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CUSP is a powerful formalism that recovers, from first principles and with no free parameter, all the macroscopic properties of dark matter haloes found in cosmological N-body simulations and unveils the origin of their characteristic features. Since it is not restricted by the limitations of simulations, it covers the whole mass and redshift ranges. In the present Paper we use CUSP to calculate the mass-scale relations holding for halo density profiles fitted to the usual NFW and Einasto functions in the most relevant cosmologies and for the most usual mass definitions. We clarify the origin of these relations and provide accurate analytic expressions holding for all masses and redshifts. The performance of those expressions is compared to that of previous models and to the mass-concentration relation spanning more than 20 orders of magnitude in mass at $z=0$ obtained in recent simulations of a 100 GeV WIMP universe., Comment: 16 pages, 14 figures, accepted for publication in MNRAS

[eng] The overwhelming evidence for the existence of dark matter in the Universe, and the discovery of the neutrino masses, are striking indicators of the need for new physics beyond the ΛCDM and Standard Model paradigms. Dark matter (DM) constitutes 85 % of the matter in the Universe, but its fundamental nature remains a mystery. Moreover, the physical mechanism responsible for the neutrino masses is unknown. A complete theoretical framework – consistent with all observations – that incorporates a microscopic description of dark matter into the standard models of cosmology and particle physics, as well as an understanding of the origin and scale of the neutrino masses, is a key common goal. Cosmological observables are promising in this regard and can provide unique insights into the nature of these elusive particles. This thesis focuses on the synergy between cosmology and particle physics in answering these fundamental questions. To this end, I present examples of how upcoming measurements probing the high-redshift Universe can unveil new insights into the nature of dark matter and the complementarity between cosmological observations and terrestrial experiments in determining the neutrino mass hierarchy. The first part of the research presented in this thesis studies the signatures of non-gravitational DM interactions on cosmological observables. I compute the effects of DM decay and annihilation on the thermal and ionisation history of the Universe, and the imprint on the 21 cm line intensity mapping signal from the dark ages. I examine the potential to detect such a signature with forthcoming 21 cm line intensity mapping measurements, presenting forecasted constraints for both upcoming and next-generation experiments. Next, the effects of DM-baryon scattering in the post-recombination Universe are explored. In this work, I consider for the first time the direct contribution of such interactions on the baryon and dark matter temperature perturbations and the resulting evolution of cosmological density perturbations. In particular, I show that these contributions lead to a large enhancement of the baryon temperature power spectrum and a further suppression of matter clustering at small scales, which can alter both the amplitude and time evolution of the 21 cm signal from cosmic dawn and reionization. In the second part of this thesis, I look at the question of neutrino masses and the mass hierarchy from the lens of cosmology. Cosmological surveys provide the tightest constraints on the absolute mass scale of neutrinos, and are closing in on the minimum mass bound allowed under the inverted hierarchy. Using the latest results from global fits to neutrino oscillations experiments combined with cosmological constraints on the sum of the masses, I perform a Bayesian analysis to constrain the individual neutrino masses and evaluate the Bayesian Evidence for each of the neutrino mass orderings. The results show that current data provide strong Bayesian preference for the normal mass hierarchy, even under widely different prior assumptions, which has important implications for particle physics. Finally, I conclude the thesis with a summary of the key results and examine their relevance within the broader context of the field. Moreover, I discuss future prospects and potential avenues to follow up this work., [spa] Las pruebas irrefutables de la existencia de la materia oscura (DM) en el Universo, y el descubrimiento de las masas de neutrinos, son llamativos indicadores de la necesidad de una nueva física más allá de los paradigmas ΛCDM y del Modelo Estándar. Un marco teórico completo que incorpore una descripción microscópica de la materia oscura a los modelos estándar de cosmología y física de partículas, así como una comprensión del origen de las masas de neutrinos, es un objetivo común clave. Esta tesis se centra en la sinergia entre la cosmología y la física de partículas para responder a estas cuestiones fundamentales. La primera parte de la tesis estudia las firmas de las interacciones de la DM en los observables cosmológicos. Calculo los efectos de la desintegración y la aniquilación de DM en la historia térmica y de ionización del Universo, y la huella en la señal cosmológica de 21 cm de las Dark Ages. Examino el potencial para detectar dicha señal con las futuras observaciones de 21 cm y presento las limitaciones previstas para los experimentos próximos. A continuación, se exploran los efectos cosmológicos de la dispersión elástica entre el DM y los bariones. Considero la contribución de estas interacciones en las perturbaciones de temperatura de los bariones y de la DM y la evolución de las perturbaciones de densidad cosmológicas. Muestro que estas contribuciones puedne alterar tanto la amplitud como la evolución temporal de la señal de 21 cm de la época del Cosmic Dawn. En la segunda parte de la tesis, examino la cuestión de las masas de los neutrinos y la jerarquía de masas desde el punto de vista de la cosmología. Utilizando los últimos resultados de los experimentos de oscilaciones de neutrinos, combinados con las restricciones cosmológicas sobre la suma de las masas, realizo un análisis Bayesiano para inferir las masas de los neutrinos y evaluar la evidencia Bayesiana para cada uno de los ordenamientos de masas de neutrinos. Los resultados muestran que los datos actuales proporcionan una fuerte preferencia Bayesiana por la jerarquía de masas normal, incluso bajo probabilidades a priori muy diferentes, lo que tiene importantes implicaciones para la física de partículas.

Primordial black holes in the asteroid-mass window ($\sim 10^{-16}$ to $10^{-11} \rm M_{\odot}$), which might constitute all the dark matter, can be captured by stars when they traverse them at low enough velocity. After being placed on a bound orbit during star formation, they can repeatedly cross the star if the orbit happens to be highly eccentric, slow down by dynamical friction and end up in the stellar core. The rate of these captures is highest in halos of high dark matter density and low velocity dispersion, when the first stars form at redshift $z \sim 20$. We compute this capture rate for low-metallicity stars of $0.3$ to $1\rm M_{\odot}$, and find that a high fraction of these stars formed in the first dwarf galaxies would capture a primordial black hole, which would then grow by accretion up to a mass that may be close to the total star mass. We show the capture rate of primordial black holes does not depend on their mass over this asteroid-mass window, and should not be much affected by external tidal perturbations. These low-mass stellar black holes could be discovered today in low-metallicity, old binary systems in the Milky Way containing a surviving low-mass main-sequence star or a white dwarf, or via gravitational waves emitted in a merger with another compact object. No mechanisms in standard stellar evolution theory are known to form black holes of less than a Chandrasekhar mass, so detecting a low-mass black hole would fundamentally impact our understanding of stellar evolution, dark matter and the early Universe., 11 pages, 7 figures, 1 table - submitted to MNRAS. v2 : matching version accepted in MNRAS

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2022, Tutora: Àngels Ramos Gómez, We study how the presence of bosonic self-interacting dark matter influences the properties of admixed neutron stars. We only consider the gravitational interaction between baryonic and dark matter. We also explore different possibilities for the unknown mass, mχ, and self-coupling, λ, of the dark matter component, as well as different ratios of the central energy densities of dark and baryonic matter, ϵc D/ϵc B. Two scenarios are found: for mχ = 400 MeV, the dark matter is contained in the core of the star, which decreases its mass and radius with increasing dark matter fraction, whereas an extended halo of dark matter is formed for mχ = 100 MeV. The tidal deformability obtained from the gravitational waves of a binary neutron star merger favors the dark matter core scenario and puts severe constraints on the self-coupling value

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2022, Tutor: Jordi Miralda Escudé, In this report the motion of a dark matter minihalo around the Milky Way is studied, focusing on an encounter with a star that modifies the orbits of the axions inside the minihalo.The number of axions escaping from the minihalo due to the tidal acceleration caused by the star is simulated, analyzing their distribution around the minihalo and their evolution.

