On the calculation of multiplicities for representations of SU(n)

For some family of representations of SU(n) the explicit formulae for the multiplicity of a given representation in arbitrary tensor product are derived. The adjoint representation and the representations acting in the symmetrical and antisymmetrical tensors are contained in the considered family as the simplest cases.     

The momentum constraints of general relativity and spatial conformal isometries

Transverse-tracefree (TT-) tensors on (R ³,g _ab), withg _ab an asymptotically flat metric of fast decay at infinity, are studied. When the source tensor from which these TT tensors are constructed has fast fall-off at infinity, TT tensors allow a multipole-type expansion. Wheng _ab has no conformal Killing vectors (CKV's) it is proven that any finite but otherwise arbitrary set of moments can be realized by a suitable TT tensor. When CKV's exist there are obstructions — certain (combinations of) moments have to vanish — which we study.Supported by Fonds zur Förderung der wissenschaftlichen Forschung in Österreich, Project No. P9376-PHY.Partially supported by Forbairt Grant SC/94/225.     

Averaging out the Einstein equations

A general scheme to average out an arbitrary 4-dimensional Riemannian space and to construct the geometry of the averaged space is proposed. It is shown that the averaged manifold has a metric and two equi-affine symmetric connections. The geometry of the space is characterized by the tensors of Riemannian and non-Riemannian curvatures, an affine deformation tensor being the result of non-metricity of one of the connections. To average out the differential Bianchi identities, correlation 2-form, 3-form and 4-form are introduced and the differential relations on these correlations tensors are derived, the relations being integrable on an arbitrary averaged manifold. Upon assuming a splitting rule for the average of the product including a covariantly constant tensor, an averaging out of the Einstein equations has been carried out which brings additional terms with the correlation tensors into them. As shown by averaging out the contracted Bianchi identities, the equations of motion for the averaged energy-momentum tensor do also include the geometric correction terms. Considering the gravitational induction tensor to be the Riemannian curvature tensor (then the non-Riemannian one is the macroscopic gravitational field), a theorem that relates the algebraic structure of the averaged microscopic metric with that of the induction tensor is proved. Due to the theorem the same field operator as in the Einstein equations is manifestly extracted from the averaged ones. Physical interpretation and application of the relations and equations obtained to treat macroscopic gravity are discussed.     

Lorentz covariant spin two superspaces

Superalgebras including generators having spins up to two and realisable as tangent vector fields on Lorentz covariant generalised superspaces are considered. The latter have a representation content reminiscent of configuration spaces of (super)gravity theories. The most general canonical supercommutation relations for the corresponding phase space coordinates allowed by Lorentz covariance are discussed. By including generators transforming according to every Lorentz representation having spin up to two, we obtain, from the super Jacobi identities, the complete set of quadratic equations for the Lorentz covariant structure constants. These defining equations for spin 2 Heisenberg superalgebras are highly overdetermined. Nevertheless, non-trivial solutions can indeed be found. By making some simplifying assumptions, we explicitly construct several classes of these superalgebras.     

The space of Lorentz metrics

The set of allC ² Lorentz metrics on a non-compact four-manifold is given the Whitney fineC ² topology. It is shown that this provides the correct framework within which to discuss the global properties of spacetime manifolds in general, and the singularity theorems in particular. The main result is a theorem showing that the Robertson-Walker big bang (global infinite density singularity in the finite past) is stable under sufficiently small, but otherwise arbitrary, finiteC ² perturbations of the metric tensor.Based, in part, on a thesis submitted to the Mathematics Department of the University of Pittsburgh.     

Gauge hierarchies of SU(N) grand unification

The structure of spontaneous breaking of SU(N) gauge symmetry for grand unification is investigated. The results obtained are applied to the analysis of SU(8) symmetry for which possible ways of breaking and intermediate symmetries are considered. It is assumed that the SU(8) group unifies the subgroups of colour, standard electroweak and horizontal symmetries. We find conditions which it is necessary to impose on the vacuum expectation values of Higgs multiplets to provide an arbitrary breaking pattern of SU(N) symmetry and conserve any intermediate symmetry. If in the SU(8) models considered fermions and mirror fermions do not violate the (V-A) and (V+A) structure of weak interactions, then their masses should not be greater than ～10² GeV. It is also shown that the contributions of fermion and Higgs multiplets to the renormalization group equation for the coupling constant of any subgroup of SU(N) are identical. Renormalization group identities for the case of arbitrary SU(N) breaking are given where the contribution of Higgs multiplets have been taken into account (but they cancel each other). Using these identities one can calculate the mass values for the breaking of the intermediate symmetries in the SU(8) models, and also exclude part of the possible breaking patterns.     

