arXiv subjects

Federico Mescia

Publications and source records attributed to Federico Mescia.

At least 19 recordsLinked to original sources

arXiv2026

New measurements in leptonic kaon and pion decays: experimental and theoretical perspectives

We study the future prospects for precision measurements of purely leptonic charged-current kaon and pion decays. In particular, we consider the single ratios $R_{K\pi}^{\ell=\mu,e} = \Gamma(K \to \ell\nu) / \Gamma(\pi \to \ell\nu)$, for which many experimental uncertainties cancel, as well as the double ratio $R_{K\pi}^e / R_{K\pi}^\mu$, which provides a particularly sensitive probe of new physics. This study is timely in light of two converging developments. On the experimental side, a new conceptual design for a dedicated setup based on a slow-extracted proton beam and a multi-year data-taking program, is expected to achieve a precision at the $10^{-4}$ level. On the theory side, recent lattice-QCD calculations have reached a comparable level of accuracy. Finally, we assess the impact of these next-generation measurements on searches for physics beyond the Standard Model and show that they can provide constraints that are either competitive with or complementary to existing bounds.

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arXiv2026

How invisible can QCD axions be? From Supernova emission to Cherenkov signals

We investigate the scenario of maximally invisible axions, namely QCD axions whose interactions with matter arise exclusively from the irreducible coupling to gluons responsible for solving the strong-CP problem. We first analyze the production of such axions in core-collapse supernovae. In particular, we derive the corresponding SN 1987A cooling constraint and compute the emission spectra for the dominant production channels, namely nucleon-nucleon bremsstrahlung and pion conversion. We then investigate the prospects for detecting maximally invisible axions in Cherenkov detectors, with the goal of establishing a robust lower bound on the overall detectability of QCD axions.

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arXiv2026

Constraints on a Light Leptophilic Scalar from Dark-Sector Couplings

We study a minimal framework where a Majorana fermion dark matter particle interacts with a light scalar mediator coupled mainly to electrons. We examine both freeze-out and freeze-in production to determine the regions of parameter space that yield the correct relic abundance with particular emphasis on a detailed comparison with results in the recent literature. The analysis includes cosmological and astrophysical constraints as well as laboratory bounds from electron-recoil experiments, fixed target searches, and precision measurements. The combined results identify a narrow but viable parameter region, favoring sub-GeV dark matter, and define clear targets for future experimental tests. This highlights the strong complementarity between direct-detection experiments and collider searches. We additionally investigate the mediator-mass region around 17 MeV, motivated by the hints reported by the ATOMKI experiment and the PADME collaboration, including couplings between the mediator and light quarks. Direct searches already constrain a large region of the parameter space, even when dark matter is produced via freeze-in, pointing again to sub-GeV dark matter.

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arXiv2026

ALP production in Lepton Flavour Violating meson, tau and gauge boson decays

In this paper we study axion-like particles (ALPs) with lepton-flavour-violating (LFV) couplings in the mass regime above the muon threshold, $m_a>m_\mu$, where the strong bound from the exotic muon decay $\mu\to ea$ no longer apply and the decay channel $a\to e\mu$ becomes kinematically accessible. In this region, the ALP typically decays promptly, motivating new search strategies based on its production in decays involving virtual muons. We analyse charged-meson and $W$ decays, neutral-current processes such as $Z$ and quarkonium decays, and, when couplings to the third generation are present, LFV $\tau$ decays. The subsequent decay $a\to e\mu$ leads to striking LFV signatures with negligible Standard Model backgrounds. Combining these production modes with current low-energy constraints, we assess the sensitivity of future high-energy $e^+e^-$ colliders, flavour factories such as Belle II and STCF, fixed-target experiments such as NA62, and proton beam-dump facilities such as SHiP. Overall, our results identify LFV ALP production in meson, gauge-boson, quarkonium and $\tau$ decays (with displaced vertices) as a promising and largely unexplored avenue to test ALP interactions with charged leptons above the muon mass threshold.

