arXiv subjects

Gino Isidori

Publications and source records attributed to Gino Isidori.

At least 19 recordsLinked to original sources

arXiv2026

Probing Flavour Deconstruction via Primordial Gravitational Waves

We study the production of primordial gravitational waves (GWs) from first-order phase transitions (FOPTs) in extensions of the Standard Model based on Flavour Deconstruction (FD). The link fields inherent to FD generically form a rich scalar sector, with sizeable couplings at the TeV scale, providing natural conditions for strong FOPTs and correspondingly large GW emission. We identify the key parameters controlling the GW spectrum and enabling its detection at future GW observatories. In particular, we find that while FD scenarios can yield detectable signals, the resulting spectra typically peak at higher frequencies than the millihertz range. As a consequence, a positive observation at LISA is possible but not guaranteed, while the signal falls in the range of mid-band proposals, making FD models an intriguing target for upcoming GW searches.

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arXiv2026

Disentangling short- vs. long-distance dynamics in $B\to K^{*}μ^+μ^-$

We present an updated data-driven analysis of short- vs. long-distance dynamics in $B\to K^{*}μ^+μ^-$. The analysis is based on the recent LHCb measurement of the full angular distribution of this process, taking advantage of the previously published global amplitude fit. Thanks to the precise di-lepton invariant-mass binning and angular observables directly sensitive to absorptive phases, current data provide novel insights into non-local contributions. We analyze the latter using a dispersive description, whose free parameters are determined via the amplitude fit. The dispersive model provides a satisfactory overall description of current data, without the need to introduce additional ad hoc hadronic parameters. The extracted value of the short-distance coefficient $C_9$ is lower than its Standard Model prediction, but significantly closer to it than in analyses where long-distance contributions are not constrained by data. The overall tension with the SM does not exceed the $2σ$ level. We also obtain precise postdictions for the angular observables $S_{7,8,9}$, and envisage novel consistency tests among them. In view of future, more precise data, these could provide valuable tests of the description of non-local effects in this process that, if further validated, would enable an even more robust extraction of short-distance information.

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arXiv2026

Probing Lepton Flavour Universality with $Λ_b$ decays to $τ^+τ^-$ final states

We present a study of the rare baryonic decay $Λ_b \to Λτ^+ τ^-$ as a probe of new physics (NP) coupled preferentially to third-generation fermions. Within the Standard Model, we evaluate the branching ratio and the lepton-flavour-universality (LFU) ratio $R_Λ^{τ/μ}$, including both perturbative and long-distance charm contributions. We show that the LFU ratio can be predicted with an uncertainty below 10%. Possible NP effects arising from lepton non-universal dynamics are analysed within an effective field theory framework motivated by the current anomalies in $b \to cτν$ and $b \to sμ^+μ^-$ transitions. In this context, $R_Λ^{τ/μ}$ can be enhanced by several orders of magnitude, offering a clear target for upcoming searches. The implications for the related mode $Λ_b \to pKτ^+τ^-$ are also briefly discussed.

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arXiv2025

A Composite Theory of Higgs and Flavour

We introduce a composite Higgs model in which a flavour deconstructed gauge group is embedded in the strong sector. The pattern of global symmetry breaking yields, as pseudo-Nambu-Goldstone (pNGB) bosons, both a Standard Model (SM)-like Higgs and the link field whose vacuum expectation value breaks the flavour non-universal gauge group down to the SM. Inevitably, a third pNGB appears, transforming as a second Higgs doublet coupled only to the light generations. This heavy Higgs naturally mediates suppressed light Yukawa couplings, providing a solution to the flavour puzzle. At the same time, new physics contributions to flavour violating observables are CKM- and chirally suppressed, while electric dipole moment bounds are evaded through an automatic mass alignment in the light fermion sector. The result is a natural framework for addressing the origin of both Higgs and flavour hierarchies, with reduced Higgs mass tuning and minimised impact in flavour observables, that is best tested by high-$p_T$ and precision electroweak measurements.

