2,118 research outputs found
Harmonic Analysis of Linear Fields on the Nilgeometric Cosmological Model
To analyze linear field equations on a locally homogeneous spacetime by means
of separation of variables, it is necessary to set up appropriate harmonics
according to its symmetry group. In this paper, the harmonics are presented for
a spatially compactified Bianchi II cosmological model -- the nilgeometric
model. Based on the group structure of the Bianchi II group (also known as the
Heisenberg group) and the compactified spatial topology, the irreducible
differential regular representations and the multiplicity of each irreducible
representation, as well as the explicit form of the harmonics are all
completely determined. They are also extended to vector harmonics. It is
demonstrated that the Klein-Gordon and Maxwell equations actually reduce to
systems of ODEs, with an asymptotic solution for a special case.Comment: 28 pages, no figures, revised version to appear in JM
Scalar fields on SL(2,R) and H^2 x R geometric spacetimes and linear perturbations
Using appropriate harmonics, we study the future asymptotic behavior of
massless scalar fields on a class of cosmological vacuum spacetimes. The
spatial manifold is assumed to be a circle bundle over a higher genus surface
with a locally homogeneous metric. Such a manifold corresponds to the
SL(2,R)-geometry (Bianchi VIII type) or the H^2 x R-geometry (Bianchi III
type). After a technical preparation including an introduction of suitable
harmonics for the circle-fibered Bianchi VIII to separate variables, we derive
systems of ordinary differential equations for the scalar field. We present
future asymptotic solutions for these equations in a special case, and find
that there is a close similarity with those on the circle-fibered Bianchi III
spacetime. We discuss implications of this similarity, especially to
(gravitational) linear perturbations. We also point out that this similarity
can be explained by the "fiber term dominated behavior" of the two models.Comment: 23 pages, no figures, to be published in Class. Quant. Gravi
On the equivalence of two deformation schemes in quantum field theory
Two recent deformation schemes for quantum field theories on the
two-dimensional Minkowski space, making use of deformed field operators and
Longo-Witten endomorphisms, respectively, are shown to be equivalent.Comment: 14 pages, no figure. The final version is available under Open
Access. CC-B
Effect of a standardised dietary restriction protocol on multiple laboratory strains of Drosophila melanogaster
Background:
Outcomes of lifespan studies in model organisms are particularly susceptible to variations in technical procedures. This is especially true of dietary restriction, which is implemented in many different ways among laboratories.
Principal Findings:
In this study, we have examined the effect of laboratory stock maintenance, genotype differences and microbial infection on the ability of dietary restriction (DR) to extend life in the fruit fly Drosophila melanogaster. None of these factors block the DR effect.
Conclusions:
These data lend support to the idea that nutrient restriction genuinely extends lifespan in flies, and that any mechanistic discoveries made with this model are of potential relevance to the determinants of lifespan in other organisms
Construction of wedge-local nets of observables through Longo-Witten endomorphisms. II
In the first part, we have constructed several families of interacting
wedge-local nets of von Neumann algebras. In particular, there has been
discovered a family of models based on the endomorphisms of the U(1)-current
algebra of Longo-Witten.
