| Abstract: |
The biggest problem in cosmology is explaining the recently observed accelerated expansion of
the universe. Within the framework of General Relativity (GR), the acceleration originates from
"dark energy". Alternatively, there could be no dark energy, but a large-distance modification
to GR may account for the late-time acceleration of the universe. The simplest model is the
DGP braneworld, which has the same number of parameters as the standard LCDM model.
This model is seriously challenged by observations, and also faces theoretical problems.
But it remains an important toy model for exploring modified gravity theories. I will review
its properties, its confrontation with observations, and some of its possible generalizations.
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