Giorgio Arcadi

Introduction: Next-generation direct detection experiments will probe dark matter (DM) scattering cross-sections deep into the neutrino fog, the regime where coherent neutrino scattering becomes an irreducible background. We investigate whether thermally produced weakly interacting massive particles (WIMPs) can naturally populate this regime while satisfying relic density and indirect detection constraints. Adopting as a case study the 2HD+a, a two-Higgs doublet model with h,H,A,H ^± scalar states supplemented by a light singlet pseudoscalar Higgs state a. Methodology: The study of the model has been performed through extensive parameter scans using a combination of publicly available packages, referenced in the main text, and codes realized in purpose, as, for example, in the case of the loop-induced DM scattering cross-section. Three main scenarios have been depicted: high singlet-doublet mixing (sin θ ≥ 10 ⁻³ ), suppressed singlet-doublet mixing (sin θ < 10 ⁻³ ) and two component DM scenario (sin θ = 0). In each scenario the scan has been repeated for the Type-I and Type-II configurations. Results: We evaluate all the viable parameter space compared to current LZ and FERMI-LAT bounds and projected XLZD and CTA sensitivities. We find that the single component setup lies naturally below the neutrino floor for DM masses above 100 GeV while, on the contrary, most of the parameter space of the two component DM scenario is strongly disfavored already considering current limits alone. The parameter space of both single and two component DM scenario can be nevertheless broadened by considering specific relations among the model parameters to suppress the coupling between the 125 GeV bosons and two a states. Discussion: Overall, our results provide strong motivation to fully exploit future ton-scale detectors.

A bstract: In theories with extended scalar sectors the lightest new scalar degree of freedom might be accessible at colliders. Going beyond simplified models, such a theory can be described in a gauge-invariant and agnostic way via an EFT with a non-linearly realized electroweak symmetry. In this extended HEFT, depending on the SU (2) nature of the new scalar in the UV, operators will be suppressed by different powers of a heavy mass scale. We use dimensional analysis to systematically evaluate expected hierarchies between Wilson coefficients, leading to structural relations between potential LHC observables, such as di-boson resonances, tau pair production or the di-photon channel. Once future collider data reveals a hint of a new scalar field, it can be fitted to this extended HEFT and such a structural analysis will help interpret it with respect to possible UV models, circumventing the need to individually test each possible model on the data or to fix the SU (2) representation of the new scalar beforehand. For illustration, the framework is applied to the tentative 95 GeV resonance. In addition to its usefulness for collider physics, the extended HEFT can also be beneficial for low-energy observables, allowing to describe new scalars in an agnostic way.

There are several excesses of events in current LHC data, yet not exceeding the level of significance which would make them to be considered as firm. They point to the possibility of the presence of a new Higgs particle in the spectrum, in addition to the already observed 125 GeV state. In particular, there are excesses involving a diphoton resonance at invariant masses of about 95 GeV, 152 GeV and 650 GeV accompanied to an extra scalar. We have, in addition, the recent observation of a toponium at a mass of about 350 GeV. In this paper, we aim to explain such experimental hints in the framework of a two Higgs doublet model supplemented by a relatively light pseudoscalar Higgs boson a which would correspond to the putative resonance in most cases. This realistic 2HD+a scenario is attractive as it is has the virtue to pass all experimental constraints from high-precision experiments and collider searches and, at the same time, to allow for a viable explanation of the dark matter in the universe. We first update the present constraints on the model, in particular taking into account the latest results on dark matter and Higgs searches, as well the high-precision measurements, including those from Higgs and flavor physics. We then show that the additional Higgs states with the proper mass spectrum and adjusted couplings to fermions, would explain all the LHC excesses (but individually) while passing the former experimental constraints as well as the theoretical ones.

We establish comprehensive theoretical benchmarks for weakly interacting massive particles (WIMPs) accessible to ultimate direct detection experiments, focusing on the challenging parameter space between current experimental limits and the irreducible neutrino background. We systematically examine both thermal freeze-out and freeze-in production mechanisms across a range of simplified dark matter models, including s -channel scalar and vector portals, t -channel mediator scenarios, and electroweakly interacting multiplets. For thermal relics, we identify parameter regions where suppressed direct detection cross sections naturally arise through momentum-dependent interactions and blind-spot configurations, while maintaining the correct relic abundance. We extensively investigate freeze-in scenarios, demonstrating how feebly interacting massive particles in portal models can populate experimentally accessible parameter space despite their ultraweak couplings. Additionally, we explore how nonstandard cosmological histories—including early matter domination and fast-expanding Universe scenarios—can dramatically alter the relationship between relic density and detection prospects, opening new avenues for discovery. Our analysis provides a roadmap for next-generation experiments approaching the neutrino floor, highlighting complementary detection strategies and identifying the most promising theoretical targets for ultimate sensitivity dark matter searches. These benchmarks establish the theoretical foundation for the final push toward comprehensive coverage of well-motivated WIMP parameter space.

