We present an explicit cosmological model where inflation and dark energy both could arise from the dynamics of the same scalar field .
We present our discussion in the framework where the inflaton field \phi attains a nearly constant velocity m _ { \lower 2.0 pt \hbox { $ \scriptstyle P$ } } ^ { -1 } |d \phi / dN| \equiv \alpha + \beta \exp ( % \beta N ) ( where N \equiv \ln a is the e-folding time ) during inflation .
We show that the model with | \alpha| < 0.25 and \beta < 0 can easily satisfy inflationary constraints , including the spectral index of scalar fluctuations ( n _ { s } = 0.96 \pm 0.013 ) , tensor-to-scalar ratio ( r < 0.28 ) and also the bound imposed on \Omega _ { \lower 2.0 pt \hbox { $ \scriptstyle \phi$ } } during the nucleosynthesis epoch ( \Omega _ { \phi } ( 1 { MeV } ) < 0.1 ) .
In our construction , the scalar field potential always scales proportionally to the square of the Hubble expansion rate .
One may thereby account for the two vastly different energy scales associated with the Hubble parameters at early and late epochs .
The inflaton energy could also produce an observationally significant effective dark energy at a late epoch without violating local gravity tests .