Theory HEP Seminar

The Analytic Structure of Non-Global Logarithms

Duff Neil

MIT

Non-global logarithms (NGLs) are a manifestation of how the soft emissions of a gauge theory like QCD will generically entangle all angular regions of phase space. They have presented a challenge to understand and resum, thus making many naive factorization predictions uncontrolled approximations. Using insights about the phenomenology of soft jets coming from the field of jet substructure, I will discuss how the analytic structure of non-global logarithms is markedly different from the standard sudakov resummations typically found in pQCD. I will contrast two expansions for the NGL series, one in terms of partonic free states, and another in terms of "dressed" jets, and explain how the properties of the jets explain the limits to the validity of fixed order perturbation theory, even when restricting to a leading logarithmic level. Time permitting, I will also delve into the connections NGLs have to small-x physics, in particular, how saturation manifests in purely final state QCD cross-sections.