  We present recent results concerning the measurement and analysis of the
effective action in four-dimensional Causal Dynamical Triangulations. The
action describes quantum fluctuations of the spatial volume of the CDT universe
(or alternatively the scale factor) after integrating out other degrees of
freedom. We use the covariance of volume fluctuations to measure and
parametrize the effective action inside the de Sitter phase, also called the C
phase. We show that the action is consistent with a simple discretization of
the minisuperspace action (with a reversed overall sign). We discuss possible
subleading corrections and show how to construct a more complicated effective
action comprising both integer and half-integer discrete proper time layers. We
introduce a new method of the effective action measurement based on the
transfer matrix. We show that the results of the new method are fully
consistent with the covariance matrix method inside the de Sitter phase. We use
the new method to measure the effective action in the small volume range and to
explain the behaviour of the stalk part of the CDT triangulations. Finally we
use the transfer matrix method to measure and parametrize the effective action
inside the A and B phases, and to analyze the phase transitions. The results
lead to an unexpected discovery of a new "bifurcation" phase separating the
"old" C and B phases. We analyze geometric properties of triangulations inside
the new phase and draw a new phase diagram.
