FLASY 2025 - 11th Workshop on Flavour Symmetries and Consequences in Accelerators and Cosmology

30 Jun 2025, 00:30 → 4 Jul 2025, 18:00 Europe/Rome

Aula Magna Architettura "Adalberto Libera" (Roma Tre)

FLASY 2025 was the 11th Workshop on Flavour Symmetries and Consequences in Accelerators and Cosmology.

[ Update: Please write to flasy2025@grupposymposia.it to request a certificate of attendence ]

[ Update: Thank you for contributing to a nice and productive workshop!

                 See you in Gyeongju, Korea for FLASY 2026! ]

[ Update: The group photo is now online! ]

This workshop brought together researchers in the fields of flavour symmetries, neutrino physics, Higgs physics, CP violation, accelerator physics, and cosmology to present new results and foster discussions that could lead to new and fruitful collaborations. 

FLASY 2025 took place from June 30 to July 4 in Rome, Italy.

Plenary speakers:   

• S. Antusch (University of Basel)
• F. Brizioli (U. Perugia and INFN Perugia) [for the NA62 Collab.]
• G. Burdman (U. São Paulo)
• P. W. Cattaneo (INFN Pavia) [for the MEGII Collab.]
• M.-C. Chen (UC, Irvine)
• S. C. Chuliá (València U., IFIC)
• C. Cornella (CERN)
• G.-J. Ding (USTC, Hefei)
• F. Feruglio (INFN Padova)
• M. Ghosh (Boskovic Inst., Zagreb)
• C. Hagedorn (València U., IFIC)
• P. Harrison (Warwick U.)
• J. Harz (Mainz U.)
• S. Jäger (University of Sussex)
• S. K. Kang (Seoul Natl. U.)
• T. Kephart (U. Vanderbilt)
• S. King (U. Southampton)
• E. Lisi (INFN Bari)
• E. Ma (University of California Riverside)
• A. Marrone (INFN Bari and U. Bari)
• G. Martinelli (U. Roma and INFN Roma)
• M. Mondragon (UNAM, Mexico)
• M. Nardecchia (U. Roma)
• E. Nardi (INFN, LNF and NICPB, Tallinn)
• H. Päs (T. U. Dortmund)
• S. Pascoli (INFN Bologna and U. Bologna)
• E. Peinado (Mexico U.)
• S. T. Petcov (Tokyo U., IPMU and SISSA Trieste)
• M. Ratz (UC, Irvine)
• G. Ricciardi (Naples U.)
• M. Tanimoto (Niigata U.)
• A. Titov (U. Padova and INFN Padova)
• A. Trautner (CFTP, IST Lisbon)
• J. Turner (Durham U., IPPP)
• I. dM. Varzielas (CFTP, IST Lisbon)
• Z.-z. Xing (IHEP, CAS and Peking U., CHEP)

Local Organising Committee:   

• D. Meloni (Chair, Roma Tre U.)
• F. Mescia (INFN, LNF)
• S. Morisi (Naples U.)
• M. Parriciatu (Roma Tre U.)
• J. Penedo (Co-chair, INFN Roma Tre)

 

FLASY 2025 was supported by:

Poster_FLASY2025_ultimate.pdf

Monday 30 June

08:00 → 09:30 Registration

09:30 → 11:00 Morning session

Convener: Davide Meloni (Istituto Nazionale di Fisica Nucleare)

09:30 Opening

Speakers: Domizia Orestano (Istituto Nazionale di Fisica Nucleare), Davide Meloni (Dipartimento di Matematica e Fisica & INFN Roma Tre)

FLASY.pdf

09:50 Unitarity triangle angles explained: a predictive new quark mass matrix texture

We propose a novel quark mass matrix texture-pair with five free parameters, which fits the four quark mass ratios $m_s/m_b$, $m_d/m_b$, $m_c/m_t$, $m_u/m_t$, and the four
CKM quark mixing observables. The matrices each have one texture zero, but the main innovation here is a ``geometric'' ansatz exploiting a pair of small complex expansion parameters, based on the geometry of the Unitarity Triangle. The fit to the observables is in good agreement with current experimental values renormalised to $\sim\!\!10^4$ TeV, and offers decisive tests against future high-precision measurements of the unitarity triangle angles at the weak scale. We identify two novel symmetries of these mass matrices which explain the phenomenologically-successful relations $\alpha\equiv\phi_2\simeq \pi/2$ and $\beta\equiv\phi_1\simeq\pi/8$.

Speaker: Paul Harrison (University of warwick)

Harrison.pdf

10:30 The mu-tau reflection symmetry of Majorana neutrinos in a cross seesaw system

In the canonical seesaw framework flavor mixing and CP violation in weak charged current interactions of light and heavy Majorana neutrinos are correlated with each other and described respectively by the $3\times 3$ matrices $U$ and $R$. We show that the very possibility of $\big|U^{}_{\mu i}\big| = \big|U^{}_{\tau i}\big|$ (for $i = 1, 2, 3$), which is strongly indicated by current neutrino oscillation data as a good approximation, automatically leads to a novel relation $\big|R^{}_{\mu i}\big| = \big|R^{}_{\tau i}\big|$ (for $i = 1, 2, 3$). We show that behind these two sets of equalities and the experimental evidence for leptonic CP violation lies a minimal flavor symmetry: the overall neutrino mass term keeps invariant when the left-handed neutrino fields transform as $\nu^{}_{e \rm L} \to (\nu^{}_{e \rm L})^c$, $\nu^{}_{\mu \rm L} \to (\nu^{}_{\tau \rm L})^c$, $\nu^{}_{\tau \rm L} \to (\nu^{}_{\mu \rm L})^c$ and the right-handed neutrino fields undergo an arbitrary unitary CP transformation. Such a generalized $\mu$-$\tau$ reflection symmetry, together with the fact that all the active-sterile flavor mixing angles in $R$ are expected to be considerably smaller than the active flavor mixing angles in $U$, provides an intriguing illustration of the emergence of a cross seesaw system for both neutrino masses and flavor mixing effects of Majorana neutrinos.

Speaker: Zhi-zhong Xing (Institute of High Energy Physics, Chinese Academy of Sciences)

2025Flasy.pdf

11:00 → 11:30 Coffee break

11:30 → 12:30 Morning session

Convener: Davide Meloni (Istituto Nazionale di Fisica Nucleare)

11:30 Global neutrino analysis 2025: Knowns and Unknowns

Speaker: Eligio Lisi (Istituto Nazionale di Fisica Nucleare)

Lisi_FLASY_2025_final.pdf

12:00 The Modular Blueprint of Flavor: Quarks and Leptons Entangled

In theories of flavor based on modular invariance, correlations between quark and lepton observables are a natural expectation. These arise from their shared dependence on a common modulus field, from joint experimental constraints, and—in the context of Grand Unified Theories (GUTs) — from possible embedding into common gauge multiplets. Despite this, most bottom-up modular flavor models developed so far have analyzed the quark and lepton sectors independently, making it impossible to explore their potential interconnections.

