arXiv:1007.5145v1 [hep-th] 29 Jul 2010 CPHT-RR054.0710 DESY 10-115 OUTP-10/16P One-loop Yukawa Couplings in Local Models Joseph P. Conlon1,2,Mark Goodsell3andEran Palti4 1Rudolf Peierls Center for Theoretical Physics, 1 Keble Road, Oxford, OX1 3NP, United Kingdom 2Balliol College, Oxford, OX1 3BJ, United Kingdom 3Deutsches Elektronen-Synchrotron DESY, Notkestrasse 85, D-22603 Hamburg, Germany. 4Centre de Physique Theorique, Ecole Polytechnique, CNRS, 91128 Palaiseau, France. j.conlon1@physics.ox.ac.uk, mark.goodsell@desy.de, eran.palti@cpht.polytechnique.fr Abstract We calculate the one-loop Yukawa couplings and threshold corrections for supersymmetric local models of branes at singularities in type IIB string theory.We compute the corrections coming both from wavefunction and vertex renormalisation.The former comes in the IR from conventional field theory running and in the UV from threshold corrections that cause it to run from the winding scale associated to the full Calabi-Yau volume.The vertex correction is naively absent as it appears to correspond to superpotential renormalisation.However, we find that while the Wilsonian superpotential is not renormalised there is a physical vertex correction in the 1PI action associated to light particle loops.
Contents 1Introduction2 2CFT Building Blocks3 2.1Vertex operators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .4 2.2Bosonic Correlators . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .6 2.2.1Internal untwisted quantum correlators. . . . . . . . . . . . . . . . . . . . . . . .6 2.2.2Momentum exponential correlators and pole structures . . . . . . . . . . . . . . . .7 2.3Fermionic and Ghost Correlators. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .8 2.4Partition functions. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .9 2.5The Model. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .10 3Yukawa threshold corrections11 3.1General structure . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .12 3.23-point amplitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .15 3.34-point amplitude . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .23 4Summary and discussion28 AGauge Threshold Corrections29 BTheta Identities32 CDetermination of Amplitude via Lorentz Structure33 1Introduction Loop corrections to effective actions play an important general role in physics. Supersymmetric theories are celebrated for their special behaviour at loop level and for the protection of holomorphic properties against renormalisation. Specifically, the superpotential does not get perturbatively renormalised and the gauge kinetic function is perturbatively renormalised only at one-loop. The study of one-loop gauge cou- plings and their threshold corrections has been carried out extensively in both field and string theory. In this context there is an important distinction between the Wilsonian gauge kinetic function, renormalised only at one-loop, and the physical coupling, which is corrected at all orders.The study of one-loop Yukawa couplings in string theory has been less extensive, and the distinction between holomorphic and physical couplings less clearly drawn. Here holomorphy properties have been taken to imply that Yukawa couplings only receive one-loop corrections from wavefunction renormalisation. 2
In this paper we study one-loop Yukawa couplings for supersymmetric models of branes at singularities in type IIB string theory. These models are local in the sense that for much of the calculation the global compact completion of the internal manifold does not play a role [1]. Previous studies of one-loop Yukawa couplings in heterotic and type IIA settings have been performed in [2–5].There are two important motivations for this work. The first is that the one-loop behaviour of running couplings in local models is especially interesting with respect to the volume of the full global manifold.For gauge threshold corrections, studied in [6–8], gauge couplings run to a scale set by the global volume of the manifold, the so called winding scale, rather than the local string scale.This has important consequences both practically, as for the case of local GUT models it implies the string scale is an order of magnitude below the GUT scale, and conceptually, in the sense of understanding the extent to which a local model can be decoupled from the bulk. It is natural to investigate the same behaviour for Yukawa couplings, where indeed we find precisely this property, with UV threshold corrections implying that the Yukawas are renormalised up to the winding scale rather than the naive cutoff, the local string scale. The second motivation arose during the calculation and involves the distinction between physical and holomorphic couplings. In [9–11] it was argued that for supersymmetric field theories with massless particles, in apparent contradiction to the non-renormalisation theorem, it is possible for superpotential operators to receive finite loop corrections that are not associated to wavefunction renormalisation. In the case of Yukawa couplings this corresponds to vertex renormalisation. The vertex correction is generated in the IR by integrating over light loop momenta.While the Wilsonian superpotential - corresponding to an action at a scaleEwith light modes yet to be integrated over - is not renormalised, the vertex correction is a physical feature of the 1PI action.We find that local models of branes at singularities (and we expect also more general intersecting brane constructions) fall within this class of theories. We demonstrate explicit one-loop vertex renormalisation from the world-sheet perspective thereby giving, to our knowledge, the first realisation of this effect in string theory. The paper is structured as follows.In section 2 we review the basic CFT building blocks that are needed for the computation. This section establishes notation and convention, as well as reviewing bosonic and fermionic correlators on the torus and annulus. We also introduce the model that we study throughout this paper: fractional D3 branes on theC3/Z4orbifold. Section 3 contains the main calculation. We first compute the one-loop Yukawas via a 3-point scattering amplitude computation. This demonstrates the key renormalisation properties of the Yukawas but also contains some ambiguities regarding the off-shell continuation.We subsequently resolve these by performing a 4-point calculation that reduces to the 3- point amplitude in a certain limit. We describe the structure of the string diagram and how it generates both wavefunction and vertex renormalisation. In section 4 we present a summary and discussion of our results. The appendix contains a warm-up calculation of gauge threshold corrections as well as various properties ofϑ-functions. 2CFT Building Blocks The computation of the amplitudes requires the evaluation of various CFT correlators between world-sheet fields that are introduced through the vertex operators. In this section we collate the relevant correlators and also other miscellaneous CFT results that are used.An incomplete list of useful references for these CFT correlators are [4, 18–26].All the amplitudes evaluated in this paper are cylinder (annulus) 3
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