Lecture abstract

Time:   15. October 2020
Place:   XIX Serbian Astronomical Conference (SAC19)
Title:   Cosmological constant problem in discretized quantum gravity
Abstract:
The cosmological constant (CC) problem is one of the main unsolved problems in quantum field theory, and it is expected to be somehow resolved within the context of some theory of quanutm gravity (QG).

One of the recently proposed models is the so-called {\it spincube model} of QG [1], a categorical generalization of spinfoam models developed within the framework of Loop Quantum Gravity. The main advantage of the spincube model over previous models is the ability to couple matter fields to gravity. This opens up the possibility to discuss the CC problem. As it turns out, the spincube model indeed does offer a plausible resolution of the CC problem [2].

Using the effective action framework, one can compute the effective value of the CC in the model. It is given as a sum of three terms: the classical CC, the quantum gravity CC and the matter CC. Since the observations can only measure the sum of these three terms, we can choose the classical CC to cancel the matter CC. Hence the effective CC is given only by the quantum gravity contribution, which is determined by the path-integral measure, and must necessarily be much smaller than one, as a consequence of the analyticity requirement for the model. Finally, since the path-integral measure depends on a free parameter, this parameter can be chosen such that the effective CC gives the observed value.

We will discuss the obtained results, as well as some issues that require further research.

[1] A. Miković and M. Vojinović, Class. Quant. Grav. 29, 165003 (2012) [arXiv:1110.4694].
[2] A. Miković and M. Vojinović, Europhys. Lett. 110, 40008 (2015) [arXiv:1407.1394].