Symmetries of coset spaces and Kaluza-Klein supergravity

Known theorems about the isometry group of a general coset space $\text{G}\text{H}$ are reviewed. The Killing vectors on $\text{G}\text{H}$ are explicitly constructed. Rescalings of the coset vielbeins are discussed, and a simple criterion to find which rescalings preserve the isometry group is given. A general expression for the Riemann and Ricci tensors in terms of the rescaled vielbeins and the group structure constants is derived. These results have useful applications in Kaluza-Klein theories. As an example, the round and the squashed seven-spheres that have been used to compactify d = 11 supergravity are discussed, and it is shown that they can be identified with two appropriately rescaled coset spaces $\text{SO(5)}\text{SO(3)}$.     

Killing spinors on Lorentzian manifolds

The aim of this paper is to describe some results concerning the geometry of Lorentzian manifolds admitting Killing spinors. We prove that there are imaginary Killing spinors on simply connected Lorentzian Einstein–Sasaki manifolds. In the Riemannian case, an odd-dimensional complete simply connected manifold (of dimension n≠7) is Einstein–Sasaki if and only if it admits a non-trivial Killing spinor to . The analogous result does not hold in the Lorentzian case. We give an example of a non-Einstein Lorentzian manifold admitting an imaginary Killing spinor. A Lorentzian manifold admitting a real Killing spinor is at least locally a codimension one warped product with a special warping function. The fiber of the warped product is either a Riemannian manifold with a real or imaginary Killing spinor or with a parallel spinor, or it again is a Lorentzian manifold with a real Killing spinor. Conversely, all warped products of that form admit real Killing spinors.     

7-Dimensional compact Riemannian manifolds with Killing spinors

Using a link between Einstein-Sasakian structures and Killing spinors we prove a general construction principle of odd-dimensional Riemannian manifolds with real Killing spinors. In dimensionn=7 we classify all compact Riemannian manifolds with two or three Killing spinors. Finally we classify nonflat 7-dimensional Riemannian manifolds with parallel spinor fields.     

Scalar manifolds and Jordan pairs in supergravity

It is shown how the concept of a Jordan pair, which generalizes that of Jordan algebra and links Jordan algebras to Lie algebras, enters a model for supergravity-studied recently by Günaydin, Sierra, and Townsend, called magical supergravity. This model is very briefly reviewed, as are the reasons that led, starting from the theory of Jordan algebras, to the definition and development of Jordan pairs. Examples of Jordan pairs are given, which show the beauty, simplicity, and usefulness of such objects.     

Diagrammar and metamorphosis of coset symmetries in dimensionally reduced type IIB supergravity

Studying the reduction of type IIB supergravity from ten to three spacetime dimensions, we describe the metamorphosis of the Dynkin diagram for gravity line “caterpillar” into a type IIB supergravity “ dragonfly” that is triggered by the inclusion of scalars and antisymmetric tensor fields. The final diagram corresponds to type IIB string theory E₈ global symmetry group, which is the subgroup of the conjectured E₁₁ hidden symmetry group. Application of the results for getting the type IIA/IIB T-duality rules and for searching for type IIB vacua solutions is considered.     

Quantum interference effects in Einstein-Maxwell,supergravity and non-abelian Kaluza-Klein theories

Quantum interference effects in Einstein-Maxwell, supergravity and non-abelian Kaluza-Klein theories have been calculated following the idea of Parthasarathy, Rajasekharan and Vasedevan.     

Geometry of coset spaces and massless modes of the squashed seven-sphere in supergravity

We derive some general results for Killing vectors on arbitrary coset manifolds and explicitly exhibit the squashed seven-sphere as the coset space Sp₄×Sp₂/Sp₂×Sp₂. Using these results, we then analyze the zero-mass sector of supergravity of the squashed S⁷ and argue that it is not interpretable as a spontaneously broken version of N=8 supergravity. We also point out the existence of a new solution which combines squashing and torsion.     

