36 research outputs found
From black holes to baby universes in CGHS gravity
We study gravity, a variant of the matterless
Callan-Giddings-Harvey-Strominger model. We show that it describes a universal
sector of the near horizon perturbations of non-extremal black holes in higher
dimensions. In many respects this theory can be viewed as a flat space analog
of Jackiw-Teitelboim gravity. The result for the Euclidean path integral
implies that is dual to a Gaussian ensemble that we
describe in detail. The simplicity of this theory allows us to compute exact
quantities such as the quenched free energy and provides a useful playground to
study baby universes, averages and factorization. We also give evidence for the
existence of a non-perturbative completion in terms of a matrix model. Finally,
flat wormhole solutions are discussed.Comment: 55 pages, v2: minor changes, published versio
Lessons on Eternal Traversable Wormholes in AdS
We attempt to construct eternal traversable wormholes connecting two
asymptotically AdS regions by introducing a static coupling between their dual
CFTs. We prove that there are no semiclassical traversable wormholes with
Poincar\'e invariance in the boundary directions in higher than two spacetime
dimensions. We critically examine the possibility of evading our result by
coupling a large number of bulk fields. Static, traversable wormholes with less
symmetry may be possible, and could be constructed using the ingredients we
develop here.Comment: 22 pages, 4 figures. v2: minor additions, matches published versio
Holography of information in de Sitter space
We study the natural norm on the space of solutions to the Wheeler-DeWitt
equation in an asymptotically de Sitter spacetime. We propose that the norm is
obtained by integrating the squared wavefunctional over field configurations
and dividing by the volume of the diff-and-Weyl group. We impose appropriate
gauge conditions to fix the diff-and-Weyl redundancy and obtain a finite
expression for the norm using the Faddeev-Popov procedure. This leads to a
ghost action that has zero modes corresponding to a residual conformal subgroup
of the diff-and-Weyl group. By keeping track of these zero modes, we show that
Higuchi's norm for group-averaged states emerges from our prescription in the
nongravitational limit. We apply our formalism to cosmological correlators and
propose that they should be understood as gauge-fixed observables. We identify
the symmetries of these observables. In a nongravitational theory, it is
necessary to specify such correlators everywhere on a Cauchy slice to identify
a state in the Hilbert space. In a theory of quantum gravity, we demonstrate a
version of the principle of holography of information: cosmological correlators
in an arbitrarily small region suffice to completely specify the state.Comment: 44 page
Gravitational perturbations from NHEK to Kerr
We revisit the spectrum of linear axisymmetric gravitational perturbations of
the (near-)extreme Kerr black hole. Our aim is to characterise those
perturbations that are responsible for the deviations away from extremality,
and to contrast them with the linearized perturbations treated in the
Newman-Penrose formalism. For the near horizon region of the (near-)extreme
Kerr solution, i.e. the (near-)NHEK background, we provide a complete
characterisation of axisymmetric modes. This involves an infinite tower of
propagating modes together with the much subtler low-lying mode sectors that
contain the deformations driving the black hole away from extremality. Our
analysis includes their effects on the line element, their contributions to
Iyer-Wald charges around the NHEK geometry, and how to reconstitute them as
gravitational perturbations on Kerr. We present in detail how regularity
conditions along the angular variables modify the dynamical properties of the
low-lying sector, and in particular their role in the new developments of
nearly-AdS holography.Comment: 73 pages, 1 figure; v2: minor typos corrected; v3: matches published
versio
The Hilbert space of de Sitter quantum gravity
We obtain solutions of the Wheeler-DeWitt equation with positive cosmological
constant for a closed universe in the large-volume limit. We argue that this
space of solutions provides a complete basis for the Hilbert space of quantum
gravity in an asymptotically de Sitter spacetime. Our solutions take the form
of a universal phase factor multiplied by distinct diffeomorphism invariant
functionals, with simple Weyl transformation properties, that obey the same
Ward identities as a CFT partition function. The Euclidean vacuum corresponds
to a specific choice of such a functional but other choices are equally valid.
Each functional can be thought of as specifying a "theory" and, in this sense,
the space of solutions is like "theory space". We describe another basis for
the Hilbert space where all states are represented as excitations of the vacuum
that have a specific constrained structure. This gives the finite
generalization of the basis proposed by Higuchi in terms of group averaging,
which we recover in the nongravitational limit.Comment: 47 page
Quantum information geometry of driven CFTs
Driven quantum systems exhibit a large variety of interesting and sometimes
exotic phenomena. Of particular interest are driven conformal field theories
(CFTs) which describe quantum many-body systems at criticality. In this paper,
we develop both a spacetime and a quantum information geometry perspective on
driven 2d CFTs. We show that for a large class of driving protocols the
theories admit an alternative but equivalent formulation in terms of a CFT
defined on a spacetime with a time-dependent metric. We prove this equivalence
both in the operator formulation as well as in the path integral description of
the theory. A complementary quantum information geometric perspective for
driven 2d CFTs employs the so-called Bogoliubov-Kubo-Mori (BKM) metric, which
is the counterpart of the Fisher metric of classical information theory, and
which is obtained from a perturbative expansion of relative entropy. We compute
the BKM metric for the universal sector of Virasoro excitations of a thermal
state, which captures a large class of driving protocols, and find it to be a
useful tool to classify and characterize different types of driving. For
M\"obius driving by the SL(2,R) subgroup, the BKM metric becomes the hyperbolic
metric on the unit disk. We show how the non-trivial dynamics of Floquet driven
CFTs is encoded in the BKM geometry via M\"obius transformations. This allows
us to identify ergodic and non-ergodic regimes in the driving. We also explain
how holographic driven CFTs are dual to driven BTZ black holes with evolving
horizons. The deformation of the black hole horizon towards and away from the
asymptotic boundary provides a holographic understanding of heating and cooling
in Floquet CFTs.Comment: 82 pages including references, 14 figure