In this talk, we present a comparative study of joint quark–lepton fits across different classes of modular flavor models, with the aim of uncovering the nontrivial interplay between the two sectors. We focus in particular on how correlations among observables emerge depending on the model's number of free parameters relative to the number of available experimental constraints. When the number of parameters exceeds the number of constraints, correlations may be washed out or hidden by flat directions in parameter space. Conversely, in more predictive scenarios with fewer parameters, correlations can become sharp and testable.

We illustrate these features with concrete examples, highlighting how the modulus $\tau$ can mediate non-obvious links between the quark and lepton flavor patterns.

Speaker: Antonio Marrone (Istituto Nazionale di Fisica Nucleare)

Flasy2025_Marrone.pdf

12:30 → 14:30 Free time for lunch

14:30 → 16:00 Afternoon session

Convener: Joao Penedo (INFN Roma Tre)

14:30 Modular invariance and the strong CP problem

I discuss a set of conditions under which the strong CP problem is solved by spontaneous CP violation. Such conditions find their natural realization in anomaly-free modular invariant supersymmetric theories, suggesting a common solution to the strong CP problem and the flavor puzzle. In its minimal realization, this solution requires a single chiral multiplet, beyond those of the MSSM. If one of its spin-zero components is light, it provides a viable Dark Matter candidate.

Speaker: Ferruccio Feruglio (Istituto Nazionale di Fisica Nucleare)

Feruglio_Flasy2025v2.pdf

15:00 Flavor symmetries and DM stability

Speaker: Eduardo Peinado

Flasy2025Romatre2.pdf

15:30 Lepton Number Violation: From the Cosmos to the Lab

Speaker: Julia Harz (Technical University of Munich (TUM))

FLASY2025.pdf

16:00 → 16:30 Coffee break

16:30 → 17:30 Afternoon session

Convener: Joao Penedo (INFN Roma Tre)

16:30 Updated result from µ+→e+ γ search in MEGII and future projects

We report the result of the search for the decay µ+ → e+ γ undertaken at the Paul Scherrer
Institut in Switzerland with the MEG II experiment using the data collected in the 2021–2022
physics runs. The MEG II detector consists of a spectrometer built around a solenoidal
magnet delivering a gradient field, consisting of a large cylindrical drift chamber and a
highly segmented timing counter for positron detection, and a large liquid xenon detector
for gamma-ray detection.
The sensitivity of this search improves significantly that obtained with the full MEG dataset,
obtained in a data taking period of about one fourth that of MEG,
thanks to the superior performances of the new detector.
Additional improvements are expected with the data collected during the years 2023–2024.
The data-taking will continue in the coming years.
We report also on the ongoing activity for designing a future experiment for µ+ → e+ detection
with an expected improvement in sensitivity of an additional order of magnitude compared to the
full MEG II data set, based on gamma-ray converter and innovative technology for tracking.

Speaker: Paolo Walter Cattaneo (Istituto Nazionale di Fisica Nucleare)

MEGIIFLASY.pdf

17:00 Observation of the 𝐾⁺ → 𝜋⁺𝜈𝜈 decay and measurement of its branching ratio at NA62

Speaker: Francesco Brizioli (INFN Perugia (IT))

Flasy25_NA62_Brizioli.pdf

17:30 → 19:30 Welcome cocktail

Tuesday 1 July

08:30 → 09:00 Registration

09:00 → 11:00 Morning session

Convener: Ferruccio Feruglio (Istituto Nazionale di Fisica Nucleare)

09:00 Modular-Symmetry-Protected Seesaw Mechanism

In the presence of a finite modular flavour symmetry, fermion mass hierarchies may be
generated by a slight deviation of the modulus from a symmetric point. We point out that
this small parameter governing charged-lepton mass hierarchies may also be responsible
for the breaking of lepton number in a symmetry-protected low-scale seesaw, sourcing
active neutrino masses and the mass splitting of a pseudo-Dirac pair of heavy neutrinos.
We discuss the phenomenological implications of this mechanism,

Speaker: Serguey Petcov (Istituto Nazionale di Fisica Nucleare)

PetcovFLASY010725.pdf

09:30 Quark and Lepton Mass Hierarchies from Modular Flavour Symmetry with Weightons

Speaker: Steve King (University of Southampton)

FLASY King 25.pdf

10:00 Flavor Symmetries and Winding Modes

Modular flavor symmetries are realized in string theory. These symmetries act on KK and winding modes. We show that winding modes (i) are key for the interpretation of modular flavor symmetries, (ii) are gauge fields responsible for conventional flavor symmetries, (iii) have different subsets become massless at different critical values of the modulus, and (iv) play an interesting role in CP violation.

Speaker: Michael Ratz (UC Irvine)

FLASY25_Ratz-1.pdf

10:30 Non-holomorphic modular symmetry

The original modular flavor symmetry requires supersymmetry to enforce the Yukawa couplings to be holomorphic modular forms. The non-holomorphic modular symmetry is a generation in which supersymmetry is unnecessary in principle. In this talk, we shall present motivation, the formalism and application of non-holomorphic modular symmetry. A predictive model for both quarks and leptons will be presented, the phenomenological predictions are explored.

Speaker: Gui-Jun Ding (University of Science and Technology of China)

Non-holomorphic_modular_symmetry_Rome.pdf

11:00 → 11:30 Coffee break

11:30 → 12:30 Morning session

Convener: Arsenii Titov (University of Padua and INFN)

11:30 Two Tales about Modular Flavor Symmetries

Speaker: Mu-Chun Chen (University of California at Irvine)

FLASY2025_MCChen.pdf

12:00 CP violations of quarks and leptons in the setup with T^2/Z_3 orbifold compactification

CP invariance is a very attractive solution to the strong CP problem in QCD. This solution requires the vanishing phase of (det M_d det M_u) of the mass matrices for the down- and up-type quarks. It happens if we have several zeros in the quark mass matrices. We proceed a systematic construction of texture zeros for the quark sector in the T^2/Z3 orbifold compactification. We also extend the mass construction to the neutrino sector and derive predictions on the CP violating parameter in the neutrino oscillation and the mass parameter of neutrinoless double beta decay. We can naturally explain the positive sign of the baryon asymmetry in the present universe.

Speaker: Morimitsu Tanimoto (Niigata University)

Tanimoto-FLASY2025-1.pdf

12:30 → 14:30 Free time for lunch

14:30 → 16:00 Parallel session I: 1-I

Convener: Matteo Parriciatu (Istituto Nazionale di Fisica Nucleare)

14:30 Neutrino mass sum rules from modular $A_4$ symmetry

In this talk, I will discuss a type-ii seesaw using the modular $A_4$ flavour symmetry. We propose a simple and minimalistic model that restricts the neutrino oscillation parameter space and, most importantly, introduces a sum rule in the physical neutrino masses. When combined with the mass squared differences observed in neutrino oscillations, this sum rule determines the absolute neutrino mass
scale. This has significant implications for cosmology, neutrinoless double beta decay experiments and direct neutrino mass measurements. In particular, the model predicts $\Sigma_i m_i \approx$ 0.1 eV for both normal and inverted ordering, and thus can be fully probed by the current generation of cosmological probes in the upcoming years.