A bstract: We investigate benchmark scenarios for Weakly Interacting Massive Particles (WIMPs) that naturally evade current direct detection constraints by featuring suppressed spin-independent cross-sections. Focusing on three representative models — the Singlet-Doublet fermion model, its extension to a Two-Higgs-Doublet plus pseudoscalar sector (2HDM+ a ), and a dark SU(3) gauge model, we systematically analyze the interplay between thermal freeze-out, direct detection blind spots, and radiative corrections. In each case, we identify viable regions of parameter space where the predicted dark matter relic abundance is consistent with observations while elastic scattering rates lie below current exclusion limits and, in some cases, but now always, below the neutrino floor. Loop-induced effects are shown to play a critical role, particularly in scenarios with suppressed tree-level interactions. Our findings demonstrate that models with rich electroweak and scalar sectors can populate the experimentally challenging, yet phenomenologically motivated parameter space between existing constraints and the ultimate sensitivity of current-technology direct detection experiments.

The dark matter problem, together with the discovery of neutrino masses from the observation of the oscillation phenomenon, represents one of the most important open questions in particle physics. A concurrent solution arises when one of the right-handed neutrinos, necessary for the generation of light neutrino masses, is the dark matter candidate. In this letter, we study the generation of such a dark matter candidate relying solely on the presence of neutrino mixing. This tightly links the generation of dark matter with searches in laboratory experiments on top of the usual indirect dark matter probes. We find that the regions of parameter space producing the observed dark matter abundance can be probed with electroweak precision observables, charged lepton flavor violation searches, as well as, collider searches when the mass of the heavy neutrino lies at the TeV scale.

We establish comprehensive theoretical benchmarks for Weakly Interacting Massive Particles (WIMPs) accessible to ultimate direct detection experiments, focusing on the challenging parameter space between current experimental limits and the irreducible neutrino background. We systematically examine both thermal freeze-out and freeze-in production mechanisms across a range of simplified dark matter models, including s-channel scalar and vector portals, t-channel mediator scenarios, and electroweakly interacting multiplets. For thermal relics, we identify parameter regions where suppressed direct detection cross-sections naturally arise through momentum-dependent interactions and blind-spot configurations, while maintaining the correct relic abundance. We extensively investigate freeze-in scenarios, demonstrating how feebly interacting massive particles (FIMPs) in portal models can populate experimentally accessible parameter space despite their ultra-weak couplings. Additionally, we explore how non-standard cosmological histories including early matter domination and fast-expanding Universe scenarios can dramatically alter the relationship between relic density and detection prospects, opening new avenues for discovery. Our analysis provides a roadmap for next-generation experiments approaching the neutrino floor, highlighting complementary detection strategies and identifying the most promising theoretical targets for ultimate sensitivity dark matter searches. These benchmarks establish the theoretical foundation for the final push toward comprehensive coverage of well-motivated WIMP parameter space.

In this work we illustrate a general framework to describe the LHC phenomenology of extended scalar (and fermion) sectors, with focus on dark matter (DM) physics, based on an effective field theory (EFT) with non-linearly realized electroweak symmetry. Generalizing Higgs EFT (HEFT), the setup allows to include a generic set of new scalar resonances, without the need to specify their UV origin, that could for example be at the interface of the Standard Model (SM) and the DM world. In particular, we study the case of fermionic DM interacting with the SM via two mediators, each of which can possess either CP property and originate from various electroweak representations in the UV theory. Besides trilinear interactions between the mediators and DM or SM pairs (including pairs of gauge field-strength tensors), the EFT contains all further gauge-invariant operators up to mass dimension D = 5. While remaining theoretically consistent, this setup offers enough flexibility to capture the phenomenology of many benchmark models used to interpret the results of experimental DM and BSM searches, such as two-Higgs doublet extensions of the SM or singlet extensions. Furthermore, the presence of two mediators with potentially sizable couplings allows to account for a broad variety of interesting collider signatures, as for example detectable mono-h and mono-Z signals. Correlations can be employed to diagnose the nature of the new particles.