arXiv subjects

Giorgio Arcadi

Publications and source records attributed to Giorgio Arcadi.

At least 19 recordsLinked to original sources

arXiv2026

Charting Dark Matter down to the neutrino floor/fog in the 2HD+a scenario

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 model, we have performed comprehensive parameter scans over the Type-I and Type-II Yukawa configurations. We have included the limit of strongly suppressed singlet--doublet {\it A-a} mixing sin$\theta \! \to \! 0$ and we show that annihilation into {\it ha} and ${\it Ha}$ final states sustains the correct relic density while loop-induced direct detection cross-sections naturally land inside the neutrino fog; in the same limit the light pseudoscalar boson becomes long-lived, featuring displaced-vertex signatures when produced at colliders. Finally, in the case of zero mixing, we have considered a new possibility for DM phenomenology as the $a$ state becomes cosmologically stable and, consequently, an additional DM component. We map all the viable parameter space against 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 present limit. 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. Our results represent in any case a motivation to fully exploit future tonne-scale detectors.

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arXiv2026

Baryogenesis and Dark Matter from non-thermally produced WIMPs

We illustrate, via a simplified model, a scenario in which the baryon-asymmetry and, possibly the dark matter component of the Universe are simultaneously generated by the decay of a WIMP-like mother particle, in turn produced non-thermally during an epoch of Early Matter domination. We first consider the standard evolution of the Universe and introduce TeV-scale BSM particles, finding that this paradigm cannot produce enough baryon asymmetry. This deficiency can be resolved by considering a non-standard scenario, with a matter-dominated phase prior to radiation-domination. Finally, we include a dark matter candidate, which is non-thermally produced during the Early Matter domination. Our results demonstrate an interesting common origin of baryon asymmetry and Dark Matter, with the particle masses lying within the collider-detectable range, thanks to the presence of non-standard evolution in the early Universe.

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arXiv2025

Characterizing LHC-Resonances in extended HEFT: information on the nature of extended scalar sectors

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.

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arXiv2025

Interpreting the current Higgs excesses at the LHC in the 2HD+a framework

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 and an extra scalar might accompany the recent observation of a toponium at a mass of about 350 GeV. Several interpretations of these excesses have been attempted in extensions of the Standard Model. In this paper, we aim to explain them 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.

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arXiv2025

t-channel dark matter at the LHC -- a whitepaper

This report, summarising work achieved in the context of the LHC Dark Matter Working Group, investigates the phenomenology of $t$-channel dark matter models, spanning minimal setups with a single dark matter candidate and mediator to more complex constructions closer to UV-complete models. For each considered class of models, we examine collider, cosmological and astrophysical implications. In addition, we explore scenarios with either promptly decaying or long-lived particles, as well as featuring diverse dark matter production mechanisms in the early universe. By providing a unified analysis framework, numerical tools and guidelines, this work aims to support future experimental and theoretical efforts in exploring $t$-channel dark matter models at colliders and in cosmology.

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arXiv2025

Beyond the Veil: Charting WIMP Territories at the Neutrino Floor

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.

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arXiv2025

WIMPs Below the Radar: Blind Spots and Benchmarks Beyond the Neutrino Floor

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.

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arXiv2025

Updated BBN Bounds on Hadronic Injection in the Early Universe: The Gravitino Problem

Late-decaying particles naturally arise in many extensions of the Standard Model, directly impacting key cosmological processes in the early universe, such as Big Bang Nucleosynthesis (BBN). BBN studies often consider electromagnetic energy injection episodes only, but in practice long-lived particles are also amenable to hadronic decays. The latter can greatly alter the predicted abundances of light elements such as $\mathrm{D}/\mathrm{H}$, $Y_p$, ${}^3\mathrm{He}/\mathrm{D}$, and ${}^7\mathrm{Li}/\mathrm{H}$. Incorporating up-to-date measurements, we place constraints on the primordial abundance of long-lived particles as a function of their lifetime. Lastly, we apply our results to the gravitino problem and set bounds on the reheating temperature, which controls the gravitino primordial abundance.

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arXiv2025

Is there a (Pseudo)Scalar at 95 GeV?

We discuss the possibility of interpreting the recent experimental hints, in favour of a 95 GeV resonance, with extensions of the Standard Model featuring an extra Higgs doublet and SM scalar (2HDM+s) or pseudoscalar singlet (2HDM+a). The possibility of reproducing the experimental anomalies will be compared with the theoretical constraints on the extended Higgs sector as well as complementary bounds coming from flavour physics as well as other colliders searchers. For both the 2HDM+s and 2HDM+a we will consider a generic natural flavour conserving (NFC) as well as the customary Type-I, -II, -X and -Y configurations of the Yukawa coupling to the BSM Higgs bosons.

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arXiv2024

Dark Particles at the LHC: LHC-Friendly Dark Matter Characterization via Non-Linear EFT

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.

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arXiv2024

$Z^\prime$-mediated dark matter freeze-in at stronger coupling

We study freeze-in production of fermionic dark matter mediated by a $Z^\prime$ gauge boson. In particular, we explore the regime of Boltzmann-suppressed production, when the Standard Model (SM) thermal bath temperature never exceeds the dark matter mass. The corresponding gauge coupling is then required to be significant, up to order one. As a result, this class of freeze-in models can be probed by the current and future direct dark matter detection experiments.

