862 research outputs found
Early Universe Constraints on Time Variation of Fundamental Constants
We study the time variation of fundamental constants in the early Universe.
Using data from primordial light nuclei abundances, CMB and the 2dFGRS power
spectrum, we put constraints on the time variation of the fine structure
constant , and the Higgs vacuum expectation value leads to a variation
in the electron mass, among other effects. Along the same line, we study the
variation of and the electron mass . In a purely phenomenological
fashion, we derive a relationship between both variations.Comment: 18 pages, 12 figures, accepted for publication in Physical Review
Bardeen-Petterson effect and the disk structure of the Seyfert galaxy NGC 1068
VLBA high spatial resolution observations of the disk structure of the active
galactic nucleus NGC 1068 has recently revealed that the kinematics and
geometry of this AGN is well characterized by an outer disk of H2O maser
emission having a compact milliarcsecond (parsec) scale structure, which is
encircling a thin rotating inner disk surrounding a ~10^7 M_\sun compact
mass, likely a black hole. A curious feature in this source is the occurrence
of a misalignment between the inner and outer parts of the disk, with the
galaxy's radio jet being orthogonal to the inner disk. We interpret this
peculiar configuration as due to the Bardeen-Petterson effect, a general
relativistic effect that warps an initially inclined (to the black hole
equator) viscous disk, and drives the angular momentum vector of its inner part
into alignment with the rotating black hole spin. We estimate the time-scale
for both angular momenta to get aligned as a function the spin parameter of the
Kerr black hole. We also reproduce the shape of the parsec and kiloparsec scale
jets, assuming a model in which the jet is precessing with a period and
aperture angle that decrease exponentially with time, as expected from the
Bardeen-Petterson effect.Comment: 12 pages, 3 figures, accepted for publication in The Astrophysical
Journa
A multi-institutional and interdisciplinary approach to the assessment of vulnerability and adaptation to climate change in the Peruvian Central Andes: problems and prospects
A local integrated assessment of the vulnerability and adaptation to climate change in the Mantaro River Basin, located in Peruvian Central Andes, was developed between years 2003 to 2005. In this paper we present some lessons learned during the development of this study, emphasizing the multi-institutional and interdisciplinary efforts, briefly showing the methodological aspects, and pointing out the main problems found
Nonlinear electrodynamics and CMB polarization
Recently WMAP and BOOMERanG experiments have set stringent constraints on the
polarization angle of photons propagating in an expanding universe: . The polarization of the Cosmic Microwave
Background radiation (CMB) is reviewed in the context of nonlinear
electrodynamics (NLED). We compute the polarization angle of photons
propagating in a cosmological background with planar symmetry. For this
purpose, we use the Pagels-Tomboulis (PT) Lagrangian density describing NLED,
which has the form , where , and the parameter featuring the
non-Maxwellian character of the PT nonlinear description of the electromagnetic
interaction. After looking at the polarization components in the plane
orthogonal to the ()-direction of propagation of the CMB photons, the
polarization angle is defined in terms of the eccentricity of the universe, a
geometrical property whose evolution on cosmic time (from the last scattering
surface to the present) is constrained by the strength of magnetic fields over
extragalactic distances.Comment: 17 pages, 2 figures, minor changes, references adde
Observational evidence of spin-induced precession in active galactic nuclei
We show that it is possible to explain the physical origin of jet precession
in active galactic nuclei (AGNs) through the misalignment between the rotation
axes of the accretion disk and of the Kerr black hole. We apply this scenario
to quasars, Seyfert galaxies and also to the Galactic Center black hole Sgr A*,
for which signatures of either jet or disk precession have been found. The
formalism adopted is parameterized by the ratio of the precession period to the
black hole mass and can be used to put constraints to the physical properties
of the accretion disk as well as to the black hole spin in those systems.Comment: 10 pages, 1 figure, accepted for publication in ApJ Letter
Testing Primordial Abundances With Sterile Neutrinos
The mixing between sterile and active neutrinos is taken into account in the
calculation of Big Bang Nucleosynthesis. The abundances of primordial elements,
like D, 3He, 4He and 7Li, are calculated by including sterile neutrinos, and by
using finite chemical potentials. It is found that the resulting theoretical
abundances are consistent with WMAP data on baryonic densities, and with limits
of LSND on mixing angles, only if 7Li is excluded from the statistical analysis
of theoretical and experimental results.Comment: 7 pages, 3 figures, 1 table, 34 reference
Effects of CPT and Lorentz Invariance Violation on Pulsar Kicks
The breakdown of Lorentz's and CPT invariance, as described by the Extension
of the Standard Model, gives rise to a modification of the dispersion relation
of particles. Consequences of such a modification are reviewed in the framework
of pulsar kicks induced by neutrino oscillations (active-sterile conversion). A
peculiar feature of the modified energy-momentum relations is the occurrence of
terms of the form \delta {\bbox \Pi}\cdot {\bf {\hat p}}, where \delta
{\bbox \Pi} accounts for the difference of spatial components of flavor
depending coefficients which lead to the departure of the Lorentz symmetry, and
, being the neutrino momentum. Owing to the
relative orientation of with respect to \delta {\bbox \Pi}, the
{\it coupling} \delta {\bbox \Pi}\cdot {\bf {\hat p}} may induce the
mechanism to generate the observed pulsar velocities. Topics related to the
velocity distribution of pulsars are also discussed.Comment: 10 pages, 1 figur
I. Flux and color variations of the quadruply imaged quasar HE 0435-1223
aims: We present VRi photometric observations of the quadruply imaged quasar
HE 0435-1223, carried out with the Danish 1.54m telescope at the La Silla
Observatory. Our aim was to monitor and study the magnitudes and colors of each
lensed component as a function of time. methods: We monitored the object during
two seasons (2008 and 2009) in the VRi spectral bands, and reduced the data
with two independent techniques: difference imaging and PSF (Point Spread
Function) fitting.results: Between these two seasons, our results show an
evident decrease in flux by ~0.2-0.4 magnitudes of the four lensed components
in the three filters. We also found a significant increase (~0.05-0.015) in
their V-R and R-i color indices. conclusions: These flux and color variations
are very likely caused by intrinsic variations of the quasar between the
observed epochs. Microlensing effects probably also affect the brightest "A"
lensed component.Comment: 10 pages, 8 figure
Neutrino Oscillations at Supernova Core Bounce Generate the Strongest Gravitational-Wave Bursts
During the core bounce of a supernova collapse resonant active-to-active
(), as well as active-to-sterile () neutrino
() oscillations can take place. Besides, over this phase weak magnetism
increases antineutrino () mean free paths, and thus its luminosity.
Because the oscillation feeds mass-energy into the target species, the
large mass-squared difference between species () implies a
huge amount of power to be given off as gravitational waves (^{-1}\nu\nu\nu$ diffusion (convection and cooling) or quadrupole moments of
the neutron star matter. This new feature turns these bursts the more promising
supernova gravitational-wave signal that may be detected by observatories as
LIGO, VIRGO, etc., for distances far out to the VIRGO cluster of galaxies.Comment: 10 pages, 1 figure, Proceedings of International Workshop on
Astronomy and Relativistic Astrophysics, Olinda (Brazil), October 12-16
(2003), to be published in Int. J. Mod. Phys.
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