Angle Θ13 Research Articles

Potential to Identify the Neutrino Mass Ordering with Reactor Antineutrinos in JUNO

Abstract The Jiangmen Underground Neutrino Observatory (JUNO) is a multi-purpose neutrino experiment under construction in South of China. This paper presents an updated estimate of JUNO's sensitivity to the neutrino mass ordering using the reactor antineutrinos emitted from eight nuclear reactor cores in the Taishan and Yangjiang nuclear power plants. This measurement is planned by studying the fine interference pattern caused by quasi-vacuum oscillations in the oscillated antineutrino spectrum at a baseline of 52.5~km and is completely independent of the CP violating phase and the neutrino mixing angle θ23. The sensitivity is obtained through a joint analysis of JUNO and TAO detectors utilizing the best available knowledge to date about the location and overburden of the JUNO experimental site, the local and global nuclear reactors, the JUNO and TAO detectors responses, the expected event rates and spectra of signal and backgrounds, and the systematic uncertainties of the analysis inputs. It is found that a 3σ median sensitivity to reject the wrong mass ordering hypothesis can be reached with an exposure of about 6.5 years × 26.6~GW thermal power.Content from this work may be used under the terms of the Creative Commons Attribution 3.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI. Article funded by SCOAP3 and published under licence by Chinese Physical Society and the Institute of High Energy Physics of the Chinese Academy of Science and the Institute of Modern Physics of the Chinese Academy of Sciences and IOP Publishing Ltd.

Sensitivity of octant of θ23, CP violation and mass hierarchy in NOνA with multinucleon and detector effects

In this work, we investigate how multinucleon enhancement and RPA (Random Phase Approximation) suppression can affect the measurement of three unknown neutrino oscillation parameters — the CP-violating phase δCP, the octant of the atmospheric mixing angle θ23, and the determination of the mass hierarchy, in the appearance channel of the NOνA experiment. We include the presence of the detector effect as well in the analysis, which is crucial for capturing realistic experimental scenarios. We also conducted a comparison between the nuclear model Effective Spectral Function (calculated within the RFG model) with and without Transverse Enhancement in terms of sensitivity analysis. It is found that the analysis using our comprehensive model QE(+RPA)+2p2h along with Effective Spectral Function+Transverse Enhancement exhibits significantly enhanced sensitivity compared to the pure QE interaction process, in all the cases. Also, the higher octant of θ23, the lower half plane of δCP, and the normal mass hierarchy (HO-LHP-NH) exhibit improved sensitivity, enabling a more precise determination of the corresponding parameters. Furthermore, it is also noted that improving the performance of the detector also improves the results. Thus, including multinucleon effects and improving detector efficiency have the potential to enhance the capabilities of the NOνA (and other long baseline) experiment in conducting precise parameter studies.

Fast exact algorithm for neutrino oscillation in constant matter density

A recently published method [1,2] for solving the neutrino evolution equation with constant matter density is further refined and used to lay out an exact algorithm for computing oscillation probabilities, which is moderately faster than previous methods when looping through neutrinos of different energies. In particular, the three examples of ν(−)e survival, ν(−)μ survival and ν(−)e appearance probabilities are written in terms of mixing angles, mass differences and matter electron density. A program based on this new method is found to be roughly twice as fast as, and in agreement with, the leading GLoBES package. Furthermore, the behaviour of all relevant effective parameters is sketched out in terms of a range of neutrino energies, or matter electron densities. For instance, the ν(−)e survival probability in constant matter density is found to have no dependence on the mixing angle θ23 or the CP-violating phase δ13.

