3,256 research outputs found

### First-order Formalism and Odd-derivative Actions

In this pedagogical note, we discuss obstacles to the usual Palatini
formulations of gauge and gravity theories in presence of odd-derivative order,
Chern-Simons, terms.Comment: 4 pages. Dedicated to Rafael Sorkin on his 60th Birthda

### No Bel-Robinson Tensor for Quadratic Curvature Theories

We attempt to generalize the familiar covariantly conserved Bel-Robinson
tensor B_{mnab} ~ R R of GR and its recent topologically massive third
derivative order counterpart B ~ RDR, to quadratic curvature actions. Two very
different models of current interest are examined: fourth order D=3 "new
massive", and second order D>4 Lanczos-Lovelock, gravity. On dimensional
grounds, the candidates here become B ~ DRDR+RRR. For the D=3 model, there
indeed exist conserved B ~ dRdR in the linearized limit. However, despite a
plethora of available cubic terms, B cannot be extended to the full theory. The
D>4 models are not even linearizable about flat space, since their field
equations are quadratic in curvature; they also have no viable B, a fact that
persists even if one includes cosmological or Einstein terms to allow
linearization about the resulting dS vacua. These results are an unexpected, if
hardly unique, example of linearization instability.Comment: published versio

### Duality invariance of all free bosonic and fermionic gauge fields

We give a simple general extension to all free bosonic and fermionic massless
gauge fields of a recent proof that spin 2 is duality invariant in flat space.
We also discuss its validity in (A)dS backgrounds and the relevance of
supersymmetry.Comment: 3 page

### Novel Properties of Massive Higher Spin Fields

I outline a series of results obtained in collaboration with A. Waldron on
the properties of massive higher (s>1) spin fields in cosmological, constant
curvature, backgrounds and the resulting unexpected qualitative effects on
their degrees of freedom and unitarity properties. The dimensional parameter
\L extends the flat space m-line to a (m^2,\L) "phase" plane in which these
novel phenomena unfold. In this light, I discuss a possible partial
resurrection of deSitter supergravity. I will also exhibit the well-known
causality problems of coupling these systems to gravity and, for complex
fields, to electromagnetism, systematizing some of the occasionally
misunderstood obstacles to interactions, particularly for s = 3/2 and 2.Comment: 9 pages, 1 figure. Invited talk at "Renormalization Group and
Anomalies in Gravity and Cosmology", Ouro Preto, Brazil, March 17-23, 200

### 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

### Some Interesting Properties of Field theories with an Infinite Number of Fields

We give an indication that gravity coupled to an infinite number of fields
might be a renormalizable theory. A toy model with an infinite number of
interacting fermions in four-dimentional space-time is analyzed. The model is
finite at any order in perturbation theory. However, perturbation theory is
valid only for external momenta smaller than $\lambda ^{-\frac{1}{2}}$ , where
$\lambda$ is the coupling constant.Comment: 12 pages, LaTe

### Higher Derivative Chern--Simons Extensions

We study the higher-derivative extensions of the D=3 Abelian Chern--Simons
topological invariant that would appear in a perturbative effective action's
momentum expansion. The leading, third-derivative, extension I_ECS turns out to
be unique. It remains parity-odd but depends only on the field strength, hence
no longer carries large gauge information, nor is it topological because metric
dependence accompanies the additional covariant derivatives, whose positions
are seen to be fixed by gauge invariance. Viewed as an independent action,
I_ECS requires the field strength to obey the wave equation. The more
interesting model, adjoining I_ECS to the Maxwell action, describes a pair of
excitations. One is massless, the other a massive ghost, as we exhibit both via
the propagator and by performing the Hamiltonian decomposition. We also present
this model's total stress tensor and energy. Other actions involving I_ECS are
also noted.Comment: 3 typos fixed. 5 page

### 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.

### Birkhoff for Lovelock Redux

We show succinctly that all metric theories with second order field equations
obey Birkhoff's theorem: their spherically symmetric solutions are static.Comment: Submitted to CQ

### Closed Form Effective Conformal Anomaly Actions in D$\geq$4

I present, in any D$\geq$4, closed-form type B conformal anomaly effective
actions incorporating the logarithmic scaling cutoff dependence that generates
these anomalies. Their construction is based on a novel class of Weyl-invariant
tensor operators. The only known type A actions in D$\geq$4 are extensions of
the Polyakov integral in D=2; despite contrary appearances, we show that their
nonlocality does not conflict with general anomaly requirements. They are,
however, physically unsatisfactory, prompting a brief attempt at better
versions.Comment: 8 pages. Improved discussion of type A actions. Some references adde

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