Modern Physics Letters A

We investigate the behavior of small perturbations around the Kaluza–Klein monopole in the five-dimensional space–time. We find that the even parity gravitational wave does not propagate in the five-dimensional space–time with Kaluza–Klein monopole provided that the gravitational wave is constant in the fifth direction. We conclude that a gravitational wave and a U(1) magnetic monopole do not coexist in five-dimensional Kaluza–Klein space–time.

We show that the quantum probabilistic distribution over the space in the spectator world can be associated to a metric in which the particle lives. According to this geometrical view, the metric in the particle world is "contracted" or "stretched" in an inverse proportion to the probability distribution.

We use the method of QCD sum rules in the presence of the external electromagnetic F_μν field to analyze radiative decays of charmed or bottomed mesons such as D*→ Dγ and B*→ Bγ, in a model-independent manner upon making use of the susceptibilities obtained previously from the study of baryon magnetic moments. Our predictions on D* decays agree very well with the experimental data. There are differences among the various theoretical predictions on B* decays and future experimental data should help to discriminate among the various predictions.

A manifestly N=2 supersymmetric coset formalism is applied to analyze the "fermionic" extensions of N=2, a=4 and a=-2 KdV hierarchies. Both hierarchies can be obtained from a manifest N=2 coset construction. This coset is defined as the quotient of some local but nonlinear superalgebra by a Û (1) subalgebra. Three superextensions of N=2 KdV hierarchy are proposed, among which one seems to be entirely new.

Nontrivial extensions of three-dimensional Poincaré algebra, beyond the supersymmetric one, are explicitly constructed. These algebraic structures are the natural three-dimensional generalizations of fractional supersymmetry of order F already considered in one and two dimensions. Representations of these algebras are exhibited, and unitarity is explicitly checked. It is then shown that these extensions generate symmetries which connect fractional spin states or anyons. Finally, a natural classification arises according to the decomposition of F into its product of prime numbers leading to subsystems with smaller symmetries.

We give several pieces of evidence to show that extremal black holes cannot be obtained as limits of non-extremal black holes. We review arguments in the literature showing that the entropy of extremal black holes is zero, while that of near-extremal ones obey the Bekenstein–Hawking formula. However, from the counting of degeneracy of quantum (BPS) states of string theory the entropy of extremal stringy black holes obeys the area law. An attempt is made to reconcile these arguments.

The Proca model is quantized in an open-path dependent representation that generalizes the loop representation of gauge theories. The starting point is a gauge-invariant Lagrangian that reduces to the Proca Lagrangian when certain gauge is selected.

A generating function for the Parke–Taylor amplitudes with any number of positive helicity gravitons in addition to the positive helicity gluons is obtained using the recently constructed self-dual classical solution of the type of perturbiner in Yang–Mills theory interacting with gravity.

The supersymmetric generalization of Poisson–Lie T-duality in the N=2 superconformal WZNW models on the compact groups is considered. It is shown that the role of Drinfeld's doubles play the complexifications of the corresponding compact groups. These complex doubles are used to define the natural actions of the isotropic subgroups forming the doubles on the group manifolds of the N=2 superconformal WZNW models. The Poisson–Lie T-duality in N=2 superconformal U(2)-WZNW model is considered in details. It is shown that this model admits Poisson–Lie symmetries with respect to the isotropic subgroups forming Drinfeld's double Gl(2,C). Poisson–Lie T-duality transformation maps this model into itself but acts nontrivially on the space of classical solutions. Supersymmetric generalization of Poisson–Lie T-duality in N=2 superconformal WZNW models on the compact groups of higher dimensions is proposed.