Literatura académica sobre el tema "Spinory"

This thesis reviews the method of Mafra, Schlotterer, and Stieberger (2011) for computing the full colour ordered N-point open superstring amplitude using the Pure Spinor formalism. We introduce relevant elements of super Yang-Mills theory and examine the basics of the Pure Spinor formalism, with a focus on tools for amplitude computation. We then define a series of objects with increasingly useful BRST transformation properties, which greatly simplify the calculations, and show how these properties can be determined using a diagrammatic method. Finally, we use the explicit four- and five-point amplitude computations as stepping stones to compute the general N-point amplitude, which factors into a set of kinematic integrals multiplying SYM subamplitudes.

Orientador: Julio Marny Hoff da Silva<br>Resumo: Espinores exóticos surgem quando a topologia da variedade $M$ tomada como sendo o espaço-tempo é suposta ser não-trivial, no sentindo que seu grupo fundamental é não-trivial: $\pi_1(M) \neq 0$. Assim, um novo termo exótico $\partial_\mu \theta$ surge na equação dinâmica destes espinores, e novas propriedades se apresentam. A não-trivialidade de $\pi_1(M)$ pode ser diretamente ligada a própria existência de buracos negros. Assim, estudamos, nesta tese, relações entre estruturas espinoriais exóticas e a taxa de emissão de radiação Hawking por buracos negros assintoticamente \textit{flat} em Relatividade Geral, encontrando equações diferenciais para o termo exótico, o que dá a possibilidade de inferir uma forma explícita para $\theta$. Também, tratamos aqui dos chamados espinores RIM, que são espinores que respeitam uma equação dinâmica não-linear chamada de equação não-linear de Heisenberg. Apresentamos dois lemas relativos a estes espinores: um deles encontrando restrições para ocorrer a decomposição de espinores de Dirac em termos de espinores RIM, e outro que nega a existência de espinores RIM exóticos, ou seja, relaciona a existência de espinores RIM a própria estrutura topológica do espaço-tempo. Ainda, encontramos um método de classificarmos os espinores RIM nas classes de Lounesto. Por fim, apresentamos, na forma de dois teoremas, maneiras de deformar homotopicamente tais espinores no que chamamos de \textit{spinor-plane}.<br>Abstract: Exotic spinors emerge when the topology associatd to the manifold $M$, which is token as being the spacetime, is suppose to be non-trivial, in the sense that its fundamental group is non-trivial: $\pi_1(M) \neq 0$. Thus, a new exotic term $\partial_\mu \theta$ rises from the dynamical equation related to these spinors, and new properties are in order. The non-triviality of $\pi_1(M)$ may be directly linked to the very existence of black holes. In this vein, we study some relations between exotic spinorial structures and the Hawking radiation emission rate by asymptotically flat black holes solutions of General Relativity, finding an equation from which an explicity form for the exotic term could be inferred. Moreover, we work on the so-called RIM spinors, which are spinor fields satisfying a non-linear dynamical equation known as Heiseing non-linear equation. We present two \textit{lemmata} related to these spinors: one of them gives us restrictions for the decompostion of Dirac fields in terms of RIM spinors to occur, while the other deny the existence of exotic RIM spinors, i.e., it relates the very existence of RIM spinors to the spacetime topological structure. Besides, we develop a classifying method for RIM spinors into the Lounesto classes. Finally, we present, in the form of two theorems, ways to homotopically deform such spinors in what we call the spinor-plane.<br>Doutor

This thesis is based on five articles, four of which have been published in the Journal of Mathematical Physics, Physical Review D, Modern Physics Letters A and Journal of High Energy Physics. The fifth has been submitted to Mathematika. In these works we study several distinct problems within the broad subject area of Mathematical Physics. The common feature is that all these works deal with rotations of one form or another. In particular, we show an equivalence between the massless and massive Dirac equations and models based on the concept of rotating material points. We also solve an open problem in Einstein-Cartan theory, namely, we find a natural matter source for a non-trivial spin angular momentum tensor. Finally, we construct a complete class of non-standard (non-local) spinor field theories and examine their possible applications in Cosmology.

