Finalized PhD theses

Nombre d'entrades: 86

Lyman-alpha Intensity Mapping forecast with the PAU Survey

Estat: defended (03/03/2021)
Estudiant: Pablo Renard
Supervisat per: Enrique Gaztañaga
Universitat: Universitat Autònoma de Barcelona

In the upcoming years, the amount of observational data available for astrophysics as a whole, and particularly cosmology, is expected to increase by orders of magnitude due to the new observational programs and technological advancements. To fully capitalise on these upcoming observations, new statistical…
Estat: defended (03/03/2021)
Estudiant: Pablo Renard
Supervisat per: Enrique Gaztañaga
Universitat: Universitat Autònoma de Barcelona

In the upcoming years, the amount of observational data available for astrophysics as a whole, and particularly cosmology, is expected to increase by orders of magnitude due to the new observational programs and technological advancements. To fully capitalise on these upcoming observations, new statistical methods to draw scientific results have to be developed and applied. Intensity Mapping is one of such new methods, which consists in the tracing of a sharp spectral feature (e.g., a emission line) in angular coordinates and redshift, without considering resolved objects.
This thesis is focused on the simulation and evaluation of Intensity Mapping with the Lyα line by cross-correlating two kinds of optical surveys: the narrow-band photometric survey PAUS, and the spectroscopic surveys eBOSS and DESI. The former should contain extended Lyα emission from the intergalactic medium in the background of the images, while the latter contains the Lyα forest (i.e., the set of absorption lines generated by the intergalactic medium) in their quasar spectra. Cross-correlating both then should yield a signal of the diffuse Lyα emission, despite the foregrounds and noise in PAUS images.
In order to simulate this, a hydrodynamic simulation specifically designed for the study of Lyα in the intergalactic medium has been used to simulate both Lyα emission and absorption, while the foregrounds in PAUS images have been modeled using a deep lightcone mock catalogue and fitting spectral energy distributions to its objects. Instrumental/atmospheric noise has been added to the simulated PAUS images by directly measuring the noise from sets of masked and stacked images, and introducing it on the simulation as a Gaussian distribution. Besides, a cross-correlation code in Python has been developed from scratch, optimised and validated in the framework of the thesis to compute the cross-correlations.The results are presented in a probabilistic manner: for different cases (PAUS-eBOSS, PAUS-DESI and two hypothetical PAUS extensions with DESI) 1,000 cross-correlations are computed with different realisations of the instrumental/atmospheric noise of PAUS images, as well as quasar positions. With the optimistic approximation of uncorrelated instrumental noise (which would require further work in data reduction), even the largest PAUS extension considered only yields a probability of detection of ∼ 15%; using the actual correlated noise all the probabilities become negligible.
In spite of these negative results, some valuable conclusions are extracted. The different kinds of two-point correlation functions (monopole, parallel and perpendicular to the line of sight) show complementary behaviours: monopole and parallel perform better at larger scales, while perpendicular samples better the scales smaller than 10 Mpc/h. Besides, the redshift smoothing in the Lyα signal due to the photometric filters has been properly implemented in the theoretical model, and can even be used to predict the scales with better SNR for each correlation function. Therefore, these findings indicate that this methodology may be more suitable for broad-band surveys; we conclude the thesis giving some basic guidelines on how this study could be replicated for broad-band data.

Thermo-elastic contributions to the acceleration noise on-board LISA Pathfinder

Estat: defended (29/10/2019)
Estudiant: Rivas, F.
Supervisat per: Miquel Nofrarias Serra; Carlos Sopuerta
Universitat: Universitat Autònoma de Barcelona

Thermal gradients on board the LISA Pathfinder mission can induce effects with a potential impact to perturb the main differential acceleration measurement between both free-falling test masses.