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2022, Tutor: Jordi Miralda Escudé, In a wide variety of axion models, a relevant fraction of all Dark Matter (DM) is expected to bound in dense small-scale substructures, called axion miniclusters. Despite they enhance the local DM density, the crossing of miniclusters through Earth are rare events occurring once in 105 years making direct detection inefficient. Although dense, a small fraction of these structures become unbound by tidal interaction with astronomical objects, as shown mainly with stars. The perspectives of detection will depend on which fraction of axion minicluster gets disrupted and therefore, tidal interactions are reviewed in detail in this paper. As a result of the destruction, tidal axion streams are expected to form along the minicluster’s previous direction in a coherentand large shape. Stream crossings are more probable events so it has been analysed if density may still be larger than the local DM density and therefore, be a real chance in direct detection systems such as haloscopes

We identify Gaia 0007-1605 A,C as the first inner brown dwarf-white dwarf binary of a hierarchical triple system in which the outer component is another white dwarf (Gaia 0007-1605 B). From optical/near-infrared spectroscopy obtained at the Very Large Telescope with the X-Shooter instrument and/or from Gaia photometry plus spectral energy distribution fitting, we determine the effective temperatures and masses of the two white dwarfs (12,018 ± 68 K and 0.54 ± 0.01 M ⊙ for Gaia 0007-1605 A and 4445 ± 116 K and 0.56 ± 0.05 M ⊙ for Gaia 0007-1605 B) and the effective temperature of the brown dwarf (1850 ± 50 K; corresponding to spectral type L3 ± 1). By analyzing the available TESS light curves of Gaia 0007-1605 A,C we detect a signal at 1.0446 ± 0.0015 days with an amplitude of 6.25 ppt, which we interpret as the orbital period modulated from irradiation effects of the white dwarf on the brown dwarf's surface. This drives us to speculate that the inner binary evolved through a common-envelope phase in the past. Using the outer white dwarf as a cosmochronometer and analyzing the kinematic properties of the system, we conclude that the triple system is about 10 Gyr old., A.R.M. acknowledges support from Grant RYC-2016–20254 funded by MCIN/AEI/10.13039/501100011033 and by ESF Investing in your future. S.X. is supported by the international Gemini Observatory, a program of NSF's NOIRLab, which is managed by the Association of Universities for Research in Astronomy (AURA) under a cooperative agreement with the National Science Foundation, on behalf of the Gemini partnership of Argentina, Brazil, Canada, Chile, the Republic of Korea, and the United States of America. R.R. has received funding from the postdoctoral fellowship program Beatriu de Pinós, funded by the Secretary of Universities and Research (Government of Catalonia) and by the Horizon 2020 program of research and innovation of the European Union under the Maria Skłodowska-Curie grant agreement No. 801370. S.T. and A.R.M. acknowledge support from the MINECO under the PID2020-117252GB-I00 grant. F.J.E. acknowledges financial support from the Spanish MINECO/FEDER through the grant MDM-2017–0737 at Centro de Astrobiología (CSIC-INTA), Unidad de Excelencia María de Maeztu. P.C. acknowledges financial support from the Government of Comunidad Autónoma de Madrid (Spain), via postdoctoral grant Atracción de Talento Investigador 2019-T2/TIC-14760.

With this Paper we complete a comprehensive study of substructure in dark matter haloes. In Paper I we derived the radial distribution and mass function (MF) of accreted subhaloes (scaled to the radius and mass of the host halo) and showed they are essentially universal. This is not the case, however, for those of stripped subhaloes, which depend on halo mass and assembly history. In Paper II we derived these latter properties in the simplest case of purely accreting haloes. Here we extend the study to ordinary haloes having suffered major mergers. After showing that all the properties of substructure are encoded in the mean truncated-to-original subhalo mass ratio profile, we demonstrate that the dependence of the subhalo MF on halo mass arises from their mass-dependent concentration, while the shape of the subhalo radial distribution depends on the time of the last major merger of the host halo. In this sense, the latter property is a better probe of halo formation time than the former. Unfortunately, this is not the case for the radial distribution of satellites as this profile is essentially disconnected from subhalo stripping and the properties of accreted subhaloes are independent of the halo formation time., 14 pages, 12 figures. Accepted for publication in MNRAS

[Context] Isolated stellar-mass black holes accrete gas from their surroundings, often at supersonic speeds, and can form outflows that may influence the accreted gas. The latter process, known as mechanical feedback, can significantly affect the accretion rate., [Aims] We use hydrodynamical simulations to assess the impact of mechanical feedback on the accretion rate when the black hole moves supersonically through a uniform medium., [Methods] We carried out three-dimensional (3D) hydrodynamical simulations of outflows fueled by accretion that interact with a uniform medium, probing scales equivalent to and larger than the accretor gravitational sphere of influence. In the simulations, the accretor is at rest and the medium moves at supersonic speeds. The outflow power is assumed to be proportional to the accretion rate. The simulations were run for different outflow-medium motion angles and velocity ratios. We also investigated the impact of different degrees of outflow collimation, accretor size, and resolution., [Results] In general, the accretion rate is significantly affected by mechanical feedback. There is a minor reduction in accretion for outflows perpendicular to the medium motion, but the reduction quickly becomes more significant for smaller angles. Moreover, the decrease in accretion becomes greater for smaller medium-to-outflow velocity ratios. On the other hand, the impact of outflow collimation seems moderate. Mechanical feedback is enhanced when the accretor size is reduced. For a population of black holes with random outflow orientations, the average accretion rate drops by (low–high resolution) ∼0.2 − 0.4 and ∼0.1 − 0.2 for medium-to-outflow velocity ratios of 1/20 and 1/100, respectively, when compared to the corresponding cases without outflow., [Conclusions] Our results strongly indicate that on the considered scales, mechanical feedback can easily reduce the energy available from supersonic accretion by at least a factor of a few. This aspect should be taken into account when studying the mechanical, thermal, and non-thermal output of isolated black holes., V.B-R. acknowledges f inancial support from the State Agency for Research of the Spanish Ministry of Science and Innovation under grant PID2019-105510GB-C31 and through the “Unit of Excellence María de Maeztu 2020-2023” award to the Institute of Cosmos Sciences (CEX2019-000918-M). V.B-R. is Correspondent Researcher of CONICET, Argentina, at the IAR.

