Impact of Clustering on the <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:mmultiscripts><mml:mrow><mml:mi>Li</mml:mi></mml:mrow><mml:mprescripts/><mml:none/><mml:mrow><mml:mn>8</mml:mn></mml:mrow></mml:mmultiscripts></mml:mrow></mml:math> <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mi>β</mml:mi></mml:math> Decay and Recoil Form Factors

We place unprecedented constraints on recoil corrections in the β decay of ^{8}Li, by identifying a strong correlation between them and the ^{8}Li ground state quadrupole moment in large-scale ab initio calculations. The results are essential for improving the sensitivity of high-precision experiments that probe the weak interaction theory and test physics beyond the standard model. In addition, our calculations predict a 2^{+} state of the α+α system that is energetically accessible to β decay but has not been observed in the experimental ^{8}Be energy spectrum, and has an important effect on the recoil corrections and β decay for the A=8 systems. This state and an associated 0^{+} state are notoriously difficult to model due to their cluster structure and collective correlations, but become feasible for calculations in the ab initio symmetry-adapted no-core shell-model framework.