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arXiv2025

Charm rescattering in $B^0\to K^0\bar{\ell}\ell$: an improved analysis

We improve upon previous explicit estimates of charm rescattering contributions to the decay $B^0\to K^0\bar{\ell}\ell$ by including contributions from dipole interactions with the intermediate charm-meson states, and by further investigating the structure of the electromagnetic form factors. Using a model of fundamental meson fields inspired by heavy-hadron chiral perturbation theory, augmented by form factors motivated by theoretical considerations as well as experimental data, we provide a thorough investigation of rescattering contributions induced by intermediate $D^{(*)}D^{(*)}_s$ states.

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arXiv2025

Physics Briefing Book: Input for the 2026 update of the European Strategy for Particle Physics

The European Strategy for Particle Physics (ESPP) reflects the vision and presents concrete plans of the European particle physics community for advancing human knowledge in fundamental physics. The ESPP is updated every five-to-six years through a community-driven process. It commences with the submission of specific proposals and other input from the community at large, outlining projects envisioned for the near-, mid-, and long-term future. All submitted contributions are evaluated by the Physics Preparatory Group (PPG), and a preliminary analysis is presented at a Symposium meant to foster a broad community discussion on the scientific value and feasibility of the various ideas proposed. The outcomes of the analysis and the deliberations at the Symposium are synthesized in the current Briefing Book, which provides an important input in the deliberations of the Strategy recommendations by the European Strategy Group (ESG).

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arXiv2025

Anarchic neutrinos from flavor deconstruction: phenomenology of the lepton sector

We investigate the neutrino sector in the framework of flavor deconstruction with an inverse-seesaw realization. This setup naturally links the hierarchical charged-fermion masses to the anarchic pattern of light-neutrino mixing. We determine the viable parameter space consistent with oscillation data and study the phenomenology of heavy neutral leptons (HNL) and lepton-flavor-violating (LFV) processes. Current bounds from direct HNL searches and LFV decays constrain the right-handed neutrino scale to a few TeV, while future $μ\to e$ experiments will probe most of the region with $Λ\lesssim 10~\text{TeV}$. Among possible realizations, models deconstructing $\mathrm{SU}(2)_\mathrm{L} \times \mathrm{U}(1)_\mathrm{B-L}$ or $\mathrm{SU}(2)_\mathrm{L} \times \mathrm{U}(1)_\mathrm{R} \times \mathrm{U}(1)_\mathrm{B-L}$ are those allowing the lowest deconstruction scale.

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arXiv2025

Third-Family Quark-Lepton Unification and Electroweak Precision Tests

We analyze the compatibility of the hypothesis of third-family quark-lepton unification at the TeV scale with electroweak precision data, lepton flavor universality tests, and high-$p_T$ constraints. We work within the framework of the UV complete flavor non-universal 4321 gauge model, which is matched at one loop to the Standard Model Effective Field Theory. For consistency, all electroweak precision observables are also computed at one loop within the effective field theory. At tree level, the most sizeable corrections are to $W\rightarrow τν_τ$ and $Z \to ν_τν_τ$ due to integrating out a pseudo-Dirac singlet fermion required by the model for neutrino mass generation. At loop level, the new colored states of the model generate large flavor-universal contributions to the electroweak precision observables via leading- and next-to-leading log running effects, yielding a significant improvement in the electroweak fit (including an increase in the $W$-boson mass). These effects cannot be decoupled if the model addresses the charged-current $B$-meson anomalies. Overall, we find good compatibility between the data sets, while simultaneously satisfying all low- and high-energy constraints.

