Two-Point One-Loop Fermionic Amplitudes in Constant Homogeneous Magnetic Field

Two-point one-loop fermionic amplitudes modifiled by a constant homogeneous magnetic fileld are studied. In addition to the amplitudes resulted after an insertion of scalar, pseudoscalar, vector and axial-vector fermionic currents, we calculate similar amplitudes with the tensor and (pseudo)scalar vertices. The crossed-field limit of these amplitudes is presented. The tensor current is a fermionic part of the Pauli Lagrangian relevant for the electromagnetic interaction of fermions through the anomalous magnetic moment and its contribution to the photon polarization operator is briefly discussed.

Tensor form factor for the D → π(K) transitions with Twisted Mass fermions.

We present a preliminary lattice calculation of the D → π and D → K tensor form factors fT (q2) as a function of the squared 4-momentum transfer q2. ETMC recently computed the vector and scalar form factors f+(q2) and f0(q2) describing D → π(K)lv semileptonic decays analyzing the vector current and the scalar density. The study of the weak tensor current, which is directly related to the tensor form factor, completes the set of hadronic matrix element regulating the transition between these two pseudoscalar mesons within and beyond the Standard Model where a non-zero tensor coupling is possible. Our analysis is based on the gauge configurations produced by the European Twisted Mass Collaboration with Nf = 2 + 1 + 1 flavors of dynamical quarks. We simulated at three different values of the lattice spacing and with pion masses as small as 210 MeV and with the valence heavy quark in the mass range from ≃ 0.7 mc to ≃ 1.2mc. The matrix element of the tensor current are determined for a plethora of kinematical conditions in which parent and child mesons are either moving or at rest. As for the vector and scalar form factors, Lorentz symmetry breaking due to hypercubic effects is clearly observed in the data. We will present preliminary results on the removal of such hypercubic lattice effects.

TOPOLOGICAL ZERO-THICKNESS COSMIC STRINGS

In this paper, based on the gauge potential decomposition and the ϕ-mapping theories, we study the topological structures and properties of the cosmic strings that arise in the Abelian–Higgs gauge theory in the zero-thickness limit. After a detailed discussion, we conclude that the topological tensor current introduced in our model is a better and more basic starting point than the generally used Nambu–Goto effective action for studying cosmic strings.