Made available in DSpace on 2014-12-17T15:14:58Z (GMT). No. of bitstreams: 1 CalistroSCN.pdf: 698756 bytes, checksum: 2ee4fe2f9e66e82eba6613dc8d66afde (MD5) Previous issue date: 2006-07-07 / Coordena??o de Aperfei?oamento de Pessoal de N?vel Superior / In this work we obtain the cosmological solutions and investigate the thermodynamics of matter creation in two diferent contexts. In the first we propose a cosmological model with a time varying speed of light c. We consider two diferent time dependence of c for a at Friedmann-Robertson- Walker (FRW) universe. We write the energy conservation law arising from Einstein equations and study how particles are created as c decreases with cosmic epoch. The variation of c is coupled to a cosmological Λ term and both singular and non-singular solutions are possible. We calculate the "adiabatic" particle creation rate and the total number of particles as a function of time and find the constrains imposed by the second law of thermodynamics upon the models. In the second scenario, we study the nonlinearity of the electrodynamics as a source of matter creation in the cosmological models with at FRW geometry. We write the energy conservation law arising from Einstein field equations with cosmological term Λ, solve the field equations and study how particles are created as the magnetic field B changes with cosmic epoch. We obtain solutions for the adiabatic particle creation rate, the total number of particles and the scale factor as a function of time in three cases: Λ = 0, Λ = constant and Λ α H2 (cosmological term proportional to the Hubble parameter). In all cases, the second law of thermodynamics demands that the universe is not contracting (H ≥ 0). The first two solutions are non-singular and exhibit in ationary periods. The third case studied allows an always in ationary universe for a suficiently large cosmological term / Neste trabalho, n?s obtemos as solu??es cosmol?gicas e investigamos a termodin?mica da cria??o de mat?ria em dois contextos diferentes. No primeiro, n?s propomos um modelo cosmol?gico com a velocidade da luz c variando com o tempo. N?s consideramos duas depend?ncias temporais diferentes para c em um universo plano de Friedmann-Robertson-Walker (FRW). N?s escrevemos a lei da conserva??o da energia que surge das equa??es de Einstein e estudamos como as part?culas s?o criadas quando c decresce com o tempo c?smico. A varia??o de c ? acoplada a um termo cosmol?gico Λ e solu??es singulares e n?o-singulares s?o poss?veis. N?s calculamos a taxa de cria?o adiab?tica de part?culas e o n?mero total de partculas como fun??o do tempo e encontramos os v?nculos impostos pela segunda lei da termodin?mica sobre esses modelos. No segundo cen?rio, n?s estudamos a n?o-linearidade da eletrodin?mica como uma fonte de cria??o de mat?ria em modelos cosmol?gicos com geometria de FRW. N?s escrevemos a lei de conserva??o da energia obtida a partir das equa??es de Einstein com termo cosmol?gico A, resolvemos as equa??es de campo e estudamos como as part?culas s?o criadas quando o campo magn?tico B muda com a ?poca c?smica. N?s obtemos solu??es para a taxa de cria??o adiab?tica de part?culas, o n?mero total de part?culas e o fator de escala como uma fun??o do tempo em tr?s casos: Λ = 0, Λ = constante e Λ / H2 (termo cosmol?gico proporcional ao par?metro de Hubble). Em todos os casos, a segunda lei da termodin?mica imp?e que o universo n?o est? em contra??o (H ≥ 0). As primeiras duas solu??es s?o n?o-singulares e exibem per?odos in acion?rios. O terceiro caso permite universos sempre in acion?rios para um termo cosmol?gico suficientemente grande