PhD thesis defense
Marco Crisostomi from University of L'Aquila and Paris 7 (co-tutorship) will defend his PhD thesis in theoretical physics.
Title: Massive Gravity
A study of modifications of General Relativity (GR) at large distances is presented . GR is the unique theory of a self interacting massless spin two field, the graviton; our study considers the case where the spin two field is instead massive. For a long time, it was believed that such kind of theories were inconsistent due to a ghost instability that generically emerges at nonlinear level. Only recently this problem has been overcome and several modifications that evade this instability have been found. The simplest version of massive gravity theory consists in adding to the Einstein-Hilbert action a potential built from non-derivative self-couplings of the metric. As matter of fact such modification needs additional structure besides the metric. We present the canonical analysis for a general massive deformation of GR in a fully non-perturbative and background independent way and show the conditions that a potential has to satisfy in order to avoid such a instability. Among the possible candidates, we find that Lorentz invariance considerably restricts the viable potentials and, when Minkowski space is required as a background, they probably reduce to a single one.
For this potential we analyze the basic phenomenology in the framework of bigravity theories, where the extra metric needed is taken dynamical. For spherically symmetric solutions, though a discontinuity in the zero mass limit is present at linear level, we show that GR can be recovered close to the source, via the Vainshtein mechanism. Far from the source the static potential has Yukawa behaviour.
The study of cosmological solutions and their linear perturbations is also discussed. In particular, FRW solutions exist and are very close to the ones in GR at early time; at late time the universe flows in a dS phase. Unfortunately, scalar cosmological perturbations show an exponential instability that signals the unreliability of the standard perturbation theory in sharp contrast to GR.
E. Copeland, University of Nottingham
K. Koyama, University of Porthsmouth
M. Maggiore, University of Geneva
S. F. Hassan, University of Stockolm
A. Padilla, University of Nottingham
Advisor L. Pilo, University of L'Aquila
co-Advisor C. Charmousis, Laboratoire de Physique Theorique, Orsay
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For the PhDOct 11, 2017 Masters Thesis Defense Presentation —…11 Apr 2016 Presenting your high-quality design presentation put together than to begin with a25 minute conference paper presentation.
Thesis Defences Masters Thesis ..
The final examination consists of two parts: a public presentation of research and a private oral examination given by the thesis committee immediately after the presentation. Students should at least allow three hours for completion of both the public presentation and private oral examination. Form 152, Acceptance of Dissertation, must be signed by all committee members after successful defense of the thesis.
and supervisor to schedule the defence date and ..
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One defense for this kind of claim is an analysis of the complexity,or completeness, or whatever, of the theoretical algorithm. In computer science,the more common defense is based on empirical results from running anexperiment.A good defense here means more than one example, and answers to questionssuch as the following. What are the capabilities and limits of your experiment?How often do the things that your experiment does come up in the real world?What's involved in extending it? If it's easy to extend, why haven't you?If your example is a piece of a larger system, how realistic are yourassumptionsabout input and output?