[en] The renormalized perturbation expansion for the line width of the van der Pol oscillator is extended to fifth order. The results of the previously obtained fourth order are thereby improved for pump strength a approx. < 5. No indication of a breakdown of the expansion, even for strong pumping, is found. (orig.)

[en] Far above threshold the production process e⁺e^- → t t can be analyzed using effective field theories. In this paper we consider the invariant-mass distribution of top-jets and report about our computation of the two-loop heavy-quark jet-function. This is a key part of a next-to-next-to-leading order analysis, and already allows for a resummation of all large logs which effect the shape of the top-invariant-mass distribution at next-to-next-to-leading log order. A top-mass scheme is defined which is suitable for measurements involving jets, and whose anomalous dimension is determined by the cusp-anomalous dimension to all orders in perturbation theory.

[en] I present an outline of chiral perturbation theory and discuss some recent developments in the field

No abstract available

No abstract available

[en] We discuss the validity of the perturbation treatments and we derive some expressions for the Moessbauer lineshape both without and with the noise approximation

[en] A small-time approach to the description of the time-dependent perturbation theory is proposed. For this purpose we assume that within the interaction-region the particle is not necessarily a point-like one, thus also considering additionally, a large imaginary contribution (Im Vsub(ii)<<0) of the interaction potential which is confined inside the small-time region. It can be then proved that the validity of the so implied Schroedinger equation with the nonhermitian (hermitian) interaction can be assured only up to a certain upper (lower) bound of the time-parameter. Alternatively, such results are able to probe, in this way also, the existence of a nonzero intrinsic time-dispersion

[en] We study cutoff effects at tree-level of perturbation theory for maximally twisted mass Wilson, overlap and the recently proposed Creutz fermions. We demonstrate that all three kinds of lattice fermions exhibit the expected O(a²) scaling behaviour in the lattice spacing. In addition, the sizes of these cutoff effects are comparable for the three kinds of lattice fermions considered here. Furthermore, we analyze situations when twisted mass fermions are not exactly at maximal twist and when overlap fermions are studied in comparison to twisted mass fermions when the quark masses are not matched

[en] This is an investigation of conditions under which the property that a flow has a (unique) measure with maximal entropy is stable under local perturbations of the base

[en] The perturbation of symmetries and Mei adiabatic invariants of nonholonomic systems with servoconstraints are studied. The exact invariants in the form of Mei conserved quantities introduced by the Mei symmetry of nonholonomic systems with servoconstraints without perturbations are given. Based on the definition of higher-order adiabatic invariants of mechanical systems, the perturbation of Mei symmetries for nonholonomic systems with servoconstraints under the action of small disturbance is investigated, and Mei adiabatic invatiants of the system are obtained. An example is given to illustrate the application of the results