Do gluons carry half of the nucleon momentum?

TL;DR

This paper challenges the conventional belief that gluons carry half of the nucleon momentum, proposing a gauge-invariant definition that reduces this fraction to about one fifth, prompting a reexamination of nucleon spin structure.

Contribution

It introduces a gauge-invariant approach to defining gluon momentum, significantly revising the expected momentum fraction in the nucleon.

Findings

Gluons carry about one fifth of the nucleon momentum with the new definition.

The traditional half-momentum estimate is due to an unsuitable definition.

Implications for nucleon spin structure and experimental tests are discussed.

Abstract

We examine the conventional picture that gluons carry about half of the nucleon momentum in the asymptotic limit. We reveal that this large fraction is due to an unsuitable definition of the gluon momentum in an interacting theory. If defined in a gauge-invariant and consistent way, the asymptotic gluon momentum fraction is computed to be only about one fifth. This result suggests that the asymptotic limit of the nucleon spin structure should also be reexamined. Possible experimental test of our finding is discussed in terms of novel parton distribution functions.