Temperature gradients across the housing induce forces through three different effects, namely asymmetric outgassing, radiation pressure and radiometer effect. The latter is related to the residual gas pressure around the test mass and, therefore,  allows the estimation of the Brownian noise contribution, one of the limiting noise contributions for a future observatory like LISA.

Apart from thermal forces arising due to gradients around the test mass, thermo-elastic effects can also contribute to the instrument noise. There are two locations where such a distortion can be critical. First, the optical window, i.e. the interface between the optical bench and the test mass. This optical element –-the only not bonded on the Zerodur optical bench--- is clamped in a Titanium ring and therefore is susceptible to mechanical stress or changes in the refractive index due to thermal gradients across the glass. The second location are the struts holding the optical bench inside the thermal shield acting as the main thermal link to the outside (thermally noisier) environment. Temperature changes in these structures can induce net displacements or tilts of the bench with direct impact on the interferometer read-out. 

This thesis describes the ultra-stable temperature environment on-board and report on the thermal experiments performed on-board to characterise these effects and estimate their contribution in the mission noise budget.
Thermal gradients on board the LISA Pathfinder mission can induce effects with a potential impact to perturb the main differential acceleration measurement between both free-falling test masses. Temperature gradients across the housing induce forces through three different effects, namely asymmetric…
Estat: defended (29/10/2019)
Estudiant: Rivas, F.
Supervisat per: Miquel Nofrarias Serra; Carlos Sopuerta
Universitat: Universitat Autònoma de Barcelona

Thermal gradients on board the LISA Pathfinder mission can induce effects with a potential impact to perturb the main differential acceleration measurement between both free-falling test masses.

Temperature gradients across the housing induce forces through three different effects, namely asymmetric outgassing, radiation pressure and radiometer effect. The latter is related to the residual gas pressure around the test mass and, therefore,  allows the estimation of the Brownian noise contribution, one of the limiting noise contributions for a future observatory like LISA.

Apart from thermal forces arising due to gradients around the test mass, thermo-elastic effects can also contribute to the instrument noise. There are two locations where such a distortion can be critical. First, the optical window, i.e. the interface between the optical bench and the test mass. This optical element –-the only not bonded on the Zerodur optical bench--- is clamped in a Titanium ring and therefore is susceptible to mechanical stress or changes in the refractive index due to thermal gradients across the glass. The second location are the struts holding the optical bench inside the thermal shield acting as the main thermal link to the outside (thermally noisier) environment. Temperature changes in these structures can induce net displacements or tilts of the bench with direct impact on the interferometer read-out. 

This thesis describes the ultra-stable temperature environment on-board and report on the thermal experiments performed on-board to characterise these effects and estimate their contribution in the mission noise budget.

Study of the Relativistic Dynamics of Extreme-Mass-Ratio Inspirals

Estat: defended (24/10/2019)
Estudiant: Oltean, M.
Supervisat per: Carlos Sopuerta ; Spallicci, A.
Universitat: Universitat Autònoma de Barcelona

The principal subject of this thesis is the gravitational two-body problem in the extreme-mass-ratio regime - that is, where one mass is significantly smaller than the other - in the full context of our contemporary theory of gravity, general relativity. We divide this work into two broad parts: the first provides an overview of the theory of general relativity along with the basic mathematical methods underlying it, focusing on its canonical formulation and perturbation techniques; the second is dedicated to a presentation of our novel work in these areas, focusing on the problems of entropy, motion and the self-force in general relativity.

We begin in Part I, accordingly, by offering a historical introduction to general relativity as well as a discussion on current motivation from gravitational wave astronomy in Chapter 1. Then, in Chapter 2, we turn to a detailed technical exposition of this theory, focusing on its canonical (Hamiltonian) formulation. We end this part of the thesis with a rigorous development of perturbation methods in Chapter 3. For the convenience of the reader, we summarize some basic concepts in differential geometry needed for treating these topics in Appendix A.

