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Igor Pesando

Publications and source records attributed to Igor Pesando.

At least 37 records · Page 2Linked to original sources
arXiv2013

Deformed N=2 theories, generalized recursion relations and S-duality

We study the non-perturbative properties of N=2 super conformal field theories in four dimensions using localization techniques. In particular we consider SU(2) gauge theories, deformed by a generic epsilon-background, with four fundamental flavors or with one adjoint hypermultiplet. In both cases we explicitly compute the first few instanton corrections to the partition function and the prepotential using Nekrasov's approach. These results allow to reconstruct exact expressions involving quasi-modular functions of the bare gauge coupling constant and to show that the prepotential terms satisfy a modular anomaly equation that takes the form of a recursion relation with an explicitly epsilon-dependent term. We then investigate the implications of this recursion relation on the modular properties of the effective theory and find that with a suitable redefinition of the prepotential and of the effective coupling it is possible, at least up to the third order in the deformation parameters, to cast the S-duality relations in the same form as they appear in the Seiberg-Witten solution of the undeformed theory.

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arXiv2011

The generating function of amplitudes with N twisted and M untwisted states

We show that the generating function of all amplitudes with N twisted and M untwisted states, i.e. the Reggeon vertex for magnetized branes on R^2 can be computed once the correlator of N non excited twisted states and the corresponding Green function are known and we give an explicit expression as a functional of the these objects

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arXiv2011

Strings in an arbitrary constant magnetic field with arbitrary constant metric and stringy form factors

We quantize the open string in an arbitrary constant magnetic field with a non factorized metric on a torus. We then discuss carefully the vertexes which describe the emission of dipole open strings and closed strings in the non compact limit. Finally we compute various stringy form factors which in the compact case induces a Kaehler and complex structure dependence and suppression of some amplitudes with KK states.

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arXiv2010

F-theoretic vs microscopic description of a conformal N=2 SYM theory

The F-theory background of four D7 branes in a type I' orientifold was conjectured to be described by the Seiberg-Witten curve for the superconformal SU(2) gauge theory with four flavors. This relation was explained by considering in this background a probe D3 brane, which supports this theory with SU(2) realized as Sp(1). Here we explicitly compute the non-perturbative corrections to the D7/D3 system in type I' due to D-instantons. This computation provides both the quartic effective action on the D7 branes and the quadratic effective action on the D3 brane; the latter agrees with the F-theoretic prediction. The action obtained in this way is related to the one derived from the usual instanton calculus à la Nekrasov (or from its AGT realization in terms of Liouville conformal blocks) by means of a non-perturbative redefinition of the coupling constant. We also point out an intriguing relation between the four-dimensional theory on the probe D3 brane, which has a SO(8) flavor symmetry, and the eight-dimensional dynamics on the D7 branes. On the latter, SO(8) represents a gauge group and the flavor masses correspond to the vacuum expectation values of an adjoint scalar field m: what we find is that the exact effective coupling in four dimensions is obtained from its perturbative part by taking into account in its mass dependence the full quantum dynamics of the field m in eight dimensions.

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arXiv2009

Exotic instanton counting and heterotic/type I' duality

We compute the partition function for the exotic instanton system corresponding to D-instantons on D7 branes in Type I' theory. We exploit the BRST structure of the moduli action and its deformation by RR background to fully localize the integration. The resulting prepotential describes non-perturbative corrections to the quartic couplings of the gauge field F living on the D7's. The results match perfectly those obtained in the dual heterotic theory from a protected 1-loop computation, thus providing a non-trivial test of the duality itself.

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arXiv2009

Classical solutions for exotic instantons?

We consider the D7/D(--1) system in Type I' as a prototypical "exotic" brane instanton. With respect to systems such as the D3/D(-1) ones, which correspond to gauge instantons in four dimensions, exotic systems lack the bosonic mixed moduli w of the ADHM construction, related to the instanton size, and their possible field-theoretical interpretation as classical solutions is an important open question. For the system at hand, we propose that it corresponds to the point-like limit of the eight-dimensional so-called SO(8) instanton solution. This configuration is a solution of the quartic term of the non-abelian D7 action, i.e., the term which stays finite in the limit in which alpha' goes to zero with the string coupling fixed that preserves the D(-1) effects. As a necessary consistency condition, we check that the next order term in the non-abelian effective action vanishes on the SO(8) solution so that the limit we take is well-defined.

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arXiv2007

Instantons in N=2 magnetized D-brane worlds

In a toroidal orbifold of type IIB string theory we study instanton effects in N=2 super Yang-Mills theories engineered with systems of wrapped magnetized D9 branes and Euclidean D5 branes. We analyze the various open string sectors in this brane system and study the 1-loop amplitudes described by annulus diagrams with mixed boundary conditions, explaining their role in the stringy instanton calculus. We show in particular that the non-holomorphic terms in these annulus amplitudes precisely reconstruct the appropriate Kahler metric factors that are needed to write the instanton correlators in terms of purely holomorphic variables. We also explicitly derive the correct holomorphic structure of the instanton induced low energy effective action in the Coulomb branch.

