207 research outputs found
Dinner with Jesus and Other Left-Handed Story-Sermons
Reviewed Book: Chatfield, Donald F. Dinner with Jesus and Other Left-Handed Story-Sermons. Grand Rapids: Zondervan, 1988
Causal Structure of Vacuum Solutions to Conformal(Weyl) Gravity
Using Penrose diagrams the causal structure of the static spherically
symmetric vacuum solution to conformal (Weyl) gravity is investigated. A
striking aspect of the solution is an unexpected physical singularity at
caused by a linear term in the metric. We explain how to calculate the
deflection of light in coordinates where the metric is manifestly conformal to
flat i.e. in coordinates where light moves in straight lines.Comment: 18 pages, 2 figures, title and abstract changed, contents essentially
unaltered accepted for publication in General Relativity and Gravitatio
Local and global gravity
Our long experience with Newtonian potentials has inured us to the view that
gravity only produces local effects. In this paper we challenge this quite
deeply ingrained notion and explicitly identify some intrinsically global
gravitational effects. In particular we show that the global cosmological
Hubble flow can actually modify the motions of stars and gas within individual
galaxies, and even do so in a way which can apparently eliminate the need for
galactic dark matter. Also we show that a classical light wave acquires an
observable, global, path dependent phase in traversing a gravitational field.
Both of these effects serve to underscore the intrinsic difference between
non-relativistic and relativistic gravity.Comment: LaTeX, 20 pages plus three figures in two postscript files. To appear
in a special issue of Foundations of Physics honoring Professor Lawrence
Horwitz on the occasion of his 65th birthday; A. van der Merwe and S. Raby,
Editors, Plenum Publishing Company, N.Y., 199
Newtonian Limit of Conformal Gravity
We study the weak-field limit of the static spherically symmetric solution of
the locally conformally invariant theory advocated in the recent past by
Mannheim and Kazanas as an alternative to Einstein's General Relativity. In
contrast with the previous works, we consider the physically relevant case
where the scalar field that breaks conformal symmetry and generates fermion
masses is nonzero. In the physical gauge, in which this scalar field is
constant in space-time, the solution reproduces the weak-field limit of the
Schwarzschild--(anti)DeSitter solution modified by an additional term that,
depending on the sign of the Weyl term in the action, is either oscillatory or
exponential as a function of the radial distance. Such behavior reflects the
presence of, correspondingly, either a tachion or a massive ghost in the
spectrum, which is a serious drawback of the theory under discussion.Comment: 9 pages, comments and references added; the version to be published
in Phys. Rev.
Implications of Cosmic Repulsion for Gravitational Theory
In this paper we present a general, model independent analysis of a recently
detected apparent cosmic repulsion, and discuss its potential implications for
gravitational theory. In particular, we show that a negatively spatially curved
universe acts like a diverging refractive medium, to thus naturally cause
galaxies to accelerate away from each other. Additionally, we show that it is
possible for a cosmic acceleration to only be temporary, with some accelerating
universes actually being able to subsequently recontract.Comment: RevTeX, 13 page
Higher Dimensional Schwinger-like Anomalous Effective Action
We construct explicit form of the anomalous effective action, in arbitrary
even dimension, for Abelian vector and axial gauge fields coupled to Dirac
fermions. It turns out to be a surprisingly simple extension of 2D Schwinger
model effective action.Comment: 7 pages, no figures, ReVTeX, to appear in Phys.Rev.
Energy in Generic Higher Curvature Gravity Theories
We define and compute the energy of higher curvature gravity theories in
arbitrary dimensions. Generically, these theories admit constant curvature
vacua (even in the absence of an explicit cosmological constant), and
asymptotically constant curvature solutions with non-trivial energy properties.
For concreteness, we study quadratic curvature models in detail. Among them,
the one whose action is the square of the traceless Ricci tensor always has
zero energy, unlike conformal (Weyl) gravity. We also study the string-inspired
Einstein-Gauss-Bonnet model and show that both its flat and Anti-de-Sitter
vacua are stable.Comment: 18 pages, typos corrected, one footnote added, to appear in Phys.
Rev.
The tetralogy of Birkhoff theorems
We classify the existent Birkhoff-type theorems into four classes: First, in
field theory, the theorem states the absence of helicity 0- and spin 0-parts of
the gravitational field. Second, in relativistic astrophysics, it is the
statement that the gravitational far-field of a spherically symmetric star
carries, apart from its mass, no information about the star; therefore, a
radially oscillating star has a static gravitational far-field. Third, in
mathematical physics, Birkhoff's theorem reads: up to singular exceptions of
measure zero, the spherically symmetric solutions of Einstein's vacuum field
equation with Lambda = 0 can be expressed by the Schwarzschild metric; for
Lambda unequal 0, it is the Schwarzschild-de Sitter metric instead. Fourth, in
differential geometry, any statement of the type: every member of a family of
pseudo-Riemannian space-times has more isometries than expected from the
original metric ansatz, carries the name Birkhoff-type theorem. Within the
fourth of these classes we present some new results with further values of
dimension and signature of the related spaces; including them are some
counterexamples: families of space-times where no Birkhoff-type theorem is
valid. These counterexamples further confirm the conjecture, that the
Birkhoff-type theorems have their origin in the property, that the two
eigenvalues of the Ricci tensor of two-dimensional pseudo-Riemannian spaces
always coincide, a property not having an analogy in higher dimensions. Hence,
Birkhoff-type theorems exist only for those physical situations which are
reducible to two dimensions.Comment: 26 pages, updated references, minor text changes, accepted by Gen.
Relat. Gra
Quantum Diffeomorphisms and Conformal Symmetry
We analyze the constraints of general coordinate invariance for quantum
theories possessing conformal symmetry in four dimensions. The character of
these constraints simplifies enormously on the Einstein universe . The global conformal symmetry algebra of this space determines
uniquely a finite shift in the Hamiltonian constraint from its classical value.
In other words, the global Wheeler-De Witt equation is {\it modified} at the
quantum level in a well-defined way in this case. We argue that the higher
moments of should not be imposed on the physical states {\it a priori}
either, but only the weaker condition . We
present an explicit example of the quantization and diffeomorphism constraints
on for a free conformal scalar field.Comment: PlainTeX File, 37 page
Renormalization Group and Decoupling in Curved Space: II. The Standard Model and Beyond
We continue the study of the renormalization group and decoupling of massive
fields in curved space, started in the previous article and analyse the higher
derivative sector of the vacuum metric-dependent action of the Standard Model.
The QCD sector at low-energies is described in terms of the composite effective
fields. For fermions and scalars the massless limit shows perfect
correspondence with the conformal anomaly, but similar limit in a massive
vector case requires an extra compensating scalar. In all three cases the
decoupling goes smoothly and monotonic. A particularly interesting case is the
renormalization group flow in the theory with broken supersymmetry, where the
sign of one of the beta-functions changes on the way from the UV to IR.Comment: 27 pages, 8 figure
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