In Part II, we begin with a study of entropy theorems in classical Hamiltonian systems in Chapter 4, and in particular, the issue of the second law of thermodynamics in classical mechanics and general relativity, with a focus on the gravitational two-body problem. Then in Chapter 5, we develop a general approach based on conservation laws for calculating the correction to the motion of a sufficiently small object due to gravitational perturbations in general relativity. When the perturbations are attributed to the small object itself, this effect is known as the gravitational self-force. It is what drives the orbital evolution of extreme-mass-ratio inspirals: compact binary systems where one mass is much smaller than - thus effectively orbiting and eventually spiralling into - the other, expected to be among the main sources for the future space-based gravitational wave detector LISA. In Chapter 6, we present some work on the numerical computation of the scalar self-force - a helpful testbed for the gravitational case - for circular orbits in the frequency domain, using a method for tackling distributional sources in the field equations called the Particle-without-Particle method. We include also, in Appendix B, some work on the generalization of this method to general partial differential equations with distributional sources, including also applications to other areas of applied mathematics. We summarize our findings in this thesis and offer some closing reflections in Chapter 7.
The principal subject of this thesis is the gravitational two-body problem in the extreme-mass-ratio regime - that is, where one mass is significantly smaller than the other - in the full context of our contemporary theory of gravity, general relativity. We divide this work into two broad parts: the…
Estat: defended (24/10/2019)
Estudiant: Oltean, M.
Supervisat per: Carlos Sopuerta ; Spallicci, A.
Universitat: Universitat Autònoma de Barcelona

The principal subject of this thesis is the gravitational two-body problem in the extreme-mass-ratio regime - that is, where one mass is significantly smaller than the other - in the full context of our contemporary theory of gravity, general relativity. We divide this work into two broad parts: the first provides an overview of the theory of general relativity along with the basic mathematical methods underlying it, focusing on its canonical formulation and perturbation techniques; the second is dedicated to a presentation of our novel work in these areas, focusing on the problems of entropy, motion and the self-force in general relativity.

We begin in Part I, accordingly, by offering a historical introduction to general relativity as well as a discussion on current motivation from gravitational wave astronomy in Chapter 1. Then, in Chapter 2, we turn to a detailed technical exposition of this theory, focusing on its canonical (Hamiltonian) formulation. We end this part of the thesis with a rigorous development of perturbation methods in Chapter 3. For the convenience of the reader, we summarize some basic concepts in differential geometry needed for treating these topics in Appendix A.

In Part II, we begin with a study of entropy theorems in classical Hamiltonian systems in Chapter 4, and in particular, the issue of the second law of thermodynamics in classical mechanics and general relativity, with a focus on the gravitational two-body problem. Then in Chapter 5, we develop a general approach based on conservation laws for calculating the correction to the motion of a sufficiently small object due to gravitational perturbations in general relativity. When the perturbations are attributed to the small object itself, this effect is known as the gravitational self-force. It is what drives the orbital evolution of extreme-mass-ratio inspirals: compact binary systems where one mass is much smaller than - thus effectively orbiting and eventually spiralling into - the other, expected to be among the main sources for the future space-based gravitational wave detector LISA. In Chapter 6, we present some work on the numerical computation of the scalar self-force - a helpful testbed for the gravitational case - for circular orbits in the frequency domain, using a method for tackling distributional sources in the field equations called the Particle-without-Particle method. We include also, in Appendix B, some work on the generalization of this method to general partial differential equations with distributional sources, including also applications to other areas of applied mathematics. We summarize our findings in this thesis and offer some closing reflections in Chapter 7.

