Abelian Flavor Symmetry Research Articles

Froggatt-Nielsen meets the SMEFT

We study the matching of Froggatt-Nielsen theories of flavour onto the Standard Model Effective Field Theory (SMEFT), upon integrating out a heavy Beyond-the-Standard-Model (BSM) scalar ‘flavon’ whose vacuum expectation value breaks an Abelian flavour symmetry at energies ΛFN well above the electroweak scale, ΛFN> ΛSM. We include matching contributions to the infrared dSM = 6 (Warsaw basis) SMEFT sourced from ultraviolet contact terms suppressed up to order 1/ΛUV2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ {\\Lambda}_{\ extrm{UV}}^2 $$\\end{document} in the Froggatt-Nielsen Lagrangian, where ΛUV> ΛFN is an arbitrary ultraviolet scale where further unspecified BSM particles are dynamical. This includes tree-level (one-loop) ultraviolet diagrams with dFN = 6 (5) effective vertices. We first do so with a toy model, but then generalize our findings to arbitrary Frogatt-Nielsen charges. Our results indicate a rich and non-trivial signature of Froggatt-Nielsen theories on the (otherwise) model-independent operators of the SMEFT, and we briefly speculate on extending our analysis to broader classes of BSM flavour models, e.g. non-Abelian and/or gauged theories. We thus take an important step towards determining how to use rapidly developing theoretical and experimental SMEFT technologies to gain unambiguous insight into the SM’s longstanding fermion flavour puzzle.

Minimal U(1) two-Higgs-doublet models for quark and lepton flavor

In the context of the 2HDM, and assuming that neutrinos acquire masses via the Weinberg operator, we perform a systematic analysis to determine the minimal quark and lepton flavor patterns, compatible with masses, mixing and CP violation data, realizable by Abelian symmetries. We determine four minimal models for quarks, where the number of independent parameters matches the number of observables. For the lepton sector, three minimal predictive models are identified. Namely, we find scenarios with a preference for the upper/lower octant of the θ23 atmospheric mixing angle, that exhibit lower bounds on the lightest neutrino masses currently probed by cosmology and testable at future neutrinoless double beta decay experiments, even for a normally ordered neutrino masses. We investigate the phenomenology of each model taking into account all relevant theoretical, electroweak precision observables, scalar sector constraints, as well as stringent quark flavor processes such as B¯→Xsγ, Bs→μ−μ+ and meson oscillations, and the charged lepton flavor-violating decays eα−→eβ−eγ+eδ− and eα→eβγ. We show that, in some cases, Abelian flavor symmetries provide a natural framework to suppress flavor-changing neutral couplings and lead to scenarios featuring heavy neutral/charged scalar masses below the TeV scale within the reach of current experiments. Published by the American Physical Society 2024

S1 reduction of 4D mathcal{N} = 3 SCFTs and squashing independence of ABJM theories

We study the compactification of 4D mathcal{N} = 3 superconformal field theories (SCFTs) on S1, focusing on the relation between the 4D superconformal index and 3D partition function on the squashed sphere {S}_b^3 . Since the center mathfrak{u} (1) of the mathfrak{u} (3) R-symmetry of the 4D theory can mix with an mathcal{N} = 6 abelian flavor symmetry in three dimensions, the precise 4D/3D relation for the global symmetry is not obvious. Focusing on the case in which the 3D theory is the ABJM theory, we demonstrate that the above R-symmetry mixing can be precisely identified by considering the Schur limit (and/or its mathcal{N} = 3 cousin) of the 4D index. As a result, we generalize to the ABJM theories recent discussions on the connection between supersymmetry enhancement of the 4D index and squashing independence of the {S}_b^3 partition function.

Flavor changing flavon decay ɸ→tc (ɸ = HF, AF ) at the high luminosity large hadron collider

We present a study of the flavor changing decays φ → tc (φ = HF, AF ) of the CP-even and CP-odd scalar flavons at the large hadron collider and its next stage, the high-luminosity large hadron collider. The theoretical framework is an extension of the standard model that incorporates an extra complex singlet and invokes the Froggatt-Nielsen mechanism with an Abelian flavor symmetry. The projected exclusion and discovery regions in terms of the model parameters are reported. We find that AF could be detected at the LHC by considering a reasonable scenario of the model parameter space. As far as HF is concerned, we also found promising results that could be verified experimentally at the high-luminosity LHC.