Speaker: Ranjeet Kumar (Department of Physics, Indian Institute of Science Education and Research - Bhopal)

Ranjeet_FLASY25.pdf

14:50 A SU(3)C x SU(3)L x U(1)X theory with A4 modular symmetry

A $SU(3)_C\times SU(3)_L \times U(1)_X$ extension of the gauge symmetry of the Standard Model with $A_4$ modular symmetry and radiative linear seesaw is proposed. The gauge extension of the SM offer an opportunity to add new scalar fields to the model that can be used in Yukawa interactions to construct the neutrino mass matrix. In addition, $A_4$ modular symmetry is used as a flavour symmetry to forbid some entries in the neutrino mass matrix at tree level but permitted at one-loop. This model can successfully accommodate the observables of the neutrino sector.

Speaker: Nicolás Andrés Pérez Julve (UTFSM)

331_model_A4_modular_radiative_linear_sesaw_FLASY2025.pdf

15:10 Classification of Modular Symmetries in Type IIB Flux Landscape

In this work, we study modular symmetries in type IIB flux landscape by investigating symplectic basis transformations of period vectors on toroidal orbifolds.
To fix explicit cycles of a third-cohomology basis regarding the untwisted complex structure modulus, which is necessary to construct the period vectors, we find that the following two symmetries are required for the period vectors: (i) ``Scaling duality '' which is a generalized $S$-transformation of $PSL(2, \mathbb{Z})$ and (ii) the modular symmetries to be consistent with symmetries derived from mass spectra of the closed string in type IIB string theory.
Furthermore, by considering flux quanta on the cycles, we explore type IIB flux vacua on toroidal orientifolds and flux transformations under the modular symmetries of the period vectors.

Speaker: Takafumi Kai (Kyushu University)

Takafumi_Kai.pdf

15:30 Diffusion-model approach to flavor models: A case study for $S_{4}^\prime$ modular flavor model

We propose a numerical method of searching for parameters with experimental constraints in generic flavor models by utilizing diffusion models, which are classified as a type of generative artificial intelligence (generative AI). As a specific example, we consider the $S_{4}^\prime$ modular flavor model and construct a neural network that reproduces quark masses, the CKM matrix, and the Jarlskog invariant by treating free parameters in the flavor model as generating targets. By generating new parameters with the trained network, we find various phenomenologically interesting parameter regions where an analytical evaluation of the $S_{4}^\prime$ model is challenging. Additionally, we confirm that the spontaneous CP violation occurs in the $S_{4}^\prime$ model. The diffusion model enables an inverse problem approach, allowing the machine to provide a series of plausible model parameters from given experimental data. Moreover, it can serve as a versatile analytical tool for extracting new physical predictions from flavor models. References are arXiv:2503.21432 [hep-ph] and arXiv:2504.00944 [hep-ph].

Speaker: Satsuki Nishimura (Kyushu University)

FLASY2025_SatsukiNishimura.pdf

14:30 → 16:00 Parallel session II: 1-II

Convener: Julia Harz (Technical University of Munich (TUM))

14:30 Dark Hypercharge Symmetry

The gauged $U(1)_X$ extensions of the Standard Model are some of the most popular and extensively studied new physics models. In most of these models the charges of SM fermions are fixed by gauge anomaly cancellations. While the literature extensively discusses anomaly cancellation solutions in which SM fermions are "vector-like" under new symmetry, chiral solutions in which SM fermions are chiral under new symmetry are not well explored. In this work, we explore a whole new class of gauged $U(1)_X$ models where the SM fermions are chiral under the new $U(1)_X$ symmetry which we call the Dark Hypercharge symmetry. We present a comprehensive set of solutions for gauge anomaly cancellation through the inclusion of three chiral dark sector fermions. We will focus on a particularly intriguing chiral solution and demonstrate, in a model-independent manner using only the $Z'$ interaction channel, that the lightest dark fermion, is a viable Dark Matter candidate, and it can meet all current Dark Matter constraints. We also discuss the related Dark Matter and collider phenomenology of such models.

Speaker: Rahul Srivastava (Indian Institute of Science Education and Research-Bhopal)

dark_hypercharge_talk.pdf

14:50 Lepton sector and dark matter phenomenology of a minimal two loop level inverse seesaw model

We propose a minimal extension of the SM where the tiny active neutrino masses arise from an inverse seesaw mechanism at two loop level. The phenomenological consequences of the proposed model in neutrino masses and mixings, charged lepton flavor violation and dark matter are analyzed in detail. We find that the current theory successfully complies with the constraints arising from neutrino oscillation experimental data, neutrinoless double beta decay, charged lepton flavor violating process, dark matter relic density and dark matter direct detection. The obtained rates for charged lepton flavor violating processes are within the reach of experimental sensitivity.

Speaker: Rocío Branada Balbontín (Universidad Técnica Federico Santa María)

FLASY_2025 (3).pdf

15:10 Sterile neutrino DM production

The presence of a dark matter component in the Universe, together with the discovery of neutrino masses from the observation of the oscillation phenomenon, represents one of the most important open questions in particle physics today. A concurrent solution arises when one of the right-handed neutrinos, necessary for the generation of light neutrino masses, is itself the dark matter candidate. In this article, we study the generation of such a dark matter candidate relying solely on the presence of neutrino mixing. This tightly links the generation of dark matter with searches in laboratory experiments on top of the usual indirect dark matter probes. We find that the regions of parameter space producing the observed dark matter abundance can be probed indirectly with electroweak precision observables and charged lepton flavor violation searches. Given that the heavy neutrino masses need to lie at most around the TeV scale, probes at future colliders would further test this production mechanism.

Speaker: Salvador Rosauro Alcaraz (Istituto Nazionale di Fisica Nucleare)

Rosauro_nuDM_FLASY25.pdf

15:30 Revisiting a Flavor Model with Dark Matter and Leptogenesis

We revisit a supersymmetric flavor model, where realistic lepton mass matrices arise from specific flavon vacuum alignments. The model accommodates both dark matter and baryogenesis: the lightest flavino acts as a dark matter candidate, and the observed baryon asymmetry is generated via thermal leptogenesis with next-to-leading order Yukawa interactions. We show that the model is consistent with neutrino oscillation data, relic abundance, and lepton flavor violation constraints. Implications for future experiments are also discussed.

Speaker: Yusuke Shimizu (Kaishi Professional U.)

