Momentum-space entanglement from inflationary particle production

We investigate entanglement generation during cosmological inflation, focusing on the role of spacetime perturbations generated by a scalar inflaton field. We first show that gravitational particle production associated with the inflaton quantum fluctuations generates momentum-space entanglement. In particular, we highlight how the Hubble horizon emerges as the natural separation scale for fluctuation modes in bipartite approaches, computing the von Neumann entropy between sub- and super-Hubble modes. We then generalize our treatment to multipartite scenarios. The corresponding entanglement amount is quantified via the recently proposed Entanglement Distance, providing a geometric interpretation of particle entanglement in terms of the Fubini-Study metric. We observe that, in the limit of negligible squeezing, the total amount of entanglement is dominated by the infrared cutoff scale, in agreement with standard bipartite scenarios. We then show that non-negligible multipartite entanglement signatures may emerge across inflation, even during the latest stages of slow-roll, highlighting their dependence on inflationary momentum scales.