), if
you are using harvmac for the first time, make sure to adjust the "site
dependent options" at the beginning of the harvmac file. Shortened
introduction and added table 3, listing the complete massless spectrum with
U(1) charges of Model A. Version to appear in journa
Research on Architectures for Integrated Speech/Language Systems in Verbmobil
The German joint research project Verbmobil (VM) aims at the development of a
speech to speech translation system. This paper reports on research done in our
group which belongs to Verbmobil's subproject on system architectures (TP15).
Our specific research areas are the construction of parsers for spontaneous
speech, investigations in the parallelization of parsing and to contribute to
the development of a flexible communication architecture with distributed
control.Comment: 6 pages, 2 Postscript figure
IUPC: Identification and Unification of Process Constraints
Business Process Compliance (BPC) has gained significant momentum in research
and practice during the last years. Although many approaches address BPC, they
mostly assume the existence of some kind of unified base of process constraints
and focus on their verification over the business processes. However, it
remains unclear how such an inte- grated process constraint base can be built
up, even though this con- stitutes the essential prerequisite for all further
compliance checks. In addition, the heterogeneity of process constraints has
been neglected so far. Without identification and separation of process
constraints from domain rules as well as unification of process constraints,
the success- ful IT support of BPC will not be possible. In this technical
report we introduce a unified representation framework that enables the
identifica- tion of process constraints from domain rules and their later
unification within a process constraint base. Separating process constraints
from domain rules can lead to significant reduction of compliance checking
effort. Unification enables consistency checks and optimizations as well as
maintenance and evolution of the constraint base on the other side.Comment: 13 pages, 4 figures, technical repor
String Phenomenology: Past, Present and Future Perspectives
The observation of a scalar resonance at the LHC, compatible with
perturbative electroweak symmetry breaking, reinforces the Standard Model
parameterisation of all subatomic data. The logarithmic evolution of the SM
gauge and matter parameters suggests that this parameterisation remains viable
up to the Planck scale, where gravitational effects are of comparable strength.
String theory provides a perturbatively consistent scheme to explore how the
parameters of the Standard Model may be determined from a theory of quantum
gravity. The free fermionic heterotic string models provide concrete examples
of exact string solutions that reproduce the spectrum of the Minimal
Supersymmetric Standard Model. Contemporary studies entail the development of
methods to classify large classes of models. This led to the discovery of
exophobic heterotic-string vacua and the observation of spinor-vector duality,
which provides an insight to the global structure of the space of (2,0)
heterotic-string vacua. Future directions entail the study of the role of the
massive string states in these models and their incorporation in cosmological
scenarios. A complementary direction is the formulation of quantum gravity from
the principle of manifest phase space duality and the equivalence postulate of
quantum mechanics, which suggest that space is compact. The compactness of
space, which implies intrinsic regularisation, may be tightly related to the
intrinsic finite length scale, implied by string phenomenology.Comment: 35 pages. No figures. To appear in the special volume edited by
Gerald Cleaver on "Particle Physics and Quantum Gravity Implications for
Cosmology". Based on talk presented at the 2012 CERN Summer Institute on
String Phenomenolog
- …