Neutrino Eigenstates Research Articles

Quantum entanglement between neutrino eigenstates in the presence of the subsequent phase shift of the neutrino oscillations

In this letter, using von Neumann entropy we examine the entanglement entropy for the neutrino oscillations in the presence of the subsequent phase shift. We numerically show that the entanglement entropy for the subsequent periods of the two-flavor neutrino oscillations increases asymmetrically with time depending on the space-time deformation. We also explored the obtained results for the three-flavor neutrino oscillations to show that this result is also valid for the three-flavor neutrino oscillations. These results, obtained for the first time in this letter, are quite different from the computing for the standard neutrino oscillation theory. We concluded that these interesting results play an important role in the cosmology.

PTOLEMY's test of generalized neutrino interactions: unveiling challenges and constraints

Unanswered questions surrounding neutrinos have motivated investigations into physics beyond the standard model (SM) of particle physics. In particular, generalized neutrino interactions (GNI) provide a broader framework for studying these effects compared to the commonly studied non-standard neutrino interactions. These interactions are described by higher dimensional operators while maintaining the gauge symmetries of the SM. Furthermore, the cosmic neutrino background, a predicted component of the SM and standard cosmology, has yet to be directly detected. To shed light on this elusive phenomenon, we conduct a comprehensive analysis of the relevant GNI, specifically focusing on their implications for the proposed cosmic neutrino detector PTOLEMY. We make an attempt to see the capabilities and the limitations of PTOLEMY in sensing GNI while remaining optimistic regarding PTOLEMY's experimental resolution. These interactions play a significant role in modifying the electron spectrum resulting from the capture of cosmic neutrinos on radioactive tritium. This work also explores how the presence of these interactions influences the differential electron spectrum, taking into account factors such as finite experimental resolution, the mass of the lightest neutrino eigenstate, the strength of the interactions, and the ordering of neutrino mass.

A common origin for the QCD axion and sterile neutrinos from SU(5) strong dynamics

We identify the QCD axion and right-handed (sterile) neutrinos as bound states of an SU(5) chiral gauge theory with Peccei-Quinn (PQ) symmetry arising as a global symmetry of the strong dynamics. The strong dynamics is assumed to spontaneously break the PQ symmetry, producing a high-quality axion and naturally generating Majorana masses for the right-handed neutrinos at the PQ scale. The composite sterile neutrinos can directly couple to the left-handed (active) neutrinos, realizing a standard see-saw mechanism. Alternatively, the sterile neutrinos can couple to the active neutrinos via a naturally small mass mixing with additional elementary states, leading to light sterile neutrino eigenstates. The SU(5) strong dynamics therefore provides a common origin for a high-quality QCD axion and sterile neutrinos.

Dark energy and neutrino mass from a transient vacuum particle pair model

We propose that the transient vacuum fluctuations of quantum fields can be represented by transient vacuum quanta where both the lifetime and spatial extent are given by the Heisenberg Uncertainty Principle, HUP. Accordingly, a quantum field fluctuation at any spatial site results in the creation of a transient HUP-limited vacuum pair, corresponding to the particle and the antiparticle associated with that quantum field. All HUP-limited vacuum pairs, both massive and massless, are found to be on-shell particles, and are indistinguishable from each other except for differences related to their exchange symmetry. We find that the net vacuum energy density of all HUP-limited vacuum pairs is identically zero at any energy where both bosonic and fermionic transient vacuum pairs are present. The net vacuum energy density, from zero energy to the Planck limit, is found to be proportional to that of the rest mass of the lightest fermion, the lowest mass neutrino eigenstate. This net energy density is equal to the observed dark energy density if the mass of the lightest neutrino eigenstate is 3.2[Formula: see text]meV. The model predicts the absolute values of the masses of the three neutrino mass eigenstates and of the three neutrino flavor eigenstates for both normal and inverted ordering. The sum of the neutrino masses is found to be below the Planck satellite upper limit of 120[Formula: see text]meV, and the neutrino mass sum for normal ordering is below the most stringent upper bound of 78[Formula: see text]meV, indicating a preference for normal ordering.

