Using $K^0\pi^-\to\pi^-$ transitions to compute $K\to(\pi\pi)_{I=0}$ decay amplitudes at NLO in the chiral expansion

TL;DR

The paper proposes a novel method using $K^0 o o ext{pi}$ transitions to accurately compute $K o( ext{pi} ext{pi})_{I=0}$ decay amplitudes at NLO, simplifying calculations and reducing computational complexity.

Contribution

It introduces a new approach to determine weak chiral Lagrangian constants via unphysical transitions, improving precision and efficiency over traditional methods.

Findings

Eliminates s-channel disconnected diagrams in calculations.

Reduces the number of inversions needed in computations.

Provides a feasible way to evaluate decay amplitudes at NLO.

Abstract

It is proposed to compute matrix elements for the (unphysical) $K^0\pi^-\to \pi^-$ transition to determine the next-to-leading order low energy constants of the weak chiral Lagrangian. This allows us to evaluate $K\to(\pi\pi)_{I=0}$ decay amplitudes at this level of precision. This approach has several significant advantages over the use of $K\to\pi\pi$ transitions, most notably the elimination of s-channel disconnected diagrams and the use of fewer inversions.