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arXiv2025

Flavor Physics at the CEPC: a General Perspective

We discuss the landscape of flavor physics at the Circular Electron-Positron Collider (CEPC), based on the nominal luminosity outlined in its Technical Design Report. The CEPC is designed to operate in multiple modes to address a variety of tasks. At the $Z$ pole, the expected production of 4 Tera $Z$ bosons will provide unique and highly precise measurements of $Z$ boson couplings, while the substantial number of boosted heavy-flavored quarks and leptons produced in clean $Z$ decays will facilitate investigations into their flavor physics with unprecedented precision. We investigate the prospects of measuring various physics benchmarks and discuss their implications for particle theories and phenomenological models. Our studies indicate that, with its highlighted advantages and anticipated excellent detector performance, the CEPC can explore beauty and $τ$ physics in ways that are superior to or complementary with the Belle II and Large-Hadron-Collider-beauty experiments, potentially enabling the detection of new physics at energy scales of 10 TeV and above. This potential also extends to the observation of yet-to-be-discovered rare and exotic processes, as well as testing fundamental principles such as lepton flavor universality, lepton and baryon number conservation, etc., making the CEPC a vibrant platform for flavor physics research. The $WW$ threshold scan, Higgs-factory operation and top-pair productions of the CEPC further enhance its merits in this regard, especially for measuring the Cabibbo-Kobayashi-Maskawa matrix elements, and Flavor-Changing-Neutral-Current physics of Higgs boson and top quarks. We outline the requirements for detector performance and considerations for future development to achieve the anticipated scientific goals.

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arXiv2025

Explicit estimate of charm rescattering in $B^0 \to K^0 \bar{\ell} \ell$

We analyze $B^0 \to K^0 \bar{\ell}\ell$ long-distance contributions induced by the rescattering of a pair of charmed and charmed-strange mesons. We present an explicit estimate of these contributions using an effective description in terms of hadronic degrees of freedom, supplemented by data on the $B^0 \to D^*D_s (D^*_sD)$ transition in order to reproduce the corresponding discontinuity in the $B^0 \to K^0 \bar{\ell}\ell$ amplitude. The $D^* D_s (D^*_s D) K$ vertex is estimated using heavy-hadron chiral perturbation theory, obtaining an accurate description of the whole rescattering process in the low-recoil (or high-$q^2$) limit. We also present an extrapolation to the whole kinematical region introducing hadronic form factors. The explicit estimate of the leading $D^*D_s (D^*_sD)$ intermediate state leads to a long-distance amplitude which does not exceed a few percent relative to the short-distance one. The consequences of this result for the extraction of the short-distance coefficient $C_9$ are discussed.

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arXiv2025

The third-generation-philic WIMP: an EFT analysis

We consider fermionic and scalar dark matter (DM) candidates that couple predominantly to third-generation Standard Model fermions, describing their interactions within an effective field theory framework. We show that current direct-detection constraints on these interactions are more than an order of magnitude weaker than those for flavor-universal couplings: effective scales in the few-TeV range remain allowed by existing data, leaving open the possibility of a connection between this type of new physics and a solution to the electroweak hierarchy problem. Imposing the observed relic abundance from thermal freeze-out within the same effective theory, a well-defined region for a fermionic DM candidate with mass in the 1-2 TeV range emerges. Notably, this region will be fully probed by upcoming direct-detection experiments. Finally, we show that additional parameter space for both fermion and scalar cases can be recovered by going beyond the effective theory, through the introduction of a suitable vector mediator enabling resonant DM annihilation.

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arXiv2025

Kaon Physics: A Cornerstone for Future Discoveries

The kaon physics programme, long heralded as a cutting-edge frontier by the European Strategy for Particle Physics, continues to stand at the intersection of discovery and innovation in high-energy physics (HEP). With its unparalleled capacity to explore new physics at the multi-TeV scale, kaon research is poised to unveil phenomena that could reshape our understanding of the Universe. This document highlights the compelling physics case, with emphasis on exciting new opportunities for advancing kaon physics not only in Europe but also on a global stage. As an important player in the future of HEP, the kaon programme promises to drive transformative breakthroughs, inviting exploration at the forefront of scientific discovery.

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arXiv2025

Flavored Circular Collider: cornering New Physics at FCC-ee via flavor-changing processes

We illustrate the potential of a future high-intensity $e^+ e^-$ collider running at the $Z$ pole in probing extensions of the Standard Model via precise measurements of flavor-changing processes. We illustrate this potential both within effective field theories and simplified models inspired by current $B$-physics data, focusing on selected flavor-physics measurement projections at FCC-ee, and by the theoretically well-motivated scenario of TeV-scale new physics predominantly coupled to third-generation fields. In particular, we demonstrate the key role played by the interplay among different flavor-physics measurements, and between flavor and electroweak measurements, in cornering the New Physics parameter space. Updated constraints on new physics, in the limit that no deviations from the Standard Model are observed, are also presented.