FLASY2025_shimizu.pdf

14:30 → 16:00 Parallel session III: 1-III

Convener: Alessio Giarnetti

14:30 Leptogenesis with low-energy Dirac CP-violation

The present Baryon Asymmetry of the Universe (BAU) can be explained in the framework of the type-I seesaw mechanism for neutrino mass generation through leptogenesis (LG). The L-, C- and CP-violating processes involving the right-handed neutrinos can generate an early lepton asymmetry, which is later converted into the present BAU by sphalerons. Remarkably, all the necessary CP-violation necessary to explain the present BAU via LG can originate uniquely from the Dirac phase of the neutrino mixing matrix, thus providing a direct link to CP-violation in low-energy neutrino oscillations. I will review the state-of-the-art understanding of the LG mechanism and concentrate on the scenarios with low-energy Dirac CP-violation with either 2 or 3 right-handed neutrinos. Possibilities to test the discussed scenarios at low-energy neutrino experiments, at heavy neutral lepton searches and experiments looking at lepton flavour violation will also be presented.

Speaker: Alessandro Granelli (Istituto Nazionale di Fisica Nucleare)

FLASY2025 Presentation.pdf

14:50 CP violation in $B_s\to \phi\mu^+\mu^-$ Decay at FCC-$ee$

The feasibility of the time-dependent $C\!P$ violation measurement $B_s^0 \to \phi(\to K^+K^-)\mu^+\mu^-$ at the FCC-$ee$ is discussed. Future $Z$-factories offer an ideal setting for measuring this decay due to the large statistics, clean environment, particle identification, and excellent vertexing capabilities. These precision measurements are interpreted in the Weak Effective Theory (WET), providing a comprehensive understanding of $C\!P$ properties of the potential New Physics (NP) in these rare decays.

Speaker: Jason Aebischer (CERN)

flasy_JA.pdf

15:10 Vector-like quark doublets, weak-basis invariants and CP violation

Even though a fourth chiral generation of fermions is experimentally ruled out, the possibility of extending the SM with vector-like quarks (VLQs), where both chiral components transform the same way under SU(2)_L cannot be excluded. In particular, extensions of the SM involving isodoublet vector-like quarks with standard charges currently stand as the favoured candidate in explaining the Cabibbo Angle Anomalies. This stems primarily from the fact that they allow for both left-handed and right-handed charged currents. This feature of isodoublet VLQ models not only gives rise to a very rich phenomenology, but may also induce important new sources of CP violation. In turn, these sources are directly connected to the existence of additional CP-odd weak basis invariant (WBI) quantities, distinct from the single one present in the SM or those present in other VLQ models. In this talk we present these new WBI quantities and show how they may signal the presence of CP violation at extremely high energies. Moreover, we relate the structure and mass dimension of these WBIs to various types of effective rephasing invariant quantities arising from the interplay of LH and RH charged currents, thus inducing imprints on a variety of flavor observables that are unique to VLQ isodoublet extensions.

Speaker: José Bastos

FLASY_JoseBastos.pdf

15:30 Underpinnings of CP-Violation at the High-energy Frontier

I will present a general analysis for the discovery potential of CP-violation (CPV) searches in scattering processes at TeV-scale colliders in an effective field theory approach.
The CP-violating sector of the SMEFT framework will be examined in some well motivated limiting cases, based on flavour symmetries of the underlying heavy theory. In particular, we show that under naturality arguments of the underlying new physics (NP) and in the absence of (or suppressed) flavour-changing interactions, there is only a SINGLE operator which alters the top-Yukawa coupling, that can generate a non-negligible CPV effect from tree-level SMxNP interference terms. We find, however, that CPV from this operator is expected to be at best of O(1\%) and, therefore, very challenging if at all measurable at the LHC or other future high-energy colliders.
We then conclude that a potentially measurable CPV effect, of O(10\%), can arise in high-energy scattering processes ONLY if flavour-changing interactions are present in the underlying NP; in this case a sizable CPV effect can be generated at the tree-level by pure NPxNP effects and not from SMxNP interference. I will provide examples of CPV at the LHC and at a future e^+e^- collider to support these statements.

---

Based on:
e-Print: 2407.19021 (PLB 2025), e-Print: 2407.19021 (PRL 2023)

Speaker: Shaouly Bar-Shalom (Technion, Israel)

16:00 → 16:30 Coffee break

16:30 → 17:10 Parallel session I: 2-I

Convener: Matteo Parriciatu (Istituto Nazionale di Fisica Nucleare)

16:30 Viable fit to neutrino observables in possible U(2) flavor models

The explanation of neutrino masses and mixing still represents one of the open questions of the so-called “SM flavor puzzle” today. The purpose of my work is to provide a possible explanation of this problem, introducing an extension of the Standard Model based on a continuous $U(2)$ flavor symmetry (which is locally isomorphic to $SU(2) \times U(1)$), indicated as $U(2)_F$. This symmetry is spontaneously broken by the VEVs of two scalar fields, called flavons. Since the flavon VEVs depend on small parameters $\epsilon_{\phi,\chi} \sim O(0.01)$, all hierarchies in fermion masses and mixings arise from powers of these small order parameters.
Assuming that neutrinos are Majorana particles and that the light neutrinos take mass via the type-I see-saw mechanism, we can obtain a list of possible structures for the neutrino mass matrix (which we call patterns), depending on the choice of the $U(2)_F$ quantum numbers for the three RH neutrino representations.
After a numerical fit of this matrices to the neutrino observables, we obtain 13 viable patterns, which provide us interesting predictions on neutrino observables, such as the effective electron neutrino mass $m_\beta$ and the effective Majorana neutrino mass $m_{\beta\beta}$, and also on BSM phenomena such as LFV decays.

Speaker: Mirko Rettaroli (Istituto Nazionale di Fisica Nucleare)

FLASY_Rettaroli.pdf

16:50 Lepton Flavor Violating decays in a realistic U(2) flavor model

Building on the realistic U(2) flavor model proposed a few years ago by Linster and Ziegler, we conduct a comprehensive study of possible neutrino mass textures arising from the seesaw mechanism. We identify a set of viable models that provide an excellent fit to low-energy Standard Model flavor observables including neutrinos. Additionally, within an Effective Field Theory framework, we analyze lepton flavor-violating decays in these models and examine their implications for the muon anomalous magnetic moment.

Speaker: Simone Marciano (IFIC - CSIC - University of Valencia)

FLASY25_Marciano.pdf

16:30 → 17:10 Parallel session II: 2-II

Convener: Julia Harz (Technical University of Munich (TUM))

16:30 Temperature evolution in the Early Universe and Freeze-in at stronger coupling

In this talk, I will discuss the freeze-in dark matter production mechanism at low reheating temperatures. The process is Boltzmann-suppressed if the dark matter mass is above the reheating temperature, and, in this case, the coupling to the thermal bath has to be significant to account for the observed dark matter relic density. As a result, the direct DM detection experiments can already probe such freeze-in models, excluding significant parts of parameter space. The forthcoming experiments will explore this framework further, extending to lower couplings and higher reheating temperatures.

