Rank-2 Electromagnetic Backgrounds and Angular Momentum Barriers in Gravitomagnetic Spin-Quadrupole Searches

• URL: http://arxiv.org/abs/2604.20717v1
• Date: Wed, 22 Apr 2026 16:03:28 GMT
• Title: Rank-2 Electromagnetic Backgrounds and Angular Momentum Barriers in Gravitomagnetic Spin-Quadrupole Searches
• Abstract summary: Wigner-Eckart theorem mandates $j geq 3/2$ electronic states for sensitivity to the rank-2 gravitomagnetic operator.<n>Nuclear electric quadrupole hyperfine interaction generates an $sim 18$-orders-of-magnitude electromagnetic background.<n>For the molybdenum chain, this yields a first laboratory-derivable bound $|- 1| lesssim 108 - 109$ on the gyrogravitational ratio.
• Score: 0.0
• License: http://creativecommons.org/licenses/by/4.0/
• Abstract: We present a complete analysis of the angular momentum selection rules and electromagnetic backgrounds that constrain any spectroscopic search for the gravitomagnetic spin-quadrupole coupling in highly charged ions. A sequence of four barriers is identified: (i)~the Wigner-Eckart theorem mandates $j \geq 3/2$ electronic states for sensitivity to the rank-2 gravitomagnetic operator, excluding the deformation-immune $j=1/2$ states; (ii)~the nuclear electric quadrupole hyperfine interaction (HFS-E2) generates an $\sim 18$-orders-of-magnitude electromagnetic background in the required $j=3/2$ channel; (iii)~second-order HFS mixing between fine-structure levels leaves a residual $\sim 10^{-6}$ eV even after centroid extraction; (iv)~tensor nuclear polarizability (TNP), scaling with $B(E2)$ rather than $Q_s$, introduces an independent rank-2 background of $\sim 10^{-12}$ eV. We derive the algebraic conditions under which a multi-isotope, multi-transition Generalized King Plot can separate these backgrounds from the gravitational signal, and show that the minimum experimental topology requires three transitions and $N_{\text{odd}} \geq N_{\text{bkg}} + 1$ odd-spin isotopes with linearly independent nuclear parameters. For the molybdenum chain, this yields a first laboratory-derivable bound $|χ- 1| \lesssim 10^{8} - 10^9$ on the gyrogravitational ratio, limited by current precision on nuclear quadrupole moments and transition rates. We quantify the experimental milestones needed to improve this bound by each order of magnitude, providing a roadmap for future searches.

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