181 research outputs found
The Cosmological Constant in the Quantum Multiverse
Recently, a new framework for describing the multiverse has been proposed
which is based on the principles of quantum mechanics. The framework allows for
well-defined predictions, both regarding global properties of the universe and
outcomes of particular experiments, according to a single probability formula.
This provides complete unification of the eternally inflating multiverse and
many worlds in quantum mechanics. In this paper we elucidate how cosmological
parameters can be calculated in this framework, and study the probability
distribution for the value of the cosmological constant. We consider both
positive and negative values, and find that the observed value is consistent
with the calculated distribution at an order of magnitude level. In particular,
in contrast to the case of earlier measure proposals, our framework prefers a
positive cosmological constant over a negative one. These results depend only
moderately on how we model galaxy formation and life evolution therein.Comment: 18 pages, 4 figures; matches the version published in Phys. Rev.
Analytical investigation of magnetic field distributions around superconducting strips on ferromagnetic substrates
The complex-field approach is developed to derive analytical expressions of
the magnetic field distributions around superconducting strips on ferromagnetic
substrates (SC/FM strips). We consider the ferromagnetic substrates as ideal
soft magnets with an infinite magnetic permeability, neglecting the
ferromagnetic hysteresis. On the basis of the critical state model for a
superconducting strip, the ac susceptibility of a SC/FM
strip exposed to a perpendicular ac magnetic field is theoretically
investigated, and the results are compared with those for superconducting
strips on nonmagnetic substrates (SC/NM strips). The real part for
(where is the amplitude of the ac magnetic field,
is the critical current density, and is the thickness of the
superconducting strip) of a SC/FM strip is 3/4 of that of a SC/NM strip. The
imaginary part (or ac loss ) for of a SC/FM
strip is larger than that of a SC/NM strip, even when the ferromagnetic
hysteresis is neglected, and this enhancement of (or ) is due to
the edge effect of the ferromagnetic substrate.Comment: 8 pages, 6 figures, submitted to Phys. Rev.
Bulk composition and classification of the Tahara meteorite fell in Central Japan on March 1991
The Tahara meteorite which fell on March 26,1991 on a ship\u27s deck anchored at Tahara, Aichi-ken, Japan was found at Matsue-shi, Shimaneken on December 28,1992. It has been classified as an H4-5 chondrite using optical and electron microscopy and bulk chemical analysis. This equilibrated chondrite is completely different from the Mihonoseki L chondrite which fell on December 10,1992 in the same area of Japan, Shimane-ken. The retrieval process of new Japanese meteorites is similar to Antarctic meteorites of different origins which are collected in the same area
Reexamination of Mocs and Tauti chondritic meteorites: Classification with shock degree
The Mocs meteorite, which fell on February 3,1882,in Transylvania over a large area (15km by 3km) has been reclassified from a L6 to a L5-6 chondrite in this study. Six fragments of the Mocs chondrite were observed by optical microscopy and measured using electron microprobe analyses and standard wet chemical analysis. Although the petrologic type of the 6 samples is almost the same, 2 fragments : Mocs-1 and Mocs-3 show heterogeneous features (opaque shock veins and melt pockets) due to different shock degrees (S-5 and S-4,respectively). Therefore the mean shock degree of the Mocs chondrite was found to be S3-5. The Tauti meteorite which fell in 1937 in Transylvania was previously classified as L6 chondrite using the bulk chemical analyses of H. SAVU (St. Cerc. Geol., 2 (IV), 272,1959) (A. L. GRAHAM; Meteoritics, 14,1,1979; A. L. GRAHAM et al.; Catalogue of Meteorites, London, British Museum, Natural History, 1985). The chemical compositions of olivines and orthopyroxenes determined by electron microprobe analysis, the bulk chemical analysis, along with textural characteristics classify Tauti shower as L6 chondrite with a shock degree of S-3
The dynamic exponent of the Ising model on negatively curved surfaces
We investigate the dynamic critical exponent of the two-dimensional Ising
model defined on a curved surface with constant negative curvature. By using
the short-time relaxation method, we find a quantitative alteration of the
dynamic exponent from the known value for the planar Ising model. This
phenomenon is attributed to the fact that the Ising lattices embedded on
negatively curved surfaces act as ones in infinite dimensions, thus yielding
the dynamic exponent deduced from mean field theory. We further demonstrate
that the static critical exponent for the correlation length exhibits the mean
field exponent, which agrees with the existing results obtained from canonical
Monte Carlo simulations.Comment: 14 pages, 3 figures. to appear in J. Stat. Mec
Induction of Nod2 in Myelomonocytic and Intestinal Epithelial Cells via Nuclear Factor-kB Activation
Nod2, a member of the Apaf1/Nod protein family, confers responsiveness to bacterial products and activates NF-kB, a ranscription factor that plays a central role in innate immunity. Recently, genetic variation in Nod2
has been associated with susceptibility to Crohn’s disease.