Speaker: Catarina Cosme (U. Coimbra)

FLASY_CCosme.pdf

16:50 The role of nonperturbative dynamics in D-meson mixing

The theoretical predictions for the $D-\bar{D}$ mixing parameters fall significantly short of experimental measurements, with discrepancies spanning several orders of magnitude. This divergence is largely attributed to the Glashow–Iliopoulos–Maiani (GIM) mechanism, which suppresses leading-order contributions. However, higher-order corrections and nonperturbative effects have the potential to mitigate this suppression, particularly through flavor SU(3) symmetry breaking. In this work, we explore the long-distance contributions arising from nonlocal QCD condensates, incorporating for the first time the impact of mixed condensates within multiple models. Our results demonstrate an improvement in the predicted values of $D-\bar{D}$ mixing parameters by an order of magnitude, providing insights into the role of nonperturbative QCD dynamics. While the theoretical estimates remain below experimental values, this study represents a crucial step toward bridging the gap between theory and observation, highlighting the importance of nonlocal QCD effects in understanding $D-\bar{D}$ mixing.

Speaker: Lovro Dulibić (Boskovic Inst., Zagreb)

dulibic_ddmixing_FLASY.pdf

16:30 → 17:10 Parallel session III: 2-III

Convener: Stefano Morisi (Istituto Nazionale di Fisica Nucleare)

16:30 Flavor-deconstructed neutrinos

A tentative approach to explain the flavor puzzle consists of embedding the Standard Model in a larger gauge symmetry that contains a separate gauge group for each fermion family. In such gauge non-universal (or flavor-deconstructed) theories, neutrinos pose some challenges. I will discuss existing ideas in the literature and present a simple model in which flavor deconstruction naturally leads to sequential dominance for both neutrinos and charged leptons, thus providing a viable explanation for the flavor structure of the lepton sector.

Speaker: Avelino Vicente (IFIC (CSIC - U. Valencia))

a_vicente.pdf

16:50 Exploring Flavour Symmetries and Long-Lived Particles with the FASER Experiment

The FASER experiment at the LHC explores long-lived particles (LLPs) and their connections to flavour symmetries. Recent results include constraints on dark photons and axion-like particles (ALPs), which are often motivated by flavour-related dynamics, as well as the first detection of high-energy collider neutrinos, providing insights into neutrino flavour oscillations and constraints on heavy neutral leptons (HNLs). These findings offer complementary probes to other experiments, addressing key questions in flavour physics, particle interactions, and cosmology.

Speaker: Cristiano Sebastiani (CERN)

FLASY25_sebastiani.pdf

Wednesday 2 July

08:30 → 09:00 Registration

09:00 → 11:00 Morning session

Convener: Stefano Morisi (Istituto Nazionale di Fisica Nucleare)

09:00 Past, Present and Future in Flavor Physics, the Unitary Triangle Fit, Anomalies and all that

Speaker: Guido Martinelli (Istituto Nazionale di Fisica Nucleare)

Martinelli_Roma02July2025b.pdf

09:30 The flavour violating Goldstone

In this talk, I explore low-scale seesaw scenarios in which a single global U(1) symmetry — and its spontaneous breaking — plays multiple theoretical roles and determines the resulting phenomenology. I will present four example models that share a similar particle content but differ only in their charge assignments, leading to qualitatively distinct physical scenarios, where the Goldstone boson associated with the U(1) breaking (Majoron or Diracon) plays a central role. I will highlight the complementarity between low-energy flavour experiments and cosmological observations in constraining and distinguishing these models.

Speaker: Salvador Centelles Chuliá (IFIC (CSIC - U. Valencia))

FLASY_2025_slides.pdf

10:00 Mapping the theory space of the flavor puzzle: the Froggatt-Nielsen case

The hierarchical structure of fermion masses and mixings suggests the presence of an underlying mechanism, for which many ideas have been put forward. In this talk, I present a systematic framework to explore such mechanisms from a "global" perspective, as developed in recent studies of the Froggatt-Nielsen mechanism in the quark and lepton sectors (arXiv:2306.08026, 2501.00629). This global approach offers phenomenological insights, testable predictions, and may help set the stage for broader connections to other open problems in particle physics.

Speaker: Claudia Cornella (CERN)

cornella_flasy.pdf

10:30 Flavour symmetry in partially composite unification

Speaker: Sebastian Jaeger (University of Sussex)

flasy2025-jaegerV2.pdf

11:00 → 11:30 Coffee break

11:30 → 12:30 Morning session

Convener: Stefano Morisi (Istituto Nazionale di Fisica Nucleare)

11:30 Accelerated Cosmic Expansion, Mass Creation, and the QCD Axion

The present acceleration of the Universe can be sourced by the continuous generation of an energy density $\rho_b$ associated with a certain field $\varphi_b$. This idea is implemented by adding a new tensor term to Einstein equation. The creation process requires $\rho_b\neq 0$ as an initial condition, which is enforced by identifying $\varphi_b$ with the axion of a hidden gauge group that confined in recent cosmological times. Shortly before matter-dark energy equality, this led to a level crossing between $\varphi_b$ and the QCD axion, assumed to comprise dark matter. A small fraction of QCD axions converts into $\varphi_b$, generating the initial $\rho_b$ needed to trigger the creation process, offering a solution to the coincidence puzzle.

Speaker: Enrico Nardi (INFN-LNF & NICPB, Tallinn)

DE_FLASY2025_Nardi.pdf

12:00 Light New Physics, non-conserved currents and Minimal Flavour Violation

In recent years, there has been great interest in the community toward New Physics scenarios involving light new degrees of freedom. In this talk, I will discuss the importance of the ultraviolet completion of such scenarios, using the case of a light vector as an example. I will show that the resulting flavour structure is of the Minimal Flavor Violation type, and I will discuss a possible interpretation of the recent excess in the $B \to K^* E_{miss}$ channel.

Speaker: Marco Nardecchia (Istituto Nazionale di Fisica Nucleare)

Flasy_Nardecchia.pdf

12:30 → 20:00 Free afternoon

20:00 → 22:00 Conference Dinner

Thursday 3 July

08:30 → 09:00 Registration

09:00 → 11:00 Morning session

Convener: Gustavo Burdman

09:00 MonoHiggsology

Flavor symmetry and other ideas beyond the standard model may be achieved using the dark sector, while keeping only the one SM Higgs doublet.

Speaker: Ernest Ma (University of California, Riverside)

rome_25.pdf

09:30 S3 and Q6 as flavor symmetries: interplay between the scalar and fermionic sectors

We present two multi-scalar models, with S3 and Q6 flavour symmetries, respectively. We show how in general the doublet-singlet structure of these types of symmetries accommodates very well the quark sector and CKM matrix. In both models we check whether the co-bimaximal mixing pattern can be found in the neutrino sector. We use S3 as flavour symmetry in a B-L model, and we take complex vev's in the scalar potential and an inverse seesaw mechanism for generating the neutrino masses, in both cases with good fits to the respective mixing matrices. On the other hand, in the Q6 model we use a radiative seesaw to generate the neutrino masses and connect it to a dark sector, where we have 3 possible candidates. In this case, a numerical analysis shows that a combination of all LHC constraints on Higgs and exotic scalars, combined with dark matter constraints, single out a light scalar with mass ~98 GeV and a pseudoscalar with mass ~348 GeV, at the best fit point.