[eng] The existence of black holes that go beyond the mass given by their stellar origin has been known for some time. On the lower end, a subset of primordial black holes (PBHs) could form all of the dark matter with individually very low masses of up to 10-11 M⊙. On the opposite mass range Super Massive Black holes (SMBHs) have been found at very high redshifts. Using models and instrumental techniques, we study the observational consequences of both of these types of black holes. We start by studying current constraints on PBHs. We look at microlensing, which makes up the largest constraints on PBHs as dark matter, and conclude that despite its usefulness the method will not improve the constraints for lower mass ranges. We make similar analyses of gravitational waves and PBH evaporation, with the former having a lot of potential but requiring the next generation of experiments, and the later being a simple case with few further constraints. Finally, we zero in the last remaining window for PBHs to be all the dark matter around 10-12 M⊙. The PBHs in this mass range would leave little observational results, but a possible way to constrain them would be through their interaction with stars. As stars form in the very early universe, they will accrue a large dark matter density gravitationally bound to the star. If PBHs were the dark matter, they will orbit the star, following a flat eccentricity distribution. There is a chance some of the orbits of the PBHs naturally cross the star. The dynamical friction of a main sequence star on the PBH is enough to bring the PBH to the core of the star within the Hubble time, capturing it. There, the PBH will accrete the star resulting in a black hole the mass of the star. We compute the capture rate of such PBHs by a number of stars. We use stellar models from MENSA ranging from 0.3 to 1 M⊙ for the stars, compute the dynamical friction numerically using two different types and take into account the effect of perturbations coming from the rest of the galaxy. The result, which we call Ξ, is generic and can be used to compute the capture rate for any dark matter density and velocity dispersion. For the case z ∼ 20, and our models tells us that we expect stars represented on our stellar models that are very close of the center of their galaxies to end capturing a PBH and being accreted in turn. The capture rate lowers with distance, but it is still relevant at larger distances. This should result in a wealth of subsolar mass black holes that would survive to this day. We finally study the case of quasi stellar objects (QSOs), SMBHs with very high luminosity. The presence of Lymanα nebulae surrounding them is relevant, as we do not know whereas it is generic feature present in QSOs or if they are singular cases. A possible solution is through stacking. The technique allows the use of multiple images to reach depths otherwise impossible. For stacking QSOs, the upcoming survey J-PAS and its predecessor J-PLUS are the most promising. We use stacking in J-PLUS for a total of ∼ 1, 550 QSOs and more than three hundred thousand stars, the later to obtain an accurate recreation of the points spread. We find that J-PLUS cannot reach the magnitude needed, but we reach very high depths for the star stack in line with our projections. We expect to reach the magnitude needed to observe the diffuse Lymanα signal with J-PAS., [cat] La tesi doctoral consisteix en un estudi de forats negres de massa extrema i les seves possibles conseqüències observacionals. Forats negres de molt baixa massa, forats negres primordials, podrien ser tota la matèria fosca però només en un rang de masses molt petit. Tot i aquestes limitacions queda un espai en un rang de masses properes a les d’asteroides i molt poques maneres d’aconseguir possibles observables de la seva existència. Una forma seria la captura d’aquests forats negres per part d’una estrella de seqüència principal. Això podria passar a alts redshifts, amb altes densitats i baixes velocitats. Analitzem aquest cas i proposem un model. A pesar de simplificacions, el nostre model millora sobre la literatura alhora de calcular numèricament la fricció dinàmica de dos formes diferents amb models estel·lars punters i amb un mecanisme que aproxima l’efecte de pertorbacions externes sobre el sistema. Utilitzem també un paràmetre que anomenem Xi que ens permet generalitzar els resultats. En el cas d’alts redshifts, concloem que la captura de forats negres primordials seria important, eliminant un percentatge notable d’estrelles i deixant molts forats negres de massa subsolar. L’altre extrem són els forats negres supermassius, entre ells els quàsars. Una forma d’estudiar-los és a través de nebuloses Lyman alfa. Són molt febles, pel que es dubta la seva existència per qualsevol quàsar. Amb la tècnica stacking, consistent en sumar imatges per reduir el soroll tèrmic, arribem a les majors profunditats necessàries, tot i que també magnifica la Point Spread Function (PSF). Utilitzem el cartografiatge J-PLUS pel stacking com a pas previ al futur cartografiatge J-PAS. J-PLUS no arriba a les magnituds necessàries per descobrir les nebuloses amb quàsars, però amb estrelles arribem a magnituds molt altes. Esperem que amb J-PAS hauria de ser fàcil veure les nebuloses.

[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., [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.

We present the first detailed 3D kinematic analysis of a sample of 3133 white dwarfs that use Gaia astrometry plus radial velocities, which were measured either by Gaia or by ground based spectroscopic observations. The sample includes either isolated white dwarfs that have direct radial velocity measurements, or white dwarfs that belong to common proper motion pairs that contain nondegenerate companions with available radial velocities. A subset of common proper motion pairs also have metal abundances that have been measured by large scale spectroscopic surveys or by our own follow-up observations. We used the white dwarfs as astrophysical clocks, by determining their masses and total ages via interpolation with dedicated evolutionary models. We also used the nondegenerate companions in common proper motions to chemically tag of the population. Combining accurate radial velocities with Gaia astrometry and proper motions, we derived the velocity components of our sample in the Galactic rest frame and their Galactic orbital parameters. The sample is mostly located within ~300 pc from the Sun. It contains predominantly (90-95%) thin-disk stars with close-to-circular Galactic orbits, while the remaining 5-10% of stars have more eccentric trajectories and belong to the thick disk. We identified seven isolated white dwarfs and two common proper motion pairs as halo members. We determined the age - velocity dispersion relation for the thin-disk members, which shows signatures of dynamical heating and saturation after 4-6 Gyr. We observed a mild anti-correlation between [Fe/H] and the radial component of the average - velocity dispersion, showing that dynamical mixing of populations takes place in the Galactic disk, as was detected via the analysis of other samples of FGK stars. [Abridged], Accepted for publication (Raddi et al. 2022, A&A, 658, A22). 16 pages, 14 figures, 9 tables. Tables 2, 4, 5, 6, and 7 are available as pdf files and in electronic form via http://cdsarc.u-strasbg.fr/viz-bin/cat/J/A+A/658/A22

Recently a new kind of quintessential inflation coming from the Lorentzian distribution has been introduced in [1,2]. The model leads to a very simple potential, which basically depends on two parameters, belonging to the class of $\alpha$-attractors and depicting correctly the early and late time accelerations of our universe. The potential emphasizes a {\it cosmological seesaw mechanism} (CSSM) that produces a large inflationary vacuum energy in one side of the potential and a very small value of dark energy on the right hand side of the potential. {Here we show that the model agrees with the recent observations and with the reheating constraints. Therefore the model gives a reasonable scenario beyond the standard $\Lambda$CDM that includes the inflationary epoch.}, Comment: 9 pages; 5 figures; accepted for publishing in JCAP

