arXiv subjects

Luca Di Luzio

Publications and source records attributed to Luca Di Luzio.

At least 37 records · Page 2Linked to original sources

arXiv2025

Model Independent Tests of the Hadronic Vacuum Polarization Contribution to the Muon $g$$-$$2$

The hadronic vacuum polarization (HVP) contributions to the muon $g$$-$$2$ are the crucial quantity to resolve whether new physics is present or not in the comparison between the Standard Model (SM) prediction and experimental measurements at Fermilab. They are commonly and historically determined via dispersion relations using a vast catalogue of experimentally measured, low-energy $e^+e^-\to \,\rm{hadrons}$ cross section data as input. These dispersive estimates result in a SM prediction that exhibits a muon $g$$-$$2$ discrepancy of more than $5σ$ when compared to experiment. However, recent lattice QCD evaluations of the HVP and a new hadronic cross section measurement from the CMD-3 experiment favor a no-new-physics scenario and, therefore, exhibit a common tension with the previous $e^+e^-\to \,\rm{hadrons}$ data. This study explores the current and future implications of these two scenarios on other observables that are also sensitive to the HVP contributions in the hope that they may provide independent tests of the current tensions observed in the muon $g$$-$$2$.

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arXiv2025

Do Finite Density Effects Jeopardize Axion Nucleophobia in Supernovae?

Nucleophobic axion models, wherein axion couplings to both protons and neutrons are simultaneously suppressed, can relax the stringent constraints from SN 1987A. However, it remains uncertain whether these models maintain their nucleophobic property under the influence of finite baryon density effects. These are especially relevant in astrophysical environments near saturation density, such as Supernovae (SNe). In this study, we demonstrate that the nucleophobic solution remains viable also at finite density. Furthermore, we show that the SN axion bound relaxes significantly in nucleophobic models, even when accounting for the integration over the non-homogeneous environment of the SN core.

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arXiv2025

Axion Window on New Macroscopic Forces

Axion-mediated forces are enhanced by the presence of CP-violating axion couplings, which are however tightly constrained by electric dipole moment (EDM) searches. We discuss the underlying hypotheses behind different sources of CP violation at high energies and the interplay between axion-mediated force experiments and EDM observables. Specifically, we identify various mechanisms, based on new sources of CP violation or Peccei-Quinn symmetry breaking, that can significantly relax EDM constraints, leading to a substantial redefinition of the QCD axion window for axion-mediated forces. By considerably enlarging the QCD axion parameter space, our results provide a well-motivated target for experiments probing scalar axion couplings to matter fields. These include fifth-force tests of gravity, as well as searches for spin-dependent forces via precision magnetometry, proton storage rings and ultracold molecules.

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arXiv2024

Axion production via trapped misalignment from Peccei-Quinn symmetry breaking

The Peccei-Quinn (PQ) symmetry does not need to be exact, and even a tiny source of PQ breaking not aligned with the QCD anomaly might have significant phenomenological implications. In this study, we examine the effects of a general class of PQ-breaking operators on the axion cosmological production via misalignment, focussing on both temperature-dependent and independent PQ-breaking potentials. In particular, we show that a variant of the trapped misalignment mechanism can delay the onset of axion oscillation, leading to an axion dark matter window with $m_a \gg 10^{-5}$ eV. This scenario is testable through various experimental approaches, including standard axion haloscopes and helioscopes, as well as searches for electric dipole moments and axion-mediated forces.

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arXiv2024

Alpha radioactivity deep-underground as a probe of axion dark matter

We propose to investigate the time modulation of radioisotope decays deep underground as a method to explore axion dark matter. In this work, we focus on the $α$-decay of heavy isotopes and develop a theoretical description for the $θ$-dependence of $α$-decay half-lives, which enables us to predict the time variation of $α$-radioactivity in response to an oscillating axion dark matter background. To probe this scenario, we have recently constructed and installed a setup deep underground at the Gran Sasso Laboratory, based on the $α$-decay of Americium-241. This prototype experiment, named RadioAxion-$α$, will allow us to explore a broad range of oscillation's periods, from a micro-second up to one year, thus providing competitive limits on the axion decay constant across 13 orders of magnitude in the axion mass, ranging from $10^{-9}$ eV to $10^{-20}$ eV after one month of data collection, and down to $10^{-22}$ eV after three years.

