# Cosmological Dynamics of D-BIonic and DBI Scalar Field and Coincidence Problem of Dark Energy

## TL;DR

This paper explores the cosmological behavior of D-BIonic and DBI scalar fields coupled to matter, demonstrating they can produce accelerated expansion and address the coincidence problem with smaller matter couplings than traditional models.

## Contribution

It introduces a new analytic scaling solution in D-BIonic theory that explains dark energy and the coincidence problem with smaller matter couplings, thanks to a screening mechanism.

## Key findings

- The D-BIonic model yields an attractor solution for accelerated expansion.
- It allows for observed matter density with smaller coupling constants.
- The model can solve the coincidence problem effectively.

## Abstract

We study the cosmological dynamics of D-BIonic and DBI scalar field, which is coupled to matter fluid. For the exponential potential and the exponential couplings, we find a new analytic scaling solution yielding the accelerated expansion of the Universe. Since it is shown to be an attractor for some range of the coupling parameters, the density parameter of matter fluid can be the observed value, as in the coupled quintessence with a canonical scalar field. Contrary to the usual coupled quintessence, where the value of matter couple giving observed density parameter is too large to satisfy observational constraint from CMB, we show that the D-BIonic theory can give similar solution with much smaller value of matter coupling. As a result, together with the fact that the D-BIonic theory has a screening mechanism, the D-BIonic theory can solve the so-called coincidence problem as well as the dark energy problem.