  The first direct determination of the ground-state-to-ground-state $Q$ values
of the $\beta^-$ decay $^{76}$As $\rightarrow$ $^{76}$Se and the
electron-capture decay $^{155}$Tb $\rightarrow$ $^{155}$Gd was performed
utilizing the double Penning trap mass spectrometer JYFLTRAP. By measuring the
atomic mass difference of the decay pairs via the phase-imaging
ion-cyclotron-resonance (PI-ICR) technique, the $Q$ values of $^{76}$As
$\rightarrow$ $^{76}$Se and $^{155}$Tb $\rightarrow$ $^{155}$Gd were determined
to be 2959.265(74) keV and 814.94(18) keV, respectively. The precision was
increased relative to earlier measurements by factors of 12 and 57,
respectively. The new $Q$ values are 1.33 keV and 5 keV lower compared to the
values adopted in the most recent Atomic Mass Evaluation 2020. With the newly
determined ground-state-to-ground-state $Q$ values combined with the excitation
energy from $\gamma$-ray spectroscopy, the $Q$ values for
ground-state-to-excited-state transitions $^{76}$As (ground state)
$\rightarrow$ $^{76}$Se$^*$ (2968.4(7) keV) and $^{155}$Tb (ground state)
$\rightarrow$ $^{155}$Gd$^*$ (815.731(3) keV) were derived to be -9.13(70) keV
and -0.79(18) keV. Thus we have confirmed that both of the $\beta^{-}$-decay
and EC-decay candidate transitions are energetically forbidden at a level of at
least 4$\sigma$, thus definitely excluding these two cases from the list of
potential candidates for the search of low-$Q$-value $\beta^-$ or EC decays to
determine the electron-(anti)neutrino mass.
