Absolute Neutrino Mass Research Articles

Yukawa sector in nonsupersymmetric renormalizable SO(10)

We discuss the ordinary, non-supersymmetric SO(10) as a theory of fermion masses and mixings. We construct two minimal versions of the Yukawa sector based on $\bar{126}_H $ and either $10_H$ or $120_H$. The latter case is of particular interest since it connects the absolute neutrino mass scale with the size of the atmospheric mixing angle $\theta_A$. It also relates the smallness of $V_{cb}$ with the largeness of $\theta_A$. These results are based on the analytic study of the second and third generations. Furthermore, we discuss the structure of the light Higgs and the role of the Peccei-Quinn symmetry for dark matter and the predictivity of the theory.

Conditions for detectingCPviolation via neutrinoless double beta decay

Neutrinoless double beta decay data, together with information on the absolute neutrino masses obtained from the future KATRIN experiment and/or astrophysical measurements, provide a chance to find $CP$ violation in the lepton sector with Majorana neutrinos. We derive and discuss necessary conditions which make discovery of such $CP$ violation possible for the future neutrino oscillation and mass measurements data.

Leptogenesis in unified theories with Type II see-saw

In some classes of flavour models based on unified theories with a type I see-saw mechanism, the prediction for the mass of the lightest right-handed neutrino is in conflict with the lower bound from the requirement of successful thermal leptogenesis. We investigate how lifting the absolute neutrino mass scale by adding a type II see-saw contribution proportional to the unit matrix can solve this problem. Generically, lifting the neutrino mass scale increases the prediction for the mass of the lightest right-handed neutrino while the decay asymmetry is enhanced and washout effects are reduced, relaxing the lower bound on the mass of the lightest right-handed neutrino from thermal leptogenesis. For instance in classes of unified theories where the lightest right-handed neutrino dominates the type I see-saw contribution, we find that thermal leptogenesis becomes possible if the neutrino mass scale is larger than about 0.15 eV, making this scenario testable by neutrinoless double beta decay experiments in the near future.

Electromagnetic design and inner electrode for the KATRIN main spectrometer

Since the recent experimental findings in the field of neutrino flavor oscillations, one of the most prominent tasks in neutrino physics has been to determine the absolute neutrino mass scale. The KATRIN experiment, which is currently being set up at Forschungszentrum Karlsruhe, Germany, will perform a measurement of m ( ν ̄ e ) with a sensitivity of 0.2 eV (90% C.L.). In this talk the electromagnetic design of the KATRIN main spectrometer and the layout of the inner electrode system in particular will be described.

The absolute neutrino mass scale, neutrino mass spectrum, Majorana CP-violation and neutrinoless double-beta decay

Assuming 3-ν mixing, massive Majorana neutrinos and neutrinoless double-beta ((ββ)0ν-) decay generated only by the (V−A) charged current weak interaction via the exchange of the three Majorana neutrinos, we briefly review the predictions for the effective Majorana mass |〈m〉| in (ββ)0ν-decay and reanalyze the physics potential of future (ββ)0ν-decay experiments to provide information on the type of neutrino mass spectrum, the absolute scale of neutrino masses, and Majorana CP-violation in the lepton sector. Using as input the most recent experimental results on neutrino oscillation parameters and the prospective precision that can be achieved in future measurements of the latter, we perform a statistical analysis of a (ββ)0ν-decay half-life measurement taking into account experimental and theoretical errors, as well as the uncertainty implied by the imprecise knowledge of the corresponding nuclear matrix element (NME). We show, in particular, how the possibility to discriminate between the different types of neutrino mass spectra and the constraints on the absolute neutrino mass scale depend on the mean value and the experimental error of |〈m〉| and on the NME uncertainty. The constraints on Majorana CP-violation phases in the neutrino mixing matrix, which can be obtained from a measurement of |〈m〉| and additional data on the sum of neutrino masses, are also investigated in detail. We estimate the required experimental accuracies on both types of measurements, and the required precision in the NME permitting to address the issue of Majorana CP-violation in the lepton sector.

