355 research outputs found
Two-photon decays of hadronic molecules
In many calculations of the two--photon decay of hadronic molecules, the
decay matrix element is estimated using the wave function at the origin
prescription, in analogy to the two-photon decay of parapositronium. We
question the applicability of this procedure to the two-photon decay of
hadronic molecules for it introduces an uncontrolled model dependence into the
calculation. As an alternative approach, we propose an explicit evaluation of
the hadron loop. For shallow bound states, this can be done as an expansion in
powers of the range of the molecule binding force. In the leading order one
gets the well-known point-like limit answer. We estimate, in a self-consistent
and gauge invariant way, the leading range corrections for the two-photon decay
width of weakly bound hadronic molecules emerging from kaon loops. We find them
to be small. The role of possible short-ranged operators and of the width of
the scalars remains to be investigated.Comment: LaTeX2e, 26 pages, new figure and additional appendix added, version
to appear in Phys.Rev.
Production of the Smallest QED Atom: True Muonium (mu^+ mu^-)
The "true muonium" (mu^+ mu-) and "true tauonium" (tau^+ tau^-) bound states
are not only the heaviest, but also the most compact pure QED systems. The
rapid weak decay of the tau makes the observation of true tauonium difficult.
However, as we show, the production and study of true muonium is possible at
modern electron-positron colliders.Comment: 4 pages, ReVTeX, 4 eps figures; minor wording changes and reordering
of a reference. Version accepted by Phys. Rev. Let
One more hard three-loop correction to parapositronium energy levels
A hard three-loop correction to parapositronium energy levels of order
is calculated. This nonlogarithmic contribution is due to the
insertions of one-loop photon propagator in the fermion lines in the diagrams
with virtual two-photon annihilation. We obtained for this energy shift.Comment: Version to be published in Phys. Rev.D, results unchange
Two fermion relativistic bound states: hyperfine shifts
We discuss the hyperfine shifts of the Positronium levels in a relativistic
framework, starting from a two fermion wave equation where, in addition to the
Coulomb potential, the magnetic interaction between spins is described by a
Breit term. We write the system of four first order differential equations
describing this model. We discuss its mathematical features, mainly in relation
to possible singularities that may appear at finite values of the radial
coordinate. We solve the boundary value problems both in the singular and non
singular cases and we develop a perturbation scheme, well suited for numerical
computations, that allows to calculate the hyperfine shifts for any level,
according to well established physical arguments that the Breit term must be
treated at the first perturbative order. We discuss our results, comparing them
with the corresponding values obtained from semi-classical expansions.Comment: 16 page
The "recoil" correction of order to hyperfine splitting of positronium ground state
The "recoil" correction of order to the hyperfine splitting of
positronium ground state was found. The formalism employed is based on the
noncovariant perturbation theory in QED. Equation for two-particle component of
full (many-body) wave function is used, in which effective Hamiltonian depends
on the energy of a system. The effective Hamiltonian is not restricted to the
nonrelativistic region, so there is no need in any regularization. To evaluate
integrals over loop momenta, they are divided into "hard" and "soft" parts,
coming from large and small momenta respectively. Soft contributions were found
analytically, and hard ones are evaluated by numerical integration. Some soft
terms due to the retardation cancel each other. To calculate the "hard"
contributions, a great number of noncovariant graphs is replaced by only a few
covariant ones. The hard contribution was found in two ways. The first way is
to evaluate contributions of separate graphs, using the Coulomb gauge. The
second one is to calculate full hard contribution as a whole using the Feynman
gauge. The final result for the "recoil" correction is 0.381(6) m\al^6 and
agrees with those of previous papers. Diagram-to-diagram comparison with the
revised results of Adkins&Sapirstein was done. All the results agree, so the
"recoil" correction is now firmly established. This means a considerable
disagreement with the experimental data.Comment: 28 pages, latex including latex figure
The bound mu+ mu- system
We consider the hyperfine structure, the atomic spectrum and the decay
channels of the bound mu+ mu- system (dimuonium). The annihilation lifetimes of
low-lying atomic states of the system lie in the nanosecond range range. The
decay rates could be measured by detection of the decay products (high energy
photons or electron-positron pairs). The hyperfine structure splitting of the
dimuonic system and its decay rate are influenced by electronic vacuum
polarization effects in the far time-like asymptotic region. This constitutes a
previously unexplored kinematic regime. We evaluate next--to-leading order
radiative corrections to the decay rate of low-lying atomic states. We also
obtain order alpha^5 corrections to the hyperfine splitting of the 1S and 2S
levels.Comment: 10 figures (eps format) attached, Scheduled tentatively by PRA for
Nov/Dec 199
The roots of "Western European societal evolution". A concept of Europe by JenĆ SzƱcs
JenĆ SzƱcs wrote his essay entitled Sketch on the three regions of Europe in the early 1980s in Hungary. During these years, a historically well-argued opinion emphasising a substantial difference between Central European and Eastern European societies was warmly received in various circles of the political opposition. In a wider European perspective SzƱcs used the old âliberty toposâ which claims that the history of Europe is no other than the fulfillment of liberty. In his Sketch, SzƱcs does not only concentrate on questions concerning the Middle Ages in Western Europe. Yet it is this stream of thought which brought a new perspective to explaining European history. His picture of the Middle Ages represents well that there is a way to integrate all typical Western motifs of post-war self-definition into a single theory. Mainly, the âliberty motifâ, as a sign of âEuropeanismâ â in the interpretation of BibĂłâs concept, Anglo-saxon Marxists and Weberâs social theory â, developed from medieval concepts of state and society and from an analysis of economic and social structures. SzƱcsâs historical aspect was a typical intellectual product of the 1980s: this was the time when a few Central European historians started to outline non-Marxist aspects of social theory and categories of modernisation theories, but concealing them with Marxist terminology
Nonequilibrium thermodynamics of interacting tunneling transport: variational grand potential, density-functional formulation, and nature of steady-state forces
The standard formulation of tunneling transport rests on an open-boundary
modeling. There, conserving approximations to nonequilibrium Green function or
quantum-statistical mechanics provide consistent but computational costly
approaches; alternatively, use of density-dependent ballistic-transport
calculations [e.g., Phys. Rev. B 52, 5335 (1995)], here denoted `DBT', provide
computationally efficient (approximate) atomistic characterizations of the
electron behavior but has until now lacked a formal justification. This paper
presents an exact, variational nonequilibrium thermodynamic theory for fully
interacting tunneling and provides a rigorous foundation for frozen-nuclei DBT
calculations as a lowest order approximation to an exact nonequilibrium
thermodynamics density functional evaluation. The theory starts from the
complete electron nonequilibrium quantum statistical mechanics and I identify
the operator for the nonequilibrium Gibbs free energy. I demonstrate a minimal
property of a functional for the nonequilibrium thermodynamic grand potential
which thus uniquely identifies the solution as the exact nonequilibrium density
matrix. I also show that a uniqueness-of-density proof from a closely related
study [Phys. Rev. B 78, 165109 (2008)] makes it possible to provide a
single-particle formulation based on universal electron-density functionals. I
illustrate a formal evaluation of the thermodynamics grand potential value
which is closely related to the variation in scattering phase shifts and hence
to Friedel density oscillations. This paper also discusses the difference
between the here-presented exact thermodynamics forces and the often-used
electrostatic forces. Finally the paper documents an inherent adiabatic nature
of the thermodynamics forces and observes that these are suited for a
nonequilibrium implementation of the Born-Oppenheimer approximation.Comment: 37 pages, 3 Figure
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