  During the last decades, our understanding of the universe has reached a
remarkable level, being able to test cosmological predictions with an
astonishing precision. Nonetheless, the nature, composition, mass and
interactions of the Dark Matter still remain unknown, presenting one of the
most intriguing conundrums in current cosmology. In this doctoral thesis,
signatures of Dark Matter candidates which can leave an impact on the process
of formation of structures and on the evolution of the Intergalactic Medium are
studied. This thesis is organized in three parts. Part I is devoted to a broad
introduction to the fundamentals, describing the state of the art of the topics
considered. The basics of the $\Lambda$CDM are presented in Chapter 1. Chapter
2 overviews the historical progress of evidences of Dark Matter, followed by a
discussion of the status and small-scale issues of the Cold Dark Matter
paradigm, examining two alternative non-standard scenarios: Warm Dark Matter
and Interacting Dark Matter. Chapter 3 considers Primordial Black Holes as
another Dark Matter candidate, discussing the effects of accretion of
surrounding matter and the enhancement of small-scale fluctuations due to the
Poisson shot noise, both of which could leave an observational impact in the
Intergalactic Medium. The fundamentals of the 21 cm cosmological signal are
reviewed in Chapter 4, summarizing the main processes which drive the
brightness temperature, and discussing its spatial fluctuations via the power
spectrum. Finally, Chapter 5 is dedicated to the ionization and thermal
evolution of the Intergalactic Medium during the Cosmic Dawn and the
Reionization epochs. Part II includes seven original scientific articles
published during the development of the PhD, which constitute the main work of
this thesis. Finally, Part III contains a summary of the main results in
Spanish.
