1,486 research outputs found
The attractor mechanism as a distillation procedure
In a recent paper it has been shown that for double extremal static
spherically symmetric BPS black hole solutions in the STU model the well-known
process of moduli stabilization at the horizon can be recast in a form of a
distillation procedure of a three-qubit entangled state of GHZ-type. By
studying the full flow in moduli space in this paper we investigate this
distillation procedure in more detail. We introduce a three-qubit state with
amplitudes depending on the conserved charges the warp factor, and the moduli.
We show that for the recently discovered non-BPS solutions it is possible to
see how the distillation procedure unfolds itself as we approach the horizon.
For the non-BPS seed solutions at the asymptotically Minkowski region we are
starting with a three-qubit state having seven nonequal nonvanishing amplitudes
and finally at the horizon we get a GHZ state with merely four nonvanishing
ones with equal magnitudes. The magnitude of the surviving nonvanishing
amplitudes is proportional to the macroscopic black hole entropy. A systematic
study of such attractor states shows that their properties reflect the
structure of the fake superpotential. We also demonstrate that when starting
with the very special values for the moduli corresponding to flat directions
the uniform structure at the horizon deteriorates due to errors generalizing
the usual bit flips acting on the qubits of the attractor states.Comment: 38 pages LaTe
Spectral Templates from Multicolor Redshift Surveys
Understanding how the physical properties of galaxies (e.g. their spectral
type or age) evolve as a function of redshift relies on having an accurate
representation of galaxy spectral energy distributions. While it has been known
for some time that galaxy spectra can be reconstructed from a handful of
orthogonal basis templates, the underlying basis is poorly constrained. The
limiting factor has been the lack of large samples of galaxies (covering a wide
range in spectral type) with high signal-to-noise spectrophotometric
observations. To alleviate this problem we introduce here a new technique for
reconstructing galaxy spectral energy distributions directly from samples of
galaxies with broadband photometric data and spectroscopic redshifts.
Exploiting the statistical approach of the Karhunen-Loeve expansion, our
iterative training procedure increasingly improves the eigenbasis, so that it
provides better agreement with the photometry. We demonstrate the utility of
this approach by applying these improved spectral energy distributions to the
estimation of photometric redshifts for the HDF sample of galaxies. We find
that in a small number of iterations the dispersion in the photometric
redshifts estimator (a comparison between predicted and measured redshifts) can
decrease by up to a factor of 2.Comment: 25 pages, 9 figures, LaTeX AASTeX, accepted for publication in A
Galaxy Zoo : Building the low-mass end of the red sequence with local post-starburst galaxies
We present a study of local post-starburst galaxies (PSGs) using the photometric and spectroscopic observations from the Sloan Digital Sky Survey and the results from the Galaxy Zoo project. We find that the majority of our local PSG population have neither early- nor late-type morphologies but occupy a well-defined space within the colour-stellar mass diagram, most notably, the low-mass end of the 'green valley' below the transition mass thought to be the mass division between low-mass star-forming galaxies and high-mass passively evolving bulge-dominated galaxies. Our analysis suggests that it is likely that local PSGs will quickly transform into 'red', low-mass early-type galaxies as the stellar morphologies of the 'green' PSGs largely resemble that of the early-type galaxies within the same mass range. We propose that the current population of PSGs represents a population of galaxies which is rapidly transitioning between the star-forming and the passively evolving phases. Subsequently, these PSGs will contribute towards the build-up of the low-mass end of the 'red sequence' once the current population of young stars fade and stars are no longer being formed. These results are consistent with the idea of 'downsizing' where the build-up of smaller galaxies occurs at later epochs.Peer reviewe
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