Narrow Results

An appropriately placed array of new generation neutrino detectors, in conjunction with the use of nuclear devices as a source of intense flux of neutrinos, can serve as a powerful precision probe of neutrino–oscillation parameters. If such detectors are made mobile by placing them on a criss-crossing grid of railway tracks, one may under certain hostile circumstances use them to locate nuclear powered vehicles like submarines, aircraft carriers and any other strong neutrino sources. Since neutrinos cannot be shielded, it may not be possible to escape detection.

We show explicitly that four neutrino models of the 2+2 variety still provide an acceptable global fit to the solar, atmospheric and LSND neutrino data. The goodness of fit, defined in the usual way, is found to be 0.26 for the simplest such model. That is, we find that there is a 26% probability of obtaining a worse global fit to the neutrino data. We also make some specific comments on the paper, "Ruling out four-neutrino oscillation interpretations of the LSND anomaly", hep-ph/0207157, and explain why they reached drastically different conclusions.

The electron and muon number violating muonium–antimuonium oscillation process can proceed provided that neutrinos have nonzero masses and mix among the various generations. Modifying the Standard Model only by the inclusion of singlet right-handed neutrino fields and allowing for general neutrino masses and mixings, the leading order matrix element contributing to this process is computed. For the particularly interesting case where the neutrino masses are generated by a seesaw mechanism with a very large Majorana mass M_R≫M_W, it is found that both the very light and very heavy Majorana neutrinos each give comparable contributions to the oscillation time scale proportional to . Present experimental limits set by the non-observation of the oscillation process sets a lower limit on M_R of roughly of order 10⁴ GeV.

Within the context of the seesaw mechanism, we review the possible connection between the CP-violating phases which appear in the lepton unitary mixing matrix and are measurable in neutrino oscillations and other low-energy processes, with the ones which play a role in the generation of the baryon asymmetry of the universe through the leptogenesis mechanism.

It has been hypothesized recently that core collapse supernovae are triggered by mildly relativistic jets following observations of radio properties of these explosions. Association of a jet, similar to a gamma-ray burst jet but only slower, allows shock acceleration of particles to high energy and non-thermal neutrino emission from a supernova. Detection of these high energy neutrinos in upcoming kilometer scale Cherenkov detectors may be the only direct way to probe inside these astrophysical phenomena as electromagnetic radiation is thermal and contains little information. Calculation of high energy neutrino signal from a simple and slow jet model buried inside the pre-supernova star is reviewed here. The detection prospect of these neutrinos in water or ice detector is also discussed in this brief review. Jetted core collapse supernovae in nearby galaxies may provide the strongest high energy neutrino signal from point sources.

We investigate the interaction between the cosmological relic neutrinos, and primordial gravitational waves entering the horizon before the electroweak phase transition, corresponding to observable frequencies today ν₀≳10^-5Hz. We give an analytic formula for the traceless transverse part of the anisotropic stress tensor, due to weakly interacting neutrinos, and derive an integro-differential equation describing the propagation of cosmological gravitational waves at these conditions. We find that this leads to a decrease of the wave intensity in the frequency region accessible to the LISA space interferometer, that is at the present the most promising way to obtain a direct detection of a cosmological gravitational wave. The absorbed intensity does not depend neither on the perturbation wavelength, nor on the details of neutrino interactions, and is affected only by the neutrino fraction f_ν. The transmitted intensity amounts to 88% for the standard value f_ν=0.40523. An approximate formula for non-standard values of f_ν is given.

Quantitative bounds on Lorentz symmetry violation in the neutrino sector have been obtained by analyzing existing laboratory data on neutron β decay and pion leptonic decays. In particular some parameters appearing in the energy–momentum dispersion relations for ν_e and ν_μ have been constrained in two typical cases arising in many models accounting for Lorentz violation.

The author reviews a model for the emission of high energy cosmic rays, gamma-rays and neutrinos from AGN (Active Galactic Nuclei) that he has proposed since 1985. Further discussion of the knee energy phenomenon of the cosmic ray energy spectrum requires the existence of a heavy particle with mass in the knee energy range. A possible method of detecting such a particle in the Pierre Auger Project is suggested. Also presented is a relation between the spectra of neutrinos and gamma-rays emitted from AGN. This relation can be tested by high energy neutrino detectors such as ICECUBE, the Mediterranean Sea Detector and possibly by the Pierre Auger Project.

We examine dark matter annihilation in the Universe today. We first discuss the suggestion that the Galactic positron flux, which is difficult to account for with astrophysical sources, is produced by the annihilation of dark matter in the Galactic halo. We show that the positrons produced would necessarily be accompanied by a flux of gamma rays which exceed observational constraints, unless the dark matter mass is very low. We shall also derive a very general bond on the dark matter annihilation cross section. By considering annihilation into all Standard Model particles, we show that the least detectable final states, namely neutrinos, define an upper bound on the total annihilation cross section. Calculating the cosmic diffuse neutrino signal, and comparing it to the measured terrestrial atmospheric neutrino background, we derive a robust limit that is much stronger than the unitarity bound in the most interesting mass range. We conclude that dark matter self-annihilation rates cannot be large enough to have a significant effect on the density profiles of dark matter halos.

