For any near-threshold asymptotic regime and for any Feynman diagram (involving loop and/or phase space integrals), a systematic prescription for explicitly constructing all-logs, all-powers (all-twists) expansions in perfectly factorized form with explicit integrals for coefficients, is presented. The distribution-theoretic nature of the method of asymptotic operation employed allows treatment...

We discuss the determination of the infrared singularities of massive one-loop 5-point functions with Mellin-Barnes (MB) representations. Massless internal lines may lead to poles in the ε expansion of the Feynman diagram, while unresolved massless final state particles give endpoint singularities of the phase space integrals. MB integrals are an elegant tool for their common treatment. An eval...

A " natural " model for the QCD invariant (running) coupling, free of the IR singularity, is proposed. It is based upon the hypothesis of finite gluon mass m gl existence and, technically, uses an accurate treating of threshold behavior of Feynman diagram contribution. The model correlates with the unitarity condition. Quantitative estimate, performed in the one-loop approximation yields a reas...

The Melvin{Morton conjecture says how the Alexander{Conway knot invariant function can be read from the coloured Jones function. It has been proved by D. Bar-Natan and S. Garoufalidis. They reduced the conjecture to a statement about weight systems. The proof of the latter is the most diicult part of their paper. We give a new proof of the statement based on the Feynman diagram description of t...

Acausal features of quantum electrodynamic processes are discussed. While these processes are not present for the classical electrodynamic theory, in the quantum electrodynamic theory, acausal processes are well known to exist. For example, any Feynman diagram with a " loop " in space-time describes a " particle " which may move forward in time or backward in time or in space-like directions. T...

The two-photon production by motion of a charged particle in a medium is considered. This process is called Čerenkov-Compton effect (ČCE) because the production of photons is calculated from the Feynman diagram for the Compton effect in a medium. This process is not forbidden in quantum electrodynamics of dielectric media.The cross section of this process in Mandelstam variables is calculated. ...

We provide a leading singularity analysis protocol in Baikov representation, for the searching of Feynman integrals with uniform transcendental (UT) weight. This approach is powered by recent developments rationalizing square roots and syzygy computations, particularly suitable finding UT multiple mass scales. demonstrate power our determining basis two-loop diagram three external

A new version of application Pauli-Villars regularized Green functions in the quantum field theory using higher derivatives is proposed. In this version the regularizing mass M is large but finite. Our approach is demonstrated and discussed on the example of QED. It is shown that in our case there are no ultraviolet divergences and-on the example of the selfenergy spinor Feynman diagram-no infr...

We compute the one-loop corrections to the tachyon potentials in both, bosonic and supersymmetric, cases by worldsheet methods. In fact, there is no contradiction between this approach and the Feynman diagram expansions arising from the tree level effective actions. In the process, we also get some insight on tachyon condensation from the viewpoint of closed string modes and show that there is ...