The package TopoID and its applications to Higgs physics

Transcription

1 The package TopoID and its applications to Higgs physics Jens Hoff (DESY, KIT) Theory Seminar, University of Zurich 3rd of November, 2015

2 1 TopoID Polynomial ordering Topology classification Relations among Feynman integrals Topology merging Partial fractioning 2 N 3 LO Higgs production: qq -channel Optical theorem and Cutkosky s rules Calculation Results 3 NLO and NNLO Higgs pair production Differential factorization Soft-virtual approximation Asymptotic expansion Calculation Results 2 / 38

3 TopoID Topology IDentification ---> _ \ >--- \ \ \ + / \ _ \ / \ \ \ \ / /\ \ \ \ / /\ \ / / +--->--- \ \ \/ / _/ / \ \/ / _/ / / \ _ \ / / \ / _ / + \ / \ ---> _ >--- Idea: Generic, process independent Mathematica package Feynman diagrams reduced result (Laporta not included) Topology construction (identification, minimal sets; partial fractioning; factorization,... ) Handle properties (completeness, linear dependence; subtopologies, scalelessness, symmetries; graphs, unitarity cuts,... ) FORM code generator (diagram mapping, topology processing, integral reduction,... ) Master integral identification (base changes, non-trivial relations,... ) 3 / 38

4 TopoID Polynomial ordering Bring the polynomial P with m terms into unique form ˆP by renaming the n variables {x j}: [Pak; 12] 1 Convert P into m (n+1) matrix M (0) (row: term, 1st column: coefficient, remaining columns: powers of {x j }) 2 Start with considering the above M (0) and the 2nd column (k = 1) 3 Compute for all considered matrices M (k),σ all transpositions of columns k and k + 1,... (and collect perputations σ) 4 Sort rows in each matrix lexicographically by the first k columns 5 Extract in columns k the lexicographically largest vector 6 Keep only matrices with this maximal vector; If k < n 1: k k + 1 and goto Step 3 7 Each remaining matrix encodes the same unique ˆP σ and a permutation of variables σ 4 / 38

5 TopoID Polynomial ordering 1 Convert P into m (n+1) matrix M (0) (row: term, 1st column: coefficient, remaining columns: powers of {x j }) 2 Start with considering the above M (0) and the 2nd column (k = 1) P = x x 1x 2 + x2 2 + x3 2 M (0) = (Step 1) S (1) = { M (0)(123) = M (0)}, k = 1 (Step 2) 4 / 38

6 TopoID Polynomial ordering 3 Compute for all considered matrices M (k),σ all transpositions of columns k and k + 1,... (and collect perputations σ) S (1) : M (1)(123) = , M (1)(213) = , M (1)(321) = (Step 3-1) 4 / 38

7 TopoID Polynomial ordering 4 Sort rows in each matrix lexicographically by the first k columns S (1) : M (1)(123) = , M (1)(213) = , M (1)(321) = (Step 4-1) 4 / 38

8 TopoID Polynomial ordering 5 Extract in columns k the lexicographically largest vector 6 Keep only matrices with this maximal vector; If k < n 1: k k + 1 and goto Step 3 0 ˆM (1) 0 = 2 1 (Step 5-1) S (2) = { M (1)(123), M (1)(213)}, k = 2 (Step 6-1) 4 / 38

9 TopoID Polynomial ordering 3 Compute for all considered matrices M (k),σ all transpositions of columns k and k + 1,... (and collect perputations σ) S (2) : M (2)(123) = , M (2)(132) = , M (2)(213) = , M (2)(231) = (Step 3-2) 4 / 38

10 TopoID Polynomial ordering 4 Sort rows in each matrix lexicographically by the first k columns S (2) : M (2)(123) = , M (2)(132) = , M (2)(213) = , M (2)(231) = (Step 4-2) 4 / 38

11 TopoID Polynomial ordering 5 Extract in columns k the lexicographically largest vector 6 Keep only matrices with this maximal vector; If k < n 1: k k + 1 and goto Step 3 0 ˆM (2) 2 = 0 1 (Step 5-2) S (2) = { M (2)(123), M (2)(213)} (Step 6-2) 4 / 38

