This series consists of talks in the area of Quantum Gravity.
We argue that the
scale-free spectrum that is observed in the cosmic microwave background is the
result of a phase transition in the early universe. The observed tilt of
the spectrum, which has been measured to be 0.04, is shown to be equal to the
anomalous scaling dimension of the correlation function. The phase
transition replaces inflation as the mechanism that produces this spectrum. The tilt further indicates that there is a fundamental small length scale in
nature that we have not yet observed in any other way.
A defining feature of holographic dualities is that, along with the bulk equations of motion, boundary correlators at any given time t determine those of observables deep in the bulk. We argue that this property emerges from the bulk gravitational Gauss law together with bulk quantum entanglement as embodied in the Reeh-Schlieder theorem. Stringy bulk degrees of freedom are not required and play little role even when they exist. As an example we study a toy model whose matter sector is a free scalar field.
Binary pulsars are excellent laboratories to test the building blocks of Einstein's theory of General
Recently powerful techniques have emerged for performing multi-loop computations of scattering amplitudes in quantum gravity and supergravity. These techniques include generalized unitarity and the double-copy property, related to color-kinematics duality in gauge theory. Using these techniques, the ultraviolet divergence structure of N=8 supergravity, and more recently pure N=4 supergravity, have been assessed, not only in four space-time dimensions but also in higher dimensions.
Causal dynamical triangulations (CDT) define a nonperturbative path integral for quantum gravity as a sum over triangulations. Causality is enforced on the kinematical level by means of a preferred
foliation.
By way of presenting some classic and many new results, my talk will indulge shamelessly in
advertising "Causal Dynamical Triangulations (CDT)" as a hands-on approach to nonperturbative quantum gravity that reaches where other approaches currently don't. After summarizing the rationale and basic ingredients of CDT quantum gravity and some of its key findings (like the emergence of a classical de Sitter space), I will focus on some very recent results: how we uncovered the presence of a second-order phase transition (so far unique in 4D quantum
Effective field
theory techniques allow reliable quantum calculations in general relativity at
low energy. After a review of these techniques, I will discuss the attempts to
define the gravitational corrections to running gauge couplings and to the
couplings of gravity itself. I will also describe an attempt to understand the
relation between the effective field theory and Asymptotic Safety in the region
where they overlap.
I will describe recent work in collaboration with Adam
Henderson, Alok Laddha, and Madhavan Varadarajan on the loop quantization of a
certain $G_{\mathrm{N}}\rightarrow 0$ limit of Euclidean gravity, introduced by
Smolin. The model allows one to test various quantization choices one is faced
with in loop quantum gravity, but in a simplified setting. The main results are the construction of
finite-triangulation Hamiltonian and diffeomorphism constraint operators whose
continuum limits can be evaluated in a precise sense, such that the quantum
I present a candidate for a new derivation of black hole
entropy. The key observation is that the action of General Relativity in
bounded regions has an imaginary part, arising from the boundary term. The
formula for this imaginary part is closely related to the Bekenstein-Hawking
entropy formula, and coincides with it for certain classes of regions. This
remains true in the presence of matter, and generalizes appropriately to
Lovelock gravity. The imaginary part of the action is a versatile notion,
I
will describe a discrete model of spacetime which is quantum-mechanical,
causal, and background free. The kinematics is described by networks whose
vertices are labelled with arrows. These networks can be evolved forwards (or
backwards) in time by using unitary replacement rules. The arrow structure
permits one to define dynamics without using an absolute time parameter.
Based on arXiv:1201.2489.