23,785 research outputs found
The MC@NLO 2.2 Event Generator
This is the user's manual of MC@NLO 2.2. This package is a practical
implementation, based upon the HERWIG event generator, of the MC@NLO formalism,
which allows one to incorporate NLO QCD matrix elements consistently into a
parton shower framework. Processes available in this version include the
hadroproduction of Higgs bosons, single vector bosons, vector boson pairs, and
heavy quark-antiquark pairs. This document is self-contained, but we emphasise
the main differences with respect to previous versions.Comment: 17 pages, no figures. Version 2 has more details on some features.
Program available at http://www.hep.phy.cam.ac.uk/theory/webber/MCatNLO
The MC@NLO 3.4 Event Generator
This is the user's manual of MC@NLO 3.4. This package is a practical
implementation, based upon the HERWIG event generator, of the MC@NLO formalism,
which allows one to incorporate NLO QCD matrix elements consistently into a
parton shower framework. Processes available in this version include the
hadroproduction of single vector and Higgs bosons, vector boson pairs, heavy
quark pairs, single top, single top in association with a W, lepton pairs, and
Higgs bosons in association with a W or Z. Spin correlations are included for
all processes except ZZ and WZ production. This document is self-contained, but
we emphasise the main differences with respect to previous versions.Comment: 30 page
On the Evolution, Numbers, and Characteristics of Close-Binary Supersoft Sources
The ability to perform detailed evolutionary calculations is essential to the
development of a well-defined and testable binary model. Unfortunately,
traditional evolutionary calculations cannot be used to follow a significant
fraction of possible close-binary supersoft sources (CBSSs). It is therefore
important to examine the input physics carefully, to be sure that all relevant
and potentially important physical processes are included. In this paper we
continue a line of research begun last year, and explore the role that winds
are expected to play in the evolution of CBSSs. We find that at least a subset
of the systems that seemed to be candidates for common envelope evolution may
survive, if radiation emitted by white dwarf drives winds from the system. We
study the effects of winds on the binary evolution of CBSSs, and compute the
number and characteristics of CBSSs expected to be presently active in galaxies
such as our own or M31.Comment: 13 pages; figures included in 0.33 M postscript file; in Supersoft
X-ray Sources, ed. J. Greiner (Springer-Verlag: Berlin) (1996
QCD Sum Rules on the Lattice
We study the work of Leinweber by applying the Continuum Model of QCD Sum
Rules (QCDSR) to the analysis of (quenched) lattice correlation functions. We
expand upon his work in several areas and find that, while the QCDSR Continuum
Model very adequately fits lattice data, it does so only for non-physical
values of its parameters. The non-relativistic model is found to predict
essentially the same form for the correlation functions as the QCDSR Continuum
Model but without the latter's restrictions. By fitting lattice data to a
general form which includes the non-relativistic quark model as a special case,
we confirm it as the model of choice.Comment: Talk presented by C.R. Allton at LAT97, Edinburgh. 3 pages, uses
espcrc2.st
The Progenitors of Type Ia Supernovae: II. Are they Double-Degenerate Binaries? The Symbiotic Channel
In order for a white dwarf (WD) to achieve the Chandrasekhar mass, M_C, and
explode as a Type Ia supernova (SNIa), it must interact with another star,
either accreting matter from or merging with it. The failure to identify the
types of binaries which produce SNeIa is the "progenitor problem". Its solution
is required if we are to utilize the full potential of SNeIa to elucidate basic
cosmological and physical principles. In single-degenerate models, a WD
accretes and burns matter at high rates. Nuclear-burning WDs (NBWDs) with mass
close to M_C are hot and luminous, potentially detectable as supersoft x-ray
sources (SSSs). In previous work we showed that > 90-99% of the required number
of progenitors do not appear as SSSs during most of the crucial phase of mass
increase. The obvious implication is that double-degenerate (DD) binaries form
the main class of progenitors. We show in this paper, however, that many
binaries that later become DDs must pass through a long-lived NBWD phase during
which they are potentially detectable as SSSs. The paucity of SSSs is therefore
not a strong argument in favor of DD models. Those NBWDs that are the
progenitors of DD binaries are likely to appear as symbiotic binaries for
intervals > 10^6 years. In fact, symbiotic pre-DDs should be common, whether or
not the WDs eventually produce SNeIa. The key to solving the progenitor problem
lies in understanding the appearance of NBWDs. Most do not appear as SSSs most
of the time. We therefore consider the evolution of NBWDs to address the
question of what their appearance may be and how we can hope to detect them.Comment: 24 pages; 5 figures; submitted to Ap
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