Neutrino phenomenology in a model with generalized CP symmetry within type-I seesaw framework

We investigate the consequences of generalized CP (GCP) symmetry within the context of the two Higgs doublet model (2HDM), specifically focusing on the lepton sector. Utilizing the type-I seesaw framework, we study an intriguing connection between the Dirac Yukawa couplings originating from both Higgs fields, leading to a reduction in the number of independent Yukawa couplings and simplifying the scalar and Yukawa sectors when compared to the general 2HDM. The constraints coming from CP symmetry of class three (CP3) results in two right-handed neutrinos having equal masses and leads to a diagonal right-handed Majorana neutrino mass matrix. Notably, CP symmetry experiences a soft breaking due to the phase associated with the vacuum expectation value of the second Higgs doublet. The model aligns well with observed charged lepton masses and neutrino oscillation data, explaining both masses and mixing angles, and yields distinct predictions for normal and inverted neutrino mass hierarchies. It features a novel interplay between atmospheric mixing angle θ23 and neutrino mass hierarchy: The angle θ23 is below maximal for the normal hierarchy and above maximal for inverted hierarchy. Another interesting feature of the model is inherent CP violation for the inverted hierarchy. Published by the American Physical Society 2024

Non-SUSY lepton flavor model with the three Higgs doublet model

Abstract We propose a simple non-supersymmetric lepton flavor model with A4 symmetry. The A4 group is a minimal one that includes triplet irreducible representation. We introduce three Higgs doublets, which are assigned as a triplet of the A4 symmetry. It is natural that there are three generations of the Higgs fields, as with the standard model fermions. We analyze the potential and find the vacuum expectation values for the local minimum. In the vacuum expectation values, we obtain the charged lepton, Dirac neutrino, and right-handed Majorana neutrino mass matrices. By using the type-I seesaw mechanism, we get the left-handed Majorana neutrino mass matrix. In the NuFIT 5.1 data, we predict the Dirac CP phase and the Majorana phases for the only inverted neutrino mass hierarchy. In particular, the Dirac CP phase and lepton mixing angle θ23 are strongly correlated. If θ23 is more precisely measured, the Dirac CP phase is more precisely predicted, and vice versa. We also predict the effective mass for neutrinoless double beta decay mee ≃ 47.1 [meV] and the lightest neutrino mass m3 ≃ 0.789–1.43 [meV]. This will be testable with our model in near-future neutrino experiments.

Neutrino mass and mixing models with eclectic flavor symmetry ∆(27) ⋊ T′

The Kähler potentials of modular symmetry models receive unsuppressed contributions which may be controlled by a flavor symmetry, where the combination of the two symmetry types is referred to as eclectic flavor symmetry. After briefly reviewing the consistency conditions of eclectic flavor symmetry models, including those with generalised (g)CP, we perform a comprehensive bottom-up study of eclectic flavor symmetry models based on Ω(1) ≅ ∆(27) ⋊ T′, consisting of the flavor symmetry ∆(27) in a semi-direct product with the modular symmetry T′. The modular transformations of different ∆(27) multiplets are given by solving the consistency condition. The eight nontrivial singlets of ∆(27) are related by T′ modular symmetry, and they have to be present or absent simultaneously in any Ω(1) model. The most general forms of the superpotential and Kähler potential invariant under Ω(1) are discussed, and the corresponding fermion mass matrices are presented. Based on the eclectic flavor group Ω(1), two concrete lepton models which can successfully describe the experimental data of lepton masses and mixing parameters are constructed. For the two models without gCP, all six mixing parameters vary in small regions. A nearly maximal atmospheric mixing angle θ23 and Dirac CP phase δCP are obtained in the first model. After considering the compatible gCP symmetry and the assumption of mathfrak{R}tau = 0 in the first model, the μ − τ reflection symmetry is preserved in the charged lepton diagonal basis. As a consequence, the atmospheric mixing angle and Dirac CP phase are predicted to be maximal, and two Majorana CP phases are predicted to be π.

A minimal modular invariant neutrino model

We present a neutrino mass model based on modular symmetry with the fewest input parameters to date, which successfully accounts for the 12 lepton masses and mixing parameters through 6 real free parameters including the modulus. The neutrino masses are predicted to be normal ordering, the atmospheric angle θ23 is quite close to maximal value and the Dirac CP phase δCP is about 1.34π. We also study the soft supersymmetry breaking terms due to the modulus F-term in this minimal model, which are constrained to be the non-holomorphic modular forms. The radiative lepton flavor violation process μ → eγ is discussed.

