Stability of Massive Cosmological Gravitons

We analyze the physics of massive spin 2 fields in (A)dS backgrounds and exhibit that: The theory is stable only for masses m^2 >= 2\Lambda/3, where the conserved energy associated with the background timelike Killing vector is positive, while the instability for m^2<2\Lambda/3 is traceable to the helicity 0 energy. The stable, unitary, partially massless theory at m^2=2\Lambda/3 describes 4 propagating degrees of freedom, corresponding to helicities (+/-2,+/-1) but contains no 0 helicity excitation.Comment: 13 pages, LaTeX, version to appear in Phys. Lett.

Energy in Topologically Massive Gravity

We define conserved gravitational charges in -cosmologically extended- topologically massive gravity, exhibit them in surface integral form about their de-Sitter or flat vacua and verify their correctness in terms of two basic types of solution.Comment: 6 page

Arbitrary Spin Representations in de Sitter from dS/CFT with Applications to dS Supergravity

We present a simple group representation analysis of massive, and particularly ``partially massless'', fields of arbitrary spin in de Sitter spaces of any dimension. The method uses bulk to boundary propagators to relate these fields to Euclidean conformal ones at one dimension lower. These results are then used to revisit an old question: can a consistent de Sitter supergravity be constructed, at least within its intrinsic horizon?Comment: 19 pages LaTex, references added, version to appear Nucl. Phys.

A Note on Stress-Tensors, Conservation and Equations of Motion

Some unusual relations between stress tensors, conservation and equations of motion are briefly reviewed.Comment: 4 pages. Invited contribution, A. Peres Festschrift, to be published in Found. Phy

Constant Curvature Algebras and Higher Spin Action Generating Functions

The algebra of differential geometry operations on symmetric tensors over constant curvature manifolds forms a novel deformation of the sl(2,R) [semidirect product] R^2 Lie algebra. We present a simple calculus for calculations in its universal enveloping algebra. As an application, we derive generating functions for the actions and gauge invariances of massive, partially massless and massless (for both bose and fermi statistics) higher spins on constant curvature backgrounds. These are formulated in terms of a minimal set of covariant, unconstrained, fields rather than towers of auxiliary fields. Partially massless gauge transformations are shown to arise as degeneracies of the flat, massless gauge transformation in one dimension higher. Moreover, our results and calculus offer a considerable simplification over existing techniques for handling higher spins. In particular, we show how theories of arbitrary spin in dimension d can be rewritten in terms of a single scalar field in dimension 2d where the d additional dimensions correspond to coordinate differentials. We also develop an analogous framework for spinor-tensor fields in terms of the corresponding superalgebra.Comment: 44 pages, LaTeX, 2 .eps figure

Graviton-Graviton Scattering, Bel-Robinson and Energy (Pseudo)-Tensors

Motivated by recent work involving the graviton-graviton tree scattering amplitude, and its twin descriptions as the square of the Bel-Robinson tensor, B_{\m\n\a\b}, and as the "current-current interaction" square of gravitational energy pseudo-tensors t_{\a\b},we find an exact tensor-square root equality B_{\mn\a\b} = \pa^2_\mn t_{\a\b}, for a combination of Einstein and Landau-Lifschitz t_\ab, in Riemann normal coordinates. In the process, we relate, on-shell, the usual superpotential basis for classifying pseudo-tensors with one spanned by polynomials in the curvature.Comment: 7 page

Gauge Field Improvement,Form-Scalar Duality and Conformal Invariance

The problem of maintaining scale and conformal invariance in Maxwell and general N-form gauge theories away from their critical dimension d=2(N+1) is analyzed.We first exhibit the underlying group-theoretical clash between locality,gauge,Lorentz and conformal invariance require- ments. "Improved" traceless stress tensors are then constructed;each violates one of the above criteria.However,when d=N+2,there is a duality equivalence between N-form models and massless scalars.Here we show that conformal invariance is not lost,by constructing a quasilocal gauge invariant improved stress tensor.The correlators of the scalar theory are then reproduced,including the latter's trace anomaly.Comment: 8 pages ,CERN-TH.7224 IAS 94/2

Inconsistencies of Massive Charged Gravitating Higher Spins

We examine the causality and degrees of freedom (DoF) problems encountered by charged, gravitating, massive higher spin fields. For spin s=3/2, making the metric dynamical yields improved causality bounds. These involve only the mass, the product eM_P of the charge and Planck mass and the cosmological constant \Lambda. The bounds are themselves related to a gauge invariance of the timelike component of the field equation at the onset of acausality. While propagation is causal in arbitrary E/M backgrounds, the allowed mass ranges of parameters are of Planck order. Generically, interacting spins s>3/2 are subject to DoF violations as well as to acausality; the former must be overcome before analysis of the latter can even begin. Here we review both difficulties for charged s=2 and show that while a g-factor of 1/2 solves the DoF problem, acausality persists for any g. Separately we establish that no s=2 theory --DoF preserving or otherwise -- can be tree unitary.Comment: 25 pages, late

Gravity Theories with Lightlike Sources in D=3

Spacetimes generated by a lightlike particle source for topologically massive gravity and its limits - Einstein gravity and the pure gravitational Chern-Simons model - are obtained both by solving the field equations and by infinite boosts of static metrics. The resulting geometries are the first known solutions of topologically massive gravity that are asymptotically flat and generated by compact matter sources. Explicit metrics describing various multiphoton solutions are also derived. For Einstein gravity, we also construct such solutions by null boost identifications of Minkowski space and thereby obtain limits on the energies of the sources.Comment: 11 pages, harvmac. The sign conventions for topologically massive gravity used in the original version are replaced by those standard in the literatur