Search results for "Theoretical physics"
showing 10 items of 751 documents
Quantum rings for beginners II: Bosons versus fermions
2012
The purpose of this overview article, which can be viewed as a supplement to our previous review on quantum rings, [S. Viefers {\it et al}, Physica E {\bf 21} (2004), 1-35], is to highlight the differences of boson and fermion systems in one-dimensional (1D) and quasi-one-dimensional (Q1D) quantum rings. In particular this involves comparing their many-body spectra and other properties, in various regimes and models, including spinless and spinful particles, finite versus infinite interaction, and continuum versus lattice models. Our aim is to present the topic in a comprehensive way, focusing on small systems where the many-body problem can be solved exactly. Mapping out the similarities a…
Fermion Condensation in Finite Systems
2014
Here we consider another example of systems, in which fermion condensation takes place. These are what is called finite Fermi systems, i.e. systems with finite number of fermions, contrary to a solid, where the number of electrons is practically infinite. An example of a finite Fermi system is an atomic nucleus, having finite number of nucleons, protons and neutrons, which are fermions. Here we show that the fermion condensation manifests itself in finite Fermi systems as a forced merger of all, discreet for finite systems, single-particle levels, lying near the Fermi surface. On the first sight, this merger contradicts the standard Landau quasiparticle picture. Nevertheless, similar to inf…
Quasiparticle Mean Field: BCS and Beyond
2007
In the previous two chapters we have laid the foundation for the BCS theory to describe open-shell nuclei. The properties of BCS solutions were compared with exact results from schematic solvable models. In this chapter we go into the details of numerical solution of the BCS equations. The implications of these solutions are discussed through applications to ds- and pf-shell nuclei.
Comment on “Accurate ground-state phase diagram of the one-dimensional extended Hubbard model at half filling”
2004
In PRB 68, 153101 (2003), Guoping Zhang presented density-matrix renormalization group (DMRG) results which contradict my DMRG calculations and Hirsch's quantum Monte Carlo (QMC) simulations for the charge-density-wave (CDW) phase boundary in the one-dimensional extended Hubbard model at half filling. In this Comment I show that Zhang's results are inaccurate and that his criticism of my work is groundless.
Edwin Power and the birth of dressed atoms
2006
This paper reviews the main results of a twenty year-long international collaborative effort led by the late E.A. Power on the physics of atoms dressed by the vacuum electromagnetic field. The presentation uses the historical, rather than the logical, order of development. This permits one to shed light on the influence of Power's personality and human qualities on the birth and evolution of the notion of the dressed atom, which is central to modern non-relativistic QED.
Dynamics of a subconstituent picture of weak interactions
1985
We use sum rules in order to discuss the dynamics of the simplest subconstituent model of weak interactions with elementary spin 1/2 fermions and scalar bosons. Vacuum condensates of the scalars play an essential role and lead to features quite different from QCD. With a certain vacuum structure vector dominance of the composite W-mesons is a good approximation, and we also see a clear signal for massless fermions in the two-point function of composite fermions. Thus such a model is in good agreement with standard phenomenology. Composite Higgs particles are also investigated. The effective interaction is evidently of the gauge type.
(Regular) pseudo-bosons versus bosons
2012
We discuss in which sense the so-called {\em regular pseudo-bosons}, recently introduced by Trifonov and analyzed in some details by the author, are related to ordinary bosons. We repeat the same analysis also for {\em pseudo-bosons}, and we analyze the role played by certain intertwining operators, which may be bounded or not.
Glass transitions and scaling laws within an alternative mode-coupling theory
2015
Idealized glass transitions are discussed within an alternative mode-coupling theory (TMCT) proposed by Tokuyama [Physica A 395, 31 (2014)]. This is done in order to identify common ground with and differences from the conventional mode-coupling theory (MCT). It is proven that both theories imply the same scaling laws for the transition dynamics, which are characterized by two power-law decay functions and two diverging power-law time scales. However, the values for the corresponding anomalous exponents calculated within both theories differ from each other. It is proven that the TMCT, contrary to the MCT, does not describe transitions with continuously vanishing arrested parts of the corre…
Magnetic exchange between metal ions with unquenched orbital angular momenta: basic concepts and relevance to molecular magnetism
2010
This review article is a first attempt to give a systematic and comprehensive description (in the framework of the unified theoretical approach) of the exchange interactions in polynuclear systems based on orbitally degenerate metal ions in the context of their relevance to the modern molecular magnetism. Interest in these systems is related to the fundamental problems of magnetism and at the same time steered by a number of impressive potential applications of molecular magnets, like high-density memory storage units, nanoscale qubits, spintronics and photoswitchable devices. In the presence of orbital degeneracy, the conventional spin Hamiltonian (Heisenberg–Dirac–van Vleck model) becomes…
Riemann solvers in relativistic astrophysics
1999
AbstractOur contribution reviews High Resolution Shock Capturing methods (HRSC) in the field of relativistic hydrodynamics with special emphasis on Riemann solvers. HRSC techniques achieve highly accurate numerical approximations (formally second order or better) in smooth regions of the flow, and capture the motion of unresolved steep gradients without creating spurious oscillations. One objective of our contribution is to show how these techniques have been extended to relativistic hydrodynamics, making it possible to explore some challenging astrophysical scenarios. We will review recent literature concerning the main properties of different special relativistic Riemann solvers, and disc…