Most of the elementary particles discovered in the past century have Compton wavelengths that are much smaller than the size of the atom, and, therefore, cannot mediate long-range forces. In the early Universe, however, the situation is very different: the horizon size is small, and interactions that are typically short-ranged can effectively behave as long-range forces. Of particular interest are attractive Yukawa interactions. These forces can induce instabilities analogous to gravitational collapse — yet typically much stronger — allowing structure formation even during the radiation-dominated era. At the same time, the associated scalar radiation efficiently carries away energy and angular momentum, further enabling collapse. The resulting primordial structure formation and subsequent dynamics produce a rich phenomenology with implications across particle physics and cosmology. In this talk, I will discuss how such long-range forces can influence dark matter, baryogenesis, and the generation of gravitational waves.

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Understanding the confinement mechanism in gauge theories and the universality of effective string-like descriptions of gauge flux tubes remains a fundamental challenge in modern physics. We probe string modes of motion with dynamical matter in a digital quantum simulation of a (2+1) dimensional gauge theory using a superconducting quantum processor with up to 144 qubits, stretching the hardware capabilities with quantum-circuit depths comprising up to 192 two-qubit layers. We realize the Z_2-Higgs model (Z_2HM) through an optimized embedding into a heavy-hex superconducting qubit architecture, directly mapping matter and gauge fields to vertex and link superconducting qubits, respectively. Using the structure of local gauge symmetries, we implement a comprehensive suite of error suppression, mitigation, and correction strategies to enable real-time observation and manipulation of electric strings connecting dynamical charges. Our results resolve a dynamical hierarchy of longitudinal oscillations and transverse bending at the end points of the string, which are precursors to hadronization and rotational spectra of mesons. We further explore multi-string processes, observing the fragmentation and recombination of strings. The experimental design supports 300,000 measurement shots per circuit, totaling 600,000 shots per time step, enabling high-fidelity statistics. We employ extensive tensor network simulations using the basis update and Galerkin method to predict large-scale real-time dynamics and validate our error-aware protocols. This work establishes a milestone for probing non-perturbative gauge dynamics via superconducting quantum simulation and elucidates the real-time behavior of confining strings. Ref: CERN-TH-2025-111 [arXiv:2507.08088]

Ultracold neutrons (UCN) enable long observation times up to several hundred seconds, opening unique possibilities for precision measurements in low-energy particle physics. However, producing large quantities is challenging and most experiments throughout UCN physics have been statistically limited. Advances in producing UCN with low-temperature superfluid helium have recently led to long-duration storage experiments, with unprecedented UCN density, in the new instrument SuperSUN at the Institut Laue-Langevin in Grenoble. I will describe the construction and operation of SuperSUN, the interpretation of measurements performed to date, and the challenges associated with transporting and studying UCN at extremely low energies. Prospects for physics measurements with the PanEDM experiment, and other highlighted applications, will also be presented.