Higher resolution photometric redshifts for cosmological surveys

Estat: defended (02/10/2019)
Estudiant: Alex Alarcon Gonzalez
Supervisat per: Enrique Gaztañaga
Universitat: Universitat Autònoma de Barcelona

We use PAU Survey data to improve measurements of  photometric redhifts
This PhD thesis is focused on the measurement of photometric redshifts in imaging galaxy surveys and its applications to extract cosmological information. In the first part of this thesis we forecast a galaxy survey with very precise redshift information, which can come either from spectroscopy or many…
Estat: defended (02/10/2019)
Estudiant: Alex Alarcon Gonzalez
Supervisat per: Enrique Gaztañaga
Universitat: Universitat Autònoma de Barcelona

This PhD thesis is focused on the measurement of photometric redshifts in imaging galaxy surveys and its applications to extract cosmological information. In the first part of this thesis we forecast a galaxy survey with very precise redshift information, which can come either from spectroscopy or many narrow band images, using the Fisher matrix formalism. We use galaxy clustering, how galaxies group together in space, dividing a sample into two subsamples using other observable parameters. Using two overlapping subsamples reduces the sample variance in the observables, which improves the precision with which one can measure the expansion and growth history of the universe. In the second part of this thesis we measure highly precise photometric redshifts using the data from a novel imaging galaxy survey PAUS that contains a unique set of 40 narrow band filters. We develop two algorithms which use maximum likelihood or Bayesian evidence statistics to infer the redshift probability of each galaxy, which requires modeling both the continuum and emission line galaxy flux. The algorithm contains several corrections to account for systematic effects present in the data calibration which are tested in simulations developed for this purpose. The measurement of PAUS redshifts enables the science of the galaxy survey and can also be used to calibrate the redshift distribution of lensing surveys. The last part of this thesis implements for the first time a hierarchical Bayesian model in an N-body simulation to measure the redshift distribution of a lensing survey using both photometric and density information. Weak lensing is a very powerful tool to extract cosmological information, but it is very sensitive to any bias in the mean redshift of a sample of source galaxies. This method consistently combines all sources of information and merges the main techniques used in the literature to estimate redshift distributions.

Fluid models of accelerating Universe, Doctor of Science thesis which is superior of PHD

Estat: defended (08/11/2018)
Estudiant: A V Timoshkin
Supervisat per: Sergei D Odintsov
Universitat: Tomsk State Pedagogical University

This DS thesis which is superior of PHD  is devoted to description of DE and inflationary universe via fluid models.
Estat: defended (08/11/2018)
Estudiant: A V Timoshkin
Supervisat per: Sergei D Odintsov
Universitat: Tomsk State Pedagogical University

This DS thesis which is superior of PHD  is devoted to description of DE and inflationary universe via fluid models.

Physico-chemical properties of chondritic meteorites: clues on the origin and evolution of their parent bodies

Estat: defended (06/07/2018)
Estudiant: Moyano Cambero, C.E.
Supervisat per: Josep M. Trigo-Rodríguez
Universitat: Universitat Autònoma de Barcelona

Durant aquesta tesi es pretén aprofundir en les propietats físiques, mineralògiques i reflectives de petits asteroides no diferenciats, així com en el seu procés de formació, a través de mostres de meteorits, particularment de les anomenades condrites carbonàcies. Primer de tot es dedicarà part de la tesi a adquirir el bagatge necessari, que inclou els següents punts: - El disc protoplanetary: zones de formació d’asteroides - Descripció de les classes d’asteroides: classes espectrals - Asteroides diferenciats contra no diferenciats: mineralogia distintiva - Grups de meteorits i la seva relació amb asteroides: comparació espectral entre espectres remots i de laboratori. Diferències principals - Processos físics en funcionament sobre les superfícies d’asteroides: alteració espacial (excavació de cràters, bretxació, implantació elemental, rastres de rajos còsmics...) - Evolució col·lisional: propietats de les superfícies cobertes de regòlit (inèrcia tèrmica, conductivitat, etc.) - Comparació d’asteroides i meteorits: mineralogia i química principal D’altra banda les mostres s’analitzaran mitjançant tècniques molt variades d’anàlisi i processat de dades. Objectius: - Obtenir noves pistes sobre els processos de formació d’asteroides i l’origen dels meteorits per mitjà de la comparació dels espectres de reflexió d’ambdós tipus d’objectes. - Obtenir informació de la història evolutiva dels asteroides a través dels anàlisis mineralògics i de la química principal. - Estudiar els processos físics que tenen lloc a les superfícies d’asteroides i els mecanismes que envien els meteorits fins la Terra.
Undifferentiated meteorites are the building blocks of undifferentiated bodies, comprising most of the Solar System objects. They are characterized by bearing refractory particles and igneous glassy spherules, the last ones being called chondrules. These rocks, so-called chondrites from the omnipresent…
Estat: defended (06/07/2018)
Estudiant: Moyano Cambero, C.E.
Supervisat per: Josep M. Trigo-Rodríguez
Universitat: Universitat Autònoma de Barcelona