Neutrino mixing and leptogenesis in a L_e-L_mu -L_tau model

We present a simple extension of the Standard Model with three right-handed neutrinos in a SUSY framework, with an additional hbox {U}(1)_text {F} abelian flavor symmetry with a non standard leptonic charge L_e-L_mu -L_tau for lepton doublets and arbitrary right-handed charges. Our model predicts an inverted neutrino mass hierarchy and it is able to reproduce the experimental values of the mixing angles of the PMNS matrix and of the r=Delta m_text {sun}^2/Delta m_text {atm}^2 ratio, with only a moderate fine tuning of the Lagrangian free parameters. The baryon asymmetry of the Universe is generated via thermal leptogenesis through CP-violating decays of the heavy right-handed neutrinos. We present a detailed numerical solution of the relevant Boltzmann equation, accounting for the impact of the distribution of the asymmetry in the various lepton flavors.

A split seesaw model with hidden neutrinoless double beta decay but successful leptogenesis

In a paper by Asaka, Ishida and Tanaka (Phys. Rev. D 103:015014, 2021), they proposed a novel possibility (which will be referred to as the AIT ansatz) that, in spite of the Majorana nature of neutrinos, the neutrinoless double beta (0nu beta beta ) decay can be hidden. In the original AIT model, the AIT ansatz is realized in the minimal seesaw model with two right-handed neutrinos which have a hierarchical mass structure: the lighter and heavier right-handed neutrinos are respectively much lighter and heavier than the typical Fermi-momentum scale of nuclei. However, the original AIT model does not accommodate a successful leptogenesis. For this problem, in this paper we study a split seesaw model with one lighter right-handed neutrino but two heavier right-handed neutrinos which can realize the AIT ansatz and accommodate a successful leptogenesis simultaneously. We first give the condition on the neutrino Yukawa couplings for realizing the AIT ansatz, discuss its realization by employing an Abelian flavor symmetry, and study its implications for the mixing of the lighter right-handed neutrino with three left-handed neutrinos. We then successively study the implications for leptogenesis of the interesting scenarios where M_{{textrm{D}}} is a triangular matrix (which has maximally-restricted texture zeros, in line with the simplicity principle) or respects the mu -tau reflection symmetry (which is well motivated by the experimental results), on top of the AIT ansatz.

Neutrino Masses and Leptogenesis in a Le − Lμ − Lτ model

We present a simple extension of the Standard Model with three right-handed neutrinos in a SUSY framework, with an additional U(1)F abelian flavor symmetry with a non standard leptonic charge for lepton doublets and arbitrary right-handed charges. We show how it is possible to provide the correct predictions for the mixing angles of the PMNS matrix and for the parameter with a moderate fine tuning. The baryon asymmetry of the Universe is generated via thermal leptogenesis through CP-violating decays of the heavy right-handed neutrinos. We present a detailed numerical solution of the relevant Boltzmann equation accounting for the impact of the distribution of the asymmetry in the lepton flavors.

Texture of one equality in neutrino mass matrix

We carry out a phenomenological and analytical study of the texture structures for the Majorana neutrino mass matrix characterized by one single equality between two independent matrix elements, with vanishing non-physical phases whose role in the definition we clarify. We find that fourteen textures are viable in both types of hierarchy, whereas the remaining fifteenth one is viable only in normal hierarchy. We also present symmetry realizations for some patterns by using Abelian flavor symmetries within type-I, type-II and mixed type-(I+II) seesaw scenarios.

Monodromy defects in free field theories

We study co-dimension two monodromy defects in theories of conformally coupled scalars and free Dirac fermions in arbitrary d dimensions. We characterise this family of conformal defects by computing the one-point functions of the stress-tensor and conserved current for Abelian flavour symmetries as well as two-point functions of the displacement operator. In the case of d = 4, the normalisation of these correlation functions are related to defect Weyl anomaly coefficients, and thus provide crucial information about the defect conformal field theory. We provide explicit checks on the values of the defect central charges by calculating the universal part of the defect contribution to entanglement entropy, and further, we use our results to extract the universal part of the vacuum Rényi entropy. Moreover, we leverage the non-supersymmetric free field results to compute a novel defect Weyl anomaly coefficient in a d = 4 theory of free mathcal{N} = 2 hypermultiplets. Including singular modes in the defect operator product expansion of fundamental fields, we identify notable relevant deformations in the singular defect theories and show that they trigger a renormalisation group flow towards an IR fixed point with the most regular defect OPE. We also study Gukov-Witten defects in free d = 4 Maxwell theory and show that their central charges vanish.