Speaker: Myriam Mondragon (Instituto de Fisica, UNAM)

FLASY2025_Mondragon.pdf

10:00 Model Building with LieART

We have been developing the Mathematica package LieART for handling Lie group representation, their products and their decomposition to maximal subgroups. LieART can be a useful tool for model building and other applications. We will give an overview.

Speaker: Thomas Kephart (Vanderbilt University)

KephartFLASY3July2025RomeTalkTWK.pdf

10:30 331 Models partial anatomy

Some key topics characterizing 331 models and their viability—both from
a theoretical and phenomenological perspective—are discussed.

Speaker: Giulia Ricciardi (Istituto Nazionale di Fisica Nucleare)

seminarV3.pdf

11:00 → 11:30 Coffee break

11:30 → 11:45 Group photo

11:45 → 12:45 Morning session

Convener: Claudia Hagedorn (IFIC - UV/CSIC)

11:45 Neutrinos and rich dark sectors

In this talk I will discuss the connection between neutrinos and dark sectors. Neutrino masses remain unexplained. Their origin could arise in models at scales below the electroweak one, the so-called dark sectors. I will focus on rich dark sectors that have multiple sectors, in analogy to the Standard Model. I will review how neutrino masses can be generated in such models and how the latter could be tested in experimental and astroparticle physics experiments.

Speaker: Silvia Pascoli (University of Bologna)

Flasy_Pascoli.pdf

12:15 Probing SUSY at Gravitational Wave Observatories

Under the assumption that the 2023 pulsar timing array (PTA) results for a stochastic gravitational wave (GW) background at nanohertz frequencies is generated by metastable cosmic strings, we analyze the potential of present and future GW observatories for probing the change of particle degrees of freedom caused, e.g., by a supersymmetric (SUSY) extension of the Standard Model (SM). We find that signs of the characteristic doubling of degrees of freedom predicted by SUSY could be detected at Einstein Telescope and Cosmic Explorer even if the masses of the SUSY partner particles are as high as about $10^4$ TeV, far above the reach of any currently envisioned particle collider. We also discuss the detection prospects for the case that some entropy production, e.g. from a late decaying modulus field inducing a temporary matter domination phase in the evolution of the universe, somewhat dilutes the GW spectrum, delaying discovery of the stochastic GW background at LIGO-Virgo-KAGRA. In our analysis we focus on SUSY, but any theory beyond the SM predicting a significant increase of particle degrees of freedom could be probed this way. We furthermore discuss the generation of metastable cosmic strings from the breaking of GUT and flavour symmetries, and how the PTA results allow to identify promising classes of models.

Speaker: Stefan Antusch (University of Basel)

Antusch_FLASY25.pdf

12:45 → 14:30 Free time for lunch

14:30 → 16:00 Parallel session I: 3-I

Convener: Davide Meloni (Istituto Nazionale di Fisica Nucleare)

14:30 Effective description of Nelson-Barr theories

In Nelson-Barr theories built to solve the strong CP problem, vector-like quarks (VLQs) transmit the spontaneous CP breaking from a scalar sector to the CP conserving version of the SM. We perform the full one-loop matching calculations at the CP breaking scale up to dimension five and partial matching calculations at the VLQ scale to track the relevant corrections to the theta parameter at low energy. We find that the additional dimension five operators indeed induce the RGE running of theta at one-loop. The effect is relevant when the separation between the CP breaking scale and the VLQ scale is large. We discuss some results for simple models, including a version based on non-conventional CP where the contribution at one-loop vanishes.

Speaker: Celso Nishi (Federal University of ABC)

flasy25-Nishi.pdf

14:50 Flavored Peccei-Quinn symmetries in the minimal νDFSZ model

In this talk, I will describe minimal DFSZ models extended with two right-handed neutrinos to realize the minimal type-I seesaw mechanism. The models incorporate flavored U(1) PQ symmetries that account for the observed pattern of quark and lepton masses and mixings. I will discuss the resulting phenomenology, including axion dark matter and cosmology, axion couplings to photons and fermions, highlighting the implications for flavor-violating axion interactions.

Speaker: José Rocha (CFTP-IST, Lisbon)

JRRocha.pdf

15:10 Axion framework with colour-mediated Dirac neutrino masses

I will discuss our recent paper arXiv:2501.13156 where we propose a KSVZ-type axion framework in which vector-like quarks (VLQ) and coloured scalars generate Dirac neutrino masses radiatively. The global Peccei-Quinn symmetry (under which the exotic fermions are charged) addresses the strong CP problem and ensures the Dirac nature of neutrinos. The axion also accounts for the observed cosmological dark matter. We systematically explore all viable VLQ representations. Depending on the specific scenario, the framework predicts distinct axion-to-photon couplings, testable through haloscope and helioscope experiments, as well as potentially significant flavor-violating quark-axion interactions.

Speaker: Aditya Batra (CFTP-IST, Lisbon)

FLASY2025.pdf

15:30 QCD axion and inflation from modular flavor symmetry

We study the stabilization of an modulus by Coleman-Weinberg potential generated by coupling with matter fields, which is controlled by modular flavor symmetry. In this model we can not only regard the $\mathrm{Re}\,\tau$ direction as the QCD axion but also propose new potential model for inflation using the same potential.

Speaker: Komei Goto (Keio University)

20250703_KomeiGoto_FLASY2025.pdf

14:30 → 16:00 Parallel session II: 3-II

Convener: Simone Marciano (IFIC - CSIC - University of Valencia)

14:30 Flavor puzzle in three Higgs-doublet models: Insights from BGL and lessons from flavor data

We study a variant of the 3HDM, referred to as the BGL-3HDM, incorporating a U $(1)_1 \times U(1)_2$ symmetry, which can distinguish the primary sources of mass for different fermion generations. In the version considered here, the Yukawa matrices in the down-quark and charged lepton sectors are diagonal, thereby eliminating tree-level FCNCs in these sectors. FCNCs mediated by neutral nonstandard Higgses are confined to the up-quark sector only. No new BSM parameters are introduced by the Yukawa sector of the model, making it as economical as the NFC versions of 3HDM with a $U(1)_1 \times U(1)_2$ symmetry in terms of the number of free parameters. However, even in the down-quark and in the charged lepton sectors, flavor diagonal but nonuniversal Higgs couplings set this model apart from the NFC versions of the 3HDM.

Speaker: Miguel Levy (Basel University)

FLASY_Levy.pdf

14:50 The Electric Dipole Moment of the electron in the decoupling limit of the aligned Two-Higgs Doublet Model

We present a discussion of model-independent contributions to the EDM of the electron.
We focus on those contributions that emerge from a heavy scalar sector that is linearly realized. In particular, we explore the decoupling limit of the aligned 2HDM.
In this model, Barr-Zee diagrams with a fermion loop produce logarithmically-enhanced contributions that are proportional to potentially large new sources of CP violation. In the decoupling limit these contributions are generated by effective dimension-6 operators via the mixing of four-fermion operators into electroweak dipole operators.
These logarithmic contributions are not present in more constrained versions of the 2HDM where a $\mathcal Z_2$ symmetry is imposed, since it controls the basis of effective operators needed to describe the new physics contributions to the electron EDM. Thus, the $\mathcal Z_2$ symmetry provides a suppression mechanism.
We then study how the experimental bounds on the electron EDM constrain the set of parameters of the aligned 2HDM.

