23 research outputs found
Observational Signatures of Quantum Gravity in Interferometers
We consider the uncertainty in the arm length of an interferometer due to
metric fluctuations from the quantum nature of gravity, proposing a concrete
microscopic model of energy fluctuations in holographic degrees of freedom on
the surface bounding a causally connected region of spacetime. In our model,
fluctuations longitudinal to the beam direction accumulate in the infrared and
feature strong long distance correlation in the transverse direction. This
leads to a signal that could be observed in a gravitational wave
interferometer. We connect the positional uncertainty principle arising from
our calculations to the 't Hooft gravitational S-matrix.Comment: 6 pages, 1 figur
Wall Crossing, Discrete Attractor Flow and Borcherds Algebra
The appearance of a generalized (or Borcherds-) Kac-Moody algebra in the
spectrum of BPS dyons in N=4, d=4 string theory is elucidated. From the
low-energy supergravity analysis, we identify its root lattice as the lattice
of the T-duality invariants of the dyonic charges, the symmetry group of the
root system as the extended S-duality group PGL(2,Z) of the theory, and the
walls of Weyl chambers as the walls of marginal stability for the relevant
two-centered solutions. This leads to an interpretation for the Weyl group as
the group of wall-crossing, or the group of discrete attractor flows.
Furthermore we propose an equivalence between a "second-quantized multiplicity"
of a charge- and moduli-dependent highest weight vector and the dyon
degeneracy, and show that the wall-crossing formula following from our proposal
agrees with the wall-crossing formula obtained from the supergravity analysis.
This can be thought of as providing a microscopic derivation of the
wall-crossing formula of this theory.Comment: This is a contribution to the Special Issue on Kac-Moody Algebras and
Applications, published in SIGMA (Symmetry, Integrability and Geometry:
Methods and Applications) at http://www.emis.de/journals/SIGMA
A Black Hole Levitron
We study the problem of spatially stabilising four dimensional extremal black
holes in background electric/magnetic fields. Whilst looking for stationary
stable solutions describing black holes kept in external fields we find that
taking a continuum limit of Denef et al's multi-center solutions provides a
supergravity description of such backgrounds within which a black hole can be
trapped in a given volume. This is realised by levitating a black hole over a
magnetic dipole base. We comment on how such a construction resembles a
mechanical Levitron.Comment: 5 pages, 1 figur
Towards non-AdS Holography via the Long String Phenomenon
The microscopic description of AdS space obeys the holographic principle in
the sense that the number of microscopic degrees of freedom is given by the
area of the holographic boundary. We assume the same applies to the microscopic
holographic theories for non-AdS spacetimes, specifically for Minkowski, de
Sitter, and AdS below its curvature radius. By taking general lessons from
AdS/CFT we derive the cut-off energy of the holographic theories for these
non-AdS geometries. Contrary to AdS/CFT, the excitation energy decreases
towards the IR in the bulk, which is related to the negative specific heat of
black holes. We construct a conformal mapping between the non-AdS geometries
and spacetimes, and relate the microscopic properties
of the holographic theories for non-AdS spaces to those of symmetric product
CFTs. We find that the mechanism responsible for the inversion of the
energy-distance relation corresponds to the long string phenomenon. This same
mechanism naturally explains the negative specific heat for non-AdS black holes
and the value of the vacuum energy in (A)dS spacetimes.Comment: 38+3 pages, 5 figures. v2: typos corrected, references added. v3:
added refs and clarifications in the conclusion; matches published versio
Observational Signatures of Quantum Gravity in Interferometers
We consider the uncertainty in the arm length of an interferometer due to metric fluctuations from the quantum nature of gravity, proposing a concrete microscopic model of energy fluctuations in holographic degrees of freedom on the surface bounding a causally connected region of spacetime. In our model, fluctuations longitudinal to the beam direction accumulate in the infrared and feature strong long distance correlation in the transverse direction. This leads to a signal that could be observed in a gravitational wave interferometer. We connect the positional uncertainty principle arising from our calculations to the 't Hooft gravitational S-matrix
Quantum Black Hole Evaporation
We investigate a recently proposed model for a full quantum description of
two-dimensional black hole evaporation, in which a reflecting boundary
condition is imposed in the strong coupling region. It is shown that in this
model each initial state is mapped to a well-defined asymptotic out-state,
provided one performs a certain projection in the gravitational zero mode
sector. We find that for an incoming localized energy pulse, the corresponding
out-going state contains approximately thermal radiation, in accordance with
semi-classical predictions. In addition, our model allows for certain acausal
strong coupling effects near the singularity, that give rise to corrections to
the Hawking spectrum and restore the coherence of the out-state. To an
asymptotic observer these corrections appear to originate from behind the
receding apparent horizon and start to influence the out-going state long
before the black hole has emitted most of its mass. Finally, by putting the
system in a finite box, we are able to derive some algebraic properties of the
scattering matrix and prove that the final state contains all initial
information.Comment: 37 pages (figs 2 and 3 included as uuencoded compressed tar file),
Latex, needs epsf.tex, PUPT-1395, IASSNS-HEP-93/25 (revised version has minor
corrections, one reference added
N=8 superconformal gauge theories and M2 branes
Based on recent developments, in this letter we find 2+1 dimensional gauge
theories with scale invariance and N=8 supersymmetry. The gauge theories are
defined by a Lagrangian and are based on an infinite set of 3-algebras,
constructed as an extension of ordinary Lie algebras. Recent no-go theorems on
the existence of 3-algebras are circumvented by relaxing the assumption that
the invariant metric is positive definite. The gauge group is non compact, and
its maximally compact subgroup can be chosen to be any ordinary Lie group,
under which the matter fields are adjoints or singlets. The theories are parity
invariant and do not admit any tunable coupling constant. In the case of SU(N)
the moduli space of vacua contains a branch of the form (R^8)^N/S_N. These
properties are expected for the field theory living on a stack of M2 branes.Comment: 14 pages, no figure
Dying Dyons Don't Count
The dyonic 1/4-BPS states in 4D string theory with N=4 spacetime
supersymmetry are counted by a Siegel modular form. The pole structure of the
modular form leads to a contour dependence in the counting formula obscuring
its duality invariance. We exhibit the relation between this ambiguity and the
(dis-)appearance of bound states of 1/2-BPS configurations. Using this insight
we propose a precise moduli-dependent contour prescription for the counting
formula. We then show that the degeneracies are duality-invariant and are
correctly adjusted at the walls of marginal stability to account for the
(dis-)appearance of the two-centered bound states. Especially, for large black
holes none of these bound states exists at the attractor point and none of
these ambiguous poles contributes to the counting formula. Using this fact we
also propose a second, moduli-independent contour which counts the "immortal
dyons" that are stable everywhere.Comment: 27 pages, 2 figures; one minus sign correcte
Penrose Limits and Non-local theories
We investigate Penrose limits of two classes of non-local theories, little
string theories and non-commutative gauge theories. Penrose limits of the
near-horizon geometry of NS5-branes help to shed some light on the high energy
spectrum of little string theories. We attempt to understand renormalization
group flow in these theories by considering Penrose limits wherein the null
geodesic also has a radial component. In particular, we demonstrate that it is
possible to construct a pp-wave spacetime which interpolates between the linear
dilaton and the AdS regions for the Type IIA NS5-brane. Similar analysis is
considered for the holographic dual geometry to non-commutative field theories.Comment: 27 pages, LaTeX; v2: added reference