Probing Fundamental Interactions with the Hottest and Largest Laboratory

• Francesco D'Eramo (University of Padua & INFN Padua)

The early universe was filled with a plasma of particles in thermal equilibrium, providing a natural laboratory for particle physics under extreme environments. These unique circumstances offer distinct advantages, such as reaching energies unattainable on Earth and the existence of unstable particles from the Standard Model that do not populate significantly our current universe. In this talk, I will present novel studies on how this primordial laboratory can be leveraged to deepen our understanding of particle physics. I will focus on three main scenarios, classified by the lifetime of hypothetical new particles: (i) very unstable particles that act solely as portals to new degrees of freedom; (ii) metastable particles whose decays deposit energy into the primordial universe, leaving detectable traces in cosmological observables; (iii) stable particles that persist to this day, manifesting as dark matter or dark radiation.

Exploring Celestial Objects as Optimal Detectors for Dark Matter

• Pooja Bhattacharjee (University of Nova Gorica)

A diverse array of celestial objects has been considered as potential platforms for indirect dark matter detection. I investigate a spectrum of candidates—including Brown Dwarfs, White Dwarfs, Neutron Stars, and Dwarf Spheroidal Galaxies—to identify which holds the greatest promise for uncovering dark matter and which serves as the most effective dark matter detector. This presentation will quantify the suitability of these objects across different detection regimes by critically examining key assumptions underlying search sensitivities. I will demonstrate how various celestial objects can provide complementary signals, enhancing the robustness of dark matter detection efforts. Additionally, I will discuss the unique opportunities and limitations of different search strategies, highlighting how the interplay of these regimes defines the optimal roles of celestial objects as dark matter detectors.

Primordial Black Holes -- Positivist Perspective and Quantum Quiddity

• Florian Kühnel (MPP & LMU Munich)

Primordial black holes are black holes that may have formed in the early Universe. Their masses potentially span a range from as low as the Planck mass up to many orders of magnitude above the solar mass. This, in particular, includes those black holes recently discovered through gravitational waves, and (part of) these may conceivably be of primordial origin. After a general introduction on primordial black holes, I review the observational hints for their existence -- from a variety of lensing, dynamical, accretion and gravitational-wave effects. As I will show, all of these (over 20) may be explained by a single and simple unified model, naturally shaped by the thermal history of the Universe. If time permits, I discuss how recent advances in our understanding of quantum effects in black holes impact PBHs. On the one hand, this concerns deviations from Hawking radiation in the form of the memory-burden effect. On the other hand, I will discuss vorticity, which we recently conjectured to be a new characteristic of (near-extremally rotating) black holes. In the second part of my talk, I will present novel results on large-scale simulations of spatially-correlated random fields, being able to resolve events as rare as one in 10^{13}, and discuss their application to PBHs.

Cosmological perturbations from dark sectors

• Pedro Schwaller (JGU Mainz)

There is strong evidence for the existence of a dark sector that explains dark matter and its interactions. While its interactions with visible matter might be feeble and difficult to probe, dark sectors can influence cosmological observables through purely via gravity. I will discuss two such opportunities. First, large fluctuations in the energy density of the dark sector shortly before CMB emission induce spectral distortions of the CMB spectrum. They therefore provide a probe of e.g. phase transitions, cosmic strings or domain walls at late times, complementary to gravitational wave observations. Second, isocurvature perturbations are a smoking gun of non-minimal cosmological initial conditions. We argue that in realistic scenarios a mixture of neutrino and matter isocurvature is generated, e.g. due to dark radiation which is the remnant of a dark sector. We introduce a new isocurvature mixing angle and obtain the first constraints on it from PLANCK data, finding a modest preference for the presence of pure neutrino isocurvature. Furthermore we show that in the presence of dark radiation isocurvature, the matter isocurvature is sensitive to the DM production mechanism and can distinguish freeze-in and freeze-out scenarios.