Session Q06: Quantum Aspects of Gravitation

Live

While the flat space two-body problem is integrable, the generally-relativistic one is not. It is however a problem of great theoretical and practical interest in light of the ongoing observations of gravitational waves by the LIGO/Virgo observatories. In the appropriate classical limit, quantum scattering amplitude-based techniques can yield the classical interaction of massive bodies to all orders in their velocities and to fixed order in the expansion in Newton's constant, that is a fixed order in the post-Minkowskian (relativistic weak-field) expansion. In this talk we review an amplitudes-based framework for such calculations and the derivation of the long-sought third order in the post-Minkowskian expansion for the conservative Hamiltonian of a compact binary system with spinless constituents. We also describe the scattering angle at this order, a first comparison with numerical GR and the extension of this formalism to binaries with spinning constituents.   

Live

Observations from the WMAP and Planck satellites have revealed certain features in the temperature anisotropies of the cosmic microwave background that are in tension with the standard model of cosmology. These signals appear only at large angular scales, and are known as `large scale anomalies’. The statistical significance of each of them is low, and range between 2.5 and 3 standard deviations. But, as pointed out by the Planck Collaboration, their collective significance may be large, and could point towards new physics. However, the peculiar details of these anomalies have challenged the imagination of theorists during the last few years. I will argue in this talk that the observed features could be relics from a cosmic bounce that took place before inflation, and hence they carry information about the physics that replaces the big bang singularity.   

Live

Scale-symmetry is providing a new guiding principle in the understanding of the quantum structure of spacetime, most importantly in the asymptotic-safety approach to quantum gravity.will review the key idea of the approach, the evidence for its viability and highlight open questions, before presenting work aimed at bridging the gap between the quantum-gravity regime and phenomenology in particle physics.