  With the kinetic freeze-out nucleons and antinucleons obtained from the quark
combination model, we study the production of light nuclei and antinuclei in
the (anti-)nucleon coalescence mechanism in relativistic heavy ion collisions.
We derive analytic formulas of the momentum distributions of different light
nuclei and apply them to compute transverse momentum ($p_T$) spectra of
(anti-)deuterons ($d$, $\bar d$) and (anti-)tritons ($t$, $\bar t$) in Au-Au
collisions at $\sqrt{s_{NN}}=$7.7, 11.5, 19.6, 27, 39, 54.4 GeV. We find that
the experimental data available for these $p_T$ spectra can be well reproduced.
We further study the yields and yield ratios of different light (anti-)nuclei
and naturally explain their interesting behaviors as a function of the
collision energy. We especially point out that the multi-particle yield ratio
$tp/d^2$ should be carefully corrected from hyperon weak decays for protons to
probe the production characteristics of light nuclei. All of our results show
that the coalescence mechanism for (anti-)nucleons plays a dominant role for
the production of light nuclei and antinuclei at the RHIC beam energy scan
energies.