[eng] This thesis has been devoted to the study of the gravitational collapse of spherically symmetric perturbations on a Friedman-Robertson-Walker (FRW) universe filled by a perfect fluid. Large cosmological perturbations generated by inflation, are known to be statistically almost spherical. For this reason, this thesis aims to provide the conditions for Primordial Black Hole (PBH) formation due to the collapse of inflationary density fluctuations. PBHs are considered one of the best candidate for the missing dark matter (DM). To simulate the collapse of large spherical overdensities, it has been used a pseudo-spectral method which maps differential equations into an algebraic system. The numerical code developed, allows to outline the conditions for black hole formation with a greater than ever precision in some extreme cases. By using a combination of an excision technique and analytical estimations of accretion rates, it was found that the estimation of the black hole’s masses via a self-similar scaling law, gets worse and worse for larger and larger values. In addition, it was also found that the accretion of the BH masses relevant for the DM abundance, follows the law MBH,f roughly equal to 3MBH,i where, MBH,I is the initial mass of the BH at the time of apparent horizon formation and MBH,f is the final mass of the BH after the accretion process. In the case in which the fluid permeating the universe is of the form p equal to wρ, where p is the pressure, ρ is the density of the fluid and w is a constant, it is here shown that for w greater or equal to 1/3 the conditions for black hole formation, to a very good approximation, only depend upon the curvature of the local excess-mass (compaction function) around its peak value (δc), δc (the ”threshold” for PBH formation) and the equation of state of the collapsing fluid. This fact, has been used to build an analytical formula for δc in the case of w greater or equal to 1/3, which is accurate enough to be used for cosmological applications, conversely to previous attempts. For smaller w’s instead, the knowledge of the full shape of the compaction function is necessary, in contradiction to previous claims. Moreover, while the threshold for w greater or equal to 1/3 does not strongly depend from the full shape of the compaction function, in this thesis it is also shown that the BH mass does. While inflationary fluctuations are predominantly Gaussianly distributed at the cosmic microwave back-ground scales, those leading to PBH formation at smaller scales can have larger non-Gaussianities (NG). In the final part of this thesis, it was considered the effect (numerically and analytically) of those NG to the threshold for primordial black hole formation. By monitoring the non-gaussian parameter fNL, it was found that; i) for fNL roughly greater than 3.5, the population of PBH coming from false vacuum regions dominates over that coming from the collapse of large adiabatic overdensities; ii) the effect of the statistical dispersion of profiles is small in determining δc of the mean profile., [spa] Esta tesis pretende proporcionar las condiciones necesarias para la formación de Agujeros Negros Primordiales (PBHs) producidos por el colapso de perturbaciones cosmológicas. Los PBHs se consideran uno de los mejores candidatos para la materia oscura, cuya composición es todavía un misterio. Para simular el colapso de grandes sobredensidades esféricas y obtener las condiciones para la formación de un PBH, se ha utilizado un método pseudoespectral que mapea ecuaciones diferenciales en un sistema algebraico. En el caso en el que el fluido que impregna el universo se comporte como un fluido perfecto (p igual a wρ, donde p es la presión, ρ es la densidad del fluido y w es una constante), hemos comprobado que para w mayor o igual a 1/3 las condiciones para la formación de un agujero negro, en una muy buena aproximación, solo dependen de la curvatura del exceso de masa local (también llamado función de compactación) alrededor de su valor máximo (δc) , δc (el ” umbral ” para la formación de PBH) y la ecuación de estado del fluido que colapsa. Este remarcable resultado se ha utilizado para construir una fórmula analítica para δc en el caso de w mayor o igual a 1/3, que es lo suficientemente precisa como para usarse en aplicaciones cosmológicas. En cambio, para w más pequeños, es necesario conocer la forma completa de la función de compactación. Por otro lado, si bien es cierto que las fluctuaciones inflacionarias se distribuyen predominantemente de manera gaussiana en las escalas del fondo de microondas cósmicas, las que conducen a la formación de PBH a menores escalas pueden distribuirse de forma altamente no gaussiana (NG). En la parte final de esta tesis, se ha considerado el efecto de esas NGs en el umbral de formación de agujeros negros primordiales, tanto numérica como analíticamente.

An exponential kind of quintessential inflation potential motivated by supergravity is studied. This type belongs to the class of {\alpha}-attractor models. The model was studied for the first time by Dimopoulos and Owen in [J. Cosmol. Astropart. Phys. 06 (2017) 027], in which the authors introduced a negative cosmological constant in order to ensure a zero-vacuum energy density at late times. However, in this paper, we disregard this cosmological constant, showing that the obtained results are very close to the ones obtained recently in the context of Lorentzian quintessential inflation and thus depicting with great accuracy the early- and late-time acceleration of our Universe. The model is compatible with the recent observations. Finally, we review the treatment of the {\alpha}-attractor and we show that our potential depicts the late time cosmic acceleration with an effective equation of state equal to -1., Comment: 11 pages; 4 figures. arXiv admin note: text overlap with arXiv:2102.09514

The dynamics of interacting dark matter-dark energy models is characterized through an interaction rate function quantifying the energy flow between these dark sectors. In most of the interaction functions, the expansion rate Hubble function is considered and sometimes it is argued that, as the interaction function is a local property, the inclusion of the Hubble function may influence the overall dynamics. This is the starting point of the present article where we consider a very simple interacting cosmic scenario between vacuum energy and the cold dark matter characterized by various interaction functions originated from a general interaction function: $Q= \Gamma\rho_{c}^{\alpha }\rho_{x}^{1-\alpha -\beta}(\rho_{c}+\rho_{x})^{\beta}$, where $\rho_c$, $\rho_x$ are respectively the cold dark matter density and vacuum energy density; $\alpha$, $\beta$ are real numbers and $\Gamma$ is the coupling parameter with dimension equal to the dimension of the Hubble rate. We investigate four distinct interacting cosmic scenarios and constrain them both theoretically and observationally. Our analyses clearly reveal that the interaction models should be carefully handled., Comment: 14 pages, 9 figures and 4 tables. We dedicate this work to the memory of Prof. John D. Barrow. The article has been accepted for publication by Phys. Rev. D

The ConflUent System of Peak trajectories (CUSP) is a rigorous formalism in the framework of the peak theory that allows one to derive from first principles andno free parameters the typical halo properties from the statistics of peaks in the filtered Gaussian random field of density perturbations. The predicted halo mass function, spherically averaged density, velocity dispersion, velocity anisotropy, ellipticity, prolateness and potential profiles, as well as the abundance and number density profiles of accreted and stripped subhalos and diffuse dark matter accurately recover the results of cosmological $N$-body simulations. CUSP is thus a powerful tool for the calculation, in any desired hierarchical cosmology with Gaussian perturbations, of halo properties beyond the mass, redshift and radial ranges covered by simulations. More importantly, CUSP unravels the origin of the characteristic features of those properties. In the present Paper we culminate its construction. We show that all halo properties but those related with subhalo stripping are independent of the assembly history of those objects, and that the Gaussian is the only smoothing window able to find the finite collapsing patches while properly accounting for the entropy increase produced in major mergers., 22 pages, 6 figures. Published in the ApJ. Minor corrections with respect to the published version

