  We benefit from the lattice QCD determination by the HPQCD of the Standard
Model (SM) form factors for the $\bar B_s\to D_s$ [Phys. Rev. D 101, 074513
(2020)] and the SM and tensor ones for the $\bar B_s\to D_s^{*}$
(arXiv:2304.03137 [hep-lat]) semileptonic decays, and the heavy quark effective
theory (HQET) relations for the analogous $B\to D^{(*)}$ decays obtained by
F.U. Bernlochner et al. in Phys. Rev. D 95, 115008 (2017), to extract the
leading and sub-leading Isgur-Wise functions for the $\bar B_s\to D_s^{(*)}$
decays. Further use of the HQET relations allows us to evaluate the
corresponding scalar, pseudoscalar and tensor form factors needed for a
phenomenological study of new physics (NP) effects on the $\bar B_s\to
D_s^{(*)}$ semileptonic decay. At present, the experimental values for the
ratios ${\cal R}_{D^{(*)}}=\Gamma[\bar B\to
D^{(*)}\tau^-\bar\nu_\tau]/\Gamma[\bar B\to D^{(*)}e^-(\mu^-)\bar\nu_{e(\mu)}]$
are the best signal in favor of lepton flavor universality violation (LFUV)
seen in charged current (CC) $b\to c$ decays. In this work we conduct a study
of NP effects on the $\bar B_s\to D_s^{(*)}\tau^-\bar\nu_\tau$ semileptonic
decays by comparing tau spin, angular and spin-angular asymmetry distributions
obtained within the SM and three different NP scenarios. As expected from SU(3)
light-flavor symmetry, we get results close to the ones found in a similar
analysis of the $\bar B\to D^{(*)}$ case. The measurement of the $\bar B_s\to
D_s^{(*)}\ell\bar\nu_\ell$ semileptonic decays, which is within reach of
present experiments, could then be of relevance in helping to establish or rule
out LFUV in CC $b\to c$ transitions.
