Astrophysical observations have put unprecedentedly tight constraints on cosmological theories. The Λ CDM model, mathematically simple and fits observational data sets well, is preferred for explaining the behavior of universe. But many basic features of the dark sectors are still unknown, which leaves room for various nonstandard cosmological hypotheses. As the pressure of the cosmological constant dark energy is unvarying, ignoring contributions from radiation and curvature terms at low redshift, the effective pressure keeps constant. In this paper, we propose two parametric models for a non-constant effective pressure in order to study the tiny deviation from Λ CDM at low redshift. We recover our phenomenological models in the scenarios of quintessence and phantom fields, and we explore the behavior of the scalar field and potential. We constrain our model parameters with SNe Ia and BAO observations, and we detect subtle hints of ωde<-1 from the data-fitting results of both models, which indicates possibly a phantom dark energy scenario at present

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This paper was published in Open Access Repository.

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