Undifferentiated meteorites are the building blocks of undifferentiated bodies, comprising most of the Solar System objects. They are characterized by bearing refractory particles and igneous glassy spherules, the last ones being called chondrules. These rocks, so-called chondrites from the omnipresent chondrules that they contain, are often called accretionary or primordial materials. Such components were preserved in bodies of few hundred kilometers in diameter, being represented by small asteroids or comets. Those bodies never experienced chemical segregation and consequently are the legacy of the materials that formed the protoplanetary disk around the Sun about 4.6 Gyrs ago. By studying undifferentiated meteorites arrived from different parent bodies we can get clues on the physico-chemical processes at work in our planetary system over the eons. This thesis starts from the study of these free-delivered samples to gain insight into the properties of small bodies, their volatile content and evolution over time. The chondrites contain clues exhibiting complex accretionary histories in asteroids and comets. We have selected some of these chondrites to discuss the main physical processes affecting chondritic bodies since their consolidation: thermal metamorphism and aqueous alteration. Finally, as an application, we discuss aqueous alteration processes in one of the most primitive Martian meteorites: Allan Hills 84001 orthopyroxenite. By studying different meteorites, is expected to accomplish another goal of this Ph.D. thesis: understanding the pathways and influence of water contained in chondritic meteorites to increase the volatile content of terrestrial planets. Understanding the pathways of water in the enrichment in volatiles of planetary bodies is a first step to understand how materials from the outer protoplanetary disk reached planetary embryos, consolidated from dry planetesimals available in the inner disk, into water bearing planetary bodies like Mars or Earth.
 

Resonance dynamics in hot and dense nuclear matter

Estat: defended (18/12/2017)
Estudiant: Ilner, A.
Supervisat per: Laura Tolos ; Bratkovskaya, E.

Analysis of the strange hadrons in heavy-ion collisions
Resonance dynamics in hot and dense nuclear matter
Estat: defended (18/12/2017)
Estudiant: Ilner, A.
Supervisat per: Laura Tolos ; Bratkovskaya, E.

Resonance dynamics in hot and dense nuclear matter

High energy emission from classical and recurrent novae

Estat: defended (09/10/2017)
Estudiant: Laura Delgado
Supervisat per: Margarita Hernanz Carbó
Universitat: Universitat Autònoma de Barcelona

In recent years, several nova explosions - eight classical novae and two symbiotic recurrent novae - have been detected by Fermi/LAT at E>100 MeV. In most cases, this emission has been observed early after the explosion, around the optical maximum, and for a short period of time. The high-energy gamma-ray…
Estat: defended (09/10/2017)
Estudiant: Laura Delgado
Supervisat per: Margarita Hernanz Carbó
Universitat: Universitat Autònoma de Barcelona

