9,215 research outputs found
Test of QEDPS: A Monte Carlo for the hard photon distributions in e+ e- annihilation proecss
The validity of a photon shower generator QEDPS has been examined in detail.
This is formulated based on the leading-logarithmic renormalization equation
for the electron structure function and it provides a photon shower along the
initial e+-. The main interest in the present work is to test the reliability
of the generator to describe a process accompanying hard photons which are
detected. For this purpose, by taking the HZ production as the basic reaction,
the total cross section and some distributions of the hard photons are compared
between two cases that these photons come from either those generated by QEDPS
or the hard process e+e- -> H Z gamma gamma. The comparison performed for the
single and the double hard photon has shown a satisfactory agreement which
demonstrated that the model is self-consistent.Comment: 22 pages, 4 Postscript figures, LaTeX, uses epsf.te
A QED Shower Including the Next-to-leading Logarithm Correction in e+e- Annihilation
We develop an event generator, NLL-QEDPS, based on the QED shower including
the next-to-leading logarithm correction in the e^+e^- annihilation. The shower
model is the Monte Carlo technique to solve the renormalization group equation
so that they can calculate contributions of alpha^m log^n(S/m_e^2) for any m
and n systematically. Here alpha is the QED coupling, m_e is the mass of
electron and S is the square of the total energy in the e^+e^- system. While
the previous QEDPS is limited to the leading logarithm approximation which
includes only contributions of (alpha log(S/m_e^2))^n, the model developed here
contains terms of alpha(alpha log(S/m_e^2))^n, the the next-to-leading
logarithm correction.
The shower model is formulated for the initial radiation in the e^+e^-
annihilation. The generator based on it gives us events with q^2, which is a
virtual mass squared of the virtual photon and/or Z-boson, in accuracy of
0.04%, except for small q^2/S.Comment: 35 pages, 1 figure(eps-file
ASCA Slew Survey
We are systematically analyzing ASCA GIS data taken during the satellite
attitude maneuver operation. Our motivation is to search for serendipitous hard
X-ray sources and make the ASCA Slew Survey catalog.
During its operational life from 1993 February to 2000 July, ASCA carried out
more than 2,500 maneuver operations, and total exposure time during the
maneuver was ~415 ksec after data screening. Preliminary results are briefly
reported.Comment: Proceedings for "X-ray surveys in the light of new observations",
Santander (Spain), 2002 September. 1 pag
Thermal Renormalons in Scalar Field Theory
In the frame of the scalar theory , we explore the occurrence of
thermal renormalons, i. e. temperature dependent singularities in the Borel
plane. The discussion of a particular renormalon type diagram at finite
temperature, using Thermofield Dynamics, allows us to establish that these
singularities actually get a temperature dependence. This dependence appears in
the residues of the poles, remaining their positions unchanged with
temperature.Comment: 12 pages, 3 figures, uses feynMF. Minor correction
Finite Temperature Renormalization of the - and -Models at Zero Momentum
A self-consistent renormalization scheme at finite temperature and zero
momentum is used together with the finite temperature renormalization group to
study the temperature dependence of the mass and the coupling to one-loop order
in the - and -models. It is found that the critical
temperature is shifted relative to the naive one-loop result and the coupling
constants at the critical temperature get large corrections. In the high
temperature limit of the \phiff-model the coupling decreases.Comment: 16 pages, plain Latex, NORDITA-92/38
The s-Process Nucleosynthesis in Extremely Metal-Poor Stars as the Generating Mechanism of Carbon Enhanced Metal-Poor Stars
The origin of carbon-enhanced metal-poor (CEMP) stars plays a key role in
characterising the formation and evolution of the first stars and the Galaxy
since the extremely-poor (EMP) stars with [Fe/H] \leq -2.5 share the common
features of carbon enhancement in their surface chemical compositions. The
origin of these stars is not yet established due to the controversy of the
origin of CEMP stars without the enhancement of s-process element abundances,
i.e., so called CEMP-no stars. In this paper, we elaborate the s-process
nucleosynthesis in the EMP AGB stars and explore the origin of CEMP stars. We
find that the efficiency of the s-process is controlled by O rather than Fe at
[Fe/H] \lesssim -2. We demonstrate that the relative abundances of Sr, Ba, Pb
to C are explained in terms of the wind accretion from AGB stars in binary
systems.Comment: The Proceedings of the Nuclei in the Cosmos XIV, in pres
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