Proofs of existence of local potentials for trace-free symmetric 2-forms using dimensionally dependent identities

We exploit four-dimensional tensor identities to give a very simple proof of the existence of a Lanczos potential for a Weyl tensor in four dimensions with any signature, and to show that the potential satisfies a simple linear second-order differential equation, e.g., a wave equation in Lorentz signature. Furthermore, we exploit higher-dimensional tensor identities to obtain the analogous results for (m, m)-forms in 2m dimensions.     

The Spin-Statistics Theorem in Arbitrary Dimensions

We investigate the spin-statistics connection in arbitrary dimensions for hermitian spinor or tensor quantum fields with a rotationally invariant bilinear Lagrangian density. We use essentially the same simple method as for space dimension D=3. We find the usual connection (tensors as bosons and spinors as fermions) for D=8n+3,8n+4,8n+5, but only bosons for spinors and tensors in dimensions 8n±1 and 8n. In dimensions 4n+2 the spinors may be chosen as bosons or fermions. The argument hinges on finding the identity representation of the rotation group either on the symmetric or the antisymmetric part of the square of the field representation. Permanent address of L.J. Boya: Departamento de Física Teórica, Universidad de Zaragoza, 50009 Zaragoza, Spain     

Properties of SO(8) extended supergravity

The conjectured SU(8) invariance of the field equations of SO(8) extended supergravity is used to elucidate the general structure of the extended theories. Due to the representation content of the spinless fields this does not lead to a complete determination of the theory, as was the case for N = 4. The non-polynomial modifications by spinless fields are given in terms of a number of SU(8) covariant tensors, for which various identities are derived and discussed.     

On the exponential of the 2-forms in relativity

A study of intrinsic properties of proper Lorentz tensors (tensor fields defining proper Lorentz transformations at every point of space-time) is made, giving rise to their covariant decompositions. The exponential series for a generic 2-form is covariantly summed, and the resulting proper Lorentz tensor is expressed as a linear combination of the metric tensor, the 2-form, its dual and its energy tensor. Some covariant expressions for the 2-form corresponding to the logarithmic branches of a proper Lorentz tensor are given. Some properties of the Lorentz group are easily found, concerning the surjectivity, local injectivity and local inversibility of the exponential map.     

Lorentz cobordism

A Lorentz cobordism between two (in general nondiffeomorphic) 3-manifoldsM ₀,M ₁ is a pair (M,v), whereM is a differentiable 4-manifold andv is a differentiable vector field onM, such that 1) the boundary ofM is the disjoint union ofM ₀ andM ₁, 2)v is everywhere nonzero, 3)v is interior normal onM ₀ and exterior normal onM ₁. Such a manifoldM admits a Lorentz tensor with respect to whichM ₀ andM ₁ are spacelike hypersurfaces; thus a Lorentz cobordism is a model of a portion of a spacetime in which the topology of spacelike hypersurfaces is changing. We discuss the form that these changes can take, and give two methods for constructing a Lorentz cobordism between two nondiffeomorphic 3-manifolds. We comment on the possible relevance of Lorentz cobordism to the problem of gravitational collapse.     

Symmetric hyperbolic systems for a large class of fields in arbitrary dimension

Symmetric hyperbolic systems of equations are explicitly constructed for a general class of tensor fields by considering their structure as r-fold forms. The hyperbolizations depend on 2r−1 arbitrary timelike vectors. The importance of the so-called “superenergy” tensors, which provide the necessary symmetric positive matrices, is emphasized and made explicit. Thereby, a unified treatment of many physical systems is achieved, as well as of the sometimes called “higher order” systems. The characteristics of these symmetric hyperbolic systems are always physical, and directly related to the null directions of the superenergy tensor, which are in particular principal null directions of the tensor field solutions. Generic energy estimates and inequalities are presented too. Examples are included, in particular a mixed gravitational-scalar field system at the level of the Bianchi equations.     

Higher dimensional classicalW-algebras

ClassicalW-algebras in higher dimensions are constructed. This is achieved by generalizing the classical Gel'fand-Dickey brackets to the commutative limit of the ring of classical pseudodifferential operators in arbitrary dimension. TheseW-algebras are the Poisson structures associated with a higher dimensional version of the Khokhlov-Zabolotskaya hierarchy (dispersionless KP-hierarchy). The two dimensional case is worked out explicitly and it is shown that the role of DiffS(1) is taken by the algebra of generators of local diffeomorphisms in two dimensions.     