Neutrino wave packet propagation in gravitational fields

We discuss the propagation of neutrino wave packets in a Lense–Thirring metric using a gravitational phase approach. We show that the neutrino oscillation length is altered by gravitational corrections and that neutrinos are subject to helicity flip induced by stellar rotation. For the case of a rapidly rotating neutron star, we show that absolute neutrino masses can be derived, in principle, from rotational contributions to the mass-induced energy shift, without recourse to mass generation models presently discussed in the literature.

Direct determination of the neutrino masses

The only model-independent method to determine the absolute neutrino mass scale is still the investigation of a β decay spectrum near its endpoint. The tritium β decay experiments at Mainz and Troitsk have recently been finished yielding upper limits on the neutrino mass of about 2 eV. The bolometric experiments using 187Re reached a sensitivity on the neutrino mass of 15 eV. The new Karlsruhe Tritium Neutrino Experiment (KATRIN) will enhance the sensitivity on the neutrino mass by another order of magnitude down to 0.2 eV by using a very strong windowless gaseous molecular tritium source and a huge ultra-high resolution electrostatic spectrometer of MAC-E-Filter type to probe the cosmological relevant neutrino mass range and scenarios of quasi-degenerated neutrino masses. To cite this article: C. Weinheimer, C. R. Physique 6 (2005).

Double beta decay versus cosmology: MajoranaCPphases and nuclear matrix elements

We discuss the relation between the absolute neutrino mass scale, the effective mass measured in neutrinoless double beta decay, and the Majorana $CP$ phases. Emphasis is placed on estimating the upper bound on the nuclear matrix element entering calculations of the double beta decay half-life. Combining the claimed evidence for neutrinoless double beta decay with the neutrino mass bound from cosmology, one of the Majorana $CP$ phases can be constrained.

Testing varying neutrino mass with short gamma ray bursts

In this paper we study the possibility of probing for the absolute neutrino mass and its variation with short Gamma Ray Burst (GRB). We have calculated the flight time difference between a massive neutrino and a photon in two different approaches to mass varying neutrinos. Firstly we parametrize the neutrino mass as a function of redshift in a model independent way, then we consider two specific models where the neutrino mass varies during the evolution of the Quintessence fields. Our calculations show in general the value of the time delay is changed substantially relative to a constant neutrino mass. Furthermore our numerical results show that the flight time delay in these models is expected to be larger than the duration time of the short GRB, which opens a possibility of testing the scenario of mass varying neutrino with the short GRB.

Mass varying neutrinos in the Sun

In this work we study the phenomenological consequences of the dependence of mass varying neutrinos on the neutrino density in the Sun, which we precisely compute in each point along the neutrino trajectory. We find that a generic characteristic of these scenarios is that they establish a connection between the effective Δ m 2 in the Sun and the absolute neutrino mass scale. This does not lead to any new allowed region in the oscillation parameter space. On the contrary, due to this effect, the description of solar neutrino data worsens for large absolute mass. As a consequence a lower bound on the level of degeneracy can be derived from the combined analysis of the solar and KamLAND data. In particular this implies that the analysis favours normal over inverted mass orderings. These results, in combination with a positive independent determination of the absolute neutrino mass, can be used as a test of these scenarios together with a precise determination of the energy dependence of the survival probability of solar neutrinos, in particular for low energies.

Phenomenology of Absolute Neutrino Masses

The phenomenology of absolute neutrino masses is reviewed, focusing on tritium β decay, cosmological measurements and neutrinoless double- β decay.

Thermal leptogenesis

Thermal leptogenesis is reviewed with particular emphasis on the derivation of the constraints on neutrino masses, including a stringent upper bound on the absolute neutrino mass scale mi<0.1 eV.