Absolute neutrino mass scale and dark matter stability from flavour symmetry

We explore a simple but extremely predictive extension of the scotogenic model. We promote the scotogenic symmetry ℤ2 to the flavour non-Abelian symmetry Σ(81), which can also automatically protect dark matter stability. In addition, Σ(81) leads to striking predictions in the lepton sector: only Inverted Ordering is realised, the absolute neutrino mass scale is predicted to be mlightest≈ 7.5×10−4 eV and the Majorana phases are correlated in such a way that |mee| ≈ 0.018 eV. The model also leads to a strong correlation between the solar mixing angle θ12 and δCP, which may be falsified by the next generation of neutrino oscillation experiments. The setup is minimal in the sense that no additional symmetries or flavons are required.

Renormalizable standard model extension with S4 symmetry for neutrino mass and mixing

We suggest a renormalizable standard model extension based on S4 symmetry that accommodates the recent observed neutrino oscillation pattern. Through the type-I seesaw mechanism, the smallness of the active neutrino mass and its hierarchy are produced. The model generates the updated data on neutrino parameters in which the reactor neutrino mixing angle θ13, the atmospheric neutrino mixing θ23, and the Dirac phase δ for both NH and IH belong to 1σ range, while the solar mixing angle θ12 = 35.70° belongs to 2σ range. The effective masses are found to be 〈 mee〉 = 5.74 meV for NH and 〈 mee〉 = 48.1 meV for IH within their allowed constraints.

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.

Power improvement of a cluster of three Savonius wind turbines using the variable-speed control method

The average power output of multiple Savonius wind turbines optimally arranged in a cluster is improved significantly compared to that of an isolated turbine due to the coupling effect. Previous investigations focused on the influence of the configuration and the initial phase angles of Savonius turbines operating at the same rotational speed in a cluster. This paper proposes to adopt the variable-speed control method to improve the power output of a three-turbine cluster, and simultaneously avoid the requirement for the accurate initial phase angle settings of the turbines. The Taguchi method is used to optimize the configuration of the cluster. The distances between the centers of adjacent turbines (L1-2, L1-3), the configuration angles (θ1-2, θ1-3), and the combination of rotational directions (RD) are taken as Taguchi experimental factors. The optimal configuration of the cluster is determined to be L1-2 = 2.0D, L1-3 = 2.4D, θ1-2 = 110°, θ1-3 = 110°, and RD = (-,+,-). The influence strength of the factors is ranked as configuration angle, RD, and distance between turbines. In addition, the average power coefficient of the turbines in the optimal cluster is 1.425 times that of an isolated turbine and the tip speed ratios of the three turbines are 1.13, 1.14, and 1.09.

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.

Diagonal reflection symmetries, four-zero texture, and trimaximal mixing with predicted θ13 in an A4 symmetric model

Abstract In this paper, we impose a magic symmetry on the neutrino mass matrix mν with universal four-zero texture and diagonal reflection symmetries. Due to the magic symmetry, the Maki–Nakagawa–Sakata matrix inevitably has trimaximal mixing. Since the lepton sector has only six free parameters, the physical observables of leptons are all determined from the charged lepton masses mei, the neutrino mass differences $\Delta m_{i1}^{2}$, and the mixing angle θ23. This scheme predicts sin θ13 = 0.149, which is almost equal to the latest best fit, as a function of the lepton masses me, μ and the mass differences $\Delta m_{i1}^{2}$. Moreover, even if the mass matrix has perturbations that break the magic symmetry, the prediction of sin θ13 is retained with good accuracy for the four-zero texture with diagonal reflection symmetries.

Resolving the LMA-dark NSI degeneracy with coherent neutrino-nucleus scattering

In the presence of non-standard neutrino interactions (NSI), a degeneracy exists in neutrino oscillation data, which involves the flipping of the octant of the mixing angle θ12 and the type of the neutrino mass ordering. In this article, we revisit the status of this degeneracy in the light of recent data on coherent elastic neutrino-nucleus scattering (CEνNS) from the COHERENT experiment. For general relative couplings to up and down quarks, the degeneracy is disfavoured at the 2σ level by the latest data but remains at a higher confidence level. We investigate the requirements of future CEνNS measurements to resolve the degeneracy with high significance. We find that a measurement involving both, electron and muon neutrino flavours and a target with a neutron-to-proton ratio close to 1 is required. For example, an experiment with a silicon target at the European Spallation Source can resolve the degeneracy at more than 4σ for arbitrary relative couplings to up and down quarks.

