11,187 research outputs found
Luminous Supernovae
Supernovae (SNe), the luminous explosions of stars, were observed since
antiquity, with typical peak luminosity not exceeding 1.2x10^{43} erg/s
(absolute magnitude >-19.5 mag). It is only in the last dozen years that
numerous examples of SNe that are substantially super-luminous (>7x10^{43}
erg/s; <-21 mag absolute) were well-documented. Reviewing the accumulated
evidence, we define three broad classes of super-luminous SN events (SLSNe).
Hydrogen-rich events (SLSN-II) radiate photons diffusing out from thick
hydrogen layers where they have been deposited by strong shocks, and often show
signs of interaction with circumstellar material. SLSN-R, a rare class of
hydrogen-poor events, are powered by very large amounts of radioactive 56Ni and
arguably result from explosions of very massive stars due to the pair
instability. A third, distinct group of hydrogen-poor events emits photons from
rapidly-expanding hydrogen-poor material distributed over large radii, and are
not powered by radioactivity (SLSN-I). These may be the hydrogen-poor analogs
of SLSN-II.Comment: This manuscript has been accepted for publication in Science (to
appear August 24). This version has not undergone final editing. Please refer
to the complete version of record at http://www.sciencemag.org/. The
manuscript may not be reproduced or used in any manner that does not fall
within the fair use provisions of the Copyright Act without the prior,
written permission of AAA
In-medium nuclear interactions of low-energy hadrons
Experimental and theoretical developments of the last decade in the study of
exotic atoms and some related low-energy reactions are reviewed, in order to
provide information on the in-medium hadron-nucleon t matrix over a wide range
of densities up to central nuclear densities. In particular, we review pionic
deeply bound atomic states and related evidence for partial restoration of
chiral symmetry in dense nuclear matter. The case for relatively narrow deeply
bound atomic states for antikaons and antiprotons is made, based on the physics
of strong nuclear absorption. Recent experimental suggestions for signals of
antikaon-nuclear deeply bound states are reviewed, and dynamical models for
calculating binding energies, widths and densities of antikaon nuclear states
are discussed. Specific features of low-energy in-medium interactions of kaons,
antiprotons and of Sigma hyperons are discussed, and suggestions to study
experimentally Cascade atoms are reviewed.Comment: 86 pages, 44 figures, slight revisions, references added, Physics
Reports (in press
Chiral dynamics of -hyperons in the nuclear medium
Using SU(3) chiral perturbation theory we calculate the density-dependent
complex mean field of a -hyperon in
isospin-symmetric nuclear matter. The leading long-range -interaction arises from one-kaon exchange and from two-pion exchange with a
- or a -hyperon in the intermediate state. We find from the
conversion process at nuclear matter saturation density
fm an imaginary single-particle potential of
MeV, in fair agreement with existing empirical
determinations. The genuine long-range contributions from iterated (second
order) one-pion exchange with an intermediate - or -hyperon
sum up to a moderately repulsive real single-particle potential of
MeV. Recently measured ) inclusive spectra
related to -formation in heavy nuclei give evidence for a
-nucleus repulsion of similar size. Our results suggest that the net
effect of the short-range -interaction on the -nuclear mean
field could be small.Comment: 7 pages, 2 figures, published in: Phys. Rev. C 71, 068201 (2005
Few-body calculations of -nuclear quasibound states
We report on precise hyperspherical-basis calculations of and quasibound states, using energy dependent interaction potentials
derived from coupled-channel models of the nucleon
resonance. The attraction generated in these models is too weak to
generate a two-body bound state. No bound-state solution was found in
our calculations in models where Re fm, with the scattering length, covering thereby the majority of
resonance models. A near-threshold bound-state
solution, with separation energy of less than 1 MeV and width of about
15 MeV, was obtained in the 2005 Green-Wycech model where Re fm. The role of handling self consistently the subthreshold
interaction is carefully studied.Comment: a second footnote added in v2, matching published versio
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