657 research outputs found
Pion Pair Production with Higher Order Radiative Corrections in Low Energy e+e- Collisions
The complete one-loop QED initial state, final state and initial--final state
interference corrections to the process e+e- -> pi+pi- are presented. Analytic
formulae are given for the virtual and for the real photon corrections. The
total cross section, the pion angular distribution and the pi+pi- invariant
mass distribution are investigated in the regime of experimentally realistic
kinematical cuts. It is shown that in addition to the full one-loop corrections
also two-loop initial state corrections and even the resummation of higher
order soft photon logarithms can be necessary if at least per cent accuracy is
required. For the data analysis we focus on an inclusive treatment of all
photons. The theoretical error concerning our treatment of radiative
corrections is then estimated to be less than 2 per mille for both the
measurement of the total cross section and the pi+pi- invariant mass
distribution. In addition we discuss the model uncertainty due to the pion
substructure. Altogether the precision of the theoretical prediction matches
the requirements of low energy e+e- experiments like the ones going on at DAFNE
or VEPP-2M.Comment: 16 pages 9 figures 7 tables; 6 figs added+text; modified Eqs.(56,68),
enhanced appendice
On the difference between the pole and the MSbar masses of the top quark at the electroweak scale
We argue that for a Higgs boson mass M_H ~125 GeV, as suggested by recent
Higgs searches at the LHC, the inclusion of electroweak radiative corrections
in the relationship between the pole and MS-bar masses of the top quark reduces
the difference to about 1 GeV. This is relevant for the scheme dependence of
electroweak observables, such as the rho parameter, as well as for the
extraction of the top quark mass from experimental data. In fact, the value
currently extracted by reconstructing the invariant mass of the top quark decay
products is expected to be close to the pole mass, while the analysis of the
total cross section of top quark pair production yields a clean determination
of the MS-bar mass.Comment: 15 pages, 1 figure; discussion extended, figure improved, references
added; accepted for publication in Phys. Lett.
Self-consistence of the Standard Model via the renormalization group analysis
A short review of recent renormalization group analyses of the
self-consistence of the Standard Model is presented.Comment: 10 pages; 5 figures; To appear in the Proceedings of the 16th
International Workshop ACAT- 2014 (Advanced Computing and Analysis Techniques
in physics), Prague, Czech Republic, 01-05 September 201
Hadronic Contributions to the Photon Vacuum Polarization and their Role in Precision Physics
I review recent evaluations of the hadronic contribution to the shift in the
fine structure constant and to the anomalous magnetic moment of the muon.
Substantial progress in a precise determination of these important observables
is a consequence of substantially improved total cross section measurement by
the CMD-2 and BES II collaborations and an improved theoretical understanding.
Prospects for further possible progress is discussed.Comment: 17 pages 7 figures 2 tables, update: incl. CMD-2 data, reference
Non-hermitian Exact Local Bosonic Algorithm for Dynamical Quarks
We present an exact version of the local bosonic algorithm for the simulation
of dynamical quarks in lattice QCD. This version is based on a non-hermitian
polynomial approximation of the inverse of the quark matrix. A Metropolis test
corrects the systematic errors. Two variants of this test are presented. For
both of them, a formal proof is given that this Monte Carlo algorithm converges
to the right distribution. Simulation data are presented for different lattice
parameters. The dynamics of the algorithm and its scaling in lattice volume and
quark mass are investigated.Comment: 32 pages, LaTex, 8 ps figure
Four-fermion production with RACOONWW
RACOONWW is an event generator for e+e- --> WW --> 4fermions(+gamma) that
includes full tree-level predictions for e+e- --> 4f and e+e- --> 4f+gamma as
well as O(alpha) corrections to e+e- --> 4f in the so-called double-pole
approximation. We briefly sketch the concept of the calculation on which this
generator is based and present some numerical results.Comment: 9 pages, latex, 6 postscript files, to appear in the proceedings of
the UK Phenomenology Workshop on Collider Physics, Durham, UK, 19-24
September, 199
Adaptive Step Size for Hybrid Monte Carlo Algorithm
We implement an adaptive step size method for the Hybrid Monte Carlo a
lgorithm. The adaptive step size is given by solving a symmetric error
equation. An integr ator with such an adaptive step size is reversible.
Although we observe appreciable variations of the step size, the overhead of
the method exceeds its benefits. We propose an explanation for this phenomenon.Comment: 13 pages, 5 Postscript figures, late
Exact Local Bosonic Algorithm for Dynamical Quarks
We present an exact local bosonic algorithm for the simulation of dynamical
fermions in lattice QCD. We show that this algorithm is a viable alternative to
the Hybrid Monte Carlo algorithm.Comment: 3 pages, 1 PostScript figure; Talk presented at LATTICE96(algorithms
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