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Ivancevic_Applied-Diff-Geom

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736 <strong>Applied</strong> <strong>Diff</strong>erential <strong>Geom</strong>etry: A Modern Introductionis unbroken. Our main goal is to determine – as quantitatively as possible– how this picture is modified quantum mechanically.The quantum moduli space is described by the global supersymmetryversion of special geometry. The Kähler potential, K =Im(a D (u)ā(ū)), determines the metric (or, equivalently the kinetic terms).The pair (a D , a) is a holomorphic section of an SL(2, Z) bundle over thepunctured complex u plane. They are related by N = 2 supersymmetry toa U(1) gauge multiplet. a is related by N = 2 to the semiclassical ‘photon’while a D is related to its dual – ‘the magnetic photon’. The gauge kineticenergy is proportional to∫d 2 θ ∂a D∂a W 2 α. (4.222)In this N = 2 theory, the one–loop approximation to K is exact (there areno higher order perturbative corrections and there are no U(1) instantonson R 4 ) leading toa D = − ik2π a log(a/Λ).The lack of asymptotic freedom appears here as a breakdown of the theoryat |a| = Λ/e, where the metric on the moduli space Im( ∂a D∂a) vanishes andthe effective gauge coupling is singular. This is the famous Landau pole.For large |u| the theory is semiclassical anda ∼ = √ 2u, a D∼2 = i a log a. (4.223)πThese expressions are modified by instanton corrections. The exact expressionswere determined as the periods on a torusy 2 = (x 2 − Λ 4 )(x − u) (4.224)of the meromorphic 1–form λ = √ 2 dx (x−u)2π y. In (4.224), Λ is the dynamicallygenerated mass scale of the theory.The spectrum contains dyons labelled by various magnetic and electriccharges. Stable states with magnetic and electric charges (n m , n e ) havemasses given by the BPS formulaM 2 = 2|Z| 2 = 2|n e a(u) + n m a D (u)| 2 . (4.225)There are two singular points on the quantum moduli space at u = ±Λ 2 ;they are points at which a magnetic monopole becomes massless. When an

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