15,524 research outputs found
Abelian D-terms and the superpartner spectrum of anomaly-mediated supersymmetry breaking
We address the tachyonic slepton problem of anomaly mediated supersymmetry
breaking using abelian D-terms. We demonstrate that the most general extra U(1)
symmetry that does not disrupt gauge coupling unification has a large set of
possible charges that solves the problem. It is shown that previous studies in
this direction that added both an extra hypercharge D-term and another D-term
induced by B-L symmetry (or similar) can be mapped into a single D-term of the
general ancillary U(1)_a. The U(1)_a formalism enables identifying the sign of
squark mass corrections which leads to an upper bound of the entire
superpartner spectrum given knowledge of just one superpartner mass.Comment: 10 pages, 2 figures, [v2] reference added, [v3] Eq. (9) corrected,
results unaffected, [v4] version to be published in Phys. Rev. D, expanded
parameter space for figures to match tex
Four Lessons in Versatility or How Query Languages Adapt to the Web
Exposing not only human-centered information, but machine-processable data on the Web is one of the commonalities of recent Web trends. It has enabled a new kind of applications and businesses where the data is used in ways not foreseen by the data providers. Yet this exposition has fractured the Web into islands of data, each in different Web formats: Some providers choose XML, others RDF, again others JSON or OWL, for their data, even in similar domains. This fracturing stifles innovation as application builders have to cope not only with one Web stack (e.g., XML technology) but with several ones, each of considerable complexity. With Xcerpt we have developed a rule- and pattern based query language that aims to give shield application builders from much of this complexity: In a single query language XML and RDF data can be accessed, processed, combined, and re-published. Though the need for combined access to XML and RDF data has been recognized in previous work (including the W3C’s GRDDL), our approach differs in four main aspects: (1) We provide a single language (rather than two separate or embedded languages), thus minimizing the conceptual overhead of dealing with disparate data formats. (2) Both the declarative (logic-based) and the operational semantics are unified in that they apply for querying XML and RDF in the same way. (3) We show that the resulting query language can be implemented reusing traditional database technology, if desirable. Nevertheless, we also give a unified evaluation approach based on interval labelings of graphs that is at least as fast as existing approaches for tree-shaped XML data, yet provides linear time and space querying also for many RDF graphs. We believe that Web query languages are the right tool for declarative data access in Web applications and that Xcerpt is a significant step towards a more convenient, yet highly efficient data access in a “Web of Data”
Quantum gravity: unification of principles and interactions, and promises of spectral geometry
Quantum gravity was born as that branch of modern theoretical physics that
tries to unify its guiding principles, i.e., quantum mechanics and general
relativity. Nowadays it is providing new insight into the unification of all
fundamental interactions, while giving rise to new developments in modern
mathematics. It is however unclear whether it will ever become a falsifiable
physical theory, since it deals with Planck-scale physics. Reviewing a wide
range of spectral geometry from index theory to spectral triples, we hope to
dismiss the general opinion that the mere mathematical complexity of the
unification programme will obstruct that programme.Comment: This is a contribution to the Proceedings of the 2007 Midwest
Geometry Conference in honor of Thomas P. Branson, published in SIGMA
(Symmetry, Integrability and Geometry: Methods and Applications) at
http://www.emis.de/journals/SIGMA
The prospects for mathematical logic in the twenty-first century
The four authors present their speculations about the future developments of
mathematical logic in the twenty-first century. The areas of recursion theory,
proof theory and logic for computer science, model theory, and set theory are
discussed independently.Comment: Association for Symbolic Logi
A Lambda Term Representation Inspired by Linear Ordered Logic
We introduce a new nameless representation of lambda terms inspired by
ordered logic. At a lambda abstraction, number and relative position of all
occurrences of the bound variable are stored, and application carries the
additional information where to cut the variable context into function and
argument part. This way, complete information about free variable occurrence is
available at each subterm without requiring a traversal, and environments can
be kept exact such that they only assign values to variables that actually
occur in the associated term. Our approach avoids space leaks in interpreters
that build function closures.
In this article, we prove correctness of the new representation and present
an experimental evaluation of its performance in a proof checker for the
Edinburgh Logical Framework.
Keywords: representation of binders, explicit substitutions, ordered
contexts, space leaks, Logical Framework.Comment: In Proceedings LFMTP 2011, arXiv:1110.668
On the Relative Usefulness of Fireballs
In CSL-LICS 2014, Accattoli and Dal Lago showed that there is an
implementation of the ordinary (i.e. strong, pure, call-by-name)
-calculus into models like RAM machines which is polynomial in the
number of -steps, answering a long-standing question. The key ingredient
was the use of a calculus with useful sharing, a new notion whose complexity
was shown to be polynomial, but whose implementation was not explored. This
paper, meant to be complementary, studies useful sharing in a call-by-value
scenario and from a practical point of view. We introduce the Fireball
Calculus, a natural extension of call-by-value to open terms for which the
problem is as hard as for the ordinary lambda-calculus. We present three
results. First, we adapt the solution of Accattoli and Dal Lago, improving the
meta-theory of useful sharing. Then, we refine the picture by introducing the
GLAMoUr, a simple abstract machine implementing the Fireball Calculus extended
with useful sharing. Its key feature is that usefulness of a step is
tested---surprisingly---in constant time. Third, we provide a further
optimization that leads to an implementation having only a linear overhead with
respect to the number of -steps.Comment: Technical report for the LICS 2015 submission with the same titl
Lectures on Unification
In these lectures we review the motivation, principles of and
(circumstantial) evidence for the program of unification of the fundamental
forces. In an appendix, we review the group theory pertinent to the program.Comment: 28 pages plain LaTeX, to be run twice. Lectures given at the Sixth
ICTP-BCSPIN School on Current Trends in High Energy Physics and Cosmology,
Kathmandu, Nepal, May 19-June 3 199
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