The terms glass'' and liquid'' are defined in a dynamic sense, with a sublinear response rho=partial derivativeital E/partial derivativeital jvert barsub ital jr arrow0 characterizing the truly ...superconducting vortex glass and a finite resistivity rho(ital jr arrow0)gt0 being the signature of the liquid phase. The smallness of ital jsub ital c/ital jsub o allows one to discuss the influence of quenched disorder in terms of the weak collective pinning theory. Supplementing the traditional theory of weak collective pinning to take into account thermal and quantum fluctuations, as well as the new scaling concepts for elastic media subject to a random potential, this modern version of the weak collective pinning theory consistently accounts for a large number of novel phenomena, such as the broad resistive transition, thermally assisted flux flow, giant and quantum creep, and the glassiness of the solid state. The strong layering of the oxides introduces additional new features into the thermodynamic phase diagram, such as a layer decoupling transition, and modifies the mechanism of pinning and creep in various ways. The presence of strong (correlated) disorder in the form of twin boundaries or columnar defects not only is technologically relevant but also provides the framework for the physical realization of novel thermodynamic phases such as the Bose glass. On a macroscopic scale the vortex system exhibits self-organized criticality, with both the spatial and the temporal scale accessible to experimental investigations.
Various experimental methods based on positron annihilation have evolved into important tools for researching the structure and properties of condensed matter. In particular, positron techniques are ...useful for the investigation of defects in solids and for the investigation of solid surfaces. Experimental methods need a comprehensive theory for a deep, quantitative understanding of the results. In the case of positron annihilation, the relevant theory includes models needed to describe the positron states as well as the different interaction processes in matter. In this review the present status of the theory of positrons in solids and on solid surfaces is given. The review consists of three main parts describing (a) the interaction processes, (b) the theory and methods for calculating positron states, and (c) selected recent results of positron studies of condensed matter.
The macroscopic electric polarization of a crystal is often defined as the dipole of a unit cell. In fact, such a dipole moment is ill defined, and the above definition is incorrect. Looking more ...closely, the quantity generally measured is ital differential polarization, defined with respect to a reference state'' of the same material. Such differential polarizations include either derivatives of the polarization (dielectric permittivity, Born effective charges, piezoelectricity, pyroelectricity) or finite differences (ferroelectricity). On the theoretical side, the differential concept is basic as well. Owing to continuity, a polarization difference is equivalent to a macroscopic current, which is directly accessible to the theory as a bulk property. Polarization is a quantum phenomenon and cannot be treated with a classical model, particularly whenever delocalized valence electrons are present in the dielectric. In a quantum picture, the current is basically a property of the ital phase of the wave functions, as opposed to the charge, which is a property of their modulus. An elegant and complete theory has recently been developed by King-Smith and Vanderbilt, in which the polarization difference between any two crystal states--in a null electric field--takes the form of a geometric quantum phase. This gives a comprehensive account of this theory, which is relevant for dealing with transverse-optic phonons, piezoelectricity, and ferroelectricity. Its relation to the established concepts of linear-response theory is also discussed. Within the geometric phase approach, the relevant polarization difference occurs as the circuit integral of a Berry connection (or vector potential''), while the corresponding curvature (or magnetic field'') provides the macroscopic linear response.
We argue that the spectrum of the QCD Dirac operator near zero virtuality can be described by random matrix theory. As in the case of the classical random matrix ensembles of Dyson we have three ...different cases: the chiral orthogonal ensemble, the chiral unitary ensemble, and the chiral symplectic ensemble. They correspond to gauge groups SU(2) in the fundamental representation, SU(ital Nsub ital c), ital Nsub ital cge3 in the fundamental representation, and non-Abelian gauge groups SU(ital Nsub ital c) for all ital Nsub ital c with fermions in the adjoint representation, respectively. The joint probability density reproduces Leutwyler-Smilga sum rules.