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arXiv2024

On the oscillating electric dipole moment induced by axion-fermion couplings

It has been recently claimed that the axion coupling to fermions is responsible for an oscillating electric dipole moment (EDM) in the background of axion dark matter. In this work, we re-examine the derivation of this effect. Contrary to previous studies, we point out the physical relevance of an axion boundary term, which is crucial in restoring the axion shift symmetry and drastically affects the EDM phenomenology. To describe the latter, we introduce the notion of a time-averaged effective axion EDM, which encodes the boundary term and whose magnitude depends on the oscillation regime. For slow oscillations, the boundary term washes out the standard oscillating EDM, resulting in an exact cancellation in the static limit. Conversely, during fast oscillations, the boundary term amplifies the effective EDM relatively to the standard EDM contribution. This observable is especially interesting in the case of the electron EDM. For an $\mathcal{O}(1)$ axion-electron coupling, the overall size of the effective EDM in the regime of intermediate or fast oscillations is comparable to the present static EDM limit.

hep-ph↗

arXiv2024

Radiative Quarkonium decays into an Invisible ALP

In this talk the ALP production from radiative quarkonium decays is presented. To this purpose, the relevant cross-section is computed from a $d=5$ effective Lagrangian containing simultaneous ALP couplings to $b(c)$-quarks and photons. The interplay between resonant and non-resonant contributions is shown to be relevant for experiments operating at $\sqrt{s}=m_{Υ(nS)}$, with $n=1,2,3$, while the non-resonant contribution dominates at the $Υ(4S)$ resonance. These effects imply that the experimental searches performed at with different experimental setups are sensitive to complementary combinations of ALP couplings. To illustrate these results, constraints from existing BaBar, Belle and Belle II data on ALPs decaying into invisible final states are derived. Finally, constrains from the recent BESIII measurements of the $J/Ψ\to γ\,a$ decay rate are also included for comparison.

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arXiv2024

Axion-Like Particles in Radiative Quarkonia Decays

Radiative quarkonia decays offer an ideal setting for probing Axion-Like Particle (ALP) interactions. This paper provides a comprehensive review of ALP production mechanisms through the $e^+ e^- \to γ\,a$ process at B- and Charm-factories, alongside an analysis of potential ALP decay channels. We derive constraints on ALP couplings to Standard Model (SM) fields, based on recent experimental results on quarkonia decays by the Belle II and BESIII collaborations. The analysis distinguishes between "invisible" and "visible" ALP decay scenarios. The "invisible" scenario, characterised by a mono-$γ$ plus missing-energy signature, enables stringent limits on ALP-photon and ALP-quark ($b$ or $c$) couplings. Moreover, extensive research at flavour factories has explored various "visible" ALP decays into SM final states, which depend on a larger set of ALP-SM couplings. To streamline the "visible" ALP scenario, we introduce additional theoretical assumptions, such as universal ALP-fermion couplings, or we adopt specific benchmark ALP models, aiming to minimise the number of independent variables in our analysis.

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arXiv2023

CP-Violating Axions: A Theory Review

We review the physics case for CP-violating axions. In the first part, we focus on the Quantum Chromodynamics (QCD) axion and argue that new sources of CP violation beyond QCD misalign the axion solution to the strong CP problem and can manifest themselves via a tiny scalar axion-nucleon component. We hence highlight recent advancements in calculating this scalar axion-nucleon coupling, a parameter that could be probed via axion-mediated force experiments. In the second part, we focus on axion-like particle (ALP) interactions entailing the most general sources of CP violation. After classifying the full set of CP-violating Jarlskog invariants, we report on recent calculations of ALP contributions to permanent electric dipole moments. We finally speculate on possible ultraviolet completions of the CP-violating ALP.

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arXiv2023

Running effects on QCD axion phenomenology

We study the impact of renormalization group effects on QCD axion phenomenology. Focusing on the DFSZ model, we argue that the relevance of running effects for the axion couplings crucially depends on the scale where the heavier Higgs scalars are integrated out. We study the impact of these effects on astrophysical and cosmological bounds as well as on the sensitivity of helioscopes experiments such as IAXO and XENONnT, showing that they can be sizable even in the most conservative case in which the two Higgs doublets remain as light as the TeV scale. We provide simple analytical expressions that accurately fit the numerical solutions of the renormalization group equations as a function of the mass scale of the heavy scalars.

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arXiv2023

Closing in on new chiral leptons at the LHC

We study the phenomenological viability of chiral extensions of the Standard Model, with new chiral fermions acquiring their mass through interactions with a single Higgs. We examine constraints from electroweak precision tests, Higgs physics and direct searches at the LHC. Our analysis indicates that purely chiral scenarios are perturbatively excluded by the combination of Higgs coupling measurements and LHC direct searches. However, allowing for a partial contribution from vector-like masses opens up the parameter space and non-decoupled exotic leptons could account for the observed 2$σ$ deviation in $h \to Zγ$. This scenario will be further tested in the high-luminosity phase of the LHC.

