[en] In the Standard Model of elementary particles, there are three massless neutrino species that interact through the weak force. During the last several years, experiments involving solar, atmospheric, reactor and accelerator neutrinos have adduced robust evidence for the existence of neutrino oscillations, implying that neutrinos have masses. Oscillation experiments only provide bounds on the neutrino mass squared differences while cosmology supply a tool to study the absolute scale of neutrino masses. In the early universe, the standard model neutrinos are in thermal equilibrium at temperatures larger than about a MeV, after which they decouple when they are still relativistic, leaving a distribution of relic neutrinos that contribute to the energy density of the universe. These neutrinos affect the expansion rate of the universe and change the epoch of matter-radiation equality, leaving an imprint on the Cosmic Microwave Background (CMB) anisotropies and on structure formation. After becoming non-relativistic, they suppress the growth of matter density fluctuations and galaxy clustering. These observations have been used to place new constraints on neutrino physics with an upper bound on the sum of neutrino masses m <0.6 eV at 95% CL. This bound depends on the combination of data sets and on the cosmological model. The simplest explanations of neutrino mass require the existence of right handed, singlet neutrino states. However, there is no fundamental symmetry in the standard model that fixes the number of such sterile states. This means that there may be sterile neutrinos in nature. Cosmological data provide also the possibility of a measurement of the relativistic energy density of the universe in terms of the effective number of neutrinos. If the effective number of neutrinos Neff is larger than the Standard Model prediction of Neff = 3.046 at the Big Bang Nucleosynthesis (BBN) era, the relativistic degrees of freedom, and, consequently, the Hubble expansion rate will also be larger causing weak interactions to become un effective earlier. This will lead to a larger neutronto-proton ratio and will change the standard BBN predictions for light element abundances. My tesis is focused on the study of cosmological neutrino constraints using the most recent and available cosmological data. In particular I explore the bounds on the active and sterile neutrino masses as well as on the number of steriles neutrino species within the "CDM cosmological scenario as well as in other extended scenarios.

[es] El Modelo Estándard de partículas fundamentales asume que hay tres especies de neutrinos sin masa que interactúan a través de la fuerza débil. Durante los últimos años, los experimentos con neutrinos solares, atmosférico, aquellos de reactores y aceleradores han aportado pruebas sólidas de la existencia de oscilaciones del neutrino. Esto implica que los neutrinos tienen masa. Sin embargo, los experimentos de oscilaciones determinan sólo la diferencias relativas de las masas de los neutrinos; la escala absoluta de masas puede determinarse mediante datos cosmológico. Las masas de los neutrinos afectan los distintos observables cosmológicos, in particular, a la evolución de las perturbaciones de materia, a la formación de estructuras y a la CMB (Cosmic Microwave Background). La tesis se centra en el estudio de cómo poner cotas a los parámetros cosmologicos, en particular de los neutrinos, que describen la imagen de nuestro universo, aprovechando de los nuevos datos cosmológicos.