Author(s): A. Nanda, D. Comparat, O. Dulieu, S. Lahs, C. Malbrunot, L. Nowak, M. C. Simon, and E. Widmann We have performed hyperfine spectroscopy of two transitions in ground-state deuterium and searched for violations of $CPT$ and Lorentz symmetry that would manifest as sidereal variations of the observed transition frequencies. Several nonrelativistic proton coefficients of the Standard-Model extensi… [Phys. Rev. Lett. 137, 031802] Published Tue Jul 14, 2026