##### Meeting

#### VI Avogadro Meeting on Strings, Supergravity and Gauge theories

**Dec, 20 2010 - Dec, 22 2010**

For their accommodation the participants can contact Studio Guidi (tel: +39 055 241561; fax: +39 055 2346178)

**Organizers**

F. Bigazzi (Università di Firenze e INFN), A. L. Cotrone (Università di Torino e INFN),

C. Maccaferri (ULB - Bruxelles), L. Martucci (INFN, Sez. Roma Tor Vergata).

Local Support: A. Cappelli, D. Seminara (INFN - Università di Firenze).

**Contact**

eventi@studioguidisrl.it

**Abstract**

The meeting, primarily targeted at young italian string theorists and postdocs, is meant as an occasion to discuss, in an informal atmosphere, recent developments in string theory and related areas. The meeting is organized in thematic sessions. There will be five half-day sessions, each focusing on a specific topic, with a 90 minutes blackboard presentation by two speakers and a subsequent discussion where all participants can make questions, comments, and share their understanding and doubts.

**Topics**

- Recent developments in Flux Compactifications:

D. Cassani (Padova U.), L. Martucci (INFN, Sez. Roma Tor Vergata)

- Galileon at GGI:

P. Creminelli (ICTP, Trieste), A. Nicolis (Columbia U. & ISCAP, New York), E. Trincherini (SISSA, Trieste).

- Holographic Optics:

A. Amariti (UC, San Diego), D. Forcella (ENS, Paris and ULB, Bruxelles), A. Mariotti (VUB, Bruxelles).

- Higher Spins and Holography:

C. Iazeolla (Bologna U.), L. Mazzucato (SUNY, Stony Brook)

- Dual Superconformal Symmetry:

L. Ferro (Humboldt U., Berlin), R.
Ricci (Imperial Coll., London)

**Talks**

Dec, 20 2010 - 09:30 | D. Cassani, L. Martucci | Recent developments in Flux Compactifications | We discuss some recent topics in flux compactifications, focusing on the search for de Sitter solutions of string theory. This is a challenging open problem that, in order to evade a series of no-go theorems, requires various non-trivial ingredients, such as orientifold sources and significant warping. We present the various approaches that have been explored, both in a four-dimensional and a ten-dimensional perspective. We emphasize the achievements, in particular some tree-level solutions on SU(3) structure manifolds, as well as what still remains to do. We try to point out the general features that seem necessary in order to obtain de Sitter solutions. | |||||

Dec, 20 2010 - 14:30 | P. Creminelli, A. Nicolis, E. Trincherini | Galileon at GGI | We will review several aspects of so-called galileon theories: their peculiar field-theoretical properties, their relevance for IR modifications of gravity in the present universe, their ability to violate the null-energy condition within effective field theory, and their relevance for alternative early universe scenarios. | |||||

Dec, 21 2010 - 09:30 | A. Amariti, D. Forcella, A. Mariotti | Holographic Optics | Electromagnetic waves in continous media have been a large field of investigation in the last years. Indeed light waves have an amazing behavior in a new class of artificial material (metamaterials), created in laboratories about a decade ago. One of the most attractive properties is the negative refractive index: namely the energy flux and the phase velocity of a wave packet are in opposite direction for a certain range of frequencies. It is promising both for applications (perfect lenses, cloaking, invisibility) both for theoretical developments. In the first part of the lecture we show that negative refraction is an ubiquitous property of strongly coupled system described by relativistic hydrodynamics. As an example we test this idea with AdS/CFT. Indeed we show that negative refraction is generic in a material described by a field theory dual to an AdS_5 RN Black Hole. In the second part of the lecture we observe that the crucial property satisfied by these systems is the wavelength dependence of the optical dispersion relations (namely spatial dispersion). In crystal optics this spatial dependence of the response function is connected with the creation of additional light waves (ALWs) in the crystal itself. We show that these ALWs are common in media described by AdS/CFT. | Slides | ||||

Dec, 21 2010 - 14:30 | C. Iazeolla, L. Mazzucato | Higher Spins and Holography | We will introduce the holographic correspondence between the O(N) model and the higher spin gravity theory in anti-de Sitter space. We will review the existing evidence for such a correspondence and describe a recent attempt to derive the duality from first principles, using the exact renormalization group equations. We shall describe some of the peculiar features of the higher-spin gravity theory and how they are encoded in the Vasiliev equations, that capture the classical dynamics of infinitely many fields of all spins at all orders in the interactions. In particular, we shall present a conceptual route to the Vasiliev equations, highlighting their underlying algebraic structure and some relevant aspects of their covariant first-order formulation (\"unfolded\" formulation) that have been instrumental in writing down consistent non-linear deformations to all orders in closed form. | |||||

Dec, 22 2010 - 09:30 | L. Ferro, R. Ricci | Dual Superconformal Symmetry | Scattering amplitudes in N=4 super Yang-Mills theory have been studied extensively in recent years, due to their remarkable features. In particular, planar amplitudes exhibit a hidden symmetry, dual superconformal symmetry, not related (at least not in an obvious way) to the standard superconformal one. We will review how this symmetry becomes manifest by introducing the dual supercoordinate space. We will explain the relation between scattering amplitudes and Wilson loops. Then we will discuss how dual and standard superconformal symmetries together constitute Yangian symmetry. The same dual superconformal symmetry also emerges at strong coupling as can be seen from string theory. In analogy to gauge theory we will see that combining bosonic T-duality with a duality transformation on the fermionic variables maps the superstring action into itself. One implication is that, after duality, the superstring has a dual superconformal symmetry group. Furthermore this dual superconformal symmetry can be seen as a consequence of the integrability of the superstring. |