Minimal inverse-seesaw mechanism with Abelian flavour symmetries

We study the phenomenology of the minimal (2, 2) inverse-seesaw model supplemented with Abelian flavour symmetries. To ensure maximal predictability, we establish the most restrictive flavour patterns which can be realised by those symmetries. This setup requires adding an extra scalar doublet and two complex scalar singlets to the Standard Model, paving the way to implement spontaneous CP violation. It is shown that such CP-violating effects can be successfully communicated to the lepton sector through couplings of the scalar singlets to the new sterile fermions. The Majorana and Dirac CP phases turn out to be related, and the active-sterile neutrino mixing is determined by the active neutrino masses, mixing angles and CP phases. We investigate the constraints imposed on the model by the current experimental limits on lepton flavour-violating decays, especially those on the branching ratio BR(μ → eγ) and the capture rate CR(μ − e, Au). The prospects to further test the framework put forward in this work are also discussed in view of the projected sensitivities of future experimental searches sensitive to the presence of heavy sterile neutrinos. Namely, we investigate at which extent upcoming searches for μ → eγ, μ → 3e and μ − e conversion in nuclei will be able to test our model, and how complementary will future high-energy collider and beam-dump experiments be in that task.

Coulomb and Higgs branches from canonical singularities. Part 0

Five- and four-dimensional superconformal field theories with eight supercharges arise from canonical threefold singularities in M-theory and Type IIB string theory, respectively. We study their Coulomb and Higgs branches using crepant resolutions and deformations of the singularities. We propose a relation between the resulting moduli spaces, by compactifying the theories to 3d, followed by 3d mathcal{N} = 4 mirror symmetry and an S-type gauging of an abelian flavor symmetry. In particular, we use this correspondence to determine the Higgs branch of some 5d SCFTs and their magnetic quivers from the geometry. As an application of the general framework, we observe that singularities that engineer Argyres-Douglas theories in Type IIB also give rise to rank-0 5d SCFTs in M-theory. We also compute the higher-form symmetries of the 4d and 5d SCFTs, including the one-form symmetries of generalized Argyres-Douglas theories of type (G, G′).

Anomaly-free 2HDMs with a gauged Abelian symmetry and two generations of right-handed neutrinos

Despite the popularity of two-Higgs-doublet models (2HDMs) with a gauged abelian flavor symmetry, the allowed Yukawa textures have only been partly explored so far. In this work, we classify and compare every anomaly-free instance, in the case of having two generations of right-handed neutrinos and a type-I seesaw mechanism. We found 16 valid implementations in total, out of which 11 agree well with current experimental bounds. To our knowledge, neither of these models have been considered previously.

Testing lepton flavor models at ESSnuSB

We review and investigate lepton flavor models, stemming from discrete non- Abelian flavor symmetries, described by one or two free model parameters. First, we confront eleven one- and seven two-parameter models with current results on leptonic mixing angles from global fits to neutrino oscillation data. We find that five of the one- and five of the two-parameter models survive the confrontation test at 3σ. Second, we investigate how these ten one- and two-parameter lepton flavor models may be discriminated at the proposed ESSnuSB experiment in Sweden. We show that the three one-parameter models that predict sin δCP = 0 can be distinguished from those two that predict | sin δCP| = 1 by at least 7σ. Finally, we find that three of the five one-parameter models can be excluded by at least 5σ and two of the one-parameter as well as at most two of the five two-parameter models can be excluded by at least 3σ with ESSnuSB if the true values of the leptonic mixing parameters remain close to the present best-fit values.

