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 A034997 Number of generalized retarded functions in quantum field theory. 2
 2, 6, 32, 370, 11292, 1066044, 347326352, 419172756930, 1955230985997140 (list; graph; refs; listen; history; text; internal format)
 OFFSET 1,1 COMMENTS a(d) is the number of parts into which d-dimensional space (x_1,...,x_d) is split by a set of (2^d - 1) hyperplanes c_1 x_1 + c_2 x_2 + ... + c_d x_d =0 where c_j are 0 or +1 and we exclude the case with all c=0. Also, a(d) is the number of independent real-time Green functions of quantum field theory produced when analytically continuing from Euclidean time/energy (d+1 = number of energy/time variables). These are also known as "generalized retarded functions". The numbers up to d=6 were first produced by T. S. Evans using a Pascal program, strictly as upper bounds only. M. van Eijck wrote a C program using a direct enumeration of hyperplanes which confirmed these and produced the value for d=7. Kamiya et al. showed how to find these numbers and some associated polynomials using more sophisticated methods, giving results up to d=7. T. S. Evans added a(8) on Aug 01 2011 using an updated version of van Eijck's program, which took 7 days on a standard desktop computer. REFERENCES Björner, Anders. "Positive Sum Systems", in Bruno Benedetti, Emanuele Delucchi, and Luca Moci, editors, Combinatorial Methods in Topology and Algebra. Springer International Publishing, 2015. 157-171. M. van Eijck, Thermal Field Theory and Finite-Temperature Renormalisation Group, PhD thesis, Univ. Amsterdam, 4th Dec. 1995. LINKS Louis J. Billera, Sara C. Billey, and Vasu Tewari, Boolean product polynomials and Schur-positivity, arXiv:1806.02943 [math.CO], 2018. L. J. Billera, J. T. Moore, C. D. Moraites, Y. Wang and K. Williams, Maximal unbalanced families, arXiv preprint arXiv:1209.2309 [math.CO], 2012. - From N. J. A. Sloane, Dec 26 2012 Taylor Brysiewicz, Holger Eble, and Lukas Kühne, Enumerating chambers of hyperplane arrangements with symmetry, arXiv:2105.14542 [math.CO], 2021. Antoine Deza, Mingfei Hao, and Lionel Pournin, Sizing the White Whale, arXiv:2205.13309 [math.CO], 2022. Antoine Deza, George Manoussakis, and Shmuel Onn, Primitive Zonotopes, Discrete & Computational Geometry, 2017, p. 1-13. (See p. 5.) T. S. Evans, N-point finite temperature expectation values at real times, Nuclear Physics B 374 (1992) 340-370. T. S. Evans, What is being calculated with Thermal Field Theory?, arXiv:hep-ph/9404262, 1994-2011 and in "Particle Physics and Cosmology: Proceedings of the Ninth Lake Louise Winter School", World Scientific, 1995 (ISBN 9810221002). Samuel C. Gutekunst, Karola Mészáros, and T. Kyle Petersen, Root Cones and the Resonance Arrangement, arXiv:1903.06595 [math.CO], 2019. Lukas Kühne, The Universality of the Resonance Arrangement and its Betti Numbers, arXiv:2008.10553 [math.CO], 2020. H. Kamiya, A. Takemura and H. Terao, Ranking patterns of unfolding models of codimension one, Advances in Applied Mathematics 47 (2011) 379 - 400. Lars Kastner and Marta Panizzut, Hyperplane arrangements in polymake, arXiv:2003.13548 [math.CO], 2020. Zhengwei Liu, William Norledge, and Adrian Ocneanu, The adjoint braid arrangement as a combinatorial Lie algebra via the Steinmann relations, arXiv:1901.03243 [math.CO], 2019. William Norledge and Adrian Ocneanu, Hopf monoids, permutohedral tangent cones, and generalized retarded functions, arXiv:1911.11736 [math.CO], 2019. EXAMPLE a(1)=2 because the point x=0 splits the real line into two parts, the positive and negative reals. a(2)=6 because we can split two-dimensional space into 6 parts using lines x=0, y=0 and x+y=0. CROSSREFS Sequence in context: A056642 A001199 A232469 * A067735 A326901 A332537 Adjacent sequences: A034994 A034995 A034996 * A034998 A034999 A035000 KEYWORD nonn,more AUTHOR EXTENSIONS a(9) from Zachary Chroman, Feb 19 2021 STATUS approved

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Last modified December 10 02:09 EST 2022. Contains 358712 sequences. (Running on oeis4.)