共查询到20条相似文献,搜索用时 15 毫秒
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Zygmunt Zolnierek 《Journal of Physics and Chemistry of Solids》1984,45(5):523-528
A modification of the point charge model is proposed, taking into account the electronegatives of the metal and ligand atoms. On this basis empirical formulas for the effective ligand (L) charge and its distance with respect to the metal (M) origin have been set up. For a VM valent metal atom, surrounded by NL-nearest ligands at distance R0, the respective relations qeff = vM(?L/?M ? 1)/NR0?L/(?L+ ?M) are obtained. When applied to almost forty lanthanide and actinide non-metallic compounds the model shows reasonable agreement with the experimental data available. 相似文献
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G. Felder 《Journal of Geometry and Physics》1993,11(1-4):397-407
These are three introductory lectures on the relation between representations of affine Kac-Moody algebras, homology of configuration spaces with local coefficient systems, and quantum groups. The first lecture contains background on highest weight representations of affine Kac-Moody algebras. In the second lecture, conformal blocks, the Friedan-Shenker connection and the Knizhnik-Zamolodchikov (KZ) equation are reviewed. In the third lecture, the case of slz is studied in more detail. Integral representations of solutions of the KZ equation are derived, and recent results, obtained in collaboration with C. Wieczerkowski, on the relation between integration cycles and representations of Uq (sl2) are explained. 相似文献
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In this paper, we study the role of zero point energies in light front quantized field theories using a simple scalar field model with quartic coupling. In the equal time formalism, the zero point energies are renormalized by normal ordering with respect to some vacuum state, which is varied to determine the true, interacting vacuum. On the light front, we shall see that this procedure acquires an unexpected subtlety due to the equivalence of the ultraviolet (k +→∞) and infrared (k +→0) limits of the light front momentum. In order for the divergent zero point contributions toP + andP ? to cancel, we find that the product of the infrared and ultraviolet cutoffs must be a finite constant whose value is determined by the coupling constants of the theory. As an application, we determine the vacuum structure of the theory in two dimensions as a function of the quartic coupling. Finally, we discuss the implications of our result for the discretized versions of light front quantization. 相似文献
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A simple recursive expansion algorithm for the integrals of tree level superstring five point amplitudes in a flat background is given which reduces the expansion to simple symbol(ic) manipulations. This approach can be used for instance to prove the expansion is maximally transcendental to all orders and to verify several conjectures made in recent literature to high order. Closed string amplitudes follow from these open string results by the KLT relations. To obtain insight into these results in particular the maximal R-symmetry violating amplitudes (MRV) in type IIB superstring theory are studied. The obtained expansion of the open string amplitudes reduces the analysis for MRV amplitudes to the classification of completely symmetric polynomials of the external legs, up to momentum conservation. Using Molien?s theorem as a counting tool this problem is solved by constructing an explicit nine element basis for this class. This theorem may be of wider interest: as is illustrated at higher points it can be used to calculate dimensions of polynomials of external momenta invariant under any finite group for in principle any number of legs, up to momentum conservation. 相似文献
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The causal approach to perturbative quantum field theory is presented in detail, which goes back to a seminal work by Henri Epstein and Vladimir Jurko Glaser in 1973 [12]. Causal perturbation theory is a mathematically rigorous approach to renormalization theory, which makes it possible to put the theoretical setup of perturbative quantum field theory on a sound mathematical basis. Epstein and Glaser solved this problem for a special class of distributions, the time-ordered products, that fulfill a causality condition, which itself is a basic requirement in axiomatic quantum field theory. In their original work, Epstein and Glaser studied only theories involving scalar particles. In this review, the extension of the method to theories with higher spin, including gravity, is presented. Furthermore, specific examples are presented in order to highlight the technical differences between the causal method and other regularization methods, like, e.g. dimensional regularization. 相似文献
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Hopf algebras and quantum groups have recently been applied to the analysis of the combinatorics of Feynman graphs in relativistic quantum field theory. On the other hand, in accordance with the program of deformation quantization, the relation between star products and the perturbative expansion in field theory has also been the subject of intensive study. In the present work we clarify the relation between these two approaches. We show how these techniques can be applied in a unified way to quantum systems with a finite number of degrees of freedom and to quantum field theories. In particular, we find that the time-ordered product of quantum fields is the Weyl transform of a certain twisted product. We also show that one can pass from systems involving bosons to systems with fermions, essentially just by replacing the symmetric algebra of the relevant vector space by its exterior algebra. 相似文献
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On the basis of generalized 6j-symbols we give a formulation of topological quantum field theories for 3-manifolds including observables in the form of coloured graphs. It is shown that the 6j-symbols associated with deformations of the classical groups at primitive even roots of unity provide examples of this construction. Calculational methods are developed which, in particular, yield the dimensions of the state spaces as well as a rather simple proof of the relation, previously found by Turaev and Walker for the case ofU
