Dirac CP-violating Phase Research Articles

A lepton model with nearly Cobimaximal mixing

Cobimaximal mixing predicts π/4 and 3π/2 for the atmospheric angle and the Dirac CP-violating phase, respectively. These values are in tension with the neutrino global fits. If this pattern was behind the lepton mixings, then it would have to be broken. In that case, in this paper, we explore the S3 flavor symmetry within the B − L gauge model where the aforementioned scheme comes from the neutrino sector but the charged lepton contribution breaks the well known predictions so the mixing observables as well as the mee mass can be accommodated quite well according to the available data. Notably, the predicted regions for the Dirac CP-violating phase would allow us to test the model in future experiments.

Neutrino Phenomenology and keV Dark Matter in the Two-Higgs Doublet Model with A4 Symmetry

Abstract We propose a minimal extended seesaw scheme based on the discrete symmetry $A_4\times Z_4\times Z_2\times Z_8$, which can successfully address neutrino phenomenology and keV sterile neutrino dark matter. The lepton mass hierarchy is naturally achieved. Active neutrino mixing angles can reached the best-fit points with the predictive Dirac CP violation phase. The active–sterile mixing matrix elements are small enough to access the observed cosmological dark matter abundance constraint with keV sterile neutrino dark matter. The effective neutrino masses are predicted to be in the ranges of the recent experimental limits.

Dirac CP violation phase in the neutrino sector with A4 flavour symmetry

Dear Editors, On behalf of all co-authors i would like to submit our paper entitled " Dirac CP violation phase in the neutrino sector with A4 flavour symmetry " for publication in the VNU Journal ò Science: Mathematics and Physics. Looking forward to hearing from you. With best regards, Trần Tiến Mạnh

A minimal inverse seesaw model with S4 flavour symmetry

We construct an S4 flavour symmetric minimal inverse seesaw model where the standard model is extended by adding two right-handed and two standard model gauge singlet neutrinos to explain the origin of tiny neutrino masses. The resulting model describes the lepton mass spectra and flavour mixing quite well for the case of the normal hierarchy of neutrino masses. The prediction of the model on the Dirac CP-violating phase is centered around 370.087°. Furthermore, using the allowed region for the model parameters, we have calculated the value of the effective Majorana neutrino mass, |〈mee〉|, which characterizes neutrinoless double beta decay.

Three Neutrinos and the Formula for the Dirac CP Violation Phase

Three Neutrinos and the Formula for the Dirac CP Violation Phase

Confronting the prediction of leptonic Dirac CP -violating phase with experiments

We update and improve past efforts to predict the leptonic Dirac CP-violating phase with models that predict perturbatively modified tribimaximal or bimaximal mixing. Simple perturbations are applied to both mixing patterns in the form of rotations between two sectors. By translating these perturbed mixing matrices to the standard parameterization for the neutrino mixing matrix we derive relations between the Dirac CP-phase and the oscillation angles. We use these relations together with current experimental results to constrain the allowed range for the CP-phase and determine its probability density. Furthermore, we elaborate on the prospects for future experiments probing on the perturbations considered in this work. We present a model with $A_4$ modular symmetry that is consistent with one of the described perturbed scenarios and successfully predicts current oscillation parameter data.

Flavour and dark matter in a scoto/type-II seesaw model

The neutrino mass and dark matter (DM) problems are addressed in a Standard Model extension where the type-II seesaw and scotogenic mechanisms coexist. The model features a flavour \U0001d4b58 discrete symmetry which is broken down to a \U0001d4b52, stabilising the (scalar or fermion) DM particle. Spontaneous CP violation is implemented through the complex vacuum expectation value of a singlet scalar field, inducing observable CP-violating effects in the lepton sector. The structure of the effective neutrino mass matrix leads to constraints on the low-energy neutrino observables, namely the atmospheric neutrino mixing angle θ23, the Dirac CP-violating phase δ and the absolute neutrino mass scale mlightest. In particular, in most cases, the model selects one θ23 octant with δ ≃ 3π/2. Moreover, the obtained lower bounds on mlightest are typically in the range probed by cosmology. We also analyse the constraints imposed on the model by current experimental limits on charged lepton flavour violating (cLFV) processes, as well as future projected sensitivities. It is shown that the Higgs triplet and scotogenic contributions to cLFV never overlap and that the interplay among Yukawa couplings, dark charged scalar masses and mixing leads to a wide parameter-space region compatible with current experimental bounds. We investigate the scalar and fermion DM parameter space of our model by considering relic density, direct-detection (DD) and collider constraints. For scalar DM the mass interval 68 GeV ≲ mDM ≲ 90 GeV is viable and will be probed by future DD searches. In the fermion DM case, correct relic density is always obtained for mDM ≳ 45 GeV thanks to dark fermion-scalar coannihilation channels.