Here, we report that expression of Nod2 is induced upon differentiation of CD34+ hematopoietic progenitor cells into granulocyte or monocyte/macrophages. In peripheral
blood cells, the highest levels of Nod2 were
observed in CD14+ (monocytes), CD15+ (granulocytes), and CD40+/CD86+ (dendritic cells) cell populations. Notably, stimulation of myeloblastic and epithelial cells with bacterial lipopolysaccharide or TNF resulted in
up-regulation of Nod2. A search for consensus sites within the Nod2 promoter revealed a NF-kB binding element that was required for transcriptional activity in
response to TNF . Moreover, ectopic expression of p65 induced transactivation, whereas that of dominant-negative I B blocked the transcriptional activity of the
Nod2 promoter. Upon stimulation with TNF or lipopolysaccharide, both p50 and p65 subunits of NF-kB were bound to the Nod2 promoter. Thus, Nod2 expression is enhanced by proinflammatory cytokines and bacterial
components via NF-kB, a mechanism that may contribute to the amplification of the innate immune response and susceptibility to inflammatory disease
Quintessence, scalar-tensor theories and non-Newtonian gravity
We discuss some of the issues which we encounter when we try to invoke the
scalar-tensor theories of gravitation as a theoretical basis of quintessence.
One of the advantages of appealing to these theories is that they allow us to
implement the scenario of a ``decaying cosmological constant,'' which offers a
reasonable understanding of why the observed upper bound of the cosmological
constant is smaller than the theoretically natural value by as much as 120
orders of magnitude. In this context, the scalar field can be a candidate of
quintessence in a broader sense. We find, however, a serious drawback in the
prototype Brans-Dicke model with added; a static universe in the
physical conformal frame which is chosen to have constant particle masses. We
propose a remedy by modifying the matter coupling of the scalar field taking
advantage of scale invariance and its breakdown through quantum anomaly. By
combining this with a conjecture on another cosmological constant problem
coming from the vacuum energy of matter fields, we expect a possible link
between quintessence and non-Newtonian gravity featuring violation of Weak
Equivalence Principle and intermediate force range, likely within the
experimental constraints. A new prediction is also offered on the
time-variability of the gravitational constant.Comment: 12 pages LaTex including 1 eps figur
Geometric effects on critical behaviours of the Ising model
We investigate the critical behaviour of the two-dimensional Ising model
defined on a curved surface with a constant negative curvature. Finite-size
scaling analysis reveals that the critical exponents for the zero-field
magnetic susceptibility and the correlation length deviate from those for the
Ising lattice model on a flat plane. Furthermore, when reducing the effects of
boundary spins, the values of the critical exponents tend to those derived from
the mean field theory. These findings evidence that the underlying geometric
character is responsible for the critical properties the Ising model when the
lattice is embedded on negatively curved surfaces.Comment: 16 pages, 6 figures, to appear in J. Phys. A: Math. Ge
Low-Scale See-Saw Mechanisms for Light Neutrinos
Alternatives to the see-saw mechanism are explored in supersymmetric models
with three right-handed or sterile neutrinos. Tree-level Yukawa couplings can
be drastically suppressed in a natural way to give sub-eV Dirac neutrino
masses. If, in addition, a B-L gauge symmetry broken at a large scale M_G is
introduced, a wider range of possibilities opens up. The value of the
right-handed neutrino mass M_R can be easily disentangled from that of M_G.
Dirac and Majorana neutrino masses at the eV scale can be generated radiatively
through the exchange of sneutrinos and neutralinos. Dirac masses m_D owe their
smallness to the pattern of light-heavy scales in the neutralino mass matrix.
The smallness of the Majorana masses m_L is linked to a similar see-saw pattern
in the sneutrino mass matrix. Two distinct scenarios emerge. In the first, with
very small or vanishing M_R, the physical neutrino eigenstates are, for each
generation, either two light Majorana states with mixing angle ranging from
very small to maximal, depending on the ratio m_D/M_R, or one light Dirac
state. In the second scenario, with a large value of M_R, the physical
eigenstates are two nearly unmixed Majorana states with masses \sim m_L and
\sim M_R. In both cases, the (B-L)-breaking scale M_G is, in general, much
smaller than that in the traditional see-saw mechanism.Comment: 31 pages, Latex, references added, version to appear in Phys. Rev.
Roadmap on photonic, electronic and atomic collision physics: II. Electron and antimatter interactions
We publish three Roadmaps on photonic, electronic and atomic collision physics in order to celebrate the 60th anniversary of the ICPEAC conference. In Roadmap II we focus on electron and antimatter interactions. Modern theoretical and experimental approaches provide detailed insight into the many body quantum dynamics of leptonic collisions with targets of varying complexity ranging from neutral and charged atoms to large biomolecules and clusters. These developments have been driven by technological progress and by the needs of adjacent areas of science such as astrophysics, plasma physics and radiation biophysics. This Roadmap aims at looking back along the road, explaining the evolution of the field, and looking forward, collecting contributions from eighteen leading groups from the field
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