12 TopoID Polynomial ordering 7 Each remaining matrix encodes the same unique ˆP σ and a permutation of variables σ ˆP = P = x x x x 1x 2, ˆσ = {(123),(213)} (Step 7) 4 / 38

13 TopoID Polynomial ordering ˆP = P = x x x x 1x 2, ˆσ = {(123),(213)} (Step 7) P already in canonical form; two permutations {(123),(213)} (213) denotes (x 1, x 2, x 3) (x 2, x 1, x 3); symmetry of P under x 1 x 2 Application to Feynman integrals Use U + F from the Feynman representation Unique identifier Û + ˆF; independent of momentum space representation Returned permutations: symmetries of Feynman integrals Many useful applications 4 / 38

14 TopoID Topology classification Minimal set for NNLO Higgs production: Note: Sufficient for all diagrams 5 / 38

15 TopoID Relations among Feynman integrals Non-trivial relation for NNLO Higgs production: = + (...) + (...) Cross-topology relations; not from Laporta reduction Simplify calculation Usefull cross-checks 6 / 38

16 TopoID Topology classification Minimal set for NNLO Higgs production: 7 / 38

17 TopoID Topology merging 3-loop massless propagators: q 1 = k 1, q 2 = p k 1, q 3 = k 2, q 4 = p k 1 k 2, q 5 = k 3, q 6 = p k 1 k 2 k 3, q 7 = k 1 + k 2 + k 3, q 8 = k 1 + k 2, q 9 = k 1 + k 3. q 8 q 1 q 7 P 3 (a 1,..., a 8, 0) = p q 3 q p 5 q 2 q 4 q 4 q 6 P 3 (a 1, 0, a 3,..., a 9 ) = p q 5 p q 1 q 8 q9 q 7 q 1 q 7 P 3 (a 1,..., a 7, 0, a 9 ) = p p q 3 q 5 q 3 q 9 q 6 q 2 q 4 q 6 1 external, 3 internal momenta 9 scalar products 3 incomplete topologies with 8 lines Identify greatest common subtopology Find supertopology with these 3 different graphs as subtopologies 8 / 38

18 TopoID Partial fractioning Partial fractioning for NLO Higgs production: p 1 p 2 d2 p 2 d 3 d 4 d 1 p1 d d 2 2 d 3 d 4 d d 3 d 4 4 d 1 d 1 Via Gröbner basis: d 2 d 3 d 1 d 4 m 2 H + s + d 1 + d 2 d 3 d 3 ( ) 1 m 2 H d 4 d + s + d 1 + d 2 d 4 4 d 2 ( ) 1 m 2 H d 3 d 4 d 3 d s d 1 + d 3 + d 4 4 d 1 ( ) 1 m 2 H d 2 d 3 d 4 d 2 d 3 d s d 2 + d 3 + d ) (d 1 + d 2 d 3 d 4 ) d 1 d 2 d 3 d 4 (m 2H s d 1 d 2 d 3 d 4 9 / 38

19 N 3 LO Higgs production: qq -channel Motivation and introduction Higgs production at the LHC dominated by gluon fusion After [Anastasiou, Duhr, Dulat, Furlan, Gehrmann, Herzog, Mistlberger; 14, 15]: 2.2% corrections, 3% uncertainty at N 3 LO Cross-check Loop-induced process, dominated by top quark mass Effective field theory with top quark integrated out: L Y,eff = H v C1O1 and O1 = 1 4 Ga µνg a,µν M t M t s, mh C 1 s, mh Reduced numbers of scales and loops: single dimensionless variable x = m 2 H/s (soft: x 1) Finite matching coefficient C 1 needed to 4-loop [Chetyrkin, Kniehl, Steinhauser; 98] [Schröder, Steinhauser; 06] [Chetyrkin, Kühn, Sturm; 06] 10 / 38

