(Non-)perturbative tests of the AdS/CFT correspondence

I summarize perturbative and non-perturbative field theory tests of the holographic correspondence between type IIB superstring on AdS_5xS^5 and N=4 SYM theory. The holographic duality between D-instantons and YM instantons is briefly described. Non renormalization of two- and three-point functions of CPO's and their extremal and next-to-extremal correlators are then reviewed. Finally, partial non-renormalization of four-point functions of lowest CPO's is analyzed in view of the interpretation of short distance logarithmic behaviours in terms of anomalous dimensions of unprotected operators.Comment: 9 pages, Latex, style file espcrc2.sty. Typos corrected, references added. Talk given at the D.V. Volkov Memorial Conference ``Supersymmetry and Quantum Field Theory'', 25-30 July 2000, Kharkov, to be published in Nuclear Physics B Conference Supplements. Summary of the lectures delivered at the school ``Latest developments in M-Theory'', Institut Henri Poincare', Paris, 1-8 February 200

Non-renormalisation of extremal correlators in N=4 SYM theory

We show that extremal correlators of chiral primary operators in N=4 supersymmetric Yang-Mills theory with SU(N) gauge group are neither renormalised at first order in perturbation theory nor receive contribution from any instanton sector at leading order in the semiclassical expansion. This lends support to the strongest version of a new prediction recently put forward on the basis of the AdS/SCFT correspondence.Comment: 13 pages, LaTeX2e; definition of extremal correlators moved to the introduction, references added; final version to appear in Physics Letters

Revisiting light stringy states in view of the 750 GeV diphoton excess

We investigate light massive string states that appear at brane intersections. They replicate the massless spectrum in a richer fashion and may be parametrically lighter than standard Regge excitations. We identify the first few physical states and determine their BRST invariant vertex operators. In the supersymmetric case we reconstruct the super-multiplet structure. We then compute some simple interactions, such as the decay rate of a massive scalar or vector into two massless fermions. Finally we suggest an alternative interpretation of the 750 GeV diphoton excess at LHC in terms of a light massive string state, a replica of the Standard Model Higgs.Comment: 29 pages, 5 eps figures. v

RG-flows and Open/Closed String Duality

We discuss the interpaly between IR and UV divergences in theories with open and unoriented strings in view of the AdS/CFT correspondence. We start by deriving general formulas for the computation of threshold corrections to gauge couplings in generic configurations with open and unoriented strings. These allow us to discuss the IR/UV correspondence between beta-function coefficients and ``dilaton'' tadpoles for several brane configurations probed by D3-branes. Finally we comment on the AdS supergravity descriptions of gauge theories that are (super)conformal in the large N limit.Comment: Minor corrections. References added. Version to be published in JHEP08(2000)035. 22 pages, Late

Anomalies & Tadpoles

We show that massless RR tadpoles in vacuum configurations with open and unoriented strings are always related to anomalies. RR tadpoles arising from sectors of the internal SCFT with non-vanishing Witten index are in one-to-one correspondence with conventional irreducible anomalies. The anomalous content of the remaining RR tadpoles can be disclosed by considering anomalous amplitudes with higher numbers of external legs. We then provide an explicit parametrization of the anomaly polynomial in terms of the boundary reflection coefficients, i.e. one-point functions of massless RR fields on the disk. After factorization of the reducible anomaly, we extract the relevant WZ couplings in the effective lagrangians.Comment: 20 pages, Late