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Today’s algorithm for computation of loop corrections Dim. reg. Graph generation QGRAF, GRACE, FeynArts Reduction of integrals IBP id., Tensor red. Evaluation.

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Presentation on theme: "Today’s algorithm for computation of loop corrections Dim. reg. Graph generation QGRAF, GRACE, FeynArts Reduction of integrals IBP id., Tensor red. Evaluation."— Presentation transcript:

1 Today’s algorithm for computation of loop corrections Dim. reg. Graph generation QGRAF, GRACE, FeynArts Reduction of integrals IBP id., Tensor red. Evaluation of Master integrals Diff. eq., Mellin-Barnes, sector decomp. Lots of mathematics

2 Y. Sumino (Tohoku Univ.) Reduction of loop integrals to master integrals

3 Loop integrals in standard form Express each diagram in terms of standard integrals 1 loop 2 loop 3 loop Each can be represented by a lattice site in N-dim. space NB: is negative, when representing a numerator. e.g. A diagram for QCD potential

4 Integration-by-parts (IBP) Identities In dim. reg. Ex. at 1-loop: Chetyrkin, Tkachov

5 O (3-loop) 21-dim. space Reduction by Laporta algorithm

6 O (3-loop) 21-dim. space Reduction by Laporta algorithm

7 O (3-loop) 21-dim. space Reduction by Laporta algorithm

8 O (3-loop) 21-dim. space Reduction by Laporta algorithm

9 O (3-loop) 21-dim. space Reduction by Laporta algorithm

10 O (3-loop) 21-dim. space Reduction by Laporta algorithm

11 O (3-loop) 21-dim. space Reduction by Laporta algorithm

12 (3-loop) 21-dim. space O Reduction by Laporta algorithm

13 O (3-loop) 21-dim. space Reduction by Laporta algorithm

14 O (3-loop) 21-dim. space Master integrals Reduction by Laporta algorithm

15 O Evolution in 12-dim. subspace Out of only 12 of them are linearly independent. An improvement

16 Linearly dependent propagator denominators 1 loop case: 4 master integrals (well known) Use to reduce the number of D i ’s.

17 In the case of QCD potential 1 loop: 1 master integral 2 loop: 5 master integrals 3 loop: 40 master integrals

18 More about implementation of Laporta alg. cf. JHEP07(2004)046 IBP ids = A huge system of linear eqs. Laporta alg. = Reduction of complicated loop integrals to a small set of simpler integrals via Gauss elimination method. 1.Specify complexity of an integral a.More D i ’s b.More positive powers of D i ’s c.More negative powers of D i ’s 2.Rewrite complicated integrals by simpler ones iteratively. O simpler more complex

19 Example of Step 2. Substitute to (2): Substitute to (3): Pick one identity. Apply all known reduction relations. Solve the obtained eq for the most comlex variable. Obtain a new reduction relation.

20 Generalized unitarity (e.g. BlackHat, Njet,...) [Bern, Dixon, Dunbar, Kosower, ; Ellis Giele Kunst Melnikov 2008; Badger...] Integrand reduction (OPP method) (e.g. MadLoop [Ossola, Papadopoulos, Pittau 2006; del Aguila, Pittau 2004; Mastrolia, Ossola, Reiter,Tramontano 2010;...] Tensor reduction (e.g. Golem, Openloops) [Passarino, Veltman 1979; Denner, Dittmaier 2005; Binoth Guillet, Heinrich, Pilon, Reiter 2008;Cascioli, Maierhofer, Pozzorini 2011;...] New One-loop Computation Technologies (mainly for LHC)

21 Improvement 2. O (1) Assign a numerical value to temporarily and complete reduction. (2) Identify the necessary IBP identities and reorder them; Then reprocess the reduction with general. Many inactive IBP id’s are generated and solved in Laporta algorithm. Manageable by a contemporary desktop/laptop PC


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