Portal de Periódicos da CAPES

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

2018; American Physical Society; Volume: 97; Issue: 8 Linguagem: Inglês

10.1103/physrevd.97.084055

2470-0037

Muxin Han, Zichang Huang, Antonia Zipfel,

Cosmology and Gravitation Theories

In recent years, the calculation of the first nonvanishing 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 spin foam graviton propagators rely heavily on the so-called double scaling limit where spins $j$ are large and the Barbero-Immirzi parameter $\ensuremath{\gamma}$ is small such that the area $A\ensuremath{\propto}j\ensuremath{\gamma}$ 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 [H. M. Haggard, M. Han, W. Kaminski, and A. Riello, Nucl. Phys. B900, 1 (2015).] by Haggard, Han, Kaminski, and Riello and discuss alternative definitions of a graviton propagator, in which the double scaling limit can be avoided.