Search for eV Sterile Neutrinos – The Stereo Experiment

In the recent years, major milestones in neutrino physics were accomplished at nuclear reactors: the smallest neutrino mixing angle θ13 was determined with high precision and the emitted antineutrino spectrum was measured at unprecedented resolution. However, two anomalies, the first one related to the absolute flux and the second one to the spectral shape, have yet to be solved. The flux anomaly is known as the Reactor Antineutrino Anomaly and could be caused by the existence of a light sterile neutrino eigenstate participating in the neutrino oscillation phenomenon. Introducing a sterile state implies the presence of a fourth mass eigenstate, while global fits favour oscillation parameters around sin2(2θ) = 0.09 and Δm2 = 1.8eV2.The Stereo experiment was built to finally solve this puzzle. It is one of the first running experiments built to search for eV sterile neutrinos and takes data since end of 2016 at ILL Grenoble, France. At a short baseline of 10 metres, it measures the antineutrino flux and spectrum emitted by a compact research reactor. The segmentation of the detector in six target cells allows for independent measurements of the neutrino spectrum at multiple baselines. An active-sterile flavour oscillation could be unambiguously detected, as it distorts the spectral shape of each cell’s measurement differently.This contribution gives an overview on the Stereo experiment, along with details on the detector design, detection principle and the current status of data analysis.

Study of Galaxy Distributions with SDSS DR14 Data and Measurement of Neutrino Masses

We study galaxy distributions with Sloan Digital Sky Survey SDSS DR14 data and with simulations searching for variables that can constrain neutrino masses. To be specific, we consider the scenario of three active neutrino eigenstates with approximately the same mass, so Σmv=3mv. Fitting the predictions of the ΛCDM model to the Sachs-Wolfe effect, σ8, the galaxy power spectrum Pga1(k) , fluctuations of galaxy counts in spheres of radii ranging from 16/h to 128/h Mpc, Baryon Acoustic Oscillation (BAO) measurements, and h=0.678±0.009, in various combinations, with free spectral index n, and free galaxy bias and galaxy bias slope, we obtain consistent measurements of Σmv. The results depend on h, so we have presented confidence contours in the (Σmv, h) plane. A global fit with h=0.678±0.009 obtains eV, and the amplitude and spectral index of the power spectrum of linear density fluctuations P(k): , and n=1.021±0.075. The fit also returns the galaxy bias b including its scale dependence.

Measurements of the Cosmological Parameters Ω<sub>m</sub> and <i>H</i><sub>0</sub>

From Baryon Acoustic Oscillation measurements with Sloan Digital Sky Survey SDSS DR14 galaxies, and the acoustic horizon angle measured by the Planck Collaboration, we obtain Ωm=0.2724±0.0047, and h+0.020⋅∑mv=0.7038±0.0060, assuming flat space and a cosmological constant. We combine this result with the 2018 Planck “TT, TE, EE + lowE + lensing” analysis, and update a study of ∑mv with new direct measurements of σ8, and obtain ∑mv=0.27±0.08 eV assuming three nearly degenerate neutrino eigenstates. Measurements are consistent with Ωk=0, and Ωde(a)=ΩΛ constant.

Neutrino mass generation and leptogenesis via pseudo-Nambu-Goldstone Higgs portal

We consider an extension of the Standard Model with the global symmetry breaking pattern SO(5)/SO(4), where the Higgs boson arises as a pseudo-Nambu-Goldstone boson. The scalar content of the theory consists of a Standard-Model-like Higgs field and an extra real scalar field. The flavour sector of the model is extended by two right-handed neutrinos compatible with the observed light-neutrino phenomenology, and we find that the correct vacuum alignment determines the mass of the heavier neutrino eigenstate to be around 80 TeV. The new singlet-scalar state generates dynamically a Majorana mass term for the heavy neutrino states. We show how the model leads to the correct baryon asymmetry of the universe via leptogenesis in the case of two degenerate or hierarchical heavy neutrinos.

