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Dinstantons in CalabiYau compactifications
Auteur(s): Alexandrov S.
Conférence invité: String Field Theory 2022 (Prague, CZ, 20230912)
Résumé: Euclidean Dbranes wrapped on nontrivial cycles of a CalabiYau threefold are known to affect the metric on the hypermultiplet moduli space determining the effective action of type II strings on such manifolds. After reviewing the existing results on the instanton corrected metric following from a combination of constraints imposed by supersymmetry and dualities, I'll show how the Dinstanton effects can be computed by a direct worldsheet approach. This required solving several conceptual and technical problems, which also paved the way for extension of this approach to compactifications with lower supersymmetry. The talk is based on joint work with A. Sen and B. Stefanski.



Joyce structures, twistors and topological strings
Auteur(s): Alexandrov S.
Conférence invité: BPS states, mirror symmetry, and exact WKB II (Sheffield, GB, 20220905)
Résumé: As shown by T. Bridgeland, a RiemannHilbert problem determined by DonaldsonThomas invariants naturally gives rise to the socalled Joyce structure. It can be characterized by a function known as Plebanski potential, or its close cousin Joyce potential. I'll show that a twistorial solution to the RH problem provides a simple integral expressions for both potentials. Then I'll explain the relation of this solution to the conformal limit of the twistor spaces
appearing in gauge and string theories, and physical interpretation acquired by
the two potentials in these setups. For the case of the resolved conifold, I'll present a recipe to make the twistorial solution welldefined despite an infinite BPS spectrum, and trace out the emergence of a taufunction, its relation to topological strings and its behavior under Sduality to the twistorial implementation of instantons in string theory.



Dinstantons and superpotential
Auteur(s): Alexandrov S.
Conférence invité: Strings and Geometry 2022 (Utrecht, NL, 20220502)
Ref HAL: hal03664125_v1
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Résumé: I'll present the computation of a Dinstanton induced superpotential in an orientifold CalabiYau compactification of type II string theory using a direct worldsheet approach.



Dinstantons in string compactifications
Auteur(s): Alexandrov S.
Conference: Eurostrings 2022 (Lyon, FR, 20220425)
Ref HAL: hal03664123_v1
Exporter : BibTex  endNote
Résumé: Euclidean Dbranes wrapped on nontrivial cycles of a CalabiYau threefold are known to affect the metric on the hypermultiplet moduli space determining the effective action of type II strings on such manifolds. After reviewing the existing results on the instanton corrected metric following from a combination of constraints imposed by supersymmetry and dualities, I'll show how the Dinstanton effects can be computed by a direct worldsheet approach. It required solving several conceptual and technical problems and has recently been extended to compactifications with lower supersymmetry. The talk is based on joint work with A. Sen and B. Stefanski.



Dinstanton Induced Superpotential
Auteur(s): Alexandrov S., Fırat Atakan Hilmi, Kim Manki, Sen Ashoke, Stefański Bogdan
(Article) Publié:
Journal Of High Energy Physics, vol. 2022 p.90 (2022)
Texte intégral en Openaccess :
Ref HAL: hal03635867_v1
Ref Arxiv: 2204.02981
DOI: 10.1007/JHEP07(2022)090
Ref. & Cit.: NASA ADS
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Résumé: We use string field theory to fix the normalization of the Dinstanton corrections to the superpotential involving the moduli fields of type II string theory compactified on an orientifold of a CalabiYau threefold in the absence of fluxes. We focus on $O(1)$ instantons whose only zero modes are the four bosonic modes associated with translation of the instanton in noncompact directions and a pair of fermionic zero modes associated with the two supercharges broken by the instanton. We work with a generic superconformal field theory and express our answer in terms of the spectrum of open strings on the instanton. We analyse the contribution of multiinstantons of this kind to the superpotential and argue that it vanishes when background fluxes are absent.



Modular bootstrap for D4D2D0 indices on compact CalabiYau threefolds
Auteur(s): Alexandrov S., Gaddam Nava, Manschot Jan, Pioline Boris
(Document sans référence bibliographique) 20220405 Texte intégral en Openaccess :
Ref HAL: hal03635855_v1
Ref Arxiv: 2204.02207
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
Résumé: We investigate the modularity constraints on the generating series $h_r(\tau)$ of BPS indices counting D4D2D0 bound states with fixed D4brane charge $r$ in type IIA string theory compactified on complete Intersection CalabiYau threefolds with $b_2 = 1$. For unit D4brane, $h_1$ transforms as a (vectorvalued) modular form under the action of $SL(2,Z)$ and thus is completely determined by its polar terms. We propose an Ansatz for these terms in terms of rank 1 DonaldsonThomas invariants, which incorporates contributions from a single D6antiD6 pair. Using an explicit overcomplete basis of the relevant space of weakly holomorphic modular forms (valid for any $r$), we find that for 10 of the 13 allowed threefolds, the Ansatz leads to a solution for $h_1$ with integer Fourier coefficients, thereby predicting an infinite series of DT invariants.For $r > 1$, $h_r$ is mock modular and determined by its polar part together with its shadow. Restricting to $r = 2$, we use the generating series of Hurwitz class numbers to construct a series $h^{\rm an}_2$ with exactly the same modular anomaly as $h_2$, so that the difference $h_{2}h^{\rm an}_2$ is an ordinary modular form fixed by its polar terms. For lack of a satisfactory Ansatz, we leave the determination of these polar terms as an open problem.



Dinstantons in Type II string theory on CalabiYau threefolds
Auteur(s): Alexandrov S.
(Séminaires)
Trinity College (Dublin, IE), 20211117
Résumé: Euclidean Dbranes wrapped on nontrivial cycles of a CalabiYau threefold are known to affect the metric on the hypermultiplet moduli space determining the effective action of type II strings on such manifolds. After reviewing the existing results on the instanton corrected metric following from a combination of constraints imposed by supersymmetry and dualities, I'll show how the Dinstanton effects can be computed by a direct worldsheet approach. It required solving several conceptual and technical problems and can now be extended to compactifications with lower supersymmetry. The talk is based on joint work with A. Sen and B. Stefanski.