20 N 3 LO Higgs production: qq -channel Status LO calculation (exact) [Ellis et al.; 76] [Wilczek et at.; 77] [Georgi et al.; 78] [Rizzo; 80] NLO (exact) [Dawson; 91] [Djouadi, Spira, Zerwas; 91] NNLO (EFT) soft expansion to 3rd order valid to O(1%) [Harlander, Kilgore; 02] [Anastasiou, Melnikov; 02] [Ravindran, Smith, van Neerven; 03] NNLO O ( 1/M 2 t ) corrections NNLO +1% [Pak, Rogal, Steinhauser; 09-11] [Harlander, Mantler, Marzani, Ozeren; 09-10] N 3 LO IR counterterms 3-loop splitting functions [Moch, Vermaseren, Vogt; 02] NNLO master integrals to higher orders in ǫ [Pak, Rogal, Steinhauser; 11] [Anastasiou, Bühler, Duhr, Herzog; 12] Cross sections and convolution integrals [Höschele, JH, Pak, Steinhauser, Ueda; 12, 13] [Bühler, Lazopoulos; 13] N 3 LO scale variation O(2% 8%) [Bühler, Lazopoulos; 13] 11 / 38

21 N 3 LO Higgs production: qq -channel Status N 3 LO corrections VV 2 and V 3 3-loop gluon form factor [Baikov, Chetyrkin, Smirnov 2, Steinhauser; 09] [Gehrmann, Glover, Huber, Ikizlerli, Studerus; 09] VRV exact in x [Anastasiou, Duhr, Dulat, Herzog, Mistlberger; 13] [Kilgore; 14] V 2 R exact in x [Dulat, Mistlberger; 14] [Duhr, Gehrmann, Jaquier; 14] VR 2 expansion in x 1 [Anastasiou, Duhr, Dulat, Furlan, Gehrmann; 14] [Li, von Manteuffel, Schabinger, Zhu; 14], [Anastasiou, Duhr, Dulat, Furlan, Herzog, Mistlberger; 15] R 3 expansion in x 1 [Anastasiou, Duhr, Dulat, Mistlberger; 13] 37 terms in the x 1 expansion [Anastasiou, Duhr, Dulat, Furlan, Gehrmann, Herzog, Mistlberger; 14, 15] Sufficient for phenomenology VV 2 V 3 qq -channel exact in x (VR 2, R 3 ) [Höschele, JH, Ueda; 14] [Anzai, Hasselhuhn, Höschele, JH, Kilgore, Steinhauser, Ueda; 15] Independent cross-check Many different resummations [Catani et al.] [Moch et al.] [Ahrens et al.] [de Florian et al.] [Ball et al.] [... ] 12 / 38

22 N 3 LO Higgs production: qq -channel Status N 3 LO corrections VV 2 and V 3 3-loop gluon form factor [Baikov, Chetyrkin, Smirnov 2, Steinhauser; 09] [Gehrmann, Glover, Huber, Ikizlerli, Studerus; 09] VRV exact in x [Anastasiou, Duhr, Dulat, Herzog, Mistlberger; 13] [Kilgore; 14] V 2 R exact in x [Dulat, Mistlberger; 14] [Duhr, Gehrmann, Jaquier; 14] VR 2 expansion in x 1 [Anastasiou, Duhr, Dulat, Furlan, Gehrmann; 14] [Li, von Manteuffel, Schabinger, Zhu; 14], [Anastasiou, Duhr, Dulat, Furlan, Herzog, Mistlberger; 15] R 3 expansion in x 1 [Anastasiou, Duhr, Dulat, Mistlberger; 13] 37 terms in the x 1 expansion [Anastasiou, Duhr, Dulat, Furlan, Gehrmann, Herzog, Mistlberger; 14, 15] Sufficient for phenomenology qq -channel exact in x (VR 2, R 3 ) [Höschele, JH, Ueda; 14] [Anzai, Hasselhuhn, Höschele, JH, Kilgore, Steinhauser, Ueda; 15] Independent cross-check Many different resummations [Catani et al.] [Moch et al.] [Ahrens et al.] [de Florian et al.] [Ball et al.] [... ] VRV V 2 R 12 / 38

