Publications (156)238.76 Total impact

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ABSTRACT: The dual formulation of planar N = 4 superYangMills scattering amplitudes makes manifest that the integrand has only logarithmic singularities and no poles at infinity. Recently, ArkaniHamed, Bourjaily, Cachazo and Trnka conjectured the same singularity properties hold to all loop orders in the nonplanar sector as well. Here we conjecture that to all loop orders these constraints give us the key analytic information contained in dual conformal symmetry. We also conjecture that to all loop orders, while N = 8 supergravity has poles at infinity, at least at four points it has only logarithmic singularities at finite locations. We provide nontrivial evidence for these conjectures. For the threeloop fourpoint N = 4 superYangMills amplitude, we explicitly construct a complete basis of diagram integrands that has only logarithmic singularities and no poles at infinity. We then express the complete amplitude in terms of the basis diagrams, with the coefficients determined by unitarity. We also give examples at three loops showing how to make the logarithmic singularity properties manifest via dlog forms. We give additional evidence at four and five loops supporting the nonplanar logarithmic singularity conjecture. Furthermore, we present a variety of examples illustrating that these constraints are more restrictive than dual conformal symmetry. Our investigations show that the singularity structures of planar and nonplanar amplitudes in N = 4 superYangMills are strikingly similar. While it is not clear how to extend either dual conformal symmetry or a dual formulation to the nonplanar sector, these results suggest that related concepts might exist and await discovery. Finally, we describe the singularity structure of N = 8 supergravity at three loops and beyond. 
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ABSTRACT: Electroweak vectorboson production, accompanied by multiple jets, is an important background to searches for physics beyond the Standard Model. A precise and quantitative understanding of this process is helpful in constraining deviations from known physics. We study four key ratios in $W + n$jet production at the LHC. We compute the ratio of cross sections for $W + n$ to $W + (n1)$jet production as a function of the minimum jet transverse momentum. We also study the ratio differentially, as a function of the $W$boson transverse momentum; as a function of the scalar sum of the jet transverse energy, $H_T^{\rm jets}$; and as a function of certain jet transverse momenta. We show how to use such ratios to extrapolate differential cross sections to $W+6$jet production at nexttoleading order, and we crosscheck the method against a direct calculation at leading order. We predict the differential distribution in $H_T^{\rm jets}$ for $W+6$ jets at nexttoleading order using such an extrapolation. We use the BlackHat software library together with SHERPA to perform the computations. 
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ABSTRACT: We determine the minimum dimension at which divergences first occur in halfmaximal 16supercharge supergravity at three loops. For the fourpoint amplitudes, we find that the critical dimension is D=14/3 and give the explicit form of the divergence. We also give the divergence of an additional piece that gives us access to theories with higher degrees of supersymmetry, in particular 20 and 32supercharge supergravities. We give the divergences of halfmaximal supergravity when matter vector multiplets are included as well. Explicit forms of various divergences at one and two loops are also given. 
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ABSTRACT: We show that the fourloop fourpoint amplitudes of N = 5 supergravity are ultraviolet finite in four dimensions, contrary to expectations based on supersymmetry and dualitysymmetry arguments. We explain why the diagrams of any covariant local formalism cannot manifestly exhibit the necessary cancellations for finiteness but instead require a new type of nontrivial ultraviolet cancellation that we call "enhanced cancellations". We also show that the threeloop fourpoint amplitudes in N = 4 and N = 5 supergravity theories display enhanced cancellations. To construct the loop integrand, we use the duality between color and kinematics. We apply standard methods for extracting ultraviolet divergences in conjunction with the FIRE5 integral reduction program to arrive at the fourloop results. 
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ABSTRACT: We study $W$boson production accompanied by multiple jets at 7 TeV at the LHC. We study the jetproduction ratio, of total cross sections for $W$+$n$ to $W$+($n1$)jet production, and the ratio of distributions in the total transverse hadronic jet energy $H_{\rm T}^{\rm jets}$. We use the ratios to extrapolate the total cross section, and the differential distribution in $H_{\rm T}^{\rm jets}$, to $W$+6jet production. We use the BlackHat software library in conjunction with SHERPA to perform the computations. 
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ABSTRACT: In this contribution, we present an intermediate storage format for nexttoleading order (NLO) events and explain the advantages of presenting a NLO calculation in this format. We also present some recent applications, including the calculation of PDF uncertainties and the combination of different multiplicity samples for the prediction of gap fractions in inclusive dijet events. 
