# A comparative study of the $S_1$ and $U_1$ leptoquark effects in the light quark regime

## TL;DR

This paper compares the effects of two leptoquarks, $S_1$ and $U_1$, on light quark phenomenology, analyzing constraints from flavor physics, LHC, and IceCube, and assessing their impact on current experimental data fits.

## Contribution

It provides a comprehensive, updated analysis of $S_1$ and $U_1$ leptoquarks considering recent experimental constraints and their influence on flavor physics, collider searches, and neutrino observations.

## Key findings

- Flavor physics constraints are most restrictive.
- LHC limits dominate at higher leptoquark masses.
- $S_1$ marginally improves IceCube data fit, $U_1$ slightly worsens it.

## Abstract

We study the phenomenology of two leptoquarks, the Standard Model $SU(2)$ singlets $S_1$ and $U_1$, with regard to the latest experimental data from the low-energy flavor physics measurements, LHC, and the IceCube neutrino experiment. We consider a scenario when scalar (vector) leptoquark $S_1$ ($U_1$) couples exclusively to the down quark and the neutrinos (charged leptons) of all flavors, where the leptoquark in question couples to the SM lepton doublets. The couplings of $S_1$ ($U_1$) to the up-type quarks and the charged leptons (neutrinos) are in turn uniquely determined via $SU(2)$ symmetry. We find that the most important constraints on the leptoquark parameter space originate from flavor physics measurements, followed by the LHC search limits that take over the flavor physics ones in the large LQ mass regime. We furthermore show that $S_1$ ($U_1$) marginally improves (spoils) the fit of the current IceCube data with respect to the SM case within the region of parameter space that is otherwise consistent with various low-energy flavor physics measurements and the latest LHC input. Our study offers an up-to-date analysis for these two leptoquarks in view of the latest experimental data.