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Mar28-12, 07:48 PM
Sci Advisor
PF Gold
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P: 23,215
Big bounce from gravitational four-fermion interaction
I.B. Khriplovich
(Submitted on 27 Mar 2012)
The four-fermion gravitational interaction is induced by torsion, and gets dominating on the Planck scale. The regular, axial-axial part of this interaction by itself does not stop the gravitational compression. However, the anomalous, vector-vector interaction results in a natural way in big bounce.
4 pages.
Minimal Length Scale Scenarios for Quantum Gravity
Sabine Hossenfelder
(Submitted on 28 Mar 2012)
We review the question whether the fundamental laws of nature limit our ability to probe arbitrarily short distances. First, we examine what insights can be gained from thought experiments for probes of shortest distances, and summarize what can be learned from different approaches to a theory of quantum gravity. Then we discuss some models that have been developed to implement a minimal length scale into quantum mechanics and quantum field theory. These models have entered the literature under the names of generalized uncertainty principle or modified dispersion relation, and have allowed to study the effects of a minimal length scale in quantum mechanics, quantum electrodynamics, thermodynamics, black hole physics and cosmology. Finally, we touch upon the question if there are ways to circumvent the manifestation of a minimal length scale in short-distance physics.
86 pages, prepared for Living Reviews in Relativity
Intersecting Quantum Gravity with Noncommutative Geometry - a Review
Johannes Aastrup, Jesper M. Grimstrup
(Submitted on 28 Mar 2012)
We review applications of noncommutative geometry in canonical quantum gravity. First, we show that the framework of loop quantum gravity includes natural noncommutative structures which have, hitherto, not been explored. Next, we present the construction of a spectral triple over an algebra of holonomy loops. The spectral triple, which encodes the kinematics of quantum gravity, gives rise to a natural class of semiclassical states which entail emerging fermionic degrees of freedom. In the particular semiclassical approximation where all gravitational degrees of freedom are turned off, a free fermionic quantum field theory emerges. We end the paper with an extended outlook section.