This thesis is concerned with the theory of spinors, embeddings and everywhere invariance with applications to general relativity. The approach is entirely geometric with particular emphasis on the use of natural structures. A clear indication of the interaction between the above topics is given; this Interaction then sheds light on various aspects of general relativity theory. The main ideas discussed are:- (i) Spinors, conformal structure and the spacetime projective null bundle framework. (ii) Spaces of embeddings. (ill) Embeddings and spin structure. (iv) Null embeddings and the null limit (a technique for obtaining differential equations on null hypersurfaces). (v) Quasi-local momentum. (vi) The space of metrics, natural group actions and generalized conformal structure. (vii) Everywhere invariance and the invariance equation as a method for obtaining spacetime symmetries. Three appendices are also provided:- These give comprehensive summaries of the theories of principal bundles, conformal structure and asymptotic simplicity.

Ultracold atomic gases have established themselves as quantum systems, which are clean and offer a high degree of control over crucial parameters. They are well isolated from their environment and thus offer the possibility to study coherent many-body dynamics. In this thesis, we address the dynamics of ultracold Fermions with large spin. Fermionic spinor gases differ from the typical situation in condensed matter physics, due to both the presence of the trap and the possibility of having fermions with large (>1/2) spin. Compared to the spin-1/2 case, large spin fermions must have one of two possible new properties. Either they obey an enhanced SU(N) symmetry, or they feature spin-changing collisions and a quadratic Zeeman shift. Here, we address the latter case. In the weakly interacting scenario, there are three different regimes. For very weak interactions, the system is in the collisionless regime and interactions can be taken into account on a mean-field level. For stronger interactions, collisions ensure local equilibrium and the system is described by hydrodynamic equations. For the intermediate regime however, there is no simple description. Moreover, the scattering cross-section for spin-changing and spin-conserving collisions can be different for large-spin fermions and we find a situation, where the system is hydrodynamic with respect to one process but not the other. In this thesis, a semi-classical Boltzmann equation with full spin coherence is developed, which allows to interpolate between the collisionless and hydrodynamic regime in the presence of the trap and for large spins. This approach goes beyond mean-field theory and treats the single-particle dynamics as an open system coupled to an environment given by all other particles. We find good agreement with experiments performed in the group of Klaus Sengstock at Hamburg University, using ultracold Potassium-40. We begin by investigating the effect of the harmonic trap on a collisionless system. We find a dynamical mechanism for spin-segregation, the mean-field driven creation of two domains of opposite magnetization in phase-space. The effect finds a transparent explanation when introducing the concept of dynamically induced long-range interactions, occurring when the fast phase-space rotation induced by a strong parabolic trap effectively smears out the contact interactions. Further results in this thesis have been achieved in collaboration with the experimental group in Hamburg. In the first project, we study the collective excitations of a trapped four-component Fermi gas. Long wavelength spin waves are excited by using a magnetic field gradient to wind up a spin spiral. During the subsequent dynamics, the spin components oscillate in the trap, while the total density remains constant. The dynamics can be understood quantitatively by disentangling it into dipolar, nematic and octupolar configurations. In a further experiment with spin-9/2 fermions, it was found that spin-changing interactions can lead to collective and coherent oscillations of the spin state of the whole Fermi sea with long lifetimes. It is found theoretically, that these giant oscillations are protected from spatial dephasing by dynamically induced long-range interactions. We identify the suppression of such oscillations in the high-density regime as the consequence of incoherent non-forward scattering. In the last project, we study collision processes