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Alexander Yelkhovsky

Publications and source records attributed to Alexander Yelkhovsky.

16 recordsLinked to original sources
arXiv2018

Finite volume solution for two-phase flow in a straight capillary

The problem of two-phase flow in straight capillaries of polygonal cross section displays many of the dynamic characteristics of rapid interfacial motions associated with pore-scale displacements in porous media. Fluid inertia is known to be important in these displacements but is usually ignored in network models commonly used to predict macroscopic flow properties. This study presents a numerical model for two-phase flow which describes the spatial and temporal evolution of the interface between the fluids. The model is based on an averaged Navier-Stokes equation and is shown to be successful in predicting the complex dynamics of both capillary rise in round capillaries and imbibition along the corners of polygonal capillaries. The model can form the basis for more realistic network models which capture the effect of capillary, viscous and inertial forces on pore-scale interfacial dynamics and consequent macroscopic flow properties.

physics.flu-dyn↗
arXiv2001

Recoil correction to the magnetic moment of a bound electron

The effect of a finite nuclear mass on the magnetic moment of the electron bound in the ground state of a hydrogen-like ion is analyzed. Using the exact in Zαexpression for the recoil shift of the energy, I calculate the order (Zα)^4 m/M correction to the electron gyromagnetic ratio. The theoretical uncertainty in the prediction for the experimentally interesting carbon ion is decreased to the level of 1.2x10^-9. This provides a factor of two improvement in the precision of the atomic mass of the electron.

hep-ph↗
arXiv2001

Ionization Potential of the Helium Atom

Ground state ionization potential of the He^4 atom is evaluated to be 5 945 204 221 (42) MHz. Along with lower order contributions, this result includes all effects of the relative orders alpha^4, alpha^3*m_e/m_alpha and alpha^5*ln^2(alpha).

physics.atom-ph↗
arXiv2001

Quantum Electrodynamics of the Helium Atom

Using singlet S states of the helium atom as an example, I describe precise calculation of energy levels in few-electron atoms. In particular, a complete set of effective operators is derived which generates O(m*alpha^6) relativistic and radiative corrections to the Schr"odinger energy. Average values of these operators can be calculated using a variational Schr"odinger wave function.

hep-ph↗
arXiv2000

O(alpha^3 ln alpha) corrections to muonium and positronium hyperfine splitting

We compute O(alpha^3 ln alpha) relative corrections to the ground state hyperfine splitting of a QED two body bound state with different masses of constituents. The general result is then applied to muonium and positronium. In particular, a new value of the muon to electron mass ratio is derived from the muonium ground state hyperfine splitting.

hep-ph↗
arXiv2000

O(alpha^3 ln alpha) corrections to positronium decay rates

We compute O(alpha^3 ln alpha) corrections to the decay rates of para- and orthopositronium into two and three photons, respectively. For this calculation we employ the nonrelativistic QED regularized dimensionally and we explain how in this framework the logarithms of the fine structure constant can be extracted.

hep-ph↗
arXiv2000

Anomalous magnetic moment of a bound electron

We study binding corrections to the gyromagnetic factor g_e of an electron in hydrogen-like ions. We argue that the leading order binding effects in radiative corrections Delta g_rad are universal to all orders in alpha/pi and the complete result reads Delta g_rad = (g_free - 2) [1+(Z alpha)^2/6] + O[alpha/pi (Zalpha)^4]. The theoretical uncertainty in the prediction for the experimentally interesting carbon ion is decreased by a factor of about 3.

hep-ph↗
arXiv2000

alpha^2 corrections to parapositronium decay: a detailed description

We present details of our recent calculation of alpha^2 corrections to the parapositronium decay into two photons. These corrections are rather small and our final result for the parapositronium lifetime agrees well with the most recent measurement. Implications for orthopositronium decays are briefly discussed.

hep-ph↗
arXiv2000

alpha^2 corrections to parapositronium decay

Two-loop QED corrections to the decay rate of parapositronium (p-Ps) into two photons are presented. We find Gamma(p-Ps --> 2 photons) = 7989.64(2)/microsec. The non-logarithmic O(alpha^2) corrections turn out to be small, contrary to some earlier estimates. We speculate that the so-called ``orthopositronium lifetime puzzle'' will not likely be solved by large QED corrections.

hep-ph↗
arXiv1999

Recent results with heavy quarks and light lepton bound states

Recent results on second order quantum corrections to semileptonic decays of b quarks and positronium spectroscopy are reviewed. Similarities between calculations in these seemingly different problems are demonstrated. Technical aspects of solving systems of recurrence relations, and application of dimensional regularization to bound states are explained.

hep-ph↗
arXiv1999

Positronium S state spectrum: analytic results at O(m alpha^6)

We present an analytic calculation of the O(m alpha^6) recoil and radiative recoil corrections to energy levels of positronium nS states and their hyperfine splitting. A complete analytic formula valid to O(m alpha^6) is given for the spectrum of S states. Technical aspects of the calculation are discussed in detail. Theoretical predictions are given for various energy intervals and compared with experimental results.

hep-ph↗
arXiv1998

Top quark production at threshold with O(alpha_s^2) accuracy

We calculate the next-to-next-to-leading order correction to the cross section for top quark pair production in e+e- annihilation in the threshold region, resumming all O [ (alpha_s/beta)^n (alpha_s^2, beta^2, alpha_s beta) ] terms of perturbation series. We find that the magnitude of the NNLO correction is comparable to the size of the NLO corrections.

hep-ph↗
arXiv1998

The b quark low-scale running mass from Upsilon sum rules

The b quark low-scale running mass m_kin is determined from an analysis of the Upsilon sum rules in the next-to-next-to-leading order (NNLO). It is demonstrated that using this mass one can significantly improve the convergence of the perturbation series for the spectral density moments. We obtain m_kin(1 GeV) = 4.56 \pm 0.06 GeV. Using this result we derive the value of the MS-bar mass m: m(m) = 4.20 \pm 0.1 GeV. Contrary to the low-scale running mass, the pole mass of the b quark cannot be reliably determined from the sum rules. As a byproduct of our study we find the NNLO analytical expression for the cross section e+e- --> Q\bar Q of the quark antiquark pair production in the threshold region, as well as the energy levels and the wave functions at the origin for the ^1S_3 bound states of Q\bar Q.

hep-ph↗
arXiv1998

Top quark production near threshold: on resummation of O( (β_0α_s)^n) QCD corrections

We discuss the resummation of the potentially large O((β_0α_s)^n) QCD corrections to the total cross section of the process e^+e^- \to t \bar t near the threshold. In this approximation, the cross section factorization into the short- and long-distance parts is valid. The short-distance correction is reduced to the production vertex renormalization. It amounts to -9.5% and is well under control. The long distance corrections are accounted for as the effect of the coupling's running in the QCD potential. We argue that the accuracy of present predictions for the cross section in the scheme with the running QCD coupling is about 10%.

hep-ph↗