Daniel Sudarsky

Lorentz Invariance and Quantum Gravity: An Additional Fine-Tuning Problem?

Trying to combine standard quantum field theories with gravity leads to a breakdown of the usual structure of space time at around the Planck length, 1.6x10(-35) m, with possible violations of Lorentz invariance. Calculations of preferred-frame effects in quantum gravity have further motivated high precision searches for Lorentz violation. Here, we explain that combining known elementary particle interactions with a Planck-scale preferred frame gives rise to Lorentz violation at the percent level, some 20 orders of magnitude higher than earlier estimates, unless the bare parameters of the theory are unnaturally strongly fine tuned. Therefore an important task is not just the improvement of the precision of searches for violations of Lorentz invariance, but also the search for theoretical mechanisms for automatically preserving Lorentz invariance.

Observational bounds on quantum gravity signals using existing data.

We consider a new set of effects arising from the quantum gravity corrections to the propagation of fields, associated with fluctuations of the spacetime geometry. Using already existing experimental data, we can put bounds on these effects that are more stringent by several orders of magnitude than those expected to be obtained in astrophysical observations. In fact these results can be already interpreted as questioning the whole scenario of linear (in

On the quantum origin of the seeds of cosmic structure

l_P

Alternative approach to the galactic dark matter problem

) corrections to the dispersion relations for free fields in Lorentz violating theories.

A simple proof of a no-hair theorem in Einstein-Higgs theory

The current understanding of the quantum origin of cosmic structure is discussed critically. We point out that in the existing treatments a transition from a symmetric quantum state to an (essentially classical) non-symmetric state is implicitly assumed, but not specified or analysed in any detail. In facing this issue, we are led to conclude that new physics is required to explain the apparent predictive power of the usual schemes. Furthermore, we show that the novel way of looking at the relevant issues opens new windows from where relevant information might be extracted regarding cosmological issues and perhaps even clues about aspects of quantum gravity.

Reanalysis of the Eoumltvös experiment.

We discuss scenarios in which the galactic dark matter in spiral galaxies is described by a long range coherent field which settles in a stationary configuration that might account for the features of the galactic rotation curves. The simplest possibility is to consider scalar fields, so we discuss, in particular, two mechanisms that would account for the settlement of the scalar field in a nontrivial configuration in the absence of a direct coupling of the field with ordinary matter: topological defects and spontaneous scalarization.

Non-minimally coupled scalar fields and isolated horizons

We give a new simple proof of the fact that there are no non-trivial black holes with a regular horizon in Einstein-Higgs theory with any number of scalar fields and an arbitrary potential. We also give a brief discussion on the contrast between this theory and the Einstein-Yang-Mills theory that is responsible for the difference in the set of solutions allowed by each one.

Do collapsed boson stars result in new types of black holes

We have carefully reexamined the results of the experiment of Eoetvoes, Pekar, and Fekete, which compared the accelerations of various materials to the Earth. We find that the Eoetvoes-Pekar-Fekete data are sensitive to the composition of the materials used, and that their results support the existence of an intermediate-range coupling to baryon number or hypercharge.

Cosmological constraints on non-standard inflationary quantum collapse models

The isolated horizon framework is extended to include non-minimally coupled scalar fields. As expected from the analysis based on Killing horizons, entropy is no longer given just by (a quarter of) the horizon area but also depends on the scalar field. In a subsequent paper these results will serve as a point of departure for a statistical mechanical derivation of entropy using quantum geometry.

Continuous spontaneous localization wave function collapse model as a mechanism for the emergence of cosmological asymmetries in inflation

We prove a general no-hair theorem which is then applied to the case of a theory that consists of a number of complex scalar fields minimally coupled to gravity that vary harmonically with time and has an arbitrary potential. This establishes that in the spherically symmetric case there are no black hole analogues of the regular boson star configurations.