Next-to-tribimaximal mixing against CP violation and baryon asymmetry signs

Four next-to-tribimaximal (NTBM) mixing patterns are widely considered as the feasible candidates for the observed leptonic mixing structure. With the recent measurements from T2K, as well as intensive global fits, the interval of $\sin\delta_{ CP} > 0$ for the Dirac CP-violating phase is persistently small in the normal ordering while $\sin\delta_{ CP} < 0$ is successively obtained up to $3\sigma$ level in the inverted ordering. In this paper, we advocate the fitting results of Dirac CP-violating phase as a constraint, and show that, it can basically rule out half of the regions allowed by the constraint from three mixing angles only. In addition, given the small $\sin\delta_{ CP} > 0$ interval, we find that a unique NTBM pattern can be selected out of the four candidates within $3\sigma$ uncertainty of the latest NuFIT 5.1, when the patterns are exposed to a Yukawa texture-independent leptogenesis for the baryon asymmetry of the Universe. For the surviving pattern, we find an interesting correlation between the Dirac CP-violating phase and the octant of atmospheric angle $\theta_{23}$ , where $\theta_{23}>45^\circ$ can be predicted once $5\pi/6 < \delta_{CP} <\pi$ in the normal ordering can be confirmed in the future measurements.

Primordial neutrino asymmetry evolution with full mean-field effects and collisions

Neutrino oscillations and mean-field effects considerably enrich the phenomenology of neutrino evolution in the early Universe. Taking into account these effects, most notably the neutrino self-interaction mean-field contribution, we revisit the problem of the evolution of primordial neutrino asymmetries including for the first time the complete expression for collisions, which describe scattering and annihilations with electrons/positrons and reactions among (anti)neutrinos. We show that a generalisation of the adiabatic transfer of averaged oscillations (ATAO) scheme, a numerical method previously developed without neutrino degeneracy and based on the large separation of time scales in this problem, is sufficient to reach the same accuracy as the full quantum kinetic equation integration, but is notably faster. This approximation highlights the physics of synchronous oscillations at play in the evolution of neutrino chemical potentials, especially in the particular case with only two-neutrino mixing. In particular, it allows to understand what controls the beginning and the amplitude of oscillations, but also why there is a subsequent regime of collective oscillations with larger frequencies. We also find that it is very important to use the full collision term instead of relying on damping-like approximations, in order not to overestimate how collisions reduce these synchronous oscillations. Finally we study qualitatively how mixing parameters affect the final neutrino configuration, and in particular we show that the CP-violating Dirac phase cannot substantially affect the final N eff nor the final electronic (anti)-neutrino spectrum, and thus should not affect cosmological observables.

Fermion spectrum with normal neutrino mass ordering in a nonrenormalizable [formula omitted] model based on [formula omitted] symmetry

We construct a nonrenormalizable B−L model with Σ(18)×Z2 symmetry that can explain the observed SM quark mass and mixing pattern as well as the neutrino oscillation data with normal mass ordering in which the best-fit values of the large atmospheric neutrino mixing angle θ23 and the Dirac CP-violating phase δCP are located in the higher octant and third quadrant, respectively. The smallness of the active neutrino mass is generated from type I-seesaw mechanism with only one SU(2)L Higgs doublet. In numerical analysis, we consider the neutrino oscillation parameters, including two neutrino mass squared differences Δm212,Δm312, three mixing angles s122,s132,s232 and one Dirac CP violating phase δ, as input parameters and find out the other undetermined neutrino parameters including the sum of neutrino masses, the effective neutrino mass 〈mee〉 and three free parameters α,ω12 and ω22. The sum of neutrino masses and the effective neutrino masses are respectively predicted to be Σmν=76.7meV and 〈mee〉=13.0meV which are well consistent with the recent experimental constraints. The quark masses are in good agreement with the recent experimental data while the quark mixings are consistent with the recent constraints on the CKM matrix.

