Regular solutions in $f(T)$-Yang-Mills theory

TL;DR

This paper investigates regular solutions in extended $f(T)$ gravity coupled with Yang-Mills fields, revealing that nonlinear torsion terms significantly affect the existence and number of such solutions, with potential absence at high nonlinear orders.

Contribution

It introduces the study of regular solutions in $f(T)$-Yang-Mills theory with nonlinear torsion terms, showing how these terms influence solution existence and properties.

Findings

For $f(T)=T$, recovers Einstein-Yang-Mills solitons.

Nonlinear torsion terms reduce the number of regular solutions.

Beyond critical coupling values, no regular solutions exist.

Abstract

We consider extended covariant teleparallel $(f(T))$ gravity whose action is analytic in the torsion scalar and which is sourced by an $su(2)$ valued Yang-Mills field. Specifically, we search for regular solutions to the coupled $f(T)$ Yang-Mills system. For $f(T)=T$ we, not surprisingly, recover the Bartnik-McKinnon solitons of Einstein Yang-Mills theory. However, interesting effects are discovered with the addition of terms in the action which are nonlinear in the torsion scalar, which we specifically study up to cubic order. With the addition of the nonlinear terms the number of regular solutions becomes finite. As well, beyond critical values of the coupling constants we find that there exist \emph{no} regular solutions. These behaviors are asymmetric with respect to the sign of the nonlinear coupling constants and the elimination of regular solutions turns out to be extremely sensitive to the presence of the cubic coupling. It may be possible, therefore, that with sufficiently high powers of torsion in the action, there may be no regular Yang-Mills static solutions.