Constraints on Unparticle Interactions from Invisible Decays of Z, Quarkonia and Neutrinos

TL;DR

This paper investigates constraints on unparticle interactions through invisible decay modes of Z bosons, quarkonia, and neutrinos, revealing that the unparticle scale can vary widely depending on the unparticle dimension.

Contribution

It provides new bounds on the unparticle interaction scale based on invisible decay measurements, highlighting the sensitivity to the unparticle dimension d_U.

Findings

Unparticle scale can exceed 10^4 TeV for d_U close to 1.

For d_U around 2, the unparticle scale can be below 1 TeV.

Invisible neutrino decay constraints can imply unparticle scales above the Planck mass.

Abstract

Unparticles ($\U$) interact weakly with particles. The direct signature of unparticles will be in the form of missing energy. We study constraints on unparticle interactions using totally invisible decay modes of $Z$, vector quarkonia $V$ and neutrinos. The constraints on the unparticle interaction scale $\Lambda_\U$ are very sensitive to the dimension $d_\U$ of the unparticles. From invisible $Z$ and $V$ decays, we find that with $d_\U$ close to 1 for vector $\U$, the unparticle scale $\Lambda_\U$ can be more than $10^4$ TeV, and for $d_\U$ around 2, the scale can be lower than one TeV. From invisible neutrino decays, we find that if $d_\U$ is close to 3/2, the scale can be more than the Planck mass, but with $d_\U$ around 2 the scale can be as low as a few hundred GeV. We also study the possibility of using $V (Z)\to \gamma + \U$ to constrain unparticle interactions, and find that present data give weak constraints.