23 N 3 LO Higgs production: qq -channel Status N 3 LO corrections VV 2 and V 3 3-loop gluon form factor [Baikov, Chetyrkin, Smirnov 2, Steinhauser; 09] [Gehrmann, Glover, Huber, Ikizlerli, Studerus; 09] VRV exact in x [Anastasiou, Duhr, Dulat, Herzog, Mistlberger; 13] [Kilgore; 14] V 2 R exact in x [Dulat, Mistlberger; 14] [Duhr, Gehrmann, Jaquier; 14] VR 2 expansion in x 1 [Anastasiou, Duhr, Dulat, Furlan, Gehrmann; 14] [Li, von Manteuffel, Schabinger, Zhu; 14], [Anastasiou, Duhr, Dulat, Furlan, Herzog, Mistlberger; 15] R 3 expansion in x 1 [Anastasiou, Duhr, Dulat, Mistlberger; 13] 37 terms in the x 1 expansion [Anastasiou, Duhr, Dulat, Furlan, Gehrmann, Herzog, Mistlberger; 14, 15] Sufficient for phenomenology qq -channel exact in x (VR 2, R 3 ) [Höschele, JH, Ueda; 14] [Anzai, Hasselhuhn, Höschele, JH, Kilgore, Steinhauser, Ueda; 15] Independent cross-check Many different resummations [Catani et al.] [Moch et al.] [Ahrens et al.] [de Florian et al.] [Ball et al.] [... ] VR 2 R 3 12 / 38

24 N 3 LO Higgs production: qq -channel Generalities 1 Reduction of integrals with full x-dependence Only contributing cuts 2 Construct differential equations for master integrals Canonical basis (in general: coupled system) 3 Soft limit x 1 as boundary condition Leading term using Mellin-Barnes representation Canonical differential equations: d dx mi(x, ǫ) = ǫ Aij(x) mj(x, ǫ) with d = 4 2 ǫ [Henn et al.; ] ǫ- and x-dependence factorize Solve order-by-order in ǫ A ij: alphabet of appearing functions E.g. Harmonic Polylogarithms (HPLs): H w (x) = x 0 dx f w1 ( x ) H wn 1 ( x ) and f 0 (x) = 1 x, f ±1(x) = 1 1 x 13 / 38

25 Optical theorem and Cutkosky s rules Higher-order corrections: Virtual More loop integrations Real Additional final state particles (different phase spaces) Optical theorem: σ(i f) f dπ f M(i f) 2 Disc M(i i) Cutkosky s rules: Consider only valid diagrammatic cuts for Disc Two connectivity components Separate in- and outgoing momenta (s-channel) Contribute to the process (1 or 2 Higgs, 0 to 3 parton lines) 14 / 38

26 Optical theorem and Cutkosky s rules E.g. to NNLO: dπ dπ dπ = / 38

27 Optical theorem and Cutkosky s rules Optical theorem: σ(i f) f dπ f M(i f) 2 Disc M(i i) Pros Cons Forward scattering simplified kinematics Common treatment of loop and phase space integrals Calculation of Disc only for master integrals More loops and diagrams Only total cross section (naively) Approach first used in [Anastasiou, Melnikov; 02] 16 / 38

28 Optical theorem and Cutkosky s rules Handling cut-diagrams: Filter diagrams Fast graph-based algorithm build into Perl script to process QGRAF output N 3 LO Higgs: NNLO Higgs pair (SV): Assist reduction 1 2 Build also into TopoID pass to Laporta reduction Typically: only O(10%) of subtopologies (or relations) 17 / 38

29 N 3 LO Higgs production: qq -channel Calculation: toolchain Reduction 1 Generate Feynman diagrams QGRAF [Nogueira; 93] 2 Select diagrams with specific cuts filter [JH, Pak; (unpublished)] 3 Map diagrams to topologies ( graph information) exp [Harlander, Seidensticker, Steinhauser; 98] reg [Pak; (unpublished)] 4 Reduction to scalar integrals ( generic topologies) FORM [Kuipers, Ueda, Vermaseren, Vollinga; 13] 5 Reduction to master integrals ( basic topologies) rows [JH, Pak; (unpublished)] FIRE [Smirnov] 6 Minimal basis of master integrals TopoID [JH, Pak; (unpublished)] 220 diagrams, e.g. 18 / 38

