arXiv subjects

Arturo de Giorgi

Publications and source records attributed to Arturo de Giorgi.

27 records · Page 2Linked to original sources

arXiv2024

GeV ALP from TeV Vector-like leptons

We present a model where a GeV axion-like-particle (ALP) is predicted in a large portion of the parameter space due to the presence of explicit Peccei-Quinn symmetry-breaking terms in an exotic leptonic sector. The latter provides a solution to the muon $g-2$ anomaly, within the framework of the Linear Seesaw neutrino mechanism. The spectrum is extended by a complex scalar singlet only transforming under the Peccei-Quinn symmetry, which generates the ALP. Its couplings with fermions can continuously span over many orders of magnitude, which constitutes a specific feature of this model in contrast to generic ultraviolet constructions. Interestingly, these couplings are suppressed by the ALP characteristic scale that can be as low as the TeV scale, which represents a novel feature of the model and opens up to several phenomenological consequences.

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arXiv2024

The Minimal Massive Majoron Seesaw Model

A convincing explanation of the smallness of neutrino masses is represented by the Type-I Seesaw mechanism, where the two measured neutrino mass differences can be generated by introducing at least two right-handed neutrinos. In an ultraviolet complete model, it is possible to dynamically generate the heavy Majorana scale through the spontaneous symmetry breaking of a global Abelian symmetry and the most economical realisation consists in coupling the two exotic neutral leptons to a singlet complex scalar field. The associated Goldstone boson is often dubbed as Majoron, which may achieve a non-vanishing mass by means of a small term that explicitly breaks the Abelian symmetry. In a generic model, the neutrino and Majoron mass generation mechanisms are completely uncorrelated. In this paper, instead, we reduce the landscape of possible models proposing a unique, minimal and predictive framework in which these two types of masses are strictly tied and arise from the same source. Bounds from various terrestrial and astrophysical experiments are discussed.

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arXiv2023

Flavour and Higgs physics in $Z_2$-symmetric 2HD models near the decoupling limit

With no evidence of any exotic particle detected so far beyond the Standard Model, the new physics may lie above the presently accessible energies at colliders and, at low-energies, can be accounted for via an effective description. The interplay of flavour and Higgs physics data allows setting stringent bounds on the parameters of the effective Lagrangian. In this paper, we focus on $Z_2$-symmetric two Higgs doublet models near the decoupling limit: the corresponding effective description relies on only a few parameters, thus predicting many interesting correlations between observables that work as tests of the theory. We present the results of a global fit to the existing data, updating and extending over the past literature. We comment on the triple Higgs coupling as a probe of an extended scalar sector and on the recent CDF II measurement of the $W$-mass.

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arXiv2023

The Low-Scale Seesaw Solution to the $M_W$ and $(g-2)_μ$ Anomalies

The recent CDF-II measurement of the $W$-boson mass shows a strong tension with the corresponding Standard Model prediction. Once active neutrino masses are explained in the context of the Low-Scale Seesaw mechanisms, this tension can be resolved. We investigate the possibility of explaining the longstanding muon anomalous magnetic moment anomaly within the same frameworks. We present a simplified extension of the Standard Model, accounting only for the second lepton generation, that describes a massive active neutrino and provides a combined solution to these anomalies. The model is renormalisable and introduces in the spectrum, beyond the sterile species of the Low-Scale Seesaw mechanism, only one pair of exotic vector-like leptons, doublets under the electroweak symmetry. We moreover discuss the extension of this model to the realistic three-family case.

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arXiv2023

Probing HNL-ALP couplings at colliders

Axion-like particles (ALPs) and heavy neutral leptons (HNLs) are both well-motivated extensions of the Standard Model. As ALPs couple to on-shell fermions proportionally to their masses, processes involving both types of particles may give rise, for TeV HNLs, to relevant phenomenology at colliders. In this work, we point out a particularly clean process, whose final state consists of four jets and two charged leptons, and we estimate its current and future sensitivity at the LHC. For on-shell HNLs, i) there is no dependence on the overall scale of the mixing between HNLs and the active neutrinos, making this process sensitive down to the type-I Seesaw line; ii) the signal strength of the process is sizable only as far as the HNL masses are below a few TeVs, contrary to what the proportionality to masses of the ALP couplings may suggest. Although ALPs and HNLs have been mainly studied independently in the literature, considering their interplay may lead to joint limits that are much stronger than those on the individual particles taken separately. This concise study paves the way for similar searches at colliders and other experiments.

