Reinterpreting the ATLAS bounds on heavy neutral leptons in a realistic neutrino oscillation model

Heavy neutral leptons (HNLs) are hypothetical particles, motivated in the first place by their ability to explain neutrino oscillations. Experimental searches for HNLs are typically conducted under the assumption of a single HNL mixing with a single neutrino flavor. However, the resulting exclusion limits may not directly constrain the corresponding mixing angles in realistic HNL models — those which can explain neutrino oscillations. The reinterpretation of the results of these experimental searches turns out to be a non-trivial task, that requires significant knowledge of the details of the experiment. In this work, we perform a reinterpretation of the latest ATLAS search for HNLs decaying promptly to a tri-lepton final state. We show that in a realistic model with two HNLs, the actual limits can vary by several orders of magnitude depending on the free parameters of the model. Marginalizing over the unknown model parameters leads to an exclusion limit on the total mixing angle which can be up to 3 orders of magnitude weaker than the limits reported in ref. [1]. This demonstrates that the reinterpretation of results from experimental searches is a necessary step to obtain meaningful limits on realistic models. We detail a few steps that can be taken by experimental collaborations in order to simplify the reuse of their results.

Exploring the new physics phases in 3+1 scenario in neutrino oscillation experiments

The various global analyses of available neutrino oscillation data indicate the presence of the standard 3 + 0 neutrino oscillation picture. However, there are a few short baseline anomalies that point to the possible existence of a fourth neutrino (with mass in the eV-scale), essentially sterile in nature. Should sterile neutrino exist in nature and its presence is not taken into consideration properly in the analyses of neutrino data, the interference terms arising due to the additional CP phases in presence of a sterile neutrino can severely impact the physics searches in long baseline (LBL) neutrino oscillation experiments. In the current work we consider one light (eV-scale) sterile neutrino and probe all the three CP phases (δ13, δ24, δ34) in the context of the upcoming Deep Underground Neutrino Experiment (DUNE) and also estimate how the results improve when data from NOvA, T2K and T2HK are added in the analysis. We illustrate the ∆χ2 correlations of the CP phases among each other, and also with the three active-sterile mixing angles. Finally, we briefly illustrate how the relevant parameter spaces in the context of neutrinoless double beta decay get modified in light of the bounds in presence of a light sterile neutrino.

Type-I seesaw mechanism for neutrino mass and mixing in gauged B − L model with D4 × Z4 flavor symmetry

In this paper, we study a non-renormalizable [Formula: see text] extension of the Standard Model with [Formula: see text] and [Formula: see text] symmetries accommodating the most recent neutrino data within the type-I seesaw mechanism. The two squared mass differences and three mixing angles can get the best-fit values while the leptonic Dirac CP phase is in [Formula: see text] range of the best-fit values for both normal and inverted orderings. The sum of active neutrino mass and the effective neutrino masses are, respectively, predicted to be [Formula: see text], [Formula: see text] and [Formula: see text] for normal ordering while [Formula: see text], [Formula: see text] and [Formula: see text] for inverted ordering, which are well consistent with the current experimental constraints.

Search for signatures of sterile neutrinos with Double Chooz

We present a search for signatures of neutrino mixing of electron anti-neutrinos with additional hypothetical sterile neutrino flavors using the Double Chooz experiment. The search is based on data from 5 years of operation of Double Chooz, including 2 years in the two-detector configuration. The analysis is based on a profile likelihood, i.e. comparing the data to the model prediction of disappearance in a data-to-data comparison of the two respective detectors. The analysis is optimized for a model of three active and one sterile neutrino. It is sensitive in the typical mass range $${5 \times 10^{-3}}\,\mathrm{eV}^2 \lesssim \varDelta m^2_{41} \lesssim {3 \times 10^{-1}}\,\mathrm{eV}^2 $$ 5 × 10 - 3 eV 2 ≲ Δ m 41 2 ≲ 3 × 10 - 1 eV 2 for mixing angles down to $$\sin ^2 2\theta _{14} \gtrsim {0.02} $$ sin 2 2 θ 14 ≳ 0.02 . No significant disappearance additionally to the conventional disappearance related to $$\theta _{13} $$ θ 13 is observed and correspondingly exclusion bounds on the sterile mixing parameter $$\theta _{14} $$ θ 14 as a function of $$ \varDelta m^2_{41} $$ Δ m 41 2 are obtained.