[cat] En aquesta tesi s’estudien diferents models cosmològics, tots ells caracteritzats per considerar, de manera efectiva, una lleu evolució temporal de l’Energia Fosca, en contrast amb l’actual model estàndard de la cosmologia. El terme Energia Fosca s’utilitza per fer referència a una misteriosa forma d’energia que sembla impregnar tots els racons del Univers i que provoca que les galàxies s’allunyin les unes de les altres. El ritme predit d’expansió del Univers varia d’un model a un altre així com la quantitat d’estructura observada i la distribució d’aquesta. Degut al bon moment de la cosmologia observacional tenim a la nostre disposició una gran quantitat de dades que ens permeten posar a prova els diferents models existents. Un exemple d’aquests models, seria el Running Vacuum Model (RVM), que ha estat estudiat en detall en aquesta tesi i que considera una expressió per la densitat d’energia del buit motivada en el context de les Teories Quàntiques de Camp. Un altre exemple de models cosmològics serien els anomenats models de camp escalar que suposen que l’equació d’estat de l’Energia Fosca, en el moment present, és lleugerament diferent del valor predit pel model estàndard. No noées s’han considerat models acomodats dins del marc de la teoria de la Relativitat General, sinó que també s’han estudiat les prediccions teòriques del model presentat per Brans i Dicke al 1961 i que resulta ser el primer intent d’extensió de la teoria d’Einstein. El model de Brans i Dicke està caracteritzat pel fet que la interacció gravitatòria està no només mediada per un camp tensorial, sinó també per un camp escalar. Les prediccions teòriques dels diferents models estudiats, tant a nivell de background com a nivell de pertorbacions, han sigut contrastades amb les mes recents dades cosmològiques revelant que l'anteriorment esmentada evolució temporal de l’Energia Fosca ajuda a rebaixar, de manera considerable, algunes de les tensions que afecten al model estàndard. La comparació teoria-observacions s’ha dut a terme mitjançant una rigorosa metodologia que involucra diferents eines estadístiques. Per tant les conclusions obtingudes al llarg d’aquesta tesi es basen en un procés robust i en un estudi detallat dels diferents models cosmològics considerants., [eng] The high quality observations performed during the last two decades, have allowed to demonstrate, with high confidence range, that the Universe is in expansion and to be more precise in accelerated expansion. In order to explain the accelerated evolution the name of dark energy was coined. It refers to a some mysterious form of diffuse energy presumably permeating all corners of the Universe as a whole. We may say that the canonical picture of our Universe defined in the framework of General Relativity, whose field equation were found by Einstein in 1917, is built upon the assumption that the observed acceleration is caused, in fact, by a rigid cosmological constant term denoted by Λ. Thanks to the aforementioned cosmological measurements, we have been able to pin down its value to an impressive level. Dark energy is not the only element, beyond the conventional baryons and photons, required by the observations since we also need large amounts of what is commonly call as dark matter. We call such an overall picture of the Universe the “concordance (or standard) cosmological model” or simply ΛCDM. Therefore, we attribute the observed accelerated expansion of the Universe to the existence of a repulsive force, exerted by the Λ term, which works against the attractive gravitational force and tends to push the clusters of galaxies apart at a speed continuously increasing with the cosmic expansion. Throughout this thesis a wide variety of models, beyond the standard model have been studied. The corresponding analyses have been carried out by studying in detail the theoretical predictions at the background and perturbation level, with the purpose of testing them with the large amount of cosmological data which we currently we have access to. The ultimate goal is to see if we can detect signals of new physics that help to alleviate some of the tensions that affect the ΛCDM. The concordance model, has remained robust and unbeaten for a long time since it is roughly consistent with a large body of cosmological data. Because of this fact, it is not reasonable to look for models with a very different behaviour than the ΛCDM, but to study models that exhibit small departures with respect to the standard model in key aspects. We have studied the Running Vacuum Models (RVM) in depth. They are characterized by having a time-evolving vacuum energy density, whose functional expression is motivated in the context of Quantum Field Theory in curved space-time. It is fundamental that its expression contains a constant term, which mimics the standard behaviour in order to first generate the transition from a decelerated to an accelerated Universe and to ensure that the fit of the structure formation data is not ruined. We have also studied the Peebles & Ratra model, which is a particularly successful scalar field model φCDM for which the potential takes the form V (φ) ∼ φ−α . The dimensionless parameter α encodes the extra degree of freedom that this model has with respect to the standard model. It is found to be small and positive, therefore V (φ) can mimic and approximate cosmological constant that is decreasing slowly with time. In the late Universe the contribution of the scalar field, φ, surfaces over the matter density, thus becoming the dominant component. Not all the models studied are motivated within a theoretical framework, since we have also considered some interesting phenomenological approaches. Last but not least, at the end of the thesis the Brans & Dicke (BD) gravity model was studied in detail. The main feature of this model is that the Newtonian constant coupling GN is replaced by a dynamical scalar field G(t) = 1/ψ(t), coupled to the curvature. As a consequence the gravitational interaction is not only mediated by the metric field, as in the General Relativity case but also for the aforementioned scalar field ψ. The obtained results clearly point out to an interesting conclusion, those models which consider an effective time-evolving dark energy are able to alleviate some of the tensions affecting the ΛCDM. Among the different tensions there are two that stand out, namely the σ8 -tension and the H0-tension.

This is the first of a series of three Papers devoted to the study of halo substructure in hierarchical cosmologies by means of the CUSP formalism. In the present Paper we derive the properties of subhaloes and diffuse dark matter (dDM) accreted onto haloes and their progenitors. Specifically, we relate the dDM present at any time in the inter-halo medium of the real Universe or a cosmological simulation with the corresponding free-streaming mass or the halo resolution mass, respectively, and establish the link between subhaloes and their seeds in the initial density field. By monitoring the collapse and virialisation of haloes, we derive from first principles and with no single free parameter the abundance and radial distribution of dDM and subhaloes accreted onto them. Our predictions are in excellent agreement with the results of simulations, but for the predicted fraction of accreted dDM, which is larger than reported in previous works as they only count the dDM accreted onto the final halo, not onto its progenitors. The derivation pursued here clarifies the origin of some key features of substructure. Overall, our results demonstrate that CUSP is a powerful tool for understanding halo substructure and extending the results of simulations to haloes with arbitrary masses, redshifts and formation times in any hierarchical cosmology endowed with random Gaussian density perturbations., Comment: 12 pages, 5 figures. Accepted for publication in MNRAS. Minor changes to match with the published version

