14,617 research outputs found
Peak statistics on COBE maps
We perform the stastistics of temperature maxima and minima in COBE-DMR
2-year maps. For power-law spectra the surface distribution of peaks implies an
amplitude consistent with more conventional analyses of COBE data (for
instance, we get K for a spectral index but not with the measured quadrupole K. This
provides further support for the existence an infrared cutoff in the cosmic
spectrum.Comment: Latex file, Astronomy & Astrophysics L-aa style. Hardcopy figures
available separately, send requests to [email protected]
Regularity of the stress-energy tensor for extremal Reissner-Nordstrom black holes
We calculate the expectation values of the stress-energy tensor for both a
massless minimally-coupled and dilaton-coupled 2D field propagating on an
extremal Reissner-Nordstrom black hole, showing its regularity on the horizon
in contrast with previous claims in the literature.Comment: 10 pages, 1 figure; Talk given at QG05, Cala Gonone (Italy),
September 200
A torsional completion of gravity for Dirac matter fields and its applications to neutrino oscillations
In this paper, we consider the torsional completion of gravitation for an
underlying background filled with Dirac fields, applying it to the problem of
neutrino oscillations: we discuss the effects of the induced torsional
interactions as corrections to the neutrino oscillation mechanism.Comment: 4 page
Static quantum corrections to the Schwarzschild spacetime
We study static quantum corrections of the Schwarzschild metric in the
Boulware vacuum state. Due to the absence of a complete analytic expression for
the full semiclassical Einstein equations we approach the problem by
considering the s-wave approximation and solve numerically the associated
backreaction equations. The solution, including quantum effects due to pure
vacuum polarization, is similar to the classical Schwarzschild solution up to
the vicinity of the classical horizon. However, the radial function has a
minimum at a time-like surface close to the location of the classical event
horizon. There the g_{00} component of the metric reaches a very small but
non-zero value. The analysis unravels how a curvature singularity emerges
beyond this bouncing point. We briefly discuss the physical consequences of
these results by extrapolating them to a dynamical collapsing scenario.Comment: 10 pages; Talk given at QG05, Cala Gonone (Italy), September 200
Quantum effects in Acoustic Black Holes: the Backreaction
We investigate the backreaction equations for an acoustic black hole formed
in a Laval nozzle under the assumption that the motion of the fluid is
one-dimensional. The solution in the near-horizon region shows that as phonons
are (thermally) radiated the sonic horizon shrinks and the temperature
decreases. This contrasts with the behaviour of Schwarzschild black holes, and
is similar to what happens in the evaporation of (near-extremal)
Reissner-Nordstrom black holes (i.e. infinite evaporation time). Finally, by
appropriate boundary conditions the solution is extended in both the asymptotic
regions of the nozzle.Comment: 23 pages, latex, 1 figure; revised version, to appear in Phys. Rev.
The synchrotron foreground and CMB temperature-polarization cross correlation power spectrum from the first year WMAP data
We analyse the temperature-polarization cross-correlation in the Galactic
synchrotron template that we have recently developed, and between the template
and CMB temperature maps derived from WMAP data. Since the polarized
synchrotron template itself uses WMAP data, we can estimate residual
synchrotron contamination in the CMB angular spectrum. While
appears to be contamined by synchrotron, no evidence for
contamination is found in the multipole range which is most relevant for the
fit of the cosmological optical depth.Comment: Accepted for pubblication on MNRAS Lette
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