117446785
Comment on "Nuclear structure corrections in muonic deuterium"
A recent letter [1] investigated the effects of deuteron polarizability in the mu D atom. The importance of understanding this atom has been heightened because of the possible light it could shed on the proton radius puzzle. Here we confirm, clarify, and emphasize the significance of the result [1] that the effects of the third Zemach moment are canceled by part of the deuteron polarizability effects. 1. K. Pachucki, Phys. Rev. Lett. 106, 193007 (2011)
122904929
Isobar dynamics and pion-nucleus elastic scattering
Abstract A new formalism is developed for studying pion-nucleus scattering in a model which takes into account the dynamics of the (3, 3) pion-nucleon resonance, or Δ isobar. This treatment is used to calculate π + elastic scattering from 16 O, 40 Ca, 48 Ca and 208 Pb at energies from 114 to 240 MeV. Some results for π − elastic scattering are also given. From fits to π + scattering data it is found that the Δ-nucleus interaction is well described by a spherical local complex potential proportional to the nuclear density. The central strength of this potential depends on energy but not on nuclear mass number. Some difficulties in determining the parameters of this potential from elastic scattering are discussed.
118854850
Polarized quark distributions in nuclear matter
We compute the polarized quark distribution function of a bound nucleon. The chiral quark-soliton model provides the quark and antiquark substructure of the nucleon embedded in nuclear matter. Nuclear effects cause significant modifications to the polarized distributions, including an enhancement of the axial coupling constant.
356245
Current algebra and the cloudy-bag model.
Two versions of the cloudy-bag model (surface and volume coupling) satisfy the commutation relations of current algebra. Perturbation-theory evaluations of various observables are compared for the two treatments. The electromagnetic properties are essentially the same in both versions. The volume-coupling model contains, in lowest order, a pion-quark contact interaction that contributes to the axial-vector current. Including the effect of this term leads to a computed value of g/sub A/ of about 1.25, if the radius of the nucleon bag is around 1.0 fm.
119513589
Shapes of the proton
A model proton wave function, constructed using Poincar\'e invariance and constrained by recent electromagnetic form factor data, is used to study the shape of the proton. Spin-dependent quark densities are defined as matrix elements of density operators in proton states of definite polarization, and shown to have an infinite variety of nonspherical shapes. For high momentum quarks with spin parallel to that of the proton, the shape resembles that of a peanut, but for quarks with antiparallel spin the shape is that of a bagel.
120464871
Deuteron photodisintegration: Impulse approximation and gauge invariance
We study the question of whether calculations of deuteron photodisintegration respect gauge invariance, and show that the impulse approximation is in severe disagreement with gauge invariance. The method in which Siegert's theorem is implemented is consistent with gauge invariance to within ten percent. We introduce a modification of the impulse approximation in which the current is conserved exactly. For deuteron photodisintegration this method yields essentially the same results as that of Partovi. Our method can easily be applied to electron- or neutrino-nucleus scattering.
199082345
Search for X-ray induced decay of the 31-yr isomer of 178Hf using synchrotron radiation
Isomeric {sup 178}Hf (t{sub 1/2} = 31 yr, E{sub x} = 2.446 MeV, J{sup {pi}} = 16{sup +}) was bombarded by a white beam of x-rays from the Advanced Photon Source at Argonne National Laboratory. A search was made for x-ray induced decay of the isomer by detecting prompt and delayed {gamma} rays associated with the decay. No induced decay was observed. Upper limits for such a process for x-ray energies between 7-100 keV were set. The limits between 7 and 30 keV are below {approx} 3 x 10{sup -27} cm{sup 2}-keV for induced decay that bypasses the 4-s isomer and {approx} 5 x 10{sup -27} cm{sup 2}-keV for induced decay that is delayed through this isomer, orders of magnitude below values at which induced decay was reported previously. These limits are consistent with what is known about the properties of atomic nuclei.
37692138
Dirac-Born-Infeld genesis: an improved violation of the null energy condition.
We show that the Dirac-Born-Infeld conformal galileons, derived from the world-volume theory of a 3-brane moving in an anti-de Sitter bulk, admit a background, stable under quantum corrections, which violates the null energy condition. The perturbations around this background are stable and propagate subluminally. Unlike other known examples of null energy condition violation, such as ghost condensation and conformal galileons, this theory also admits a stable, Poincaré-invariant vacuum. The 2 → 2 amplitude satisfies standard analyticity conditions. The full S matrix is likely not analytic, however, since perturbations around deformations of the Poincaré invariant vacuum propagate superluminally.
121788713
Nuclear resonance excitation by synchrotron radiation
We have excited the 14-keV level of the Fe/sup 57/ nucleus using synchroton radiation, and observed the conversion electrons emitted in the decay of that state. We believe this to be the first observation of nuclear excitation via synchrotron-produced x rays.