Talks

It is a prime interest to understand gravitational physics and to develop cosmological applications exploiting the next generation of surveys, scheduled to be launched in the near future, such as SDSS3, DES, XCS, JDEM or EUCLID. The future precision surveys are promising to resolve outstanding problems in modern physics. With the level of precision available in future surveys, we can use the high resolution maps expected to be gained from next-generation surveys to test the foundations of gravity and particle physics. The gravity known to us at solar system scales (GR: general relativity) is possibly challenged at cosmological scales. The measured cosmic acceleration that we have ascribed to the presence of dark energy (DE) could be a signal that GR is broken in some way.

I will describe a new connection between supersymmetry, geometry and computer science. An exploration of the equations of supersymmetry has revealed a geometrical sub-structure whose classification depends on self-dual error correcting codes.

The BCFW recursion relations define Yang-Mills and gravity amplitudes in terms of lower-point amplitudes. I will discuss several connections between the internal consistency of this recursive definition and the allowed interactions of massless, higher-spin particles.

For a quantum system with a d-dimensional Hilbert space, a symmetric informationally complete measurement (SIC) can be thought of as a set of d^2 pure states all having the same overlap. Constructions of SICs for composite systems usually do not make use of the composite structure but treat the system as a whole. Indeed for some cases, one can prove that a SIC cannot have the symmetry that one naturally associates with the composite structure. In this talk I give one example showing how a SIC for three qubits can be constructed from SICs for the individual qubits. I ask whether the strategy used in this example might apply to other composite cases.

Although the observational evidence for cosmological inflation is growing, the physical mechanism behind it is still unknown. In part this is because inflation probably occurred at energy scales many orders of magnitude higher than that at man-made or astrophysical particle accelerators. So how can we learn about inflation? How does it constrain microphysical theory? One approach to answering these questions is primarily theoretical: attempting to embed inflation in fundamental theories of quantum gravity, such as string theory. Another approach is primarily observational: looking for signatures left by light fields that existed during inflation, such as isocurvature fluctuations from the QCD-axion. In this talk I discuss work on these two approaches.

The problem of the quantum backreaction in expanding spaces is an old, as yet unresolved, question. In this talk I will consider the one-loop backreaction of a massless scalar which couples to the Ricci scalar in an expanding space with constant deceleration. I will show that the infrared divergences, which generically plague the one loop stress energy, can be removed by matching onto an earlier radiation era. An insignificant backreaction occurs, unless the coupling to the Ricci scalar is negative. Similar results hold for the graviton backreaction.