2,124 research outputs found
Sum Rules for Magnetic Moments and Polarizabilities in QED and Chiral Effective-Field Theory
We elaborate on a recently proposed extension of the Gerasimov-Drell-Hearn
(GDH) sum rule which is achieved by taking derivatives with respect to the
anomalous magnetic moment. The new sum rule features a {\it linear} relation
between the anomalous magnetic moment and the dispersion integral over a
cross-section quantity. We find some analogy of the linearized form of the GDH
sum rule with the `sideways dispersion relations'. As an example, we apply the
linear sum rule to reproduce the famous Schwinger's correction to the magnetic
moment in QED from a tree-level cross-section calculation and outline the
procedure for computing the two-loop correction from a one-loop cross-section
calculation. The polarizabilities of the electron in QED are considered as well
by using the other forward-Compton-scattering sum rules. We also employ the sum
rules to study the magnetic moment and polarizabilities of the nucleon in a
relativistic chiral EFT framework. In particular we investigate the chiral
extrapolation of these quantities.Comment: 24 pages, 7 figures; several additions, published versio
Towards the Theory of Non--Abelian Tensor Fields I
We present a triangulation--independent area--ordering prescription which
naturally generalizes the well known path ordering one. For such a prescription
it is natural that the two--form ``connection'' should carry three ``color''
indices rather than two as it is in the case of the ordinary one--form gauge
connection. To define the prescription in question we have to define how to
{\it exponentiate} a matrix with three indices. The definition uses the fusion
rule structure constants.Comment: 22 pages, 18 figure
Pion Form Factor in Chiral Limit of Hard-Wall AdS/QCD Model
We develop a formalism to calculate form factor and charge density
distribution of pion in the chiral limit using the holographic dual model of
QCD with hard-wall cutoff. We introduce two conjugate pion wave functions and
present analytic expressions for these functions and for the pion form factor.
They allow to relate such observables as the pion decay constant and the pion
charge electric radius to the values of chiral condensate and hard-wall cutoff
scale. The evolution of the pion form factor to large values of the momentum
transfer is discussed, and results are compared to existing experimental data.Comment: 21 page, 7 figures. Short comparison with NJL predictions for pion
radius and new references added. To be published in Phys.Rev.
Proton structure corrections to hyperfine splitting in muonic hydrogen
We present the derivation of the formulas for the proton structure-dependent
terms in the hyperfine splitting of muonic hydrogen. We use compatible
conventions throughout the calculations to derive a consistent set of formulas
that reconcile differences between our results and some specific terms in
earlier work. Convention conversion corrections are explicitly presented, which
reduce the calculated hyperfine splitting by about 46 ppm. We also note that
using only modern fits to the proton elastic form factors gives a smaller than
historical spread of Zemach radii and leads to a reduced uncertainty in the
hyperfine splitting. Additionally, hyperfine splittings have an impact on the
muonic hydrogen Lamb shift/proton radius measurement, however the correction we
advocate has a small effect there.Comment: 6 pages, 3 figure
Proton structure corrections to electronic and muonic hydrogen hyperfine splitting
We present a precise determination of the polarizability and other proton
structure dependent contributions to the hydrogen hyperfine splitting, based
heavily on the most recent published data on proton spin dependent structure
functions from the EG1 experiment at the Jefferson Laboratory. As a result, the
total calculated hyperfine splitting now has a standard deviation slightly
under 1 part-per-million, and is about 1 standard deviation away from the
measured value. We also present results for muonic hydrogen hyperfine
splitting, taking care to ensure the compatibility of the recoil and
polarizability terms.Comment: 9 pages, 1 figur
Parton distributions in radiative corrections to the cross section of electron-proton scattering
The structure function approach and the parton picture, developed for the
theoretical description of the deep inelastic electron-proton scattering, also
proved to be very effective for calculation of radiative corrections in Quantum
Electrodynamics. We use them to calculate radiative corrections to the cross
section of electron-proton scattering due to electron-photon interaction, in
the experimental setup with the recoil proton detection, proposed by A.A.
Vorobev to measure the proton radius. In the one-loop approximation, explicit
expressions for these corrections are obtained for arbitrary momentum
transfers. It is shown that, at momentum transfers small compared with the
proton mass, various contributions to the corrections mutually cancel each
other with power accuracy. In two loops, the corrections are obtained in the
leading logarithmic approximation.Comment: arXiv admin note: text overlap with arXiv:1812.1071
Ising model with a boundary magnetic field - an example of a boundary flow
In hep-th/0312197 a nonperturbative proof of the g-theorem of Affleck and
Ludwig was put forward. In this paper we illustrate how the proof of
hep-th/0312197 works on the example of the 2D Ising model at criticality
perturbed by a boundary magnetic field. For this model we present explicit
computations of all the quantities entering the proof including various contact
terms. A free massless boson with a boundary mass term is considered as a
warm-up example.Comment: 1+20 pages, Latex, 2 eps figures; v2: references adde
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