Formación de Jets por agujeros negros viajando a altas velocidades en un campo magnético

Tesis (Lic. en Física)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2018.En este trabajo se continuó el estudio numérico de formación de jets por agujeros negros viajandoa altas velocidades con respecto a un campo magnético uniforme comenzado en [1]. El esquema numérico implementado es el utilizado en [2] el cual presenta un esquema numérico 3D para la evolución de las ecuaciones de la electrodinámica force-freealrededor de un agujero negro de Kerr.Tratamos en este trabajo tres situaciones físicas distintas: i) Un agujero negro de Schwarzschild viajando con velocidades ortogonales al campo magnético asintóticamente uniforme. ii) Un agujero negro de Schwarzschild viajando con velocidades no ortogonales al campo magnético asintóticamente uniforme. iii) Un agujero negro de Kerr en la situación de i) donde el eje de rotación del agujero negro puede estar, o no, alineado con el campo magnético asintóticamente uniforme.This work continues the numerical study of jet formation as result of black holes traveling with fast velocities with respect to a uniform magnetic eld, study that was started in [1]. The numerical scheme implemented is the one used in [2], which presents a novel 3D numerical implementation of the force-free electrodynamics evolution around a Kerr black hole. We study three different physical situations: i) A Schwarzschild black hole traveling with velocities that are orthogonal to the asymptotically uniform magnetic eld. ii) A Schwarzschild black hole traveling with velocities that are not orthogonal to the asymptotically uniform magnetic eld. iii) A Kerr black hole in the i) scenario, where the axis of rotation of the black can be aligned, or not, to the asymptotically uniform magnetic eld

Gravitational collapse in Quadratic Gravity

This study explores the gravitational collapse of a massless scalar field within Quadratic Gravity treated as a dimension-four operator Effective Field Theory extension to General Relativity. The additional degrees of freedom associated with the higher derivatives in this theory are removed by an Order Reduction approach, where the truncated expansion nature of the theory is exploited. Through simulations, we find scenarios where solutions remain within the bounds of the Effective Field Theory while displaying significant deviations from General Relativity in the dynamics of curvature invariants during the collapse. Limitations of the approach taken, the Effective Field Theory approximation, and the appearance of instabilities are also discussed

Studying the largest scales in the Universe with the kinetic Sunyaev-Zel'dovich effect

As we progress further into the era of precision cosmology, new avenues to test our fundamental models of the Universe are opening up. This Ph.D. thesis is concerned with the development and understanding of a technique known as kinetic Sunyaev-Zel'dovich (kSZ) velocity reconstruction, which aims to extract information about the Universe on the largest accessible scales using measurements of the Cosmic Microwave Background (CMB) anisotropies sourced by the kSZ effect and data from galaxy redshift surveys. kSZ velocity reconstruction estimates the remote CMB dipole, i.e. the l=1 multipole moment of the observed CMB sky as seen by observers on our past lightcone. This observable probes cosmological perturbations on scales of several Gpc, and thus has the potential to be a valuable source of information on the fundamental early Universe phenomena that leaves imprints on such scales. Preliminary forecasts from the foundational literature on kSZ velocity reconstruction indicate that high signal to noise reconstructions of the remote dipole will be possible in the context of next generation CMB experiments and galaxy surveys. The goal of this thesis is to further develop the technical details of the technique and provide motivation for its use as a tool to probe physics on ultra-large scales. Chapter 1 elaborates on the motivation behind this thesis and provides a review of the key material necessary to understand kSZ velocity reconstruction. Chapter 2 presents an extended formalism for kSZ velocity reconstruction, which describes new sources of noise and bias and incorporates more realistic experimental conditions. Forecasts for the reconstruction of the remote dipole are presented in the same chapter, and these show that high signal to noise is still achievable using the new estimators. Chapter 3 presents the first suite of N-body simulations of remote dipole reconstruction on our past lightcone, which implement a novel methodology to treat the wide range of scales involved in kSZ velocity reconstruction (tens of Mpc to tens of Gpc). These simulations were used to test the robustness of the reconstruction technique against the effects of gravitational non-linearities, redshift space distortions, and CMB lensing. Additionally, these simulations were used to demonstrate the relevance of large scale contributions to the remote dipole that are not captured by other approaches to kSZ velocity reconstruction. Chapter 4 presents an analysis of parameter constraints on CMB anomalies models, aimed to demonstrate that the reconstructed remote CMB dipole and the reconstructed remote CMB quadrupole (obtained using a similar technique to kSZ velocity reconstruction) can help us go beyond the constraints achievable with traditional probes of the anomalies like the primary CMB temperature, primary CMB polarization, and large-scale galaxy distribution

Estabilidad lineal de agujeros negros

Tesis (Lic. en Física)--Universidad Nacional de Córdoba, Facultad de Matemática, Astronomía, Física y Computación, 2016.Se estudia la existencia de energías conservadas para las perturbaciones lineales con simetría axial en la región exterior del agujero negro de Schwarzschild, para perturbaciones que no han alcanzado el horizonte. Con dichas cantidades, se construyen cotas para la perturbación en la región exterior del agujero negro mediante técnicas de análisis funcional y desigualdades geométricas.The existence of conserved energies for linear and axially symmetric perturbations of the exterior of the Schwarzschild black hole is studied, in particular for those perturbations which have not reached the event horizon. Using these conserved quantities, bounds for the linear perturbation are constructed with help of functional analysis and geometrical inequalities technics

Black hole dynamics in Effective Field Theory extensions to General Relativity

This thesis aims to develop and implement mathematical and numerical techniques to enable the study of deviations from General Relativity (GR) in the nonlinear regime. The focus is on studying the nonlinear dynamics of higher derivative Effective Field Theory (EFT) extensions to GR and employing innovative methods to address the associated mathematical and practical challenges. To this end, we utilize two crucial techniques: the Fixing the Equations method, which controls spurious high frequencies, and the Order reduction approach to address challenges related to higher than second order time derivatives and ghosts. The research starts with a detailed study of black hole dynamics in a higher derivative extension of General Relativity described by a dimension-eight operator EFT. A fully nonlinear/non-perturbative treatment is presented for constructing initial data and studying its dynamical behavior in spherical symmetry when coupled to a massless scalar field. Subsequently, we extend the previous work to explore the evolution of black holes merging in quasi-circular orbits within the same higher-derivative EFT extension. This scenario poses more demanding challenges; a toy model and the single-boosted black hole scenario are considered to build up to the binary merger case. The effects of modifications on the dynamics and gravitational wave emission in the binary merger scenario are studied. The research work culminates with a study of gravitational collapse in Quadratic Gravity, the leading order correction to GR from an EFT perspective in the presence of matter fields. An Order Reduction approach is used to eliminate additional degrees of freedom associated with higher order time derivatives. We study the collapse of a massless scalar field into a black hole in spherical symmetry. We explore the stability of our simulations, whether the solutions remain within the bounds of EFT, and their deviations from General Relativity during the collapse

Modelling self-consistently beyond General Relativity

The majority of extensions to General Relativity display mathematical pathologies (higher derivatives, character change in equations that can be classified within PDE theory, and even unclassifiable ones) that cause severe difficulties to study them, especially in dynamical regimes. We present here an approach that enables their consistent treatment and extraction of physical consequences. We illustrate this method in the context of single and merging black holes in a highly challenging beyond GR theory.Comment: 10 pages, 8 figure