19 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
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
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
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
Emergent Gravity and the Dark Universe
Recent theoretical progress indicates that spacetime and gravity emerge
together from the entanglement structure of an underlying microscopic theory.
These ideas are best understood in Anti-de Sitter space, where they rely on the
area law for entanglement entropy. The extension to de Sitter space requires
taking into account the entropy and temperature associated with the
cosmological horizon. Using insights from string theory, black hole physics and
quantum information theory we argue that the positive dark energy leads to a
thermal volume law contribution to the entropy that overtakes the area law
precisely at the cosmological horizon. Due to the competition between area and
volume law entanglement the microscopic de Sitter states do not thermalise at
sub-Hubble scales: they exhibit memory effects in the form of an entropy
displacement caused by matter. The emergent laws of gravity contain an
additional 'dark' gravitational force describing the 'elastic' response due to
the entropy displacement. We derive an estimate of the strength of this extra
force in terms of the baryonic mass, Newton's constant and the Hubble
acceleration scale a_0 =cH_0, and provide evidence for the fact that this
additional `dark gravity~force' explains the observed phenomena in galaxies and
clusters currently attributed to dark matter
Black hole entropy and long strings
We discuss whether black hole entropy counts short or long range microstates
in quantum gravity. In brick wall and induced gravity models the entropy arises
due to short distance correlations across the event horizon cut off at the
Planck length. However, the energy of these short range degrees of freedom is
too high compared to the black hole energy. We argue that the long string
phenomenon, which naturally appears in matrix quantum mechanics, resolves this
issue by lowering the excitation energy per degree of freedom. This mechanism
also reduces the total number of microscopic degrees of freedom in a given
volume, leading to a correct estimate of the Bekenstein-Hawking formula for
black hole entropy.Comment: 9 pages, Essay written for the Gravity Research Foundation 2022
Awards for Essays on Gravitatio
Strings from quivers, membranes from moose
We consider = 2 moose/quiver gauge theories corresponding to N1 D3-branes at a 2/N2 singularity in the ``large moose'' limit where N1 and N2 are scaled to infinity together. In the dual holographic description, this scaling gives rise to a maximally supersymmetric pp-wave background with a compact light-cone direction. We identify the gauge theory operators that describe the Discrete Light-Cone Quantization (DLCQ) of the string in this background. For each discrete light-cone momentum and winding sector there is a separate ground state and Fock space. The large moose/quiver diagram provides a useful graphical representation of the string and its excitations. This representation has a natural explanation in a T-dual language. The dual theory is a non-relativistic type-IIA string wound around the T-dual direction, and bound by a quadratic newtonian potential. We end with some comments on D-string/D-particle states, a possible lift to M-theory and the relation to deconstruction