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arXiv2026

Axions at the meV Crossroads: Theory, Cosmology, Astrophysics, and Experiments

The meV mass range has emerged as a focal point in axion physics, where advances in theory, cosmology, astrophysics, and experimental techniques converge. Axions in this mass range are theoretically well motivated, can arise in ultraviolet-complete models, and can have significant cosmological impacts as dark matter or dark radiation. In parallel, their efficient production in stellar and supernova environments provides powerful astrophysical probes. Here, we provide a comprehensive overview of meV axions across these domains, highlighting both established results and open questions. We discuss the theoretical underpinnings of meV axions, their cosmological and astrophysical signatures, and the diverse experimental strategies -- ranging from helioscopes and haloscopes to quasiparticle systems and large-volume Cherenkov detectors -- that aim to explore this regime. The convergence of these approaches emphasizes the pivotal role of the meV mass range for axion discovery in the coming years, identifying meV axions as a key probe for testing beyond-Standard-Model physics. This review document is the direct outcome of the discussions at the dedicated workshop "The meV Mass Axion Frontier: Challenges and Opportunities", held at Laboratori Nazionali di Frascati (IT) on 27--28 October 2025, and organized by the EU funded COST Action "Cosmic WISPers in the Dark Universe: Theory, astrophysics, and experiments" (CA21106, https://www.cost.eu/actions/CA21106). Its aim is to provide an overview of current efforts in meV axion research, their motivations, and the research goals that animate the community involved in this search.

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arXiv2026

Axion-Like Electrophilic Portal for Pion Dark Matter

We investigate a scenario where Strongly Interacting Massive Particle (SIMP) dark matter interacts with an axion-like particle (ALP) that couples exclusively to electrons. This minimal setup provides interactions which enforce thermal equilibrium between dark matter and the SM in the early Universe. We analyze the cosmological evolution of the dark sector and the constraints arising from dark matter annihilations, ALP laboratory searches and astrophysical observations. Our results show that the allowed parameter space is wider than previous studies and an ALP with mass $m_a \sim {\cal O}(10)~\text{MeV}$ can act as a viable portal between the visible and dark sectors. Interestingly, this mass range overlaps with the parameter space suggested by the reported $X_{17}$ anomaly. Furthermore, the introduction of non-vanishing $\theta$ angle in the dark sector of the model opens up the parameter space to heavy ALP masses.

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arXiv2026

Dark Matter emission at Belle II and NA62 in Minimal Flavor Violation framework

Minimal Flavor Violation (MFV) provides a compelling framework for exploring physics beyond the Standard Model, in which new QCD-singlet fields transforming under the global $\mathrm{SU}(3)^3$ quark flavor symmetry can naturally be stable and act as dark matter (DM) candidates. We show that the DM-MFV framework naturally accommodates the excess in either $K^+ \to \pi^+ \nu \bar{\nu}$ or $B^+ \to K^+ \nu \bar{\nu}$, while a unified explanation of both channels simultaneously cannot be achieved within a minimal setup containing only a single dark matter multiplet with nearly degenerate masses. Overall, our findings underscore the intricate interplay between MFV-based model building, flavored dark matter scenarios, and precision flavor experiments, highlighting flavored dark matter as a framework that is both theoretically robust and experimentally testable.

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arXiv2025

High-quality Peccei-Quinn symmetry from the interplay of vertical and horizontal gauge symmetries

We explore a class of axion models where an accidental $\mathrm{U}(1)$ Peccei-Quinn (PQ) symmetry automatically emerges from the interplay of vertical (grand-unified) and horizontal (flavor) gauge symmetries. We study a specific Pati-Salam realization in detail, and aim to generalize the conclusions. We show that our specific model offers protection from PQ-violating operators to high dimension, and demonstrate that the model can reproduce the Standard Model flavor structure. A distinctive feature of the vertical-horizontal setup is the presence of parametrically light fermions, known as anomalons, which are introduced to cancel the gauge anomalies of the flavor symmetry. We also identify a major challenge to building a fully realistic model, most notably that of Landau poles in gauge couplings before the Planck scale. For the specific model investigated, the pre-inflationary PQ-breaking scenario predicts the axion mass window to be $m_a \in [2 \times 10^{-8}, 10^{-3}]\,\mathrm{eV}$. Conversely, a high-quality axion may be obtained instead in the post-inflationary scenario, with axion mass $m_a \gtrsim 0.01\,\mathrm{eV}$, and anomalon masses predicted below the $\mathrm{eV}$ scale. We elaborate on anomalons' cosmological production in the early universe, highlighting how measurements of $ΔN_{\rm eff}$ could serve as a low-energy probe of the ultraviolet dynamics addressing the PQ quality problem.

