27,614 research outputs found
Primordial torsion fields as an explanation of the anisotropy in cosmological electromagnetic propagation
In this note we provide a simple explanation of the recent finding of
anisotropy in electromagnetic (EM) propagation claimed by Nodland and Ralston
(astro-ph/9704196). We consider, as a possible origin of such effect, the
effective coupling between EM fields and some tiny background torsion field.
The coupling is obtained after integrating out charged fermions, it is gauge
invariant and does not require the introduction of any new physics.Comment: 8 pages, LaTeX, one figure, enlarged version with minor correction
Dark energy in motion
Recent large-scale peculiar velocity surveys suggest that large matter
volumes could be moving with appreciable velocity with respect to the CMB rest
frame. If confirmed, such results could conflict with the Cosmological
Principle according to which the matter and CMB rest frames should converge on
very large scales. In this work we explore the possibility that such large
scale bulk flows are due, not to the motion of matter with respect to the CMB,
but to the flow of dark energy with respect to matter. Indeed, when dark energy
is moving, the usual definition of the CMB rest frame as that in which the CMB
dipole vanishes is not appropriate. We find instead that the dipole vanishes
for observers at rest with respect to the cosmic center of mass, i.e. in motion
with respect to the background radiation.Comment: 9 pages, 1 figure. Essay selected for "Honorable Mention" in the 2006
Awards for Essays on Gravitation (Gravity Research Foundation
The dynamical nature of time
It is usually assumed that the "" parameter in the equations of dynamics
can be identified with the indication of the pointer of a clock. Things are not
so easy, however. In fact, since the equations of motion can be written in
terms of but also of , being any well behaved function, each
one of those infinite parametric times is as good as the Newtonian one to
study classical dynamics. Here we show that the relation between the
mathematical parametric time in the equations of dynamics and the physical
dynamical time that is measured with clocks is more complex and subtle
than usually assumed. These two times, therefore, must be carefully
distinguished since their difference may have significant consequences.
Furthermore, we show that not all the dynamical clock-times are necessarily
equivalent and that the observational fingerprint of this non-equivalence has
the same form as that of the Pioneer anomaly.Comment: 13 pages, no figure
Cosmic Rays from Heavy Dark Matter from the Galactic Center
The gamma-ray fluxes observed by the High Energy Stereoscopic System (HESS)
from the J1745-290 Galactic Center source is well fitted by the secondary
photons coming from Dark Matter (DM) annihilation in particle-antiparticle
standard model pairs over a diffuse power-law background. The spectral features
of the signal are consistent with different channels: light quarks,
electro-weak gauge bosons and top-antitop production. The amount of photons and
morphology of the signal localized within a region of few parsecs, require
compressed DM profiles as those resulting from baryonic contraction, which
offer large enhancements in the signal over DM alone simulations. The fits
return a heavy WIMP, with a mass above 10 TeV, but well below the unitarity
limit for thermal relic annihilation. The fitted background spectral index is
compatible with the Fermi-Large Area Telescope (LAT) data from the same region.
This possibility can be potentially tested with the observations of other high
energy cosmic rays.Comment: Proceedings of the European Physical Society Conference on High
Energy Physics EPS-HEP2013, 18-24 July 2013, Stockholm (Sweden
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