30 N 3 LO Higgs production: qq -channel Calculation: 17 topologies with 3- and 4-particle cuts 19 / 38

31 N 3 LO Higgs production: qq -channel Calculation: e.g. sea snake topology = { 1} 20 / 38

32 N 3 LO Higgs production: qq -channel Results: functions beyond HPLs Laporta: 332 master integrals; TopoID: 108 and cancellation of ξ Some Feynman integrals generate functions with alphabet beyond HPLs: { } 1, 1, 1, 1, 1 x 1 x 1+x 1+4 x x 1+4 x Traced back to common subtopology: Numerical implementation in Mathematica: { ( )} 1 Change alphabet to x, 1 1 x, 1 1+x, x, 1 1 x 1+4 x 1 Use series expansions x 0 and x 1 10 digits in 1 second Note: x (1 x) /x 2 Cyclotomic Polylogarithms Representation as Goncharov Polylogarithms (linear denominators) { } Letters of 6th roots of unity; here only: 1 x, 1 1 x, 1 ( 1) 1 3 x 21 / 38

33 NLO and NNLO Higgs pair production Motivation Higgs Potential in the Standard Model: V(H) = 1 2 m2 HH 2 + λvh λh4, λ SM = m2 H 2v , v: Higgs vev. Verify mechanism of spontaneous symmetry breaking in the SM Measure the Higgs self-coupling sensitive process Σ LO gg HH fb a b c s GeV 2 (a) (b) + (c) / 38

34 NLO and NNLO Higgs pair production Theory status Prospects for the 14 TeV: b bγγ-channel, 600 fb 1 : λ 0 [Baur, Plehn, Rainwater; 04] b bγγ-, b bτ + τ -channels: promising ; b bw + W -channel: not promising [Baglio, Djouadi, Gröber, Mühlleitner, Quevillon, Spira; 13] 600 fb 1 : λ > 0; 3000 fb 1 : λ +30% 20% (ratio with Higgs cross section) [Goertz, Papaefstathiou, Yang, Zurita; 13] And many others, e.g.: [Dolan, Englert, Spannowsky; 12] [Papaefstathiou, Yang, Zurita; 13] [Barr, Dolan, Englert, Spannowsky; 13] [Barger, Everett, Jackson, Shaughnessy; 14] [Englert, Krauss, Spannowsky, Thompson; 15] [... ] Until now: Higgs pair production not observed in b bb b- and b bγγ-channels (as expected in the SM) [ATLAS; 15] [CMS; 15] Wait for HL-LHC 23 / 38

35 NLO and NNLO Higgs pair production Theory status Known since long: LO result with exact M t dependence [Glover, van der Bij; 88] [Plehn, Spira, Zerwas; 98] NLO result in M t limit [Dawson, Dittmaier, Spira; 98] σ H 20 LO fb+ 20 NLO,Mt fb for s H = 14 TeV, µ = 2m H More recently: NLO + NNLL (M t ) NLO +20% [Shao, Li, Li, Wang; 13] NNLO w/ or w/o soft-virtual approx. (M t ) NLO +20% [de Florian, Mazzitelli; 13] O ( 1/M 8 t ) corrections at NLO NLO +10% [Grigo, JH, Melnikov, Steinhauser; 13] NLO real exact in M t, NLO virt. for M t NLO 10% [Maltoni, Vryonidou, Zaro; 14] Cross-check of virtual NNLO corrs.; NNLO matching coefficient for gghh-coupling NNLO +1% [Grigo, Melnikov, Steinhauser; 14] Improved O ( ) ( ) 1/Mt 12 NLO, O 1/M 4 t NNLO soft-virt. corrections [Grigo, JH, Steinhauser; 15 ] 24 / 38

36 NLO and NNLO Higgs pair production Generalities Operate on full-theory diagrams at NLO and NNLO Virt. corrs. in two independent calculations: amplitude (differential; 2-/3-loop) forward scattering (total; 4-/5-loop) Real corrs.: only via forward scattering at NLO Perform expansion for M t ; improve upon effective theory results for NLO [Dawson, Dittmaier, Spira; 98], NNLO [de Florian, Mazzitelli; 13] Laporta reduction to master integrals for the soft subdiagrams Remaining hard massive tadpoles via MATAD Master integrals as series around s = 2m H (not in this talk) 25 / 38

