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Théorie des Champs & Physique Mathématique
(16) Production(s) de l'année 2021


Bouncing Cosmological Isotropic Solutions in ScalarTensor Gravity
Auteur(s): Polarski D., Starobinsky A.A., Verbin Y.
(Document sans référence bibliographique) Texte intégral en Openaccess :
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Ref Arxiv: 2111.07319
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Ref. & Cit.: NASA ADS
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Résumé: Bouncing nonsingular isotropic cosmological solutions are investigated in a simple model of scalartensor gravity. New families of such solutions are found and their properties are presented and analyzed using an effective potential as the main tool. Bouncing solutions are shown to exist for a Higgslike selfinteraction potential which is bounded from below, in contrast to previous solutions that appeared in the literature based on potentials which were unbounded from below. In the simplest version of a scalar field with the quartic potential and conformal coupling to gravity, bouncing spatially flat solutions either have the Hubble function diverging in the past before the bounce, but with a wellbehaved future, or are globally regular but unstable with respect to anisotropic or inhomogeneous perturbations at some finite values of the scalar field and curvature. Regular solutions can only exist in the part of the parameter space where the maximum of the effective potential is larger than the first zero of the potential, and gravity becomes repulsive at the bounce.



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.



Euclidean Dbranes in Type IIB string theory on CalabiYau threefolds
Auteur(s): Alexandrov S., Sen Ashoke, Stefański Bogdan
(Document sans référence bibliographique) Texte intégral en Openaccess :
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Ref Arxiv: 2110.06949
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Résumé: We compute the contribution of Euclidean Dbranes in type IIB string theory on CalabiYau threefolds to the metric on the hypermultiplet moduli space in the large volume, weak coupling limit. Our results are in perfect agreement with the predictions based on Sduality, mirror symmetry and supersymmetry.



Emergence and background independence: lessons from another camp
Auteur(s): Alexandrov S.
Conférence invité: The LyonMarseille workshop on Quantum Gravity 2021 (Lyon, FR, 20211007)
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Résumé: I'll explain several lessons suggested for the issues of emergence of spacetime and background independence in quantum gravity by models of noncritical and topological strings.



Dinstantons in Type II string theory on CalabiYau threefolds
Auteur(s): Alexandrov S.
Conférence invité: Workshop on Black Holes, BPS and Quantum Information (Lisbonne (on line), PT, 20210920)
Texte intégral en Openaccess :
Ref HAL: hal03355857_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 can now be extended to compactifications with lower supersymmetry.The talk is based on joint work with A. Sen and B. Stefanski.



Dinstantons in Type IIA string theory on CalabiYau threefolds
Auteur(s): Alexandrov S., Sen Ashoke, Stefański Bogdan
(Article) Publié:
Journal Of High Energy Physics, vol. 2021 p.18 (2021)
Texte intégral en Openaccess :
Ref HAL: hal03319142_v1
Ref Arxiv: 2108.04265
DOI: 10.1007/JHEP11(2021)018
Ref. & Cit.: NASA ADS
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Résumé: Type IIA string theory compactified on a CalabiYau threefold has a hypermultiplet moduli space whose metric is known to receive nonperturbative corrections from Euclidean D2branes wrapped on 3cycles. These corrections have been computed earlier by making use of mirror symmetry, Sduality and twistorial description of quaternionic geometries. In this paper we compute the leading corrections in each homology class using a direct worldsheet approach without relying on any duality symmetry or supersymmetry. Our results are in perfect agreement with the earlier predictions.



Conformal TBA for resolved conifolds
Auteur(s): Alexandrov S., Pioline Boris
(Document sans référence bibliographique) 20210622 Texte intégral en Openaccess :
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Ref Arxiv: 2106.12006
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Résumé: We revisit the RiemannHilbert problem determined by DonaldsonThomas invariants for the resolved conifold and for other small crepant resolutions. While this problem can be recast as a system of TBAtype equations in the conformal limit, solutions are illdefined due to divergences in the sum over infinite trajectories in the spectrum of D2D0brane bound states. We explore various prescriptions to make the sum welldefined, show that one of them reproduces the existing solution in the literature, and identify an alternative solution which is better behaved in a certain limit. Furthermore, we show that a suitable asymptotic expansion of the $\tau$ function reproduces the genus expansion of the topological string partition function for any small crepant resolution. As a byproduct, we conjecture a new integral representation for the double sine function.
