Matching Long and Short Distances in Large-Nc QCD

It is shown, with the example of the experimentally known Adler function, that there is no matching in the intermediate region between the two asymptotic regimes described by perturbative QCD (for the very short-distances) and by chiral perturbation theory (for the very long-distances). We then propose to consider an approximation of large-Nc QCD which consists in restricting the hadronic spectrum in the channels with J^P quantum numbers 0^-, 1^-, 0^+ and 1^+ to the lightest state and treating the rest of the narrow states as a perturbative QCD continuum; the onset of this continuum being fixed by consistency constraints from the operator product expansion. We show how to construct the low-energy effective Lagrangian which describes this approximation. The number of free parameters in the resulting effective Lagrangian can be reduced, in the chiral limit where the light quark masses are set to zero, to just one mass scale and one dimensionless constant to all orders in chiral perturbation theory. A comparison of the corresponding predictions, to O(p^4) in the chiral expansion, with the phenomenologically known couplings is also made.Comment: 35 pages, 9 figures, LaTeX. Added a couple of reference

Electroweak Hadronic Contributions to the muon g-2

We reanalyze the two-loop electroweak hadronic contributions to the muon g-2 that may be enhanced by large logarithms. The present evaluation is improved over those already existing in the literature by the implementation of the current algebra Ward identities and the inclusion of the correct short-distance QCD behaviour of the relevant hadronic Green's function.Comment: 29 pages, 6 figures, LaTeX. Typos fixe

Decay of pseudoscalars into lepton pairs and large-Nc QCD

The counterterm combination that describes the decay of pseudoscalar mesons into charged lepton pairs at lowest order in chiral perturbation theory is considered within the framework of QCD in the limit of a large number of colours Nc. When further restricted to the lowest meson dominance approximation to large-Nc QCD, our results agree well with the available experimental data.Comment: 5 pages, 2 figure

New nonrenormalization theorems for anomalous three point functions

Nonrenormalization theorems involving the transverse, i.e. non anomalous, part of the correlator in perturbative QCD are proven. Some of their consequences and questions they raise are discussed.Comment: 14 pages. People added in the acknowledgements. Minor changes to match version to appear in journa

Disposition of valganciclovir during continuous renal replacement therapy in two lung transplant recipients

Objectives To determine whether valganciclovir 450 mg every 48 h for cytomegalovirus (CMV) prophylaxis provides appropriate ganciclovir exposure in solid organ transplant recipients during continuous renal replacement therapy (CRRT). Patients and methods Ganciclovir pharmacokinetics was intensively studied in two lung transplant recipients under valganciclovir 450 mg every 48 h over one dosing interval. In vitro experiments using blank whole blood spiked with ganciclovir further investigated exchanges between plasma and erythrocytes. Results Ganciclovir disposition was characterized by apparent total body clearance of 3.3 and 5.8 L/h, terminal half-life of 16.9 and 14.1 h, and apparent volume of distribution of 60.3 and 104.9 L in Patients 1 and 2, respectively. The observed sieving coefficient was 1.05 and 0.96, and the haemofiltration clearance was 3.3 and 3.1 L/h. In vitro experiments confirmed rapid efflux of ganciclovir from red blood cells into plasma, increasing the apparent efficacy of haemofiltration. Conclusions A valganciclovir dosage of 450 mg every 48 h appears adequate for patients under CRRT requiring prophylaxis for CMV infection, providing concentration levels in the range reported for 900 mg once daily dosing outside renal failur

Analyticity, crossing and the absorptive parts of the one-loop contributions to the quark-quark-gluon gauge boson four-point function

Starting from the known one-loop result for the $e^{+}e^{-}$-annihilation process $e^{+}e^{-}\stackrel{\gamma,Z} {\longrightarrow} q\bar{q}g$ with massless quarks we employ analyticity and crossing to determine the absorptive parts of the corresponding one-loop contributions in Deep Inelastic Scattering (DIS) and in the Drell-Yan process (DY). Whereas the ${\cal O}(\alpha_s^2)$ absorptive parts generate a non-measurable phase factor in the $e^{+}e^{-}$-annihilation channel one obtains measurable phase effects from the one-loop contributions in the deep inelastic and in the Drell-Yan case. We compare our results with the results of previous calculations where the absorptive parts in DIS and in the DY process were calculated directly in the respective channels. We also present some new results on the dispersive and absorptive contributions of the triangle anomaly graph to the DIS process.Comment: 23 pages, 5 figures, typos corrected. Version to appear in Phys. Rev.

Hadronic light-by-light scattering contribution to the muon g-2: an effective field theory approach

The hadronic light-by-light contribution to a_{mu}, the anomalous magnetic moment of the muon, is discussed from the point of view of an effective low-energy theory. As an application, the coefficient of the leading logarithm arising from the two-loop graphs involving two anomalous vertices is computed, and found to be positive. This corresponds to a positive sign for the pion-pole contribution to the hadronic light-by-light correction to a_{mu}, and to a sizeable reduction of the discrepancy between the present experimental value of a_{mu} and its theoretical counterpart in the standard model.Comment: 4 pages, 1 figure. v2: published versio

Structure analysis of the virtual Compton scattering amplitude at low energies

We analyze virtual Compton scattering off the nucleon at low energies in a covariant, model-independent formalism. We define a set of invariant functions which, once the irregular nucleon pole terms have been subtracted in a gauge-invariant fashion, is free of poles and kinematical zeros. The covariant treatment naturally allows one to implement the constraints due to Lorentz and gauge invariance, crossing symmetry, and the discrete symmetries. In particular, when applied to the $ep\to e'p'\gamma$ reaction, charge-conjugation symmetry in combination with nucleon crossing generates four relations among the ten originally proposed generalized polarizabilities of the nucleon.Comment: 19 pages, LaTeX2e/RevTeX, no figures, original sections IV.-VI. removed, to be discussed in a separate publication, none of the conclusions change

Virtual Compton scattering off the nucleon at low energies

We investigate the low-energy behavior of the four-point Green's function $\Gamma^{\mu\nu}$ describing virtual Compton scattering off the nucleon. Using Lorentz invariance, gauge invariance, and crossing symmetry, we derive the leading terms of an expansion of the operator in the four-momenta $q$ and $q'$ of the initial and final photon, respectively. The model-independent result is expressed in terms of the electromagnetic form factors of the free nucleon, i.e., on-shell information which one obtains from electron-nucleon scattering experiments. Model-dependent terms appear in the operator at $O(q_\alpha q'_\beta)$, whereas the orders $O(q_\alpha q_\beta)$ and $O(q'_\alpha q'_\beta)$ are contained in the low-energy theorem for $\Gamma^{\mu\nu}$, i.e., no new parameters appear. We discuss the leading terms of the matrix element and comment on the use of on-shell equivalent electromagnetic vertices in the calculation of ``Born terms'' for virtual Compton scattering.Comment: 26 pages, RevTex, to appear in Phys. Rev.