# Dual QCD Insight into BSM Hadronic Matrix Elements for $K^0$--$\bar K^0$ Mixing from Lattice QCD

Buras, Andrzej J. (Institute for Advanced Study, TU München, Lichtenbergstr.~2a, 85748 Garching, Germany) ; Gérard, Jean-Marc (Centre for Cosmology, Particle Physics and Phenomenology (CP3), Université Catholique de Louvain, Chemin du Cyclotron 2, 1348 Louvain-la-Neuve, Belgium)

12 March 2019

Abstract: We calculate BSM hadronic matrix elements for $K^0$--$\bar K^0$ mixing in the Dual QCD approach (DQCD). The ETM, SWME and RBC-UKQCD lattice collaborations find the matrix elements of the BSM density--density operators $\mathcal{O}_i$ with $i=2$--5 to be rather different from their vacuum insertion values (VIA) with $B_2\approx 0.5$, $B_3\approx B_5\approx 0.7$ and $B_4\approx 0.9$ at $\mu=3$ GeV to be compared with $B_i=1$ in the VIA. We demonstrate that this pattern can be reconstructed within the DQCD through the non-perturbative meson evolution from very low scales, where factorization of matrix elements is valid, to scales $\mathcal{O}$(1 GeV) with subsequent perturbative quark--gluon evolution to $\mu=3$ GeV. This turns out to be possible in spite of a very different pattern displayed at low scales with $B_2=1.2$, $B_3=3.0$, $B_4=1.0$ and $B_5\approx 0.2$ in the large-$N$ limit, $N$ being the number of colours. Our results imply that the inclusion of meson evolution in the phenomenology of any non-leptonic transition like $K^0$--$\bar K^0$ mixing and $K\to\pi\pi$ decays is mandatory. While meson evolution, as demonstrated in our paper, is hidden in lattice QCD results, to our knowledge, DQCD is the only analytic approach for non-leptonic transitions and decays which takes this important {strong} dynamics into account.

Published in: Acta Physica Polonica B 50 (2019) 121-140