Changing the Bayesian prior: Absolute neutrino mass constraints in nonlocal gravity

Prior change is discussed in observational constraints studies of nonlocally modified gravity. In the latter, a model characterized by a modification of the form $\sim m^2 R\Box^{-2}R$ to the Einstein-Hilbert action was compared against the base $\Lambda$CDM one in a Bayesian way. It was found that the competing modified gravity model is significantly disfavored (at $22 \,$:$\, 1$ in terms of betting-odds) against $\Lambda$CDM given CMB+SNIa+BAO data, because of a dominant tension appearing in the $H_0 \,$-$\, \Omega_M$ plan. We identify the underlying mechanism generating such a tension and show that it is mostly caused by the late-time, quite smooth, phantom nature of the effective dark energy described by the nonlocal model. We find possible solutions for it to be resolved and explore a given one that consists in extending the initial baseline from one massive neutrino eigenstate to three degenerate ones, whose absolute mass $\sum m_\nu \, / \, 3$ is allowed to take values within a reasonable prior interval. As a net effect, the absolute neutrino mass is inferred to be non-vanishing at $2 \sigma$ level, best-fitting at $\sum m_\nu \approx 0.21 {\, \rm eV}$, and the Bayesian tension disappears rendering the nonlocal gravity model statistically equivalent to $\Lambda$CDM, given recent CMB+SNIa+BAO data. We also discuss constraints from growth rate measurements $f \sigma_8$ whose fit is found to be improved by a larger massive neutrino fraction as well. The $\nu$-extended nonlocal model also prefers a higher value of $H_0$ than $\Lambda$CDM, therefore in better agreement with local measurements.

Probing neutrino nature at Borexino detector with chromium neutrino source

In this paper, we indicate a possibility of utilizing the intense chromium source ($\sim 370 PBq$) in probing the neutrino nature in low energy neutrino experiments with the ultra-low threshold and background real-time Borexino detector located near the source ($\sim 8 m$). We analyze the elastic scattering of electron neutrinos (Dirac or Majorana, respectively) on the unpolarized electrons in the relativistic neutrino limit. We assume that the incoming neutrino beam is the superposition of left-right chiral states. Left chiral neutrinos may be detected by the standard $V A$ and non-standard scalar $S_L$, tensor $T_L$ interactions, while right chiral ones partake only in the exotic $V + A$ and $S_R, T_R$ interactions. Our model-independent study is carried out for the flavour (current) neutrino eigenstates. We compute the expected event number for the standard $V-A$ interaction of the left chiral neutrinos using the current experimental values of standard couplings and in the case of left-right chiral superposition. We show that the significant decrement in the event number due to the interference terms between the standard and exotic interactions for the Majorana $\nu_e$'s may appear. The $90 \%$ C. L. sensitivity contours in the planes of corresponding exotic couplings are also found. The presence of interferences in the Majorana case gives the stronger constraints than for the Dirac neutrinos, even if the neutrino source is placed outside the detector.

Geometric phase for neutrino propagation in magnetic field

The geometric phase for neutrinos propagating in an adiabatically varying magnetic field in matter is calculated. It is shown that for neutrino propagation in sufficiently large magnetic field the neutrino eigenstates develop a significant geometric phase. The geometric phase varies from 2$\pi$ for magnetic fields $\sim$ fraction of a micro gauss to $\pi$ for fields $\sim 10^7$ gauss or more. The variation of geometric phase with magnetic field parameters is shown and its phenomenological implications are discussed.

Velocity-induced neutrino oscillation and its possible implications for long baseline neutrinos

If the three types of active neutrinos possess different maximum attainable velocities and the neutrino eigenstates in the velocity basis are different from those in the flavor (and mass) basis, then this will induce a flavor oscillation in addition to the normal mass-flavor oscillation. Here we study such an oscillation scenario in three neutrino framework including also the matter effect and apply our results to demonstrate its consequences for long baseline (LBL) neutrinos. We also predict the possible signatures in terms of yields in a possible LBL neutrino experiment.

