Dissertações em Física (Mestrado) - PPGF/ICEN
URI Permanente para esta coleçãohttps://repositorio.ufpa.br/handle/2011/2340
O Mestrado Acadêmico iniciou-se em 2003 e pertence ao Programa de Pós-Graduação em Física (PPGF) do Instituto de Ciências Exatas e Naturais (ICEN) da Universidade Federal do Pará (UFPA).
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Navegando Dissertações em Física (Mestrado) - PPGF/ICEN por Orientadores "CRISPINO, Luís Carlos Bassalo"
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Item Acesso aberto (Open Access) Fonte escalar acoplada ao campo de Klein-Gordon orbitando um objeto estelar(Universidade Federal do Pará, 2006-02) MEIRA FILHO, Damião Pedro; CRISPINO, Luís Carlos Bassalo; http://lattes.cnpq.br/4033994493756291In this work we determine, using Quantum Field Theory in tree level, the scalar radiation emitted by a source in uniform circular motion in Minkowski spacetime, assuming Newtonian gravitation, and in the curved spacetime of a chargeless black hole with null angular momentum, assuming General Relativity. We perform this calculation analitically for the case of Minkowski spacetime and numerically for Schwarzschild spacetime. In the black hole case we obtain the analytic form and the normalization of the modes in the asymptotic regions. We verify, for stable circular orbits acording to general relativity, that the emitted power in Schwarzschild spacetime is lower than the one obtained in Minkowski spacetime assuming Newtonian gravitation. We obtain that only a little amount of the emitted radiation is absorbed by black hole. We also verify that the difference between the emitted powers in Schwarzschild and Minkowski cases decreases if the mass of ¯eld is increased. In Schwarzschild spacetime, the amount of radiation absorbed by the black hole increases for higher values of the mass of the scalar field.Item Acesso aberto (Open Access) Modos quasinormais e pólos de Regge para os buracos acústicos canônicos(Universidade Federal do Pará, 2010-10-08) OLIVEIRA, Leandro Amador de; CRISPINO, Luís Carlos BassaloUsing the relativistic framework in the study of the propagation of linear perturbations in ideal fluids, we obtain a strong anology with the results found in the Theory of General Relativity. In this context, according to Unruh [W. Unruh, Phys. Rev. Letters 46, 1351 (1981)], it is possible to mimic a spacetime with an effective metric in an ideal fluid, barotropic, irrotacional and perturbed by acoustic waves. These spacetimes are called acoustic spacetimes and satisfy the geometric and kinematic properties of a curved spacetimes. In this work, we study the quasinormal modes and the Regge poles for the so called canonical acoustic hole. In our study, we use an asymptotic expansion method proposed by Dolan e Ottewill [S. R. Dolan and A. C. Ottewill, Class. Quantum Gravity 26, 225003 (2009)] to compute, for arbitrary overtones n, the quasinormal frequencies and angular momentum of the Regge poles, as well as their correspondent wavefunctions. The quasinormal frequencies and quasinormal wavefunction are expanded in inverse powers of L = l + 1/2 , where l is the angular momentum, while the angular momentum and wavefunction of the Regge poles are expanded in inverse powers of the frequency of oscillation of the canonical acoustic hole. We validate our results against existing ones obtained using Wentzel-Kramers-Brillouin (WKB) approximation, and we obtain excellent agreement in the limit of the eikonal approximation (l ≥ 2 e l > n).Item Acesso aberto (Open Access) Potenciais pseudo-newtonianos e a radiação escalar emitida por uma fonte girando ao redor de um objeto estelar(Universidade Federal do Pará, 2010) CRUZ FILHO, Jaime Luis Cardoso da; CRISPINO, Luís Carlos Bassalo; http://lattes.cnpq.br/4033994493756291We use the pseudo-newtonian potentials proposed by Paczynski and Wiita, Nowak and Wagoner and Artemova et al. to calculate the scalar radiation emitted by a source in uniform circular motion around a stellar object. We compare the results obtained in this approach with the results obtained via quantum eld theory in Schwarzschild spacetime. We find that, up to the marginally stable circular orbit (R = 6M) the potential that better reproduces the Schwarzschild result is the Nowak and Wagoner one. Between this orbit and the last unstable circular orbit (R = 3M) neither one of the pseudo-newtonian potentials produce satisfactory results, and the newtonian potential turns out to be the best approximation. The Paczy nski and Wiita potential, the most used in the literature to analyze accretion disks, generates the less satisfactory results for this situation.Item Acesso aberto (Open Access) Quantização canônica do campo de Proca no espaço-tempo de Rindler e interação de uma fonte uniformemente acelerada com o banho térmico de Unruh(Universidade Federal do Pará, 2010) CORRÊA, Emerson Benedito Sousa; CASTIÑEIRAS RODRÍGUEZ, Jorge; CRISPINO, Luís Carlos Bassalo; http://lattes.cnpq.br/4033994493756291; http://lattes.cnpq.br/5047254977931140We perform the canonical quantization of the massive vector field, first with respect to inertial observers and then with respect to accelerated observers. We investigate how the uniformly accelerated source in Minkowski inertial vacuum interacts with the massive vector field through the computation of its total response rate. This response rate is computed with respect to two different frames, one inertial and the other co-accelerated with that