  In this paper we investigate the cosmological consequences of a continuous
matter creation associated with the production of particles by the
gravitational field acting on the quantum vacuum. To illustrate this, three
phenomenological models are considered. An equivalent scalar field description
is presented for each models. The effects on the cosmic microwave background
power spectrum are analyzed for the first time in the context of adiabatic
matter creation cosmology. Further, we introduce a model independent treatment,
$Om$, which depends only on the Hubble expansion rate and the cosmological
redshift to distinguish any cosmological model from $\Lambda$CDM by providing a
null test for the cosmological constant, meaning that, for any two redshifts
$z_1$, $z_2$, $Om (z)$ is same, i.e. $Om (z_1)- Om (z_2)= 0$. Also, this
diagnostic can differentiate between several cosmological models by indicating
their quintessential/ phantom behavior without knowing the accurate value of
the matter density, and the present value of the Hubble parameter. For our
models, we find that particle production rate is inversely proportional to
$Om$. Finally, the validity of the generalized second law of thermodynamics
bounded by the apparent horizon has been examined.
