49,755 research outputs found
Strong-field gravitational-wave emission in Schwarzschild and Kerr geometries: some general considerations
We show how the concurrent implementation of the exact solutions of the
Einstein equations, of the equations of motion of the test particles, and of
the relativistic estimate of the emission of gravitational waves from test
particles, can establish a priori constraints on the possible phenomena
occurring in Nature. Two examples of test particles starting at infinite
distance or from finite distance in a circular orbit around a Kerr black hole
are considered: the first leads to a well defined gravitational wave burst the
second to a smooth merging into the black hole. This analysis is necessary for
the study of the waveforms in merging binary systems.Comment: Resubmitted to PRD after Referee repor
The Berry-Tabor conjecture for spin chains of Haldane-Shastry type
According to a long-standing conjecture of Berry and Tabor, the distribution
of the spacings between consecutive levels of a "generic'' integrable model
should follow Poisson's law. In contrast, the spacings distribution of chaotic
systems typically follows Wigner's law. An important exception to the
Berry-Tabor conjecture is the integrable spin chain with long-range
interactions introduced by Haldane and Shastry in 1988, whose spacings
distribution is neither Poissonian nor of Wigner's type. In this letter we
argue that the cumulative spacings distribution of this chain should follow the
"square root of a logarithm'' law recently proposed by us as a characteristic
feature of all spin chains of Haldane-Shastry type. We also show in detail that
the latter law is valid for the rational counterpart of the Haldane-Shastry
chain introduced by Polychronakos.Comment: LaTeX with revtex4, 6 pages, 6 figure
Discovery of a deep Seyfert-2 galaxy at z = 0.222 behind NGC 300
We report on the unveiling of the nature of the unidentified X-ray source
3XMM J005450.3-373849 as a Seyfert-2 galaxy located behind the spiral galaxy
NGC 300 using Hubble Space Telescope data, new spectroscopic Gemini
observations and available XMM-Newton and Chandra data. We show that the X-ray
source is positionally coincident with an extended optical source, composed by
a marginally resolved nucleus/bulge, surrounded by an elliptical disc-like
feature and two symmetrical outer rings. The optical spectrum is typical of a
Seyfert-2 galaxy redshifted to z=0.222 +/- 0.001, which confirms that the
source is not physically related to NGC 300. At this redshift the source would
be located at 909+/-4 Mpc (comoving distance in the standard model). The X-ray
spectra of the source are well-fitted by an absorbed power-law model. By tying
between the six available spectra, we found a variable index
running from ~2 in 2000-2001 years, to 1.4-1.6 in the 2005-2014
period. Alternatively, by tying , we found variable absorption columns
of N_H ~ 0.34 x cm in 2000-2001 years, and 0.54-0.75 x
cm in the 2005-2014 period. Although we cannot distinguish
between an spectral or absorption origin, from the derived unabsorbed X-ray
fluxes, we are able to assure the presence of long-term X-ray variability.
Furthermore, the unabsorbed X-ray luminosities of 0.8-2 x 10 erg
s derived in the X-ray band are in agreement with a weakly obscured
Seyfert-2 AGN at .Comment: MNRAS, accepte
Restrictions on the coherence of the ultrafast optical emission from an electron-hole pairs condensate
We report on the transfer of coherence from a quantum-well electron-hole
condensate to the light it emits. As a function of density, the coherence of
the electron-hole pair system evolves from being full for the low density
Bose-Einstein condensate to a chaotic behavior for a high density BCS-like
state. This degree of coherence is transfered to the light emitted in a damped
oscillatory way in the ultrafast regime. Additionally, the photon field
exhibits squeezing properties during the transfer time. We analyze the effect
of light frequency and separation between electron and hole layers on the
optical coherence. Our results suggest new type of ultrafast experiments for
detecting electron-hole pair condensation.Comment: 4 pages,3 figures, to be published in Physical Review Letters. Minor
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