On the presence of twinlike models in cosmology
  We study cosmological models described by a single real scalar field. We work within the first-order framework, and we show how the first-order equations simplify the investigation, leading to a direct search of twinlike theories. The procedure is used to introduce distinct models that support the same first-order equations, with the very same energy densities and pressure in flat spacetime. The presence of curvature forbids the construction of twinlike models in the cosmological scenario here investigated. 
D. Bazeia, J. D. Dantas
hep-th gr-qc hep-ph