1,868 research outputs found
Cosmology at the boundary of de Sitter using the dS/QFT correspondence
Using the dS/QFT correspondence in the context of inflation allows for the study of interesting, otherwise inaccessible physics. In particular, by studying inflation via its dual field theory at the boundary of the de Sitter space, it may be possible to study a regime of strongly coupled gravity at early times. The purpose of this work is to completely express cosmological observables in terms of the free parameters of a dual field theory and to compare them with CMB data. In this way, constraints on the observational parameters constrains the validity of the strongly coupled inflation picture by imposing limits on the parameters of the field theory. The fit with data defines a limit for the consistency and validity of the approach taken and shows that, within this limit, the model is almost unconstrained, but quite predictive, producing power spectra of density perturbations extremely near scale invariance
Water and democracy: new roles for civil society in water governance
In most democratic countries, government officials make water-allocation decisions. Citizens depend on these officials and their technical advisors to take account of both technical and political considerations in determining which water uses get priority, what infrastructure investments to make and what water quality standards to apply. In many parts of the world, water users and stakeholders have additional opportunities to comment on such decisions before they are implemented. Under some circumstances, citizens can challenge water management decisions in court. This is not enough. More direct democracy, involving stakeholders before such decisions are made, can produce fairer and increasingly sustainable results. The steps in collaborative adaptive management – a form of stakeholder engagement particularly appropriate to managing complex water networks – are described in this article along with the reasons that traditional forms of representative democracy are inadequate when it comes to water policy
Asymptotic Behavior of 2-d Black Holes
We consider the solutions of the field equations for the large dilaton
gravity model in dimensions recently proposed by Callan, Giddings, Harvey
and Strominger (CGHS). We find time dependant solutions with finite mass and
vanishing flux in the weak coupling regime, as well as solutions which lie
entirely in the Liouville region.Comment: 10 page
Black Hole Complementarity vs. Locality
The evaporation of a large mass black hole can be described throughout most
of its lifetime by a low-energy effective theory defined on a suitably chosen
set of smooth spacelike hypersurfaces. The conventional argument for
information loss rests on the assumption that the effective theory is a local
quantum field theory. We present evidence that this assumption fails in the
context of string theory. The commutator of operators in light-front string
theory, corresponding to certain low-energy observers on opposite sides of the
event horizon, remains large even when these observers are spacelike separated
by a macroscopic distance. This suggests that degrees of freedom inside a black
hole should not be viewed as independent from those outside the event horizon.
These nonlocal effects are only significant under extreme kinematic
circumstances, such as in the high-redshift geometry of a black hole.
Commutators of space-like separated operators corresponding to ordinary
low-energy observers in Minkowski space are strongly suppressed in string
theory.Comment: 32 pages, harvmac, 3 figure
The Number of States of Two Dimensional Critical String Theory
We discuss string theory vacua which have the wrong number of spacetime
dimensions, and give a crude argument that vacua with more than four large
dimensions are improbable. We then turn to two dimensional vacua, which naively
appear to violate Bekenstein's entropy principle. A classical analysis shows
that the naive perturbative counting of states is unjustified. All excited
states of the system have strong coupling singularities which prevent us from
concluding that they really exist. A speculative interpretation of the
classical solutions suggests only a finite number of states will be found in
regions bounded by a finite area. We also argue that the vacuum degeneracy of
two dimensional classical string theory is removed in quantum mechanics. The
system appears to be in a Kosterlitz-Thouless phase. This leads to the
conclusion that it is also improbable to have only two large spacetime
dimensions in string theory. However, we note that, unlike our argument for
high dimensions, our conclusions about the ground state have neglected two
dimensional quantum gravitational effects, and are at best incomplete.Comment: 12 pages, harvma
The Wave Function of Vasiliev's Universe - A Few Slices Thereof
