A matrix representation of the evolution operator associated with a nonlinear stochastic flow with additive noise is used to compute its spectrum. In the weak noise limit a perturbative expansion for the spectrum is formulated in terms of local matrix representations of the evolution operator centered on classical periodic orbits. The evaluation of perturbative corrections is easier to implemen...

Timelike T-duality of string theory appears as a symmetry of time evolution in string field theory, exchanging evolution through times t and 1/t, and exchanging boundary states with backgrounds. This is demonstrated by constructing the string field Schrödinger functional, the generator of time evolution, based on Feynman diagram arguments and in analogy with quantum field theory. There the func...

We construct a cubic field theory which provides all genus amplitudes of the topological A-model for all non-compact toric Calabi-Yau threefolds. The topology of a given Feynman diagram encodes the topology of a fixed Calabi-Yau, with Schwinger parameters playing the role of Kähler classes of the threefold. We interpret this result as an operatorial computation of the amplitudes in the B-model ...

The Feynman diagram generator FeynArts and the computer algebra program FormCalc allow for an automatic computation of 2→ 2 and 2→ 3 scattering processes in High Energy Physics. We have extended this package by four new kinematical routines and adapted one existing routine in order to accomodate also twoand three-body decays of massive particles. This makes it possible to compute automatically ...

We suggest that at any given order of Feynman diagram calculation for a QCD observable all renormalization group (RG)-predictable terms should be resummed to all-orders. This “complete” RG-improvement (CORGI) serves to separate the perturbation series into infinite subsets of terms which when summed are renormalization scheme (RS)-invariant. Crucially all ultraviolet logarithms involving the di...

Starting from the parametric representation of a Feynman diagram, we obtain it’s well defined value in dimensional regularisation by changing the integrals over parameters into contour integrals. That way we eventually arrive at a representation consisting of well-defined compact integrals. The result is a simple transformation of the integrand which gives the analytic continuation of a wide cl...

We study the QCD scattering amplitudes for q̄q → gg and q̄q → ggg where q is a massive fermion. Using a particular choice of massive fermion spinor we are able to derive very compact expressions for the partial spin amplitudes for the 2 → 2 process. We then investigate the corresponding 2 → 3 amplitudes using the BCFW recursion technique. For the helicity conserving partial amplitudes we again de...

The scalar two-loop master diagram is revisited in the massive cases needed for the computation of boson and fermion propagators in QED and QCD. By means of the causal method it is possible in a straightforward manner to express the propagators as double integrals. In the case of vacuum polarization both integrations can be carried out in terms of polylogarithms, whereas the last integral in th...

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 f...