Do squarks have to be degenerate? Constraining the mass splitting with Kaon and D mixing

TL;DR

This paper investigates the constraints on the mass difference between the first two generations of left-handed squarks using Kaon and D meson mixing data, highlighting the importance of electroweak gaugino contributions and the dependence on gluino mass.

Contribution

It provides a detailed analysis of flavor constraints on squark mass splitting, emphasizing the role of electroweak gauginos and the impact of gluino mass on these bounds.

Findings

Strong constraints for light gluinos

Weaker constraints if gluinos are heavier than squarks

Possible cancellations among new physics contributions

Abstract

We study the constraints on the mass-splitting of the first two generations of left-handed squarks obtained from Delta M_K, epsilon_K and D mixing. The different contributions from gluino, neutralino and chargino diagrams are examined in detail, concluding that it is not justified to neglect electroweak gaugino diagrams if the squark mass matrices contain flavor non-diagonal LL elements. We find that the constraints on the mass-splitting are very strong for light gluino masses. However, if the gluino is heavier than the squarks the constraints on the mass-splitting are much weaker. There are even large regions in parameter space where the different NP contributions cancel each other, leaving the mass-splitting nearly unconstrained.