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Physique Théorique
(51) Production(s) de l'année 2022
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D-instantons in string compactifications
Auteur(s): Alexandrov S.
Conference: Eurostrings 2022 (Lyon, FR, 2022-04-25)
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Résumé: Euclidean D-branes wrapped on non-trivial cycles of a Calabi-Yau 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 D-instanton 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.
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Microscopic origin of excess wings in relaxation spectra of supercooled liquids
Auteur(s): Guiselin B., Scalliet C., Berthier L.
(Article) Publié:
Nature Physics, vol. 18 p.468-+ (2022)
Texte intégral en Openaccess :
Ref HAL: hal-03662093_v1
Ref Arxiv: 2103.01569
DOI: 10.1038/s41567-022-01508-z
WoS: WOS:000770232200001
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Résumé: Glass formation is encountered in diverse materials. Experiments have revealed that dynamic relaxation spectra of supercooled liquids generically become asymmetric near the glass transition temperature, Tg, where an extended power law emerges at high frequencies. The microscopic origin of this "wing" remains unknown, and was so far inaccessible to simulations. Here, we develop a novel computational approach and study the equilibrium dynamics of model supercooled liquids near Tg. We demonstrate the emergence of a power law wing in numerical spectra, which originates from relaxation at rare, localised regions over broadly-distributed timescales. We rationalise the asymmetric shape of relaxation spectra by constructing an empirical model associating heterogeneous activated dynamics with dynamic facilitation, which are the two minimal physical ingredients revealed by our simulations. Our work offers a glimpse of the molecular motion responsible for glass formation at relevant experimental conditions.
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Mapping cell cortex rheology to tissue rheology, and vice-versa
Auteur(s): Moisdon Étienne, Seez Pierre, Noûs Camille, Molino F., Marcq Philippe, Gay Cyprien
(Article) Publié:
Physical Review E, vol. 106 p.034403 (2022)
Texte intégral en Openaccess :
Ref HAL: hal-03649586_v2
Ref Arxiv: 2204.10907
DOI: 10.1103/PhysRevE.106.034403
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Résumé: The mechanics of biological tissuesmainly proceeds from the cell cortex rheology.A direct, explicit link between cortex rheology and tissue rheology remains lacking, yet would be instrumental in understanding how modulations of cortical mechanics may impact tissue mechanical behaviour.Using an ordered geometry built on 3D hexagonal, incompressible cells,we build a mapping relatingthe cortical rheology to the monolayer tissue rheology.Our approach shows that the tissue low frequency elastic modulusis proportional to the rest tension of the cortex,as expected from the physics of liquid foamsas well as of tensegrity structures.A fractional visco-contractile cortex rheologyis predicted to yield a high-frequency fractional visco-elastic monolayer rheology, where such a fractional behaviour has been recently observed experimentally at each scale separately.In particular cases, the mapping may be inverted, allowing toderive from a given tissue rheology the underlying cortex rheology. Interestingly, applying the same approach to a 2D hexagonal tiling fails,which suggests that the 2D character of planar cell cortex-based models may be unsuitable to account for realistic monolayer rheologies.We provide quantitative predictions, amenable to experimental tests through standard perturbation assays ofcortex constituents, and hope to foster new, challenging mechanicalexperiments on cell monolayers.
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Relaxation dynamics in the energy landscape of glass-forming liquids
Auteur(s): Nishikawa Y., Ozawa M., Ikeda A., Chaudhuri Pinaki, Berthier L.
(Article) Publié:
Physical Review X, vol. p.021001 (2022)
Texte intégral en Openaccess :
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Ref Arxiv: 2106.01755
DOI: 10.1103/PhysRevX.12.021001
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Résumé: We numerically study the zero-temperature relaxation dynamics of several glass-forming models to their inherent structures, following quenches from equilibrium configurations sampled across a wide range of initial temperatures. In a mean-field Mari-Kurchan model, we find that relaxation changes from a power-law to an exponential decay below a well-defined temperature, consistent with recent findings in mean-field $p$-spin models. By contrast, for finite-dimensional systems, the relaxation is always algebraic, with a non-trivial universal exponent at high temperatures crossing over to a harmonic value at low temperatures. We demonstrate that this apparent evolution is controlled by a temperature-dependent population of localised glassy excitations. Our work unifies several recent lines of studies aiming at a detailed characterisation of the complex potential energy landscape of glass-formers, and challenges both mean-field and real space descriptions of glasses.
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D-instanton 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 :
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Ref Arxiv: 2204.02981
DOI: 10.1007/JHEP07(2022)090
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Résumé: We use string field theory to fix the normalization of the D-instanton corrections to the superpotential involving the moduli fields of type II string theory compactified on an orientifold of a Calabi-Yau 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 non-compact 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 multi-instantons of this kind to the superpotential and argue that it vanishes when background fluxes are absent.
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Modular bootstrap for D4-D2-D0 indices on compact Calabi-Yau threefolds
Auteur(s): Alexandrov S., Gaddam Nava, Manschot Jan, Pioline Boris
(Document sans référence bibliographique) 2022-04-05Texte intégral en Openaccess :
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Ref Arxiv: 2204.02207
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Résumé: We investigate the modularity constraints on the generating series $h_r(\tau)$ of BPS indices counting D4-D2-D0 bound states with fixed D4-brane charge $r$ in type IIA string theory compactified on complete Intersection Calabi-Yau threefolds with $b_2 = 1$. For unit D4-brane, $h_1$ transforms as a (vector-valued) 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 Donaldson-Thomas invariants, which incorporates contributions from a single D6-anti-D6 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.
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Etude par dynamique moléculaire de la conductance ionique à l'échelle nanoscopique: rôle du modèle de l'eau et des paramètres géométriques
Auteur(s): Mejri Alia, Mazouzi Kamel, Herlem Guillaume, Picaud Fabien, Hennequin Theo, Palmeri J., Manghi Manoel
(Article) Publié:
Journal Of Molecular Liquids, vol. 351 p.118575 (2022)
Texte intégral en Openaccess :
Ref HAL: hal-03590631_v1
DOI: 10.1016/j.molliq.2022.118575
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Résumé: Le transport ultra-efficace de l'eau et des ions à l'échelle nanométrique est étudié par des simulations de dynamique moléculaire. Les nanotubes de carbone (CNTs) sont utilisés ici comme dispositifs nanofluidiques en raison de leur structure interne lisse et du compromis d'une composition très simple pour une énorme variété de propriétés. Le transport d'ions solvatés se déplaçant à l'intérieur du nanotube de carbone sous l'application d'une différence de potentiel externe a permis de mesurer le courant ionique établi à travers la zone interne du tube. Pour être le plus exhaustif possible, trois modèles d'eau populaires ont été testés pour étudier le transport ionique à l'intérieur de ce nanocanal artificiel. Les paramètres géométriques clés de la structure en carbone ont également été variés révélant une dépendance particulière de la conductance ionique à chaque paramètre étudié en accord avec le modèle théorique présenté dans cet article. Fichier révisé Version propre-Pour la mise en page Cliquez ici pour voir les références liées
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