1,779 research outputs found
Semi-classical equation of state and specific heats for neutron-star inner crust with proton shell corrections
An approach to the equation of state for the inner crust of neutron stars
based on Skyrme-type forces is presented. Working within the Wigner-Seitz
picture, the energy is calculated by the TETF (temperature-dependent extended
Thomas-Fermi) method, with proton shell corrections added self-consistently by
the Strutinsky-integral method. Using a Skyrme force that has been fitted to
both neutron matter and to essentially all the nuclear mass data, we find
strong proton shell effects: proton numbers = 50, 40 and 20 are the only
values possible in the inner crust, assuming that nuclear equilibrium is
maintained in the cooling neutron star right down to the ambient temperature.
Convergence problems with the TETF expansion for the entropy, and our way of
handling them, are discussed. Full TETF expressions for the specific heat of
inhomogeneous nuclear matter are presented. Our treatment of the electron gas,
including its specific heat, is essentially exact, and is described in detail.Comment: 41 pages, 6 figure
alpha^2 corrections to parapositronium decay: a detailed description
We present details of our recent calculation of alpha^2 corrections to the
parapositronium decay into two photons. These corrections are rather small and
our final result for the parapositronium lifetime agrees well with the most
recent measurement. Implications for orthopositronium decays are briefly
discussed.Comment: 18 pages, late
Positronium S state spectrum: analytic results at O(m alpha^6)
We present an analytic calculation of the O(m alpha^6) recoil and radiative
recoil corrections to energy levels of positronium nS states and their
hyperfine splitting. A complete analytic formula valid to O(m alpha^6) is given
for the spectrum of S states. Technical aspects of the calculation are
discussed in detail. Theoretical predictions are given for various energy
intervals and compared with experimental results.Comment: 29 pages, revte
Order \alpha^2 corrections to the decay rate of orthopositronium
Order \alpha^2 corrections to the decay rate of orthopositronium are
calculated in the framework of nonrelativistic QED. The resulting contribution
is found to be in significant disagreement with one set of experimental
measurements though another experiment is in agreement with theory.Comment: 7 pages, 1 figur
Lagrangian formulation for noncommutative nonlinear systems
In this work we use the well known formalism developed by Faddeev and Jackiw
to introduce noncommutativity within two nonlinear systems, the SU(2) Skyrme
and O(3) nonlinear sigma models. The final result is the Lagrangian
formulations for the noncommutative versions of both models. The possibility of
obtaining different noncommutative versions for these nonlinear systems is
demonstrated.Comment: 8 pages. Revex 4.
Nucleon-nucleon interaction in the Skyrme model
We consider the interaction of two skyrmions in the framework of the sudden
approximation. The widely used product ansatz is investigated. Its failure in
reproducing an attractive central potential is associated with terms that
violate G-parity. We discuss the construction of alternative ans\"atze and
identify a plausible solution to the problem.Comment: 18 pages, 9 figure
Precision Study of Positronium: Testing Bound State QED Theory
As an unstable light pure leptonic system, positronium is a very specific
probe atom to test bound state QED. In contrast to ordinary QED for free
leptons, the bound state QED theory is not so well understood and bound state
approaches deserve highly accurate tests. We present a brief overview of
precision studies of positronium paying special attention to uncertainties of
theory as well as comparison of theory and experiment. We also consider in
detail advantages and disadvantages of positronium tests compared to other QED
experiments.Comment: A talk presented at Workshop on Positronium Physics (ETH Zurich, May
30-31, 2003
One-loop corrections of order (Z alpha)^6m_1/m_2, (Z alpha)^7 to the muonium fine structure
The corrections of order (Z alpha)^6m_1/m_2 and (Z alpha)^7 from one-loop
two-photon exchange diagrams to the energy spectra of the hydrogenic atoms are
calculated with the help of the Taylor expansion of corresponding integrands.
The method of averaging the quasipotential over the wave functions in the
d-dimensional coordinate space is formulated. The numerical values of the
obtained contributions to the fine structure of muonium, hydrogen and
positronium are presented.Comment: Talk given at the XVIth International Workshop High-Energy Physics
and Quantum Field Theory (QFTHEP2001), Moscow, Russia, 6-12 Sep 2001, 12
pages, REVTE
Cosmological perturbations on local systems
We study the effect of cosmological expansion on orbits--galactic, planetary,
or atomic--subject to an inverse-square force law. We obtain the laws of motion
for gravitational or electrical interactions from general relativity--in
particular, we find the gravitational field of a mass distribution in an
expanding universe by applying perturbation theory to the Robertson-Walker
metric. Cosmological expansion induces an ( force where
is the cosmological scale factor. In a locally Newtonian framework, we
show that the term represents the effect of a continuous
distribution of cosmological material in Hubble flow, and that the total force
on an object, due to the cosmological material plus the matter perturbation,
can be represented as the negative gradient of a gravitational potential whose
source is the material actually present. We also consider the effect on local
dynamics of the cosmological constant. We calculate the perihelion precession
of elliptical orbits due to the cosmological constant induced force, and work
out a generalized virial relation applicable to gravitationally bound clusters.Comment: 10 page
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