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ABSTRACT: We show that at tree level, onshell gauge invariance can be used to fully determine the first subleading softgluon behavior and the first two subleading softgraviton behaviors. Our proofs of the behaviors for ngluon and ngraviton tree amplitudes are valid in D dimensions and are similar to Low's proof of universality of the first subleading behavior of photons. In contrast to photons coupling to massive particles, in four dimensions the soft behaviors of gluons and gravitons are corrected by loop effects. We comment on how such corrections arise from this perspective. We also show that loop corrections in graviton amplitudes arising from scalar loops appear only at the second soft subleading order. This case is particularly transparent because it is not entangled with graviton infrared singularities. Our result suggests that if we set aside the issue of infrared singularities, softgraviton Ward identities of extended BMS symmetry are not anomalous through the first subleading order. 
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ABSTRACT: Cachazo and Strominger recently proposed a new softgraviton theorem that generalizes the leading behavior found by Weinberg. In addition, they proved its validity at tree level. This extension was motivated by a Virasoro symmetry of the gravity Smatrix related to BMS symmetry. As shown long ago by Weinberg, the leading behavior is not corrected by loops. In contrast, we show that the subleading behavior is anomalous and modified by loop effects. We argue that there are no new types of corrections to the first subleading behavior beyond one loop and to the second subleading behavior beyond two loops. To facilitate our investigation, we introduce a new momentumconservation prescription for defining the subleading terms of the soft limit. We discuss the looplevel subleading soft behavior of gaugetheory amplitudes before turning to gravity amplitudes. 
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ABSTRACT: We present nexttoleading order QCD predictions for cross sections and for a comprehensive set of distributions in diphoton + 2jet production at the Large Hadron Collider. We consider the contributions from loop amplitudes for two photons and four gluons, but we neglect top quarks. We use BlackHat together with SHERPA to carry out the computation. We use a Frixione cone isolation for the photons. We study standard sets of cuts on the jets and the photons, and also sets of cuts appropriate for studying backgrounds to Higgsboson production via vectorboson fusion. 
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ABSTRACT: We demonstrate that pure N=4 supergravity is ultraviolet divergent at four loops. The form of the divergence suggests that it is due to the rigid U(1) dualitysymmetry anomaly of the theory. This is the first known example of an ultraviolet divergence in a pure ungauged supergravity theory in four dimensions. We use the duality between color and kinematics to construct the integrand of the fourloop fourpoint amplitude, whose ultraviolet divergence is then extracted by standard integration techniques.Physical Review Letters 12/2013; 111(23):231302. DOI:10.1103/PhysRevLett.111.231302 · 7.73 Impact Factor 
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ABSTRACT: We present results from a recent calculation of prompt photonpair production in association with two jets to nexttoleading order (NLO) at the LHC. The virtual contribution is evaluated using the BlackHat library, a numerical implementation of onshell methods for oneloop amplitudes, in conjunction with SHERPA. We study four sets of cuts: standard jet cuts, a set of Higgsrelated cuts suggested by ATLAS, and corresponding sets which isolate the kinematic region where the process becomes the largest background to Higgs production via vectorboson fusion. 
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ABSTRACT: We present an eventfile format for the dissemination of nexttoleadingorder (NLO) predictions for QCD processes at hadron colliders. The files contain all information required to compute generic jetbased infraredsafe observables at fixed order (without showering or hadronization), and to recompute observables with different factorization and renormalization scales. The files also make it possible to evaluate cross sections and distributions with different parton distribution functions. This in turn makes it possible to estimate uncertainties in NLO predictions of a wide variety of observables without recomputing the shortdistance matrix elements. The event files allow a user to choose among a wide range of commonlyused jet algorithms and jetsize parameters. We provide event files for a $W$ or $Z$ boson accompanied by up to four jets, and for purejet events with up to four jets. The files are for the Large Hadron Collider with a center of mass energy of 7 or 8 TeV. A C++ library along with a Python interface for handling these files are also provided and described in this article. The library allows a user to read the event files and recompute observables transparently for different pdf sets and factorization and renormalization scales.Computer Physics Communications 10/2013; 185(5). DOI:10.1016/j.cpc.2014.01.011 · 2.41 Impact Factor 
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ABSTRACT: We present recent nexttoleading order (NLO) results in perturbative QCD obtained using the BlackHat software library. We discuss the use of ntuples to separate the lengthy matrixelement computations from the analysis process. The use of ntuples allows many analyses to be carried out on the same phasespace samples, and also allows experimenters to conduct their own analyses using the original NLO computation.Journal of Physics Conference Series 10/2013; 523. DOI:10.1088/17426596/523/1/012051 
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ABSTRACT: We present a study on highperformance computing and largescale distributed computing for perturbative QCD calculations. 