37 Differential factorization Factorization of the LO result exact in M t for: Total cross section σ (i) = (i) σ (0) with Differential cross section σ (i) = s exact = σ(0) exact σ exp (0) 4m 2 H (i) = σ(i) exp s 4m 2 H dq 2 σ (0) exp, σ (i) exp = ( dσ (0) exact dq 2 ) ( (0) ) dσ exp dq 2 dq 2 dσ (i) exp dq 2 N n=0 dσ (i) exp dq 2 c (i) n ρ n, ρ = m2 H M 2 t Cure the invalidity of the M t expansion for the large-q 2 region Virt. corrs. via amplitude: access to Q 2 -dependence δ ( s Q 2) Real corrs. via optical theorem (naively): only total cross section Use the soft-virtual approximation [de Florian, Mazzitelli; 12] 26 / 38

38 Soft-virtual approximation Split σ into its contributions (works also for dσ/dq 2 ): σ = σ virt+ren + σ real+split = finite = Σ div +Σ fin + Σ }{{ soft +Σ }}{{} hard =Σ SV =finite =Σ H =finite Σ div universal for color-less final state [de Florian, Mazzitelli; 12] Compute σ virt+ren as ρ-expansion Solve σ virt+ren = Σ div +Σ fin for Σ fin Σ div and Σ soft (soft coll. counterterms + soft real corrs.) exact σ LO (include M t effects) Q 2 dσ dq = 2 σlo zg(z) with σ (SV) = 1 z = Q2 s, dzσ LO (zs) G (SV) (z) with 1 δ G(z) = G SV(z)+G H (z) δ = 1 4m2 H s G (i) SV (z) constructed from σ(i) [de Florian, Mazzitelli; 12] [Grigo, JH, Steinhauser; 15] fin and σlo only 27 / 38

39 Asymptotic expansion Expand at integrand level for all contributing regions series expansion in analytic result Hierarchy: Mt 2 s, mh 2 series in ρ = mh/m 2 t 2 Effectively reduce number of loops and scales Here: regions correspond to subgraphs (in general more than one) Hard mass expansion: subgraphs must contain all heavy lines Example: NLO real with one region { M 2 t, m 2 H, s } { M 2 t } { m 2 H, s } { M 2 t } 28 / 38

40 Asymptotic expansion Expand at integrand level for all contributing regions series expansion in analytic result Hierarchy: Mt 2 s, mh 2 series in ρ = mh/m 2 t 2 Effectively reduce number of loops and scales Here: regions correspond to subgraphs (in general more than one) Hard mass expansion: subgraphs must contain all heavy lines Example: NLO virt. with two regions { M 2 t, m 2 H, s } { M 2 t } { m 2 H, s } { M 2 t } + { M 2 t } { m 2 H, s } { M 2 t } 28 / 38

41 NLO and NNLO Higgs pair production Calculation (via optical theorem) LO topology: Virt. NLO topologies: Real NLO topologies: 29 / 38

42 NLO and NNLO Higgs pair production Calculation (via optical theorem) Virt. NNLO topologies: Note: Different regions in asymptotic expansion different loop-orders Here: multiplied with 1- to 3-loop massive tadpoles 30 / 38

43 NLO and NNLO Higgs pair production Calculation (via optical theorem) Virt. and real LO-NLO master integrals: Virt. NNLO master integrals (in addition): 31 / 38

44 NLO and NNLO Higgs pair production Splitting in soft-virtual and real contributions at NLO Partonic NLO correction; total factorization δσ NLO [fb] SV+H SV H ρ 0 ρ 1 ρ 2 ρ 3 ρ 4 ρ 5 ρ s [GeV] Using µ = 2m H (also in the following) Different behavior for higher orders in ρ expansion: SV increasing H descreasing (flat for s 400 GeV) SV numerically dominant 32 / 38

45 NLO and NNLO Higgs pair production Total vs. differential factorization (DF) at NLO DF applied only to SV part; H treated via total factorization (i.e. identical) δσ NLO [fb] SV+H SV(DF)+H ρ 0 ρ 1 ρ 2 ρ 3 ρ 4 ρ 5 ρ s [GeV] Maxima of DF curves at lower s; smaller cross sections Improvement of convergence: difference of ρ 0 and corrections to ρ 6 (for s = 400 GeV): 0.25 fb vs fb (Partonic K-factor: behavior at top quark pair threshold not washed out) 33 / 38

