arXiv subjects

A. Yelkhovsky

Publications and source records attributed to A. Yelkhovsky.

5 recordsLinked to original sources

arXiv2000

Top-Antitop Pair Production close to Threshold: Synopsis of recent NNLO Results

Using non-relativistic effective theories, new next-to-next-to-leading order (NNLO) QCD corrections to the total $t\bar t$ production cross section at the Linear Collider have been calculated recently. In this article the NNLO calculations of several groups are compared and the remaining uncertainties are discussed. The theoretical prospects for an accurate determination of top quark mass parameters are discussed in detail. An outlook on possible future improvements is given.

hep-ph↗

arXiv1998

Positronium hyperfine splitting: analytical value at m*alpha^6

We present an analytic calculation of the m*alpha^6 recoil corrections to the hyperfine splitting (HFS) of the ground state energy levels in positronium. We find ΔE_{\rm rec} = m alpha^6 (-1/6 ln(alpha) + 331/432 -ln(2)/4 - 17 Zeta(3)/(8 pi^2) + 5/(12 pi^2)) \approx m alpha^6 (- 1/6 ln(alpha) + 0.37632), confirming Pachucki's numerical result \cite{Ph}. We present a complete analytic formula for the m*alpha^6 HFS of the positronium ground state and, including m*alpha^7*ln^2(alpha) effects, find E(1^3S_1)-E(1^1S_0))_{theory} = 203 392(1) MHz. This differs from the experimental results by about 3 standard deviations.

hep-ph↗

arXiv1997

Vacuum Polarization Contribution to Hydrogen and Positronium Energies

Relative order α(Zα)^3 shift of the energy levels induced by the vacuum polarization is reexamined for a bound system of two particles with masses m and M. Recent results for hydrogen and for positronium are shown to contain an error due to the inadequate procedure of the infrared divergence handling. Numerically, the correction to the ground state energy constitutes 0.647 kHz for hydrogen and 46.7 kHz for positronium.

hep-ph↗

arXiv1997

Recoil Correction to Hydrogen Energy Levels: A Revision

Recent calculations of the order (Zα)^4(m/M)Ry pure recoil correction to hydrogen energy levels are critically revised. The origins of errors made in the previous works are elucidated. In the framework of a successive approach, we obtain the new result for the correction to S levels. It amounts to -16.4 kHz in the ground state and -1.9 kHz in the 2S state.

physics.atom-ph↗

arXiv1995

Order (Zα)^4 m/M Ry Correction to Hydrogen Levels

The first in m/M and fourth in Zα(pure recoil) correction to a hydrogen energy level is found. This correction comprises two contributions, one coming from the atomic scale, the other from distances of the Compton wavelength order. Two different perturbation schemes are used to calculate the former. One of them exploits as unperturbed the solution to the Dirac-Coulomb problem, the nucleus' slow motion being the source of the perturbation. The alternative scheme treats both the electron and the nucleus as slow, while relativistic effects are considered perturbatively. The short-distance contribution is found in the Feynman and Coulomb gauges. Recent results for P levels are confirmed, in contrast with those for S levels. Numerically, the shift equals 2.77 kHz for the ground state and 0.51 kHz for 2S state.

hep-ph↗