2020 global reassessment of the neutrino oscillation picture

We present an updated global fit of neutrino oscillation data in the simplest three-neutrino framework. In the present study we include up-to-date analyses from a number of experiments. Concerning the atmospheric and solar sectors, besides the data considered previously, we give updated analyses of IceCube DeepCore and Sudbury Neutrino Observatory data, respectively. We have also included the latest electron antineutrino data collected by the Daya Bay and RENO reactor experiments, and the long-baseline T2K and NOνA measurements, as reported in the Neutrino 2020 conference. All in all, these new analyses result in more accurate measurements of θ13, θ12, Delta {m}_{21}^2 and left|Delta {m}_{31}^2right| . The best fit value for the atmospheric angle θ23 lies in the second octant, but first octant solutions remain allowed at ∼ 2.4σ. Regarding CP violation measurements, the preferred value of δ we obtain is 1.08π (1.58π) for normal (inverted) neutrino mass ordering. The global analysis still prefers normal neutrino mass ordering with 2.5σ statistical significance. This preference is milder than the one found in previous global analyses. These new results should be regarded as robust due to the agreement found between our Bayesian and frequentist approaches. Taking into account only oscillation data, there is a weak/moderate preference for the normal neutrino mass ordering of 2.00σ. While adding neutrinoless double beta decay from the latest Gerda, CUORE and KamLAND-Zen results barely modifies this picture, cosmological measurements raise the preference to 2.68σ within a conservative approach. A more aggressive data set combination of cosmological observations leads to a similar preference for normal with respect to inverted mass ordering, namely 2.70σ. This very same cosmological data set provides 2σ upper limits on the total neutrino mass corresponding to Σmν< 0.12 (0.15) eV in the normal (inverted) neutrino mass ordering scenario. The bounds on the neutrino mixing parameters and masses presented in this up-to-date global fit analysis include all currently available neutrino physics inputs.

Radiative generation of realistic neutrino mixing with A4

Radiative generation of realistic mixing in neutrino sector is studied at one-loop level in a scotogenic A4×Z2 symmetric framework. A scheme of obtaining non-zero θ13 through small mass splitting in right-handed neutrino sector is proposed. The model consists of three right-handed neutrinos, two of which were required to be degenerate in masses to yield the common structure of the left-handed neutrino mass matrix that corresponds to θ13=0, θ23=π/4 and any θ120 in particular the choices specific to the Tribimaximal (TBM), Bimaximal (BM) and Golden Ratio (GR) mixings. Non-zero θ13, deviations of θ23 from maximality and small corrections to the solar mixing angle θ12 can be generated in one stroke by shifting from this degeneracy in the right-handed neutrino sector by a small amount. The lightest among the three Z2 odd inert SU(2)L doublet scalars present in the model can be a potential dark matter candidate.

On resolving the dark LMA solution at neutrino oscillation experiments

In presence of non standard interactions (NSI), the solar neutrino data is consistent with two solutions, one close to the standard LMA solution with sin2θ12 ≃ 0.31 and another with {sin}^2{theta}_{12}^Dsimeq 0.69left(=1-{sin}^2{theta}_{12}right) . The latter has been called the Dark LMA (DLMA) solution in the literature and essentially brings an octant degeneracy in the measurement of the mixing angle θ12. This θ12 octant degeneracy is hard to resolve via oscillations because of the existence of the so-called “generalised mass hierarchy degeneracy” of the neutrino mass matrix in presence of NSI. One might think that if the mass hierarchy is independently determined in a non-oscillation experiment such as neutrino-less double beta decay, one might be able to break the θ12 octant degeneracy. In this paper we study this in detail in the context of long-baseline experiments (Pμμ channel) as well as reactor experiments (Pee channel) and show that if we combine information from both long-baseline and reactor experiments we can find the correct octant and hence value of θ12. We elaborate the reasons for it and study the prospects of determining the θ12 octant using T2HK, DUNE and JUNO experiments. Of course, one would need information on the neutrino mass hierarchy as well.