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arXiv2025

Flavour Physics and CP Violation

These lectures provide a concise introduction to flavor physics, within and beyond the Standard Model, with main focus on B-physics phenomenology and some recent developments. The first lecture is an introduction to the flavor sector of the Standard Model. The second lecture is devoted to B-meson mixing and rare B decays. The last lecture contains a general discussion about flavor physics beyond the Standard Model, with a highlighting of recent developments related to the idea of flavor deconstruction.

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arXiv2025

Probing third-generation New Physics with $K\to πν\barν$ and $B\to K^{(*)} ν\barν$

The recent observation of the $K^+ \to π^+ ν\barν$ decay by NA62 is an important milestone in precision flavor physics. Together with evidence of $B^+ \to K^+ν\barν$ reported by Belle-II, they are the only FCNC decays involving third-family leptons where a precision close to the SM expectation has been reached. We study the implications of these recent results in the context of a new physics scenario aligned to the third generation, with an approximate $U(2)^5$ flavor symmetry acting on the light families. We find that the slight excess observed in both channels supports the hypothesis of non-standard TeV dynamics of this type, as also hinted at by other $B$-meson decays, consistently with bounds from colliders and electroweak observables. We further discuss how future improvements in precision could affect this picture, highlighting the discovery potential in these di-neutrino modes.

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arXiv2025

Flavour Deconstructing the Composite Higgs

We present a flavour non-universal extension of the Standard Model combined with the idea of Higgs compositeness. At the TeV scale, the gauge groups $SU(2)_R$ and $U(1)_{B-L}$ are assumed to act in a non-universal manner on light- and third-generation fermions, while the Higgs emerges as a pseudo Nambu-Goldstone boson of the spontaneous global symmetry breaking $Sp(4)\to SU(2)_L\times SU(2)_R^{[3]}$, attributed to new strong dynamics. The flavour deconstruction means the couplings of the light families to the composite sector (and therefore the pNGB Higgs) are suppressed by powers of a heavy mass scale (from which the Higgs is nevertheless shielded by compositeness), explaining the flavour puzzle. We present a detailed analysis of the radiatively generated Higgs potential, showing how this intrinsically-flavoured framework has the ingredients to justify the unavoidable tuning in the Higgs potential necessary to separate electroweak and composite scales. This happens for large enough values of the $SU(2)_R^{[3]}$ gauge coupling and light enough flavoured gauge bosons resulting from the deconstruction, whose phenomenology is also investigated. The model is compatible with current experimental bounds and predicts new states at the TeV scale, which are within the reach of near future experimental searches.

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arXiv2024

Neutrino Anarchy from Flavor Deconstruction

Flavor deconstruction refers to non-universal gauge extensions where the original gauge symmetry is deconstructed into separate copies, one for each family. A hierarchical chain of symmetry breaking provides an attractive low-scale solution to the flavor puzzle, consistent with flavor-changing neutral currents and finite naturalness. Although successful in explaining the origin of flavor hierarchies in the quark and charged lepton sectors, existing models have struggled with the large and seemingly anarchic mixing observed in neutrino oscillations. This letter identifies conditions under which neutrino anarchy may arise from flavor deconstruction in generic models with right-handed neutrinos. When deconstruction is applied to carefully chosen subgroups of the extended gauge symmetry, hierarchies in the seesaw formula cancel out.

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arXiv2023

Minimal flavour deconstruction

We construct two concrete examples of flavour non-universal gauge theories which, after the inclusion of all $d\leq 4$ gauge invariant operators, allow to describe the observed pattern of flavour in the charged fermion sector without any small Yukawa coupling ($y \gtrsim 0.1$). Guided by the criterium of minimality, we assume that flavour non universality is confined to the Abelian sector of the gauge group: the universal hypercharge emerges after a sequence of symmetry-breaking steps characterised by two high mass scales, $Λ_{[23]} < Λ_{[12]}$, where the second and the first fermion generations get their mass respectively. At least in one of the two models the smaller of these scales can be in the 10 TeV range, consistently with current bounds from flavour observables. Both models are extended to include as well neutrino masses and mixings.

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