Publications (111)229.19 Total impact
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ABSTRACT: We extend the hexagon function bootstrap to the nexttomaximallyhelicityviolating (NMHV) configuration for sixpoint scattering in planar \${\cal N}=4\$ superYangMills theory at three loops. Constraints from the \$\bar{Q}\$ differential equation, from the operator product expansion (OPE) for Wilson loops with operator insertions, and from multiRegge factorization, lead to a unique answer for the threeloop ratio function. The threeloop result also predicts additional terms in the OPE expansion, as well as the behavior of NMHV amplitudes in the multiRegge limit at one higher logarithmic accuracy (NNLL) than was used as input. Both predictions are in agreement with recent results from the fluxtube approach. We also study the multiparticle factorization of multiloop amplitudes for the first time. We find that the function controlling this factorization is purely logarithmic through three loops. We show that a function \$U\$, which is closely related to the parityeven part of the ratio function \$V\$, is remarkably simple; only five of the nine possible final entries in its symbol are nonvanishing. We study the analytic and numerical behavior of both the parityeven and parityodd parts of the ratio function on simple lines traversing the space of cross ratios \$(u,v,w)\$, as well as on a few twodimensional planes. Finally, we present an empirical formula for $V$ in terms of elements of the coproduct of the sixgluon MHV remainder function \$R_6\$ at one higher loop, which works through three loops for \$V\$ (four loops for \$R_6\$).08/2014;  [Show abstract] [Hide abstract]
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.07/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We describe the hexagon function bootstrap for solving for sixgluon scattering amplitudes in the large $N_c$ limit of ${\cal N}=4$ superYangMills theory. In this method, an ansatz for the finite part of these amplitudes is constrained at the level of amplitudes, not integrands, using boundary information. In the nearcollinear limit, the dual picture of the amplitudes as Wilson loops leads to an operator product expansion which has been solved using integrability by Basso, Sever and Vieira. Factorization of the amplitudes in the multiRegge limit provides additional boundary data. This bootstrap has been applied successfully through four loops for the maximally helicity violating (MHV) configuration of gluon helicities, and through three loops for the nonMHV case.07/2014;  [Show abstract] [Hide abstract]
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.02/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We present the fourloop remainder function for sixgluon scattering with maximal helicity violation in planar N=4 superYangMills theory, as an analytic function of three dualconformal cross ratios. The function is constructed entirely from its analytic properties, without ever inspecting any multiloop integrand. We employ the same approach used at three loops, writing an ansatz in terms of hexagon functions, and fixing coefficients in the ansatz using the multiRegge limit and the operator product expansion in the nearcollinear limit. We express the result in terms of multiple polylogarithms, and in terms of the coproduct for the associated Hopf algebra. From the remainder function, we extract the BFKL eigenvalue at nexttonexttoleading logarithmic accuracy (NNLLA), and the impact factor at NNNLLA. We plot the remainder function along various lines and on one surface, studying ratios of successive loop orders. As seen previously through three loops, these ratios are surprisingly constant over large regions in the space of cross ratios, and they are not far from the value expected at asymptotically large orders of perturbation theory.Journal of High Energy Physics 02/2014; 2014(6). · 5.62 Impact Factor  [Show abstract] [Hide abstract]
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.12/2013;  [Show abstract] [Hide abstract]
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). · 2.41 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: I provide a basic introduction to modern helicity amplitude methods, including color organization, the spinor helicity formalism, and factorization properties. I also describe the BCFW (onshell) recursion relation at tree level, and explain how similar ideas  unitarity and onshell methods  work at the loop level. These notes are based on lectures delivered at the 2012 CERN Summer School and at TASI 2013.10/2013;  [Show abstract] [Hide abstract]
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.  [Show abstract] [Hide abstract]
