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Search Results: 1 - 10 of 174544 matches for " Alan E. Friedman "
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Numerical Radiation Reaction for a Scalar Charge in Kerr Circular Orbit
Samuel E. Gralla,John L. Friedman,Alan G. Wiseman
Physics , 2005,
Abstract: We numerically calculate the dissipative part of the self-force on a scalar charge moving on a circular, geodesic, equatorial orbit in Kerr spacetime. The solution to the scalar field equation is computed by separating variables and is expressed as a mode sum over radial and angular modes. The force is then computed in two ways: a direct, instantaneous force calculation which uses the half-retarded-minus-half-advanced field, and an indirect method which uses the energy and angular momentum flux at the horizon and at infinity to infer the force. We are able to show numerically and analytically that the force-per-mode is the same for both methods. To enforce the boundary conditions (ingoing radiation at the horizon and outgoing radiation at infinity for the retarded solution) numerical solutions to the radial equation are matched to asymptotic expansions for the fields at the boundaries. Recursion relations for the coefficients in the asymptotic expansions are given in an appendix.
Unified approach to nuclear densities from exotic atoms
E. Friedman
Physics , 2008, DOI: 10.1007/s10751-009-0066-x
Abstract: Parameters of nuclear density distributions are derived from least-squares fits to strong interaction observables in exotic atoms. Global analyses of antiprotonic and pionic atoms show reasonably good agreement between the two types of probes regarding the average behaviour of root-mean-square radii of the neutron distributions. Apparent conflict regarding the shape of the neutron distribution is attributed to different radial sensitivities of these two probes.
Future directions in kaonic atom physics
E. Friedman
Physics , 2011, DOI: 10.1007/s10751-011-0515-1
Abstract: Recent progress and open problems in kaonic atom physics are presented. A connection between phenomenological deep potentials and the underlying $K^-N$ interaction is established as well as the need for a theory for multinucleon absorption of kaons. $K^-$ absorption at rest to specific $\Lambda $ hypernuclei states is briefly discussed.
Evidence for partial chiral symmetry restoration from pionic atoms
E. Friedman
Physics , 2001, DOI: 10.1016/S0370-2693(01)01326-0
Abstract: Extensive data on strong interaction effects in pionic atoms are analyzed with a density-dependent isovector scattering amplitude suggested recently by Weise to result from a density dependence of the pion decay constant. Most of the so-called `missing s-wave repulsion' is removed when adopting this approach, thus indicating a partial chiral symmetry restoration in dense matter. The resulting potentials describe quite well also elastic scattering of 20 MeV pions on Ca. Further tests with elastic scattering are desirable.
Medium Effects of Low Energy Pions
E. Friedman
Physics , 2003,
Abstract: Fits of pion-nucleus potentials to large sets of pionic atom data reveal departures of parameter values from the corresponding free $\pi N$ parameters. These medium effects can be quantitatively reproduced by a chiral-motivated model where the pion decay constant is modified in the medium or by including the empirical on-shell energy dependence of the amplitudes. No consistency is obtained between pionic atoms and the free $\pi N$ interaction when an extreme off-shell chiral model is used. The role of the size of data sets is briefly discussed.
Antineutron and antiproton nuclear interactions at very low energies
E. Friedman
Physics , 2014, DOI: 10.1016/j.nuclphysa.2014.02.010
Abstract: Experimental annihilation cross sections of antineutrons and antiprotons at very low energies are compared. Features of Coulomb focusing are observed for $\bar p$ annihilation on protons. Direct comparisons for heavier targets are not straightforward due to lack of overlap between targets and energies of experimental results for $\bar p$ and $\bar n$. Nevertheless, the annihilation cross sections for $\bar n$ on nuclei cannot be described by an optical potential that fits well all the available data on $\bar p$ interactions with nuclei. Comparisons made with the help of this potential reveal in the $\bar n$ data features similar to Coulomb focusing. Direct comparisons between $\bar n$ and $\bar p$ annihilations at very low energies would be possible when $\bar p$ cross sections are measured on the same targets and at the same energies as the available cross sections for $\bar n$. Such measurements may be possible in the foreseeable future.
Overview of pion-nucleus interaction at low energies
E. Friedman
Physics , 2006, DOI: 10.1142/S0217751X07035355
Abstract: Predictions of the existence of well-defined deeply bound pionic atom states for heavy nuclei and the eventual observation of such states by the (d,3He) reaction have revived interest in the pion-nucleus interaction at threshold and in its relation to the corresponding pion-nucleon interaction. Explanation of the 'anomalous' s-wave repulsion in terms of partial restoration of chiral symmetry and/or in terms of energy-dependence effects have been tested in global fits to pionic atom data and in a recent dedicated elastic scattering experiment. The role of neutron density distributions in this context is discussed in detail for the first time.
Low-Energy Antinucleon-Nucleus Interaction Revisited
E. Friedman
Physics , 2015, DOI: 10.1007/s10751-015-1144-x
Abstract: Annihilation cross sections of antiprotons and antineutrons on the proton between 50 and 400 MeV/c show Coulomb focusing below 200 MeV/c and almost no charge-dependence above 200 MeV/c. Similar comparisons for heavier targets are not possible for lack of overlap between nuclear targets studied with $\bar p$ and $\bar n$ beams. Interpolating between $\bar p$-nucleus annihilation cross sections with the help of an optical potential to compare with $\bar n$-nucleus annihilation cross sections reveal unexpected features of Coulomb interactions in the latter. Direct comparisons between $\bar n$-nucleus and $\bar p$-nucleus annihilations at very low energies could be possible if $\bar p$ cross sections are measured on the same targets and at the same energies as the available cross sections for $\bar n$. Such measurements may be feasible in the foreseeable future.
Neutron skins of $^{208}$Pb and $^{48}$Ca from pionic probes
E. Friedman
Physics , 2012, DOI: 10.1016/j.nuclphysa.2012.09.007
Abstract: The neutron skin of $^{208}$Pb has received considerable attention in recent years. A variety of strongly-interacting probes depict a rather consistent picture but pionic probes have not been referred to in this context. We present here neutron-skin values from pionic atoms and from total reaction cross sections of $\pi ^+$ between 0.7 and 2 GeV/c which fit well into the picture. In addition we show that a neutron skin for $^{48}$Ca can be obtained from existing data on pionic atoms and the result agrees with pion scattering experiments and with the scattering of $\alpha $ particles.
Density dependence of the s-wave repulsion in pionic atoms
E. Friedman
Physics , 2002, DOI: 10.1016/S0375-9474(02)01126-0
Abstract: Several mechanisms of density dependence of the s-wave repulsion in pionic atoms, beyond the conventional model, are tested by parameter fits to a large (106 points) set of data from $^{16}$O to $^{238}$U, including `deeply bound' states in $^{205}$Pb. Special attention is paid to the proper choice of nuclear density distributions. A density-dependent isovector scattering amplitude suggested recently by Weise to result from a density dependence of the pion decay constant is introduced and found to account for most of the so-called anomalous repulsion. The presence of such an effect might indicate partial chiral symmetry restoration in dense matter. The anomalous repulsion is fully accounted for when an additional relativistic impulse approximation term is included in the potential.
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