401 research outputs found
Higher-Order Nuclear-Polarizability Corrections in Atomic Hydrogen
Nuclear-polarizability corrections that go beyond unretarded-dipole
approximation are calculated analytically for hydrogenic (atomic) S-states.
These retardation corrections are evaluated numerically for deuterium and
contribute -0.68 kHz, for a total polarization correction of 18.58(7) kHz. Our
results are in agreement with one previous numerical calculation, and the
retardation corrections completely account for the difference between two
previous calculations. The uncertainty in the deuterium polarizability
correction is substantially reduced. At the level of 0.01 kHz for deuterium,
only three primary nuclear observables contribute: the electric polarizability,
, the paramagnetic susceptibility, , and the third Zemach
moment, . Cartesian multipole decomposition of the virtual
Compton amplitude and its concomitant gauge sum rules are used in the analysis.Comment: 26 pages, latex, 1 figure -- Submitted to Phys. Rev. C -- epsfig.sty
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Charge Density of the Neutron
A model-independent analysis of the infinite-momentum-frame charge density of
partons in the transverse plane is presented for the nucleon. We find that the
neutron parton charge density is negative at the center, so that the square of
the transverse charge radius is positive, in contrast with many expectations.
Additionally, the proton's central u quark charge density is larger than that
of the d quark by about 70 %. The proton (neutron) charge density has a long
range positively (negatively) charged component.Comment: 7 pages, three figures The replacement mainly concerns correcting an
error made in computing the proton up and down quark densities from the
correctly computed proton and neutron charge densities. The proton central u
quark density is now larger than that of the d quar
Nuclear Polarizabilities and Logarithmic Sum Rules
The electric polarizability and logarithmic mean-excitation energy are
calculated for the deuteron using techniques introduced in atomic physics.
These results are then used to improve limits on the atomic-deuterium frequency
shift due to nuclear polarization in the unretarded dipole limit, as well as
confirming previous results.Comment: 7 pages, latex -- To appear in Phys. Rev. C -
Nuclear Sizes and the Isotope Shift
Darwin-Foldy nuclear-size corrections in electronic atoms and nuclear radii
are discussed from the nuclear-physics perspective. Interpretation of precise
isotope-shift measurements is formalism dependent, and care must be exercised
in interpreting these results and those obtained from relativistic electron
scattering from nuclei. We strongly advocate that the entire nuclear-charge
operator be used in calculating nuclear-size corrections in atoms, rather than
relegating portions of it to the non-radiative recoil corrections. A
preliminary examination of the intrinsic deuteron radius obtained from
isotope-shift measurements suggests the presence of small meson-exchange
currents (exotic binding contributions of relativistic order) in the nuclear
charge operator, which contribute approximately 1/2%.Comment: 17 pages, latex, 1 figure -- Submitted to Phys. Rev. A -- epsfig.sty
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Equivalence of Nonstatic Two-Pion-Exchange Nucleon-Nucleon Potentials
Off-shell aspects of the one-pion-exchange potential and their relationship
to different forms of the nonstatic (subleading-order) chiral two-pion-exchange
nucleon-nucleon potential are discussed. Various types of off-shell behavior
are categorized and numerous examples are given. Recently derived potentials
based on chiral approaches are supplemented by a rather general form of the
two-pion-exchange potential derived using old-fashioned methods. The latter is
closely related to a general form of one-pion-exchange relativistic corrections
and nonstatic two-pion-exchange three-nucleon forces developed long ago.Comment: 16 pages, latex -- Phys. Rev. C (to appear) -- Published versio
Nuclear currents based on the integral form of the continuity equation
We present an approach to obtain new forms of the nuclear electromagnetic
current, which is based on an integral form of the continuity equation. The
procedure can be used to restore current conservation in model calculations in
which the continuity equation is not verified. Besides, it provides, as a
particular result, the so-called Siegert's form of the nuclear current, first
obtained by Friar and Fallieros by extending Siegert's theorem to arbitrary
values of the momentum transfer. The new currents are explicitly conserved and
permit a straightforward analysis of their behavior at both low and high
momentum transfers. The results are illustrated with a simple nuclear model
which includes a harmonic oscillator mean potential.Comment: 19 pages, revtex, plus 2 PS figure
Nucleus polarizability contribution to the hydrogen-deuterium isotope shift
The correction to the hydrogen-deuterium isotope shift due to the proton and
deuteron polarizability is evaluated on the basis of modern experimental data
on the structure functions of inelastic lepton-nucleus scattering. The
numerical value of this contribution is equal 63\pm 12 Hz.Comment: 5 page
Lamb shift in muonic helium ion
The Lamb shift (2P_{1/2}-2S_{1/2}) in the muonic helium ion (mu ^4_2He)^+ is
calculated with the account of contributions of orders alpha^3, alpha^4,
alpha^5 and alpha^6. Special attention is given to corrections of the electron
vacuum polarization, the nuclear structure and recoil effects. The obtained
numerical value of the Lamb shift 1379.028 meV can be considered as a reliable
estimate for the comparison with experimental data.Comment: 18 pages, 11 figure
Radiative Correction to the Nuclear-Size Effect and Hydrogen-Deuterium Isotopic Shift
The radiative correction to the nuclear charge radius contribution to the
Lamb shift of order is calculated. In view of the
recent high precision experimental data, this theoretical correction produces a
significant contribution to the hydrogen-deuterium isotopic shift.Comment: 5 pages, REVTEX, replaced with the final version, to be published in
Phys.Rev. A, two references adde
The Nucleon-Mass Difference in Chiral Perturbation Theory and Nuclear Forces
A new method is developed for treating the effect of the neutron-proton mass
difference in isospin-violating nuclear forces. Previous treatments utilized an
awkward subtraction scheme to generate these forces. A field redefinition is
used to remove that mass difference from the Lagrangian (and hence from
asymptotic nucleon states) and replace its effect by effective interactions.
Previous calculations of static Class II charge-independence-breaking and Class
III charge-symmetry-breaking potentials are verified using the new scheme,
which is also used to calculate Class IV nuclear forces. Two-body forces of the
latter type are found to be identical to previously obtained results. A novel
three-body force is also found. Problems involving Galilean invariance with
Class IV one-pion-exchange forces are identified and resolved.Comment: 20 pages, 2 figures, latex - submitted to Physical Review
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