| 1. |
- Bijnens, Johan, et al.
(författare)
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Six-meson amplitude in QCD-like theories
- 2022
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Ingår i: Physical Review D. - 2470-0010. ; 106:5
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Tidskriftsartikel (refereegranskat)abstract
- We calculate the relativistic six-meson scattering amplitude at low energy within the framework of QCD-like theories with n degenerate quark flavors at next-to-leading order in the chiral counting. We discuss the cases of complex, real and pseudoreal representations, i.e. with global symmetry and breaking patterns SU(n)×SU(n)/SU(n) (extending the QCD case), SU(2n)/SO(2n), and SU(2n)/Sp(2n). In case of the one-particle-irreducible part, we obtain analytical expressions in terms of ten six-meson subamplitudes based on the flavor and group structures. We extend on our previous results obtained within the framework of the O(N+1)/O(N) nonlinear sigma model, with N being the number of meson flavors. This work allows for studying a number of properties of six-particle amplitudes at one-loop level.
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| 2. |
- Husek, Tomáš, et al.
(författare)
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Constraints on leptoquarks from lepton-flavour-violating tau-lepton processes
- 2022
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Ingår i: Journal of High Energy Physics. - 1029-8479. ; 2022:4
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Tidskriftsartikel (refereegranskat)abstract
- Leptoquarks are ubiquitous in several extensions of the Standard Model and seem to be able to accommodate the universality-violation-driven B-meson-decay anomalies and the (g −2)μ discrepancy interpreted as deviations from the Standard Model predictions. In addition, the search for lepton-flavour violation in the charged sector is, at present, a major research program that could also be facilitated by the dynamics generated by leptoquarks. In this article, we consider a rather wide framework of both scalar and vector leptoquarks as the generators of lepton-flavour violation in processes involving the tau lepton. We single out its couplings to leptoquarks, thus breaking universality in the lepton sector, and we integrate out leptoquarks at tree level, generating the corresponding dimension-6 operators of the Standard Model Effective Field Theory. In ref. [1] we obtained model-independent bounds on the Wilson coefficients of those operators contributing to lepton-flavour-violating hadron tau decays and ℓ–τ conversion in nuclei, with ℓ = e, μ. Hence, we use those results to translate the bounds into the couplings of leptoquarks to the Standard Model fermions.
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| 3. |
- Husek, Tomáš
(författare)
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Standard Model estimate of K+ →π+4e branching ratio
- 2022
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Ingår i: Physical Review D. - 2470-0010. ; 106:7
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Tidskriftsartikel (refereegranskat)abstract
- The branching ratio of the K+→π+e+e-e+e- (K+→π+4e) decay is calculated at leading order in the Standard Model. The dominance of the neutral-pion pole determines the overall branching ratio to be B(K+→π+4e)=B(K+→π+π0)B(π0→4e)≈7.0(3)×10-6. The significance of this contribution is very much concentrated in the context of the whole available phase space, throughout most of which the one-photon-exchange topology is prevalent in turn. It is thus interesting to present branching ratios for only parts of the allowed kinematical region. We find, for instance, B(K+→π+4e,m4e>150 MeV)=6.0(6)×10-11.
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