Metastability in Bubbling AdS Space

We study the dynamics of probe M5 branes with dissolved M2 charge in bubbling geometries with SO(4) x SO(4) symmetry. These solutions were constructed by Bena-Warner and Lin-Lunin-Maldacena and correspond to the vacua of the maximally supersymmetric mass-deformed M2 brane theory. We find that supersymmetric probe M2 branes polarize into M5 brane shells whose backreaction creates an additional bubble in the geometry. We explicitly check that the supersymmetric polarization potential agrees with the one found within the Polchinski-Strassler approximation. The main result of this paper is that probe M2 branes whose orientation is opposite to the background flux can polarize into metastable M5 brane shells. These decay to a supersymmetric configuration via brane-flux annihilation. Our findings suggest the existence of metastable states in the mass-deformed M2 brane theory.Comment: 38 pages, 8 figure

On Inflation and de Sitter in Non-Geometric String Backgrounds

We study the problem of obtaining de Sitter and inflationary vacua from dimensional reduction of double field theory (DFT) on nongeometric string backgrounds. In this context, we consider a new class of effective potentials that admit Minkowski and de Sitter minima. We then construct a simple model of chaotic inflation arising from T-fold backgrounds and we discuss the possibility of trans-Planckian field range from nongeometric monodromies as well as the conditions required to get slow roll.Comment: 21 pages, 2 figures, references added, typos corrected, note adde

The monodromy of T-folds and T-fects

We construct a class of codimension-2 solutions in supergravity that realize T-folds with arbitrary $O(2,2,\mathbb{Z})$ monodromy and we develop a geometric point of view in which the monodromy is identified with a product of Dehn twists of an auxiliary surface $\Sigma$ fibered on a base $\mathcal{B}$. These defects, that we call T-fects, are identified by the monodromy of the mapping torus obtained by fibering $\Sigma$ over the boundary of a small disk encircling a degeneration. We determine all possible local geometries by solving the corresponding Cauchy-Riemann equations, that imply the equations of motion for a semi-flat metric ansatz. We discuss the relation with the F-theoretic approach and we consider a generalization to the T-duality group of the heterotic theory with a Wilson line.Comment: 60 pages, 12 figure

Tachyonic Anti-M2 Branes

We study the dynamics of anti-M2 branes in a warped Stenzel solution with M2 charges dissolved in fluxes by taking into account their full backreaction on the geometry. The resulting supergravity solution has a singular magnetic four-form flux in the near-brane region. We examine the possible resolution of this singularity via the polarization of anti-M2 branes into M5 branes, and compute the corresponding polarization potential for branes smeared on the finite-size four-sphere at the tip of the Stenzel space. We find that the potential has no minimum. We then use the potential for smeared branes to compute the one corresponding to a stack of localized anti-M2 branes, and use this potential to compute the force between two anti-M2 branes at tip of the Stenzel space. We find that this force, which is zero in the probe approximation, is in fact repulsive. This surprising result points to a tachyonic instability of anti-M2 branes in backgrounds with M2 brane charge dissolved in flux.Comment: 36 pages, 4 figures; v2: typos corrected, references added; v3: comments adde

Università degli Studi di Firenze - Facoltà di Ingegneria - Corso di Laurea in Ingegneria Edile Tesi di Laurea Specialistica: ATTENUAZIONE DELLA RISPOSTA INDOTTA DAL VENTO SU EDIFICI ALTI TRAMITE L’IMPIEGO DI SMORZATORI A MASSA LIQUIDA: UN CASO DI STUDIO Autore: Tommaso MASSAI Relatori: Prof. Ing. Gianni BARTOLI, Prof. Ing. Claudio BORRI, Prof. Ing. Luca FACCHINI, Prof. Ing. Paolo SPINELLI Anno Accademico: 2009/2010

Nell'articolo viene presentata una sintesi dei risultati di una ricerca volta ad indagare la possibilità di introdurre smorzatori a massa liquida (TLD, Tuned Liquid Dampers) per attenuare le oscillazioni indotte dal vento in edifici alti. In particolare, è stato analizzato il caso di un edificio alto in corso di costruzione a Milano (la Torre Garibaldi, che ospiterà i nuovi uffici del Comune di Milano): partendo dai valori dei coefficienti di pressione e di forza misurati in galleria del vento, sono state valutate le accelerazioni massime sotto vento previste nell'edificio, valutando l'efficienza di più configurazioni di TLD ottenute variando la frequenza (o le frequenze) degli smorzatori rispetto alle frequenze proprie della struttura. Prof. Gianni BARTOL

Polchinski-Strassler does not uplift Klebanov-Strassler

Anti-D3-branes at the tip of the Klebanov-Strassler solution with D3-charge dissolved in fluxes give rise, in the probe approximation, to a metastable state. The fully back-reacted smeared solution has singular three-form fluxes in the IR, whose presence suggests a stringy resolution by brane polarization a la Polchinski-Strassler. In this paper we show that there is no polarization into anti-D5-branes wrapping the $S^2$ of the conifold at a finite radius. The singularities therefore do not seem to be physical, signaling that antibranes cannot be used to uplift AdS and obtain a very large landscape of de Sitter vacua in string theory.Comment: 30 pages, 2 figures, JHEP style; v2: typos corrected, references added; v3: comments added and sign typo correcte