Revealing the Majorana nature of neutrinos through a precision measurement of the CP phase

We show that it is possible to reveal the nature of neutrino by measuring the Majorana phase at the DUNE experiment. The Majorana phase is activated in the neutrino oscillation framework due to the introduction of a decoherence environment. Being that depending on the value of the Majorana phase and the intensity of decoherence, the measurement of the Dirac CP violation phase δCP can be highly spoiled. We will notice the latter by comparing the measurements of the CP phases that will take place in DUNE and T2HK. Finally, we will also assess the possibility of the measurement itself of the Majorana phase at DUNE.

Predictions for the leptonic Dirac CP-violating phase

In this paper, we explore the theoretical constraints on the observable parameters of neutrino mixing on predictions for the leptonic Dirac CP-violating phase within a well-studied class of simple theoretical models that includes a single source of CP violation due to charged lepton corrections. The approach guarantees that a physically meaningful prediction for the most likely values for the leptonic Dirac CP-violating phase is obtained.

SU(5) GUTs with A4 modular symmetry

We combine SU(5) Grand Unified Theories (GUTs) with A4 modular symmetry and present a comprehensive analysis of the resulting quark and lepton mass matrices for all the simplest cases. Classifying the models according to the representation assignments of the matter fields under A4, we find that there are seven types of SU(5) models with A4 modular symmetry. We present 53 benchmark models with the fewest free parameters. The parameter space of each model is scanned to optimize the agreement between predictions and experimental data, and predictions for the masses and mixing parameters of quarks and leptons are given at the best fitting points. The best fit predictions for the leptonic CP violating Dirac phase, the lightest neutrino mass and the neutrinoless double beta decay parameter when displayed graphically are observed to cover a wide range of possible values, but are clustered around particular regions, allowing future neutrino experiments to discriminate between the different types of models.

Leptonic sum rules from flavour models with modular symmetries

Sum rules in the lepton sector provide an extremely valuable tool to classify flavour models in terms of relations between neutrino masses and mixing parameters testable in a plethora of experiments. In this manuscript we identify new leptonic sum rules arising in models with modular symmetries with residual symmetries. These models simultaneously present neutrino mass sum rules, involving masses and Majorana phases, and mixing sum rules, connecting the mixing angles and the Dirac CP-violating phase. The simultaneous appearance of both types of sum rules leads to some non-trivial interplay, for instance, the allowed absolute neutrino mass scale exhibits a dependence on the Dirac CP-violating phase. We derive analytical expressions for these novel sum rules and present their allowed parameter ranges as well as their predictions at upcoming neutrino experiments.

Spontaneous CP violation by modulus \u03c4 in A4 model of lepton flavors

We discuss the modular A4 invariant model of leptons combining with the generalized CP symmetry. In our model, both CP and modular symmetries are broken spontaneously by the vacuum expectation value of the modulus τ. The source of the CP violation is a non-trivial value of Re[τ] while other parameters of the model are real. The allowed region of τ is in very narrow one close to the fixed point τ = i for both normal hierarchy (NH) and inverted ones (IH) of neutrino masses. The CP violating Dirac phase δCP is predicted clearly in [98°, 110°] and [250°, 262°] for NH at 3 σ confidence level. On the other hand, δCP is in [95°, 100°] and [260°, 265°] for IH at 5 σ confidence level. The predicted ∑mi is in [82, 102] meV for NH and ∑mi = [134, 180] meV for IH. The effective mass 〈mee〉 for the 0νββ decay is predicted in [12.5, 20.5] meV and [54, 67] meV for NH and IH, respectively.

