1,261 research outputs found
Exact cosmological solutions with nonminimal derivative coupling
We consider a gravitational theory of a scalar field with nonminimal
derivative coupling to curvature. The coupling terms have the form and where
and are coupling parameters with dimensions of
length-squared. In general, field equations of the theory contain third
derivatives of and . However, in the case
the derivative coupling term reads and the order of corresponding field equations
is reduced up to second one. Assuming , we study the
spatially-flat Friedman-Robertson-Walker model with a scale factor and
find new exact cosmological solutions. It is shown that properties of the model
at early stages crucially depends on the sign of . For negative
the model has an initial cosmological singularity, i.e. in the limit ; and for positive the universe
at early stages has the quasi-de Sitter behavior, i.e. in the
limit , where . The corresponding scalar
field is exponentially growing at , i.e. . At late stages the universe evolution does not depend on
at all; namely, for any one has at
. Summarizing, we conclude that a cosmological model with
nonminimal derivative coupling of the form is able to explain in a unique manner both a
quasi-de Sitter phase and an exit from it without any fine-tuned potential.Comment: 7 pages, 2 figures. Accepted to PR
Screening and finite size corrections to the octupole and Schiff moments
Parity (P) and time reversal (T) violating nuclear forces create P, T -odd
moments in expansion of the nuclear electrostatic potential. We derive
expression for the nuclear electric octupole field which includes the electron
screening correction (similar to the screening term in the Schiff moment). Then
we calculate the Z alpha corrections to the Schiff moment which appear due to
the finite nuclear size. Such corrections are important in heavy atoms with
nuclear charge Z > 50. The Schiff and octupole moments induce atomic electric
dipole moments (EDM) and P, T -odd interactions in molecules which are measured
in numerous experiments to test CP-violation theories
Relativistic corrections to the nuclear Schiff moment
Parity and time invariance violating (-odd) atomic electric dipole
moments (EDM) are induced by interaction between atomic electrons and nuclear
-odd moments which are produced by -odd nuclear forces. The nuclear
EDM is screened by atomic electrons. The EDM of a non-relativistic atom with
closed electron subshells is induced by the nuclear Schiff moment. For heavy
relativistic atoms EDM is induced by the nuclear local dipole moments which
differ by 10-50% from the Schiff moments calculated previously.
We calculate the local dipole moments for and where the most accurate atomic and molecular EDM measurements have been
performed.Comment: 3 pages, no figures, brief repor
Extension of the Schiff theorem to ions and molecules
According to the Schiff theorem the nuclear electric dipole moment (EDM) is
screened in neutral atoms. In ions this screening is incomplete. We extend a
derivation of the Schiff theorem to ions and molecules. The finite nuclear size
effects are considered including Z^2 alpha^2 corrections to the nuclear Schiff
moment which are significant in all atoms and molecules of experimental
interest. We show that in majority of ionized atoms the nuclear EDM
contribution to the atomic EDM dominates while in molecules the contribution of
the Schiff moment dominates. We also consider the screening of electron EDM in
ions
Cosmology with nonminimal kinetic coupling and a Higgs-like potential
We consider cosmological dynamics in the theory of gravity with the scalar
field possessing the nonminimal kinetic coupling to curvature given as , and the Higgs-like potential
. Using the dynamical system
method, we analyze stationary points, their stability, and all possible
asymptotical regimes of the model under consideration. We show that the Higgs
field with the kinetic coupling provides an existence of accelerated regimes of
the Universe evolution. There are three possible cosmological scenarios with
acceleration: (i) {\em The late-time inflation} when the Hubble parameter tends
to the constant value,
as , while the scalar field tends to zero, , so that
the Higgs potential reaches its local maximum .
(ii) {\em The Big Rip} when and
as . (iii) {\em The Little Rip}
when and as
. Also, we derive modified slow-roll conditions for the Higgs field
and demonstrate that they lead to the Little Rip scenario.Comment: 29 pages, 11 figures, discussions and references added, to be
published on JCA
Black Hole in Thermal Equilibrium with a Spin-2 Quantum Field
An approximate form for the vacuum averaged stress-energy tensor of a
conformal spin-2 quantum field on a black hole background is employed as a
source term in the semiclassical Einstein equations. Analytic corrections to
the Schwarzschild metric are obtained to first order in , where denotes the mass of the black hole. The approximate
tensor possesses the exact trace anomaly and the proper asymptotic behavior at
spatial infinity, is conserved with respect to the background metric and is
uniquely defined up to a free parameter , which relates to the
average quantum fluctuation of the field at the horizon. We are able to
determine and calculate an explicit upper bound on by requiring that
the entropy due to the back-reaction be a positive increasing function in .
A lower bound for can be established by requiring that the metric
perturbations be uniformly small throughout the region , where
is the radius of perturbative validity of the modified metric. Additional
insight into the nature of the perturbed spacetime outside the black hole is
provided by studying the effective potential for test particles in the vicinity
of the horizon.Comment: 21 pages in plain LaTex. Three figures available upon request from
the first autho
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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