We study the partition function of the free Sp(N) conformal field theory
recently conjectured to be dual to asymptotically de Sitter higher-spin gravity
in four-dimensions. We compute the partition function of this CFT on a round
sphere as a function of a finite mass deformation, on a squashed sphere as a
function of the squashing parameter, and on an S2xS1 geometry as a function of
the relative size of S2 and S1. We find that the partition function is
divergent at large negative mass in the first case, and for small in the
third case. It is globally peaked at zero squashing in the second case. Through
the duality this partition function contains information about the wave
function of the universe. We show that the divergence at small S1 occurs also
in Einstein gravity if certain complex solutions are included, but the
divergence in the mass parameter is new. We suggest an interpretation for this
divergence as indicating an instability of de Sitter space in higher spin
gravity, consistent with general arguments that de Sitter space cannot be
stable in quantum gravity.Comment: 30 pages plus appendices, 6 figure
Generalized Conformal Symmetry and Oblique AdS/CFT Correspondence for Matrix Theory
The large N behavior of Matrix theory is discussed on the basis of the
previously proposed generalized conformal symmetry. The concept of `oblique'
AdS/CFT correspondence, in which the conformal symmetry involves both the
space-time coordinates and the string coupling constant, is proposed. Based on
the explicit predictions for two-point correlators, possible implications for
the Matrix-theory conjecture are discussed.Comment: LaTeX, 10 pages, 2 figures, written version of the talk presented at
Strings'9
Emergence of thin shell structure during collapse in isotropic coordinates
Numerical studies of gravitational collapse in isotropic coordinates have
recently shown an interesting connection between the gravitational Lagrangian
and black hole thermodynamics. A study of the actual spacetime was not the main
focus of this work and in particular, the rich and interesting structure of the
interior has not been investigated in much detail and remains largely unknown.
We elucidate its features by performing a numerical study of the spacetime in
isotropic coordinates during gravitational collapse of a massless scalar field.
The most salient feature to emerge is the formation of a thin shell of matter
just inside the apparent horizon. The energy density and Ricci scalar peak at
the shell and there is a jump discontinuity in the extrinsic curvature across
the apparent horizon, the hallmark that a thin shell is present in its
vicinity. At late stages of the collapse, the spacetime consists of two vacuum
regions separated by the thin shell. The interior is described by an
interesting collapsing isotropic universe. It tends towards a vacuum (never
reaches a perfect vacuum) and there is a slight inhomogeneity in the interior
that plays a crucial role in the collapse process as the areal radius tends to
zero. The spacetime evolves towards a curvature (physical) singularity in the
interior, both a Weyl and Ricci singularity. In the exterior, our numerical
results match closely the analytical form of the Schwarzschild metric in
isotropic coordinates, providing a strong test of our numerical code.Comment: 24 pages, 10 figures. version to appear in Phys. Rev.
Extensivity Versus Holography in Anti-de Sitter Spaces
We study the dimensionality manifested in the AdS/CFT correspondence. We show
that the dimensionality as expressed by the high temperature behavior of a
system has a holographic nature also at the quantum level. The emergence of the
AdS black hole as a master field at high temperature leads to the screening of
the extra dimensions in its excluded volume.Comment: 15 pages, Harvma
Black Hole Horizons and Complementarity
We investigate the effect of gravitational back-reaction on the black hole
evaporation process. The standard derivation of Hawking radiation is
re-examined and extended by including gravitational interactions between the
infalling matter and the outgoing radiation. We find that these interactions
lead to substantial effects. In particular, as seen by an outside observer,
they lead to a fast growing uncertainty in the position of the infalling matter
as it approaches the horizon. We argue that this result supports the idea of
black hole complementarity, which states that, in the description of the black
hole system appropriate to outside observers, the region behind the horizon
does not establish itself as a classical region of space-time. We also give a
new formulation of this complementarity principle, which does not make any
specific reference to the location of the black hole horizon.Comment: Some minor modifications in text and the title chang
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