30,094,132 research outputs found
Axisymmetric circumstellar interaction in supernovae
Multiwavelength observations of Type II supernovae have shown evidence for
the interaction of supernovae with the dense slow winds from the red supergiant
progenitor stars. Observations of planetary nebulae and the nebula around SN
1987A show that the slow winds from extended stars frequently have an axisymme-
tric structure with a high density in the equatorial plane. We have carried out
numerical calculations of the interaction of a supernova with such an axisymme-
tric density distribution. For small values of the angular density gradient at
the pole, the asymmetry in the interaction shell is greater than, but close to,
that expected from purely radial motion. If the angular density gradient is
above a moderate value, the flow qualitatively changes and a protrusion emerges
along the axis. For a power-law supernova density profile, the flow approaches
a self-similar state in which the protrusion length is times the radius
of the main shell. The critical density gradient is larger for steeper density
profiles of the ejecta. Most of our calculations are axisymmetric, but we have
carried out a 3-dimensional calculation to show that the protrusion is not a
numerical artifact along the symmetry axis. For typical supernova parameters,
the protrusions take several years to develop. The appearance of the
shell with protrusions is similar to that observed in VLBI radio images of the
remnant 41.9 +58 in M82 and, possibly, of SN 1986J. We also considered the
possibility of asymmetric ejecta and found that it had a relatively small
effect on the asymmetry of the interaction region.Comment: 22 page postscript file (gzipped and uuencoded), 10 gzipped
postscript figures may be retrieved from
ftp://www.astro.su.se/pub/supernova/blc96_asym/ Submitted to Ap
Search for a Higgs Boson Decaying into Two Photons with the L3 Detector at LEP
A search is performed for a Higgs boson, decaying into two photons, using the
L3 data collected at centre of mass energies between = 189 and 202
GeV, corresponding to an integrated luminosity of 400 pb. The processes
, , are considered. The observed data are found to be consistent with the
expected background from standard physics processes. Limits on the branching
fraction of the Higgs boson decay into two photons as a function of the Higgs
mass are shown and a lower mass limit on a fermiophobic Higgs is derived.Comment: 3 pages, 2 postscript figures, Presented at the DPF2000 Conference,
August 9-12, 2000, The Ohio State University, Columbus, Ohi
A Fast Algorithm for Computing the p-Curvature
We design an algorithm for computing the -curvature of a differential
system in positive characteristic . For a system of dimension with
coefficients of degree at most , its complexity is \softO (p d r^\omega)
operations in the ground field (where denotes the exponent of matrix
multiplication), whereas the size of the output is about . Our
algorithm is then quasi-optimal assuming that matrix multiplication is
(\emph{i.e.} ). The main theoretical input we are using is the
existence of a well-suited ring of series with divided powers for which an
analogue of the Cauchy--Lipschitz Theorem holds.Comment: ISSAC 2015, Jul 2015, Bath, United Kingdo
Afterglow upper limits for four short duration, hard spectrum gamma-ray bursts
We present interplanetary network localization, spectral, and time history
information for four short-duration, hard spectrum gamma-ray bursts, GRB000607,
001025B, 001204, and 010119. All of these events were followed up with
sensitive radio and optical observations (the first and only such bursts to be
followed up in the radio to date), but no detections were made, demonstrating
that the short bursts do not have anomalously intense afterglows. We discuss
the upper limits, and show that the lack of observable counterparts is
consistent both with the hypothesis that the afterglow behavior of the short
bursts is like that of the long duration bursts, many of which similarly have
no detectable afterglows, as well as with the hypothesis that the short bursts
have no detectable afterglows at all. Small number statistics do not allow a
clear choice between these alternatives, but given the present detection rates
of various missions, we show that progress can be expected in the near future.Comment: 19 pages, 4 figures; Revised version, accepted by the Astrophysical
Journa
The spectroscopic evolution of the symbiotic-like recurrent nova V407 Cygni during its 2010 outburst. I. The shock and its evolution
On 2010 Mar 10, V407 Cyg was discovered in outburst, eventually reaching V< 8
and detected by Fermi. Using medium and high resolution ground-based optical
spectra, visual and Swift UV photometry, and Swift X-ray spectrophotometry, we