[eng] The standard cosmological model, ΛCDM, with the addition of an early inflationary phase, provides an accurate description of a nearly flat and homogeneous Universe, at large scales, which expands at an accelerated rate. Despite its vindication, our knowledge of the components that trigger the early formation of structures and drive the accelerated expansion of the Universe, that is, dark matter (DM) and dark energy respectively, is severely limited, given their feeble interactions with the other components of the Universe. A number of candidates from particle physics, e.g weakly interacting massive particles (WIMPs) or axions, have been proposed to constitute DM, but so far there has been no evidence to support their existence. However, the detection of a signal from the merger of a binary of black holes of stellar masses, reinvigorated the interest in an old candidate for DM, namely primordial black holes (PBHs). These black holes behave as the ones sitting at the end of stellar evolution, with the distinctive differences that they may form in significant fractions even well before the appearance of the first stars, with masses that may range from the Planck mass, to the order of MBH ∼ 1012 M. One possible formation mechanism involves perturbations originating from the fluctuations of a scalar field during inflation, that collapse after they re-enter the causal horizon in a radiation or matter domination era. The PBHs could easily form binaries in the early Universe and merge within our Hubble time, rendering them observable by the current detectors LIGO/VIRGO. The work presented in this thesis focuses on how such a population of PBHs could be utilised in order to elucidate certain spectral features of curvature perturbations characterizing the initial state of the Universe. Firstly, the effect of matter and radiation perturbations on the orbital parameter distributions of PBH binaries is studied. These perturbations are shown to provide a source of torque to the binary, particularly when their power spectrum is enhanced at the comoving scale of the binaries, leading to the suppression of the merger rate and subsequent relaxation of constraints on the PBH abundance. Secondly, the effect of primordial clustering on the distribution of orbital parameters of PBH binaries is investigated with the use of a phenomenological model of local non-Gaussianity. It is shown that due to the modal coupling of the perturbations, the merger rate and the stochastic background of gravitational waves (SBGW) sourced by merging PBH binaries, are altered. An immediate result of clustering is that the observational constraint on the abundance of PBHs in DM is relaxed considerably, allowing for significant fractions, even close to totality. Thirdly, the possibility that the SBGW from the mergers of massive PBHs could provide an explanation for the recently detected isotropic signal by the NANOGrav collaboration is considered. The presence of non-Gaussianity, sourced from a phase of constant roll, is essential in order for such massive PBHs to evade the CMB µ-distortions constraints, in which case they may have formed in small abundances, of order 0.1% with respect to DM. The present work aims to provide a more robust modelling of the observational consequences of a population of PBHs in order to gain more insight into the spectrum of primordial perturbations at small scales and therefore into the initial conditions of the early Universe., [spa] El modelo cosmológico estándar, ΛCDM, con una temprana fase de inflación, nos proporciona una descripción precisa de un Universo casi plano y homogéneo a gran escala, que se expande a un ritmo acelerado. A pesar de las evidencias observacionales, nuestro conocimiento del 95% de la energía del Universo, es decir, la materia oscura (DM) y la energía oscura, está limitado por la falta de una detección directa, debido en parte a la poca interacción, aparte de la gravitacional, que tienen con el resto de la materia. La detección de la primera señal de un sistema binario de agujeros negros, revitalizó el interés por un viejo candidato a materia oscura, los agujeros negros primordiales (PBHs). Los PBHs han recibido atención dado que se pueden formar con abundancias importantes durante el Universo temprano y con una amplia gama de posibles masas. Esta tesis se centra en su empleo para explorar el espectro de potencias de las perturbaciones de curvatura a escala pequeña. Primero, se estudia el efecto de las perturbaciones cosmológicas sobre los parámetros orbitales de los sistemas binarios de PBHs. Cuando hay una meseta de amplitud considerable en el espectro de potencia en las escalas de los sistemas binarios, la tasa de fusión se ve afectada, relajando los limites de la abundancia de PBHs. Segundo, se muestra que debido al acoplamiento modal de las perturbaciones, introducido por la presencia de no-Gaussianidad, se alteran la tasa de fusión y el resultante fondo estocástico de las ondas gravitacionales (SBGW) y que esto tambien resulta en la relajación de las restricciones de la abundancia de PBH. Tercero, se considera la posibilidad de que el SBGW proveniente de los sistemas binarios de PBHs super masivos pueda proporcionar una explicación para la señal detectada por NANOGrav. La presencia de no-Gaussianidad es esencial para que estos PBHs masivos eviten las µ-distorsiones de la CMB y se puedan haberse formado en abundancias del orden ∼ 0, 1%. Los PBHs constituyen una sonda única para explorar las condiciones iniciales del Universo y este trabajo pretende aportar un modelaje más robusto de las consecuencias observacionales de una población de PBHs.

Non-gravitational interaction between dark matter and dark energy has been considered in a spatially flat Friedmann-Lema\^{i}tre-Robertson-Walker (FLRW) universe. The interaction rate is assumed to be linear in the energy densities of dark matter and dark energy and it is also proportional to the Hubble rate of the FLRW universe. This kind of interaction model leads to an autonomous linear dynamical system, and depending on the coupling parameters, could be solved analytically by calculating the exponential of the matrix, defining the system. We show here that such interaction rate has a very deep connection with some well known cosmological theories. We then investigate the theoretical bounds on the coupling parameters of the interaction rate in order that the energy densities of the dark sector remain positive throughout the evolution of the universe and asymptotically converge to zero at very late times. Our analyses also point out that such linear interacting model may encounter with finite time future singularities depending on the coupling parameters as well as the dark energy state parameter., Comment: 17 pages, 8 figures; version accepted by Phys. Rev. D

[Context] Dark matter may consist, at least partially, of primordial black holes formed during the radiation-dominated era. The radiation produced by accretion onto primordial black holes leaves characteristic signatures on the properties of the medium at high redshift, before and after hydrogen recombination. Therefore, reliable modeling of accretion onto these objects is required to obtain robust constraints on their abundance., [Aims] We investigate the effect of mechanical feedback, that is, the impact of outflows (winds and– or –jets) on the medium, on primordial black hole accretion, and thereby on the associated radiation., [Methods] Using analytical and numerical calculations, we studied for the first time the possibility that outflows can reduce the accretion rate of primordial black holes with masses similar to those detected by the LIGO-Virgo collaboration., [Results] Despite the complexity of the accretion rate evolution, mechanical feedback is useful in to significantly reducing the primordial black hole accretion rate, at least by one order of magnitude, when outflows are aligned with the motion of the compact object. If the outflow is perpendicular to the direction of motion, the effect is less important, but it is still non-negligible., [Conclusions] Outflows from primordial black holes, even rather weak ones, can significantly decrease the accretion rate, effectively weakening abundance constraints on these objects. Our results motivate further numerical simulations with a more realistic setup, which would yield more precise quantitative predictions., V.B-R. acknowledges support by the Spanish Ministerio de Economía y Competitividad (MINECO/FEDER, UE) under grant AYA2016-76012-C3-1-P, with partial support by the European Regional Development Fund (ERDF/FEDER), MDM-2014-0369 of ICCUB (Unidad de Excelencia “María de Maeztu”), and the Catalan DEC grant 2017 SGR 643. NB is supported by the Spanish MINECO under grant BES-2015-073372.

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2019, Tutor: Alberto Manrique Oliva, In this paper, we study the effects produced by a dark matter halo on the regular or chaotic nature of the orbits of a star moving near the galactic plane. The potential consists of three components: a spherical core, a disk and an ellipsoidal dark matter halo. We run simulations with three different halo shapes at three different energies. Using Poincaré sections we visually analyze the transition from regular to chaotic orbits and confrm that the shape of the dark halo is a key element: the spherical halo keeps the orbits stable, the prolate halo induces more chaotic orbits globally while the triaxial ellipsoid only does so at the core.