Some remarks on the Hijazi inequality and generalizations of the Killing equation for spinors

We generalize the well-known lower estimates for the first eigenvalue of the Dirac operator on a compact Riemannian spin manifold proved by Friedrich [Math. Nachr. 97 (1980) 117–146] and Hijazi [Math. Phys. 104 (1986) 151–162; J. Geom. Phys. 16 (1995) 27–38]. The special solutions of the Einstein–Dirac equation constructed recently by Friedrich/Kim are examples for the limiting case of these inequalities. The discussion of the limiting case of these estimates yields two new field equations generalizing the Killing equation as well as the weak Killing equation for spinor fields. Finally, we discuss the two-and three-dimensional case in more detail.     

New compactifications of ten and eleven dimensional supergravity on manifolds which are not direct products

Solutions of ten and eleven dimensional supergravity are presented for which the space-time metric is a product of an anti-de Sitter metric and a strictly positive scalar function of the internal coordinates. The critical point of the potential of seven dimensional maximal supergravity with SO(4) symmetry is identified with such a solution.Supported in part by NSF Grant PHY 8109110 A-03Supported in part by the U.S. Department of Energy under Contract No. DE-AC-03-81ER40050, and by the Weingart Foundation     

Quantum mechanics and geometric analysis on manifolds

A central idea of modern geometric analysis is the assignment of a geometric structure, usually called thesymbol, to a differential operator. It is known that this operation is closely related to quantum mechanics. For a class of linear operators, including the Dirac operator, a geometric structure, called aco-Riemannian metric, is assigned to such symbols. Certain other topics related to the geometric structure of quantum mechanics, e.g., the symplectic structure of the projective space of Hilbert space, are briefly treated.     

Adaptive harmonic wavelet transform with applications in vibration analysis

An adaptive harmonic wavelet transform is developed by taking advantage of the flexibility of the generalized harmonic wavelets. It first constructs a partition tree, which contains a great number of disjoint partitions of the frequency axis of a signal with each corresponding to an orthogonal harmonic wavelet basis. Then it searches the tree for the partition to represent the signal most sparsely. Since the corresponding basis is adapted to the composition of the signal, the transform can well reveal its characteristics. This is demonstrated with analysis examples of some simulated and vibration signals as well as comparisons with the conventional orthogonal harmonic wavelet transforms and wavelet packet transform.     

Stability of the Bose system in Bose-Fermi mixture with attraction between bosons and fermions

An effective Hamiltonian for the Bose system in the mixture of ultracold atomic clouds of bosons and fermions is obtained by integrating out the Fermi degrees of freedom. An instability of the Bose system is found in the case of attractive interaction between components that is in good agreement with an experiment on the bosonic ⁸⁷Rb and fermionic ⁴⁰K mixture.     

The anomaly cancellation mechanism in N=1, D=4 supergravity and distorted supergravity algebra with Chern-Simon forms

A mechanism is exhibited which ensures that N=1, D=4 new minimal supergravity is free of Lorentz×U(1) anomalies, for any coupling to matter, although it contains an abelian chiral gauge field. This is achieved through the determination of a new supergravity algebra characterized by the presence of a U(1)×Lorentz Chern-Simon form in the field strength of a two-form gauge field. Our analysis provides therefore an example in which Chern-Simon type interactions do occur, while preserving local supersymmetry.     

Trace gas detect based on spectral analysis and harmonic ratio

Optical Review - A novel method of gas concentration calibration for tunable diode laser absorption spectroscopy, in which spectral analysis and harmonic signal intensity ratio measurement are...     

Invariance analysis and conservation laws of the wave equation on Vaidya manifolds

In this paper we discuss symmetries of classes of wave equations that arise as a consequence of some Vaidya metrics. We show how the wave equation is altered by the underlying geometry. In particular, a range of consequences on the form of the wave equation, the symmetries and number of conservation laws, inter alia, are altered by the manifold on which the model wave rests. We find Lie and Noether point symmetries of the corresponding wave equations and give some reductions. Some interesting physical conclusions relating to conservation laws such as energy, linear and angular momenta are also determined. We also present some interesting comparisons with the standard wave equations on a flat geometry. Finally, we pursue the existence of higher-order variational symmetries of equations on nonflat manifolds.