In this thesis we use the holographic gauge/gravity duality to study two different aspects of strongly coupled non-Abelian plasmas. In the first topic we study the effects of strong (Abelian) magnetic fields on the transport coefficients of a strongly coupled non-Abelian plasma. Due to the spatial anisotropy created by the magnetic field, the most general viscosity tensor of a magnetized plasma has 5 shear viscosity coefficients and 2 bulk viscosities. We use the holographic correspondence for a strongly coupled N=4 Supersymmetric Yang-Mills (SYM) plasma to evaluate the shear viscosity perpendicular to the magnetic field and the shear viscosity parallel to the field. In the presence of a magnetic field, the shear viscosity perpendicular to the field saturates the Kovtun-Son-Starinets viscosity bound while in the direction parallel to the field the bound is violated. The second topic investigated in this thesis is motivated by the study of the near equilibrium behavior of strongly interacting non-Abelian plasmas that display a critical point in their phase diagram. We focus on the spectra of non-hydrodynamic quasinormal modes of a strongly coupled N=4 SYM plasma in the presence of a chemical potential, which displays a critical point in equilibrium. Except close to the critical point, we observe that by increasing the chemical potential one generally increases the damping rate of the quasinormal modes, which leads to a reduction of the characteristic equilibration times in the dual strongly coupled plasma. However, as one approaches the critical point the typical equilibration time increases though its derivative with respect to the chemical potential diverges with an exponent equal to -1/2. We also find a purely imaginary non-hydrodynamical mode in the vector diffusion channel at nonzero chemical potential which dictates the equilibration time in this channel near the critical point. / Nessa tese usamos a dualidade holográfica calibre/gravidade para estudar dois aspectos diferentes de plasmas não-Abelianos fortemente acoplados. No primeiro tópico estudamos os efeitos de campos magnéticos (Abelianos) intensos sobre o coeficientes de transporte de um plasma não-Abeliano fortemente acoplado. Devido à anisotropia espacial criada pelo campo magnético, o tensor de viscosidade mais geral de um plasma magnetizado deve possuir 5 coeficientes de viscosidade de cisalhamento e 2 de viscosidade volumétrica. Usamos a correspondência holográfica para um plasma N=4 Supersimétrico de Yang-Mills (SYM) fortemente acoplado para calcular a viscosidade de cisalhamento perpendicular ao campo magnético e a viscosidade de cisalhamento paralela ao campo. Na presença do campo magnético, a viscosidade de cisalhamento perpendicular ao campo satura o limite viscoso de Kovtun-Son-Starinets enquanto que na direção paralela ao campo o limite é violado. O segundo tópico investigado nessa tese é motivado pelo estudo do comportamento próximo ao equilíbrio de plasmas não-Abelianos fortemente interagentes que exibem um ponto crítico em seus diagramas de fase. Focamos no espectro dos modos quasinormais não-hidrodinâmicos de um plasma N=4 SYM fortemente acoplado na presença de um potencial químico, que exibe um ponto crítico no equilíbrio. Exceto próximo ao ponto crítico, observamos que ao aumentar o potencial químico geralmente se intensifica a taxa de amortecimento dos modos quasinormais, que levam à redução dos tempos de equilibração característicos do plasma dual fortemente acoplado. Entretanto, aproximando-se do ponto crítico o tempo de equilibração típico aumenta embora sua derivada em relação ao potencial químico diverge com um expoente igual à -1/2. Encontramos também um modo não-hidrodinâmico puramente imaginário no canal de difusão vetorial com potencial químico não-nulo que dita o tempo de equilibração neste canal próximo do ponto crítico.