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arXiv2023

Towards a Muon Collider

A muon collider would enable the big jump ahead in energy reach that is needed for a fruitful exploration of fundamental interactions. The challenges of producing muon collisions at high luminosity and 10 TeV centre of mass energy are being investigated by the recently-formed International Muon Collider Collaboration. This Review summarises the status and the recent advances on muon colliders design, physics and detector studies. The aim is to provide a global perspective of the field and to outline directions for future work.

physics.acc-ph↗

arXiv2023

Low-energy flavour probes of light vector bosons

In this work, we construct the chiral Lagrangian for a light spin-1 boson $X$ possessing both vectorial and axial couplings to the light Standard Model quarks $u, d, s$. We then use it in order to describe the tree-level, model-independent contributions to the $ΔS = 1$ transition $K^\pm \rightarrow π^\pm X$, which is induced by Standard Model charged currents and is possibly enhanced by the emission of a longitudinally polarized $X$ boson. Such a flavour observable is then shown to set the best model-independent bounds on the diagonal axial couplings of $X$ to light quarks in the mass range allowed by the decay kinematics, improving the currently available constraints from beam-dump experiments and collider searches.

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arXiv2023

New physics behind the new muon $g$-2 puzzle?

The recent measurement of the muon $g$-2 at Fermilab confirms the previous Brookhaven result. The leading hadronic vacuum polarization (HVP) contribution to the muon $g$-2 represents a crucial ingredient to establish if the Standard Model prediction differs from the experimental value. A recent lattice QCD result by the BMW collaboration shows a tension with the low-energy $e^+e^- \to \text{hadrons}$ data which are currently used to determine the HVP contribution. We refer to this tension as the new muon $g$-2 puzzle. In this Letter we consider the possibility that new physics contributes to the $e^+e^- \to \text{hadrons}$ cross-section. This scenario could, in principle, solve the new muon $g$-2 puzzle. However, we show that this solution is excluded by a number of experimental constraints.

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arXiv2023

Flavour constraints on light spin-1 bosons within a chiral Lagrangian approach

We discuss the construction of the chiral Lagrangian for a light spin-1 boson, here denoted as $X$, featuring both vector and axial-vector couplings to light $u,d,s$ quarks. Focusing on $ΔS = 1$ transitions, we show that there are model-independent tree-level contributions to $K^\pm \to π^\pm X$, sourced by Standard Model charged currents, which receive an $m^2_K / m_X^2$ enhancement from the emission of a longitudinally polarized $X$. This flavour observable sets the strongest to date model-independent bound on the diagonal axial-vector couplings of $X$ to $u,d,s$ quarks for $m_X < m_K - m_π$, superseding the bounds arising from beam-dump and collider searches.

hep-ph↗

arXiv2023

Axion-pion thermalization rate in unitarized NLO chiral perturbation theory

We compute the axion-pion scattering $a π\to ππ$, relevant for the axion thermalization rate in the early universe, within unitarized NLO chiral perturbation theory. The latter extends the range of validity of the chiral expansion of axion-pion scattering and thus provides a crucial ingredient for the reliable determination of the relic density of thermal axions, whenever the axion decoupling temperature is below that of the QCD phase transition. Implications for cosmological observables are briefly discussed.

hep-ph↗

arXiv2023

On the IR/UV flavour connection in non-universal axion models

Non-universal axion models, with the Peccei-Quinn (PQ) symmetry acting on Standard Model (SM) fermions in a generation-dependent way, are typically accompanied by two different sources of flavour violation, dubbed here as infrared (IR) and ultraviolet (UV). The former is due to the flavour violating axion couplings to SM fermions, while the latter arises from the heavy degrees of freedom that UV complete the axion effective field theory. We point out that these two sources of flavour violation are directly related and exemplify this connection in a general class of non-universal axion model, based on a renormalizable DFSZ-like setup with two Higgs doublets (PQ-2HDM). We next discuss the interplay of axion flavour phenomenology with the signatures stemming from the heavy radial modes of the PQ-2HDM, including meson oscillation observables and charged lepton flavour violating decays. We emphasize the strong complementarity between flavour observables, LHC direct searches and standard axion physics.

hep-ph↗

arXiv2023

UV-IR interplay in axion flavour violation

Flavour-violating axions appear in models where the Peccei-Quinn(PQ) charges are generation non-universal. Consequently, this charge arrangement will also generate flavour violation in the UV sector. The typical way of implementing such an axion in a UV completion is with a DFSZ model, containing 2 Higgs doublets. In this talk we will present how to parameterize the flavour violation in the UV such that we can find a direct correlation with the flavour violation of the axion. Finally, we show in an example how this connection can help in giving information about the UV completion if an axion is found in a flavour-violating channel.

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