  To address five fundamental shortcomings of the Standard Model (SM) of
particle physics and cosmology, we propose a SMART U(1)$_X$ model which is a
$U(1)_X \times U(1)_{PQ}$ extension of the SM. The $U(1)_X$ gauge symmetry is a
generalization of the well-known $U(1)_{B-L}$ symmetry and $U(1)_{PQ}$ is the
global Peccie-Quinn (PQ) symmetry. Three right handed neutrinos are added to
cancel $U(1)_X$ related anomalies, and they play a crucial role in
understanding the observed neutrino oscillations and explaining the observed
baryon asymmetry in the universe via leptogenesis. The PQ symmetry helps
resolve the strong CP problem and also provides axion as a compelling dark
matter (DM) candidate. The $U(1)_X$ gauge symmetry enables us to implement the
inflection-point inflation scenario with $H_{inf} \lesssim 2 \times 10^{7}$
GeV, where $H_{inf}$ is the value of Hubble parameter during inflation. This
allows us to overcome a potential axion domain wall problem as well as the
axion isocurvature problem. The SMART U(1)$_X$ model can be merged with $SU(5)$
as we briefly show.