46 NLO and NNLO Higgs pair production Hadronic cross section and K-factor Technical upper cut on s (good proxy to Q 2 ): σ H (s H, s cut) = 1 4m 2 H /s H dτ scut : total cross section for 14 TeV ( ) dlgg (τ) σ(τs H ) θ(s cut τs H ) dτ σ NLO H [fb] K NLO ρ 0 ρ 1 ρ 2 ρ 3 ρ 4 ρ 5 ρ scut [GeV] Spread of ρ-orders ±10% uncertainty of EFT at NLO due to M t 34 / 38

47 NLO and NNLO Higgs pair production Revisiting NLO Lessons from NLO for NNLO: SV approximation contructed for z 1; G SV (z) can be replaced by f(z) G SV (z) Splitting into SV and H not unique Tune f(z) at NLO such that σ Σ SV f(z) = z accurate to 2% Replace RGE logarithms ( s Q 2 in the soft limit): log ( µ 2 /s ) log ( µ 2 /Q 2) Discrepancy to [Maltoni, Vryonidou, Zaro; 14]: Real corrs.: treated exactly; Virt. corrs.: EFT result Claim: 10% correction at NLO But: Dominant positive shift from virtual 1/M t-corrections (c.f. backup slide) 35 / 38

48 NLO and NNLO Higgs pair production NNLO SV corrections δσ [fb] LO exact NLO z NNLO-SV ρ 0 ρ 1 ρ 2 EFT result plus ρ- and ρ 2 -terms Peaks at smaller s Same pattern of ρ-corrections s [GeV] 40 Conv. up to s cut 400 GeV σh [fb] LO NLO ρ 0 10 z NNLO-SV ρ 0 z NNLO-SV ρ 1 z NNLO-SV ρ scut [GeV] ρ- and ρ 2 -corrections: ±2.5% M t-uncertainty at NNLO: 5% (NNLO corrs. 20%) 36 / 38

49 NLO and NNLO Higgs pair production NNLO SV K-factor 5 NLO ρ 0 4 z NNLO-SV ρ 0 z NNLO-SV ρ 1 z NNLO-SV ρ 2 KH [fb] scut [GeV] Strong raise close to threshold steeper NNLO correction For total cross section: K NNLO H / 38

50 Conclusion TopoID: Generic, process independent Mathematica package for multiloop calculations; especially for many topologies Until now: two successful applications Works also for 5-loop propagators Publication planned for ACAT 2016 qq -channel in N 3 LO Higgs production: New iterated integrals beyond HPLs appear Agreement of leading logarithms with [Anastasiou, Duhr, Dulat, Furlan, Herzog, Mistlberger; 15] Full calculation underway... Higgs pair production: Real corrections at NLO via opt. theorem; employ SV approx. at NNLO Computed expansion to O ( ) ( ) 1/Mt 12 at NLO, O 1/M 4 t at NNLO Uncertainty of EFT results due to M t: 10% at NLO, 5% at NNLO Small- s behavior as benchmark for exact calculations 38 / 38

51 Backup: NLO and NNLO Higgs pair production Partonic NLO K-factor K NLO SV(DF)+H SV+H ρ 0 ρ 1 ρ 2 ρ 3 ρ 4 ρ 5 ρ s [GeV] Note: Behavior around top quark pair threshold not washed out 39 / 38

52 Backup: NLO and NNLO Higgs pair production Splitting into real and virtual corrections at NLO δσ NLO [fb] s [GeV] V+R R V ρ 0 ρ 1 ρ 2 ρ 3 ρ 4 ρ 5 ρ 6 Note: R and V separately divergent; only finite contributions shown 40 / 38

53 Backup: NLO and NNLO Higgs pair production Total vs. differential factorization without hard contributions at NLO δσ NLO [fb] SV SV (df) ρ 0 ρ 1 ρ 2 ρ 3 ρ 4 ρ 5 ρ s [GeV] 41 / 38

54 Backup: NLO and NNLO Higgs pair production Partonic NNLO cross section for different scales choices and f(z) δσ NNLO [fb] µ = 2m H µ = Q 2 NNLO-SV z NNLO-SV s [GeV] Note: f(z) = z (better proxy) leads to higher values 42 / 38