  Canonical quantization is often used to suggest new effects in quantum
gravity, in the dynamics as well as the structure of space-time. Usually,
possible phenomena are first seen in a modified version of the classical
dynamics, for instance in an effective Friedmann equation, but there should
also be implications for a modified space-time structure. Quantum space-time
effects, however, are often ignored in this setting because they are not
obvious: they require a careful analysis of gauge transformations and the
anomaly problem. It is shown here how modified space-time structures and
effective line elements can be derived unambiguously, provided an off-shell
anomaly-free system of modified constraints exists. The resulting effective
line elements reveal signature change as an inescapable consequence of
non-classical gauge transformations in the presence of holonomy modifications.
The general framework is then specialized to black-hole models in loop quantum
gravity. In contrast to previous studies, a self-consistent space-time
structure is taken into account, leading to a new picture of black-hole
interiors.