Supersymmetry anomalies in new minimal supergravity

We determine the general structure of quantum anomalies for the R-multiplet of four dimensional mathcal{N} = 1 supersymmetric quantum field theories in the presence of background fields for an arbitrary number of Abelian flavor multiplets. By solving the Wess-Zumino consistency conditions for off-shell new minimal supergravity in four dimensions with an arbitrary number of Abelian vector multiplets, we compute the anomaly in the conservation of the supercurrent to leading non trivial order in the gravitino and vector multiplet fermions. We find that both R-symmetry and flavor anomalies necessarily lead to a supersymmetry anomaly, thus generalizing our earlier results to non superconformal theories with Abelian flavor symmetries. The anomaly in the conservation of the supercurrent leads to an anomalous transformation for the supercurrent under rigid supersymmetry on bosonic backgrounds that admit new minimal Killing spinors. The resulting deformation of the supersymmetry algebra has implications for supersymmetric localization computations on such backgrounds.

A \u03bc-\u03c4-philic scalar doublet under Zn flavor symmetry

We propose a minimal model which accommodates the long-standing anomaly of muon magnetic moment based on abelian discrete flavor symmetries. The standard model is extended by scalar doublets charged under a Zn lepton flavor symmetry. In these models, a large contribution to the muon magnetic moment can be obtained by the chirality enhancement from new scalar mediated diagrams without conflicting with the flavor symmetry. Thanks to the lepton flavor symmetry, these models automatically forbid lepton flavor violation. The minimal model is based on Z4 symmetry with only one extra scalar doublet. In this model, we show that the parameter space favored by the muon g − 2 can easily be consistent with experimental constraints and theoretical bounds such as the electroweak precision tests, lepton universality, potential stability condition and triviality bound as well as the LHC direct search mass bound. The new contributions to the muon electric dipole moment and the Higgs decay into γγ can be indirect signals of the model.

Simplified models of flavourful leptoquarks

We study the implications of single leptoquark extensions of the Standard Model (SM) under the assumption that their enhanced Yukawa sectors are invariant under global Abelian flavour symmetries already present in SM mass terms. Such symmetries, assumed to be the ‘residual’ subgroups of an ultra-violet flavour theory, have previously been considered in order to predict fermionic mixing angles. Here we focus instead on their effect on the novel flavour structures sourced by the leptoquark representations that address the present {R}_{K^{(star )}} anomalies in semileptonic rare B-decays. Combined with existing flavour data, the residual symmetries prove to be extremely constraining; we find that the (quark-lepton) leptoquark Yukawa couplings fall within mathcal {O}(10) highly predictive patterns, each with only a single free parameter, when ‘normal’ (SM-like) hierarchies are assumed. In addition, proton decay for the scalar SU(2) triplet representation is naturally avoided in the residual symmetry approach without relying on further model building. Our results indicate that a simultaneous explanation for the {R}_{K^{(star )}} anomalies and the flavour puzzle may be achieved in a simplified, model-independent formalism.

Understanding of two-zero textures of neutrino mass matrices in minimal extended seesaw mechanism and their symmetry realization

We study the texture zeros of [Formula: see text] neutrino mass matrices [Formula: see text] in the minimal extended type-I seesaw (MES) mechanism, incorporating one extra gauge singlet field “[Formula: see text]”. The [Formula: see text] MES model deals with [Formula: see text] [Formula: see text], [Formula: see text] [Formula: see text] and [Formula: see text] mass matrix [Formula: see text] which couples the right-handed neutrinos and the singlet field “[Formula: see text]”. We carry out the mapping of all possible zero textures of [Formula: see text], [Formula: see text] and [Formula: see text] with the restriction to phenomenologically predictive cases having total eight zeros of [Formula: see text] and [Formula: see text] studied in the literature. If [Formula: see text], the sterile neutrino mass, is subject to any limit, further block diagonalization of [Formula: see text] shall not be allowed to reduce it to a [Formula: see text] matrix. In [Formula: see text] [Formula: see text] scenario, the study of texture zero is totally different and interesting. With this motivation, we consider the [Formula: see text] scheme where the digits of the pair represent the number of zeros of [Formula: see text] and [Formula: see text], respectively, along with the one/two-zero textures of [Formula: see text]. There are a large number of possibilities of zeros of fermion mass matrices, but the implementation of [Formula: see text] transformations reduces it to a very minimum number of basic structures. As the [Formula: see text] MES matrix is a matrix of rank 3, so we consider only those textures with two zeros which are of rank 3 whereby the number of feasible zero textures reduces to 12, out of 15. On realizing these 12 textures under MES mechanism with [Formula: see text] picture, we arrive at certain correlations for each texture. We examine the viability of each texture by scanning their respective correlations under recent neutrino oscillation data. Also, we discuss the interplay of Dirac and Majorana CP phases in determining the viability of a texture. The allowed two-zero textures are finally realized using a discrete Abelian flavor symmetry group [Formula: see text] with the extension of Standard Model to include some scalar fields.

