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Andrzej Czarnecki

Publications and source records attributed to Andrzej Czarnecki.

At least 73 records · Page 4Linked to original sources
arXiv2010

Magnetic moment of a bound electron

Theoretical predictions underlying determinations of the fine structure constant alpha and the electron-to-proton mass ratio m_e/m_p are reviewed, with the emphasis on the bound electron magnetic anomaly g-2. The theory of the interaction of hydrogen-like ions with a magnetic field is discussed. The status of efforts aimed at the determination of O(alpha (Z alpha)^5) and O(alpha^2 (Z alpha)^5) corrections to the g factor is presented. The reevaluation of analogous corrections to the Lamb shift and the hyperfine splitting is summarized.

hep-ph↗
arXiv2010

Helicity fractions of W bosons from top quark decays at NNLO in QCD

Decay rates of unpolarized top quarks into longitudinally and transversally polarized W bosons are calculated to second order in the strong coupling constant alpha_s. Including the finite bottom quark mass and electroweak effects, the Standard Model predictions for the W boson helicity fractions are F_L=0.687(5), F_+=0.0017(1), and F_-=0.311(5).

hep-ph↗
arXiv2010

Radiative-nonrecoil corrections of order alpha^2 (Z alpha)^5 to the Lamb shift

We present results for the corrections of order alpha^2 (Z alpha)^5 to the Lamb shift. We compute all the contributing Feynman diagrams in dimensional regularization and a general covariant gauge using a mixture of analytical and numerical methods. We confirm results obtained by other groups and improve their precision. Values of the 32 master integrals for this and similar problems are provided.

hep-ph↗
arXiv2010

A remark on the Brylinski conjecture for orbifolds

We present reformulation of Mathieu's result on representing cohomology classes of symplectic manifold with symplectically harmonic forms. We apply it to the case of foliated manifolds with transversally symplectic structure and to symplectic orbifolds. We obtain in particular that such representation is always possible for compact Kähler orbifolds.

math.DG↗
arXiv2010

Two-loop corrections to the Lamb shift

We present a new calculation of the order alpha^2 (Z alpha)^5 correction to the Lamb shift, which uses methods developed for multi-loop calculations.

hep-ph↗
arXiv2008

Semi-Leptonic b-decay at Intermediate Recoil

We compute the O(α_s^2) corrections to the differential rate of the semileptonic decay b -> clv at the "intermediate recoil" point, where the c-quark mass and the invariant mass of the leptons are equal. The calculation is based on an expansion around two opposite limits of the quark masses m_{b,c}: m_c ~ m_b and m_c << m_b. The former case was previously studied; we correct and extend that result. The latter case is new. The smooth matching of both expansions provides a check of both. We clarify the discrepancy between the recent determinations of the full NNLO QCD correction to the semileptonic b -> c rate, and its earlier estimate.

hep-ph↗
arXiv2008

Semileptonic decays in the limit of a heavy daughter quark

The rate of the semileptonic decay b to c l v is calculated with order alphas^2 accuracy, as an expansion around the limit of equal masses of the b and c quarks. Recent results obtained around the limit of the c-quark much lighter than b are confirmed. Details of the new expansion method are described.

hep-ph↗
arXiv2008

Dipole Excitation of Dipositronium

The energy interval between the ground and the P-wave excited states of the recently discovered positronium molecule Ps_2 is evaluated, including the relativistic and the leading logarithmic radiative corrections, E_P-E_S = 0.181 586 7(8) a.u. The P-state, decaying usually via annihilation, is found to decay into the ground state by an electric dipole transition 19 percent of the time. Anticipated observation of this transition will provide insight into this exotic system.

hep-ph↗
arXiv2008

Heavy-to-heavy quark decays at NNLO

Details of a recent calculation of O(alpha_s^2) corrections to the decay b -> c,l,nu_l, taking into account the c-quark mass, are described. Construction of the expansion in the mass ratio m_c/m_b as well as the evaluation of new four-loop master integrals are presented. The same techniques are applicable to the muon decay, mu -> e,nu_mu,anti-nu_e. Analytical results are presented, for the physical cases as well as for a model with purely-vector couplings.

hep-ph↗
arXiv2008

Mass effects in muon and semileptonic b -> c decays

Quantum chromodynamics (QCD) effects in the semileptonic decay b -> c l nu are evaluated to the second order in the coupling constant, O(alpha_s^2), and to several orders in the expansion in quark masses, m_c/m_b. Corrections are calculated for the total decay rate as well as for the first two moments of the lepton energy and the hadron system energy distributions. Applied to the muon decay, they decrease its predicted rate by -0.43 ppm.