In this thesis we use the holographic gauge/gravity duality to study two different aspects of strongly coupled non-Abelian plasmas. In the first topic we study the effects of strong (Abelian) magnetic fields on the transport coefficients of a strongly coupled non-Abelian plasma. Due to the spatial anisotropy created by the magnetic field, the most general viscosity tensor of a magnetized plasma has 5 shear viscosity coefficients and 2 bulk viscosities. We use the holographic correspondence for a strongly coupled N=4 Supersymmetric Yang-Mills (SYM) plasma to evaluate the shear viscosity perpendicular to the magnetic field and the shear viscosity parallel to the field. In the presence of a magnetic field, the shear viscosity perpendicular to the field saturates the Kovtun-Son-Starinets viscosity bound while in the direction parallel to the field the bound is violated. The second topic investigated in this thesis is motivated by the study of the near equilibrium behavior of strongly interacting non-Abelian plasmas that display a critical point in their phase diagram. We focus on the spectra of non-hydrodynamic quasinormal modes of a strongly coupled N=4 SYM plasma in the presence of a chemical potential, which displays a critical point in equilibrium. Except close to the critical point, we observe that by increasing the chemical potential one generally increases the damping rate of the quasinormal modes, which leads to a reduction of the characteristic equilibration times in the dual strongly coupled plasma. However, as one approaches the critical point the typical equilibration time increases though its derivative with respect to the chemical potential diverges with an exponent equal to -1/2. We also find a purely imaginary non-hydrodynamical mode in the vector diffusion channel at nonzero chemical potential which dictates the equilibration time in this channel near the critical point. / Nessa tese usamos a dualidade holográfica calibre/gravidade para estudar dois aspectos diferentes de plasmas não-Abelianos fortemente acoplados. No primeiro tópico estudamos os efeitos de campos magnéticos (Abelianos) intensos sobre o coeficientes de transporte de um plasma não-Abeliano fortemente acoplado. Devido à anisotropia espacial criada pelo campo magnético, o tensor de viscosidade mais geral de um plasma magnetizado deve possuir 5 coeficientes de viscosidade de cisalhamento e 2 de viscosidade volumétrica. Usamos a correspondência holográfica para um plasma N=4 Supersimétrico de Yang-Mills (SYM) fortemente acoplado para calcular a viscosidade de cisalhamento perpendicular ao campo magnético e a viscosidade de cisalhamento paralela ao campo. Na presença do campo magnético, a viscosidade de cisalhamento perpendicular ao campo satura o limite viscoso de Kovtun-Son-Starinets enquanto que na direção paralela ao campo o limite é violado. O segundo tópico investigado nessa tese é motivado pelo estudo do comportamento próximo ao equilíbrio de plasmas não-Abelianos fortemente interagentes que exibem um ponto crítico em seus diagramas de fase. Focamos no espectro dos modos quasinormais não-hidrodinâmicos de um plasma N=4 SYM fortemente acoplado na presença de um potencial químico, que exibe um ponto crítico no equilíbrio. Exceto próximo ao ponto crítico, observamos que ao aumentar o potencial químico geralmente se intensifica a taxa de amortecimento dos modos quasinormais, que levam à redução dos tempos de equilibração característicos do plasma dual fortemente acoplado. Entretanto, aproximando-se do ponto crítico o tempo de equilibração típico aumenta embora sua derivada em relação ao potencial químico diverge com um expoente igual à -1/2. Encontramos também um modo não-hidrodinâmico puramente imaginário no canal de difusão vetorial com potencial químico não-nulo que dita o tempo de equilibração neste canal próximo do ponto crítico.

