2,274 research outputs found
Effects of a neutrino-dark energy coupling on oscillations of high-energy neutrinos
If dark energy (DE) is a dynamical field rather than a cosmological constant,
an interaction between DE and the neutrino sector could exist, modifying the
neutrino oscillation phenomenology and causing CP and apparent Lorentz
violating effects. The terms in the Hamiltonian for flavor propagation induced
by the DE-neutrino coupling do not depend on the neutrino energy, while the
ordinary components decrease as . Therefore, the DE-induced
effects are absent at lower neutrino energies, but become significant at higher
energies, allowing to be searched for by neutrino observatories. We explore the
impact of the DE-neutrino coupling on the oscillation probability and the
flavor transition in the three-flavor framework, and investigate the
CP-violating and apparent Lorentz violating effects. We find that DE-induced
effects become observable for , where is the effective mass parameter in the
DE-induced oscillation probability, and CP is violated over a wide energy
range. We also show that current and future experiments have the sensitivity to
detect anomalous effects induced by a DE-neutrino coupling and probe the new
mixing parameters. The DE-induced effects on neutrino oscillation can be
distinguished from other new physics possibilities with similar effects,
through the detection of the directional dependence of the interaction, which
is specific to this interaction with DE. However, current experiments will not
yet be able to measure the small changes of in the flavor
composition due to this directional effect.Comment: 11 pages, 15 figure
The impact of civil war on forest wildlife in West Africa: Mammals in Gola Forest, Sierra Leone
Human conflicts may sometimes benefit wildlife by depopulating wilderness areas but there is evidence from Africa that the impacts tend to be negative. The forested states of West Africa have experienced much recent human conflict but there have been no assessments of impacts on the wildlife. We conducted surveys of mammals in the 710-km2 Gola Forest reserves to assess the impact of the 1991-2001 civil war in Sierra Leone. Gola is the most important remaining tract of lowland forest in the country and a key site for the conservation of the highly threatened forests of the Upper Guinea region. We found that Gola has survived well despite being in the heart of the area occupied by the rebels. We recorded 44 species of larger mammal, including 18 threatened, near-threatened and endemic species, accounting for all species recorded in pre-war surveys and adding several more (African buffalo Syncerus caffer nanus and water chevrotain Hyemoschus aquaticus). Populations of primates were healthy with little evidence of decline. Duiker detection rates were low and further work is required to confirm their numbers as they include five species endemic (or near endemic) to the Upper Guinea region, three of which are threatened. However, the population of African forest elephants Loxodonta cyclotis has collapsed, with only a few individuals remaining from c. 110 in the mid 1980s. We conclude that peacetime pressures from the bushmeat trade, clearance for agriculture, logging and mining are likely to be far greater for Gola than the pressures from the civil war
Decreasing Diagrams for Confluence and Commutation
Like termination, confluence is a central property of rewrite systems. Unlike
for termination, however, there exists no known complexity hierarchy for
confluence. In this paper we investigate whether the decreasing diagrams
technique can be used to obtain such a hierarchy. The decreasing diagrams
technique is one of the strongest and most versatile methods for proving
confluence of abstract rewrite systems. It is complete for countable systems,
and it has many well-known confluence criteria as corollaries.
So what makes decreasing diagrams so powerful? In contrast to other
confluence techniques, decreasing diagrams employ a labelling of the steps with
labels from a well-founded order in order to conclude confluence of the
underlying unlabelled relation. Hence it is natural to ask how the size of the
label set influences the strength of the technique. In particular, what class
of abstract rewrite systems can be proven confluent using decreasing diagrams
restricted to 1 label, 2 labels, 3 labels, and so on? Surprisingly, we find
that two labels suffice for proving confluence for every abstract rewrite
system having the cofinality property, thus in particular for every confluent,
countable system.
Secondly, we show that this result stands in sharp contrast to the situation
for commutation of rewrite relations, where the hierarchy does not collapse.
