This PhD thesis explores the idea that the expanding Universe can itself make particles that later behave like dark matter. The work uses Quantum Field Theory on curved spacetime — a framework that treats quantum fields living on a changing gravitational background — because a full quantum theory of gravity is not yet available. It also studies how laboratory systems can mimic these cosmological processes with Bose‑Einstein condensates.

The thesis is organized in four parts. The first part sets the stage with the necessary background on cosmology, inflation (a brief period of very fast expansion in the early Universe), and the basics of analog gravity. In the second part the author studies particle production during inflation for several models. He focuses on “spectator” fields — fields that do not drive the expansion but feel the changing geometry — and finds that both scalar (simple, spin‑0) and vector (spin‑1) fields can, under some model choices, produce the right abundance to be a dark matter candidate. The analysis highlights the role of tachyonic instabilities, a technical term for situations where an effective mass squared becomes negative and some field modes grow exponentially, producing many particles.

The third part moves to the laboratory. It shows how sound waves (phonons) in a Bose‑Einstein condensate can be mapped onto scalar quantum fields in an expanding universe. Using that mapping, the thesis proposes ways to reconstruct a history of expansion from measured signals, to view particle production as a kind of scattering process, and to detect the quantum correlations (entanglement) created between pairs of produced excitations. These proposals aim to make some cosmological quantum effects testable in table‑top experiments.

The final part examines several important caveats. One is the ambiguity of the quantum vacuum in curved spacetime: unlike in flat space there is no single obvious definition of “no particles,” and different choices change the particle counts. The thesis also studies non‑adiabatic effects when the expansion is switched on and off. It reports that if those switch‑on and switch‑off periods are short enough, their exact duration has only a subtle effect on the measurable quantities and does not greatly change the total number of particles produced in the studied setups. The author also corrected and clarified some technical choices, such as which vacuum state is used in parts of the analysis.