Young Researchers Conference - 2007

With the discovery of many new satellite galaxies, in recent years our understanding of the Milky Way environment has undergone a dramatic transformation. I will discuss what these discoveries are telling us about galaxy formation and the nature of dark matter itself. Issues I will focus on include: identifying the least luminous dark matter halo in the Universe, distinguishing between warm and cold dark matter, and indirect dark matter detection.

We describe the measurement statistics of the balanced homodyne detection scheme in terms of the moment operators of the associated positive operator measures. In particular, we give a mathematically rigorous proof for the fact that the high amplitude limit in the local oscillator leads to a measurement of a rotated quadrature operator of the signal _eld. Using these results, we also show that each covariant phase space observable can be measured with the eight-port homodyne detector.

The spacetime or histories approach is a whole attitude to quantum mechanics in which histories are fundamental rather than states. In this talk we will review a suggested dynamics and a suggested interpretation in this framework, phrasing the dynamics of stochastic collapse models in the histories language then proceeding to explore a new realist interpretation suggested by Rafael Sorkin and examining its perspective on the Kochen-Specker result.

Warped backgrounds in string theory are useful tools for building phenomenological models of early universe cosmology and particle physics. In particular, warped backgrounds play an important role in constructing viable models of brane inflation and can help explain the presence of hierarchies in particle physics. One interesting feature of warped models is that subtle differences in the warped geometry can lead to significant differences in observational signatures in the CMB and at the LHC that can be used to distingiush different models. In this talk, I will discuss recent work in distinguishing different warped geometries through CMB and LHC observations.

We will consider stability in the string theory landscape. A survey over several classes of flux vacua with different characteristics indicates that the vast majority of flux vacua with small cosmological constant are unstable to rapid decay to a big crunch. Only vacua with large compactification radius or (approximately) supersymmetric configurations turn out to be long lived. We will speculate that regions of the landscape with approximate R-symmetry, while rare, might be cosmological attractors.

In this talk we propose a Reduced Phase Space Quantization approach to Loop Quantum Gravity. The idea is to combine the relational formalism introduced by Rovelli in the extended form developed by Dittrich and the Brown-Kuchar-Mechanism. The relational formalism can be used to construct gauge invariant observables for constrained systems such as General Relativity, while the Brown-Kuchar-Mechanism is a particular application of the relational formalism in which pressureless dust is taken as the clock of the system. By combining these two we obtain a framework in which the constraints of General Relativity deparametrize such that the algebra of observables has a very simple structure and furthermore we obtain a so called physical Hamiltonian generating the evolution of those observables. The quantization of the reduced phase space and the physical Hamiltonian can be obtained by using standard LQG techniques and gives a direct access to the physical Hilbert space, which is much harder to achieve in the standard Dirac quantization. Additionally we will analyze the quantization in the Algebraic Quantum Gravity context and discuss the differences that occur. Finally we will present recent results where this framework has been applied to cosmological perturbation theory.

Relational particle mechanics are theories of relative angles and relative (ratios of) separations only. These bear a number of resemblances to the geometrodynamical formulation of general relativity and as such are useful analogues for at least some approaches to the notorious problem of time in quantum gravity. I have recently provided a fairly complete study of the configuration spaces of these theories in spatial dimension 1 and 2, am subsequently studying the redused forms of these theories at the quantum level, and this shall provide a number of useful examples for the conceptual discussion of various problem of time strategies

After a brief motivation for studying 3d gravity, a review of Strominger argument will be given, showing that 3d quantum gravity with negative cosmological constant is a conformal field theory. Classical phase space tools will be introduced to develop semi-classical analyses of gravity with zero cosmological constant, and, with negative cosmological constant and closed timelike curves.

In this talk, I will talk about recent developments in studying strongly coupled gauge theory using the gauge/gravity duality in string theory. In particular, the inclusion of fundamental degrees of freedom and finite chemical potential is reviewed. As an example, I will discuss the results from analyzing the gravitational dual of a none-supersymmetric gauge theory at low temperature and finite baryon chemical potential.