21,360 research outputs found
Charged black holes in Vaidya backgrounds: Hawking's Radiation
In this paper we propose a class of embedded solutions of Einstein's field
equations describing non-rotating Reissner-Nordstrom-Vaidya and rotating
Kerr-Newman-Vaidya black holes.Comment: 30 pages, latex file, no figure
Spin-Orbit Coupling and Symmetry of the Order Parameter in Strontium Ruthenate
Determination of the orbital symmetry of a state in spin triplet
SrRuO superconductor is a challenge of considerable importance. Most of
the experiments show that the chiral state of the type
is realized and remains stable on lowering the temperature. Here we have
studied the stability of various superconducting states of SrRuO in the
presence of spin-orbit coupling.
Numerically we found that the chiral state is never the minimum energy. Alone
among the five states studied it has and is
therefore not affected to linear order in the coupling parameter . We
found that stability of the chiral state requires spin dependent pairing
interactions. This imposes strong constraint on the pairing mechanism.Comment: 4 pages, 4 figure
Development of large radii half-wave plates for CMB satellite missions
The successful European Space Agency (ESA) Planck mission has mapped the
Cosmic Microwave Background (CMB) temperature anisotropy with unprecedented
accuracy. However, Planck was not designed to detect the polarised components
of the CMB with comparable precision. The BICEP2 collaboration has recently
reported the first detection of the B-mode polarisation. ESA is funding the
development of critical enabling technologies associated with B-mode
polarisation detection, one of these being large diameter half-wave plates. We
compare different polarisation modulators and discuss their respective
trade-offs in terms of manufacturing, RF performance and thermo-mechanical
properties. We then select the most appropriate solution for future satellite
missions, optimized for the detection of B-modes.Comment: 16 page
Generalized Uncertainty Principle, Extra-dimensions and Holography
We consider Uncertainty Principles which take into account the role of
gravity and the possible existence of extra spatial dimensions. Explicit
expressions for such Generalized Uncertainty Principles in 4+n dimensions are
given and their holographic properties investigated. In particular, we show
that the predicted number of degrees of freedom enclosed in a given spatial
volume matches the holographic counting only for one of the available
generalizations and without extra dimensions.Comment: LaTeX, 13 pages, accepted for publication in Class. Quantum Gra
Distance Dependence in the Solar Neighborhood Age-Metallicity Relation
The age-metallicity relation for F and G dwarf stars in the solar
neighborhood, based on the stellar metallicity data of Edvardsson et al.
(1993), shows an apparent scatter that is larger than expected considering the
uncertainties in metallicities and ages. A number of theoretical models have
been put forward to explain the large scatter. However, we present evidence,
based on Edvardsson et al. (1993) data, along with Hipparcos parallaxes and new
age estimates, that the scatter in the age-metallicity relation depends on the
distance to the stars in the sample, such that stars within 30 pc of the Sun
show significantly less scatter in [Fe/H]. Stars of intermediate age from the
Edvardsson et al. sample at distances 30-80 pc from the Sun are systematically
more metal-poor than those more nearby. We also find that the slope of the
apparent age-metallicity relation is different for stars within 30 pc than for
those stars more distant. These results are most likely an artifact of
selection biases in the Edvardsson et al. star sample. We conclude that the
intrinsic dispersion in metallicity at fixed age is < 0.15 dex, consistent with
the < 0.1 dex scatter for Galactic open star clusters and the interstellar
medium.Comment: 15 pages, 5 figures, uses AASTex aaspp4 style; accepted for
publication in the Astrophysical Journa
Comparison of chemical profiles and effectiveness between Erxian decoction and mixtures of decoctions of its individual herbs : a novel approach for identification of the standard chemicals
Acknowledgements This study was partially supported by grants from the Seed Funding Programme for Basic Research (Project Number 201211159146 and 201411159213), the University of Hong Kong. We thank Mr Keith Wong and Ms Cindy Lee for their technical assistances.Peer reviewedPublisher PD
Can Strong Gravitational Lensing Constrain Dark Energy?
We discuss the ratio of the angular diameter distances from the source to the
lens, , and to the observer at present, , for various dark
energy models. It is well known that the difference of s between the
models is apparent and this quantity is used for the analysis of Type Ia
supernovae. However we investigate the difference between the ratio of the
angular diameter distances for a cosmological constant,
and that for other dark energy models,
in this paper. It has been known that there is
lens model degeneracy in using strong gravitational lensing. Thus, we
investigate the model independent observable quantity, Einstein radius
(), which is proportional to both and velocity
dispersion squared, . values depend on the parameters
of each dark energy model individually. However, for the various dark energy models, is well within
the error of for most of the parameter spaces of the dark energy
models. Thus, a single strong gravitational lensing by use of the Einstein
radius may not be a proper method to investigate the property of dark energy.
However, better understanding to the mass profile of clusters in the future or
other methods related to arc statistics rather than the distances may be used
for constraints on dark energy.Comment: 15 pages, 13 figures, Accepted in PR
Decoherence in Quantum Gravity: Issues and Critiques
An increasing number of papers have appeared in recent years on decoherence
in quantum gravity at the Planck energy. We discuss the meaning of decoherence
in quantum gravity starting from the common notion that quantum gravity is a
theory for the microscopic structures of spacetime, and invoking some generic
features of quantum decoherence from the open systems viewpoint. We dwell on a
range of issues bearing on this process including the relation between
statistical and quantum, noise from effective field theory, the meaning of
stochasticity, the origin of non-unitarity and the nature of nonlocality in
this and related contexts. To expound these issues we critique on two
representative theories: One claims that decoherence in quantum gravity scale
leads to the violation of CPT symmetry at sub-Planckian energy which is used to
explain today's particle phenomenology. The other uses this process in place
with the Brownian motion model to prove that spacetime foam behaves like a
thermal bath.Comment: 25 pages, proceedings of DICE06 (Piombino
Calculation of the Coherent Synchrotron Radiation Impedance from a Wiggler
Most studies of Coherent Synchrotron Radiation (CSR) have only considered the
radiation from independent dipole magnets. However, in the damping rings of
future linear colliders, a large fraction of the radiation power will be
emitted in damping wigglers. In this paper, the longitudinal wakefield and
impedance due to CSR in a wiggler are derived in the limit of a large wiggler
parameter . After an appropriate scaling, the results can be expressed in
terms of universal functions, which are independent of . Analytical
asymptotic results are obtained for the wakefield in the limit of large and
small distances, and for the impedance in the limit of small and high
frequencies.Comment: 10 pages, 8 figure
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