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arXiv2024

Probing a Dark Sector with Collider Physics, Direct Detection, and Gravitational Waves

We assess the complementarity between colliders, direct detection searches, and gravitational wave interferometry in probing a scenario of dark matter in the early universe. The model under consideration contains a $B-L$ gauge symmetry and a vector-like fermion which acts as the dark matter candidate. The fermion induces significant a large dark matter-nucleon scattering rate, and the $Z^\prime$ field produces clear dilepton events at colliders. Thus, direct detection experiments and colliders severely constrain the parameter space in which the correct relic density is found in agreement with the data. Nevertheless, little is known about the new scalar responsible for breaking the $B-L$ symmetry. If this breaking occurs via a first-order phase transition at a TeV scale, it could lead to gravitational waves in the mHz frequency range detectable by LISA, DECIGO, and BBO instruments. The spectrum is highly sensitive to properties of the scalar sector and gauge coupling. We show that a possible GW detection, together with information from colliders and direct detection experiments, can simultaneously pinpoint the scalar self-coupling, and narrow down the dark matter mass where a thermal relic is viable.

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arXiv2024

Roads for Right-handed Neutrino Dark Matter: Fast Expansion, Standard Freeze-out, and Early Matter Domination

Right-handed neutrinos appear in several extensions beyond the Standard Model, specially in connection to neutrino masses. Motivated by this, we present a model of right-handed neutrino dark matter that interacts with Standard Model particles through a new gauge symmetry as well as via mass mixing between the new vector field and the Z boson, and investigate different production mechanisms. We derive the dark matter relic density when the Hubble rate is faster than usual, when dark matter decouples in a matter domination epoch, and when it decouples in a radiation domination regime, which is then followed by a matter domination era. The direct detection rate features a spin-independent but velocity suppressed operators, as well as a spin-dependent operator when the mass mixing is correctly accounted for. We put all these results into perspective with existing flavor physics, atomic parity violation, and collider bounds. Lastly, we outline the region of parameter space in which a weak scale right-handed neutrino dark matter stands as a viable dark matter candidate.

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arXiv2024

Ultraheavy Dark Matter and WIMPs Production aided by Primordial Black Holes

The unitary bound restricts thermal relics to be lighter than $100$ TeV. This work investigates the production of ultraheavy dark matter and WIMPs in the presence of primordial black holes. Firstly, we describe how Hawking evaporation can produce ultraheavy dark matter with masses above $10^{12}$ GeV in radiation and matter-domination eras. Later, we assess how primordial black holes that induce a non-standard cosmology impact the predicted relic density of a thermal relic and explore the interplay between them, considering the restrictions arising from entropy injection due to the evaporation of primordial black holes. Considering a concrete B-L model, where the dark matter is a Dirac particle, we obtain the correct relic density for various freeze-out scenarios and show that a dark matter particle can nicely reproduce the correct relic density in agreement with current limits with masses above the $10$ TeV scale. Hence, this work strengthens the continuous search for heavy dark matter particles.

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arXiv2024

Thermal and non-thermal DM production in non-Standard Cosmologies: a mini review

We provide a short review of some aspects of Dark Matter production in non Standard Cosmology. Considering the simplest Higgs portal model as definite particle physics setup, we consider the impact on the parameter space corresponding to the correct relic density, and the complementary experimental constraints, of the presence, during thermal production, of an exotic component dominating the energy density of the Universe. In the second part of the work we will focus on the case that such exotic component satisfies the equation of state of matter and it can produce DM non-thermally.

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arXiv2024

Higgs Portal Dark Matter Freeze-in at Stronger Coupling: Observational Benchmarks

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.

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arXiv2024

The Waning of the WIMP: Endgame?

Weakly Interacting Massive Particles (WIMPs) continue to be considered some of the best-motivated Dark Matter (DM) candidates. No conclusive signal, despite an extensive search program that combines, often in a complementary way, direct, indirect, and collider probes, has been however detected so far. This situation might change in the near future with the advent of even larger, multi-ton Direct Detection experiments. We provide here an updated review of the WIMP paradigm, with a focus on selected models that can be probed with upcoming facilities, all relying on the standard freeze-out paradigm for the relic density. We also discuss Collider and Indirect Searches when they provide complementary experimental information.

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arXiv2023

Axion Dark Matter and additional BSM aspects in an extended 2HDM setup

We illustrate and discuss the phenomenology of a model featuring a two-Higgs doublet sector augmented by two $SU(2)$ singlet scalars. The gauge symmetry group is extended as well with a $U(1)_{B_{i}-L_{i}}$ component whose spontaneous breaking leads to the gauge boson which has an important effect in the muon (g-2). A global PQ symmetry is introduced upon its breaking we have the axion particle which is also DM in our work. In particular, we have focussed on Type-X and Type-II 2HDM models and found out that (g-2) can not be explained only by the scalar sector for Type-II 2HDM mainly due to stringent constraint from $b \rightarrow s γ$ resulted in $M_{H^{\pm}} > 800$ GeV. For Type-II 2HDM, we can have axion coupling with the gluons which generates the axion potential and possible explanation for the strong CP problem. The proposed model accommodates neutrino masses via the Type-I see-saw mechanism with an upper bound on the right-handed neutrino mass 1 GeV (1 TeV) for Type-II (Type-X) 2HDM due to the presence of Planck scale suppressed operators. Moreover, we also have additional scalars which affect the oblique parameters and hence the W-boson mass which leads us to explain the W-boson mass observed at CDF-II detector. The most stringent constraints on the masses and quartic couplings come from the perturbativity and potential bound from below conditions which leads to fine-tuning among the parameters in part of the parameter space. Finally, we discuss the possible detection prospects of the axion DM and the additional gauge boson.

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