2,107 research outputs found
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
Massive, Topologically Massive, Models
In three dimensions, there are two distinct mass-generating mechanisms for
gauge fields: adding the usual Proca/Pauli-Fierz, or the more esoteric
Chern-Simons (CS), terms. Here we analyze the three-term models where both
types are present, and their various limits. Surprisingly, in the tensor case,
these seemingly innocuous systems are physically unacceptable. If the sign of
the Einstein term is ``wrong'' as is in fact required in the CS case, then the
excitation masses are always complex; with the usual sign, there is a (known)
region of the two mass parameters where reality is restored, but instead we
show that a ghost problem arises, while, for the ``pure mass'' two-term system
without an Einstein action, complex masses are unavoidable. This contrasts with
the smooth behavior of the corresponding vector models. Separately, we show
that the ``partial masslessness'' exhibited by (plain) massive spin-2 models in
de Sitter backgrounds is formally shared by the three-term system: it also
enjoys a reduced local gauge invariance when this mass parameter is tuned to
the cosmological constant.Comment: 7 pages, typos corrected, reference adde
A note on spin two fields in curved backgrounds
We reconsider the consistency constraints on a free massless symmetric, rank
2, tensor field in a background and confirm that they uniquely require it to be
the linear deviation about (cosmological) Einstein gravity. Neither adding
non-minimal higher derivative terms nor changing the gauge transformations by
allowing terms non-analytic in the cosmological constant alters this fact.Comment: 5 pages - Minor misprints corrected - Version accepted by Class.
Quant. Gra
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
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
Curvature invariants of static spherically symmetric geometries
We construct all independent local scalar monomials in the Riemann tensor at
arbitrary dimension, for the special regime of static, spherically symmetric
geometries. Compared to general spaces, their number is significantly reduced:
the extreme example is the collapse of all invariants ~ Weyl^k, to a single
term at each k. The latter is equivalent to the Lovelock invariant L_k.
Depopulation is less extreme for invariants involving rising numbers of Ricci
tensors, and also depends on the dimension. The corresponding local
gravitational actions and their solution spaces are discussed.Comment: 14 page
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
Electric-Magnetic Black Hole Duality
We generalize duality invariance for the free Maxwell action in an arbitrary
background geometry to include the presence of electric and magnetic charges.
In particular, it follows that the actions of equally charged electric and
magnetic black holes are equal
Arbitrary p-form Galileons
We show that scalar, 0-form, Galileon actions --models whose field equations
contain only second derivatives-- can be generalized to arbitrary even p-forms.
More generally, they need not even depend on a single form, but may involve
mixed p combinations, including equal p multiplets, where odd p-fields are also
permitted: We construct, for given dimension D, general actions depending on
scalars, vectors and higher p-form field strengths, whose field equations are
of exactly second derivative order. We also discuss and illustrate their
curved-space generalizations, especially the delicate non-minimal couplings
required to maintain this order. Concrete examples of pure and mixed actions,
field equations and their curved space extensions are presented.Comment: 8 pages, no figure, RevTeX4 format, v2: minor editorial changes
reflecting the published version in PRD Rapid Communication
Holography with Gravitational Chern-Simons Term
The holographic description in the presence of gravitational Chern-Simons
term is studied. The modified gravitational equations are integrated by using
the Fefferman-Graham expansion and the holographic stress-energy tensor is
identified. The stress-energy tensor has both conformal anomaly and
gravitational or, if re-formulated in terms of the zweibein, Lorentz anomaly.
We comment on the structure of anomalies in two dimensions and show that the
two-dimensional stress-energy tensor can be reproduced by integrating the
conformal and gravitational anomalies. We study the black hole entropy in
theories with a gravitational Chern-Simons term and find that the usual
Bekenstein-Hawking entropy is modified. For the BTZ black hole the modification
is determined by area of the inner horizon. We show that the total entropy of
the BTZ black hole is precisely reproduced in a boundary CFT calculation using
the Cardy formula.Comment: 19 pages, Latex; v3: minor corrections, some clarification
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