Dualities Near the Horizon

In 4-dimensional supergravity theories, covariant under symplectic electric-magnetic duality rotations, a significant role is played by the symplectic matrix M({\phi}), related to the coupling of scalars {\phi} to vector field-strengths. In particular, this matrix enters the twisted self-duality condition for 2-form field strengths in the symplectic formulation of generalized Maxwell equations in the presence of scalar fields. In this investigation, we compute several properties of this matrix in relation to the attractor mechanism of extremal (asymptotically flat) black holes. At the attractor points with no flat directions (as in the N = 2 BPS case), this matrix enjoys a universal form in terms of the dyonic charge vector Q and the invariants of the corresponding symplectic representation RQ of the duality group G, whenever the scalar manifold is a symmetric space with G simple and non-degenerate of type E7. At attractors with flat directions, M still depends on flat directions, but not MQ, defining the so-called Freudenthal dual of Q itself. This allows for a universal expression of the symplectic vector field strengths in terms of Q, in the near-horizon Bertotti-Robinson black hole geometry.Comment: 1+31 pages, 1 Table; v2 : completely reorganized (and shortened) structure, some Sections removed; various clarifications, formulae, and Refs. added; to appear on JHE

A correspondence between modified gravity and General Relativity with scalar fields

We describe a novel procedure to map the field equations of nonlinear Ricci-based metric-affine theories of gravity, coupled to scalar matter described by a given Lagrangian, into the field equations of General Relativity coupled to a different scalar field Lagrangian. Our analysis considers examples with a single and $N$ real scalar fields, described either by canonical Lagrangians or by generalized functions of the kinetic and potential terms. In particular, we consider several explicit examples involving $f(R)$ theories and the Eddington-inspired Born-Infeld gravity model, coupled to different scalar field Lagrangians. We show how the nonlinearities of the gravitational sector of these theories can be traded to nonlinearities in the matter fields, and how the procedure allows to find new solutions on both sides of the correspondence. The potential of this procedure for applications of scalar field models in astrophysical and cosmological scenarios is highlighted.Comment: 14 pages; v2: section IIID extended, some minor corrections, references update

Mapping nonlinear gravity into General Relativity with nonlinear electrodynamics

We show that families of nonlinear gravity theories formulated in a metric-affine approach and coupled to a nonlinear theory of electrodynamics can be mapped into General Relativity (GR) coupled to another nonlinear theory of electrodynamics. This allows to generate solutions of the former from those of the latter using purely algebraic transformations. This correspondence is explicitly illustrated with the Eddington-inspired Born-Infeld theory of gravity, for which we consider a family of nonlinear electrodynamics and show that, under the map, preserve their algebraic structure. For the particular case of Maxwell electrodynamics coupled to Born-Infeld gravity we find, via this correspondence, a Born-Infeld-type nonlinear electrodynamics on the GR side. Solving the spherically symmetric electrovacuum case for the latter, we show how the map provides directly the right solutions for the former. This procedure opens a new door to explore astrophysical and cosmological scenarios in nonlinear gravity theories by exploiting the full power of the analytical and numerical methods developed within the framework of GR.Comment: 11 pages. v2: next discussions inserted, refs added; matches the version accepted for publication in EPJ

Einstein-Cartan pseudoscalaron inflation

We study a class of early universe cosmological models based on Einstein-Cartan gravity and including a higher derivative term corresponding to a power of the Holst scalar curvature. The resulting effective action is basically given by General Relativity and an additional neutral pseudoscalar field (the pseudoscalaron), unequivocally related to the corresponding components of the torsion, that necessarily acquire a dynamics. The induced pseudoscalaron potential provides a realistic inflationary phase together with a very rich postinflationary epoch, resulting by the coupling of the pseudoscalaron to ordinary matter.Comment: 18 pages, 7 figure

Born-Infeld Gravity: Constraints from Light-by-Light Scattering and an Effective Field Theory Perspective

By using a novel technique that establishes a correspondence between general relativity and metric-affine theories based on the Ricci tensor, we are able to set stringent constraints on the free parameter of Born-Infeld gravity from the ones recently obtained for Born-Infeld electrodynamics by using light-by-light scattering data from ATLAS. We also discuss how these gravity theories plus matter fit within an effective field theory framework.Comment: 7 page

ESQUINA MULTIMEDIA – MUSEUM EXHIBITION FOR THE VISUALIZATION OF CHAN CHAN ARCHAEOLOGICAL SITE

[EN] Chan Chan, an archaeological site located at Trujillo, Peru, is a huge historical settlement very large and difficult to visit and some well-conserved architecture, like Huaca Arco Iris, is very far from the core centre of the site. Furthermore many other heavy factors, as illegal excavations, marine salt transported by the wind and the sometime devastating phenomenon of the Niño, are the reasons of the lost of many decorative elements, which are covered due to conservation issues. To overcome the aforesaid problems, we designed, developed and realized the museum exhibition called “Esquina Multimedia”, providing the tourists with interactive and enjoyable applications. An Augmented Reality application has been developed in order to discover ancient artefacts that are invisible because covered by the earth (or by protection structures). A web-browser has been specifically designed to show bas-relieves, with HD visualization and with anaglyph stereoscopic view. Herewith, a wall-mounted panel representing a metric 3D reconstruction by an accurate survey of the building helps the user to find the artefact position.Pierdicca, R.; Malinverni, ES.; Frontoni, E.; Colosi, F.; Orazi, R. (2016). ESQUINA MULTIMEDIA – MUSEUM EXHIBITION FOR THE VISUALIZATION OF CHAN CHAN ARCHAEOLOGICAL SITE. En 8th International congress on archaeology, computer graphics, cultural heritage and innovation. Editorial Universitat Politècnica de València. 274-276. https://doi.org/10.4995/arqueologica8.2016.3191OCS27427