Recent investigations have suggested that the six-quark combination uuddss could be a deeply bound state (S) that has eluded detection so far, and a potential dark matter candidate. We report the first search for a stable, doubly strange six-quark state in Upsilon -> S anti-Lambda anti-Lambda decays based on a sample of 90 million Upsilon(2S) and 110 million Upsilon(3S) decays collected by the BABAR experiment. No signal is observed, and 90% confidence level limits on the combined Upsilon(2S,3S) -> S anti-Lambda anti-Lambda branching fraction in the range (1.2-1.4)x10^-7 are derived for m_S < 2.05 GeV. These bounds set stringent limits on the existence of such exotic particles., 7 pages, 4 figures, published version

[eng] Cosmology is the science that studies the Universe as whole, aiming to understand its origin, composition and evolution. During the last decades, cosmology has transitioned from a “data staved” to a “data driven” science, inaugurating what is known as precision cosmology. This huge observational effort has confirmed and fostered theoretical research, and established the standard model of cosmology: Lambda-Cold Dark Matter (LCDM). This model successfully reproduces most of the observations. However, there are some persistent tensions between experiments that might be smoking guns of new physics beyond this model. Anyways, there is a difference between modeling and understanding, and LCDM is a phenomenological model that, for instance, does not describe the nature of the dark matter or dark energy. This thesis collects part of my research focused on pushing the limits of the standard cosmological model and its assumptions, regarding also existing tensions between experiments. New strategies to optimize the performance of future experiments are also proposed and discussed. The largest existing tension is between the direct measurements of the Hubble constant using the distance ladder in the local Universe and the inferred value obtained from observations of the Cosmic Microwave Background when LCDM is assumed. A model independent reconstruction of the late-time expansion history of the Universe is carried out, which allows us to identify possible sources and solutions of the tension. We also introduce the concept of the low redshift standard ruler, and measure it in a model independent way. Finally, we introduce a statistical methodology to analyze several data sets in a conservative way, no matter the level of discrepancy between them, accounting for the potential presence of systematic errors. The role of primordial black holes as candidates for dark matter is addressed in this thesis, too. Concretely, the impact of an abundant population of primordial black holes in the rest of cosmological parameters is discussed, considering also populations with extended mass distributions. In addition, massive primordial black holes might be the seeds that are needed to explain the origin of the supermassive black holes located in the center of the galaxies. We predict the contribution of a population of massive primordial black holes to the 21 cm radiation from the dark ages. This way, observations of the 21 cm intensity mapping observations of the dark ages could be used to ascertain if the seeds of the supermassive black holes are primordial. Finally, we estimate the potential of radio-continuum galaxy surveys to constrain LCDM. These kind of experiments can survey the sky quicker than spectroscopic and optical photometric surveys and cover much larger volumes. Therefore, they will be specially powerful to constrain physics which has impact on the largest observable scales, such as primordial non Gaussianity. On the other hand, intensity mapping experiments can reach higher redshifts than galaxy surveys, but the cosmological information of this signal is coupled with astrophysics. We propose a methodology to disentangle astrophysics and optimally extract cosmological information from the intensity mapping spectrum. Thanks to this methodology, intensity mapping will constrain the expansion history of the Universe up to reionization, as shown in this thesis., [spa] El modelo estándar de cosmología, LCDM, se apoya en una cantidad ingente de observaciones extremadamente precisas, que es capaz de reproducir con gran exactitud. Sin embargo, este es un modelo fenomenológico que no es capaz de responder algunas de las preguntas fundamentales sobre el Universo, como la naturaleza de la materia oscura o la energía oscura. Además, cuando este modelo se utiliza para interpretar las observaciones, aparecen tensiones entre experimentos independientes. Estas tensiones, en el caso de no estar producidas por errores sistemáticos no tenidos en cuenta, necesitarían un modelo cosmológico diferente para ser resueltas. Esta tesis recoge trabajos publicados en revistas científicas investigando estos problemas de LCDM. Concretamente, se cubren tres temas principales: la tensión en la constante de Hubble entre las medidas directas usando la escalera de distancias y los valores inferidos a partir de las observaciones de la colaboración Planck asumiendo LCDM; el rol de los agujeros negros primordiales como semillas de los agujeros negros supermasivos, o como candidato para conformar una parte significativa de la materia oscura; y el potencial y las estrategias óptimas a aplicar en experimentos que mapean la estructura a gran escala del Universo para examinar LCDM y medir posibles desviaciones del modelo. De este modo, el trabajo aquí recogido tiene como objetivo investigar las tensiones presentes en LCDM, así como las preguntas que deja sin responder de una manera crítica y desde un punto de vista agnóstico. Además, pretende sentar las bases para futuras investigaciones en estas líneas, cuando estén disponibles nuevas y mejores observaciones, e indicar el camino para poder poner a prueba el modelo estándar de cosmología en los años venideros en regímenes en los que aún no se ha hecho ninguna medida.

International audience; We have developed a computationally competitive N-body model of a previrialized aggregation of galaxies in a flat Lambda cold dark matter Universe to assess the role of the multiple mergers that take place during the formation stage of such systems in the configuration of the remnants assembled at their centres. An analysis of a suite of 48 simulations of low-mass forming groups (M-tot,M- (gr) similar to 10(13) h(-1)M(circle dot)) demonstrates that the gravitational dynamics involved in their hierarchical collapse is capable of creating realistic first-ranked galaxies without the aid of dissipative processes. Our simulations indicate that the brightest group galaxies (BGGs) constitute a distinct population from other group members, sketching a scenario in which the assembly path of these objects is dictated largely by the formation of their host system. We detect significant differences in the distribution of S ` ersic indices and total magnitudes, as well as a luminosity gap between BGGs and the next brightest galaxy that is positively correlated with the total luminosity of the parent group. Such gaps arise from both the grow of BGGs at the expense of lesser companions and the decrease in the relevance of secondranked objects in equal measure. This results in a dearth of intermediate-mass galaxies which explains the characteristic central dip detected in their luminosity functions in dynamically young galaxy aggregations. The fact that the basic global properties of our BGGs define a thin mass Fundamental Plane strikingly similar to that followed by giant early-type galaxies in the local Universe reinforces confidence in the results obtained.

Despite its continued observational successes, there is a persistent (and growing) interest in extending cosmology beyond the standard model, ΛCDM. This is motivated by a range of apparently serious theoretical issues, involving such questions as the cosmological constant problem, the particle nature of dark matter, the validity of general relativity on large scales, the existence of anomalies in the CMB and on small scales, and the predictivity and testability of the inflationary paradigm. In this paper, we summarize the current status of ΛCDM as a physical theory, and review investigations into possible alternatives along a number of different lines, with a particular focus on highlighting the most promising directions. While the fundamental problems are proving reluctant to yield, the study of alternative cosmologies has led to considerable progress, with much more to come if hopes about forthcoming high-precision observations and new theoretical ideas are fulfilled.

