4,260 research outputs found
Languages of Dot-depth One over Infinite Words
Over finite words, languages of dot-depth one are expressively complete for
alternation-free first-order logic. This fragment is also known as the Boolean
closure of existential first-order logic. Here, the atomic formulas comprise
order, successor, minimum, and maximum predicates. Knast (1983) has shown that
it is decidable whether a language has dot-depth one. We extend Knast's result
to infinite words. In particular, we describe the class of languages definable
in alternation-free first-order logic over infinite words, and we give an
effective characterization of this fragment. This characterization has two
components. The first component is identical to Knast's algebraic property for
finite words and the second component is a topological property, namely being a
Boolean combination of Cantor sets.
As an intermediate step we consider finite and infinite words simultaneously.
We then obtain the results for infinite words as well as for finite words as
special cases. In particular, we give a new proof of Knast's Theorem on
languages of dot-depth one over finite words.Comment: Presented at LICS 201
Confronting Flavour Symmetries and extended Scalar Sectors with Lepton Flavour Violation Bounds
We discuss the tension between discrete flavour symmetries and extended
scalar sectors arising from lepton flavour violation experiments. The key point
is that extended scalar sectors will generically lead to flavour changing
neutral currents, which are strongly constrained by experiments. Due to the
large parameter space in the scalar sector such models will, however, usually
have no big problems with existing and future bounds (even though the models
might be constrained). This changes considerably once a flavour symmetry is
imposed in addition: Due to the symmetry, additional relations between the
different couplings arise and cancellations become impossible in certain cases.
The experimental bounds will then constrain the model severely and can easily
exclude it. We consider two examples which show how these considerations are
realized. The same logic should apply to a much wider class of models.Comment: 19 pages, 2 figures; Introduction extended, typos corrected, charged
lepton sector of model 2 corrected; matches journal versio
Enhancing Dark Matter Annihilation into Neutrinos
We perform a detailed and quasi model-independent analysis of direct
annihilation of Dark Matter into neutrinos. Considering different cases for
scalar and fermionic Dark Matter, we identify several settings in which this
annihilation is enhanced, contrary to some statements in the literature. They
key point is that several restrictions of, e.g., a supersymmetric framework do
not hold in general. The mass generation mechanism of the neutrinos plays an
important role, too. We illustrate our considerations by two examples that are
not (as usually) suppressed by the smallness of the neutrino mass, for which we
also present a numerical analysis. Our results can be easily used as guidelines
for model building.Comment: 33 pages, 2 figure
The GSI anomaly
Recently, an experiment at GSI Darmstadt has observed oscillating decay rates
of heavy ions. Several controversial attempts have been made to explain this
effect in terms of neutrino mixing. We briefly describe the experimental
results, give an overview of the literature, and show that the effect cannot be
due to neutrino mixing. If the effect survives, it could, however, be explained
by hypothetical internal excitations of the mother ions (~ 10^(-15) eV).Comment: Contribution to the Proceedings of Neutrino 2008, based on a talk by
M. Lindner and on a poster by the author
Determinants of Moral hazard in Microfinance: Empirical Evidence from Joint Liability Lending Schemes in Malawi
Moral hazard is widely reported as a problem in credit and insurance markets, mainly arising from information asymmetry. Although theorists have attempted to explain the success of Joint Liability Lending (JLL) schemes in mitigating moral hazard, empirical studies are rare. This paper investigates the determinants of moral hazard among JLL schemes from Malawi, using group level data from 99 farm and non-farm credit groups. Results reveal that peer selection, peer monitoring, peer pressure, dynamic incentives and variables capturing the extent of matching problems explain most of the variation in the incidence of moral hazard among credit groups. The implications are that Joint Liability Lending institutions will continue to rely on social cohesion and dynamic incentives as a means to enhancing their performance which has a direct implication on their outreach, impact and sustainability.moral hazard, joint liability, dynamic incentives, group lending, Malawi, Financial Economics,
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