Talks

The de Broglie-Bohm theory is about non-relativistic point-particles that move deterministically along trajectories. The theory reproduces the predictions of standard quantum theory given that the distribution of particle positions over an ensemble of systems, all described by the same wavefunction psi, equals the quantum equilibrium distribution |psi| squared. Numerical simulations by Valentini and Westman have illustrated that non-equilibrium particle distributions may relax to quantum equilibrium after some time. Here we consider non-equilibrium distributions and their relaxation properties for a particular class of trajectory theories, first studied in detail by Deotto and Ghirardi, that are empirically equivalent to the de Broglie-Bohm theory in quantum equilibrium. Joint work with Ward Struyve (KUL, Belgium).

It will be shown how the CSL (continuous spontaneous localization) dynamical collapse equations work. A mathematically equivalent, non-collapse, Hamiltonian formulation will be described, with interpretative differences between it and CSL briefly discussed. A random field engenders collapse in CSL, and particle energies increase due to collapse. Energy of the random field will be treated, such that energy of particles plus field is conserved. A conserved energy-momentum-stress density tensor for the random field will be presented, enabling gravitational applications. Finally, a possible role for collapse in the beginning of the universe is modeled.

Near the Planckian scales, quantum gravity is expected to drastically change the structure of spacetime, one feature of which may be noncomutativity of the coordinates. Based on the recent advances in quantum field theories on such noncommutative spaces, I will consider the fluctuations of inflaton and look for possible noncommutative corrections in the CMB. Anisotropy and non-gaussianity are the result. The resultant distribution is then compared with ACBAR, CBI and WMAP data to constrain the scale of noncommutativity parameter.

We present a string dual to finite temperature N=4 SYM coupled to Nf massless flavors with abelian symmetry. The solution includes the backreaction of the flavor up to second order in the ratio N_f/N_c times the 't Hooft coupling at the temperature of the dual QGP. The thermodynamics show a departure from conformality as a second order effect, and the energy loss of a quark through the plasma is enhanced by new degrees of freedom.

Quantum cosmology is the arena where the interpretations of quantum mechanics are pushed to their limits. For instance, the Copenhaguen interpretation cannot even be applied to this framework. With this in mind, I will describe the main results which emerge from the application of the Bohm-de Broglie interpretation to quantum cosmology, not only for an investigation of the later, but also to get a better understanding of the former in comparison with other interpretations. At first, without imposing any spacetime symmetry from the beginning, we show explicitly the breakdown of spacetime into space and time due to quantum effects, and an investigation of these latter structures within the Bohm-de Broglie picture. Afterwards, in the case of minisuperspace quantum cosmology, I will present how the notions of an evolution time parameter, cosmological singularities, and classical limit can be unambiguously defined. Cosmological non singular quantum bouncing solutions emerge, which are naturally led to th e standard cosmological model evolution before nucleosynthesis: large classical universes can be obtained without any traditional primordial inflationary expansion. A theory of quantum cosmological perturbations on these backgrounds is constructed, and almost scale invariant spectra are obtained. I argue about the possibility of testing these models against inflation. Use of the Bohm interpretation is crucial to obtain these results, which are otherwise unclear within other interpretations. Finally, I show potential discrepant results about the avoidance of cosmological singularities when different interpretations of quantum mechanics are used, and I speculate about constructing analog models where such differences could be tested.

The classic debate between Einstein and Bohr over a realistic interpretation of quantum mechanics can be cast in terms of the measurement problem: Is there an underlying ontic state prior to measurement which maps deterministically to the measured outcome? According to the Kochen-Specker theorem, such a view is patently inconsistent with quantum theory, leading to the paradox of quantum contextuality. This result, however, relies upon the (arguably unwarranted) assumption that the ontic state remains unchanged through the process of measurement and attendant interaction with the measuring device. By relaxing this assumption, it will be shown that one is able to maintain a realistic view of a pre-existing ontic state, as Einstein insisted, while allowing for changes in that ontic state relative to the chosen measurement, in accordance with Bohr. In this view, the wavefunction respresents an epistemic ensemble of ontological states, corresponding to, say, a particular preparation procedure, and its collapse is a selection of and dynamical process on one member of that ensemble. The specific case of the Mermin-Peres square will be considered, both for its simplicity and its connection to recent experimental tests of quantum contextuality.

After reframing the question of the status of the quantum state in terms of J.S. Bell's "beables", I will sketch out a new theory which -- though nonlocal in the sense required by Bell's theorem -- posits exclusively local beables. This is a theory, in particular, in which the quantum mechanical wave function plays no role whatsoever -- i.e., a theory according to which nothing corresponding to the wave function actually exists. It provides, therefore, a concrete example of how the wave function might be regarded as (at best) "epistemic".

The screening of electric charge in plasma with Bose condensate of a charged scalar field is calculated. In all previous calculations before 2009 the effects of Bose condensation have not been considered. Due to the condensate the time-time component of the photon polarization tensor in addition to the usual terms k-squared and Debye mass squared, contains infrared singular terms inversely proportional to k and k-squared. Such terms lead to power law oscillation behaviour of the screened potential, which is different form Friedel oscillations known for fermions. An analogue of Friedel oscillations in bosonic case is also considered.