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arXiv2025

Scalar Rayleigh Dark Matter: current bounds and future prospects

Dark Matter can interact with electroweak gauge bosons via higher-dimensional operators, in spite of being neutral under gauge interactions, much like neutral atoms interact with photons through Rayleigh scattering. This study explores effective interactions between a real scalar Dark Matter particle, singlet under the SM gauge group, and electroweak gauge bosons. We present a comprehensive analysis of current constraints and projected sensitivities from both lepton and hadron colliders as well as direct and indirect detection experiments in testing Rayleigh Dark Matter interactions. We find that, thanks to the complementarity between collider experiments and cosmological probes, thermally produced Rayleigh Dark Matter at the hundreds of GeV scale can be thoroughly tested with the next generation of experiments. For lighter candidates, upcoming forecasts will explore uncharted parameter space, significantly surpassing the thermal Dark Matter benchmark.

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arXiv2025

Fresh look at the diffuse ALP background from supernovae

Protoneutron stars, highly compact objects formed in the core of exploding supernovae (SNe), are powerful sources of axion-like particles (ALPs). In the SN core, ALPs are dominantly produced via nucleon-nucleon bremsstrahlung and pion conversion, resulting in an energetic ALP spectrum peaked at energies $\mathcal{O}(100)\,\rm MeV$. In this work, we revisit the diffuse ALP background, produced from all past core-collapse supernovae, and update the constraints derived from Fermi-LAT observations. Assuming the maximum ALP-nucleon coupling allowed by the SN 1987A cooling, we set the upper limit $g_{a γγ} \lesssim 2 \times 10^{-13}\,\rm GeV^{-1}$ for ALP mass $m_a\lesssim 10^{-10}\,\rm eV$, which is approximately a factor of two improvement with respect to the existing bounds. On the other hand, for $m_a \gtrsim 10^{-10}\,\rm eV$, we find that including pion conversion strengthens the bound on $g_{aγγ}$, approximately by a factor of two compared to the constraint obtained from bremsstrahlung alone. Additionally, we present a sensitivity study for future experiments such as AMEGO-X, e-ASTROGAM, GRAMS-balloon, GRAMS-satellite, and MAST. We find that the expected constraint from MAST would be comparable to Fermi-LAT bound. However, SN 1987A constraint remains one order of magnitude stronger as compared to the bound derived from the current and future gamma-ray telescopes.

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arXiv2025

Accommodating scalar resonances in the HEFT

Loss of unitarity in an effective field theory is often cured by the appearance of dynamical resonances, revealing the presence of new degrees of freedom. These resonances may manifest themselves when suitable unitarization techniques are implemented in the effective theory, which in the scalar-isoscalar channel require using the coupled-channel formalism. Experimental detection of a resonance would provide precious information on the couplings and constants of the relevant effective theory. Conversely, the absence of a resonance where the unitarized effective theory predicts it should be allows us to rule out a certaing range of couplings that would otherwise be allowed. Likewise, the appearence of unphysical (e.g. acausal) resonances is telling us that no UV completion could give rise to the corresponding couplings in the effective theory. In this talk we summarize the systematical procedure we have implemented in order to confront the effective theory with the absence or presence of resonances in the vector boson fusion channel at the LHC.

