1,942 research outputs found
QCD Radiative Correction to Zero Recoil Sum Rules for Heavy Flavor Transitions in the Small Velocity Limit.
We consider the small velocity sum rules for heavy flavour semileptonic
transitions that are used to estimate the zero recoil values of semileptonic
heavy flavour form factors. We analyze the complete O() radiative
correction to these sum rules. The corrections are universal and influence all
"model-independent" bounds previously derived for semileptonic form factors at
zero recoil.Comment: 13 pages, LaTeX, 3 figures
Precision study of positronium and precision tests of the bound state QED
Despite its very short lifetime positronium provides us with a number of
accurate tests of the bound state QED. In this note a brief overview of QED
theory and precision experiments on the spectrum and annihilation decay of the
positronium atom is presented. Special attention is paid to the accuracy of
theoretical predictions.Comment: A talk presented at 9th International Workshop on Slow Positron Beam
Techniques for Solids and Surfaces (SLOPOS), Dresden, 200
Two -loop radiative corrections to the Higgs decay width for large Higgs boson masses
This note is devoted to the calculation of the two-loop
radiative corrections to the Higgs decay width for large
values of the Higgs boson mass within the Minimal Standard Model.
The use of the Equivalence Theorem makes it possible to reduce the problem to
the consideration of the physical Higgs boson field and the Goldstone bosons
. We present analytical results for the various two- and
three-particle absorptive parts of two-loop contributions, using dispersive
techniques, analytic results for all but one of the dispersive contributions.
The typical size of the correction is percent for a Higgs boson
mass of order .Comment: 21 pages, 7 uuencoded figure
Hadronic Light-by-Light Scattering in the Muonium Hyperfine Splitting
We consider an impact of hadronic light-by-light scattering on the muonium
hyperfine structure. A shift of the hyperfine interval is calculated with the light-by-light scattering approximated
by exchange of pseudoscalar and pseudovector mesons. Constraints from the
operator product expansion in QCD are used to fix parameters of the model
similar to the one used earlier for the hadronic light-by-light scattering in
calculations of the muon anomalous magnetic moment. The pseudovector exchange
is dominant in the resulting shift, . Although the effect is tiny it is useful in understanding
the level of hadronic uncertainties.Comment: 16 pages, 7 figures, a reference adde
On Unitary Evolution of a Massless Scalar Field In A Schwarzschild Background: Hawking Radiation and the Information Paradox
We develop a Hamiltonian formalism which can be used to discuss the physics
of a massless scalar field in a gravitational background of a Schwarzschild
black hole. Using this formalism we show that the time evolution of the system
is unitary and yet all known results such as the existence of Hawking radiation
can be readily understood. We then point out that the Hamiltonian formalism
leads to interesting observations about black hole entropy and the information
paradox.Comment: 45 pages, revte
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