# name
Physical Cosmology in the Epoch of Large Surveys

# metadata.dc.contributor.other[].value
Universitat de Barcelona. Facultat de Física

# metadata.dc.description.abstract[].value
[eng] Our  understanding of the  Universe  has  advanced  tremendously in the past  few decades, with General  Relativity(GR) laying the ground for a successful model for the Universe, ΛCDM. However, there are still some fundamental  open questions that need to be explored.  It is therefore the objective of this  thesis  to highlight some of these  questions  by exploring  them  theoretically  and observationally.
In the  first part  of the  thesis,  the  Introduction, I present a background review of GR and ΛCDM. The second part  is on testing an essential assumption  in Cosmology,  the  Copernican  Principle.   By distinguishing between line-of-sight and transverse expansion rates in the most general spacetime possible, one can constrain  deviations  from the Copernican  Principle.   Observationally, this  is done by measuring  polarization of Cosmic Microwave Background(CMB) photons  that have  been  inverse-Compton scattered by galaxy clusters.
In the third  part,  the possibility that Dark Matter(DM) is part  of Grav- ity is investigated. On Cosmological scales, this hypothesis  is tested  with a case study model: Mimetic Dark Matter(MDM). By rederiving the model’s equations  of motion,  extra  free functions  and  parameters appear  in need of fine tuning  to produce  the observationally certified adiabatic initial  conditions.   To  visualize  this,  I modify the  Boltzmann code CLASS to  include MDM, and then look at CMB correlation  functions and matter power spectra,  which show that deviations  of at  least  10% from adiabatic initial  conditions  fall beyond cosmic variance  limits.
On an astrophysical scale, the hypothesis  that DM is part  of a modified gravity  theory(MGT) is tested  by examining DM-devoid galaxies.  The main argument  is that if DM is part  of a MGT,  then  this  phenomenon  should be found in every gravitational system.  The  fact that DM-devoid  galaxies exist,  while other  similar  ones are DM dominated, constrains  severely the above mentioned  hypothesis.  To quantify  this,  I derive a generalized  Virial theorem  for some MGTs,  and  show that the  extra  term  gives inconsistent results  for DM-devoid  galaxies.   Therefore,  unless fine-tuning  is used,  DM is more likely to be a non-baryonic  particle,  or a compact object such as primordial  black holes, rather than  part  of a MGT.
The  fourth  part  explores the  realm  of Quantum Field Theory(QFT) in a gravitational background. The goal is to use neutrinos(spinors) as probes for Dark  Energy(DE), to  distinguish  between  its  different  models.   After laying down a general formalism, I first investigate three types of interactions between  the two fields, in a semi-classical way, and study  the consequences on oscillations  of neutrinos  and their  dynamics.
This  framework  is later  generalized  to  a  broader  class of interactions between neutrinos, as quantum spinors, and DE, either in the form of a Cosmological  Constant(CC) or a scalar  field.  The  result  is that different DE  models  have  distinct   signatures   on  neutrino   oscillation’s  probability. This provides a proof of concept for using neutrino  oscillations in curved spacetime  as a tool to distinguish  between models of the late acceleration  of the Universe.
To put the above in an observational context,  I conclude the fourth  part by considering the full three-flavor neutrino  oscillations within the ΛCDM paradigm. This results in ternary diagrams and flux plots that could be later compared  to observations  in neutrino  observatories. The conclusion is that one can use neutrino  oscillations in curved spacetime  to distinguish  between different  values  of the  present  expansion  rate  of the  Universe,  H0.   This result  adds new insight on the Hubble tension  and explores Multimessenger astronomy  in its full capacity.
The fifth and final part  summarizes  the results  and conclusions reached for each  work.   In addition, future  perspectives  and  further  developments are discussed in this section.

# metadata.dc.description.abstract[].value
[spa] Nuestra comprensión del Universo ha avanzado enormemente en las últimas décadas, con la Relatividad General(GR) sentando las bases para un modelo exitoso para el Universo, ΛCDM. Sin embargo, todavía quedan algunas cuestiones abiertas fundamentales que deben explorarse. Por tanto, el objetivo de esta tesis es resaltar algunas de estas cuestiones explorándolas teóricamente y observacionalmente. En la primera parte de la tesis, la Introducción, presento una revisión de antecedentes de GR y ΛCDM. La segunda parte trata de probar el principio copernicano. Al distinguir entre las proporciones de expansión en línea- de-visión y transversal en el espacio-tiempo más general posible, se pueden restringir las desviaciones del principio copernicano. Observacionalmente, esto se hace midiendo la polarización de los fotones de fondo cósmico de microondas(CMB) que han sido dispersados en Compton inverso por cúmulos de galaxias. En la tercera parte, investigo la posibilidad que la Materia Oscura(DM) sea parte de las teorías modificadas de gravedad(MGT), tanto a escalas cosmológicas como astrofísicas. En el primero, al investigar un modelo específico, Mimetic Dark Matter(MDM), e incorporarlo en el código de Boltzmann CLASS, muestro que las desviaciones de al menos un 10% de las condiciones iniciales adiabáticas ponen al modelo más allá de la varianza cósmica límites. En escalas astrofísicas, obtengo un teorema de Virial generalizado para algunas MGT, y demuestro que los términos adicionales dan resultados inconsistentes cuando se comparan con galaxias desprovistas de DM. Por lo tanto, a menos que se utilice un ajuste fino, es menos probable que DM forme parte de un MGT. La cuarta parte muestra cómo los neutrinos, cuando se consideran campos de espino cuántico en el espacio-tiempo curvo, podrían distinguir entre modelos de energía oscura. Además, también muestro cómo se puede utilizar esta técnica en la expansión actual del universo, H0 . Este resultado agrega una nueva perspectiva sobre la tensión del Hubble y explora Astronomía de múltiples pasajeros en toda su capacidad. La quinta y última parte resume los resultados y conclusiones alcanzados para cada trabajo. Además, en esta sección se analizan las perspectivas futuras y los desarrollos futuros.

# metadata.dc.title[].value
Physical Cosmology in the Epoch of Large Surveys