Singularity Problem in Teleparallel Dark Energy Models
  We study future singularity in teleparallel dark energy models, particularly
its behavior and its (non)occurrence in the observationally viable models. For
the models with a general self-potential of the scalar field, we point out that
both at early times and in the future near the singularity the behavior of dark
energy can be described by the analytic solutions of the scalar field we
obtained for the model with no self-potential. As to the (non)occurrence in the
viable models, we consider a natural binding-type self-potential, the quadratic
potential, when fitting observational data, and illustrate the constraining
region up to the $3\sigma$ confidence level as well as the region where a
singularity will occur. As a result, the singularity region is outside the
$3\sigma$ constraint. Thus, although the future singularity problem potentially
exists in teleparallel dark energy models, the observationally viable models
may not suffer this problem.
