Bounds on Unparticles Couplings to Electrons: from Electron g-2 to Positronium Decays

TL;DR

This paper derives stringent bounds on unparticle-electron interactions using precise measurements of electron g-2 and positronium decays, indicating unparticles interact extremely feebly, making detection challenging.

Contribution

It provides the first comprehensive bounds on unparticle couplings to electrons based on experimental data, especially from positronium decay constraints.

Findings

Effective energy scale for vector unparticle-electron interaction exceeds 4 x 10^5 TeV.

Lower bounds on unparticle scales range from tens to hundreds of TeV.

Detection of unparticles in low energy electron systems is highly challenging.

Abstract

Unparticles as suggested recently by Georgi have surprising phenomenological implications, distinctive from any other new physics that we know of. But they must interact very feebly with ordinary matter to have avoided detection thus far. We determine how feebly they can interact with the electron, using the precisely measured quantities in QED: the electron g-2 and the bounds on invisible and exotic positronium decays. The most stringent bound comes from invisible ortho-positronium decays: the effective energy scale entering the vector unparticle-electron interaction must exceed 4 x 10^5 TeV for a scaling dimension 3/2 of the vector unparticle. The lower bounds on scales for other unparticles range from a few tens to a few hundreds TeV. This makes the detection of unparticles challenging in low energy electron systems.