201 research outputs found
Smearing Formula for Higher-Order Effective Classical Potentials
In the variational approach to quantum statistics, a smearing formula
describes efficiently the consequences of quantum fluctuations upon an
interaction potential. The result is an effective classical potential from
which the partition function can be obtained by a simple integral. In this
work, the smearing formula is extended to higher orders in the variational
perturbation theory. An application to the singular Coulomb potential exhibits
the same fast convergence with increasing orders that has been observed in
previous variational perturbation expansions of the anharmonic oscillator with
quartic potential.Comment: Author Information under
http://www.physik.fu-berlin.de/~kleinert/institution.html . Latest update of
paper also at
http://www.physik.fu-berlin.de/~kleinert/kleiner_re267/preprint.htm
Minimal Mass Matrices for Dirac Neutrinos
We consider the possibility of neutrinos being Dirac particles and study
minimal mass matrices with as much zero entries as possible. We find that up to
5 zero entries are allowed. Those matrices predict one vanishing mass state, CP
conservation and U_{e3} either zero or proportional to R, where R is the ratio
of the solar and atmospheric \Delta m^2. Matrices containing 4 zeros can be
classified in categories predicting U_{e3} = 0, U_{e3} \neq 0 but no CP
violation or |U_{e3}| \neq 0 and possible CP violation. Some cases allow to set
constraints on the neutrino masses. The characteristic value of U_{e3} capable
of distinguishing some of the cases with non-trivial phenomenological
consequences is about R/2 \sin 2 \theta_{12}. Matrices containing 3 and less
zero entries imply (with a few exceptions) no correlation for the observables.
We outline models leading to the textures based on the Froggatt-Nielsen
mechanism or the non-Abelian discrete symmetry D_4 \times Z_2.Comment: 32 pages, 3 figures. Comments and references added. To appear in JHE
Light-bending in Schwarzschild-de-Sitter: projective geometry of the optical metric
We interpret the well known fact that the equations for light rays in the
Kottler or Schwarzschild-de Sitter metric are independent of the cosmological
constant in terms of the projective equivalence of the optical metric for any
value of \Lambda. We explain why this does not imply that lensing phenomena are
independent of \Lambda. Motivated by this example, we find a large collection
of one-parameter families of projectively equivalent metrics including both the
Kottler optical geometry and the constant curvature metrics as special cases.
Using standard constructions for geodesically equivalent metrics we find
classical and quantum conserved quantities and relate these to known
quantities.Comment: 8 page
Large and Almost Maximal Neutrino Mixing within the Type II See-Saw Mechanism
Within the type II see-saw mechanism the light neutrino mass matrix is given
by a sum of a direct (or triplet) mass term and the conventional (type I)
see-saw term. Both versions of the see-saw mechanism explain naturally small
neutrino masses, but the type II scenario offers interesting additional
possibilities to explain large or almost maximal or vanishing mixings which are
discussed in this paper. We first introduce ``type II enhancement'' of neutrino
mixing, where moderate cancellations between the two terms can lead to large
neutrino mixing even if all individual mass matrices and terms generate small
mixing. However, nearly maximal or vanishing mixings are not naturally
explained in this way, unless there is a certain initial structure (symmetry)
which enforces certain elements of the matrices to be identical or related in a
special way. We therefore assume that the leading structure of the neutrino
mass matrix is the triplet term and corresponds to zero U_{e3} and maximal
theta_{23}. Small but necessary corrections are generated by the conventional
see-saw term. Then we assume that one of the two terms corresponds to an
extreme mixing scenario, such as bimaximal or tri-bimaximal mixing. Deviations
from this scheme are introduced by the second term. One can mimic Quark-Lepton
Complementarity in this way. Finally, we note that the neutrino mass matrix for
tri-bimaximal mixing can be -- depending on the mass hierarchy -- written as a
sum of two terms with simple structure. Their origin could be the two terms of
type II see-saw.Comment: 25 pages. Comments and references added, to appear in JHE
Recent advances in electronic structure theory and their influence on the accuracy of ab initio potential energy surfaces
Recent advances in electronic structure theory and the availability of high speed vector processors have substantially increased the accuracy of ab initio potential energy surfaces. The recently developed atomic natural orbital approach for basis set contraction has reduced both the basis set incompleteness and superposition errors in molecular calculations. Furthermore, full CI calculations can often be used to calibrate a CASSCF/MRCI approach that quantitatively accounts for the valence correlation energy. These computational advances also provide a vehicle for systematically improving the calculations and for estimating the residual error in the calculations. Calculations on selected diatomic and triatomic systems will be used to illustrate the accuracy that currently can be achieved for molecular systems. In particular, the F+H2 yields HF+H potential energy hypersurface is used to illustrate the impact of these computational advances on the calculation of potential energy surfaces
Exoplanetary Geophysics -- An Emerging Discipline
Thousands of extrasolar planets have been discovered, and it is clear that
the galactic planetary census draws on a diversity greatly exceeding that
exhibited by the solar system's planets. We review significant landmarks in the
chronology of extrasolar planet detection, and we give an overview of the
varied observational techniques that are brought to bear. We then discuss the
properties of the currently known distribution, using the mass-period diagram
as a guide to delineating hot Jupiters, eccentric giant planets, and a third,
highly populous, category that we term "ungiants", planets having masses less
than 30 Earth masses and orbital periods less than 100 days. We then move to a
discussion of the bulk compositions of the extrasolar planets. We discuss the
long-standing problem of radius anomalies among giant planets, as well as
issues posed by the unexpectedly large range in sizes observed for planets with
masses somewhat greater than Earth's. We discuss the use of transit
observations to probe the atmospheres of extrasolar planets; various
measurements taken during primary transit, secondary eclipse, and through the
full orbital period, can give clues to the atmospheric compositions,
structures, and meteorologies. The extrasolar planet catalog, along with the
details of our solar system and observations of star-forming regions and
protoplanetary disks, provide a backdrop for a discussion of planet formation
in which we review the elements of the favored pictures for how the terrestrial
and giant planets were assembled. We conclude by listing several research
questions that are relevant to the next ten years and beyond.Comment: Review chapter to appear in Treatise on Geophysics, 2nd Editio
Alterations in juvenile diploid and triploid African catfish skin gelatin yield and amino acid composition: effects of chlorpyrifos and butachlor exposures
Skin is a major by-product of the fisheries and aquaculture industries and is a valuable source of gelatin. This study examined the effect of triploidization on gelatin yield and proximate composition of the skin of African catfish (Clarias gariepinus). We further investigated the effects of two commonly used pesticides , chlorpyrifos (CPF) and butachlor (BUC), on the skin gelatin yield and amino acid composition in juvenile full-sibling diploid and triploid African catfish. In two separate experiments, diploid and triploid C. gariepinus were exposed for 21 days to graded CPF [mean measured: 10, 16, or 31 mg/L] or BUC concentrations [Mean measured: 22, 44, or 60 mg/L]. No differences in skin gelatin yield, amino acid or proximate compositions were observed between diploid and triploid control groups. None of the pesticide treatments affected the measured parameters in diploid fish. In triploids, however, gelatin yield was affected by CPF treatments while amino acid composition remained unchanged. Butachlor treatments did not alter any of the measured variables in triploid fish. To our knowledge, this study is the first to investigate changes in the skin gelatin yield and amino acid composition in any animal as a response to polyploidization and/or contaminant exposure
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