$\mathit{\text{Ab}}\mathit{\text{initio}}$ no-core shell model calculations of the electric dipole polarizabilities and photoabsorption cross sections of the $A=3$ mirror nuclei

We present $\mathit{\text{ab}}\mathit{\text{initio}}$ no-core shell-model calculations of the electric dipole ($E1$) polarizabilities and photoabsorption cross sections of the $A=3$ mirror nuclei ${}^3$H and ${}^3$He using the Daejeon16 nucleon-nucleon interaction. The polarizabilities are obtained by direct summation over discretized continuum states in the harmonic-oscillator basis, while the same spectral information is used to reconstruct the cross sections. This work provides the first extension of the approach from the spin-zero ${}^4$He to nonzero-spin nuclei by calculating the $1\mathrm{/}{2}^{-}$ and $3\mathrm{/}{2}^{-}$ final-state contributions separately and demonstrating their model-space convergence. In both nuclei, the $3\mathrm{/}{2}^{-}$ contribution is approximately twice the $1\mathrm{/}{2}^{-}$ contribution. After quantifying finite-basis and excitation-energy-truncation uncertainties, we identify a clear difference between the mirror polarizabilities, induced entirely by the Coulomb interaction because the Daejeon16 interaction is isospin symmetric. The reconstructed cross sections remain stable under variations of the inversion parameters of the Lorentz integral transform and exhibit the same angular-momentum hierarchy. These results extend the discretized-continuum approach to integrated and energy-resolved $E1$ observables in nonzero-spin nuclei with multiple final-state angular momenta.