Avoidance of a Landau pole by flat contributions in QED

We consider massless Quantum Electrodynamics in the momentum scheme and carry forward an approach based on Dyson–Schwinger equations to approximate both the β$\beta$-function and the renormalized photon self-energy (Yeats, 2011). Starting from the Callan–Symanzik equation, we derive a renormalization group (RG) recursion identity which implies a non-linear ODE for the anomalous dimension and extract a sufficient but not necessary criterion for the existence of a Landau pole. This criterion implies a necessary condition for QED to have no such pole. Solving the differential equation exactly for a toy model case, we integrate the corresponding RG equation for the running coupling and find that even though the β$\beta$-function entails a Landau pole it exhibits a flat contribution capable of decreasing its growth, in other cases possibly to the extent that such a pole is avoided altogether. Finally, by applying the recursion identity, we compute the photon propagator and investigate the effect of flat contributions on both spacelike and timelike photons.     

A phenomenological treatment of dual loop contributions to inclusive reactions

A phenomenological B₆ type amplitude is constructed which contains Regge singularities of twisted loop graphs such as ordinary trajectories, Regge cuts and Pomeron trajectories. With this amplitude possible implications of the different one and two-loop graphs for single particle distributions are derived for different kinematical regions including the fixed angle limit. The results emphasize the importance of dual loop contributions to single particle distributions.     

An exact treatment of some integrals appearing in the three-body contributions to transport coefficients

The convergence properties of the integral corresponding to the three-body cyclic collisions in the two-dimensional density expansion of transport coefficients are investigated. It is shown exactly that the integral considered by Oppenheim et al. and by Eu diverges logarithmically in the switching parameter ε.     

Gluonic contributions to the exclusive amplitudes

The contributions from gluonic wave functions to the amplitudes of meson production ine ⁺ e ^? annihilation, quarkonium decays and twophoton processes are calculated.     

Extragalactic contributions to the CMB signal

One of the main challenges facing upcoming Cosmic Microwave Background (CMB) experiments aiming at measuring temperature anisotropies with great accuracy will be to assess the contamination of CMB measurements by galactic and extragalactic foregrounds. On the extragalactic side, confusion noise from extragalactic sources hampers the detection of intrinsic CMB anisotropies at small angular scales. Secondary CMB anisotropies must also be carefully accounted for in order to isolate the primordial fluctuations. We present in this article a brief overview of the extragalactic contributions to the CMB. The galactic foregrounds are discussed elsewhere (Giard and Lagache, this issue). To cite this article: G. Lagache, N. Aghanim, C. R. Physique 4 (2003).     

Avoidance and treatment of complications of teflon injection of the vocal cord

The best way to avoid complications with Teflon injection of the vocal cord, as with any other surgical procedure, is proper patient selection and technique. Indications, techniques, and treatment of complications are discussed     

Electromagnetic contributions to the nucleon-nucleon interaction

The helicity amplitudes of the nucleon-nucleon one-photon exchange interaction are calculated. The anomalous magnetic moments of the proton and neutron are included in the calculations. The formalism is especially suitable for the small angle proton-proton interaction at intermediate energies. The electromagnetic phase shifts in the Born approximation are defined and calculated. The three cases of the proton-proton, the neutron-proton and the neutron-neutron interactions are dealt with separately. Analytic expressions are given for sums defined by divergent partial waves. We indicate the pecularities of the neutron-proton interaction: the singlet-triplet transitions and the t⁻¹ singularity in the differential cross section. These peculiarities require an improved treatment of the neutron-proton interaction. A modified formalism is suggested.     

Hadronic contributions to the muon magnetic moment

Zeitschrift für Physik A Hadrons and nuclei - Using the recent experimental data on the pion form factor in the time-like region limits are placed on the 2π contribution to the muon...     

Overlapping contributions to the pion-deuteron scattering length

The dependence of the pion-deuteron scattering length on the overlapping region of the two scatterers is studied. It is found that this region contributes almost 30 % to the total result.     