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ABSTRACT: In these proceedings we present results from a recent calculation for the production of a W boson in conjunction with five jets at nexttoleading order in perturbative QCD. We also use results at lower multiplicities to extrapolate the cross section to the same process with six jets. 
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ABSTRACT: We review the recently discovered duality between color and kinematics in gauge theories. This duality leads to a remarkably simple doublecopy relation between diagrammatic numerators of gravity scattering amplitudes and gaugetheory ones. We summarize nontrivial evidence that the duality and doublecopy property holds to all loop orders. We also comment on other developments, including a proof that the gaugetheory duality leads to the gravity doublecopy property, and the identification of gaugetheory Lagrangians whose double copies yield gravity Lagrangians.Nuclear Physics B  Proceedings Supplements 06/2013; DOI:10.1016/j.nuclphysbps.2010.08.019 · 0.88 Impact Factor 
Article: The Ultraviolet Structure of HalfMaximal Supergravity with Matter Multiplets at Two and Three Loops
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ABSTRACT: Using the duality between color and kinematics, we construct the two and threeloop amplitudes of halfmaximal supergravity with matter multiplets and show that new divergences occur in D=4 and D=5. Bossard, Howe and Stelle have recently conjectured the existence of 16supercharge offshell harmonic superspaces in order to explain the ultraviolet finiteness of pure halfmaximal supergravity with no matter multiplets in D=4 at three loops and in D=5 at two loops. By assuming the required superspace exists in D=5, they argued that no new divergences should occur at two loops even with the addition of abelianvector matter multiplets. Up to possible issues with the SL(2,R) global anomaly of the theory, they reached a similar conclusion in D=4 for two and three loops. The divergences we find contradict these predictions based on the existence of the desired offshell superspaces. Furthermore, our D=4 results are incompatible with the new divergences being due to the anomaly. We find that the twoloop divergences of halfmaximal supergravity are directly controlled by the divergences appearing in ordinary nonsupersymmetric YangMills theory coupled to scalars, explaining why halfmaximal supergravity develops new divergences when matter multiplets are added. We also provide a list of one and twoloop counterterms that should be helpful for constraining any future potential explanations of the observed vanishings of divergences in pure halfmaximal supergravity. 
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ABSTRACT: We present nexttoleading order QCD predictions for the total cross section and for a comprehensive set of transversemomentum distributions in W + 5jet production at the Large Hadron Collider. We neglect the small contributions from subleadingcolor virtual terms, top quarks and some terms containing four quark pairs. We also present ratios of total cross sections, and use them to obtain an extrapolation formula to an even larger number of jets. We include the decay of the $W$ boson into leptons. This is the first such computation with six finalstate vector bosons or jets. We use BlackHat together with SHERPA to carry out the computation. 
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ABSTRACT: We provide evidence in favor of the conjectured duality between color and kinematics for the case of nonsupersymmetric pure YangMills amplitudes by constructing a form of the oneloop fourpoint amplitude of this theory that makes the duality manifest. Our construction is valid in any dimension. We also describe a dualitysatisfying representation for the twoloop fourpoint amplitude with identical fourdimensional external helicities. We use these results to obtain corresponding gravity integrands for a theory containing a graviton, dilaton, and antisymmetric tensor, simply by replacing color factors with specified diagram numerators. Using this, we give explicit forms of ultraviolet divergences at one loop in four, six, and eight dimensions, and at two loops in four dimensions. 
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ABSTRACT: Using the method of maximal cuts, we construct the complete Ddimensional integrand of the fiveloop fourpoint amplitude of N = 4 superYangMills theory, including nonplanar contributions. In the critical dimension where this amplitude becomes ultraviolet divergent, we present a compact explicit expression for the nonvanishing ultraviolet divergence in terms of three vacuum integrals. This construction provides a crucial step towards obtaining the corresponding amplitude of N = 8 supergravity useful for resolving the general ultraviolet behavior of supergravity theories.Physical Review Letters 12/2012; 109(24):241602. DOI:10.1103/PhysRevLett.109.241602 · 7.73 Impact Factor
Publication Stats
8k  Citations  
238.76  Total Impact Points  
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Institutions

1993–2014

University of California, Los Angeles
 Department of Physics and Astronomy
Los Ángeles, California, United States


2012

University of California, Santa Barbara
 Kavli Institute for Theoretical Physics
Santa Barbara, California, United States


1993–2012

CERN
 Physics Department (PH)
Genève, Geneva, Switzerland


1990–2012

Los Alamos National Laboratory
 • Theoretical Division
 • Physics Division
Los Alamos, California, United States


1994–2011

Stanford University
 • SLAC National Accelerator Laboratory
 • Department of Physics
Palo Alto, CA, United States


1992

University of Pittsburgh
Pittsburgh, Pennsylvania, United States


1990–1992

University of Liverpool
Liverpool, England, United Kingdom
