Sean Fleming
University of Arizona

Thomas Mehen
Duke University

Anna Stasto
Pennsylvania State University

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Inge Dolan
(206) 685-4286

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INT Program INT-11-3

Frontiers in QCD

September 19 - November 18, 2011


This nine week program will focus on a variety of different aspects of QCD based research in which there has been a tremendous amount of recent progress, namely
  • Soft Collinear Effective Theory (SCET),
  • Analytic construction of amplitudes in field theory,
  • Small-x physics,
  • The AdS/CFT correspondence.
Many of the advances in each of these fields have occurred independently of each other, though there is significant overlap between all of them. The aim of this program is to bring together experts working in each area in order to exchange information about these recent advances, to provide an interface between high-energy and nuclear physics, and to explore the possibility of applying these methods in new contexts.


The program will be divided into three sections that are three weeks in length. During each session the focus will be
  • Weeks 1-3 (9/19-10/7): Frontiers of Perturbative QCD including factorization, resummation, SCET approaches, and advanced methods for computing gauge theory amplitudes;

    • Week 2 Workshop
      Advances in QCD: Effective Field Theory and Recursive Analytic Methods

      The past decade has seen a number of advances in treatments of gauge theories including effective theory approaches and the use of analytic methods to understand scattering amplitudes. In some cases these advances have turned hard problems into trivial problems. This workshop aims to explore these topics by focusing on soft collinear theory and recursive analytic methods in field theory.

      There will be a follow-up workshop on recursive analytic methods in field theory later in the fall.

      Amplitudes 2011

  • Weeks 4-6 (10/10-10/28): Small-x physics including resummation, high parton densities, nonlinear phenomena in parton evolution, multiple scattering and applications to high energy collisions;

  • Weeks 7-9 (10/31-11/18): AdS/CFT and applications to QCD, gauge theory, and other strongly interacting systems.

    • Week 7 will be a "focus week" dedicated to applying the AdS/CFT correspondence to the quark gluon plasma
Though each section will have its point of emphasis, we hope there will be interaction between experts all across the QCD community throughout the workshop.


Examples of questions that we hope to address during the program include:
  • Can the new on-shell methods be directly applied to study nuclear physics?
    Since the new on-shell methods only rely on physical properties of the underlying quantum field theory, it may be possible to apply them in a wider context than previously considered, including the study of nuclear phenomena which allow a perturbative description.
  • Can resummation via SCET be interfaced with the automatized implementations of on-shell methods such as BlackHat, Rocket, or CutTools?
    In SCET, one expands the QCD Lagrangian in terms of various modes that contribute at different energy scales. With the SCET Lagrangian in hand, one could envisage building computer code that automatically resums large logarithmic corrections to multi-parton scattering processes which go beyond the standard leading-logarithmic parton shower algorithms implemented in commonly used event generators such as Pythia or Herwig.
  • What can we learn from multi-parton scattering processes at low x at the LHC? Conversely, can new developments in small-x physics be used to further constrain parton distribution functions (PDFs) at low x which give large contributions to certain processes at the LHC?
    The LHC probes the small x region which is dominated by the gluon density. However, the gluon PDF is only constrained in a limited kinematical regime by deep inelastic scattering data. Therefore it suffers from large uncertainties when extrapolated to the smaller values of x which are available at the LHC. The production of heavy quarks and also Higgs production at the LHC is quite sensitive to the gluon PDF at low x. Do early data from LHC possibly hint at an increasing role of multiple parton interactions and nonlinear phenomena at these energies? Bringing together nuclear and high-energy physicists at this workshop will allow to advance the understanding of small-x physics from both viewpoints.
  • Can low-x resummation methods shed light on operator structure in SCET?
    In principle SCET includes the low-x kinematic regime, and logarithms of x should be summable via the renormalization group equations. However, the problem of resummation of small x logarithms using SCET has remained elusive, and the connection between SCET and low-x methods is not clear. Can a bridge between low-x methods and SCET be built? And can SCET be used to elucidate the non-perturbative structure of the low-x regime?
  • Can AdS/CFT or its generalizations give us quantitative/qualitative insight into aspects of QCD which are not amenable to either perturbative or lattice QCD methods?
    The AdS-CFT correspondence can elucidate the dynamics of strongly coupled gauge theories. Unlike lattice QCD, it can be to applied to problems which can only be formulated in Minkowski space. Because of this it can be applied to problems like the thermalization/equilibration of the Quark Gluon Plasma and transport processes that are directly relevant to heavy ion experiments. It would also be interesting to search for gravity duals that more closely resemble QCD as well as systematically incorporate 1/Nc corrections.