Jorge Pullin

Intersecting N loop solutions of the hamiltonian constraint of quantum gravity

Abstract Following the introduction by Ashtekar of a new set of canonical variables for the gravitational field and a new representation of quantum gravity based on them, Jacobson and Smolin presented a large class of solutions to the quantum hamiltonian constraint of general relativity based on the holonomy of the Ashtekar connection along simple loops and two intersecting loops. For all these solutions the metric is degenerate everywhere, including the point of intersection. This motivated Husain to extend the results to consider the case of three intersecting loops. However, the metric was degenerate as well on the three-loop solutions found since the loops were only allowed to have two independent tangent vectors at the point of intersection. We have developed a computer algebra code capable of generating solutions for an arbitrary number of loops. We explicitly present new four- and five-loop solutions. These are the first solutions known to have three independent tangent vectors at the intersection point. In spite of this they fail, however, to have a nondegenerate metric. We present a general argument that shows that the same situation arises for an arbitrary finite number of loops. Implications of this degeneracy for the interpretation of the connection and loop space representation of quantum gravity are also discussed.

Gravitational particle production during cosmic string formation

Abstract We calculate, using a perturbative field theory method, the rate of gravitational particle production in the formation of a straight cosmic string. We use a model in which the ends of the string expand at the speed of light. The results are compared with previous calculations.

Loop Quantum Gravity: The First 30 Years

This volume presents a snapshot of the state-of-the-art in loop quantum gravity from the perspective of younger leading researchers. It takes the reader from the basics to recent advances, thereby bridging an important gap. The aim is two-fold — to provide a contemporary introduction to the entire field for students and post-docs, and to present an overview of the current status for more senior researchers. The contributions include the latest developments that are not discussed in existing books, particularly recent advances in quantum dynamics both in the Hamiltonian and sum over histories approaches; and applications to cosmology of the early universe and to the quantum aspects of black holes.

Nonstationary one-soliton solutions of the vacuum Einstein equations with Alekseev's inverse scattering technique

Abstract We analyse nonstationary solutions to the vacuum Einstein field equations obtained using the Alekseev inverse scattering technique for the Einstein-Maxwell system via a one-soliton transformation of Minkowsky spacetime. The solutions are found to be isometric to those recently found by Economou and Tsoubelis, including as a subfamily the nonstationary cylindrically symmetric type D vacuum solutions found by Xanthopoulos.

A scenario for black hole evaporation on a quantum geometry

We incorporate elements of the recently discovered exact solutions of the quantum constraints of loop quantum gravity for vacuum spherically symmetric space-times into the paradigm of black hole evaporation due to Ashtekar and Bojowald. The quantization of the area of the surfaces of symmetry of the solutions implies that the number of nice slices that can be fit inside the black hole is finite. The foliation eventually moves through the region where the singularity in the classical theory used to be and all the particles that fell into the black hole due to Hawking radiation emerge finally as a white hole. This yields a variant of a scenario advocated by Arkani-Hamed {\em et al.} Fluctuations in the horizon that naturally arise in the quantum space time allow radiation to emerge during the evaporation process due to stimulated emission allowing evaporation to proceed beyond Page time without reaching the maximum entanglement limit until the formation of the white hole. No firewalls nor remnants arise in this scenario.

Canonical quantum gravity and consistent discretizations

This paper covers some developments in canonical quantum gravity that occurred since ICGC-2000, emphasizing the recently introduced consistent discretizations of general relativity.

GRAVITATIONAL PARTICLE PRODUCTION BY COSMIC TEXTURES

Using a perturbative technique we compute the rate of particle production in the evolution of a cosmic texture, based on the stress energy tensor introduced by Turok and Spergel. We compare the results with those for other topological defects.

Gravitational particle production in the formation of global monopoles and domain walls

Abstract We calculate the particle production due to the formation of global monopoles and domain walls. We perform the calculation using the Zeldovich-Starobinskii technique for particle production due to linearized gravity. This allows us to consider very general formation settings. We discuss the cosmological relevance of the particles produced and find that for domain walls the result is greater than for cosmic strings but still smaller than that for oscillating cosmic loops. We also compare with results obtained with other techniques.