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2018, Tutor: Federico Mescia, The dark matter annihilation cross section could suffer a boost due to the Sommerfeld enhancement at low energy. The importance of this process holds in the quantification of the effect on the cross section that an interactive potential produces before particle annihilation. In order to provide insight into the Sommerfeld enhancement we analytically compute it for the potential well and the attractive Coulomb potential. Finally, within the use of a numerical program we compute the Sommerfeld enhancement for the Yukawa potential since it is not analytically solvable

The model in which Primordial Black Holes (PBHs) constitute a non-negligible fraction of the dark matter has (re)gained popularity after the first detections of binary black hole mergers. Most of the observational constraints to date have been derived assuming a single mass for all the PBHs, although some more recent works tried to generalize constraints to the case of extended mass functions. Here we derive a general methodology to obtain constraints for any PBH Extended Mass Distribution (EMD) and any observables in the desired mass range. Starting from those obtained for a monochromatic distribution, we convert them into constraints for EMDs by using an equivalent, effective mass $M_{\rm eq}$ that depends on the specific observable. We highlight how limits of validity of the PBH modelling affect the EMD parameter space. Finally, we present converted constraints on the total abundance of PBH from microlensing, stellar distribution in ultra-faint dwarf galaxies and CMB accretion for Lognormal and Power Law mass distributions, finding that EMD constraints are generally stronger than monochromatic ones., 23 pages, 10 figures. Minor revisions. Matches published version

Treballs Finals de Grau de Física, Facultat de Física, Universitat de Barcelona, Curs: 2017, Tutor: Eduard Salvador Solé, In this paper, we introduce the astrophysical problem of dark matter (DM) mainly focusing on the observational/experimental point of view. Even though DM cannot be observed directly, there are plenty of indirect observations supporting that there is more mass than we can see. This is the case for the observed properties of galaxies, galaxy clusters and the large-scale structure of the universe. We mention the implications of DM in astrophysics and high-energy physics. We then describe the DM candidates. The first group is the ordinary DM, also known as baryonic DM, in the form of astrophysical objects. The second group is non-ordinary DM or non-baryonic DM. This group encompasses all the solutions for the problem that are not in the Standard Model (SM) of particle physics. We end up by reviewing some current experiments that could allow us to discover what kind of DM we are facing.

[EN] Using data recorded with the ANTARES telescope from 2007 to 2015, a new search for dark matter annihilation in the Milky Way has been performed. Three halo models and five annihilation channels, WIMP + WIMP -> b (b) over bar, W+W-, tau(+)tau(-), mu(+)mu(-) and v (v) over bar, with WIMP masses ranging from 50 2 GeV/C-2 to 100 Tev/C-2, were considered. No excess over the expected background was found, and limits on the thermally averaged annihilation cross-section were set., The authors acknowledge the financial support of the funding agencies: Centre National de la Recherche Scientifique (CNRS), Commissariat a l'energie atomique et aux energies alternatives (CEA), Commission Europeenne (FEDER fund and Marie Curie Program), Institut Universitaire de France (IUF), IdEx program and UnivEarthS Labex program at Sorbonne Paris Cite (ANR-10-LABX-0023 and ANR-11-IDEX-0005-02), Labex OCEVU (ANR-11-LABX-0060) and the A*MIDEX project (ANR-11-IDEX-0001-02), Region Ile-de-France (DIM-ACAV), Region Alsace (contrat CPER), Region Provence-Alpes-Cote d'Azur, Departement du Var and Ville de La Seyne-sur-Mer, France; Bundesministerium fur Bildung and Forschung (BMBF), Germany; Istituto Nazionale di Fisica Nucleare (INFN), Italy; Stichting voor Fundamenteel Onderzoek der Materie (FOM), Nederlandse Organisatie voor Wetenschappelijk Onderzoek (NWO), the Netherlands; Council of the President of the Russian Federation for young scientists and leading scientific schools supporting grants, Russia; National Authority for Scientific Research (ANCS), Romania; Ministerio de Economia y Competitividad (MINECO): Plan Estatal de Investigacion (refs. FPA2015-65150-C3-1-P, -2-P and -3-P, (MINECO/FEDER)), Severo Ochoa Centre of Excellence and MultiDark Consolider (MINECO), and Prometeo and Grisolia programs (Generalitat Valenciana), Spain; Ministry of Higher Education, Scientific Research and Professional Training, Morocco. We also acknowledge the technical support of Ifremer, AIM and Foselev Marine for the sea operation and the CC-IN2P3 for the computing facilities.

We compute the time variation of the fundamental constants (such as the ratio of the proton mass to the electron mass, the strong coupling constant, the fine structure constant and Newton's constant) within the context of the so-called running vacuum models (RVM's) of the cosmic evolution. Recently, compelling evidence has been provided showing that these models are able to fit the main cosmological data (SNIa+BAO+H(z)+LSS+BBN+CMB) significantly better than the concordance $\Lambda$CDM model. Specifically, the vacuum parameters of the RVM (i.e. those responsible for the dynamics of the vacuum energy) prove to be nonzero at a confidence level $\gtrsim3\sigma$. Here we use such remarkable status of the RVM's to make definite predictions on the cosmic time variation of the fundamental constants. It turns out that the predicted variations are close to the present observational limits. Furthermore, we find that the time variation of the dark matter particles should be crucially involved in the total mass variation of our Universe. A positive measurement of this kind of effects could be interpreted as strong support to the "micro and macro connection" (viz. the dynamical feedback between the evolution of the cosmological parameters and the time variation of the fundamental constants of the microscopic world), previously proposed by two of us (HF and JS)., Comment: Matches the published version in EPJC

We study the consequences of reheating in quintessential inflation. From simple inflationary quintessential models introduced in cite{hap, hap2}, we show that when the reheating is due to the production of heavy massive particles conformally coupled with gravity, a viable model which matches with the current observational data cite{Ade, Planck, bicep2} is only possible for reheating temperatures that range between $1$ GeV and $10^4$ GeV. On the other hand, when the universe reheats via the production of massless particles, the viability of the model is only possible when those particles are nearly conformally coupled with gravity, leading to a reheating temperature between $1$ MeV and $10^4$ GeV., Comment: Version accepted for publication in PRD

We have tested some simple quintessential inflation models, imposing that they match with the recent observational data provided by the BICEP and Planck's team and leading to a reheating temperature, which is obtained via gravitational particle production after inflation, supporting the nucleosynthesis success. Moreover, for the models coming from supergravity one needs to demand low temperatures in order to avoid problems such as the gravitino overproduction or the gravitational production of moduli fields, which are obtained only when the reheating temperature is due to the production of massless particles with a coupling constant very close to its conformal value., Comment: 21 pages, 10 figures. Version accepted for publication in EPJC

La matèria fosca i l'energia fosca, en cas d'existir, contribuirien en un 96% a l'energia de tot l'Univers, però ningú no coneix la seva autèntica naturalesa i menys encara, com interaccionen. El professor del Departament de Física Diego Pavon ha publicat recentment, juntament amb d'altres autors, un article de revisió on proposen com podria ser aquesta interacció entre matèria i energia fosques per tal d'assegurar el principi de la conservació de l'energia. La materia oscura y la energía oscura, en caso de existir, contribuirían en un 96% a la energía del Universo, pero nadie conoce su auténtica naturaleza y menos aun, cómo interaccionan. El profesor del Departamento de Física Diego Pavon ha publicado recientemente, junto a otros autores, un artículo de revisión donde proponen cómo podría ser esta interacción entre materia y energía oscuras para asegurar el principio de la conservación de la energía. Dark matter and dark energy, in case they exist, would contribute to 96% of the universe's total energy, but no one knows their authentic nature and even less, how they interact. Lecturer of the Department of Physics Diego Pavon recently published, alongside other authors, a review article proposing the nature of this interaction between dark matter and energy with the aim of guaranteeing the principle of conservation of energy.