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arXiv2022

A lesson from $R_{ττ}^{K^{(\ast)}}$ and $R_{νν}^{K^{(\ast)}}$ at Belle II

Within the assumption of Left-Handed (LH) New Physics (NP), we review the relations between $\mathcal{B}(B\to K^{(\ast)} τ^+τ^-)$ and $\mathcal{B}(B\to K^{(\ast)} ν\bar ν)$ for several Beyond the Standard Model (BSM) scenarios, commonly considered to explain the Lepton flavor Universality (LFU) violation observed in charged and neutral-current semileptonic $B$ decays. We employ the latest $R_{D^{(\ast)}}$ world averages that include the recent LHCb measurement and assess the possibility of simultaneously explaining the $B$-anomalies without spoiling current bounds on di-neutrino and di-tau modes. This is particularly relevant in light of the upcoming results by Belle II on neutrinos and the continuing improvement in accuracy and sensitivity achieved in tau modes.

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arXiv2022

Neutral $B$-anomalies from an $\mathit{on\text{-}shell}$ scalar exchange

The neutral $B$-anomalies are analysed in terms of the tree-level exchange of a (pseudo)scalar gauge singlet $a$. Solutions to both $R_{K^{(*)}}$ central bin anomalies are found within $1σ$ for ${m_{a}^2 \in [{1.1},\,{6}]\,\text{GeV}^2}$, while the low $q^2$-bin anomaly can also be accounted for with masses close to the bin threshold. The impact of these solutions on other ${b\to s e^+ e^-}$ observables is discussed in detail. Due to the $\mathit{on\text{-}shell}$ enhancement, sizable effects are expected in null tests of the SM, such as the flat term, $F_H$, of the $B\to K e^+ e^-$ angular distribution. At the same time, the observable sensitive to the $K^\ast$ polarisation, $F_L\, (B\to K^* e^+ e^-)$, and the lepton forward-backward asymmetry, ${A_{FB}\, (B\to K^* e^+ e^-)}$, can be suppressed with respect to their SM values. Corrections from the new physics to $\mathcal{B}(B_s \to e^+ e^-)$ are, on the other hand, negligible. Along with the previous observables, improved measurements of the cross section ${σ(e^+ e^- \to a (e^+ e^-) γ)}$ could potentially probe the relevant parameter space of the model. A comparison between our results and those stemming from an axion-like particle exchange is also discussed, showing that the exchange of a general scalar singlet offers a noticeably wider parameter space.

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arXiv2022

Warm dark matter from a gravitational freeze-in in extra dimensions

We study the freeze-in of gravitationally interacting dark matter in extra dimensions. Focusing on a minimal dark matter candidate that only interacts with the SM via gravity in a five-dimensional model we find that a large range of dark matter and Kaluza-Klein graviton masses can lead to the observed relic density. The preferred values of the masses and the strength of the interaction make this scenario very hard to test in terrestrial experiments. However, significant parts of the parameter space lead to warm dark matter and can be tested by cosmological and astrophysical observations.

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arXiv2021

Dark matter interacting via a massive spin-2 mediator in warped extra-dimensions

We study dark matter interacting via a massive spin-2 mediator. To have a consistent effective theory for the spin-2 particle, we work in a warped extra-dimensional model such that the mediator(s) are the Kaluza-Klein (KK) modes of the 5D graviton. We pay close attention to dark matter annihilations into KK-gravitons. Due to the high energy behavior of longitudinal modes of spin-2 fields, these channels exhibit a tremendous growth at large center of mass energies $\sqrt{s}$ if only one spin-2 mediator is considered. For the first time, we include the full KK-tower in this dark matter production process and find that this growth is unphysical and cancels once the full field content of the extra-dimensional theory is taken into account. Interestingly, this implies that it is not possible to approximate the results obtained in the full theory with a reduced set of effective interactions once $\sqrt{s}$ is greater than the first graviton mass. This casts some doubt on the universal applicability of previous studies with spin-2 mediators within an EFT framework and prompts us to revisit the phenomenological allowed parameter space of gravitationally interacting scalar dark matter in warped extra-dimensions.

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