Strong Gravity News & Events

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A journey into a black hole

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Gr@v's Ph.D. student (in collaboration with IST-Lisbon) Pedro Cunha produced a short movie illustrating a voyage into a black hole, and in particular the lensing effects visualized by an observer undergoing such journey. The journalist Catarina Lázaro (voice) and Gr@v researcher C. Herdeiro (scientific advising) collaborated in the movie, which will have a premiere on December 3rd 2016 at "Observatório Geofísico e Astronómico da Universidade de Coimbra".

Strong Gravity
Astrophysics

General parametrization of axi-symmetric black holes in metric theories of gravity

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Speaker
Roman Konoplya (Theoretische Astrophysik Tübingen (TAT)
Event date
Venue
GAP room
Event type
Seminars
Abstract: Following previous work of ours in spherical symmetry, we here propose a new parametric framework to describe the spacetime of axisymmetric black holes in generic metric theories of gravity. In this case, the metric components are functions of both the radial and the polar angular coordinates, forcing a double expansion to obtain a generic axisymmetric metric expression. In particular, we use a continued-fraction expansion in terms of a compactified radial coordinate to express the radial dependence, while we exploit a Taylor expansion in terms of the cosine of the polar angle for the polar dependence. These choices lead to a superior convergence in the radial direction and to an exact limit on the equatorial plane. As a validation of our approach, we build parametrized representations of Kerr, rotating dilaton, and Einstein-dilaton-Gauss-Bonnet black holes. The match is already very good at lowest order in the expansion and improves as new orders are added. We expect a similar behavior for any stationary and axisymmetric black-hole metric.
Strong Gravity

Mass Ladder Operators from Spacetime Conformal Symmetry

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Speaker
Masashi Kimura (CENTRA-IST)
Event date
Venue
GAP room
Event type
Seminars
Abstract: We introduce a novel type of ladder operators, which map a scalar field with a mass into another scalar field with a different mass. It is shown that such operators are constructed from closed conformal Killing vector fields $zeta^mu$ in arbitrary dimensions if $zeta^mu$ is the eigen vector of the Ricci tensor.
Strong Gravity

Non-local infinite derivative theories of gravity

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Speaker
Alexey Koshelev (U. Beira Interior)
Event date
Venue
GAP room
Event type
Seminars
Abstract: In my talk I will introduce and review the so-called non-local infinite derivative gravity theory. This gravity modification originates from string field theory and sends signs that it can be UV complete. I will explain the status of these expectations. Then I will pay special account to the possibility of singularities resolution and to application to inflation. Recent results and open questions will be discussed.
Strong Gravity

Scalar fields in AdS with arbitrary boundary conditions and associated two-point functions for the ground state

Hugo Ferreira's photo
Speaker
Hugo Ferreira (INFN Pavia / Pavia University)
Event date
Venue
GAP room
Event type
Seminars

Abstract: Anti-de Sitter is not a globally hyperbolic spacetime. When studying a field theory on anti-de Sitter, one needs an appropriate choice of boundary conditions at the conformal boundary such that the classical field equation is well-posed.

Strong Gravity