Determining the Dirac CP Violation Phase and Neutrino Mass Hierarchy

There is still a problem in neutrino physics related to the configuration of neutrino masses: Are neutrinos arranged by masses following the Standard Model as three generations of fundamental particles, Gen III>Gen II>Gen I, thus forming a structural-normal hierarchy, or deviate from that principle? The biggest obstacle that is still present is the sign of the absolute value of the difference of the square of neutrino masses. It was avoided by applying the theory of neutrino oscillation probability for each structure of the neutrino mass hierarchy. With such theoretical approach the equation of motion was derived for each structure in which Dirac CP violation phase appeared as an unknown quantity. This enables direct calculation of the explicit value for the Dirac CP violation phase. Two examples were analyzed: The first example is devoted to the normal mass ordering and the second one is devoted to the inverted mass ordering. The data used for theoretical calculations presented in this paper are obtained on the basis of the latest reassessed data by processing the results of experimental measurements. On the basis of the performed calculations, normal mass ordering is unconditionally excluded as a potential option regarding the neutrino mass ordering in nature. On the basis of the derived equation of neutrino motion, a possible numerical value of the Dirac CP violation phase and Jarlskog invariant is found.

RGE-induced mu -tau symmetry breaking: an analysis of the latest T2K results

The T2K collaboration has recently reported their results, which gives the best-fit values of the atmospheric mixing angle sin ^2 theta _{23} = 0.53 and the Dirac CP-violating phase delta = -1.89 for normal neutrino mass ordering. We give a possible theoretical origin of such values based on the mu -tau reflection symmetry. It has been found that the breaking of such symmetry using one-loop renormalization-group equations (RGEs) in the framework of minimal supersymmetric standard model can fit well with the latest T2K results and the recent global fits. To make a quantitative analysis, we have included for the first time the complete dataset of oscillation, beta decay, neutrinoless double-beta decay and cosmological observations in comparing the theory to experiments. We also further examine the importance of such breaking patterns for neutrinoless double-beta decay experiments.

New A4 lepton flavor model from S4 modular symmetry

We study a flavor model with A4 symmetry which originates from S4 modular group. In S4 symmetry, Z2 subgroup can be anomalous, and then S4 can be violated to A4. Starting with a S4 symmetric Lagrangian at the tree level, the Lagrangian at the quantum level has only A4 symmetry when Z2 in S4 is anomalous. We obtain modular forms of two singlets and a triplet representations of A4 by decomposing S4 modular forms into A4 representations. We propose a new A4 flavor model of leptons by using those A4 modular forms. We succeed in constructing a viable neutrino mass matrix through the Weinberg operator for both normal hierarchy (NH) and inverted hierarchy (IH) of neutrino masses. Our predictions of the CP violating Dirac phase δCP and the mixing sin2θ23 depend on the sum of neutrino masses for NH.

Three-flavor neutrino oscillations and beyond

In this work we summarize the current status of global neutrino oscillation analyses in the three-neutrino framework. We first describe the different data samples included in the global fit, emphasizing the role of each of them in constraining a given set of parameters. Next, we discuss the main improvements obtained thanks to the consideration of the latest experimental data. The status of the yet-unknown parameters, such as the true neutrino mass ordering, the Dirac CP-violating phase and the octant of the atmospheric mixing angle is also commented. Finally, we discuss some scenarios where the measurement of the reactor mixing angle or the CP violation phase could be significantly affected by the presence of neutrino physics beyond the Standard Model.

Testing texture two-zero neutrino mass matrices under current experimental scenario

The latest data from the Planck Collaboration presented an improved sensitivity limit of the sum of neutrino masses , at 95 confidence level (CL). On the other hand, the updated global fits of neutrino oscillation have shown a refined range of atmospheric mixing angle at the same CL. In the light of these observations, we have re-investigated the five viable cases (B1, 2, 3, 4 and C) of the texture two-zero Majorana mass matrix in the flavor basis. Using the present Planck's data, we have demonstrated that only cases B2 and B4 are now viable for normal mass ordering, while the remaining three cases do not meet the present experimental constraints at 2σ CL. The phenomenological predictions of the viable cases are also found to be in tune with the latest T2K, Super-Kamiokande and NOνA results, showing the preference for normal neutrino mass ordering (m1 < m2 < m3), a maximal Dirac CP-violating phase , and the upper octant of the neutrino mixing angle . In addition, the implication of Σ on the neutrinoless double beta decay is studied for viable cases.