Speaker: Juan Manuel Dávila Illán (IFIC (UV - CSIC))

ElectronEDM_FLASY_JM_Davila_v2.pdf

15:10 Light states in real multi-Higgs models with spontaneous CP violation

In models with extended scalar sectors consisting of multiple Higgs doublets that trigger spontaneous electroweak symmetry breaking, one might expect that the abundance of dimensionful quadratic couplings in the scalar potential allows for a regime where, apart from the would-be Goldstone bosons and a neutral Higgs-like state, all new scalars have masses much larger than the electroweak scale. For models where CP invariance holds at the lagrangian level but is broken by the vacuum, one can show that such a reasonable expectation does not hold. When perturbativity requirements are placed on the dimensionless quartic couplings, the spectrum of the new scalars includes one charged and two additional neutral states whose masses cannot be much larger than the electroweak scale.

Speaker: Miguel Nebot (University of Valencia - IFIC)

Nebot_Light-States-Real-nHDM_FLASY2025.pdf

15:30 Comparison between μ-μ+ and e-e+ colliders for charged Higgs production in the 2HDM

We study the phenomenology of the charged Higgs boson at future muon colliders. We investigate the pair production μ+μ-→H+H-, the single production μ+μ-→W±H∓, as well as the vector boson fusion (VBF) {e+e-,μ+μ-}→νν¯H+H-. We show that the neutral Higgs exchange diagrams in the muon collider case can lead to a significant boost in the cross sections through their Yukawa couplings. Our results for the muon collider are systematically compared to the corresponding ones at e+e- machines. It is demonstrated that the VBF e+e-→νν¯H+H- can compete with the mentioned 2→2 processes. We select benchmark points and perform signal-background analyses, taking into account detector simulations. We demonstrate the discovery region at 5σ and the excluded region at 2σ levels at a 3 TeV muon collider.

Speaker: Es-Said Ghourmin

16:00 → 16:30 Coffee break

16:30 → 17:30 Parallel session I: 4-I

Convener: Joao Penedo (INFN Roma Tre)

16:30 Long live the heavy ALP!

We explore the viability of axion-like particle (ALP) effective field theories (EFTs) where the ALP mass $m_a$ is comparable to or larger than the symmetry-breaking scale $f_a$, challenging the conventional hierarchy $m_a < f_a$. Using a data-driven approach, we analise four key observables: the anomalous magnetic moments of the electron and muon, as well as decays ($\mu\to e\gamma$) and ($\mu\to 3e$), considering an ALP coupled only to the less massive charged leptons with both flavour conserving and violating possibilities. Focusing on high ALP masses ($m_a>1$ GeV), we find a viable parameter space where $m_a\geq f_a$ remains consistent with experimental data within 3$\sigma$. This study highlights the potential for non-traditional ALP mass hierarchies in EFT scenarios.

Speaker: Samuel Rosende Herrero (UAM)

flasy2025talk_samuel.pdf

16:50 Tackling ALP searches in meson decays with ALPaca: a phenomenological approach

Part of the community has intensively searched for ALP signals, as well as conducted dedicated data analyses to identify potential evidence of New Physics compatible with an ALP, resulting in constraints on the ALP parameter space. Therefore, it is now the time to present a tool, ALPaca, that facilitates the combination among the different information on ALP physics.
The focus of this talk will be on a phenomenological analysis of the ALP theory using the most up-to-date data from flavour facilities, to show both the latest constraints and the potential of ALPaca to study the interplay between flavour and ALP physics.

Speaker: Marta Fuentes Zamoro (Universidad Autónoma de Madrid)

ALPaca_talk.pdf

17:10 Muon-decay parameters at COHERENT

We study the most general Lagrangian for muon decay at low energies, including light Dirac right-handed neutrinos ($\nu$WEFT), in the COHERENT experiment at the Spallation Neutron Source at Oak Ridge National Laboratory. Using the COHERENT data, we derive the first direct constraint on the Michel parameters governing the $\bar\nu_\mu$ energy distribution. We also discuss future sensitivities and assess the implications for the Lorentz structure of the interactions mediating muon decay.
We thus demonstrate that Coherent Elastic Neutrino-Nucleus Scattering (CE$\nu$NS) measurements at spallation sources are valuable probes of muon decay physics.

Speaker: Sergio de la Cruz Alzaga (IFIC (CSIC-Universidad de Valencia))

FLASY-CruzAlzaga.pdf

16:30 → 17:30 Parallel session II: 4-II

Convener: Simone Marciano (IFIC - CSIC - University of Valencia)

16:30 Searches for lepton-flavour violation in τ decays at Belle and Belle II

The Belle and Belle II experiments have collected a 1.6 ab$^{−1}$ sample of $e^+e^-$ collision data at center-of-mass energy near the $\Upsilon(nS)$ resonances. This sample contains approximately 1.5 billion $e^+e^- \to \tau^+ \tau^-$ events, which we use to search for lepton-flavour violating decays. We present searches for $\tau \to l \gamma$, tau decays into three leptons, $\tau^- \to K_S^0 l^- $ and $\tau^- \to l^- \alpha$ where $\alpha$ is an invisible scalar particle.

Speaker: Laura Salutari (Istituto Nazionale di Fisica Nucleare)

Salutari_FLASY_v2.pdf

16:50 Inverse Seesaw with flavour and CP symmetries and its phenomenology

We discuss Charged Lepton Flavour Violating (CLFV) signals in Inverse Seesaw (ISS) scenarios with 3+3 heavy sterile states and flavour and CP symmetries.

We distinguish between two options of these scenarios, each characterised by a different spectrum of the heavy sterile states and different forms of the couplings and mass matrices. For both options, different lepton mixing patterns are predicted depending on the choice of residual groups.

Compatibility of the scenario for both options with bounds on CLFV processes is studied, and bounds on the parameters are derived.

The possibility of distinguishing between the various choices of residual symmetries, as well as between the two different options, through such signals is also considered.

Speaker: Francesco Paolo Di Meglio (IFIC Valencia)

FLASY2025_Di_Meglio.pdf

17:10 Charged Lepton Flavour Violating meson decays in seesaw models

The occurrence of neutrino oscillations demands the existence of flavour violation in the charged lepton sector. The relation between the branching ratios of different charged lepton flavour-violating (CLFV) decay modes depends on the details of the neutrino mass model. In this work, we consider the three types of simple seesaw mechanisms of neutrino masses and study the correlation between the radiative CLFV decays and the meson CLFV decays. We find that the meson CLFV decay branching ratios are negligibly small in the type-II seesaw mechanism, whereas they are constrained to be at least three (two) orders of magnitude smaller than the radiative CLFV decay branching ratios in the case of type-I (type-III) seesaw mechanism. Thus, the relationship between these two modes of CLFV decays helps in distinguishing between different types of seesaw mechanisms. If the branching ratios of CLFV decays of mesons are larger than those of radiative CLFV decays, it provides a strong hint that the neutrino mass-generating mechanism is more complicated than the simple seesaw.

