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

Week 2 Workshop Schedule - All talks in room C-520 (unless otherwise noted)

Advances in QCD: Effective Field Theory and Recursive Analytic Methods

Week 2 Calendar [pdf]

Tuesday, 9/27, Room A-114

10-11 am: Chris Lee, "Probing Jet Structure More Exclusively, Effectively"
    We can probe final states in high energy collisions with varying levels of exclusivity to reveal more or less information about their jet-like structure or jet substructure. More exclusive probes create more challenges to precise and reliable prediction using field theory and the tools of factorization and resummation, due to the additional scales on which these probes depend. After a quick overview of recent progress in effective field theory to resum new classes of logarithms in exclusive jet and jet shape cross sections, I will explore in some detail the nature of non-global logarithms that arise in cross sections sensitive to multiple soft scales in sharply divided regions of phase space, such as those in which multiple jet masses are measured or in which energy vetoes are imposed on radiation outside of jets. These examples studied using effective field theory will provide some clear intuition about the physical origin of NGLs and recognizing which observables contain them.

11 am-12 pm: Saba Zuberi, "Geneva: Event Generation at NLO"

    Abstract: Geneva is a new event generator that aims to combine NLO calculations, logarithmic resummation and parton shower algorithms. Insights from SCET are used to provide a new approach to combining several jet multiplicities at NLO. In this talk I will describe the theoretical concepts behind Geneva, and give the current status of the code development.

2-3 pm: Zvi Bern, "Recent advances in NLO QCD for the LHC"

    Abstract: I will summarize recent developments in NLO QCD leading to new calculations of direct interest for LHC physics involving up to five final state objects, including jets. I will use examples from the BlackHat collaboration to show what kinds of processes are now doable and how NLO QCD can aid the experimental collaborations.

3-4 pm: Anastasia Volovich, "Symbology and Scattering Amplitudes"

4:30-5:30 pm: Jonathan Walsh, "Getting at Realistic QCD Events at the LHC"

    Abstract: I will discuss the general challenge of going beyond simple jet configurations, which is plagued by new large logarithms and requires new factorization theorems to describe. Specializing to the case of two nearby jets, I will describe an effective theory, SCET+, that is an extension of SCET. I will show how the modes in SCET+ can be found using simple kinematics, and how factorization theorems in SCET+ are assembled. Finally, I will discuss how this case is related to jet substructure. I will apply basic factorization ideas from SCET to jet substructure methods and show that significant constraints can be derived.

Wednesday, 9/28

10-11 am: Mannie Chiu, "The Rapidity Renormalization Group"

    Abstract: We introduce a systematic approach for the resummation of perturbative series which involve large logarithms not only due to large invariant mass ratios but large rapidities as well. Series of this form can appear in a variety of gauge theory observables. The formalism is utilized to calculate the jet broadening event shape in a systematic fashion to next to leading logarithmic order. An operator definition of the factorized cross section as well as a closed form of the next-to leading log cross section are presented. The result agrees with the data to within errors.

11 am-12 pm: Massimiliano Procura, "Parton Fragmentation within an Identified Jet"

    Abstract: We study the fragmentation of a light energetic hadron from a jet initiated by a light parton. Fragmenting jet functions describe the distribution in both the energy fraction of this hadron and the invariant mass of the jet. These functions are computed in terms of perturbatively calculable coefficients integrated against the standard non-perturbative fragmentation functions. As an application we study up to NNLL accuracy the process e+ e- to X pi+ on the Upsilon(4S) resonance where one measures the energy fraction of the pi+ and removes the b-quark contribution by imposing a cut on thrust. We find that including contributions up to NNLL (or NLO) can have a large impact on extracting fragmentation functions from e+ e- to dijet + h. We then extend our theoretical framework to describe transverse-momentum-dependent distributions for perturbative values of the fragmenting hadron momentum perpendicular to the jet axis.

