Past and recent data analyses gave some hints of steps in dark energy. Considering dark energy as a dynamical scalar field, we investigate several models with various steps: a step in the scalar potential, a step in the kinetic term, a step in the energy density, and a step in the equation-of-state parameter $w$. These toy models provide a workable mechanism to generate steps and features of dark energy. Remarkably, a single real scalar can cross $w=-1$ dynamically with a step in the kinetic term.

• Received 18 August 2009

DOI:https://doi.org/10.1103/PhysRevD.80.101302