hep-ph↗
arXiv2007

Positronium-ion decay

We present a precise theoretical prediction for the decay width of the bound state of two electrons and a positron (a negative positronium ion), Gamma(Ps^-) = 2.087 085(12)/ns. We include O(alpha^2) effects of hard virtual photons as well as soft corrections to the wave function and the decay amplitude. An outcome of a large-scale variational calculation, this is the first result for second-order corrections to a decay of a three-particle bound state. It will be tested experimentally in the new positronium-ion facility in Garching in Germany.

hep-ph↗
arXiv2006

Refinements in electroweak contributions to the muon anomalous magnetic moment

Effects of strong interactions on the two loop electroweak radiative corrections to the muon anomalous magnetic moment, $a_μ=(g_μ-2)/2$, are examined. Short-distance logs are shown to be unaffected. Computation of long-distance contributions is improved by use of an effective field theory approach that preserves the chiral properties of QCD and accounts for constraints from the operator product expansion. Small, previously neglected, two loop contributions, suppressed by a $1-4\sin^2θ_W$ factor, are computed and the complete three loop leading short-distance logs are reevaluated. These refinements lead to a reduction in uncertainties and a slight shift in the total electroweak contribution to $a_μ^{\rm EW} = 154(1)(2)\times 10^{-11}$ where the first error corresponds to hadronic uncertainties and the second is primarily due to the allowed Higgs mass range.

hep-ph↗
arXiv2006

Nonrelativistic QED approach to the Lamb shift

We calculate the one- and two-loop corrections of order alpha(Zalpha)^6 and alpha^2(Zalpha)^6 respectively, to the Lamb shift in hydrogen-like systems using the formalism of nonrelativistic quantum electrodynamics. We obtain general results valid for all hydrogenic states with nonvanishing orbital angular momentum and for the normalized difference of S-states. These results involve the expectation value of local effective operators and relativistic corrections to Bethe logarithms. The one-loop correction is in agreement with previous calculations for the particular cases of S, P, and D states. The two-loop correction in the order alpha^2(Zalpha)^6 includes the pure two-loop self-energy and all diagrams with closed fermion loops. The obtained results allow one to obtain improved theoretical predictions for all excited hydrogenic states.

physics.atom-ph↗
arXiv2006

Calculation of the One- and Two-Loop Lamb Shift for Arbitrary Excited Hydrogenic States

General expressions for quantum electrodynamic corrections to the one-loop self-energy [of order alpha(Zalpha)^6] and for the two-loop Lamb shift [of order alpha^2(Zα)^] are derived. The latter includes all diagrams with closed fermion loops. The general results are valid for arbitrary excited non-S hydrogenic states and for the normalized Lamb shift difference of S states, defined as Delta_n = n^3 DeltaE(nS) - DeltaE(1S). We present numerical results for one-loop and two-loop corrections for excited S, P and D states. In particular, the normalized Lamb shift difference of S states is calculated with an uncertainty of order 0.1 kHz.

physics.atom-ph↗
arXiv2005

Complete two-loop correction to the bound-electron g factor

Within a systematic approach based on the dimensionally regularized nonrelativistic quantum electrodynamics, we derive the complete result for the two-loop correction to order $(α/π)^2 (Z α)^4$ for the $g$ factor of an electron bound in an $nS$ state of a hydrogenlike ion. The results obtained significantly improve the accuracy of the theoretical predictions for the hydrogenlike carbon and oxygen ions and influence the value of the electron mass inferred from $g$ factor measurements.

physics.atom-ph↗
arXiv2004

Precision Measurements and CKM Unitarity

Determinations of $\vud$ and $\vus$ along with their implications for the unitarity test $\vud^2+\vus^2+\vub^2=1$ are discussed. The leading two loop radiative corrections to neutron $β$-decay are evaluated and used to derive a refined relationship $\vud^2 τ_n (1+3g_A^2)=4908(4)$sec. Employing $\vud =0.9740(5)$ from superallowed nuclear decays and the measured neutron lifetime $τ_n = 885.7(7)$sec, leads to the precise prediction $g_A=1.2703(8)$ which is compared with current direct experimental values. Various extractions of $\vus$ are described and updated. The long accepted Particle Data Group value of $\vus$ from fitted $K_{e3}$ decay rates suggests a deviation from CKM unitarity but it is contradicted by more recent experimental results which confirm unitarity with good precision. An outlook for possible future advances is given.

hep-ph↗
arXiv2004

Theoretical Summary of Moriond 2004: QCD and Hadronic Interactions

Theoretical talks and discussions at Rencontres de Moriond 2004 "QCD and Hadronic Interactions" are summarized. Following exciting recent experimental discoveries, theoretical developments were reported in the description of heavy ion collisions, light hadron spectroscopy, and the physics of hadrons containing heavy quarks. Some of the predictions have already been tested by subsequent experiments, notably by the very recent SELEX observation of a possible new charm-strange meson D_{sJ}(2632).

hep-ph↗