2-3 pm: Wouter Waalewijn, "Employing Helicity Amplitudes for Resummation in SCET"

    Abstract: There is a substantial effort at calculating QCD corrections to multileg processes using helicity amplitudes. We have constructed a simple and easy-to-use helicity operator basis in SCET, for which the Wilson coefficients of the matching from QCD onto SCET are directly given in terms of the color-ordered helicity amplitudes. One can therefore directly combine the fixed-order helicity amplitudes at any order that they are known analytically or numerically with a resummation of higher-order logarithmic corrections using SCET. In particular, the virtual loop amplitudes can be utilized to make predictions for exclusive jet cross sections without requiring expensive numerical integrations over real-emission phase space. Our basis is completely crossing-symmetric and allows for an easy determination of its properties under charge conjugation and parity. We demonstrate the ease of using our operator basis by providing explicit results for the matching coefficients of many different processes.

3-4 pm: Henrik Johansson, "Progress on color-dual loop amplitudes"

    Abstract: The color/kinematics duality suggest that kinematical factors of scattering amplitudes can be made to obey the same algebraic relations as color. This duality imposes severe constraints on the gauge theory amplitudes, and remarkably allows for the trivial construction of gravity amplitudes by substituting color factors for kinematical ones. This talk will cover the recent calculations of five-point multi-loop amplitudes in N=4 super-Yang-Mills and N=8 supergravity that manifestly obey the color/kinematics duality. Also, some progress on less-than-maximal supersymmetric theories will be reported.

4:30-5:30 pm: Michael Kiermaier, "A massive S-matrix from massless amplitudes"

    Abstract: I will present a systematic method to extract massive on-shell amplitudes on the Coulomb branch of N = 4 SYM from massless on-shell amplitudes at the origin of moduli space. The method leads to a new CSW-like expansion for massive amplitudes on the Coulomb branch. I will also briefly discuss an application to rational terms in QCD.

Thursday, 9/29

10-11 am: John Joseph Carrasco, "Gluons for nothing, gravitons for free"

    Abstract: I will introduce the virtues of a powerful set of relations we have been able to impose on gluon scattering in Yang-Mills theories that intimately relates all contributions (planar and non-planar) to an incredibly small number of contributing graph-topologies. This establishes a set of preferred representations for multiloop amplitudes at the integrand level. When organized in this way gluon amplitudes trivially generate gravity amplitudes in related theories. I will discuss how the existence of such a representation facilitates Yang-Mills calculation and provide pedagogic examples at tree-level and four-point multiloop in the maximally supersymmetric theory.

11 am-12 pm: Yu-tin Huang, "Amplitudes in D ≠ 4"

    Abstract: The methods for studying amplitudes in four-dimensions can be applied to theories that are defined in dimensions other than four. Applying these methods, with appropriate modification, we find surprising results for D=3 Chern-Simons matter theory which so far evades a proper string theory explanation. For D=6 we will discuss results found for two type of maximal supersymmetric theories, the old fashion super-Yang-Mills, as well as the chiral N=(2,0) theory for which no actions have been found.

2-3 pm: Lance Dixon, "Bootstrapping multi-loop, multi-leg amplitudes in planar N=4 super-Yang-Mills theory"

    Abstract: Scattering amplitudes in planar N=4 super-Yang-Mills theory are dual to polygonal Wilson loops. Alday, Gaiotto, Maldacena, Sever and Vieira have shown how an operator product expansion for the Wilson loops provides powerful constraints on the amplitudes. In 1108.4461 we combine this expansion with the symbol technology introduced by Goncharov, Spradlin, Vergu and Volovich, and solve for the symbol of the 3-loop 6-gluon amplitude, up to two constants. In the multi-Regge limit of the kinematics, we obtain the full amplitude, up to a few more constants. No loop integrals or loop integrands are required.

3-4 pm: Radu Roiban, "Manifest power counting, the UV properties of N=8 supergravity and the origin of simplicity in N=4 sYM theory"

    Abstract: We discuss the properties of N=8 supergravity which emerge from presentations of four-point amplitudes in which the UV properties of each integral are the same as the properties of the complete amplitude. We also comment on the origin of the relative simplicity of the higher-loop non-planar N=4 super-Yang-Mills amplitudes.