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Geometrical Clocks in Cosmological Perturbation Theory

Mar 22
2:00 pm o'clock to 3:30 pm o'clock
SR 02.729

The theory of linear cosmological perturbations is a well elaborated field and has been
successfully applied e.g. to model the structure formation in our universe. To deal with the
diffeomorphism invariance of general relativity, one usually introduces combinations of
the metric and matter perturbations which are gauge invariant under linearised diffeomorphisms.
Common choices for these linearised observables are the Bardeen potentials or the Mukhanov-Sasaki
variable.
With the relational observable formalism, in contrast, one can in principle construct observables
which are invariant up to all orders in the perturbations.
In our work we found that one can indeed re-derive the Bardeen potententials and the Mukhanov-
Sasaki variable with the observable formalism using geometrical clocks.
However, it turns out that the choice of clocks which naturally yield the Bardeen potentials at
first order leads to a non-standard observable algebra.