1,094 research outputs found
Weyssenhoff fluid dynamics in general relativity using a 1+3 covariant approach
The Weyssenhoff fluid is a perfect fluid with spin where the spin of the
matter fields is the source of torsion in an Einstein-Cartan framework. Obukhov
and Korotky showed that this fluid can be described as an effective fluid with
spin in general relativity. A dynamical analysis of such a fluid is performed
in a gauge invariant manner using the 1+3 covariant approach. This yields the
propagation and constraint equations for the set of dynamical variables. A
verification of these equations is performed for the special case of
irrotational flow with zero peculiar acceleration by evolving the constraints.Comment: 20 page
Jupiter as an exoplanet: UV to NIR transmission spectrum reveals hazes, a Na layer and possibly stratospheric H2O-ice clouds
Currently, the analysis of transmission spectra is the most successful
technique to probe the chemical composition of exoplanet atmospheres. But the
accuracy of these measurements is constrained by observational limitations and
the diversity of possible atmospheric compositions. Here we show the UV-VIS-IR
transmission spectrum of Jupiter, as if it were a transiting exoplanet,
obtained by observing one of its satellites, Ganymede, while passing through
Jupiter's shadow i.e., during a solar eclipse from Ganymede. The spectrum shows
strong extinction due to the presence of clouds (aerosols) and haze in the
atmosphere, and strong absorption features from CH4. More interestingly, the
comparison with radiative transfer models reveals a spectral signature, which
we attribute here to a Jupiter stratospheric layer of crystalline H2O ice. The
atomic transitions of Na are also present. These results are relevant for the
modeling and interpretation of giant transiting exoplanets. They also open a
new technique to explore the atmospheric composition of the upper layers of
Jupiter's atmosphere.Comment: Accepted for publication in ApJ Letter
Analysis of unbounded operators and random motion
We study infinite weighted graphs with view to \textquotedblleft limits at
infinity,\textquotedblright or boundaries at infinity. Examples of such
weighted graphs arise in infinite (in practice, that means \textquotedblleft
very\textquotedblright large) networks of resistors, or in statistical
mechanics models for classical or quantum systems. But more generally our
analysis includes reproducing kernel Hilbert spaces and associated operators on
them. If is some infinite set of vertices or nodes, in applications the
essential ingredient going into the definition is a reproducing kernel Hilbert
space; it measures the differences of functions on evaluated on pairs of
points in . And the Hilbert norm-squared in will represent
a suitable measure of energy. Associated unbounded operators will define a
notion or dissipation, it can be a graph Laplacian, or a more abstract
unbounded Hermitian operator defined from the reproducing kernel Hilbert space
under study. We prove that there are two closed subspaces in reproducing kernel
Hilbert space which measure quantitative notions of limits at
infinity in , one generalizes finite-energy harmonic functions in
, and the other a deficiency index of a natural operator in
associated directly with the diffusion. We establish these
results in the abstract, and we offer examples and applications. Our results
are related to, but different from, potential theoretic notions of
\textquotedblleft boundaries\textquotedblright in more standard random walk
models. Comparisons are made.Comment: 38 pages, 4 tables, 3 figure
Torsion, Dirac Field, Dark Matter and Dark Radiation
The role of torsion and a scalar field in gravitation, especially, in
the presence of a Dirac field in the background of a particular class of the
Riemann-Cartan geometry is considered here. Recently, a Lagrangian density with
Lagrange multipliers has been proposed by the author which has been obtained by
picking some particular terms from the SO(4,1) Pontryagin density, where the
scalar field causes the de Sitter connection to have the proper
dimension of a gauge field. In this article the scalar field has been linked to
the dimension of the Dirac field. Here we get the field equations for the Dirac
field and the scalar field in such a way that both of them appear to be
mutually non-interacting. In this scenario the scalar field appears to be a
natural candidate for the dark matter and the dark radiation
The Spatial Averaging Limit of Covariant Macroscopic Gravity - Scalar Corrections to the Cosmological Equations
It is known that any explicit averaging scheme of the type essential for
describing the large scale behaviour of the Universe, must necessarily yield
corrections to the Einstein equations applied in the Cosmological setting. The
question of whether or not the resulting corrections to the Einstein equations
are significant, is still a subject of debate, partly due to possible
ambiguities in the averaging schemes available. In particular, it has been
argued in the literature that the effects of averaging could be gauge
artifacts. We apply the formalism of Zalaletdinov's Macroscopic Gravity (MG)
which is a fully covariant and nonperturbative averaging scheme, in an attempt
to construct gauge independent corrections to the standard
Friedmann-Lemaitre-Robertson-Walker (FLRW) equations. We find that whereas one
cannot escape the problem of dependence on \emph{one} gauge choice -- which is
inherent in the assumption of large scale homogeneity and isotropy -- it is
however possible to construct \emph{spacetime scalar} corrections to the
standard FLRW equations. This partially addresses the criticism concerning the
corrections being gauge artifacts. For a particular initial choice of gauge
which simplifies the formalism, we explicitly construct these scalars in terms
of the underlying inhomogeneous geometry, and incidentally demonstrate that the
formal structure of the corrections with this gauge choice is identical to that
of analogous corrections derived by Buchert in the context of spatial averaging
of scalars.Comment: 18 pages, no figures, revtex4; v2 - minor clarifications added; v3 -
minor changes in presentation to improve clarity, reference added, to appear
in Phys. Rev.
An Investigation of Energy Storage Possibilities in Single Family Houses for Smart Grid Purposes
Superconductivity due to fluctuating loop currents
Orbital magnetism and the loop currents (LC) that accompany it have been
proposed to emerge in many systems, including cuprates, iridates, and kagome
superconductors. In the case of cuprates, LCs have been put forward as the
driving force behind the pseudogap, strange-metal behavior, and
-wave superconductivity. Here, we investigate whether fluctuating
intra-unit-cell loop currents can cause unconventional superconductivity. For
odd-parity LCs, we find that they are strongly repulsive in all pairing
channels near the underlying quantum-critical point (QCP). For even-parity LCs,
their fluctuations do give rise to unconventional pairing. However, this
pairing is not amplified in the vicinity of the QCP, in sharp contrast to other
known cases of pairing mediated by intra-unit-cell order parameters, such as
spin-magnetic, nematic, or ferroelectric ones. Applying our formalism to the
cuprates, we conclude that pairing mediated by fluctuating intra-unit-cell LCs
is unlikely to yield -wave superconductivity. We also show that
loop currents, if relevant for the cuprates, must vary between unit cells and
break translation symmetry.Comment: 12 pages, 7 figure
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