The stability or lack thereof of nonrelativistic fermionic systems to interactions is studied within the renormalization-group (RG) framework, in close analogy with the study of critical phenomena ...using phisup 4 scalar field theory. A brief introduction to phisup 4 theory in four dimensions and the path-integral formulation for fermions is given before turning to the problem at hand. As for the latter, the following procedure is used. First, the modes on either side of the Fermi surface within a cutoff Lambda are chosen for study, in analogy with the modes near the origin in phisup 4 theory, and a path integral is written to describe them. Next, an RG transformation that eliminates a part of these modes, but preserves the action of the noninteracting system, is identified. Finally the possible perturbations of this free-field fixed point are classified as relevant, irrelevant or marginal. A ital d=1 warmup calculation involving a system of fermions shows how, in contrast to mean-field theory, which predicts a charge-density wave for arbitrarily weak repulsion, and superconductivity for arbitrarily weak attraction, the renormalization-group approach correctly yields a scale-invariant system (Luttinger liquid) by taking into account both instabilities.
The key quantity of the heavy quark theory is the quark mass ital msub ital Q. Since quarks are unobservable one can suggest different definitions of ital msub ital Q. One of the most popular choices ...is the pole quark mass routinely used in perturbative calculations and in some analyses based on heavy quark expansions. We show that no precise definition of the pole mass can be given in the full theory once nonperturbative effects are included. Any definition of this quantity suffers from an intrinsic uncertainty of order Lambdasub QCD/ital msub ital Q. This fact is succinctly described by the existence of an infrared renormalon generating a factorial divergence in the high-order coefficients of the alphasub ital s series; the corresponding singularity in the Borel plane is situated at 2pi/ital b. A peculiar feature is that this renormalon is not associated with the matrix element of a local operator. The difference bar Lambdaequivalent toital Msub ital Hital Q-ital msub ital Qsup pole can still be defined by heavy quark effective theory, but only at the price of introducing an explicit dependence on a normalization point mu: bar Lambda(mu). Fortunately the pole mass ital msub ital Q(0) ital per ital se does not appear in calculable observable quantities.
Sterile neutrinos as dark matter Dodelson, S; Widrow, LM
Physical review letters,
01/1994, Letnik:
72, Številka:
1
Journal Article
Recenzirano
Odprti dostop
The simplest model that can accommodate a viable nonbaryonic dark matter candidate is the standard electroweak theory with the addition of right-handed (sterile) neutrinos. We consider a single ...generation of neutrinos with a Dirac mass mu and a Majorana mass ital M for the right-handed component. If ital Mmuch gtmu (standard hot dark matter corresponds to ital M=0), then sterile neutrinos are produced via oscillations in the early Universe with energy density independent of ital M. However, ital M is crucial in determining the large scale structure of the Universe; for ital Msimilar to100 eV, sterile neutrinos make an excellent warm dark matter candidate.
A generalization of the operator product expansion is used to find the differential distributions in the inclusive semileptonic weak decays of heavy flavors in QCD. In particular, the double ...distribution in electron energy and invariant mass of the lepton pair is calculated. We are able to calculate the distributions in an essentially model-indpendent way as a series in ital msub ital Qsup minus1 where ital msub ital Q is the heavy quark mass. All effects up to ital msub ital Qsup minus2 are included.
Terawatt to Petawatt Subpicosecond Lasers Perry, Michael D.; Mourou, Gerard
Science (American Association for the Advancement of Science),
05/1994, Letnik:
264, Številka:
5161
Journal Article
Recenzirano
The application of the chirped-pulse amplification technique to solid-state lasers combined with the availability of broad-bandwidth materials has made possible the development of small-scale ...terawatt and now even petawatt (1000-terawatt) laser systems. The laser technology used to produce these intense pulses and examples of new phenomena resulting from the application of these systems to atomic and plasma physics are described.
It is shown that in 2+1 dimensions, a constant magnetic field is a strong catalyst of dynamical flavor symmetry breaking, leading to generating a fermion dynamical mass even at the weakest attractive ...interaction between fermions. The effect is illustrated in the Nambu--Jona-Lasinio model in a magnetic field. The low-energy effective action in this model is derived, and the thermodynamic properties of the model are established.
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