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HEP Seminar: The Analytic Structure of Non-Global Logarithms

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Duff Neill, Los Alamos National Laboratory
When
16 November 2016 from 1:30 PM to 2:30 PM
Where
339 Davey Laboratory
Contact Name
Sarah Shandera
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Non-global logarithms (NGLs) are a manifestation of how the soft emissions of perturbative QCD will generically entangle all angular regions of phase space. They generically arise whenever one traces over the energetic degrees of freedom in one region of phase space, while tracking a shape variable that describes the distribution of radiation in a distinct region.

They have presented a challenge to understand and resum, and make many naive factorization predictions uncontrolled approximations. Using insights about 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. One can show that these jet "states" have an formally infinite radius of convergence as a function of the non-gobal logarithm. Using properties of the jet "states" that are not seen at any finite order in perturbation theory, one can show there is a limit to the validity of partonic expansion. That is, fixed order perturbation theory has a finite radius of convergence, 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 should be interpreted in purely final state QCD cross-sections.

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