Theory and Phenomenology of Exotic Isosinglet Quarks and Squarks

TL;DR

This paper investigates the theoretical properties, decay modes, and collider signatures of exotic isosinglet quarks and squarks predicted by extensions of the MSSM, considering various decay mechanisms and experimental constraints.

Contribution

It provides a detailed analysis of the production, decay, and phenomenology of heavy isosinglet quarks and squarks within E6-inspired models, highlighting possible decay channels and experimental signatures.

Findings

Exotic quarks may decay via mixing with standard quarks or through leptoquark/diquark couplings.

Stable exotic particles could decay via higher-dimension operators on cosmological timescales.

Collider and cosmological constraints limit the parameter space of these exotic particles.

Abstract

Extensions of the MSSM often predict the existence of new fermions and their scalar superpartners which are vectorlike with respect to the standard model gauge group but may be chiral under additional gauge factors. In this paper we explore the production and decay of an important example, i.e., a heavy isosinglet charge -1/3 quark and its scalar partner, using the charge assignments of a 27-plet of E6 for illustration. We emphasize that, depending on the symmetries of the low energy theory, such exotic particles may decay by the mixing of the fermion with the d, s, or b quarks; may decay by leptoquark or diquark couplings (which may nevertheless preserve a form of R-parity); or may be stable with respect to renormalizable couplings but decay by higher-dimension operators on cosmological times scales. We discuss the latter two possibilities in detail for various assumptions concerning the relative masses of the exotic fermions, scalars, and the lightest neutralino, and emphasize the necessity of considering the collider signatures in conjunction with the normal MSSM processes. Existing and projected constraints from colliders, indirect experiments, proton decay, and big bang nucleosynthesis are considered.