Thirdly, investigating the possibility of a confluence hierarchy, we
determine the first-order (non-)definability of the notion of confluence and
related properties, using techniques from finite model theory. We find that in
particular Hanf's theorem is fruitful for elegant proofs of undefinability of
properties of abstract rewrite systems
Impact of axisymmetric mass models for dwarf spheroidal galaxies on indirect dark matter searches
Dwarf spheroidals are low-luminosity satellite galaxies of the Milky Way
highly dominated by dark matter (DM). Therefore, they are prime targets to
search for signals from dark matter annihilation using gamma-ray observations.
While the typical assumption is that the dark matter density profile of these
satellite galaxies can be described by a spherical symmetric
Navarro-Frenk-White (NFW) profile, recent observational data of stellar
kinematics suggest that the DM halos around these galaxies are better described
by axisymmetric profiles. Motivated by such evidence, we analyse about seven
years of PASS8 Fermi data for seven classical dwarf galaxies, including Draco,
adopting both the widely used NFW profile and observationally-motivated
axisymmetric density profiles. For four of the selected dwarfs (Sextans,
Carina, Sculptor and Fornax) axisymmetric mass models suggest a cored density
profile rather than the commonly adopted cusped profile. We found that upper
limits on the annihilation cross section for some of these dwarfs are
significantly higher than the ones achieved using an NFW profile. Therefore,
upper limits in the literature obtained using spherical symmetric cusped
profiles, such as the NFW, might be overestimated. Our results show that it is
extremely important to use observationally motivated density profiles going
beyond the usually adopted NFW in order to obtain accurate constraints on the
dark matter annihilation cross section.Comment: 9 pages, 5 figure
Introducing a Calculus of Effects and Handlers for Natural Language Semantics
In compositional model-theoretic semantics, researchers assemble
truth-conditions or other kinds of denotations using the lambda calculus. It
was previously observed that the lambda terms and/or the denotations studied
tend to follow the same pattern: they are instances of a monad. In this paper,
we present an extension of the simply-typed lambda calculus that exploits this
uniformity using the recently discovered technique of effect handlers. We prove
that our calculus exhibits some of the key formal properties of the lambda
calculus and we use it to construct a modular semantics for a small fragment
that involves multiple distinct semantic phenomena
Discriminating Lambda-Terms Using Clocked Boehm Trees
As observed by Intrigila, there are hardly techniques available in the
lambda-calculus to prove that two lambda-terms are not beta-convertible.
Techniques employing the usual Boehm Trees are inadequate when we deal with
terms having the same Boehm Tree (BT). This is the case in particular for fixed
point combinators, as they all have the same BT. Another interesting equation,
whose consideration was suggested by Scott, is BY = BYS, an equation valid in
the classical model P-omega of lambda-calculus, and hence valid with respect to
BT-equality but nevertheless the terms are beta-inconvertible. To prove such
beta-inconvertibilities, we employ `clocked' BT's, with annotations that convey
information of the tempo in which the data in the BT are produced. Boehm Trees
are thus enriched with an intrinsic clock behaviour, leading to a refined
discrimination method for lambda-terms. The corresponding equality is strictly
intermediate between beta-convertibility and Boehm Tree equality, the equality
in the model P-omega. An analogous approach pertains to Levy-Longo and
Berarducci Trees. Our refined Boehm Trees find in particular an application in
beta-discriminating fixed point combinators (fpc's). It turns out that Scott's
equation BY = BYS is the key to unlocking a plethora of fpc's, generated by a
variety of production schemes of which the simplest was found by Boehm, stating
that new fpc's are obtained by postfixing the term SI, also known as Smullyan's
Owl. We prove that all these newly generated fpc's are indeed new, by
considering their clocked BT's. Even so, not all pairs of new fpc's can be
discriminated this way. For that purpose we increase the discrimination power
by a precision of the clock notion that we call `atomic clock'.Comment: arXiv admin note: substantial text overlap with arXiv:1002.257
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