describe the behavior of the high-velocity profile evolution for this nova
during its first three months. The peak of the X-ray emission occurred at about
day 40 with a broad maximum and decline after day 50. The main changes in the
optical spectrum began at around that time. The He II 4686A line first appeared
between days 7 and 14 and initially displayed a broad, symmetric profile that
is characteristic of all species before day 60. Low-excitation lines remained
comparatively narrow, with v(rad,max) of order 200-400 km/s. They were
systematically more symmetric than lines such as [Ca V], [Fe VII], [Fe X], and
He II, all of which showed a sequence of profile changes going from symmetric
to a blue wing similar to that of the low ionization species but with a red
wing extended to as high as 600 km/s . The Na I D doublet developed a broad
component with similar velocity width to the other low-ionization species. The
O VI Raman features were not detected. We interpret these variations as
aspherical expansion of the ejecta within the Mira wind. The blue side is from
the shock penetrating into the wind while the red wing is from the low-density
periphery. The maximum radial velocities obey power laws, v(rad,max) t^{-n}
with n ~ 1/3 for red wing and ~0.8 for the blue. (truncated)Comment: Accepted for publication, A&A (submitted: 9 Oct 2010; accepted: 1 Dec
2010) in press; based on data obtained with Swift, Nordic Optical Telescope,
Ondrejov Observatory. Corrected typo, Fermi?LAT detection was at energies
above 100 MeV (with thanks to C. C. Cheung
Strong enhancement of d-wave superconducting state in the three-band Hubbard model coupled to an apical oxygen phonon
We study the hole binding energy and pairing correlations in the three-band
Hubbard model coupled to an apical oxygen phonon, by exact diagonalization and
constrained-path Monte Carlo simulations. In the physically relevant
charge-transfer regime, we find that the hole binding energy is strongly
enhanced by the electron-phonon interaction, which is due to a novel
potential-energy-driven pairing mechanism involving reduction of both
electronic potential energy and phonon related energy. The enhancement of hole
binding energy, in combination with a phonon-induced increase of quasiparticle
weight, leads to a dramatic enhancement of the long-range part of d-wave
pairing correlations. Our results indicate that the apical oxygen phonon plays
a significant role in the superconductivity of high- cuprates.Comment: 5 pages, 5 figure
Black hole boundaries
Classical black holes and event horizons are highly non-local objects,
defined in relation to the causal past of future null infinity. Alternative,
quasilocal characterizations of black holes are often used in mathematical,
quantum, and numerical relativity. These include apparent, killing, trapping,
isolated, dynamical, and slowly evolving horizons. All of these are closely
associated with two-surfaces of zero outward null expansion. This paper reviews
the traditional definition of black holes and provides an overview of some of
the more recent work on alternative horizons.Comment: 27 pages, 8 figures, invited Einstein Centennial Review Article for
CJP, final version to appear in journal - glossary of terms added, typos
correcte
Is entanglement entropy proportional to area?
It is known that the entanglement entropy of a scalar field, found by tracing
over its degrees of freedom inside a sphere of radius , is
proportional to the area of the sphere (and not its volume). This suggests that
the origin of black hole entropy, also proportional to its horizon area, may
lie in the entanglement between the degrees of freedom inside and outside the
horizon. We examine this proposal carefully by including excited states, to
check probable deviations from the area law.Comment: 6 pages. Based on talk by S. Das at Theory Canada 1, Vancouver, 3
June, 2005. To be published in a special edition of the Canadian Journal of
Physics. Minor changes to match published versio
Maxwell-Chern-Simons Q-balls
We examine the energetics of -balls in Maxwell-Chern-Simons theory in two
space dimensions. Whereas gauged -balls are unallowed in this dimension in
the absence of a Chern-Simons term due to a divergent electromagnetic energy,
the addition of a Chern-Simons term introduces a gauge field mass and renders
finite the otherwise-divergent electromagnetic energy of the -ball. Similar
to the case of gauged -balls, Maxwell-Chern-Simons -balls have a maximal
charge. The properties of these solitons are studied as a function of the
parameters of the model considered, using a numerical technique known as
relaxation. The results are compared to expectations based on qualitative
arguments.Comment: 6 pages. Talk given at Theory CANADA 2, Perimeter Institut
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