84 research outputs found
The Road to Stueckelberg's Covariant Perturbation Theory as Illustrated by Successive Treatments of Compton Scattering
We review the history of the road to a manifestly covariant perturbative
calculus within quantum electrodynamics from the early semi-classical results
of the mid-twenties to the complete formalism of Stueckelberg in 1934. We chose
as our case study the calculation of the cross-section of the Compton effect.
We analyse Stueckelberg's paper extensively. This is our first contribution to
a study of his fundamental contributions to the theoretical physics of
twentieth century.Comment: This paper is a "working-physicist" version of a paper to be
published in Studies in History and Philosophy of Modern Physic
On the Interpretation of the Redshift in a Static Gravitational Field
The classical phenomenon of the redshift of light in a static gravitational
potential, usually called the gravitational redshift, is described in the
literature essentially in two ways: on the one hand the phenomenon is explained
through the behaviour of clocks which run the faster the higher they are
located in the potential, whereas the energy and frequency of the propagating
photon do not change with height. The light thus appears to be redshifted
relative to the frequency of the clock. On the other hand the phenomenon is
alternatively discussed (even in some authoritative texts) in terms of an
energy loss of a photon as it overcomes the gravitational attraction of the
massive body. This second approach operates with notions such as the
"gravitational mass" or the "potential energy" of a photon and we assert that
it is misleading. We do not claim to present any original ideas or to give a
comprehensive review of the subject, our goal being essentially a pedagogical
one.Comment: latex, 16 pages, to be published in American Journal of Physic
Atomic parity nonconservation and neutron radii in cesium isotopes
The interpretation of future precise experiments on atomic parity violation
in terms of parameters of the Standard Model could be hampered by uncertainties
in the atomic and nuclear structure. While the former can be overcome by
measurement in a series of isotopes, the nuclear structure requires knowledge
of the neutron density. We use the nuclear Hartree-Fock method, which includes
deformation effects, to calculate the proton and neutron densities in
{125}Cs-{139}Cs. We argue that the good agreement with the experimental charge
radii, binding energies, and ground state spins signifies that the
phenomenological nuclear force and the method of calculation that we use is
adequate. Based on this agreement, and on calculations involving different
effective interactions, we estimate the uncertainties in the differences of the
neutron radii delta_{N,N'} and conclude that they cause uncertainties in
the ratio of weak charges, the quantities determined in the atomic parity
nonconservation experiments, of less than 10^{-3}. Such an uncertainty is
smaller than the anticipated experimental error.Comment: 24 pages (RevTeX) 4 figures (Postscript/uuencoded compressed) Caltech
Preprint No. MAP-153 (March 1993
Average polarization of 12B in 12C(ÎŒ, Îœ) 12B(g.s.) reaction: Helicity of the Ï-decay muon and nature of the weak coupling
The helicity, h -, of ÎŒ - in Ï-decay has been determined as positive (h -â„+0.90) from the average polarization, P avâĄăJ B·s ÎŒă, of 12B produced in the ÎŒ -+ 12CâÎœ ÎŒ+ 12B reaction. We obtain also dynamical information on ÎŒ-capture: (i) the weak magnetism form factor, ÎŒ=4.5±1.1, and (ii) the sum of the induced pseudoscalar (g p) and the 2nd class induced tensor (g T) couplings versus g A, ( g P+g T) g A=7.1±2.7. The latter result, adopting the "canonical" value of g P g A, leads to g T g A=+1±2.7 which is compatible with zero and in strong contradiction with the value {reversed tilde equals}-6 recently advocated by Kubodera, Delorme and Rho. © 1977
The angular distribution of the reaction
The reaction is very important for low-energy
( MeV) antineutrino experiments. In this paper we calculate
the positron angular distribution, which at low energies is slightly backward.
We show that weak magnetism and recoil corrections have a large effect on the
angular distribution, making it isotropic at about 15 MeV and slightly forward
at higher energies. We also show that the behavior of the cross section and the
angular distribution can be well-understood analytically for MeV by calculating to , where is the nucleon mass. The
correct angular distribution is useful for separating events from other reactions and detector backgrounds, as well as for
possible localization of the source (e.g., a supernova) direction. We comment
on how similar corrections appear for the lepton angular distributions in the
deuteron breakup reactions and . Finally, in the reaction , the
angular distribution of the outgoing neutrons is strongly forward-peaked,
leading to a measurable separation in positron and neutron detection points,
also potentially useful for rejecting backgrounds or locating the source
direction.Comment: 10 pages, including 5 figure
Induced pseudoscalar coupling of the proton weak interaction
The induced pseudoscalar coupling is the least well known of the weak
coupling constants of the proton's charged--current interaction. Its size is
dictated by chiral symmetry arguments, and its measurement represents an
important test of quantum chromodynamics at low energies. During the past
decade a large body of new data relevant to the coupling has been
accumulated. This data includes measurements of radiative and non radiative
muon capture on targets ranging from hydrogen and few--nucleon systems to
complex nuclei. Herein the authors review the theoretical underpinnings of
, the experimental studies of , and the procedures and uncertainties
in extracting the coupling from data. Current puzzles are highlighted and
future opportunities are discussed.Comment: 58 pages, Latex, Revtex4, prepared for Reviews of Modern Physic
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