  Light nuclei production is sensitive to the baryon density fluctuations and
can be used to probe the QCD phase transition in relativistic heavy-ion
collisions. In this work, we studied the production of proton, deuteron, triton
in central Au+Au collisions at $\sqrt{s_{\mathrm{NN}}}$ = 5, 7.7, 11.5, 14.5,
19.6, 27, 39, 54.4, 62.4 and 200 GeV from a transport model (JAM). Based on the
coalescence production of light nuclei, we calculated the energy dependence of
rapidity density $dN/dy$ and particle ratios ($d/p$, $t/p$, and $t/d$). More
importantly, the yield ratio $N_{{t}} \times N_{{p}} / N_{{d}}^{2}$, which is
sensitive to the neutron density fluctuations, shows a flat energy dependence
and cannot describe the non-monotonic trend observed by the STAR experiment.
Based on the nucleon coalescence, this work can provide constraint and
reference to search for the QCD critical point and/or first order phase
transition with light nuclei production in future heavy-ion collision
experiments.
