924 research outputs found
From Railroads to Sand Dunes: An Examination of the Offsetting Doctrine in Partial Takings
Called “shadowy at best,” the offsetting doctrine in partial takings has confused “even trained legal minds” and generated inconsistent decision after inconsistent decision. The offsetting doctrine allows certain benefits, termed special, to offset condemnation awards, while general benefits may not be offset. Courts blindly adhere to the doctrine despite its underpinnings rooted in eighteenth-century public policy, which was based on concerns of overly speculative valuation and arguably erroneous fairness, as well as incorrect interpretations of Takings Clause jurisprudence. Such adherence dramatically increases the cost of financing a takings project.
In the face of blind adherence to the doctrine, municipalities are forced to balance the needs of their citizens against the needs of eighteenth-century courts, often resulting in the failure of municipalities to engage in takings for the public benefit. This Note argues that new public policy concerns warrant rejection of the doctrine in favor of a rule that allows all nonspeculative benefits to offset a condemnation award. This rule would take into account modern advances in evidence, promote fairness, simplify the judicial process, and allow municipalities to respond to twentieth-century problems while landowners receive just compensation for taken land
Trace anomaly and Hawking effect in 2D dilaton gravity theories
We investigate the classical and semiclassical features of generic 2D,
matter-coupled, dilaton gravity theories. In particular, we show that the mass,
the temperature and the flux of Hawking radiation associated with 2D black
holes are invariant under dilaton-dependent Weyl rescalings of the metric. The
relationship between quantum anomalies and Hawking radiation is discussed.Comment: 4 pages, LaTex file uses espcrc2.sty, Talk given at the Second
Conference on Constrained Dynamics and Quantum Gravity, Santa Margherita
Ligure, Italy, September 1996, to appear in the Proceeding
Generalized symmetries and invariant matter couplings in two-dimensional dilaton gravity
New features of the generalized symmetries of generic two-dimensional dilaton
models of gravity are presented and invariant gravity-matter couplings are
introduced. We show that there is a continuum set of Noether symmetries, which
contains half a de Witt algebra. Two of these symmetries are area-preserving
transformations. We show that gravity-matter couplings which are invariant
under area preserving transformations only contribute to the dynamics of the
dilaton-gravity sector with a reshaping of the dilaton potential. The
interaction with matter by means of invariant metrics is also considered. We
show in a constructive way that there are metrics which are invariant under two
of the symmetries. The most general metrics and minimal couplings that fulfil
this condition are found.Comment: LateX file, no macros, 14pp: minor changes have been made and some
misprints have been correcte
Geometric Interpretation and Classification of Global Solutions in Generalized Dilaton Gravity
Two dimensional gravity with torsion is proved to be equivalent to special
types of generalized 2d dilaton gravity. E.g. in one version, the dilaton field
is shown to be expressible by the extra scalar curvature, constructed for an
independent Lorentz connection corresponding to a nontrivial torsion.
Elimination of that dilaton field yields an equivalent torsionless theory,
nonpolynomial in curvature. These theories, although locally equivalent exhibit
quite different global properties of the general solution. We discuss the
example of a (torsionless) dilaton theory equivalent to the --model.
