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arXiv · 1711.11162

Spin foam propagator: A new perspective to include a cosmological constant

Muxin Han·Zichang Huang·Antonia Zipfel
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Abstract

In recent years, the calculation of the first non-vanishing order of the metric 2-point function or graviton propagator in a semiclassical limit has evolved as a standard test for the credibility of a proposed spin foam model. The existing results of spinfoam graviton propagator rely heavily on the so-called double scaling limit where spins $j$ are large and the Barbero-Immirzi parameter $\gamma$ is small such that the area $A\propto j\gamma$ is approximately constant. However, it seems that this double scaling limit is bound to break down in models including a cosmological constant. We explore this in detail for the recently proposed model by Haggard, Han, Kaminski and Riello and discuss alternative definitions of a graviton propagator, in which the double scaling limit can be avoided.

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Muxin Han, Zichang Huang, Antonia Zipfel. 2017-11-30. Spin foam propagator: A new perspective to include a cosmological constant. https://doi.org/10.1103/physrevd.97.084055

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