Abstracts of Quantum Gravity in the Southern Cone IV |

Abstract list is subject to change without prior notice. The current state is as of 09/28/2007. |

Alfaro, Jorge |
Monday, Oct 22 | 14:20 - 14:40 |

Quantum Gravity and Maximum Attainable Velocities in the Standard Model A main difficulty in the quantization of the gravitational field is the lack of experiments that discriminate among the theories proposed to quantize gravity. Recently we showed that the Standard Model (SM) itself contains tiny Lorentz invariance violation (LIV) terms coming from QG. All terms depend on one arbitrary parameter a that set the scale of QG effects. In this talk we review the LIV for mesons nucleons and leptons and apply it to study several effects, including the GZK anomaly. |

Anabalón, Andrés |
Tuesday, Oct 23 | 16:20 - 16:40 |

The Universe as a topological defect Four-dimensional Einstein's General Relativity is shown to arise from a gauge theory for the conformal group, SO(4,2). The theory is constructed from a topological dimensional reduction of the six-dimensional Euler density integrated over a manifold with a four-dimensional topological defect. The resulting action is a four-dimensional theory defined by a gauged Wess Zumino Witten term. An ansatz is found which reduces the full set of field equations to the ones of Einstein's General Relativity; the same ansatz when replaced in the action reduces the gauged WZW term to the Einstein-Hilbert action. |

Ashtekar, Abhay |
Monday, Oct 22 | 9:00 - 9:50 |

Quantum Extensions of Classically Singular Space-times By now there are several examples in which effects of quantum geometry became important, dominate the Planck regime and resolve classical singularities. The resulting quantum space-times are typically significantly larger than the original classical space-times. In simple examples, the physics of these quantum extensions has shed considerable light on issues such as the quantum nature of the big-bang and information loss puzzle. I will present a few examples to illustrate this growing area. |

Bañados, Máximo |
Wednesday, Oct 25 | 11:10 - 12:00 |

Eddington Action, Dark Matter and Dark Energy Motivated by a formulation of gravity near a state with zero metric, we consider general relativity coupled to Eddington's action. We show that this fluid behaves as dark energy at large scales and as dark matter at smaller scales. |

Berenstein, David |
Tuesday, Oct 23 | 10:20 - 11:10 |

Emergent geometry: the wave function of the universe in the AdS/CFT context I will explain some recent developments regarding gravity on AdS via a dual conformal field theory description. In particular, I will show how the dynamics of the conformal field theory at strong coupling localize on a particular set of prefeerd configurations. If one quantizes these special configurations one can see that different choices of wave functions correspond to different spacetime geometries in the AdS space. I will also describe some simulations of these wave functions and prospects for computer simulations of quantum gravitational physics. |

Bojowald, Martin |
Thursday, Oct 25 | 9:00 - 9:50 |

The dynamics of loop quantum gravity and its effective descriptions Loop quantum gravity suggests several characteristic properties for the dynamics of a quantum space-time, which may all have important physical implications. Recent developments have improved the understanding of effective equations applicable to background independent quantum gravity, which allows one to shed light on possible physical effects taking into account issues such as the physical inner product and anomaly-freedom. Physical applications include cosmology and the question of whether Lorentz-violating effects are implied by quantum gravity. |

Cuervo, William |
Tuesday, Oct 23 | 14:00 - 14:20 |

Connection formulation of classical closed inhomogeneous cosmologies SU(2) compact principal bundles acted upon by a 2d-compact lie group are studied as models of closed inhomogeneoous cosmologies in the context of the Ashtekar-Barbero formulation of gravity. |

Freidel, Laurent |
Monday, Oct 22 | 10:20 - 11:10 |

Spin Foam models of 4d gravity In this talk i will review the construction based on a spacetime approach of 4 dimensional quantum gravity amplitudes associated with loop quantum gravity, i-e spin foam models. I will present recent developpements in this field that resolve some of the key difficulties associated with previous models and allows us to incorporate the Immirzi parameter and shed new light on the relationship between the canonical and the spin foam framework. |

Garat, Alcides |
Wednesday, Oct 24 | 16:00 - 16:20 |

Tetrads in Geometrodynamics A new tetrad is introduced within the framework of geometrodynamics for non-null electromagnetic fields. This tetrad diagonalizes the electromagnetic stress-energy tensor and allows for maximum simplification of the expression of the electromagnetic field. The Einstein-Maxwell equations will also be simplified. The tetrad that diagonalizes the stress-energy tensor will be written in terms of the standard extremal field, and two other arbitrary vector fields. It will be proved that these two extra vector fields are available freedom that we have in the construction of a general tetrad for non-null electromagnetic fields. The fact that in geometrodynamics Maxwell's equations have zero source terms, introduces the existence of two potential vector fields, not independent from each other, natural candidates for a particular and explicit choice or example of these two vector fields. In this particular example, an unexpected question will arise at this point. If our tetrad involves in its construction the potential vectors, how is the tetrad going to be affected by electromagnetic gauge transformations. The geometry of electromagnetic fields defines at every point in spacetime two orthogonal planes related to the symmetries of the stress-energy tensor. Gauge transformations, that leave invariant the electromagnetic field, will generate proper and improper tetrad Lorentz transformations on one of the planes. Gauge transformations, that leave invariant the dual of the electromagnetic field, will generate tetrad spatial rotations on the other plane. In this way we find for the Abelian case a relationship through group isomorphisms between the internal local gauge transformations and spacetime local tetrad transformations. |

A Stringy Alternative to Inflation: The Cosmological Slingshot Scenario

We propose a cosmological model, alternative to the standard inflationary paradigm, where all problems that afflict standard non-inflationary cosmology are naturally solved. In this model, the Universe is a wandering brane moving, with non-zero angular momentum, in a warped throat on a Calabi-Yau space. It is assumed that mirage effects drive the cosmic evolution at early time. The result is a bouncing cosmology without cosmic singularity as experienced by an observer living on the brane. Density perturbations are calculated in our model and we find a slightly red spectral index, in compatibility with WMAP data.