Neutrino helicity and chirality transitions in Schwarzschild space-time

We study the helicity and chirality transitions of a high-energy neutrino propagating in a Schwarzschild space-time background. Using both traditional Schwarzschild and isotropic spherical co-ordinates, we derive an ultrarelativistic approximation of the Dirac Hamiltonian to first-order in the neutrino's rest mass, via a generalization of the Cini-Touschek transformation that incorporates non-inertial frame effects due to the noncommutative nature of the momentum states in curvilinear co-ordinates. Under general conditions, we show that neutrino's helicity is not a constant of the motion in the massless limit due to space-time curvature, while the chirality transition rate still retains an overall dependence on mass. We show that the chirality transition rate generally depends on the zeroth-order component of the neutrino's helicity transition rate under the Cini-Touschek transformation. It is also shown that the chiral current for high-energy neutrinos is altered by corrections due to curvature and frame-dependent effects, but should have no significant bearing on the chiral anomaly in curved space-time. We determine the upper bound for helicity and chirality transitions near the event horizon of a black hole. The special case of a weak-field approximation is also considered, which includes the gravitational analogue of Berry's phase first proposed by Cai and Papini. Finally, we propose a method for estimating the absolute neutrino mass and the number of right-handed chiral states from the expectation values of the helicity and chirality transition rates in the weak-field limit.

Diagnostic potential of cosmic-neutrino absorption spectroscopy

Annihilation of extremely energetic cosmic neutrinos on the relic-neutrino background can give rise to absorption lines at energies corresponding to formation of the electroweak gauge boson ${Z}^{0}$. The positions of the absorption dips are set by the masses of the relic neutrinos. Suitably intense sources of extremely energetic (${10}^{21}--{10}^{25}\mathrm{\text{\ensuremath{-}}}\mathrm{eV}$) cosmic neutrinos might therefore enable the determination of the absolute neutrino masses and the flavor composition of the mass eigenstates. Several factors---other than neutrino mass and composition---distort the absorption lines, however. We analyze the influence of the time evolution of the relic-neutrino density and the consequences of neutrino decay. We consider the sensitivity of the line shape to the age and character of extremely energetic neutrino sources, and to the thermal history of the Universe, reflected in the expansion rate. We take into account Fermi motion arising from the thermal distribution of the relic-neutrino gas. We also note the implications of Dirac vs. Majorana relics, and briefly consider unconventional neutrino histories. We ask what kinds of external information would enhance the potential of cosmic-neutrino absorption spectroscopy, and estimate the sensitivity required to make the technique a reality.

Direct Neutrino Mass Experiments

The determination of the absolute neutrino mass scale is of fundamental importance in particle physics and cosmology. Apart from indirect methods (large scale structure formation in cosmology, time-of-flight measurements of Supernova neutrinos, searching for 0νββ decay) there is only one model-independent strategy to address the neutrino mass directly: investigating the kinematics of electrons from β decay. We present an overview of the experimental strategies as well as results from experiments investigating the kinematics of β decay. Activities to reach sub-eV sensitivity in the near future by analysing the electron energy of the 3H β decay near its endpoint are reported.

Absolute Masses of Neutrinos—Experimental Results and Future Possibilities

The discovery of neutrino oscillation proved recently that neutrinos have non- vanishing masses in contrast to their description within the Standard Model of particle physics. However, the absolute neutrino mass scale, which is very important for particle physics as well as for cosmology and astrophysics, cannot be revealed by oscillation experiments. Although there are a few ways to determine the neutrino mass scale, the only model-independent method is the investigation of the electron energy spectrum of a β decay near its endpoint. The tritium β decay experiments at Mainz and Troitsk using tritium have recently been finished and have given upper limits on the neutrino mass scale of about 2 eV/c2. The bolometric experiments using 187Re have finished the first experiments yielding a sensitivity on the neutrino mass of 15 eV/c2. The new Karlsruhe Tritium Neutrino Experiment (KATRIN) will enhance the sensitivity on the neutrino mass by another order of magnitude down to 0.2 eV/c2 by an ultra-precise measurement of the tritium β decay spectrum using a very strong windowless gaseous molecular tritium source and a huge ultra-high resolution electrostatic spectrometer of MAC-E-Filter type.

