Flavour constraints on light spin-1 bosons within a chiral Lagrangian approach

Author:

Luca Di Luzio, Gabriele Levati, Paride Paradisi, Xavier Ponce Díaz

Keyword:

High Energy Physics - Phenomenology, High Energy Physics - Phenomenology (hep-ph), High Energy Physics - Experiment (hep-ex)

journal:

date:

2023-08-08 16:00:00

Abstract

We discuss the construction of the chiral Lagrangian for a light spin-1 boson, here denoted as $X$, featuring both vector and axial-vector couplings to light $u,d,s$ quarks. Focusing on $\Delta S = 1$ transitions, we show that there are model-independent tree-level contributions to $K^\pm \to \pi^\pm X$, sourced by Standard Model charged currents, which receive an $m^2_K / m_X^2$ enhancement from the emission of a longitudinally polarized $X$. This flavour observable sets the strongest to date model-independent bound on the diagonal axial-vector couplings of $X$ to $u,d,s$ quarks for $m_X < m_K - m_\pi$, superseding the bounds arising from beam-dump and collider searches.

PDF: Flavour constraints on light spin-1 bosons within a chiral Lagrangian approach.pdf