Lorentz violation constrained by triplicity of lepton families and neutrino oscillations

In this paper we postulate an algebraic model to relate the triplet characteristic of lepton families to Lorentz violation. Inspired by the two-to-one mapping between the group SL(2, C) and the Lorentz group via the Pauli grading (the elements of SL(2, C) expressed by direct sum of unit matrix and generators of SU (2) group), we grade the SL(3, C) group with the generators of SU(3), i. e. the Gell-Mann matrices, then express the SU(3) group in terms of three SU(2) subgroups, each of which stands for a lepton species and is mapped into the proper Lorentz group as in the case of the group SL(2,C). If the mapping from group SL(3,C) to the Lorentz group is constructed by choosing one SU(2) subgroup as basis, then the other two subgroups display their impact only by one more additional generator to that of the original Lorentz group. Applying the mapping result to the Dirac equation, it is found that only when the kinetic vertex γμξμ is extended to encompass γμξμ can the Dirac-equation-form be conserved. The generalized vertex is useful in producing neutrino oscillations and mass differences.     

Invariance under conformal coordinate and point transformations

Coordinate and point transformations are studied in the context of conformal symmetry. When invariance requirements on arbitrary rank tensors are involved in both contexts, the similitudes and differences in transformation laws and invariance conditions are analysed in connection with those on tensor densities of weight W. Physically interesting tensors like the metric tensor, the electromagnetic field and the energy-momentum tensor are specifically examined. Some remarks on scalar fields and densities are added.     

Inönü–Wigner contraction and $$$$ supergravity

We present a generalization of the standard Inönü–Wigner contraction by rescaling not only the generators of a Lie superalgebra but also the arbitrary constants appearing in the components of the invariant tensor. The procedure presented here allows one to obtain explicitly the Chern–Simons supergravity action of a contracted superalgebra. In particular we show that the Poincaré limit can be performed to a \(D=2+1\) \(\left( p,q\right) \) AdS Chern–Simons supergravity in presence of the exotic form. We also construct a new three-dimensional \(\left( 2,0\right) \) Maxwell Chern–Simons supergravity theory as a particular limit of \(\left( 2,0\right) \) AdS–Lorentz supergravity theory. The generalization for \(\mathcal {N}=p+q\) gravitinos is also considered.     

Invariant tensors inSU (3)

The construction of independentSU (3) tensors out of octets of fields is considered by investigating numerically invariantSU (3) tensors. A method of obtaining independent sets of these to any rank is discussed and also independent sets are explicitly displayed up to fifth rank. It is shown that this approach allows us to obtain relations among the invariant tensors, and useful new identities involving thed _ijk andf _ijk tensors are exhibited.     

Superspace geometry and N = 1 non-minimal supergravity

We investigate superspace geometry for supergravity with non-minimal auxilliary fields. We find that the kinematic constraints and the superspace Bianchi identities are sufficient to obtain complete component expansions of all superspace quantities, including the vielbein and connection superfields. We include a detailed pedagogical discussion on the analysis of constrained superspace Bianchi identities, demonstrating how these are used to derive component field content and transformation laws. We also note that local, chiral supersymmetry representations which form arbitrary representations of the Lorentz group can exist only within the context of supergravity with non-minimal auxilliary fields.     

Lorentz violation constrained by triplicity of lepton families and neutrino oscillations

In this paper we postulate an algebraic model to relate the triplet characteristic of lepton families to Lorentz violation. Inspired by the two-to-one mapping between the group SL（2, C） and the Lorentz group via the Pauli grading （the elements of SL（2, C） expressed by direct sum of unit matrix and generators of SU（2） group）, we grade the SL（3,C） group with the generators of SU（3）, i. e. the Gell-Mann matrices, then express the SU（3） group in terms of three SU（2） subgroups, each of which stands for a lepton species and is mapped into the proper Lorentz group as in the case of the group SL（2,C）. If the mapping from group SL（3,C） to the Lorentz group is constructed by choosing one SU（2） subgroup as basis, then the other two subgroups display their impact only by one more additional generator to that of the original Lorentz group. Applying the mapping result to the Dirac equation, it is found that only when the kinetic vertex -γμθ^μ is extended to encompass γ5γμθ^μ can the Dirac-equation-form be conserved. The generalized vertex is useful in producing neutrino oscillations and mass differences.     

On-shell and conformal N = 4 supergravity in superspace

We discuss the superspace geometries which are necessary to describe on-shell O(4) and SU(4) supergravity. The relation of central charge field strengths to physical spin-zero fields is exhibited and a “new” O(4) theory is shown to exist. The version of SU(4) supergravity which uses an antisymmetric tensor gauge field is found to require modifications of ordinary superspace. Finally the Poincaré supergeometry which admits the conformal N = 4 supermultiplet is constructed. It is shown that consistency of the Bianchi identities implies the existence of dimension zero auxiliary fields which are components of a non-linear multiplet.