Implications of the Muon g-2 result on the flavour structure of the lepton mass matrix

The confirmation of the discrepancy with the Standard Model predictions in the anomalous magnetic moment by the Muon g-2 experiment at Fermilab points to a low scale of new physics. Flavour symmetries broken at low energies can account for this discrepancy but these models are much more restricted, as they would also generate off-diagonal entries in the dipole moment matrix. Therefore, if we assume that the observed discrepancy in the muon $$g-2$$ g - 2 is explained by the contributions of a low-energy flavor symmetry, lepton flavour violating processes can constrain the structure of the lepton mass matrices and therefore the flavour symmetries themselves predicting these structures. We apply these ideas to several discrete flavour symmetries popular in the leptonic sector, such as $$\Delta (27)$$ Δ ( 27 ) , $$A_4$$ A 4 , and $$A_5 < imes \mathrm{CP}$$ A 5 ⋉ CP .

A New Generation of Neutrino Cross Section Experiments: Challenges and Opportunities

Our knowledge of neutrino cross sections at the GeV scale, instrumental to test CP symmetry violation in the leptonic sector, has grown substantially in the last two decades. Still, their precision and understanding are far from the standard needed in contemporary neutrino physics. Nowadays, the knowledge of the neutrino cross section at O(10%) causes the main systematic uncertainty in oscillation experiments and jeopardizes their physics reach. In this paper, we envision the opportunities for a new generation of cross section experiments to be run in parallel with DUNE and HyperKamiokande. We identify the most prominent physics goals by looking at the theory and experimental limitations of the previous generation of experiments. We highlight the priorities in the theoretical understanding of GeV cross sections and the experimental challenges of this new generation of facilities.

Flavor invariants and renormalization-group equations in the leptonic sector with massive Majorana neutrinos

In the present paper, we carry out a systematic study of the flavor invariants and their renormalization-group equations (RGEs) in the leptonic sector with three generations of charged leptons and massive Majorana neutrinos. First, following the approach of the Hilbert series from the invariant theory, we show that there are 34 basic flavor invariants in the generating set, among which 19 invariants are CP-even and the others are CP-odd. Any flavor invariants can be expressed as the polynomials of those 34 basic invariants in the generating set. Second, we explicitly construct all the basic invariants and derive their RGEs, which form a closed system of differential equations as they should. The numerical solutions to the RGEs of the basic flavor invariants have also been found. Furthermore, we demonstrate how to extract physical observables from the basic invariants. Our study is helpful for understanding the algebraic structure of flavor invariants in the leptonic sector, and also provides a novel way to explore leptonic flavor structures.

Low scale leptogenesis in a model with promising CP structure

We consider a simple extension of the standard model, which could give a solution to itsCPissues through both the Peccei–Quinn mechanism and the Nelson–Barr mechanism. Its low energy effective model coincides with the scotogenic model in the leptonic sector. Although leptogenesis is known not to work well at lower reheating temperature than$$10^9$$109 GeV in simple seesaw and scotogenic frameworks, such low reheating temperature could be consistent with both neutrino mass generation and thermal leptogenesis via newly introduced fields without referring to the resonance effect. An alternative dark matter candidate to axion is prepared as an indispensable ingredient of the model.

Neutrinos: Present and future of long baseline experiments

The results from two currently running long-baseline neutrino experiments T2K and NO[Formula: see text]A are presented, along with physics program for the next generation experiments — Hyper-K and DUNE. I will focus on hints and prospects of the discovery of CP violation in the leptonic sector.

Jarlskog determinant and data on flavor matrices

The essences of the weak [Formula: see text] violation, the quark and lepton Jarlskog invariants, are determined toward future model buildings beyond the Standard Model (SM). The equivalence of two calculations of Jarlskog invariants gives a bound on the [Formula: see text] phase in some parametrization. Satisfying the unitarity condition, we obtain the CKM and PMNS matrices from the experimental data, and present the results in matrix forms. The Jarlskog determinant [Formula: see text] in the quark sector is found to be [Formula: see text] while [Formula: see text] in the leptonic sector is [Formula: see text] in the normal hierarchy parametrization.

Sensitivity of Discrete Symmetry Tests in the Positronium System with the J-PET Detector

Study of certain angular correlations in the three-photon annihilations of the triplet state of positronium, the electron–positron bound state, may be used as a probe of potential CP and CPT-violating effects in the leptonic sector. We present the perspectives of CP and CPT tests using this process recorded with a novel detection system for photons in the positron annihilation energy range, the Jagiellonian Positron Emission Tomography (J-PET). We demonstrate the capability of this system to register three-photon annihilations with an unprecedented range of kinematical configurations and to measure the CPT-odd correlation between positronium spin and annihilation plane orientation with a precision improved by at least an order of magnitude with respect to present results. We also discuss the means to control and reduce detector asymmetries in order to allow J-PET to set the first measurement of the correlation between positronium spin and momentum of the most energetic annihilation photon which has never been studied to date.

Phenomenology of the partially aligned 2HDM with leptonic meson decays

In this paper we present a phenomenological analysis of the Partially Aligned Two Higgs Doublet Model (PA-2HDM) by using leptonic decays of mesons and [Formula: see text]–[Formula: see text] mixing. We focus our attention in a scenario where the leading contribution to FCNC is given by the tree-level interaction with the light pseudoscalar [Formula: see text] ([Formula: see text] GeV). We show how an underlying flavor symmetry controls FCNC in the quark and lepton couplings with the pseudoscalar, without alignment between Yukawa matrices. Upper bounds on the free parameters are calculated in the context of the leptonic decays [Formula: see text] and [Formula: see text] and [Formula: see text] mixing. Also, our assumptions imply that bounds on New Physics contribution in the quark sector coming from [Formula: see text] mixing impose an upper bound on the parameters for the leptonic sector. Finally we give predictions of branching ratios for leptonic decay of mesons with FCNC and LFV.

Studying background processes of the exotic neutrino-nucleus reactions

The background processes of the flavour changing neutral current (FCNC) processes, predicted by various new-physics models to occur in the presence of nuclei, are examined by computing the relevant nuclear matrix elements within the context of the quasi-particle RPA using realistic strong two-body forces. Our main goal is to explore the role of the non-standard interactions (NSI) in the leptonic sector and specifically: (i) in lepton flavour violating (LFV) processes involving neutrinos νl and ν ̃l, l = e, μ, τ and (ii) in charged lepton flavour violating (cLFV) processes involving the charged leptons l− or l+. As concrete nuclear system we have chosen the stopping target of μ− → e− conversion experiment, i.e. the 48Ti nucleus of the PRIME/PRISM experiment at J-PARC. This experiment has been designed to reduce the single event sensitivity down to 10−16–10−18 in searching for charged lepton mixing events. We also present, stringent constraints on the flavour violating parameters entering the NSI Lagrangians that have been obtained by taking advantage of our detailed nuclear structure calculations and exploiting the present limits or the sensitivity of the proposed exotic μ− → e− experiments.