In recent years, several nova explosions - eight classical novae and two symbiotic recurrent novae - have been detected by Fermi/LAT at E>100 MeV. In most cases, this emission has been observed early after the explosion, around the optical maximum, and for a short period of time. The high-energy gamma-ray emission is a consequence of neutral pion decay and/or Inverse Compton, which are related to particle (p and e-) acceleration in the strong shock between the nova ejecta and the circumstellar matter. RS Ophiuchi (2006) was the first nova for which particle acceleration was predicted. This prediction showed that the blast wave decelerated faster than expected as a consequence of the acceleration of particles in the shock and their escape.  The aim of this thesis is to study the evolution of the symbiotic recurrent novae the first days after the outburst through a multiwavelength study, mainly X-ray emission, and its relation with the acceleration of particles. In particular, we present a comprehensive multiwavelength study of the last outburst of RS Oph and V745 Sco.
RS Oph is a recurrent nova in a symbiotic system composed of a white dwarf and a red giant with a recurrence period of ~21 years. In this work, we present a new analysis of XMM-Newton's observations of RS Oph early after its 2006 outburst both with RGS and EPIC-MOS. We compare these results with those obtained for RXTE, Swift and Chandra observations, and previous studies of RGS observations. The evolution of the radio and IR emissions during the first days after the outburst was studied. The multiwavelength studies allow us to get a global picture of the shocked plasma and its relationship with the particle acceleration.

V745 Sco is also a symbiotic recurrent nova with a recurrence period of ~25 years. We present the analysis of the Swift/XRT observations of V745 Sco early after its 2014 outburst simultaneous to Fermi detection. We combine our results with Chandra and NuStar observations to get a global picture of the evolution of the nova ejecta. As in RS Oph we compiled all the radio and IR information about V745 Sco the first days after the explosion. Finally, particle acceleration in V745 Sco can be explained by a diffusive shock model at the blast wave and the subsequent escape of the very high-energy particles as in RS Oph.

With the study of these two novae, and its comparison, we demonstrate common features in the early evolution of a nova remnant and their relationship with particle acceleration in the symbiotic recurrent novae. Multiwavelength results provide new insights into the evolution of the shocked plasma and the interaction with the circumstellar material, being a powerful tool to understand the gamma-ray emission. 

The accretion flow onto white dwarfs and its X-ray emission properties

Estat: defended (21/09/2017)
Estudiant: Nataly Ospina
Supervisat per: Margarita Hernanz Carbó
Universitat: Universitat Autònoma de Barcelona

Explosive burning of hydrogen on top of accreting white dwarfs causes nova outbursts.
The binary system where classical novae occur is a cataclysmic variable whereas, some,
recurrent novae occur in symbiotic binaries. The analysis of the X-ray emission from
novae in their post outburst stages provides important information about the nova explosion
mechanism and the reestablishment of accretion. In some cases, like V2487 Oph
1998, observations with XMM-Newton a few years after outburst indicate that accretion
has been re-established and its X-ray spectra look like those of magnetic cataclysmic variables,
of the intermediate polar class.
In this work a numerical model of accretion flow onto magnetic white dwarfs and their
corresponding X-ray emission has been developed to be compared with observations
of post outburst novae where accretion is active again. Distributions of the different
physical quantities that describe the emission region have been obtained for different
masses of white dwarf and different accretion rates. The associated X-ray spectrum has
been also obtained with the main objective of studying accretion in the emission region.
These results have been applied to the nova V2487 Oph 1998 with the aim to obtain the
mass of the white dwarf since this nova has been identified as a recurrent nova, with
a previous eruption in 1900, and therefore as a good candidate for a type Ia Supernova
progenitor.
Explosive burning of hydrogen on top of accreting white dwarfs causes nova outbursts. The binary system where classical novae occur is a cataclysmic variable whereas, some, recurrent novae occur in symbiotic binaries. The analysis of the X-ray emission from novae in their post outburst stages provides…
Estat: defended (21/09/2017)
Estudiant: Nataly Ospina
Supervisat per: Margarita Hernanz Carbó
Universitat: Universitat Autònoma de Barcelona