Modulus τ linking leptonic CP violation to baryon asymmetry in A4 modular invariant flavor model

We propose an A4 modular invariant flavor model of leptons, in which both CP and modular symmetries are broken spontaneously by the vacuum expectation value of the modulus τ. The value of the modulus τ is restricted by the observed lepton mixing angles and lepton masses for the normal hierarchy of neutrino masses. The predictive Dirac CP phase δCP is in the ranges [0°, 50°], [170°, 175°] and [280°, 360°] for Re [τ] < 0, and [0°, 80°], [185°, 190°] and [310°, 360°] for Re [τ] > 0. The sum of three neutrino masses is predicted in [60, 84] meV, and the effective mass for the 0νββ decay is in [0.003, 3] meV. The modulus τ links the Dirac CP phase to the cosmological baryon asymmetry (BAU) via the leptogenesis. Due to the strong wash-out effect, the predictive baryon asymmetry YB can be at most the same order of the observed value. Then, the lightest right-handed neutrino mass is restricted in the range of M1 = [1.5, 6.5] × 1013 GeV. We find the correlation between the predictive YB and the Dirac CP phase δCP. Only two predictive δCP ranges, [5°, 40°] (Re [τ] > 0) and [320°, 355°] (Re [τ] < 0) are consistent with the BAU.

Modular origin of mass hierarchy: Froggatt-Nielsen like mechanism

We study Froggatt-Nielsen (FN) like flavor models with modular symmetry. The FN mechanism is a convincing solution to the flavor puzzle in the quark sector. The FN mechanism requires an extra U(1) gauge symmetry which is broken at high energies. Alternatively, in the framework of modular symmetry the modular weights can play the role of the FN charges of the extra U(1) symmetry. Based on the FN-like mechanism with modular symmetry we present new flavor models for the quark sector. Assuming that the three generations have a common representation under the modular symmetry, our models simply reproduce the FN-like Yukawa matrices. We also show that the realistic mass hierarchy and mixing angles, which are related to each other through the modular parameters and a scalar vev, can be realized in models with several finite modular groups (and their double covering groups) without unnatural hierarchical parameters.

Multiscalar B − L model with Σ(18) symmetry for neutrino mass and mixing

We construct a non-renormalizable [Formula: see text] model based on [Formula: see text] symmetry, whereby, neutrino mass ordering and the tiny neutrino masses are explained at tree level via type I seesaw mechanism. The model can reproduce the recent observed neutrino oscillation data in which neutrino oscillation parameters including three mixing angles [Formula: see text], Dirac CP phase plus neutrino squared-mass splittings [Formula: see text] get the best-fit values for both Normal ordering (NO) and Inverted ordering (IO). The Majorana phases are predicted to be [Formula: see text] for NO, [Formula: see text] for IO and [Formula: see text] for both NH and IO. The sum of neutrino mass and the effective neutrino mass are, respectively, predicted to be [Formula: see text] for NO while [Formula: see text] for IO and [Formula: see text] for NO while [Formula: see text] for IO which are well compatible with the most recent experimental constraints.

Model independent analysis of Dirac CP violating phase for some well-known mixing scenarios

In this paper, we present a model independent analysis of Leptonic CP violation for some well-known mixing scenarios. In particular, we considered modified schemes for bimaximal (BM), democratic (DC), hexagonal (HG) and tribimaximal (TBM) mixing for our numerical investigation. These model independent corrections to mixing matrices are parametrized in terms of complex rotation matrices [Formula: see text] with related modified PMNS matrix of the forms [Formula: see text] where [Formula: see text] is a complex rotation in [Formula: see text] sector and [Formula: see text] is unperturbed mixing scheme. We present generic formulae for mixing angles, Dirac CP phase [Formula: see text] and Jarlskog invariant [Formula: see text] in terms of correction parameters. The parameter space of each modified mixing case is scanned for fitting neutrino mixing angles using [Formula: see text] approach and the corresponding predictions for Leptonic CP phase [Formula: see text] and Jarlskog invariant [Formula: see text] has been evaluated from allowed parameter space. The obtained ranges are reported for all viable cases.

CP symmetry and symplectic modular invariance

We analyze CP symmetry in symplectic modular-invariant supersymmetric theories. We show that for genus g\ge 3g≥3 the definition of CP is unique, while two independent possibilities are allowed when g\le 2g≤2. We discuss the transformation properties of moduli, matter multiplets and modular forms in the Siegel upper half plane, as well as in invariant subspaces. We identify CP-conserving surfaces in the fundamental domain of moduli space. We make use of all these elements to build a CP and symplectic invariant model of lepton masses and mixing angles, where known data are well reproduced and observable phases are predicted in terms of a minimum number of parameters.