${\cal{P,T}}$-Odd Weak Neutral Current Interactions in the TlF Molecule

Leptoquark models may explain deviations from the Standard Model observed in decay processes involving heavy quarks at high-energy colliders. Such models give rise to low-energy parity- and time-reversal-violating phenomena in atoms and molecules. One of the leading effects among these phenomena is the nucleon-electron tensor-pseudotensor interaction when the low-energy experimental probe uses a quantum state of an atom or molecule predominantly characterized by closed electron shells. In the present paper the molecular interaction constant for the nucleon-electron tensor-pseudotensor interaction in the thallium-fluoride molecule -- used as such a sensitive probe by the CeNTREX collaboration [Quantum Sci. Technol., 6:044007, 2021] -- is calculated employing highly-correlated relativistic many-body theory. Accounting for up to quintuple excitations in the wavefunction expansion the final result is $W_T({\text{Tl)}} = -6.25 \pm 0.31\,$[$10^{-13} {\langle\Sigma\rangle}_A$ a.u.] Interelectron correlation effects on the tensor-pseudotensor interaction are studied for the first time in a molecule, and a common framework for the calculation of such effects in atoms and molecules is presented.