Abstract
We investigate statistical properties of the distribution of matter at redshift zero in disformal gravity by using N-body simulations. The disformal model studied here consists of a conformally coupled symmetron field with an additional exponential disformal term. We conduct cosmological simulations to discover the impact of the new disformal terms in the matter power spectrum, halo mass function, and radial profile of the scalar field. We calculated the disformal geodesic equation and the equation of motion for the scalar field. We then implemented these equations into the N-body code ISIS, which is a modified gravity version of the code RAMSES. The presence of a conformal symmetron field increases both the power spectrum and mass function compared to standard gravity on small scales. Our main finding is that the newly added disformal terms tend to counteract these effects and can make the evolution slightly closer to standard gravity. We finally show that the disformal terms give rise to oscillations of the scalar field in the centre of the dark matter haloes.
Highlights
Since 1998, it has been known that the universe expands at an accelerating rate that is consistent with the existence of a cosmological constant Λ (Riess et al 1998; Perlmutter et al 1999)
We show that the disformal terms give rise to oscillations of the scalar field in the centre of the dark matter haloes
A viable solution to the cosmological constant problem is to assume that the particle physics vacuum energy is totally concealed on gravitational scales, while other mechanisms are responsible for the measured expansion
Summary
Since 1998, it has been known that the universe expands at an accelerating rate that is consistent with the existence of a cosmological constant Λ (Riess et al 1998; Perlmutter et al 1999). A cancellation of that many terms is very improbable and would require extreme fine tuning. This is known as the cosmological constant problem and is a severe problem in modern physics (see Weinberg 1989, for an early introduction to this issue). A viable solution to the cosmological constant problem is to assume that the particle physics vacuum energy is totally concealed on gravitational scales, while other mechanisms are responsible for the measured expansion. One way to search for such mechanisms consist of introducing a slight modification to standard general relativity (GR) in such a way that the equations for gravity will give rise to accelerated expansion on large scales. There are innumerable models for modified gravity (see Clifton et al 2012 for a review)
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