in ultracold Potassium in greater detail. We find that they can be arranged in 3 categories: Spin-changing vs. spin-conserving collisions, processes depending on density vs. processes depending on density gradients and forward vs. lateral scattering. With this categorization, as well as the exact dependence of each process on scattering lengths and momenta, we can explain and simulate not only the coherent mean-field driven oscillations, but also relaxation effects that appear to be incoherent on the single-particle level<br>Gases atómicos ultrafríos han establecido como sistemas cuánticos limpias que ofrecen un alto grado de control sobre parámetros cruciales. Están bien aisladas de su entorno y por eso ofrecen la posibilidad de estudiar la dinámica coherente de muchos cuerpos. En esta tesis, estudiamos la dinámica de fermiones ultrafríos con spin largo. Gases espinoriales fermiónicos difieren de la situación típica en la física de materia condensada por la presencia de la trampa y la posibilidad de tener un spin largo (> 1/2). En comparación con el caso de spin 1/2, fermiones de espín largo deben tener una de dos posibles propiedades nuevas. Obedecen a una simetría ampliada SU(N), o muestran colisiones spin-cambiante y un efecto Zeeman cuadrático. Aqui tratamos el segundo caso. En el escenario de interacciónes débiles, hay tres regímenes diferentes. Para interacciones muy débiles, el sistema está en el régimen sin colisiones e interacciones se puede describir en un nivel de campo medio. Para interacciones fuertes, las colisiones garantizan el equilibrio local y el sistema es descrito por ecuaciones hidrodinámicas. Para el régimen intermedio, no hay una descripción sencilla. Ademas, la sección transversa de dispersión para colisiones spin-cambiantes y de spin-conservación puede ser diferente para fermiones de espín largo. Encontramos una situación, donde el sistema es hidrodinámico con respecto a un proceso, pero no a la otra. En esta tesis desarrollamos una ecuación de Boltzmann semi-clásica, que permite interpolar el régimen intermedio, en presencia de la trampa y para espín largo. Este enfoque trata la dinámica de un cuerpo como un sistema abierto, acoplado a un entorno determinado por todas las atomos demás. Encontramos un buen acuerdo con experimentos realizados en el grupo de Klaus Sengstock en la Universidad de Hamburgo, hechos con potasio-40 ultrafrío. Comenzamos investigando el efecto de la trampa armónica en un sistema sin colisiones. Encontramos un mecanismo dinámico par la segregación de spin, la creación de dos dominios de magnetización opuesta en el espacio fásico, impulsada por el campo medio. Encontramos una explicación transparente de este efecto con la introducción del concepto de interacciones de largo alcance inducidos dinámicamente, que se forma cuando una fuerte trampa parabólica desenfoque eficazmente las interacciones de contacto. Otros resultados de esta tesis han sido realizados en colaboración con el grupo experimental en Hamburgo. En el primer proyecto, estudiamos las excitaciones colectivas de un gas de Fermi atrapada, con cuatro componentes de spin. Ondas de spin con larga longitud de onda se excitan mediante un gradiente de campo magnético. Durante la dinámica siguiente, los componentes de spin oscilan en la trampa, mientras que la densidad total permanece constante. Podemos entender esta dinámica cuantitativamente desligandola en configuraciones dipolares, nemáticos y octupolares de espín. En un experimento siguiente con fermiones de spin 9/2, se encontró que las interacciones spin-cambiando pueden activar oscilaciones colectivas y coherentes del estado de spin de todo el mar de Fermi con duración larga. Descubrimos teóricamente, que estas oscilaciones gigantes están protegidos de desfase espacial por las interacciones de largo alcance inducidos dinámicamente. Identificamos la supresión de tales oscilaciones en el régimen de alta densidad como la consecuencia de la dispersión incoherente lateral. En el último proyecto, estudiamos los procesos de colisión en potasio ultrafrío en mas detalle. Podemos organizarlos en tres categorías: Colisiones spin-cambiante vs. spin-conservación, procesos dependiente de la densidad vs. gradientes de densidad y colisiones hacia adelante vs. laterales. Con esta clasificación y la dependencia en la longitud de dispersión y momentos, podemos explicar y simular no sólo las oscilaciones coherentes impulsados por el campo medio, sino también efectos de relajación