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arXiv2025

Axion-induced pair production: a new strategy for axion detection

We revisit and update the axion-induced pair production process in a nuclear electric field mediated by the axion-electron coupling, $a+{{}^{A}_{Z}X} \rightarrow {{}^{A}_{Z}X} + e^{+} + e^{-}$. This process emerges as one of the most efficient channels for detecting axions with energies above a few MeV in large underground detectors. It is particularly relevant for detecting axions produced in nuclear reactions, such as the $p+d~\rightarrow~{ }^3 \mathrm{He}~+~a(5.5\,\mathrm{MeV})$ reaction in the solar pp-chain, and for axions originating in supernovae. Despite recent interest in detecting high-energy axions, the pair production process has received limited attention, even in scenarios where it is the dominant detection channel. This study fills this gap by demonstrating that pair production is a highly effective detection mechanism for high-energy axions. We apply our results to axions from supernovae and the solar 5.5 MeV line, recasting the current bounds of Borexino and comparing the detection capabilities of the JUNO and Hyper-Kamiokande detectors.

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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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arXiv2024

Multi-Component Dark Matter from Minimal Flavor Violation

Minimal Flavor Violation (MFV) offers an appealing framework for exploring physics beyond the Standard Model. Interestingly, within the MFV framework, a new colorless field that transforms non-trivially under a global ${\rm SU}(3)^3$ quark flavor group can naturally be stable. Such a new field is thus a promising dark matter candidate, provided it is electrically neutral. We extend the MFV framework for dark matter and demonstrate that dark matter can naturally be multi-component across a broad parameter space. For illustration, we consider a gauge singlet, flavor triplet scalar field and identify parameter spaces for multi-component dark matter, where only the lightest flavor component is absolutely stable and heavy flavor components are decaying with lifetimes sufficiently longer than the age of the universe. Phenomenological, cosmological and astrophysical aspects of multi-component flavored dark matter are briefly discussed.

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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

Dark Matter Direct Detection in $t$-channel mediator models

We perform a comprehensive study of the Direct Detection phenomenology of singlet Dark Matter $t$-channel portal models. For that purpose, we present a complete one-loop matching onto a Heavy Dark-Matter Effective Field Theory, leading to a complete computation of the loop induced direct detection cross-section for both scalar and fermionic Dark Matter candidates. The results are compared with current and future bounds from Direct Detection experiments, as well as with the requirement of the correct Dark Matter relic density.

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arXiv2023

Introducing tools to test Higgs interactions via $WW$ scattering II: the coupled channel formalism and scalar resonances

In this work we explore in detail the presence of scalar resonances in $WW$ fusion process in the context of the LHC experiments working in the theoretical framework provided by Higgs Effective Field Theories (HEFT). While the phenomenology of vector resonances is reasonably understood in the framework of Weinberg sum-rules and unitarization studies, scalar resonances are a lot less constrained and, more importantly do depend on HEFT low-energy effective couplings different from the ones of vector resoances that are difficult to constrain experimentally. More specifically, unitarization techniques combined with the requirement of causality allows us to set non-trivial bounds on Higgs self-interactions. This is due to the need of considering coupled channels in the scalar case along the unitarization process. As a byproduct, we can gain some relevant information on the Higgs sector from $WW\to WW$ elastic processes without needing to consider two Higgs production.

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arXiv2023

Accommodating the H$(650)$ in the HEFT

Loss of unitarity in an effective field theory is often cured by the appearance of dynamical resonances, revealing the presence of new degrees of freedom. These resonances may manifest themselves when suitable unitarization techniques are implemented in the effective theory, which in the scalar-isoscalar channel require making use of the coupled-channel formalism. Conversely, experimental detection of a resonance may provide interesting information on the couplings and constants of the relevant effective theory. By applying the systematical procedure developed in previous works, we will attempt to accommodate a possible scalar resonance with mass around $650$ GeV for which there is preliminary evidence at the LHC in the vector boson fusion channel. The results are interesting: the resonance can be accommodated within the experimentally allowed range of next-to-leading order coefficients in the HEFT but in a rather non-trivial manner. Interestingly, its width and production cross section turn out to agree with the tentative experimental results.

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