Marcos Lima

Modified Gravity

Explaining the observed cosmic acceleration of the background expansion of the Universe will likely require yet unknown physics. Assuming General Relativity is the correct gravity theory up to the largest scales, one is forced to introduce a new form of energy with negative pressure, dubbed dark energy, in order to create the gravitational repulsion necessary to produce acceleration.

On the other hand, if we allow for General Relativity to be modified on cosmologically interesting scales, it may be possible to explain cosmic acceleration from such modification. The simplest modification of gravity is the cosmological constant, which can also be viewed as a form of dark energy, depending on which side of the Einstein's equations it is introduced. Other possibilities include the addition of extra dimensions to which only gravity leaks, therefore becoming weaker at large scales, as well as more phenomenological modifications to the Einstein-Hilbert action.

With Hiro Oyaizu, Fabian Schmidt and Wayne Hu, I have worked on producing and analysing N-body simulations of f(R) and DGP models of modified gravity, exploring the effects of modified gravity on the matter power spectrum, spherical collapse and the properties of dark matter halos. With Mark Wyman and Elise Jennings I have studied similar effects, including now redshift distortions, for Galileon models.