Résumé : Au cours de cette thèse nous nous sommes intéressés à différentes propriétés de transport électrique, thermique et thermoélectrique. En particulier, nous avons mis en évidence les effets Righi-Leduc anomal et planaire qui sont les équivalents thermiques des effets Hall anomal et planaire. Ces effets doivent impérativement être considérés dans l’interprétation des mesures d’effet Seebeck de Spin.Nous avons mis à profit les techniques développées dans le cadre de cette étude pour étudier l’effet Nernst dans InSb. Nous avons utilsé un modèle de distribution de porteur pour expliquer les non-linéarités de celui-ci à des champs magnétiques proches de 1T.Nous avons construit une expérience de résonance ferromagnétique dont le but sera d’étudier les implications des effets thermique et thermoélectrique dans les expérience de pompage de spin. Enfin, nous nous sommes intéréssés au transport électrique en géométrie Corbino. La géométrie Corbino est celle d’un disque dans laquelle il n’existe aucun bord libre ou des charges peuvent s’accumuler. Cela se traduit par l’apparition d’un courant de Hall ortho-radial dont la conséquence est l’augmentation de la résistance du disque. Nous avons mis en évidence une augmentation de résistance en géométrie Corbino dans CoGd et CoTb dont l’origine est l’effet Hall anomale. Bien que cet effet ne soit pas dissipatif, il a donné naissance à un courant dissipatif transverse. Nous avons également vu que cet effet entre en compétition avec la magnétorésistance anisotrope dans le permalloy.Du fait de la similitude entre l’effet Hall anomal et l’effet Hall de spin, on s’attend dans le platine à l’existence d’un fort courant de spin orthoradial sans possibilités d’accumulations dont la mise en évidence expérimentale fera l’objet de travaux futurs. / Abstract: During this PhD we studied different electric, thermal and thermoelectric properties. For instance, we characterized the anomalous and planar Righi-Leduc effects which are the thermal equivalent of the anomalous and planar Hall effects. These effect have to be taken into account when interpreting spin Seebeck measurements.We used the technics that we developped during this study to look at the Nernst effect in InSb. We developped, a carrier mobility distribution model to explain its non-linearity at fields around 1T.We built a ferromagnetic resonance experiment in order to study the impact of thermal and thermoelectric properties in spin pumping effect.Lastly, we studied electric transport in the Corbino geometry. Corbino geometry is the one of a disc where there are no free boundaries where electric charges can accumulate. This causes the apparition of an orthoradial Hall current which consequence is the increase of resistance of the disc. We showed an increase of resistance in the Corbino geometry in CoGd and CoTb originating from anomalous Hall effect. Despite the anomalous Hall effect does not dissipate, it produces an orthoradial current which dissipates. We also found in permalloy that this increase of resistance is counterbalanced by a decrease of resistance due to the anisotropic magnetoresistance.The similarity between anomalous Hall effect and spin Hall effect which share a common microscopic origin implies that we expect in platinum the apparition of an orthoradial spin current without possibility for the charges to accumulateition. This current should dissipate just the way it does for the anomalous Hall effect.The study of this spin current will be the topic of a futur study.

Turbulent phenomena are found in both natural (e.g. the Earth's oceans, the Sun's corona) and artificial (e.g. flows through pipes, the plasma in a tokamak device) settings; evidence suggests that turbulence is usually the normal behaviour in most cases. Turbulence has been studied extensively for more than a century, but a complete and consistent theoretical description of it has not yet been proposed. It is in this context that the motion of particles under the influence of turbulent fields is studied in this work, with direct numerical simulations. The thesis is structured in three main parts. The first part describes the tools that are used. Methods of integrating particle trajectories are presented, together with a discussion of the properties that these methods should have. The simulation of magnetohydrodynamic (MHD) turbulence is discussed, while also introducing fundamental concepts of fluid turbulence. Particle trajectory integration requires information that is not readily available from simulations of turbulent flows, so the interpolation methods needed to adapt the fluid simulation results are constructed as well. The second part is dedicated to the study of two MHD problems. Simulations of Kolmogorov flow in incompressible MHD are presented and discussed, and also simulations of the dynamo effect in compressible MHD. These two scenarios are chosen because large scale structures are formed spontaneously by the turbulent flow, and there is an interest in studying particle transport in the presence of structures. Studies of particle transport are discussed in the third part. The properties of the overall approach are first analyzed in detail, for stationary predefined fields. Focus is placed on the qualitative properties of the different methods presented. Charged article transport in frozen turbulent fields is then studied. Results concerning transport of particles in fully developed, time-evolving, turbulent fields are presented in the final chapter.<p><p><p>\ / Doctorat en Sciences / info:eu-repo/semantics/nonPublished