321 research outputs found
A New Basis for QED Bound State Computations
A simple method to compute QED bound state properties is presented, in which
binding energy effects are treated non-perturbatively. It is shown that to take
the effects of all ladder Coulomb photon exchanges into account, one can simply
perform the derivative of standard QED amplitudes with respect to the external
momentum. For example, the derivative of the light-by-light scattering
amplitude gives an amplitude for orthopositronium decay to three photons where
any number of Coulomb photon exchanges between the e-e+ is included.
Various applications are presented. From them, it is shown that binding
energy must be treated non-perturbatively in order to preserve the analyticity
of positronium decay amplitudes.
Interesting perspectives for quarkonium physics are briefly sketched.Comment: LaTeX, 23 pages, 16 figures. Minor corrections. Some comments adde
Do Present LEP Data Provide Evidence for Electroweak Corrections?
The Born approximation, based on instead of
, reproduces all electroweak precision measurements within their
accuracy. The low upper limits for the genuinely electroweak
corrections constitute one of the major achievements of LEP. The astonishing
smallness of these corrections results from the cancellation of a large
positive contribution from the heavy top quark and large negative contributions
from all other virtual particles. It is precisely the non-observation of
electroweak radiative corrections that places stringent upper and lower limits
on the top mass.Comment: 12 pages, preprint CERN-TH.6943/9
Suppression of decay channels in the Georgi-Machacek model
The decay mode is usually considered as one of the most promising
ways to discover new heavy neutral scalar . We show that in the
Georgi-Machacek model it is possible to get large enhancement of double SM-like
Higgs boson production due to decays while and decay channels
could be highly suppressed.Comment: 5 page
Theoretical description of mixed film formation at the air/water interface : carboxylic acidsâfatty amines
Thermodynamic parameters of mixed monolayer formation of aliphatic amines CnH2n+1NH2 and carboxylic acids CnH2n+1COOH (n = 6â16) are calculated using the quantum chemical semiempirical PM3 method. Four types of mixed dimers and tetramers amineâacid are considered. The total contribution of interactions between the hydrophilic parts of amine and acid into clusterization Gibbs energy is slightly lower than the corresponding interactions for individual surfactants. It suggests a synergetic interaction between the regarded amphiphilic compounds as proved by experimental data in the literature. Two types of competitive film formation are possible: mixed 2D film 1, where the molecules of the minor component are single distributed among the molecules of the prevailing second component (mixture of components on molecular level), and 2D film 2 with a domain structure comprised of pure component âislandsâ linked together. The dependence of the Gibbs energy of clusterization per monomer for 2D film 1 on the component mole fraction shows that the maximum synergetic effect is typical for the case that both surfactants have the same even number of carbon atoms in the hydrocarbon chain and form an equimolar mixture. Formation of 2D film 1 is more preferable than that of 2D film 2, if the difference of the hydrocarbon chain lengths is not larger than 5 methylene units. The limiting mole fraction of carboxylic acids in such mixed monolayers is 66.7%
Implications of Heavy Top
Lecture at 23 ITEP Winter School. Manifestations of heavy top at low energies
(K- and B-mesons) and high energies (Z and W physics) are discussedComment: 12 pages; ps file can be found at
http://venus.itep.ru/preprints/1995/95046.ps.g
Neutrino oscillations: deriving the plane-wave approximation in the wave-packet approach
The plane-wave approximation is widely used in the practical calculations
concerning neutrino oscillations. A simple derivation of this approximation
starting from the neutrino wave-packet framework is presented.Comment: Presented at the 36th ITEP Winter School of Physics, session
"Particle Physics", February 8-16, 2008, Otradnoe, Russi
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