Creation of Dirac neutrinos in a dense medium with a time-dependent effective potential

We consider Dirac neutrinos interacting with background fermions in the frame of the standard model. We demonstrate that a time-dependent effective potential is quite possible in a protoneutron star (PNS) at certain stages of its evolution. For the first time, we formulate a nonperturbative treatment of neutrino processes in a matter with arbitrary time-dependent effective potential. Using linearly growing effective potential, we study the typical case of a slowly varying matter interaction potential. We calculate differential mean numbers of $\nu \bar{\nu}$ pairs created from the vacuum by this potential and find that they crucially depend on the magnitude of masses of the lightest neutrino eigenstate. These distributions uniformly span up to $\sim 10$ eV energies for muon and tau neutrinos created in PNS core due to the compression just before the hydrodynamic bounce and up to $\sim 0.1$ eV energies for all three active neutrino flavors created in the neutronization. Considering different stages of the PNS evolution, we derive constraints on neutrino masses, $m_{\nu}\lesssim (10^{-8}-10^{-7})$ eV corresponding to the nonvanishing $\nu \bar{\nu}$ pairs flux produced by this mechanism. We show that one can distinguish such coherent flux from chaotic fluxes of any other origin. Part of these neutrinos, depending on the flavor and helicity, are bounded in the PNS, while antineutrinos of any flavor escape the PNS. If the created pairs are $\nu_{e}\bar{\nu}_{e}$, then a part of the corresponding neutrinos also escape the PNS. The detection of $\nu $ and $\bar{\nu}$ with such low energies is beyond current experimental techniques.

Self-organizing neutrino mixing matrix

A new and novel idea for a predictive neutrino mass matrix is presented, using the non-Abelian discrete symmetry ${A}_{4}$ and the seesaw mechanism with only two heavy neutral fermion singlets. Given the components of the one necessarily massless neutrino eigenstate, the other two massive states are automatically generated. A realistic example is discussed with predictions of a normal hierarchy of neutrino masses and maximal $CP$ violation.

Gravity-induced neutrino–antineutrino oscillation: CPT and lepton number non-conservation under gravity

We introduce a new effect in the neutrino oscillation phase which shows that the neutrino–antineutrino oscillation is possible under gravity even if the rest masses of the corresponding eigenstates are the same. This is due to CPT violation, and is possible to demonstrate if the neutrino mass eigenstates are expressed as a combination of neutrino and antineutrino eigenstates, as of the neutral kaon system, with the plausible breaking of lepton number conservation. For Majorana neutrinos, this oscillation is expected to significantly affect the inner edge of neutrino-dominated accretion discs around compact objects by influencing the neutrino sphere which controls the accretion dynamics, and then the related type-II supernova evolution and the r-process nucleosynthesis. On the other hand, in the early universe, in the presence of various lepton number violating processes, this oscillation, we argue, might have led to neutrino asymmetry which resulted in baryogenesis from the B–L symmetry by electro-weak sphaleron processes.

A new mechanism of neutrino mass generation in the NMSSM with broken lepton number

In the Minimal Supersymmetric Standard Model with bilinear R-parity violation, only one neutrino eigenstate acquires a mass at tree level, consequently experimental data on neutrinos cannot be accommodated at tree level. We show that in the Next-to-Minimal extension, where a gauge singlet superfield is added to primarily address the so-called $\mu$-problem, it is possible to generate two massive neutrino states at tree level. Hence, the global three-flavour neutrino data can be reproduced at tree level, without appealing to loop dynamics which is vulnerable to model-dependent uncertainties. We give analytical expressions for the neutrino mass eigenvalues and present examples of realistic parameter choices.

