75,363 research outputs found
Anisotropic Compacts Stars on Paraboloidal Spacetime with Linear Equation of State
New exact solutions of Einstein's field equations (EFEs) by assuming linear
equation of state, where is the radial
pressure and is the surface density, are obtained on the background
of a paraboloidal spacetime. By assuming estimated mass and radius of strange
star candidate 4U 1820-30, various physical and energy conditions are used for
estimating the range of parameter . The suitability of the model for
describing pulsars like PSR J1903+327, Vela X-1, Her X-1 and SAX J1804.3658 has
been explored and respective ranges of , for which all physical and
energy conditions are satisfied throughout the distribution, are obtained.Comment: 10 pages, 12 figures, 1 tabl
Limits on the temporal variation of the fine structure constant, quark masses and strong interaction from quasar absorption spectra and atomic clock experiments
We perform calculations of the dependence of nuclear magnetic moments on
quark masses and obtain limits on the variation of from
recent measurements of hydrogen hyperfine (21 cm) and molecular rotational
transitions in quasar absorption systems, atomic clock experiments with
hyperfine transitions in H, Rb, Cs, Yb, Hg and optical transition in
Hg. Experiments with Cd, deuterium/hydrogen, molecular SF and
Zeeman transitions in He/Xe are also discussed.Comment: 8 pages, 1 figure, uses revtex
Anelastic dynamo models with variable electrical conductivity: an application to gas giants
The observed surface dynamics of Jupiter and Saturn is dominated by a banded
system of zonal winds. Their depth remains unclear but they are thought to be
confined to the very outer envelopes where hydrogen remains molecular and the
electrical conductivity is small. The dynamo maintaining the dipole-dominated
magnetic fields of both gas giants likely operates in the deeper interior where
hydrogen assumes a metallic state. Here, we present numerical simulations that
attempt to model both the zonal winds and the interior dynamo action in an
integrated approach. Using the anelastic version of the MHD code MagIC, we
explore the effects of density stratification and radial electrical
conductivity variation. The electrical conductivity is mostly assumed to remain
constant in the thicker inner metallic region and it decays exponentially
towards the outer boundary throughout the molecular envelope. Our results show
that the combination of stronger density stratification and weaker conducting
outer layer is essential for reconciling dipole dominated dynamo action and a
fierce equatorial zonal jet. Previous simulations with homogeneous electrical
conductivity show that both are merely exclusive, with solutions either having
strong zonal winds and multipolar magnetic fields or weak zonal winds and
dipole-dominated magnetic fields. All jets tend to be geostrophic and therefore
reach right through the convective shell in our simulations. The particular
setup explored here allows a strong equatorial jet to remain confined to the
weaker conducting outer region where it does not interfere with the deeper
seated dynamo action. The flanking mid to high latitude jets, on the other
hand, have to remain faint to yield a strongly dipolar magnetic field. The
fiercer jets on Jupiter and Saturn only seem compatible with the observed
dipolar fields when they remain confined to a weaker conducting outer layer.Comment: 16 pages, 11 figures, 2 tables, submitted to PEP
3D weak lensing with spin wavelets on the ball
We construct the spin flaglet transform, a wavelet transform to analyze spin
signals in three dimensions. Spin flaglets can probe signal content localized
simultaneously in space and frequency and, moreover, are separable so that
their angular and radial properties can be controlled independently. They are
particularly suited to analyzing of cosmological observations such as the weak
gravitational lensing of galaxies. Such observations have a unique 3D
geometrical setting since they are natively made on the sky, have spin angular
symmetries, and are extended in the radial direction by additional distance or
redshift information. Flaglets are constructed in the harmonic space defined by
the Fourier-Laguerre transform, previously defined for scalar functions and
extended here to signals with spin symmetries. Thanks to various sampling
theorems, both the Fourier-Laguerre and flaglet transforms are theoretically
exact when applied to bandlimited signals. In other words, in numerical
computations the only loss of information is due to the finite representation
of floating point numbers. We develop a 3D framework relating the weak lensing
power spectrum to covariances of flaglet coefficients. We suggest that the
resulting novel flaglet weak lensing estimator offers a powerful alternative to
common 2D and 3D approaches to accurately capture cosmological information.
While standard weak lensing analyses focus on either real or harmonic space
representations (i.e., correlation functions or Fourier-Bessel power spectra,
respectively), a wavelet approach inherits the advantages of both techniques,
where both complicated sky coverage and uncertainties associated with the
physical modeling of small scales can be handled effectively. Our codes to
compute the Fourier-Laguerre and flaglet transforms are made publicly
available.Comment: 24 pages, 4 figures, version accepted for publication in PR
Doubly heavy hadrons and the domain of validity of doubly heavy diquark--anti-quark symmetry
In the limit of heavy quark masses going to infinity, a symmetry is known to
emerge in QCD relating properties of hadrons with two heavy quarks to analogous
states with one heavy anti-quark. A key question is whether the charm mass is
heavy enough so that this symmetry is manifest in at least an approximate
manner. The issue is crucial in attempting to understand the recent reports by
the SELEX Collaboration of doubly charmed baryons. We argue on very general
grounds that the charm quark mass is substantially too light for the symmetry
to emerge automatically via colour coulombic interactions. However, the
symmetry could emerge approximately depending on the dynamical details.Comment: 9 page
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