1,240 research outputs found
Cosmological evolution of a ghost scalar field
We consider a scalar field with a negative kinetic term minimally coupled to
gravity. We obtain an exact non-static spherically symmetric solution which
describes a wormhole in cosmological setting. The wormhole is shown to connect
two homogeneous spatially flat universes expanding with acceleration. Depending
on the wormhole's mass parameter the acceleration can be constant (the de
Sitter case) or infinitely growing.Comment: 8 page
The radiative potential method for calculations of QED radiative corrections to energy levels and electromagnetic amplitudes in many-electron atoms
We derive an approximate expression for a "radiative potential" which can be
used to calculate QED strong Coulomb field radiative corrections to energies
and electric dipole (E1) transition amplitudes in many-electron atoms with an
accuracy of a few percent. The expectation value of the radiative potential
gives radiative corrections to the energies. Radiative corrections to E1
amplitudes can be expressed in terms of the radiative potential and its energy
derivative (the low-energy theorem): the relative magnitude of the radiative
potential contribution is ~alpha^3 Z^2 ln(1/(alpha^2 Z^2)), while the sum of
other QED contributions is ~alpha^3 (Z_i+1)^2, where Z_i is the ion charge;
that is, for neutral atoms (Z_i=0) the radiative potential contribution exceeds
other contributions ~Z^2 times. The advantage of the radiative potential method
is that it is very simple and can be easily incorporated into many-body theory
approaches: relativistic Hartree-Fock, configuration interaction, many-body
perturbation theory, etc. As an application we have calculated the radiative
corrections to the energy levels and E1 amplitudes as well as their
contributions (-0.33% and 0.42%, respectively) to the parity non-conserving
(PNC) 6s-7s amplitude in neutral cesium (Z=55). Combining these results with
the QED correction to the weak matrix elements (-0.41%) we obtain the total QED
correction to the PNC 6s-7s amplitude, (-0.32 +/- 0.03)%. The cesium weak
charge Q_W=-72.66(29)_{exp}(36)_{theor} agrees with the Standard Model value
Q_W^{SM}=-73.19(13), the difference is 0.53(48).Comment: 29 pages, 2 figure
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