J H E P 0 3 ( 2 0 1 7 ) 0 7 9 Published for SISSA by Springer Received: August 16, 2016 Revised: January 29, 2017 Accepted: March 7, 2017 Published: March 15, 2017 Extracting OPE coefficient of Konishi at four loops Vasco Goncalves ICTP South American Institute for Fundamental Research Instituto de Fisica Teorica, UNESP, Universidad Estadual Paulista, Rua Dr. Bento T. Ferraz 271, 01140-070, Sao Paulo, SP, Brasil E-mail: vasco.dfg@gmail.com Abstract: In this short note we compute the OPE coefficient of two 20′ operators and the Konishi operator. To this end, we use the OPE decomposition of a four point function of four 20′ operators and the method of asymptotic expansions to compute the leading term, in the OPE limit, of all integrals contributing to the four point function. Keywords: AdS-CFT Correspondence, Conformal Field Theory ArXiv ePrint: 1607.02195 Open Access, c© The Authors. Article funded by SCOAP3. doi:10.1007/JHEP03(2017)079 mailto:vasco.dfg@gmail.com https://arxiv.org/abs/1607.02195 http://dx.doi.org/10.1007/JHEP03(2017)079 J H E P 0 3 ( 2 0 1 7 ) 0 7 9 Contents 1 Introduction 1 2 Four point function and OPE limit 2 2.1 Asymptotic expansions 3 2.2 Konishi from OPE limit 5 3 Conclusions 6 A Master integrals 7 1 Introduction Correlation functions of local operators in a CFT are completely determined by dimensions of all operators and their OPE coefficients. Over the last years there has been a significant progress in computing the dimensions and OPE coefficients of local operators in N = 4 SYM [1]. Integrability of the planar sector of this particular CFT has allowed the deter- mination of the spectrum of single trace operators at any value of the coupling. Recently, it was proposed a method (hereafter called the hexagon approach) to compute OPE coef- ficients of single trace operators at any value of the coupling [2]. This new approach has passed several non-trivial checks [2–4]. At weak coupling, there are new features appearing at each loop order and in the past it was useful to have these OPE coefficients computed by other means in order to check the correctness of the integrability result. The interest in the four loop stems from the appearence of a new effect in the hexagon approach due to wrapping effects [2, 3]. Thus, reproducing the result of this note will be an important non-trivial check of the integrability computation. We compute the OPE coefficient of two 20′ operators and the Konishi operator in the four loop level by doing the OPE decomposition of a four point function 20′ operators. This four point function is known only at the integrand level, so to extract the OPE coefficient we will use the method of asymptotic expansions that allows to obtain a series expansion of all integrals in OPE limit. This method has already been implemented in the past to determine the OPE coefficient at three loops [5]. In the next section we will define the four point function that we will be working with. Then we briefly review the method of asymptotic expansions and finally we extract the OPE coefficient by considering a limit of the four point function. – 1 – J H E P 0 3 ( 2 0 1 7 ) 0 7 9 2 Four point function and OPE limit In N = 4 SYM there are special operators (often called protected) that do not receive quantum corrections to their dimension and OPE coefficients or in other words, their two and three point function are the same at any coupling. However, a four point function of these operators does get corrected. One way to understand this is by writing the four point function as a sum of two three point functions, i.e. by doing the OPE decomposition 〈O(x1)O(x2)O(x3)O(x4)〉 = ∑ k c2 OOOk (x2 12x 2 34)∆O G∆k,Jk(u, v), u = x2 12x 2 34 x2 13x 2 24 , v = x2 14x 2 23 x2 13x 2 24 (2.1) where cOOOk is an OPE coefficient, G∆,J(u, v) is a conformal block (that resums the con- tribution of a conformal family to a four point function) and u and v are cross ratios. In general the OPE coefficient cOOOk and dimension ∆k depend on the coupling. Conse- quently, the four point function will inherit this dependence. Our main goal is to extract an OPE coefficient that has wrapping. This effect starts to be present at four loops for small operators, like the Konishi. The correlation function of 20′ operators is the only one that has been computed at the four loop level. For completeness let us define the 20′ operators O(x, y) = YIYJOIJ20′(x) = YIYJtr ( ΦI(x)ΦJ(x) ) , Y 2 = YIYI = 0. (2.2) where the null variables Y insure that the operator is symmetric and traceless in the R- charge indices. The four point function depends on the polarization vectors YI . Naively, one would expect a nontrivial dependence on these variables but it turns out that this dependence factorizes and consequently the four point function can be written as [16] G4 = 〈O(x1, y1) . . .O(x4, y4)〉 = ∞∑ l=0 alG (l) 4 (1, 2, 3, 4), (2.3) with the tree level result given by G(0)(1, 2, 3, 4) = (N2 − 1)2 4(4π2)4 ( y4 12y 4 34 x4 12x 4 34 + y4 13y 4 24 x4 13x 4 24 + y4 14y 4 23 x4 14x 4 23 ) + N2 − 1 (4π2)4 ( y2 12y 2 23y 2 34y 2 41 x2 12x 2 23x 2 34x 2 41 + y2 12y 2 24y 2 43y 2 31 x2 12x 2 24x 2 43x 2 31 + y2 13y 2 32y 2 24y 2 41 x2 13x 2 32x 2 24x 2 41 ) , yij = Yi · Yj (2.4) and the loop level by G (l) 4 = 2(N2 c − 1) (4π2)4 R x2 12x 2 13x 2 14x 2 23x 2 24x 2 34 l!(−4π2)l ∫ d4x5 . . . d 4x4+lf (l)(x1, . . . , x4+l), (for l ≥ 1) where a is the t’Hooft coupling a = g2Nc/(4π 2) and R contains all the dependence on the polarization vectors Y R = y2 12y 2 23y 2 34y 2 41 x2 12x 2 23x 2 34x 2 41 ( x2 13x 2 24 − x2 12x 2 34 − x2 14x 2 23 ) + y2 12y 2 24y 2 43y 2 31 x2 12x 2 24x 2 43x 2 31 ( x2 14x 2 23 − x2 12x 2 34 − x2 13x 2 24 ) + y2 13y 2 32y 2 24y 2 41 x2 13x 2 32x 2 24x 2 41 ( x2 12x 2 34 − x2 13x 2 24 − x2 14x 2 23 ) + y4 12y 4 34 x2 12x 2 34 + y4 13y 4 24 x2 13x 2 24 + y4 14y 4 23 x2 14x 2 23 . (2.5) – 2 – J H E P 0 3 ( 2 0 1 7 ) 0 7 9 The function f (l)(x1, . . . , x4+l) possesses a hidden permutation symmetry S4+l and this, together with imposing the correct OPE behavior, has led to a complete description of its form up to a high loop order [6]. An useful representation for f (l)(x1, . . . , x4+l) is [6, 7] f (l)(x1, . . . , x4+l) = P (l)(x1, . . . , x4+l) Π1≤i