Speaker: Pravesh Chndra Awasthi (Indian Institute of Technology Bombay, Mumbai, India)

flasy-pravesh.pdf

Friday 4 July

08:30 → 09:00 Registration

09:00 → 11:00 Morning session

Convener: Stefan Antusch (University of Basel)

09:00 Quantum Gravity and Flavor: Probing New Frontiers with Neutrinos

Quantum gravitational effects are expected to reveal themselves at extreme energies, cosmological distances, in a break-down of standard quantum mechanics, or in the breaking of global symmetries. Neutrinos offer a unique potential to probe such effects: they are perfect quantum probes, their masses may be related to lepton number or flavor and thus global symmetry breaking and extra-galactic neutrinos have been observed at energies up to the PeV scale. We discuss Lepton Number Violation, Quantum-Gravitational Decoherence, Altered Dispersion Relations, Holographic Scaling and Entanglement Measures and assess the future perspectives of such experimental probes of quantum gravity.

Speaker: Heinrich Päs

FLASY25.pdf

09:30 Low Temperature Baryogenesis

We explore models of baryogenesis at temperatures below the electroweak scale. In particular, we focus in a realization which makes clear the connection between low temperature baryogenesis and highly displaced vertices. The model involves the out of equilibrium decay of Majorana fermions at post-sphaleron temperatures. We present the phenomenological constraints from flavor, neutron oscillations and collider physics. We detail predictions for the displaced vertex phenomenology at various facilities either approved of being proposed. Finally, we present a version of the model where baryon number is spontaneously broken, and explore the phenomenology associated with the resulting pNGB.

Speaker: Gustavo Burdman

Burdman_FLASY25.pdf

10:00 Topological Defects from Non-Abelian Discrete Symmetries

I will discuss the formation and properties of domain walls arising from the spontaneous breaking of non-Abelian discrete symmetries, with a focus on the group S4​, commonly used in models of lepton flavour. Such symmetry breaking leads to a rich vacuum structure and the emergence of various types of domain walls. While some of these walls are unstable and decay, others can be longer lived and eventually annihilate, releasing gravitational waves. I will explore the signatures of these processes and their potential relevance to recent gravitational wave observations.

Speaker: Jessica Turner (Durham University)

FLASY_2025_JT.pdf

10:30 Baryogenesis from cosmological CP violation

We show that baryogenesis can arise from the cosmological evolution of a scalar field that governs CP-violating parameters, such as the Yukawa couplings and the theta terms of the Standard Model. During the Big Bang, this scalar may reach a CP-violating minimum, where its mass can be comparable to the inflationary Hubble scale. Such dynamics can emerge in theories featuring either a spontaneously broken local U(1) symmetry or modular invariance. The latter is present in the effective field theory capturing the geometric origin of CP violation in toroidal string compactifications. Modular baryogenesis is compatible with the modular approach to solving the strong CP problem.

Speaker: Arsenii Titov (University of Padua and INFN)

Baryogenesis_FLASY2025_Titov.pdf

11:00 → 11:30 Coffee break

11:30 → 12:30 Morning session

Convener: Salvador Centelles Chuliá (IFIC (CSIC - U. Valencia))

11:30 Selection rules for cLFV processes from residual flavour groups

We systematically investigate the possible phenomenological impact of residual flavour groups in the charged lepton sector. We consider all possible flavour charge assignments for abelian residual symmetries up to Z8. The allowed flavour structures of operators in Standard Model Effective Field Theory (up to dimension six) lead to distinctive and observable patterns of cLFV processes. We illustrate the relevance of such selection rules displaying the current bounds on and the future sensitivities to the new physics scale. These results demonstrate, in particular, the importance and discriminating power of searches for cLFV tau lepton decays and muonium to antimuonium conversion.

Speaker: Claudia Hagedorn (IFIC - UV/CSIC)

Hagedorn_FLASY2025.pdf

12:00 Modular Flavour Symmetries

I will cover some attempts at solving the flavour problem that employ modular flavour symmetries.

Speaker: Ivo de Medeiros Varzielas (CFTP, IST)

Flasy_2025.pdf

12:30 → 14:30 Free time for lunch

14:30 → 16:00 Afternoon session

Convener: Davide Meloni (Istituto Nazionale di Fisica Nucleare)

14:30 Probing flavour symmetry and modular symmetry theories in ESSnuSB and other neutrino experiments

ESSnuSB is a proposed future accelerator based experiment in Sweden to study neutrino oscillation. The main aim of this experiment is to measure the leptonic CP phase $\delta_{\rm CP}$ by probing the second oscillation maximum. The other future long-baseline experiments which will also study the phenomenon of neutrino oscillations are T2HK in Japan and DUNE in USA which . Apart from measuring the oscillation parameters, these experiments are also capable to test the viability of different theoretical models which predict the values of $\delta_{\rm CP}$ and other oscillation parameters. Two examples of such theories are flavour symmetry models and theories arising from modular symmetries. In this presentation, first I will give an overview of the ESSnuSB and the other neutrino experiments and then discuss the capability of these experiments to constrain the parameter space of a set of lepton flavour models and theories arising from modular symmetries.

Speaker: Monojit Ghosh (Ruđer Bošković Institute, Zagreb, Croatia)

flasy_ghosh.pdf

flasy_ghosh.pptx

15:00 Goofy Symmetries

Speaker: Andreas Trautner

Trautner_FLASY_25.pdf

15:30 Spontaneous CP Violation in an Axion Model: Implications for Leptonic Flavor and the Minimal Seesaw

We investigate an extension of the Dine–Fischler–Srednicki–Zhitnitsky (DFSZ) axion model that realizes spontaneous CP violation and explores its implications for leptonic flavor structure within the framework of the minimal seesaw mechanism. By introducing singlet heavy Majorana neutrinos and an additional complex singlet scalar, we construct the extended Yukawa and scalar sectors necessary for radiatively generating the CP-violating quartic couplings at the 1-loop level. We demonstrate that the CP phase arising from the spontaneous breaking of symmetry propagates into the lepton sector, influencing the Dirac neutrino mass matrix and, consequently, the CP-violating phases of the Pontecorvo–Maki–Nakagawa–Sakata (PMNS) matrix. A benchmark numerical analysis confirms the compatibility of the model with current neutrino oscillation data and illustrates how low-energy leptonic CP violation can originate from the extended scalar dynamics. This framework offers a coherent link between axion physics, spontaneous CP violation, and the flavor structure of neutrinos.

Speaker: Sin Kyu Kang (Seoul National University of Science and Technolofy)

FLASY2026.pdf

SKKANG.pdf

16:00 → 16:30 Coffee break

16:30 → 16:40 End