In this second part, we further investigate endomorphisms and interacting
models. The key ingredient is the free massless fermionic net, which contains
the U(1)-current net as the fixed point subnet with respect to the U(1) gauge
action. Through the restriction to the subnet, we construct a new family of
Longo-Witten endomorphisms on the U(1)-current net and accordingly interacting
wedge-local nets in two-dimensional spacetime. The U(1)-current net admits the
structure of particle numbers and the S-matrices of the models constructed here
do mix the spaces with different particle numbers of the bosonic Fock space.Comment: 33 pages, 1 tikz figure. The final version is available under Open
Access. CC-B
Why Hybrid Meson Coupling to Two S-wave Mesons is Suppressed
We introduce strong interaction selection rules for the two-body decay and
production of hybrid and conventional mesons coupling to two S-wave hybrid or
conventional mesons. The rules arise from symmetrization in states in the limit
of non-relativistically moving quarks. The conditions under which hybrid
coupling to S-wave states is suppressed are determined by the rules, and the
nature of their breaking is indicated.Comment: 9 pages, LaTeX, 1 eps figures, uses epsf. Minor modifications, Title
chang
Speed of Sound in the Mass Varying Neutrinos Scenario
We discuss about the speed of sound squared in the Mass Varying Neutrinos
scenario (MaVaNs). Recently, it was argued that the MaVaNs has a catastrophic
instability which is the emergence of an imaginary speed of sound at the
non-relativistic limit of neutrinos. As the result of this instability, the
neutrino-acceleron fluid cannot act as the dark energy. However, it is found
that the speed of sound squared in the neutrino-acceleron fluid could be
positive in our model. We examine the speed of sound in two cases of the scalar
potential. One is the small fractional power-law potential and another is the
logarithmic one. The power-law potential model with the right-handed neutrinos
gives a stable one.Comment: 17 pages, References added, minor modification
Embedding the Texture of the Neutrino Mass Matrix into the MaVaNs Scenario
We have embedded the texture of the neutrino mass matrix with three families
into the MaVaNs scenario. We take the power-law potential of the acceleron
field and a typical texture of active neutrinos, which is derived by the D_4
symmetry and predicts the maximal mixing of the atmospheric neutrino and the
vanishing U_{e3}. The effect of couplings among the dark fermion and active
neutrinos are studied by putting the current cosmological data and the
terrestrial neutrino experimental data. It is found that the neutrino flavor
mixings evolve as well as the neutrino masses. Especially, U_{e3} develops into
the non-vanishing one and \theta_{atm} deviates from the maximal mixing due to
couplings among the dark fermion and active neutrinos.Comment: Sections 3 and 4 are changed and one table is added. 16pages and 2
figure
Perturbations of Spatially Closed Bianchi III Spacetimes
Motivated by the recent interest in dynamical properties of topologically
nontrivial spacetimes, we study linear perturbations of spatially closed
Bianchi III vacuum spacetimes, whose spatial topology is the direct product of
a higher genus surface and the circle. We first develop necessary mode
functions, vectors, and tensors, and then perform separations of (perturbation)
variables. The perturbation equations decouple in a way that is similar to but
a generalization of those of the Regge--Wheeler spherically symmetric case. We
further achieve a decoupling of each set of perturbation equations into
gauge-dependent and independent parts, by which we obtain wave equations for
the gauge-invariant variables. We then discuss choices of gauge and stability
properties. Details of the compactification of Bianchi III manifolds and
spacetimes are presented in an appendix. In the other appendices we study
scalar field and electromagnetic equations on the same background to compare
asymptotic properties.Comment: 61 pages, 1 figure, final version with minor corrections, to appear
in Class. Quant. Gravi
What Does mu-tau Symmetry Imply about Neutrino Mixings?
The requirement of the mu-tau symmetry in the neutrino sector that yields the
maximal atmospheric neutrino mixing is shown to yield either sin(\theta_{13})=0
(referred to as C1)) or sin(\theta_{12})=0 (referred to as C2)), where
\theta_{12(13)} stands for the solar (reactor) neutrino mixing angle. We study
general properties possessed by approximately mu-tau symmetric textures. It is
argued that the tiny mu-tau symmetry breaking generally leads to
cos(2\theta_{23}) \simsin(\theta_{13}) for C1) and cos(2\theta_{23}) \sim
\Delta m^2_\odot/\Delta m^2_{atm}(\equiv R) for C2), which indicates that the
smallness of cos(2\theta_{23}) is a good measure of the mu-tau symmetry
breaking, where \Delta m^2_{atm} (\Delta m^2_\odot) stands for the square mass
differences of atmospheric (solar) neutrinos. We further find that the relation
R \sim sin^2(\theta_{13}) arises from contributions of O(sin^2(\theta_{13})) in
the estimation of the neutrino masses (m_{1,2,3}) for C1), and that possible
forms of textures are strongly restricted to realize sin^2(2\theta_{12})=O(1)
for C2). To satisfy R \sim sin^2(\theta_{13}) for C1), neutrinos exhibit the
inverted mass hierarchy, or the quasi degenerate mass pattern with | m_{1,2,3}|
\sim O(\sqrt{\Delta m^2_{atm}}), and, to realize sin^2(2\theta_{12})=O(1) for
C2), there should be an additional small parameter \eta whose size is
comparable to that of the mu-tau symmetry breaking parameter \epsilon, giving
tan(2\theta_{12}) \sim \epsilon/\eta with \eta \sim \epsilon to be compatible
with the observed large mixing.Comment: 10 pages, title slightly modified, comments added in the introdction,
typos corrected, references updated, version to appear in Physical Reviews
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