Talks

Bimetric theories of gravitation, whether empirically correct or not, are a reminder that a dynamical metric field need not have chrono-geometric significance: its null geodesics need not characterize the motion of light, nor need it be surveyed by physical rods and clocks. In standard GR, the chronometric nature of the metric field is a consequence of the strong equivalence principle, which is not a consequence of the Einstein field equations. It is argued that in understanding the special theory of relativity as the appropriate limit of general relativity, the interpretation of special relativity that best tallies with the above insight is the dynamical one defended by Pauli, Jánossy, Bell and others.

If low-scale supersymmetry exists in nature, then it it will be very likely that a number of superpartners will be discovered at the LHC. It is also very likely, however, that much of the supersymmetric spectrum will go unobserved, leaving many important holes in our understanding of the TeV scale. Direct and indirect astrophysical probes of neutralino dark matter can enable for some of these holes to be filled. By studying the interactions of the lightest neutralino, in many models, a much more complete understanding of supersymmetry can be achieved than is possible by using hadron colliders alone.

We discuss motivations, observational constraints and consequences of modifying the fundamental laws of gravity at large distances. Such modifications of gravity can be the reason for the observed late-time acceleration of the Universe, and can be differentiated from conventional dark energy via precision cosmology. The inevitable additional polarizations of graviton lead to observably large perihelion precession of the Lunar and Martian orbits. These theories also have potentially observable consequences at LHC .

In string compactifications, Kahler metrics for chiral matter fields are an essential prerequisite for the computation of soft supersymmetry breaking terms. I describe new techniques for computing these in Calabi-Yau string compactifications. This involves deducing the modular behaviour of the Kahler metric from that of the physical Yukawa couplings. Using these techniques I derive Kahler metrics for both KKLT and large-volume models. For the latter case, I discuss two applications. First, I describe the resulting soft supersymmetry breaking terms and explain why these are naturally flavour-universal. Secondly, I show how the form of the Kahler metric naturally gives the correct phenomenological scale for neutrino masses._x000D_

I will discuss various different ways of quantifying the differences between two quantum observables (POVMs). Each of these approaches gives rise to a notion of approximately measuring one observable by means of measuring some other observable. This will be illustrated in the case of position and momentum by studying the question which POVMs on phase space can reasonably be said to represent a joint approximate determination of these observables. A new, universally valid trade-off relation for the associated inaccuracies will be rigorously formulated. I will sketch the proof which is an adaptation of some interesting techniques and properties of covariant phase space observables used recently by R Werner in a related project. Recommended reading (optional): quant-ph/0405184 (R Werner), quant-ph/0609185 (PB et al), and also for further background information quant-ph/0309091 (M Hall), quant-ph/0310070 (M Ozawa), quant-ph/9803051 (DM Appleby).

Weakly interacting massive particles (WIMPs) are excellent candidates for cold dark matter. After the first millisecond, WIMPs have decoupled from standard model matter, both chemically and kinetically, they enter the free streaming regime and the formation of cosmic structure begins. Another 40 million years pass before the typical first structures enter the nonlinear regime and collapse to the first WIMPy halos. Therefore, it has been assumed that structure formation is insensitive to the WIMP field theory and can be neglected. However, this leads to a monotonically increasing power of structure formation on small scales and some kind of regularization procedure would be required to make the hierarchical picture of structure formation well defined. It will be shown that nonequilibrium processes give rise to a physical regularization of hierarchical structure formation. This has important consequences for indirect and direct dark matter searches which are sensitive to sub-galactic and sub-milli-parsec scales. Furthermore, due the existence of a physical regulator, the problem of structure formation can consistently be solved using N-body simulations.

Realizations of inflation in string theory hold the promise of connecting the theory to observational tests, and at the same time providing new insights for field theory models of inflation. I will report on progress towards realizing inflation on D-branes in type IIB string theory. Moduli stabilization effects generically lead to an eta problem in this scenario, and to analyze the model it is necessary to compute a particular correction to the nonperturbative effects arising on wrapped D-branes. I will explain this calculation, then present results for the full inflaton potential that establish the existence of successful models, albeit with qualitatively new predictions.