105 research outputs found
Revised value of the eighth-order electron g-2
The contribution to the eighth-order anomalous magnetic moment (g-2) of the
electron from a set of diagrams without closed lepton loops is recalculated
using a new FORTRAN code generated by an automatic code generator. Comparing
the contributions of individual diagrams of old and new calculations, we found
an inconsistency in the old treatment of infrared subtraction terms in two
diagrams. Correcting this error leads to the revised value -1.9144 (35)
(alpha/pi)^4 for the eighth-order term. This theoretical change induces the
shift of the inverse of the fine structure constant by -6.41180(73)x10^{-7}.Comment: 4 pages, 1 figure, typo is correcte
Proper Eighth-Order Vacuum-Polarization Function and its Contribution to the Tenth-Order Lepton g-2
This paper reports the Feynman-parametric representation of the
vacuum-polarization function consisting of 105 Feynman diagrams of the eighth
order, and its contribution to the gauge-invariant set called Set I(i) of the
tenth-order lepton anomalous magnetic moment. Numerical evaluation of this set
is carried out using FORTRAN codes generated by an automatic code generation
system gencodevpN developed specifically for this purpose. The contribution of
diagrams containing electron loop to the electron g-2 is 0.017 47 (11)
(alpha/pi)^5. The contribution of diagrams containing muon loop is 0.000 001 67
(3) (alpha/pi)^5. The contribution of tau-lepton loop is negligible at present.
The sum of all these terms is 0.017 47 (11) (alpha/pi)^5. The contribution of
diagrams containing electron loop to the muon g-2 is 0.087 1 (59) (alpha/pi)^5.
That of tau-lepton loop is 0.000 237 (1) (alpha/pi)^5. The total contribution
to a_mu, the sum of these terms and the mass-independent term, is 0.104 8 (59)
(alpha/pi)^5.Comment: 48 pages, 6 figures. References are correcte
Tenth-order lepton g-2: Contribution from diagrams containing a sixth-order light-by-light-scattering subdiagram internally
This paper reports the result of our evaluation of the tenth-order QED
correction to the lepton g-2 from Feynman diagrams which have sixth-order
light-by-light-scattering subdiagrams, none of whose vertices couple to the
external magnetic field. The gauge-invariant set of these diagrams, called Set
II(e), consists of 180 vertex diagrams. In the case of the electron g-2 (a_e),
where the light-by-light subdiagram consists of the electron loop, the
contribution to a_e is found to be - 1.344 9 (10) (\alpha /\pi)^5. The
contribution of the muon loop to a_e is - 0.000 465 (4) (\alpha /\pi)^5. The
contribution of the tau-lepton loop is about two orders of magnitudes smaller
than that of the muon loop and hence negligible. The sum of all of these
contributions to a_e is - 1.345 (1) (\alpha /\pi)^5. We have also evaluated the
contribution of Set II(e) to the muon g-2 (a_\mu). The contribution to a_\mu
from the electron loop is 3.265 (12) (\alpha /\pi)^5, while the contribution of
the tau-lepton loop is -0.038 06 (13) (\alpha /\pi)^5. The total contribution
to a_\mu, which is the sum of these two contributions and the mass-independent
part of a_e, is 1.882 (13) (\alpha /\pi)^5.Comment: 18 pages, 3 figures, REVTeX4, axodraw.sty used, changed title,
corrected uncertainty of a_mu, added a referenc
Eighth-Order Vacuum-Polarization Function Formed by Two Light-by-Light-Scattering Diagrams and its Contribution to the Tenth-Order Electron g-2
We have evaluated the contribution to the anomalous magnetic moment of the
electron from six tenth-order Feynman diagrams which contain eighth-order
vacuum-polarization function formed by two light-by-light scattering diagrams
connected by three photons. The integrals are constructed by two different
methods. In the first method the subtractive counter terms are used to deal
with ultraviolet (UV) singularities together with the requirement of
gauge-invariance. In the second method, the Ward-Takahashi identity is applied
to the light-by-light scattering amplitudes to eliminate UV singularities.
Numerical evaluation confirms that the two methods are consistent with each
other within their numerical uncertainties. Combining the two results
statistically and adding small contribution from the muons and/or tau leptons,
we obtain . We also evaluated the
contribution to the muon from the same set of diagrams and found .Comment: 27 page
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