203 research outputs found
Bosonic corrections to the effective leptonic weak mixing angle at the two-loop level
Details of the recent calculation of the two-loop bosonic corrections to the
effective leptonic weak mixing angle are presented. In particular, the
expansion in the difference of the W and Z boson masses is studied and some of
the master integrals needed are given in analytic form.Comment: 5 pages, 4 figures, to appear in the proceedings of the 7th
International Symposium on Radiative Corrections (RADCOR05), Shonan Village,
Japan, 200
Nonmarine stromatolites and the search for early life on Mars
The available evidence permits one to conclude that streams flowed and lakes developed on Mars sometime in the remote past. The lessons learned from the Earth's earliest fossil record suggest that stromatolites might have formed on Mars, speculating that: (1) biopoesis occurred on Mars during its earliest history; (2) life evolved and diversified; (3) life inhabited aqueous environments; and (4) sunlight was an important environmental resource. The most likely place to find stromatolites and possibly microbial fossils on Mars would be in ancient lake and stream deposits. If thermal spring deposits can be identified, then they too are sites for biogeological investigations. Other aspects of this study are presented
Two-loop electroweak fermionic corrections to sin^2 theta_{eff}^{b anti-b}
We present the first calculation of the two-loop electroweak fermionic
correction to the flavour-dependent effective weak-mixing angle for bottom
quarks, sin^2 theta_{eff}^{b anti-b}. For the evaluation of the missing
two-loop vertex diagrams, two methods are employed, one based on a
semi-numerical Bernstein-Tkachov algorithm and the second on asymptotic
expansions in the large top-quark mass. A third method based on dispersion
relations is used for checking the basic loop integrals. We find that for small
Higgs-boson mass values, M_H ~ 100 GeV, the correction is sizable, of order
O(10^{-4}).Comment: 17 pages, 2 figures, references added, accepted for publication in
Nucl. Phys.
ZFITTER: a semi-analytical program for fermion pair production in e+e- annihilation, from version 6.21 to version 6.42
ZFITTER is a Fortran program for the calculation of fermion pair production
and radiative corrections at high energy e+e- colliders; it is also suitable
for other applications where electroweak radiative corrections appear. ZFITTER
is based on a semi-analytical approach to the calculation of radiative
corrections in the Standard Model. We present a summary of new features of the
ZFITTER program version 6.42 compared to version 6.21. The most important
additions are: (i) some higher-order QED corrections to fermion pair
production, (ii) electroweak one-loop corrections to atomic parity violation,
(iii) electroweak one-loop corrections to nu-e nu-e-bar production, (iv)
electroweak two-loop corrections to the W boson mass and the effective weak
mixing angle.Comment: 60 pages, latex, 3 table
Stromatolites and MISS—Differences Between Relatives
Benthic microorganisms form highly organized communities called “biofilms.” A biofilm consists of the individual cells plus their extracellular polymeric substances (EPS). In marine and non-marine environments, benthic microbial communities interact with the physical sediment dynamics and other factors in the environment in order to survive. This interaction can produce distinctive sedimentary structures called microbialites. Binding, biostabilization, baffling, and trapping of sediment particles by microorganisms result in the formation of microbially induced sedimentary structures (MISS); however, if carbonate precipitation occurs in EPS, and these processes happen in a repetitive manner, a multilayered build-up can form—stromatolites. Stromatolites and MISS are first found in the early Archean, recording highly evolved microbial activity early in Earth’s history. Whereas the stromatolites show enormous morphologic and taxonomic variation, MISS seem not to have changed in morphology since their first appearance. MISS might be the older relative, but due to the lack of well-preserved sedimentary rocks older than 3.5 billion years, the origin of both stromatolites and MISS remains uncertain
Complete Two Loop Electroweak Contributions to the Muon Lifetime in the Standard Model
An independent result for the two loop fermionic contributions to the muon
lifetime in the Standard Model is obtained. Deviations are found with respect
to \cite{Freitas:2000gg}, which result in a shift of the W boson mass by
approximately -1.3 MeV over the range of Higgs boson masses from 100 GeV to 1
TeV. Supplied with the bosonic contributions from
\cite{Awramik:2002wn,Onishchenko:2002ve,Awramik:2002vu}, this shift, due to the
complete electroweak contributions, varies from -2.4 MeV to -0.6 MeV.
Additionally, a new test of the matching procedure defining the Fermi constant
is presented, which uses fermion masses as infrared regulators.Comment: 11 pages, 5 figures, Tab. 3 corrected, reference adde
On the Numerical Evaluation of Loop Integrals With Mellin-Barnes Representations
An improved method is presented for the numerical evaluation of multi-loop
integrals in dimensional regularization. The technique is based on
Mellin-Barnes representations, which have been used earlier to develop
algorithms for the extraction of ultraviolet and infrared divergencies. The
coefficients of these singularities and the non-singular part can be integrated
numerically. However, the numerical integration often does not converge for
diagrams with massive propagators and physical branch cuts. In this work,
several steps are proposed which substantially improve the behavior of the
numerical integrals. The efficacy of the method is demonstrated by calculating
several two-loop examples, some of which have not been known before.Comment: 13 pp. LaTe
Parallel Computation of Feynman diagrams with DIANA
Co-operation of the Feynman DIagram ANAlyzer (DIANA) with the underlying
operational system (UNIX) is presented. We discuss operators to run external
commands and a recent development of parallel processing facilities and an
extension in the spirit of a component model.Comment: 23 pages, Latex using psfig, epsf and alltt, 3 figure
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