Low-scale seesaw mechanisms for light neutrinos

Alternatives to the see-saw mechanism are explored in supersymmetric models with three right-handed or sterile neutrinos. Tree-level Yukawa couplings can be drastically suppressed in a natural way to give sub-eV Dirac neutrino masses. If, in addition, a B-L gauge symmetry broken at a large scale M_G is introduced, a wider range of possibilities opens up. The value of the right-handed neutrino mass M_R can be easily disentangled from that of M_G. Dirac and Majorana neutrino masses at the eV scale can be generated radiatively through the exchange of sneutrinos and neutralinos. Dirac masses m_D owe their smallness to the pattern of light-heavy scales in the neutralino mass matrix. The smallness of the Majorana masses m_L is linked to a similar see-saw pattern in the sneutrino mass matrix. Two distinct scenarios emerge. In the first, with very small or vanishing M_R, the physical neutrino eigenstates are, for each generation, either two light Majorana states with mixing angle ranging from very small to maximal, depending on the ratio m_D/M_R, or one light Dirac state. In the second scenario, with a large value of M_R, the physical eigenstates are two nearly unmixed Majorana states with masses \sim m_L and \sim M_R. In both cases, the (B-L)-breaking scale M_G is, in general, much smaller than that in the traditional see-saw mechanism.

Supersymmetric seesaw model for the (1+3)-scheme of neutrino masses

A four-neutrino spectrum with a sterile neutrino without significant involvement in the atmospheric and solar neutrino oscillation experiments has been recently advocated as the correct picture to explain all existing experimental data. We propose a supersymmetric model in which this picture can be naturally implemented. In this model, the mass for the mainly active neutrino eigenstates is induced by the seesaw mechanism with a large intermediate scale M R , whereas the mass for the mainly sterile neutrino state is closely related to supersymmetry breaking.

General cosmological constraints on the masses of stable neutrinos and other “inos”

The arguments favoring non-baryonic dark matter are summarized. In particular, if the cosmological density parameter Ω≳ 0.15, the universe must be dominated by non-baryonic matter. General cosmological constraints, independent of detailed galaxy formation scenarios, are presented on the masses of stable neutrinos and other “inos,” where ino represents any candidate particle for the dark matter in the universe: (i) The requirement that the total mass density not exceed Ω ≲ 4 restricts neutrinos to two mass ranges, ∑ m v ≲ 400 eV and m v ≳ 1 GeV. (ii) From age of the universe arguments, tighter constraints on the lower of the two mass ranges become ∑ m v ≲ 25 eV (∑ m ino ≲ 400 eV) or ∑ m v ≲ 100 eV (∑ m ino ≲ 2 keV) depending on age technique used. An actual determination of a neutrino mass puts an upper limit on the age of the universe, and in a neutrino-dominated universe Ω = 1 is only possible for ∑ m v ≳ 25 eV. (iii) From phase-space density arguments, a necessary (but not sufficient) condition for the clustering of neutrinos on large scales is that m v ≳ 3 eV. (iv) For the formation of large-scale structure, the maximum neutrino Jeans mass should not exceed supercluster scales and therefore m v ≳ 10 eV. Three neutrinos of equal mass can be excluded if one uses globular cluster determinations of the age in (ii) above. (v) If the formation of large-scale structure requires damping of small scales and hence a minimum value of the maximum neutrino Jeans mass, m ino ≲ 200 eV for dominant particles. In a universe with Ω ⋍ 1 and photon temperature T γ0 = 2.7 K, this also leads to the constraint that decoupling temperature if T D of the dominant ino is T D ≲ 100 MeV. (vi) Big-bang nucleosynthesis restricts the number of neutrino species to at most four, probably only three. These arguments are then synthesized to show that all of the independent constraints can only be simultaneously met in a “best-fit” model with 10 eV ≲ m v ≲ 25 eV for the most massive neutrino eigenstate. Independently of galaxy formation arguments and with only the extremely conservative age limit, it can still be said that 3 eV ≲ m v ≲ 100 eV. Note also that if constraint (v) is valid then the dominant ino acts in every way like a massive neutrino and thus if (vi) also holds, it probably is a massive neutrino. Differences in adiabatic and isothermal fluctuation models are discussed; in particular the GUTs preferred adiabatic mode is only consistent with limits on 3 K anisotropies if non-baryonic matter dominates. Problems on small-scales with galaxy correlation studies and equilibrium time scales in a neutrino-dominated universe with adiabatic fluctuations are discussed. For Ω ∼ 0.2–0.6 cold matter such as axions or GeV mass inos could be dominant matter, but in an Ω ⋍ 1 universe these as well as keV mass “inos” are not optimal for the dominant matter and the best fit is a neutrino of mass m v ⋍ 25 eV .