Made available in DSpace on 2015-05-15T11:46:09Z (GMT). No. of bitstreams: 1 arquivototal.pdf: 652579 bytes, checksum: a75e379418567b71eed4fc021cfeeae6 (MD5) Previous issue date: 2011-08-25 / Coordenação de Aperfeiçoamento de Pessoal de Nível Superior / We start studing semi-stable solutions for the equation u = f(u) in a smooth and bounded domain of Rn, 2 n 4. The presented result is a L1 boundedness, which holds for all semi-stable positive solution and all non-linearity f. We also show a approach about the case u = f(u) in the unitary ball of Rn. The results obtained are Lq and Wk;q estimates for semi-stable radial solutions u 2 H1 0 , the proof of a boundedness if n 9 and, in case that g is increasing and convex, u 2 W3;2 in all dimension n. / Começamos estudamos soluções semi-estáveis para a equação u = f(u) em um domínio suave limitado do Rn, 2 n 4. O resultado apresentado é uma limitação L1 a qual vale para toda solução positiva semi-estável e toda nãolinearidade f. Mostramos também uma abordagem sobre o caso u = f(u) na bola unitária do Rn. Os resultados obtidos são estimativas em Lq e Wk;q para soluções semi-estáveis radiais u 2 H1 0 , a prova de uma limitação se n 9 e, no caso em que g é crescente e convexa, u 2 W3;2 em toda dimensão n.

L'existence de la masse négative a un sens parfaitement physique du moment que les conditions d'énergie dominante sont satisfaites par le tenseur énergie-impulsion correspondant. Jusqu'à maintenant, seules des configurations de masses négatives avaient été trouvées. On démontre l'existence de bulles de masse négative stables dans un espace-temps qui s'approche asymptotiquement d'un espace-temps de de Sitter. Les bulles sont des solutions aux équations d'Einstein qui correspondent à une région intérieure qui contient une distribution de masse spécifique séparée par une coquille mince de l'espace-temps à masse négative de Schwarzschild-de Sitter à l'extérieur. Ensuite, on applique les conditions de jonction d'Israel à la frontière de la bulle ce qui impose la conservation d'énergie-impulsion à travers la surface. Les conditions de jonction donnent une équation pour un potentiel pour le rayon de la bulle qui dépend de la distribution de masse à l'intérieur, ou vice versa. Finalement, on trouve un potentiel qui aboutit à une solution stable, statique et non-singulière, ce qui crée une distribution de masse interne qui satisfait les conditions d'énergie dominante partout à l'intérieur. Cependant, la bulle ne satisfait pas ces conditions. De plus, on trouve une solution stable, statique et non-singulière pour une géométrie interne de de Sitter pure. La solution est fondamentalement différente: elle requiert que la densité d'énergie de la bulle change avec le rayon. La condition d'énergie dominante est satisfaite partout. / Negative mass makes perfect physical sense as long as the dominant energy condition is satisfied by the corresponding energy-momentum tensor. Until now, only configurations of negative mass have been found. We demonstrate the existence of stable, negative-mass bubbles in an asymptotic de Sitter space-time. The bubbles are solutions of the Einstein equations which correspond to an interior region of space-time containing a specific distribution of mass separated by a thin wall from the exact, negative mass Schwarzschild-de Sitter space-time in the exterior. Then, we apply the Israel junction conditions at the wall which impose the conservation of energy and momentum across the wall. The junction conditions give rise to an effective potential for the radius of the wall that depends on the interior mass distribution, or vice versa. Finally, we find a potential that gives rise to stable, non-singular, static solutions, which yields an interior mass distribution that everywhere satisfies the dominant energy condition. However, the energy momentum of the wall does not satisfy the dominant energy condition. Moreover, we find a stable, non-singular, static solution for a pure de Sitter geometry inside the bubble. The solution is fundamentally different: the energy density of the bubble is no longer a constant, but now varies with the radius. The dominant energy condition is everywhere satisfied.