ABSTRACT: We introduce a generating function for the coefficients of the leading logarithmic BFKL Green's function in transversemomentum space, order by order in alpha_s, in terms of singlevalued harmonic polylogarithms. As an application, we exhibit fully analytic azimuthalangle and transversemomentum distributions for MuellerNavelet jet cross sections at each order in alpha_s. We also provide a generating function for the total cross section valid to any number of loops.09/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We study the change in the diphotoninvariantmass distribution for Higgs boson decays to two photons, due to interference between the Higgs resonance in gluon fusion and the continuum background amplitude for gg→γγ. Previously, the apparent Higgs mass was found to shift by around 100 MeV in the standard model in the leadingorder approximation, which may potentially be experimentally observable. We compute the nexttoleadingorder QCD corrections to the apparent mass shift, which reduce it by about 40%. The apparent mass shift may provide a way to measure, or at least bound, the Higgs boson width at the Large Hadron Collider through "interferometry." We investigate how the shift depends on the Higgs width, in a model that maintains constant Higgs boson signal yields. At Higgs widths above 30 MeV, the mass shift is over 200 MeV and increases with the square root of the width. The apparent mass shift could be measured by comparing with the ZZ^{*} channel, where the shift is much smaller. It might be possible to measure the shift more accurately by exploiting its strong dependence on the Higgs transverse momentum.Physical Review Letters 09/2013; 111(11):111802. · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present a study on highperformance computing and largescale distributed computing for perturbative QCD calculations.09/2013;  [Show abstract] [Hide abstract]
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.08/2013;  [Show abstract] [Hide abstract]
ABSTRACT: We present the threeloop remainder function, which describes the scattering of six gluons in the maximallyhelicityviolating configuration in planar N=4 superYangMills theory, as a function of the three dual conformal cross ratios. The result can be expressed in terms of multiple Goncharov polylogarithms. We also employ a more restricted class of "hexagon functions" which have the correct branch cuts and certain other restrictions on their symbols. We classify all the hexagon functions through transcendental weight five, using the coproduct for their Hopf algebra iteratively, which amounts to a set of firstorder differential equations. The threeloop remainder function is a particular weightsix hexagon function, whose symbol was determined previously. The differential equations can be integrated numerically for generic values of the cross ratios, or analytically in certain kinematics limits, including the nearcollinear and multiRegge limits. These limits allow us to impose constraints from the operator product expansion and multiRegge factorization directly at the function level, and thereby to fix uniquely a set of Riemannzetavalued constants that could not be fixed at the level of the symbol. The nearcollinear limits agree precisely with recent predictions by Basso, Sever and Vieira based on integrability. The multiRegge limits agree with the factorization formula of Fadin and Lipatov, and determine three constants entering the impact factor at this order. We plot the threeloop remainder function for various slices of the Euclidean region of positive cross ratios, and compare it to the twoloop one. For large ranges of the cross ratios, the ratio of the threeloop to the twoloop remainder function is relatively constant, and close to 7.Journal of High Energy Physics 08/2013; 2013(12). · 5.62 Impact Factor  [Show abstract] [Hide abstract]
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.04/2013;  [Show abstract] [Hide abstract]
ABSTRACT: The connection of maximally supersymmetric YangMills theory to the (2,0) theory in six dimensions has raised the possibility that it might be perturbatively ultraviolet finite in five dimensions. We test this hypothesis by computing the coefficient of the first potential ultraviolet divergence of planar (large N_c) maximally supersymmetric YangMills theory in D = 5, which occurs at six loops. We show that the coefficient is nonvanishing. Furthermore, the numerical value of the divergence falls very close to an approximate exponential formula based on the coefficients of the divergences through five loops. This formula predicts the approximate values of the ultraviolet divergence at loop orders L > 6 in the critical dimension D = 4 + 6/L. To obtain the sixloop divergence we first construct the planar sixloop fourpoint amplitude integrand using generalized unitarity. The ultraviolet divergence follows from a set of vacuum integrals, which are obtained by expanding the integrand in the external momenta. The vacuum integrals are integrated via sector decomposition, using a modified version of the FIESTA program.Physical Review D 10/2012; 87(2):025018. · 4.69 Impact Factor 
Article: Colorkinematics duality and doublecopy construction for amplitudes from higherdimension operators
