Three thermodynamically-based parametrizations of the deceleration parameter
Abstract
We propose, and constrain with the latest observational data, three model-independent parametrizations of the cosmic deceleration parameter
q(z)
. They are well behaved and stay finite at all redshifts. We construct them by fixing the value of
q
at high redshift,
q(z≫1)=1/2
(as demanded by cosmic structure formation), and at the far future,
q(z=−1)=−1
, and smoothly interpolating
q(z)
between them. The fixed point at
z=−1
is not arbitrarily chosen; it readily follows from the second law of thermodynamics. This fairly reduces the ample latitude in parameterizing
q(z)
.