source. According with the Unruh effect, in the accelerated frame, the inertial vacuum corresponds to a thermal bath of particles. Taking into account this effect, we show explicitly that theses response rates are identicals. This result can be used to describe the interaction of static electrons with the Z 0 particles present in the Hawking radiation, provided the electrons are very close to the black hole event horizon.Item Acesso aberto (Open Access) Radiação emitida por uma carga elétrica orbitando um buraco negro de Schwarzschild segundo Teoria Quântica de Campos(Universidade Federal do Pará, 2004-01-21) FIGUEIRA, Rodrigo Murta de Andrade; CRISPINO, Luís Carlos Bassalo; http://lattes.cnpq.br/4033994493756291We performthe quantization of the massless vector field in Minkowski and Schwarz-schild spacetimes, and calculate the radiated power by an electric charge in a circular orbit around an object with mass M in both spacetimes. In the Minkowski case wend the analytical expression for the radiated power using quantum field theory and assuming Newtonian gravity. It coincides with classical Larmors result, since the calculations are performed at the tree level. Since in the Schwarzschild case it is not possible to express the solution of the radial equation in terms of well known special functions, we adopt the following two approaches: analytical approximation in the low frequency limit and numerical computing. The first approach was used as a consistency check for the numerical one. We also use quantum eld theory at tree level in the Schwarzschid case, and the radiated power is obtained both in the low frequency limit as well as numerically. After comparing the results, we conclude that for the same angular velocity of the charge (as measured by asymptotical static observers), the radiated power in Minkowski spacetime is bigger than in Schwarzschild case.Item Acesso aberto (Open Access) Seção de choque de absorção de buracos negros de Schwarzschild e de buracos acústicos canônicos(Universidade Federal do Pará, 2008-02-22) OLIVEIRA, Ednilton Santos de; CRISPINO, Luís Carlos Bassalo; http://lattes.cnpq.br/4033994493756291In this dissertation we compute the absorption cross section of Schwarzschild black holes for the massless scalar and electromagnetic fields. We also compute the absorption cross section of canonical acoustic holes for sound waves. We use a numerical method to obtain the results in arbitrary frequencies. We also obtain analytic expressions for the low- and high-frequency absorption cross sections. The numerical results are in excellent agreement with the low- and high-frequency absorption cross section values obtained analytically. In the zero-frequency limit the absorption cross section tends to the event horizon area value for both the massless scalar field in Schwarzschild spacetime and the canonical acoustic hole cases. However, as the frequency increases, these two results become very different. This shows that, although the spacetime geometry does not influence the absorption cross section in the zero-frequency limit, it is important for arbitrary frequencies. We also see that massless scalar and electromagnetic absorption cross section values for the Schwarzschild black hole coincide for high enough frequencies and angular momenta. The spin of the scattered particle, in this case, although being very important for low frequencies, becomes less relevant to the absorption cross section value as the frequency and the angular momentum of the incident particle increase.Item Acesso aberto (Open Access) Sólitons latentes, cordas negras, membranas negras e equações de estado em modelos de Kaluza-Klein(Universidade Federal do Pará, 2012-06-04) MEDEIROS, Orival Rocha de; CRISPINO, Luís Carlos Bassalo; http://lattes.cnpq.br/4033994493756291In Kaluza-Klein models with an arbitrary number of toroidal internal spaces, we investigate soliton solutions which describe the gravitational field of a massive compact object. Each di-dimensional torus has its own scale factor Ci, i = 1, ..., N, which is characterized by a parameter Yi. We single out the physically interesting solution corresponding to a pointlike mass. For the general solution we obtain equations of state in the external and internal spaces. These equations demonstrate that the point-like mass soliton has dust-like equations of state in all spaces. We also obtain the parameterized post-Newtonian parameters, which give the possibility to obtain the formulas for perihelion shift, deflection of light and time delay of radar echoes. Additionally, the gravitational experiments lead to a strong restriction on the parameters of the model: T = ƩNi=1 diYi = −(2, 1±2, 3)×10−5. The point-like mass solution with Y1 = . . . = YN = (1+ƩNi=1 di)−1 contradicts this restriction. The condition T = 0 satisfies the experimental limitation and defines a new class of solutions which are indistinguishable from general relativity. We call such solutions latent solitons. Black strings and black branes with Yi = 0 belong to this class. Moreover, the condition of stability of the internal spaces singles out black strings/branes from the latent solitons and leads uniquely to the black string/brane equations of state pi = −ε/2, i = 1, . . . ,N, in the internal spaces and to the number of the external dimensions d0 = 3. The investigation of multidimensional static spherically symmetric perfect fluid with dust-like equation of state in the external space confirms the above results.