Francesco Costa

A bstract: We explore an uncharted corner of dark matter phenomenology: non-supersymmetric spin-3/2 dark matter with baryon number violating interactions. In an effective field theory description, we identify the leading baryonic portal between the spin-3/2 state and Standard Model quarks and show that it can account for the observed dark matter abundance through UV freeze-in and Boltzmann-suppressed freeze-in, while the freeze-out region is completely excluded. The resulting phenomenology is distinctive, with relic production controlled by the competition between baryon-violating single-particle processes and baryon-conserving pair production. We map the viable parameter space against indirect detection, direct detection, and LHC monojet bounds, finding strong complementarity between these probes and especially stringent limits when production and decay are tied to the same operator. We also present a dark QCD-like ultraviolet completion in which the spin-3/2 particle arises as a composite baryon, naturally generating the effective interactions and mitigating the main theoretical obstacles of elementary higher-spin states. This framework opens a novel and testable connection between baryonic portals, confining dark sectors, and higher-spin dark matter.

We present (EvaLuator of tunnElliNg Actions), an open-source Python package designed to compute the full evolution of first-order phase transitions in the early Universe generated by particle physics models, taking into account several refinements that go beyond commonly assumed simplifications. The core of is based on a vectorized implementation of the tunnelling potential formalism, making it the first and only public code to compute finite-temperature tunnelling actions within this framework. This allows for a fast computation of the finite-temperature tunnelling action. This, in turn, enables the sampling of the full range of temperatures where two phases coexist and the use of integral expressions that track the complete evolution of the transition, providing a comprehensive picture of it. In addition, provides all the tools to compute the resulting stochastic gravitational waves spectrum, allowing for the full chain of computations – from the Lagrangian parameter inputs to the final gravitational waves spectrum – in a fast and self-contained implementation.

A bstract: Gravitational production of decoupled scalars during inflationary and post-inflationary phases is efficient and can lead to over-production. We study this production with various reheating scenarios such as a generic power-law inflaton potential V _inf ∝ ϕ ^k as well as a multi-stage reheating scenario. We derive constraints on the scalar self-interaction coupling λ _s , the mass m _s , and coefficients of quantum gravity-induced operators. We find that the constraints depend sensitively on the reheating dynamics. Our analysis demonstrates that universal gravity effects do not necessarily spoil the predictivity of non-thermal dark matter scenarios with k < 4 and low reheating temperatures, as an extended reheating phase dilutes gravitationally-produced relics. For k > 4, on the other hand, the relic abundance is enhanced during the reheating phase, leading to stringent constraints on the scalar. In multi-stage reheating, we show that the enhancement/dilution effect of subsequent reheating phases factorises.

High-Frequency Gravitational Waves (HFGWs) constitute a unique window on the early Universe as well as exotic astrophysical objects. While the current gravitational wave experiments are more dedicated to the low frequency regime, the graviton conversion into photons in a strong magnetic field constitutes a powerful tool to probe HFGWs. In this paper, we show that neutron stars, due to their extreme magnetic field, are a perfect laboratory to study the conversion of HFGWs into photons. Using realistic models for the galactic neutron star population, we calculate for the first time the expected photon flux induced by the conversion of an isotropic stochastic gravitational wave background in the magnetosphere of the ensemble of neutron stars present in the Milky Way. We compare this photon flux to the observed one from several telescopes and derive upper limits on the stochastic gravitational wave background in the frequency range 10⁸ Hz–10²⁵ Hz. We find our limits to be competitive in the frequency range 10⁸ Hz–10¹² Hz.

We study freeze-in production of Higgs portal dark matter (DM) at temperatures far below the dark matter mass. The temperature of the Standard Model (SM) thermal bath may have never been high such that dark matter production via thermal emission has been Boltzmann-suppressed. This allows for a significant coupling between the Higgs field and DM, which is being probed by the direct DM detection experiments and invisible Higgs decay searches at the LHC. We delineate the corresponding parameter space in the Higgs portal framework with dark matter of spin 0, 1/2 and 1.

Dark matter freeze-in at stronger coupling is operative when the Standard Model (SM) bath temperature never exceeds the dark matter mass. An attractive feature of this scenario is that it can be probed by direct detection experiments as well as at the LHC. In this work, we show how the mechanism can be realized in a simple UV complete framework, emphasizing the role of the maximal temperature of the SM thermal bath. We demonstrate that the maximal temperature can coincide with the reheating temperature or be close to it such that dark matter production is always Boltzmann-suppressed. This possibility is realized, for example, if the inflaton decays primarily into feebly interacting right-handed neutrinos, which subsequently generate the SM thermal bath. In this case, the SM sector temperature remains constant over cosmological times prior to reheating.