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[en] The problem of gauge and off-mass-shellness dependence of damping of collective excitations with fermion quantum numbers in quark-gluon plasma is again discussed. The calculations are carried out in the real time technique, which is the most suitable for this purpose. It is shown that the gauge-dependent part of damping survives, but it does not lead to any disaster because damping as such is not a physical quantity, i.e., it cannot be measured in experiment. All measurable characteristics of quark-gluon plasma are gauge-independent. The recent paradoxical observation concerning analytic properties of the Green function of an energetic fermion is also discussed. 26 refs., 6 figs
[en] In this article author studied phenomena, connected with growth ofcollective fluctuations level in the area of kinetic non stability of liquid.Was showed qualitative agreement of behaviour of dynamic form-factor withexperimental data on dispersal of radiation nearby to critical point
[en] The functional integral method is applied for constructing an effective Hamiltonian describing the high amplitude collective excitations in the final system of interacting fermions. It is shown that the dynamics of arbitrarily high fluctuations of the medium field in the system considered is similar to the rotator dynamics in the space with pseudoeuclidean metrics. 13 refs.; 18 figs
[en] Complete text of publication follows. Molecular dynamics (MD) simulations are performed to study the excitation properties of spherical Yukawa Balls. Results are reported for the dependence of the normal modes on screening and the interaction strength. While the low order modes are well explained by a cold fluid description deviations occur for high order modes, in particular for strong screening of the interaction potential. At strong coupling the simulations reveal additional low frequency excitations which are not included in the theoretical fluid model. The breathing mode is studied in further detail and a comparison is made between the fluid model, MD simulations and the harmonic approximation for a crystallized system.
[en] Collective plasmon excitations in a helical electron liquid on the surface of strong three-dimensional topological insulator are considered. The properties and internal structure of these excitations are studied. Due to spin-momentum locking in helical liquid on a surface of topological insulator, the collective excitations should manifest themselves as coupled charge- and spin-density waves.
[en] Many new ideas in theoretical physics come from analogies to older ideas in physics. For instance, the abstract notion of 'isospin' (or isotopic spin) originated in the prior concept of 'spin' (quantized angular momentum); likewise, the concept of 'phonon' (quantum of sound, or quantized collective excitation of a crystal) was based on the prior concept of 'photon' (quantum of light, or quantized element of the electromagnetic field). But these two examples, far from being exceptions, in fact represent the bread and butter of inventive thinking in physics. In a nutshell, intraphysics analogy-making -- borrowing by analogy with something already known in another area of physics -- is central to the progress of physics. The aim of this talk is to reveal the pervasiveness -- indeed, the indispensability -- of this kind of semi-irrational, wholly intuitive type of thinking (as opposed to more deductive mathematical inference) in the mental activity known as 'doing physics'. Speculations as to why wild analogical leaps are so crucial to the act of discovery in physics (as opposed to other disciplines) will be offered.
[en] In this paper the author reports a simplified model, where collective beam-beam oscillations can be described by a differential equation similar to the Schroedinger equation in quantum mechanics. In this case, the stability criteria can be obtained inspecting the behavior of effective potential well curves
[en] In the last years the sum rule method has been extensively employed in nuclear physics in order to investigate the properties of nuclear collective excitations. As is well known, one of the main advantages of the sum rule method is that it avoids the complete solution of the Schrodinger equation, therefore providing an alternative and direct insight on the properties of the collective motion. In this series of lectures, the authors investigate only some aspects of the sum rule approach. In particular, they discuss the different kind of physics that can be learned from the investigation of different sum rules. They discuss in details only sum rules for electric-type excitations, the nature and the properties of magnetic transitions being less systematically known