Non-Perturbative Planar Equivalence and the Absence of Closed String Tachyons.pdf

Non-Perturbative Planar Equivalence and the Absence of Closed String Tachyons.pdf

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Non-Perturbative Planar Equivalence and the Absence of Closed String Tachyons

a r X i v : h e p - t h / 0 7 0 3 2 2 9 v 3 5 A p r 2 0 0 7 Preprint typeset in JHEP style - HYPER VERSION Non-Perturbative Planar Equivalence and the Absence of Closed String Tachyons Adi Armoni Department of Physics, Swansea University, Swansea, SA2 8PP, UK. E-mail: a.armoni@swan.ac.uk Abstract: We consider ’orbifold’ and ’orientifold’ field theories from the dual closed string theory side. We argue that a necessary condition for planar equivalence to hold is the absence of a closed string tachyonic mode in the dual non-supersymmetric string. We analyze several gauge theories on R3 × S1. In the specific case of U(N) theories with symmetric/anti-symmetric fermions (’orientifold field theories’) the rel- evant closed string theory is tachyon-free at large compactification radius (due to winding modes), but it develops a tachyonic mode below a critical radius. Our find- ing is with agreement with field theory expectations of a phase transition from a C-parity violating phase to a C-parity preserving phase as the compactification ra- dius increases. In the case of U(N) × U(N) theories with bi-fundamental matter (’orbifold field theories’) a tachyon is always present in the string spectrum, at any compactification radius. We conclude that on R4 planar equivalence holds for ’ori- entfiold field theories’, but fails for ’orbifold field theories’ daughters of N = 4 SYM and suggest the same for daughters of N = 1 SYM. We also discuss examples of SO/Sp gauge theories with symmetric/anti-symmetric fermions. In this case planar equivalence holds at any compactification radius - in agreement with the absence of tachyons in the string dual. Keywords: AdS/CFT, large N , Branes. 1. Introduction Planar equivalence between supersymmetric and non-supersymmetric gauge theories [1,2] proved itself as a useful tool in the study of non-perturbative QCD (see [3,4] for reviews). Besides its important application for QCD, it is an interesting statement in field-theory per-se: a susy/n

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