The essence of this cosmological paradigm is that the Universe is filled with 70% of an energy with negative pressure, designated as "dark energy", 25% of very weakly interacting particles, known as "dark matter" and only 5% of standard baryonic matter. At the same time, Cosmology has become an important laboratory on which recent ideas of string theory and high energy physics can be explored and low-energy phenomenology studied.
Despite its success, the present cosmological paradigm presents many puzzles which remain to be explained. In particular, how did classical spacetime begin or emerge from the quantum realm? Why did inflation occur? Is there any realistic alternative to inflation? What is the this dark energy which represents about 70% of the Universe's total energy budget? More puzzling even, is the cosmological constant problem which states that if dark energy corresponds to vacuum energy, it would be 10^120 orders of magnitude smaller that would be expected from particle physics models.
My recent research has spread from proposed solutions to the cosmological constant problem, and to its close cousin, the Hierarchy problem, and has also focused on observational signatures of braneworld models arising from string theory and that can give rise to more natural realization of inflation.