Meson-exchange contributions to the nuclear charge operator

The role of the meson-exchange current correction to the nuclear charge operator is studied in electron scattering processes involving the excitation of medium and heavy nuclei to energies up to the quasi-elastic peak. The effect of these contributions in the quasi-free electron scattering process is a reduction of at most a 3% in the longitudinal response at the energy of the peak, a value which is below the experimental error and must not be taken into account in calculations in this energy region. On the other hand, the excitation of low-lying nuclear levels of neutronic character shows, with respect to the protonic ones, a considerable effect due to the inclusion of the two-body term in the charge operator. More realistic calculations, such as those performed in the random-phase approximation framework, give rise to a mixing of one particle-one hole configurations of both kinds which reduce these effects. However, it has been found that the excitation of some of these levels is sizably affected by the meson-exchange contribution. More precise experimental data concerning some of these states, such as e.g. the high-spin states in ²⁰⁸Pb, could throw some light in the problem of a more feasible determination of these effects and, as a consequence, could provide an alternative procedure to determine the charge neutron form factor.     

Scalar-leptoquark contributions to the neutrino magnetic moment

On the basis of astrophysical data on the neutrino magnetic moment, μ _ν < 3 × 10⁻¹² μ _B , constraints on the scalar-leptoquark masses are found within the minimal model involving four-color symmetry. It is shown that data on the neutrino magnetic moment are compatible with the mixing-parameter range that admits the existence of scalar leptoquarks whose masses are below 1 TeV, reaching experimental limits obtained from direct searches. In the case of mass degeneracy for the scalar leptoquarks S _m of electric charge Q = 2/3, the constraint m _{S m} > 330 GeV is obtained, which is independent of the mixing parameters of the model. The results are compared with the predictions of other leptoquark models. Original Russian Text ? A.V. Povarov, 2007, published in Yadernaya Fizika, 2007, Vol. 70, No. 5, pp. 905–911.     

Perturbative contributions to the electroweak interface tension

The main perturbative contribution to the free energy of an electroweak interface is due to the effective potential and the tree level kinetic term. The derivative corrections are investigated with one-loop perturbation theory. The action is treated in derivative, in heat kernel, and in a multi local expansion. The massive contributions turn out to be well described by the Z-factor. The massless mode, plagued by infrared problems, is numerically less important. Its perturbatively reliable part can by calculated in derivative expansion as well. A self consistent way to include the Z-factor in the formula for the interface tension is presented.     

Physical contributions to the heat capacity of nickel

Heat capacity data for solid nickel have been re-evaluated and analyzed into physical contributions, 0–1726 K. Two new sets of measurements of C_p(Ni), 333–1500 K, have been combined with literature data to produce an evaluated data set with uncertainty ? ± 2%. These smoothed data have been analyzed into vibrational harmonic, electronic, magnetic and dilatational contributions with the aid of auxiliary measurements of expansion coefficient, compressibility, vibrational and electronic densities of states, elastic constants, and magnetic exchange integral and susceptibility obtained from the literature. The vibrational harmonic term is interpreted in terms of a θ_D-vs-T curve in accord with predictions of the density-of-states distribution. The electronic contribution is smaller than predicted by free-electron theory due to a large electron-phonon effect. The electronic term for paramagnetic nickel is in good agreement with that predicted from band calculations. The magnetic contribution yields a magnetic entropy in accord with theoretical predictions, and a magnetic internal energy and critical-point behavior in agreement with the isotropic Heisenberg model. The experimental heat capacity can be accounted for without reference to vibrational anharmonic and vacancy contributions, in accord with recent calculations.     

Non-spherical contributions to the vacancy formation energy

A linear response formalism is presented which allows the calculation of the non-spherically symmetric (angular momentum index, l ≠ 0) response to a random external charge perturbation when the spherically symmetric response is available. This procedure is applied to the problem of the energy of vacancy formation so that the electron charge depletion in the vicinity of vacancy is taken into account. The non-spherical contribution to the energy formation for the alkali metals is estimated and found to be non-negligible.     

Fermionic contributions to the three-loop static potential

We consider the three-loop corrections to the static potential which are induced by a closed fermion loop. For the reduction of the occurring integrals a combination of the Gröbner and Laporta algorithm has been used and the evaluation of the master integrals has been performed with the help of the Mellin–Barnes technique. The fermionic three-loop corrections amount to 2% of the tree-level result for top quarks, 8% for bottom quarks and 27% for the charm quark system.     

On the rotational contributions to the dipole-moment derivatives

In order to get dipole-moment derivatives, $\text{?}\text{u}\text{?}\text{?S}{}_{\mathrm{j}}$ that are free from rotational contributions, we used Crawford's method applied to a new type of reference molecule. The agreement with earlier calculated rotational correction terms is good, the applicability of the new reference molecule is wider. The rotational contributions to the $\text{?}\text{u}\text{?}\text{?S}{}_{\mathrm{j}}$-quantities are presented for a number of C_2v- and C_3v-type molecules.