Search for dark matter induced de-excitation of $^{180}$Ta$\rm ^m$
  Weak-scale dark matter particles, in collisions with nuclei, can mediate
transitions between different nuclear energy levels. In particular, owing to
sizeable momentum exchange, dark matter particles can enable de-excitation of
nuclear isomers that are extremely long lived with respect to regular
radioactive decays. In this paper, we utilize data from a past experiment with
$^{180}$Ta$\rm ^m$ to search for $\gamma$-lines that would accompany dark
matter induced de-excitation of this isomer. Non-observation of such
transitions above background yields the first direct constraint on the lifetime
of $^{180}$Ta$\rm ^m$ against DM-initiated transitions: $T_{1/2}>1.3\times
10^{14}$~a at 90\% C.I. Using this result, we derive novel constraints on dark
matter models with strongly interacting relics, and on models with inelastic
dark matter particles. Existing constraints are strengthened by this
independent new method. The obtained limits are also valid for the Standard
Model $\gamma$-decay of $^{180}$Ta$\rm ^m$.
