A
bstract
I present a novel Four-Dimensional Regularization/Renormalization approach (FDR) to ultraviolet divergences in field theories which can be interpreted as a natural separation between ...physical and non physical degrees of freedom. Based on the observation that some infinities can be reabsorbed into the vacuum expectation value of the fields, rather than into the parameters of the Lagrangian, a new type of four-dimensional loop integral is introduced (the FDR integral) which is independent of any UV regulator and respects all properties required by gauge invariance. FDR reproduces the correct ABJ anomaly and no change in the definition of γ
5
is needed. With FDR the possibility is open for an approach to UV infinities in which the renormalization program is substituted by a simple reinterpretation of the appearing loop integrals as FDR ones, leading to important consequences in the context of non-renormalizable field theories. Finally, I show how FDR can also be used to regularize infrared and collinear divergences.
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We describe how NNLO final state quark-pair corrections are computed in FDR by directly enforcing gauge invariance and unitarity in the definition of the regularized divergent integrals. We give ...details of our approach and show how virtual and real contributions can be merged together without relying, explicitly or implicitly, on dimensional regularization. As an example, we recompute the
H
→
b
b
¯
+
jets
and
γ
∗
→
jets
inclusive rates at the NNLO accuracy in the large
N
F
limit of QCD. This demonstrates, for the first time, that physical results with intermediate infrared singularities can be obtained at NNLO using a fully four-dimensional procedure.
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We give an introduction to several regularization schemes that deal with ultraviolet and infrared singularities appearing in higher-order computations in quantum field theories. Comparing the ...computation of simple quantities in the various schemes, we point out similarities and differences between them.
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We present the calculation of scalar and pseudoscalar Higgs production in association with a top–antitop pair to the next-to-leading order (NLO) accuracy in QCD, interfaced with parton showers ...according to the MC@NLO formalism. We apply our results to the cases of light and very light Higgs boson production at the LHC, giving results for total rates as well as for sample differential distributions, relevant to the Higgs, to the top quarks, and to their decay products. This work constitutes the first phenomenological application of aMC@NLO, a fully automated approach to complete event generation at NLO in QCD.
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Based on the OPP technique and the HELAC framework, HELAC-1LOOP is a program that is capable of numerically evaluating QCD virtual corrections to scattering amplitudes. A detailed presentation of the ...algorithm is given, along with instructions to run the code and benchmark results. The program is part of the HELAC-NLO framework that allows for a complete evaluation of QCD NLO corrections.
Program title:HELAC-1LOOP
Catalogue identifier: AEOC_v1_0
Program summary URL:http://cpc.cs.qub.ac.uk/summaries/AEOC_v1_0.html
Program obtainable from: CPC Program Library, Queen’s University, Belfast, N. Ireland
Licensing provisions: Standard CPC licence, http://cpc.cs.qub.ac.uk/licence/licence.html
No. of lines in distributed program, including test data, etc.: 290945
No. of bytes in distributed program, including test data, etc.: 3013326
Distribution format: tar.gz
Programming language: Fortran (gfortran(http://gcc.gnu.org/fortran/), lahey95 (http://www.lahey.com), ifort3(http://software.intel.com)).
Computer: Any.
Operating system: Linux, Unix, Mac OS.
Classification: 11.1.
Nature of problem:
The evaluation of virtual one-loop amplitudes for multi-particle scattering is a long-standing problem 1. In recent years the OPP reduction technique 2 opened the road for a fully numerical approach based on the evaluation of the one-loop amplitude for well-defined values of the loop momentum.
Solution method:
By using HELAC 3–5 and CutTools 6, HELAC-1LOOP is capable of evaluating QCD virtual corrections 7. The one-loop n-particle amplitudes are constructed as part of the n+2 tree-order ones, by using the basic recursive algorithm used in HELAC. A Les Houches Event (LHE) file is produced, combining the complete information from tree-order and virtual one-loop contributions. In conjunction with real corrections, obtained with the use of HELAC-DIPOLES 8, the full NLO corrections can be computed. The program has been successfully used in many applications.
Running time:
Depending on the number of particles and generated events from seconds to days.
References:
1R.K. Ellis, Z. Kunszt, K. Melnikov and G. Zanderighi, arXiv:1105.4319hepph.2G. Ossola, C. G. Papadopoulos and R. Pittau, Nucl. Phys. B 763 (2007) 147 arXiv:hep-ph/0609007.3A. Kanaki and C. G. Papadopoulos, Comput. Phys. Commun. 132 (2000) 306 arXiv:hep-ph/0002082.4C. G. Papadopoulos, Comput. Phys. Commun. 137 (2001) 247 arXiv:hepph/ 0007335.5A. Cafarella, C. G. Papadopoulos and M. Worek, Comput. Phys. Commun. 180 (2009) 1941 arXiv:0710.2427 hep-ph.6G. Ossola, C. G. Papadopoulos and R. Pittau, JHEP 0803 (2008) 042 arXiv:0711.3596 hep-ph.7A. van Hameren, C. G. Papadopoulos and R. Pittau, JHEP 0909, 106 (2009) arXiv:0903.4665 hep-ph.8M. Czakon, C. G. Papadopoulos and M. Worek, JHEP 0908, 085 (2009) arXiv:0905.0883 hep-ph.
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We highlight the progress, current status, and open challenges of QCD-driven physics, in theory and in experiment. We discuss how the strong interaction is intimately connected to a broad sweep of ...physical problems, in settings ranging from astrophysics and cosmology to strongly coupled, complex systems in particle and condensed-matter physics, as well as to searches for physics beyond the Standard Model. We also discuss how success in describing the strong interaction impacts other fields, and, in turn, how such subjects can impact studies of the strong interaction. In the course of the work we offer a perspective on the many research streams which flow into and out of QCD, as well as a vision for future developments.
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A
bstract
When using dimensional regularization/reduction the
∊
-dimensional numerator of the 1-loop Feynman diagrams gives rise to rational contributions. I list the set of fundamental rules that ...allow the extraction of such terms at the integrand level in any theory containing scalars, vectors and fermions, such as the electroweak standard model, QCD and SUSY.
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I present a new and reliable method to test the numerical accuracy of NLO calculations based on modern OPP/Generalized Unitarity techniques. A convenient solution to
rescue most of the detected ...numerically inaccurate points is also proposed.
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