QCD axion and neutrino physics induced by hidden flavor structure

We study the reasonable requirements of two anomalous U(1)s in a flavored-axion framework for the anomaly cancellations of both U(1)-mixed gravity and U(1)Y×[U(1)]2 which in turn determine the U(1)Y charges where U(1)Y is the hypercharge gauge symmetry of the standard model. We argue that, with a flavor symmetry group, axion-induced topology in symmetry-broken phases plays crucial roles in describing how quarks and leptons are organized at a fundamental level and make deep connections with each other. A unified model, as an example, is then proposed in a simple way to describe a whole spectrum of particles where both flavored-axion interactions with normal matter and the masses and mixings of fermions emerge from the spontaneous breaking of a given symmetry group. Once a scale of active neutrino mass defined at a seesaw scale is fixed by the commensurate U(1) flavored-PQ charge of fermions, that of QCD axion decay constant FA is determined. In turn, fundamental physical parameters complementary to each other are predicted with the help of precision flavor experiments. Model predictions are extracted on the characteristics of neutrino and flavored-axion: FA=3.57−1.53+1.52×1010 GeV (consequently, QCD axion mass ma=1.52−0.46+1.14×10−4 eV, axion to photon coupling |gaγγ|=2.15−0.64+1.61×10−14GeV−1, axion to electron coupling gAee=3.29−0.98+2.47×10−14, etc.); atmospheric mixing angle θ23, Dirac CP phase δCP, and 0νββ-decay rate for normal mass ordering and inverted one by taking quantum corrections into account.

Lepton flavor mixing and CP violation in the minimal type-(I+II) seesaw model with a modular A4 symmetry

In this paper, we study the implications of the modular A4 flavor symmetry in constructing a supersymmetric minimal type-(I+II) seesaw model, in which only one right-handed neutrino and two Higgs triplets are introduced to account for the tiny neutrino masses, flavor mixing and CP violation. We consider the most economical case where the right-handed neutrino and the Higgs triplets in this model are assigned into the trivial one-dimensional irreducible representation of the modular group A4, and all the modular forms are with the lowest weights they can take. We find that the octant of the mixing angle θ23 strongly depends on the hierarchy of free model parameters in the charged-lepton sector. We also show that the neutrino mass matrix can possess an approximate μ−τ reflection symmetry for some specific values of free parameters. Moreover, our model predicts relatively large masses of three light neutrinos, thus can be easily tested in future neutrino experiments.

Why matter effects matter for JUNO

In this paper we focus on the Earth matter effects for the solar parameter determination by a medium baseline reactor experiment such as JUNO. We derive perturbative expansions for the mixing angles θ12 and θ13 as well as the Δm212 and Δm312 in terms of the matter potential relevant for JUNO. These expansions, up to second order in the matter potential, while simple, allow one to calculate the electron antineutrino survival probability to a precision much better than needed for the JUNO experiment. We use these perturbative expansions to semi-analytically explain and confirm the shift caused by the matter effects on the solar neutrino mixing parameters θ12 and Δm212 which were previously obtained by a purely numerical χ2 analysis. Since these shifts do not satisfy the naive expectations and are significant given the precision that can be achieved by the JUNO experiment, a totally independent cross check using a completely different method is of particular importance. We find that these matter effect shifts do not depend on any of the details of the detector characteristics apart from the baseline and earth mass density between reactor(s) and detector, but do depend on the normalized product of reactor neutrino spectrum times the inverse-beta decay cross-section. The results of this manuscript suggests an alternative analysis method for measuring sin2⁡θ12 and Δm212 in JUNO which would be a useful cross check of the standard analysis and for the understanding of the Wolfenstein matter effect. The explanation of these shifts together with a quantitative understanding, using a semi-analytical method, is the principal purpose of this paper.