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arXiv2007

Instanton effects in N=1 brane models and the Kahler metric of twisted matter

We consider locally consistent systems of magnetized D9 branes on an orbifolded six-torus which support N=1 gauge theories. In such realizations, the matter multiplets arise from "twisted" strings connecting different stacks of branes. The introduction of Euclidean 5 branes (E5) wrapped on the six-dimensional compact space leads to instanton effects. For instance, if the system is engineered so as to yield SQCD, a single E5 brane may account for the ADS/TVY superpotential. We discuss the subtle interplay that exists between the annuli diagrams with an E5 boundary and the holomorphicity properties of the effective low-energy action of the N=1 theory. The consistency of this picture allows to obtain information on the Kahler metric of the chiral matter multiplets arising from twisted strings.

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arXiv2007

Multibranes boundary states with open string interactions

We derive boundary states which describe configurations of multiple parallel branes with arbitrary open string states interactions in bosonic string theory. This is obtained by a careful discussion of the factorization of open/closed string states amplitudes taking care of cycles needed by ensuring vertexes commutativity: in particular the discussion reveals that already at the tree level open string knows of the existence of closed string. We also give a formal expression for computing pure closed string amplitudes using the open string formalism.

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arXiv2000

Some remarks on the free fields realization of the bosonic string on AdS3

We discuss the classical solutions of the equations of motion and the possible boundary condition for a bosonic string with Kalb-Ramond background in AdS3. It turns out that there exists three different physical sectors and that it is also possible to describe the motion on an extremal black hole background. The existence of three sectors clearly shows how one of the spectra proposed is incomplete. We consider also the classical 'canonical' transformation which maps the string fields to the classical Wakimoto ones. It turns however out that the Wakimoto fields are not free because of the boundary conditions and in order to have the usual mode expansion with reasonable behaviour under complex conjugation it is necessary to consider the complexification of AdS3 and then add some constraints. Furthermore they cover only half AdS3 and we need different patches to cover the whole space and to make the above mentioned transformation really canonical.

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arXiv2000

On the Gauge Fixing of the k Symmetry on AdS and Flat Background: the Lightcone Action for the Type IIb String on AdS_{5} X S_{5}

We explore all the possible ways of fixing the kappa symmetry for both branes and strings by means of a constant projector. We find that they can be classified according to their behaviour under Dirac conjugation and conjugation. This latter controls the maximum power of the fermionic variables in which the (super)vielbein can be expanded while the former determines which states cannot be described in the gauge. In particular there exists an interesting class of projectors for which vielbein are at most quadratic in the fermionic variables. As an example we compute the action for the type IIb on a AdS_{5} X S_{5} background with a lightcone-like projector; this action reduces to the usual lightcone GS string action in the flat limit.

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arXiv1999

The GS Type IIB Superstring Action on AdS(3) X S(3) X T(4)

We describe the type IIB supergravity background on AdS_{3} x S_{3} x T^{4} using the potentials of AdS_{3|4} x S_{3} x T^{4} and we use the supersolvable algebra associated to AdS_{3|4} to compute the kappa gauge fixed type IIB string action. From the explicit form of the action we can clearly see how passing from pure NSNS backgrounds to pure RR backgrounds the WZW term disappears.

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arXiv1998

The rigid limit in Special Kahler geometry; From K3-fibrations to Special Riemann surfaces: a detailed case study

The limiting procedure of special Kahler manifolds to their rigid limit is studied for moduli spaces of Calabi-Yau manifolds in the neighbourhood of certain singularities. In two examples we consider all the periods in and around the rigid limit, identifying the nontrivial ones in the limit as periods of a meromorphic form on the relevant Riemann surfaces. We show how the Kahler potential of the special Kahler manifold reduces to that of a rigid special Kahler manifold. We extensively make use of the structure of these Calabi-Yau manifolds as K3 fibrations, which is useful to obtain the periods even before the K3 degenerates to an ALE manifold in the limit. We study various methods to calculate the periods and their properties. The development of these methods is an important step to obtain exact results from supergravity on Calabi-Yau manifolds.

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arXiv1998

Special geometry of Calabi-Yau compactifications near a rigid limit

We discuss, in the framework of special Kahler geometry, some aspects of the "rigid limit" of type IIB string theory compactified on a Calabi-Yau threefold. We outline the general idea and demonstrate by direct analysis of a specific example how this limit is obtained. The decoupling of gravity and the reduction of special Kahler geometry from local to rigid is demonstrated explicitly, without first going to a noncompact approximation of the Calabi-Yau. In doing so, we obtain the Seiberg-Witten Riemann surfaces corresponding to different rigid limits as degenerating branches of a higher genus Riemann surface, defined for all values of the moduli. Apart from giving a nice geometrical picture, this allows one to calculate easily some gravitational corrections to e.g. the Seiberg-Witten central charge formula. We make some connections to the 2/5-brane picture, also away from the rigid limit, though only at the formal level.

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