The removal of unphysical singularities in the perturbatively calculable part pion form factor---a classic example a three-point function QCD---is discussed. Different analytization procedures sense Shirkov and Solovtsov are examined comparison with standard QCD perturbation theory. We show that demanding analyticity partonic amplitude as whole, proposed before by Karanikas Stefanis, one can make infrared finite not only strong running coupling its powers, but also cure potentially large...

We discuss the time continuous path integration in coherent-state basis a way that is free from inconsistencies. Employing this notion we reproduce known and exact results working directly continuum. Such formalism can set to develop perturbative nonperturbative approximations already quantum-field-theory community. These techniques be proven useful great variety of problems where bosonic Hamiltonians are used.

This article discusses applications of a path-integral approach to fermionic Green and vertex functions which has systematic expansion in terms contours (particle ``world lines''), thereby enabling the evaluation all-order results coupling constant. Our approach, provides an effective field theoretical framework for studying low-energy regime underlying dynamics. In particular, infrared behavior full fermion QED can be analyzed without imposing assumptions on asymptotic states charged...

A novel approach to the study of fermionic systems in d-dimensional Euclidean spacetime is presented according which an original, field-theoretical form description converted into a particle-based language. An important aspect advocated procedure that it employs resolution scale does not have serve, at same time, as ultraviolet cutoff for matter field fluctuations. At particle level description, such fluctuations are independently regularized by associated with ``proper-time'' parameter. key...

Abstract In spite of their simple description in terms rotations or symplectic transformations phase space, quadratic Hamiltonians such as those modelling the most common Gaussian operations on bosonic modes remain poorly understood entropy production. For instance, determining quantum generated by a Bogoliubov transformation is notably hard problem, with generally no known analytical solution, while it vital to characterisation communication via channels. Here we overcome this difficulty...

A field-theoretical approach to the scattering off an oscillating quantum system is developed. As a key ingredient it employs adiabatic eigenstate basis and consists of perturbative scheme for calculation geometric phases influencing transmission through time-dependent potential landscape. The main advantage identification basic diagrams which allow immediate interpretation underlying elementary physical processes contributing behavior. We apply our method simple, but prototypical, problem...

The statistical properties of a one-dimensional system are studied in the Ginzburg-Landau framework, where most general free-energy density allowing for scale invariance is introduced. grand partition function expressed as functional integral over order-parameter space and leads to an analytically soluble model. Near critical point only constant functions contribute thermodynamic potential, simulated by classical nonlinear lattice, Kadanoff scaling shown be equivalent Koba-Nielsen-Olesen...

We study a well-defined formulation of pure Yang-Mills theories in the continuum which employs an action structured by gauge-invariant loop variables. At classical level, we show how aforementioned comes arbitrarily close to standard and also prove that it yields correct equations motion. perform path-integral quantization theory establish, through direct calculation, strong-coupling confinement continuum. claim advocated constitutes nonperturbative regularization non-Abelian gauge

The Polyakov world-line path integral describing the propagation of gluon field quanta is constructed by employing background gauge fixing method and subsequently applied to analytically compute divergent terms one (gluonic) loop effective action fourth order in perturbation theory. merits proposed approach that, a given order, it reduces performing two integrations, over set Grassmann Feynman-type parameters through which manages accomodate all Feynman diagrams entering computation at once.

We study the dynamics of an interacting Bose-Hubbard chain coupled to a non-Markovian environment. Our basic tool is reduced generating functional expressed as path integral over spin-coherent states. calculate leading contribution corresponding effective action, and by minimizing it, we derive mean-field equations that can be numerically solved. With this at hand, examine influence system's initial conditions interparticle interactions on dissipative dynamics. Moreover, investigate presence...

A theoretical framework is presented to treat hadronic observables within analytic perturbative QCD beyond the leading order of coupling and for more than one single large momentum scale. The approach generalizes extends pioneering work Shirkov Solovtsov on an strong running coupling. Some applications at partonic level are also discussed.

We define the time-continuous spin coherent-state path integral in a way that is free from inconsistencies. The proposed definition used to reproduce known exact results. Such formalism opens new possibilities for applying approximations with improved accuracy and can be proven useful great variety of problems where Hamiltonians are used.