Each global solution of this model is shown to split into a set of global
solutions of generalized dilaton gravity. In contrast to the theory with
torsion the equivalent dilaton one exhibits solutions which are asymptotically
flat in special ranges of the parameters. In the simplest case of ordinary
dilaton gravity we clarify the well known problem of removing the Schwarzschild
singularity by a field redefinition.Comment: 21 pages, 6 Postscript figure
Trace anomaly and Hawking effect in generic 2D dilaton gravity theories
Black hole solutions in the context of a generic matter-coupled
two-dimensional dilaton gravity theory are discussed both at the classical and
semiclassical level. Starting from general assumptions, a criterion for the
existence of black holes is given. The relationship between conformal anomaly
and Hawking radiation is extended to a broad class of two-dimensional dilaton
gravity models. A general and simple formula relating the magnitude of the
Hawking effect to the dilaton potential evaluated on the horizon is derived.Comment: 14 pages, Plain-Tex, 4 figures in a uuencoded-gzipcompressed ps fil
Universal conservation law and modified Noether symmetry in 2d models of gravity with matter
It is well-known that all 2d models of gravity---including theories with
nonvanishing torsion and dilaton theories---can be solved exactly, if matter
interactions are absent. An absolutely (in space and time) conserved quantity
determines the global classification of all (classical) solutions. For the
special case of spherically reduced Einstein gravity it coincides with the mass
in the Schwarzschild solution. The corresponding Noether symmetry has been
derived previously by P. Widerin and one of the authors (W.K.) for a specific
2d model with nonvanishing torsion. In the present paper this is generalized to
all covariant 2d theories, including interactions with matter. The related
Noether-like symmetry differs from the usual one. The parameters for the
symmetry transformation of the geometric part and those of the matterfields are
distinct. The total conservation law (a zero-form current) results from a two
stage argument which also involves a consistency condition expressed by the
conservation of a one-form matter ``current''. The black hole is treated as a
special case.Comment: 3
Soliton Induced Singularities in 2 d Gravity and their Evaporation
Positive energy singularities induced by Sine-Gordon solitons in 1+1
dimensional dilaton gravity with positive and negative cosmological constant
are considered. When the cosmological constant is positive, the singularities
combine a white hole, a timelike singularity and a black hole joined smoothly
near the soliton center. When the cosmological constant is negative, the
solutions describe two timelike singularities joined smoothly near the soliton
center. We describe these spacetimes and examine their evaporation in the one
loop approximation.Comment: 15 pages (37.7 kb), PHYZZX. Figures available from authors
Trace anomaly induced effective action and 2d black holes for dilaton coupled supersymmetric theories
The action for 2d dilatonic supergravity with dilaton coupled matter and
dilaton multiplets is constructed. Trace anomaly and anomaly induced effective
action (in components as well as in supersymmetric form) for matter
supermultiplet on bosonic background are found. The one-loop effective action
and large- effective action for quantum dilatonic supergravity are also
calculated. Using induced effective action one can estimate the back-reaction
of dilaton coupled matter to the classical black hole solutions of dilatonic
supergravity. That is done on the example of supersymmetric CGHS model with
dilaton coupled quantum matter where Hawking radiation which turns out to be
zero is calculated. Similar 2d analysis maybe used to study spherically
symmetric collapse for other models of 4d supergravity.Comment: 21 pages, LaTeX, NDA-FP-3
Duality Twists, Orbifolds, and Fluxes
We investigate compactifications with duality twists and their relation to
orbifolds and compactifications with fluxes. Inequivalent compactifications are
classified by conjugacy classes of the U-duality group and result in gauged
supergravities in lower dimensions with nontrivial Scherk-Schwarz potentials on
the moduli space. For certain twists, this mechanism is equivalent to
introducing internal fluxes but is more general and can be used to stabilize
some of the moduli. We show that the potential has stable minima with zero
energy precisely at the fixed points of the twist group. In string theory, when
the twist belongs to the T-duality group, the theory at the minimum has an
exact CFT description as an orbifold. We also discuss more general twists by
nonperturbative U-duality transformations.Comment: 30 pages, harvmac, references and brief comments on gauged
supergravity adde
A Solvable Model of Two-Dimensional Dilaton-Gravity Coupled to a Massless Scalar Field
We present a solvable model of two-dimensional dilaton-gravity coupled to a
massless scalar field. We locally integrate the field equations and briefly
discuss the properties of the solutions. For a particular choice of the
coupling between the dilaton and the scalar field the model can be interpreted
as the two-dimensional effective theory of 2+1 cylindrical gravity minimally
coupled to a massless scalar field.Comment: 6 pages, RevTeX, to be published in Phys. Rev.
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