1,091 research outputs found
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 , where
is the coupling constant.Comment: 12 pages, LaTe
Gravity from self-interaction redux
I correct some recent misunderstandings about, and amplify some details of,
an old explicit non-geometrical derivation of GR.Comment: Final, amplified, published version; GRG (2009
Necessary Dependence of Currents on Fields They Generate
It is shown that in local (proper) Lorentz-invariant theories involving axial-vector, or tensor currents (conserved or not), the latter must vanish, if they commute at equal times with the fields they generate. The need for explicit field dependence of currents is demonstrated for gradient-coupled spinless and massive spin-one fields, as well as for electrodynamics with minimal or nonminimal coupling. The field-dependence requirement is distinct from that (already needed for free fields) of "spreading points" to make the current operators well-defined. The relation between the two, however, essentially fixes the form of this dependence. Applications are made to partially conserved currents, â_ÎŒ^ÎŒ = αÏ; if j^0 commutes with Ï, the latter vanishes
Charged gravitational instantons in five-dimensional Einstein-Gauss-Bonnet-Maxwell theory
We study a solution of the Einstein-Gauus-Bonnet theory in 5 dimensions
coupled to a Maxwell field, whose euclidean continuation gives rise to an
instanton describing black hole pair production. We also discuss the dual
theory with a 3-form field coupled to gravity.Comment: 8 pages, plain Te
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
On the variable-charged black holes embedded into de Sitter space: Hawking's radiation
In this paper we study the Hawking evaporation of masses of variable-charged
Reissner-Nordstrom and Kerr-Newman, black holes embedded into the de Sitter
universe by considering the charge to be function of radial coordinate of the
spherically symmetric metric.Comment: LaTex, p. 2
Brane Cosmology from Heterotic String Theory
We consider brane cosmologies within the context of five-dimensional actions
with O(a') higher curvature corrections. The actions are compatible with bulk
string amplitude calculations from heterotic string theory. We find wrapped
solutions that satisfy the field equations in an approximate but acceptable
manner given their complexity, where the internal four-dimensional scale factor
is naturally inflating, having an exponential De-Sitter form. The temporal
dependence of the metric components is non-trivial so that this metric cannot
be factored as in a conformally flat case. The effective Planck mass is finite
and the brane solutions localize four-dimensional gravity, while the
four-dimensional gravitational constant varies with time. The Hubble constant
can be freely specified through the initial value of the scalar field, to
conform with recent data.Comment: 15 pages, 3 figures, LaTeX, Accepted for Publication in IJT
Consistency of Semiclassical Gravity
We discuss some subtleties which arise in the semiclassical approximation to
quantum gravity. We show that integrability conditions prevent the existence of
Tomonaga-Schwinger time functions on the space of three-metrics but admit them
on superspace. The concept of semiclassical time is carefully examined. We
point out that central charges in the matter sector spoil the consistency of
the semiclassical approximation unless the full quantum theory of gravity and
matter is anomaly-free. We finally discuss consequences of these considerations
for quantum field theory in flat spacetime, but with arbitrary foliations.Comment: 12 pages, LATEX, Report Freiburg THEP-94/2
On the instability of classical dynamics in theories with higher derivatives
The development of instability in the dynamics of theories with higher
derivatives is traced in detail in the framework of the Pais-Uhlenbeck fourth
oder oscillator. For this aim the external friction force is introduced in the
model and the relevant solutions to equations of motion are investigated. As a
result, the physical implication of the energy unboundness from below in
theories under consideration is revealed.Comment: 9 pages, no figures and no tables, revtex4; a few misprints are
correcte
Implications of the Partial Width Z->bb for Supersymmetry Searches and Model-Building
Assuming that the actual values of the top quark mass at FNAL and of the
ratio of partial widths Z->bb/Z->hadrons at LEP are within their current
one-sigma reported ranges, we present a No-Lose Theorem for superpartner
searches at LEP II and an upgraded Tevatron. We impose only two theoretical
assumptions: the Lagrangian is that of the Minimal Supersymmetric Standard
Model with arbitrary soft-breaking terms, and all couplings remain perturbative
up to scales of order 10^16 GeV; there are no assumptions about the soft SUSY
breaking parameters, proton decay, cosmology, etc. In particular, if the LEP
and FNAL values hold up and supersymmetry is responsible for the discrepancy
with the SM prediction of the partial width of Z->bb, then we must have
charginos and/or top squarks observable at the upgraded machines. Furthermore,
little deviation from the SM is predicted within "super-unified" SUSY. Finally,
it appears to be extremely difficult to find any unified MSSM model, regardless
of the form of soft SUSY breaking, that can explain the partial width for large
tan(beta); in particular, no model with top-bottom-tau Yukawa coupling
unification appears to be consistent with the experiments.Comment: 15 pages, University of Michigan preprint UM-TH-94-23. LaTeX file
with 4 uuencoded figures sent separately. Compressed PS file (114Kb)
available by anonymous FTP from 141.211.96.66 in
/pub/preprints/UM-TH-94-23.ps.
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