Explosive burning of hydrogen on top of accreting white dwarfs causes nova outbursts.
The binary system where classical novae occur is a cataclysmic variable whereas, some,
recurrent novae occur in symbiotic binaries. The analysis of the X-ray emission from
novae in their post outburst stages provides important information about the nova explosion
mechanism and the reestablishment of accretion. In some cases, like V2487 Oph
1998, observations with XMM-Newton a few years after outburst indicate that accretion
has been re-established and its X-ray spectra look like those of magnetic cataclysmic variables,
of the intermediate polar class.
In this work a numerical model of accretion flow onto magnetic white dwarfs and their
corresponding X-ray emission has been developed to be compared with observations
of post outburst novae where accretion is active again. Distributions of the different
physical quantities that describe the emission region have been obtained for different
masses of white dwarf and different accretion rates. The associated X-ray spectrum has
been also obtained with the main objective of studying accretion in the emission region.
These results have been applied to the nova V2487 Oph 1998 with the aim to obtain the
mass of the white dwarf since this nova has been identified as a recurrent nova, with
a previous eruption in 1900, and therefore as a good candidate for a type Ia Supernova
progenitor.

Numerical Relativity studies in Anti-de Sitter spacetimes: Gravitational Collapse and the AdS/CFT correspondence

Estat: defended (12/07/2017)
Estudiant: Santos-Oliván, Daniel
Supervisat per: Carlos Sopuerta
Universitat: Universitat de Barcelona

Numerical Relativity is a necessary tool to explore the non-linear strong-field dynamics involved in the coalescence and merger of compact binaries (like in black hole (BH) binaries, double neutron star (NS) binaries, or BH-NS binaries). On the other hard, there is high energy phenomena, like ultra-relativistic collisions at particle accelerators or the gauge-gravity duality, where numerical relativity can be a crucial tool for making progress. The main goal of this thesis is to develop new tools in Numerical Relativity to be applied to these areas of research.
In this thesis we study three different problems using Numerical Relativity on asymptotically Anti-de Sitter (AdS) spacetimes. The first is our research on the gravitational collapse of massless scalar fields on asymptotically AdS spacetimes.  We have developed a new method that combines two different…
Estat: defended (12/07/2017)
Estudiant: Santos-Oliván, Daniel
Supervisat per: Carlos Sopuerta
Universitat: Universitat de Barcelona

In this thesis we study three different problems using Numerical Relativity on asymptotically Anti-de Sitter (AdS) spacetimes. The first is our research on the gravitational collapse of massless scalar fields on asymptotically AdS spacetimes.  We have developed a new method that combines two different formulations of the Einstein Field Equations to get closer and with more accuracy to the collapse. We have numerical evidence that in the separation of the branches there is a universal power law in the mass of the formed apparent horizons for subcritical configurations in addition to the one for supercritical ones. This new power law confirms that there is a gap in the mass of the apparent horizon. In the second part, we introduce a shock waves model in AdS to study the far-from-equilibrium regime in the heavy-ion collisions through the holographic correspondence in a non-conformal theory. In the models used until now, the shock waves correspond to conformal gauge theories while QCD is not conformal. In order to get closer to a description of the actual physical collisions we present the first shock waves collision in a nonconformal theory. With this, we show how the non-conformality increases the hydrodynamisation time and also that this can happen before the equation of state is fulfilled. In the last part, we propose the use of spectral methods for high precision computations. The exponential convergence of spectral methods can approximate functions with very high accuracy with few hundred terms in our spectral expansion while in other numerical methods it would be a few orders of magnitude larger. This makes spectral methods very attractive because they facilitate the accessibility to very small error simulations, removes the bottleneck of the memory demand and also help in the computational speed because fewer points are needed for the computation. We have tested this idea with the ANETO library for simulations in AdS spacetimes and the gravitational collapse in an asymptotically flat spacetime with very promising results. This library has been developed as a direct result of this thesis and that can be downloaded as Free Software.
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