Exploring 2-group global symmetries

We analyze four-dimensional quantum field theories with continuous 2-group global symmetries. At the level of their charges, such symmetries are identical to a product of continuous flavor or spacetime symmetries with a 1-form global symmetry U(1)B(1), which arises from a conserved 2-form current JB(2). Rather, 2-group symmetries are characterized by deformed current algebras, with quantized structure constants, which allow two flavor currents or stress tensors to fuse into JB(2). This leads to unconventional Ward identities, which constrain the allowed patterns of spontaneous 2-group symmetry breaking and other aspects of the renormalization group flow. If JB(2) is coupled to a 2-form background gauge field B(2), the 2-group current algebra modifies the behavior of B(2) under background gauge transformations. Its transformation rule takes the same form as in the Green-Schwarz mechanism, but only involves the background gauge or gravity fields that couple to the other 2-group currents. This makes it possible to partially cancel reducible ’t Hooft anomalies using Green-Schwarz counterterms for the 2-group background gauge fields. The parts that cannot be cancelled are reinterpreted as mixed, global anomalies involving U(1)B(1), which receive contributions from topological, as well as massless, degrees of freedom. Theories with 2-group symmetry are constructed by gauging an abelian flavor symmetry with suitable mixed ’t Hooft anomalies, which leads to many simple and explicit examples. Some of them have dynamical string excitations that carry U(1)B(1) charge, and 2-group symmetry determines certain ’t Hooft anomalies on the world sheets of these strings. Finally, we point out that holographic theories with 2-group global symmetries have a bulk description in terms of dynamical gauge fields that participate in a conventional Green-Schwarz mechanism.

Combined explanations of (g−2)μ,e and implications for a large muon EDM

With the long-standing tension between experiment and Standard-Model (SM) prediction in the anomalous magnetic moment of the muon, $a_\mu=(g-2)_\mu/2$, at the level of 3-4$\sigma$, it is natural to ask if there could be a sizable effect in the electric dipole moment (EDM) $d_\mu$ as well. In this context it has often been argued that in UV complete models the electron EDM, which is very precisely measured, excludes a large effect in $d_\mu$. However, the recently observed 2.5$\sigma$ tension in $a_e=(g-2)_e/2$, if confirmed, requires that the muon and electron sectors effectively decouple to avoid constraints from $\mu\to e\gamma$. We briefly discuss UV complete models that possess such a decoupling, which can be enforced by an Abelian flavor symmetry $L_\mu-L_\tau$. We show that, in such scenarios, there is no reason to expect a correlation between the electron and muon EDM, so that the latter can be sizable. New limits on $d_\mu$ improved by up to two orders of magnitude are expected from the upcoming $(g-2)_\mu$ experiments at Fermilab and J-PARC. Beyond, a proposed dedicated muon EDM experiment at PSI could further advance the limit. In this way, future improved measurements of $a_e$, $a_\mu$, as well as the fine-structure constant $\alpha$ are not only set to provide exciting precision tests of the SM, but, in combination with EDMs, to reveal crucial insights into the flavor structure of physics beyond the SM.

Charting the flavor landscape of MSSM-like Abelian heterotic orbifolds

Discovering a selection principle and the origin of flavor symmetries from an ultraviolet completion of particle physics is an interesting open task. As a step in this direction, we classify all possible flavor symmetries of 4D massless spectra emerging from supersymmetric Abelian orbifold compactifications, including roto-translations and non-factorizable compact spaces, for generic moduli values. Although these symmetries are valid in all string theories, we focus on the E8 x E8 heterotic string. We perform the widest known search of E8 x E8 Abelian orbifold compactifications, yielding over 121,000 models with MSSM-like features. About 75.4% of these models exhibit flavor symmetries containing D4 factors and only nearly 1.2% have Delta(54) factors. The remaining models are furnished with purely Abelian flavor symmetries. Our findings suggest that, should particle phenomenology arise from a heterotic orbifold, it could accommodate only one of these flavor symmetries.