9,002 research outputs found
Testing quantum superpositions of the gravitational field with Bose-Einstein condensates
We consider the gravity field of a Bose-Einstein condensate in a quantum
superposition. The gravity field then is also in a quantum superposition which
is in principle observable. Hence we have ``quantum gravity'' far away from the
so-called Planck scale
Molecular, morphological, and phytochemical evidence for a broad species concept of Plagiochila bifaria (Hepaticae)
Debate over the synonymy of the European Plagiochila killarniensis and the Neotropical P bifaria of R sect. Arrectae has focused on differences in secondary metabolite composition. The broad morphological species concept of R bifaria proposed in recent papers has now been tested by comparing nrDNA ITS1 and ITS2 sequences of R bifaria populations encompassing several different morpho- and chemotypes from the British Isles, Tenerife, Costa Rica, Brazil, Ecuador, and Bolivia, with sequences of other species of R sects. Arrectae, Rutilantes, and Fuscoluteae. Phylogenetic analyses demonstrate that specimens of P. bifaria form a well supported clade within Plagiochila sect. Arrectae. Sequences of R bifaria from the British Isles, Tenerife, and Ecuador, representing the "methyl everninate" chemotype, form a well supported subclade within the P bifaria clade. Sequences of specimens from Costa Rica, Brazil, and Bolivia are placed in the basal part of the R bifaria clade. The data support a broad species concept of P bifaria. The different chemotypes do not warrant distinct taxonomic ranks. Plagiochila centrifuga and P. compressula are treated as new synonyms of R bifaria
On the coupling of massless particles to scalar fields
It is investigated if massless particles can couple to scalar fields in a
special relativistic theory with classical particles. The only possible obvious
theory which is invariant under Lorentz transformations and reparametrization
of the affine parameter leads to trivial trajectories (straight lines) for the
massless case, and also the investigation of the massless limit of the massive
theory shows that there is no influence of the scalar field on the limiting
trajectories.
On the other hand, in contrast to this result, it is shown that massive
particles are influenced by the scalar field in this theory even in the
ultra-relativistic limit.Comment: 9 pages, no figures, uses titlepage.sty, LaTeX 2.09 file, submitted
to International Journal of Theoretical Physic
keV sterile neutrino dark matter in gauge extensions of the standard model
It is known that a keV scale sterile neutrino is a good warm dark matter
candidate. We study how this possibility could be realized in the context of
gauge extensions of the standard model. The na\"ive expectation leads to large
thermal overproduction of sterile neutrinos in this setup. However, we find
that it is possible to use out-of-equilibrium decay of the other right-handed
neutrinos of the model to dilute the present density of the keV sterile
neutrinos and achieve the observed dark matter density. We present the
universal requirements that should be satisfied by the gauge extensions of the
standard model, containing right-handed neutrinos, to be viable models of warm
dark matter, and provide a simple example in the context of the left-right
symmetric model.Comment: RevTex, 13 pages, 5 figures; journal version (corrected typos
Symmetric Brownian motor
In this paper we present a model of a symmetric Brownian motor (SBM) which
changes the sign of its velocity when the temperature gradient is inverted. The
velocity, external work and efficiency are studied as a function of the
temperatures of the baths and other relevant parameters. The motor shows a
current reversal when another parameter (a phase shift) is varied. Analytical
predictions and results from numerical simulations are performed and agree very
well. Generic properties of this type of motors are discussed.Comment: 8 pages and 10 figure
Parafermionic conformal field theory on the lattice
Finding the precise correspondence between lattice operators and the
continuum fields that describe their long-distance properties is a largely open
problem for strongly interacting critical points. Here we solve this problem
essentially completely in the case of the three-state Potts model, which
exhibits a phase transition described by a strongly interacting 'parafermion'
conformal field theory. Using symmetry arguments, insights from integrability,
and extensive simulations, we construct lattice analogues of nearly all the
relevant and marginal physical fields governing this transition. This
construction includes chiral fields such as the parafermion. Along the way we
also clarify the structure of operator product expansions between order and
disorder fields, which we confirm numerically. Our results both suggest a
systematic methodology for attacking non-free field theories on the lattice and
find broader applications in the pursuit of exotic topologically ordered phases
of matter.Comment: 27 pages, 4 figures; v2 added reference
The effect of different water temperatures on the release of the atrial natriuretic factor (ANF) during "head out water immersion (HOI)"
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