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ABSTRACT: We investigate colorkinematics duality for gaugetheory amplitudes produced by the pure nonabelian YangMills action deformed by higherdimension operators. For the operator denoted by F^3, the product of three field strengths, the existence of colorkinematic dual representations follows from stringtheory monodromy relations. We provide explicit dual representations, and show how the doublecopy construction of gravity amplitudes based on them is consistent with the KawaiLewellenTye relations. It leads to the amplitudes produced by Einstein gravity coupled to a dilaton field phi, and deformed by operators of the form phi R^2 and R^3. For operators with higher dimensions than F^3, such as F^4type operators appearing at the next order in the lowenergy expansion of bosonic and superstring theory, the situation is more complex. The color structure of some of the F^4 operators is incompatible with a simple colorkinematics duality based on structure constants f^{abc}, but even the colorcompatible F^4 operators do not admit the duality. In contrast, the next term in the alphaprime expansion of the superstring effective action  a particular linear combination of D^2 F^4 and F^5type operators  does admit the duality, at least for amplitudes with up to six external gluons.Journal of High Energy Physics 08/2012; · 5.62 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We argue that the natural functions for describing the multiRegge limit of sixgluon scattering in planar N=4 super YangMills theory are the singlevalued harmonic polylogarithmic functions introduced by Brown. These functions depend on a single complex variable and its conjugate, (w,w*). Using these functions, and formulas due to Fadin, Lipatov and Prygarin, we determine the sixgluon MHV remainder function in the leadinglogarithmic approximation (LLA) in this limit through ten loops, and the nexttoLLA (NLLA) terms through nine loops. In separate work, we have determined the symbol of the fourloop remainder function for general kinematics, up to 113 constants. Taking its multiRegge limit and matching to our fourloop LLA and NLLA results, we fix all but one of the constants that survive in this limit. The multiRegge limit factorizes in the variables (\nu,n) which are related to (w,w*) by a FourierMellin transform. We can transform the singlevalued harmonic polylogarithms to functions of (\nu,n) that incorporate harmonic sums, systematically through transcendental weight six. Combining this information with the fourloop results, we determine the eigenvalues of the BFKL kernel in the adjoint representation to NNLLA accuracy, and the MHV product of impact factors to NNNLLA accuracy, up to constants representing beyondthesymbol terms and the one symbollevel constant. Remarkably, only derivatives of the polygamma function enter these results. Finally, the LLA approximation to the sixgluon NMHV amplitude is evaluated through ten loops.Journal of High Energy Physics 07/2012; 2012(10). · 5.62 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We extend our investigation of backgrounds to new physics signals, following CMS's datadriven search for supersymmetry at the LHC. The aim is to use different sets of cuts in gamma + 3jet production to predict the irreducible Z + 3jet background (with the Z boson decaying to neutrinos) to searches with missing transverse energy + 3jet signal topologies. We compute ratios of Z + 3jet to gamma + 3jet production cross sections and kinematic distributions at nexttoleading order (NLO) in alpha_s. We compare these ratios with those obtained using a parton shower matched to leadingorder matrix elements (ME+PS). This study extends our previous work [arXiv:1106.1423 [hepph]] on the Z + 2jet to gamma + 2jet ratio. We find excellent agreement with the ratio determined from the earlier NLO results involving two instead of three jets, and agreement to within 10% between the NLO and ME+PS results for the ratios. We also examine the possibility of large QCD logarithms in these processes. Ratios of Z + njet to gamma + njet cross sections are plausibly less sensitive to such corrections than the cross sections themselves. Their effect on estimates of Z + 3jet to gamma + 3jet ratios can be assessed experimentally by measuring the gamma + 3jet to gamma + 2jet production ratio in search regions. We partially address the question of potentially large electroweak logarithms by computing the realemission part of the electroweak corrections to the ratio using ME+PS, and find that it is 1% or less. Our estimate of the remaining theoretical uncertainties in the Z to gamma ratio is in agreement with our earlier study.Physical Review D 06/2012; · 4.69 Impact Factor  Scientific American 05/2012; 306(5):3441. · 1.48 Impact Factor
Publication Stats
4k  Citations  
229.19  Total Impact Points  
Top Journals
Institutions

1994–2013

Stanford University
 SLAC National Accelerator Laboratory
Palo Alto, California, United States


2006–2012

University of California, Los Angeles
 Department of Physics and Astronomy
Los Angeles, CA, United States 
Stony Brook University
 Institute for Theoretical Physics (C.N. Yang)
Stony Brook, NY, United States


2009–2011

Massachusetts Institute of Technology
 Center for Theoretical Physics
Cambridge, MA, United States 
Max Planck Institute for Gravitational Physics (AlbertEinsteinInstitute)
Potsdam, Brandenburg, Germany


1993–2011

CERN
 Physics Department (PH)
Genève, Geneva, Switzerland


2002

Michigan State University
 Department of Physics and Astronomy
East Lansing, MI, United States


1996

CSU Mentor
Long Beach, California, United States