Observables sensitive to absolute neutrino masses: Constraints and correlations from world neutrino data

In the context of three-flavor neutrino mixing, we present a thorough study of the phenomenological constraints applicable to three observables sensitive to absolute neutrino masses: The effective neutrino mass in Tritium beta decay (m_beta); the effective Majorana neutrino mass in neutrinoless double beta decay (m_2beta); and the sum of neutrino masses in cosmology (Sigma). We discuss the correlations among these variables which arise from the combination of all the available neutrino oscillation data, in both normal and inverse neutrino mass hierarchy. We set upper limits on m_beta by combining updated results from the Mainz and Troitsk experiments. We also consider the latest results on m_2beta from the Heidelberg-Moscow experiment, both with and without the lower bound claimed by such experiment. We derive upper limits on Sigma from an updated combination of data from the Wilkinson Microwave Anisotropy Probe (WMAP) satellite and the 2 degrees Fields (2dF) Galaxy Redshifts Survey, with and without Lyman-alpha forest data from the Sloan Digital Sky Survey (SDSS), in models with a non-zero running of the spectral index of primordial inflationary perturbations. The results are discussed in terms of two-dimensional projections of the globally allowed region in the (m_beta,m_2beta,Sigma) parameter space, which neatly show the relative impact of each data set. In particular, the (in)compatibility between Sigma and m_2beta constraints is highlighted for various combinations of data. We also briefly discuss how future neutrino data (both oscillatory and non-oscillatory) can further probe the currently allowed regions.

Double-beta decay and neutrino mass

Recent achievements in the study of double-beta (ββ) decay are presented. We discuss the potential of this process to search, beyond Standard Model physics, for the QRPA-based methods used for the calculation of the relevant nuclear matrix elements and the derivation of the neutrino mass from both ββ-decay calculations and neutrino oscillation and cosmological data. The key position of the ββ-decay experiments in resolving the neutrino absolute mass is highlighted.

Relic neutrino absorption spectroscopy

Resonant annihilation of extremely high-energy cosmic neutrinos on big-bang relic anti-neutrinos (and vice versa) into Z bosons leads to sizable absorption dips in the neutrino flux to be observed at Earth. The high-energy edges of these dips are fixed, via the resonance energies, by the neutrino masses alone. Their depths are determined by the cosmic neutrino background density, by the cosmological parameters determining the expansion rate of the Universe, and by the large redshift history of the cosmic neutrino sources. We investigate the possibility of determining the existence of the cosmic neutrino background within the next decade from a measurement of these absorption dips in the neutrino flux. As a by-product, we study the prospects to infer the absolute neutrino mass scale. We find that, with the presently planned neutrino detectors (ANITA, Auger, EUSO, OWL, RICE, and SalSA) operating in the relevant energy regime above ${10}^{21}\mathrm{eV},$ relic neutrino absorption spectroscopy becomes a realistic possibility. It requires, however, the existence of extremely powerful neutrino sources, which should be opaque to nucleons and high-energy photons to evade present constraints. Furthermore, the neutrino mass spectrum must be quasidegenerate to optimize the dip, which implies ${m}_{\ensuremath{\nu}}\ensuremath{\gtrsim}0.1\mathrm{eV}$ for the lightest neutrino. With a second generation of neutrino detectors, these demanding requirements can be relaxed considerably.

Detection of a close supernova gravitational wave burst in a network of interferometers, neutrino and optical detectors

Trying to detect the gravitational wave (GW) signal emitted by a type II supernova is a main challenge for the GW community. Indeed, the corresponding waveform is not accurately modeled as the supernova physics is very complex; in addition, all the existing numerical simulations agree on the weakness of the GW emission, thus restraining the number of sources potentially detectable. Consequently, triggering the GW signal with a confidence level high enough to conclude directly to a detection is very difficult, even with the use of a network of interferometric detectors. On the other hand, one can hope to take benefit from the neutrino and optical emissions associated to the supernova explosion, in order to discover and study GW radiation in an event already detected independently. This article aims at presenting some realistic scenarios for the search of the supernova GW bursts, based on the present knowledge of the emitted signals and on the results of network data analysis simulations. Both the direct search and the confirmation of the supernova event are considered. In addition, some physical studies following the discovery of a supernova GW emission are also mentioned: from the absolute neutrino mass to the supernova physics or the black hole signature, the potential spectrum of discoveries is wide.