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(sl(2,C)), between these models and corresponding ones based on the ribbon graph construction of Reshetikhin and Turaev.Supported by DAAD and DFG, SFB 288 Differentialgeometrie und Quantenphysik 相似文献
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We show how to construct, starting from a quasi-Hopf algebra, or quasiquantum group, invariants of knots and links. In some cases, these invariants give rise to invariants of the three-manifolds obtained by surgery along these links. This happens for a finite-dimensional quasi-quantum group, whose definition involves a finite groupG, and a 3-cocycle , which was first studied by Dijkgraaf, Pasquier, and Roche. We treat this example in more detail, and argue that in this case the invariants agree with the partition function of the topological field theory of Dijkgraaf and Witten depending on the same dataG, . 相似文献
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Properties of a system consisting of a single parafermi field of order p are studied mainly in connection with gauge groups. Following the theory of Drühl, Haag and Roberts, the algebra of observables is classified into four cases according to the types of gauge groups, i.e., SO(p), O(p), U(p), and SU(p). A detailed study is made of irreducible representations of these gauge groups that are realized in the state-vector space of the parafermi field. Superselection operators which give rise to the corresponding superselection rules related to the gauge groups are studied, and their explicit expressions given. The statistical quantum number which we introduced before is found to be nothing other than the eigenvalues of a superselection operator for the gauge group O(p). 相似文献
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The energy level diagram and the wave functions for the Ti3+ ions (3d 1) in LaTiO3 are calculated using modern crystal-field theory. The relative orbital ordering of these ions in the ground state is obtained. It turns out that the states of the ground triplet are considerably split and therefore the effect of the electronic-vibrational interaction is suppressed despite the fact that the distortions of the TiO6 building block seem to be small. The components of the electric field gradient tensor at the Ti3+ nuclei sites are calculated using the wave functions of the ground states obtained. The calculated asymmetry parameter agrees well with the experimental values, which demonstrates the adequacy of the proposed orbital-ordering pattern of the Ti3+ ions in the ground state. 相似文献
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Pavlyuk M. D. Sukhanova E. A. Zykova M. P. Volchkov I. S. Kanevskii V. M. Subbotin I. A. Podurets K. M. Pavlyuk B. F. Ivanov Yu. M. 《Physics of the Solid State》2020,62(1):1-7
Physics of the Solid State - For the first time, the process of growing a CdTe crystal by the modified Obreimov–Shubnikov method using the technique of self-nucleation from the initial... 相似文献
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G. E. Volovik 《JETP Letters》2004,79(3):101-105
According to the Multiple Point Principle, our Universe is on the coexistence curve of two or more phases of the quantum vacuum. The coexistence of different quantum vacua can be regulated by the exchange of the global fermionic charges between the vacua, such as baryonic, leptonic, or family charge. If the coexistence is regulated by the baryonic charge, all the coexisting vacua exhibit the baryonic asymmetry. Due to the exchange of the baryonic charge between the vacuum and matter, which occurs above the electroweak transition, the baryonic asymmetry of the vacuum induces the baryonic asymmetry of matter in our Standard Model phase of the quantum vacuum. The present baryonic asymmetry of the Universe indicates that the characteristic energy scale, which regulates the equilibrium coexistence of different phases of quantum vacua, is about 106 GeV. 相似文献
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《Nuclear Physics B》1988,296(1):220-252
The two-dimensional conformal field theory representation of Witten's bosonic string field theory is discussed. The basic overlap equations, Kn symmetry and BRST invariance are proved directly, without the usual expansion in oscillators. The conformal field theory approach naturally provides local overlap identities which (when integrated over half the string) can be used to verify properties of the cubic action. In particular, a recently proposed diffeomorphism invariance is shown to be free of anomalies. Finally, a new class of symmetries, including generalizations of the Kn symmetries which are local in spacetime, are presented. 相似文献
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Giovanni Felder 《Communications in Mathematical Physics》1985,102(1):139-155
We study a
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planar euclidean quantum field theory with propagator 1/p
2–/2,>0. With the help of the tree expansion of Gallavotti and Nicolò [1], this non-renormalizable theory is shown to have a non-trivial ultraviolet-stable fixed point at negative coupling constant. The vicinity of the fixed point is discussed. 相似文献
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Achim Kempf 《Czechoslovak Journal of Physics》1994,44(11-12):1041-1048
Various regularisation techniques are presently emerging from the field of noncommutative geometry. We focus on the possibility of introducing nonzero minimal uncertainties in positions and momenta into the quantum field theoretical framework. Thereby we use techniques that have been developed in the field of quantum groups. The regularisation of a quadratic ultraviolet divergency inφ 4 theory is given explicitely. We also discuss the underlying idea that such uncertainties in position or momentum measurements originate in gravity. 相似文献