1,752 research outputs found
Gravitons in Flatland
We review some features of three-dimensional (3D) massive gravity theories.
In particular, we stress the role of the Schouten tensor, explore an analogy
with Lovelock gravity and discuss renormalizabilty.Comment: 11 pages, Contribution to proceedings of the workshop {\it Cosmology,
the Quantum Vacuum and Zeta Functions} in celebration of the 60th birthday of
Emilio Elizalde; Barcelona, 8-10 March, 2010. Additional references in v
Hidden supersymmetry of domain walls and cosmologies
We show that all domain-wall solutions of gravity coupled to scalar fields
for which the worldvolume geometry is Minkowski or anti-de Sitter admit Killing
spinors, and satisfy corresponding first-order equations involving a
superpotential determined by the solution. By analytic continuation, all flat
or closed FLRW cosmologies are shown to satisfy similar first-order equations
arising from the existence of ``pseudo-Killing'' spinors.Comment: 4 pages, v2:minor improvements, refs added, version to appear in PR
Massive Gravity in Three Dimensions
A particular higher-derivative extension of the Einstein-Hilbert action in
three spacetime dimensions is shown to be equivalent at the linearized level to
the (unitary) Pauli-Fierz action for a massive spin-2 field. A more general
model, which also includes `topologically-massive' gravity as a special case,
propagates the two spin 2 helicity states with different masses. We discuss the
extension to massive -extended supergravity, and we present a
`cosmological' extension that admits an anti-de Sitter vacuum.Comment: Minor corrections plus a further correction to discussion of
supersymmetry in adS vacua, Version to be publishe
More on Massive 3D Gravity
We explore the space of static solutions of the recently discovered
three-dimensional `New Massive Gravity' (NMG), allowing for either sign of the
Einstein-Hilbert term and a cosmological term parametrized by a dimensionless
constant . For we find black hole solutions asymptotic
(but not isometric) to the unique (anti) de Sitter vacuum, including extremal
black holes that interpolate between this vacuum and (a)dS. We
also investigate unitarity of linearized NMG in (a)dS vacua. We find unitary
theories for some dS vacua, but (bulk) unitarity in adS implies negative
central charge of the dual CFT, except for where the central charge
vanishes and the bulk gravitons are replaced by `massive photons'. A similar
phenomenon is found in the massless limit of NMG, for which the linearized
equations become equivalent to Maxwell's equations.Comment: 25 pages, 4 figures; v2: minor improvements and extensions,
references added; v3: version to appear in PR
Hamilton-Jacobi method for Domain Walls and Cosmologies
We use Hamiltonian methods to study curved domain walls and cosmologies. This
leads naturally to first order equations for all domain walls and cosmologies
foliated by slices of maximal symmetry. For Minkowski and AdS-sliced domain
walls (flat and closed FLRW cosmologies) we recover a recent result concerning
their (pseudo)supersymmetry. We show how domain-wall stability is consistent
with the instability of adS vacua that violate the Breitenlohner-Freedman
bound. We also explore the relationship to Hamilton-Jacobi theory and compute
the wave-function of a 3-dimensional closed universe evolving towards de Sitter
spacetime.Comment: 18 pages; v2: typos corrected, one ref added, version to appear in
PR
Dilaton Domain Walls and Dynamical Systems
Domain wall solutions of -dimensional gravity coupled to a dilaton field
with an exponential potential are shown
to be governed by an autonomous dynamical system, with a transcritical
bifurcation as a function of the parameter when . All
phase-plane trajectories are found exactly for , including
separatrices corresponding to walls that interpolate between and
adS_{d-1} \times\bR, and the exact solution is found for . Janus-type
solutions are interpreted as marginal bound states of these ``separatrix
walls''. All flat domain wall solutions, which are given exactly for any
, are shown to be supersymmetric for some superpotential ,
determined by the solution.Comment: 30 pp, 11 figs, significant revision of original. Minor additional
corrections in version to appear in journa
Staying true with the help of others: doxastic self-control through interpersonal commitment
I explore the possibility and rationality of interpersonal mechanisms of doxastic self-control, that is, ways in which individuals can make use of other people in order to get themselves to stick to their beliefs. I look, in particular, at two ways in which people can make interpersonal epistemic commitments, and thereby willingly undertake accountability to others, in order to get themselves to maintain their beliefs in the face of anticipated “epistemic temptations”. The first way is through the avowal of belief, and the second is through the establishment of collective belief. I argue that both of these forms of interpersonal epistemic commitment can function as effective tools for doxastic self-control, and, moreover, that the control they facilitate should not be dismissed as irrational from an epistemic perspective
On higher derivatives in 3D gravity and higher-spin gauge theories
The general second-order massive field equations for arbitrary positive
integer spin in three spacetime dimensions, and their "self-dual" limit to
first-order equations, are shown to be equivalent to gauge-invariant
higher-derivative field equations. We recover most known equivalences for spins
1 and 2, and find some new ones. In particular, we find a non-unitary massive
3D gravity theory with a 5th order term obtained by contraction of the Ricci
and Cotton tensors; this term is part of an N=2 super-invariant that includes
the "extended Chern-Simons" term of 3D electrodynamics. We also find a new
unitary 6th order gauge theory for "self-dual" spin 3.Comment: 23 pp. New references, improved spin-3 discussion. Minor additional
corrections in v
On massive gravitons in 2+1 dimensions
The Fierz-Pauli (FP) free field theory for massive spin 2 particles can be
extended, in a spacetime of (1+2) dimensions (3D), to a generally covariant
parity-preserving interacting field theory, in at least two ways. One is "new
massive gravity" (NMG), with an action that involves curvature-squared terms.
Another is 3D "bigravity", which involves non-linear couplings of the FP tensor
field to 3D Einstein-Hilbert gravity. We review the proof of the linearized
equivalence of both "massive 3D gravity" theories to FP theory, and we comment
on their similarities and differences.Comment: 6 pages, to appear in the proceedings of the Spanish Relativity
Meeting ERE2009, Bilbao; minor changes, reference adde
- …