We study the effect of neutrino flux regeneration by neutral current on the Standard Model prediction for the recently proposed observable angular α_SM(E). This observable has a weak dependence with the initial flux through the regeneration term in the transport equation. We want to know the impact of the initial flux uncertainties on the mentioned observable.

In this paper we give a short review of liquid argon detectors for neutrino physics. We will first introduce noble liquid detectors with particular emphasis on liquid argon and detectors of the time projection chamber variety, and we will explain why liquid argon detectors are good for neutrino physics, in particular the measurement of the mixing angle θ₁₃, CP-violating phase δ_CP and determination of the mass hierarchy through ν_e appearance on a ν_μ beam. We will stress what we consider the main achievements and the main challenges facing liquid argon detectors for neutrino physics.

IceCube is a kilometer-scale high energy neutrino telescope under construction at the South Pole, a second-generation instrument expanding the capabilities of the AMANDA telescope. The scientific portfolio of IceCube includes the detection of neutrinos from astrophysical objects such as the sources of the cosmic rays, the search for dark matter, and fundamental physics using a very large data set of atmospheric neutrinos. The design and status of IceCube are briefly reviewed, followed by a summary of results to date from AMANDA and initial IceCube results from the 2007 run, with 22 of a planned 86 strings operational. The new infill array known as Deep Core, which will extend IceCube's capabilities to energies as low as 10 GeV, is also described.

A new method based on Synge's world function is developed for determining within the WKB approximation the gravitationally induced quantum phase shift of a particle propagating in a stationary spacetime. This method avoids any calculation of geodesics. A detailed treatment is given for relativistic particles within the weak field, linear approximation of any metric theory. The method is applied to the calculation of the oscillation terms governing the interference of neutrinos considered as the superposition of two eigenstates having different masses. It is shown that the neutrino oscillations are not sensitive to the gravitomagnetic components of the metric as long as the spin contributions can be ignored. Explicit calculations are performed when the source of the field is a spherical, homogeneous body. A comparison is made with previous results obtained in Schwarzschild spacetime.

The IceCube neutrino observatory at the South Pole uses 1 km³ of instrumented ice to detect both astrophysical and atmospheric neutrinos. Expanding the capabilities of the original design, the DeepCore sub-array is a low-energy extension to IceCube which will collect atmospheric neutrinos a year. The high statistics sample will allow DeepCore to make neutrino oscillation measurements at higher energies and longer baselines than current experiments. The first successful observation of neutrino induced cascades in a neutrino telescope has recently been observed in DeepCore, which upon further cultivation should help refine atmospheric neutrino flux models. Besides the fundamental neutrino physics, the low-energy reach of DeepCore, down to as low as 10 GeV, and multi-megaton effective volume will enhance indirect searches for WIMP-like dark matter. A new proposal seeking to lower the energy reach down to GeV known as the Phased IceCube Next Generation Upgrade (or PINGU) will also be described.

The most important open problems of the today's neutrino physics are the absolute values of the neutrino masses, the determination of the Dirac or the Majorana character and better measurements of the mixing matrix elements. Results of the neutrino oscillations experiments strongly confirm that the neutrinos have nonzero masses. Experiments give information about the differences between the squares of the masses but not any knowledge on their absolute values. Similarly neutrino oscillation phenomena does not help us to understand their Dirac or Majorana character. One of the processes that could clarify this important point is the double beta decay and the search is still going on but not yielded any positive results due to the big experimental difficulties. Also the inverse of this decay, e^-e^- → W^-W^- is another process that could be tested at the accelerators. This process is possible only if the neutrinos have masses and they are Majorana particles. Since neutrinos could have very tiny masses and the cross section of the above process is proportional to the square of the effective neutrino mass it is an extremely rare process. Also it violates total lepton number by two units, Δ = 2. In the literature the inverse neutrinoless double beta scattering have been extensively studied, in this article we obtain the relevant helicity amplitudes, investigate the effects of the neutrino mixing matrix elements, especially the roles of the CP violating phases and the possible CP asymmetries.

We suggest a simple model, based on the type-I seesaw mechanism, for the lepton mass matrices. The model hinges on an Abelian symmetry which leads to mass matrices with some vanishing matrix elements. The model predicts one massless neutrino and M_eμ = 0 (M is the effective light-neutrino Majorana mass matrix). We show that these predictions agree with the present experimental data if the neutrino mass spectrum is inverted, i.e. if m₃ = 0, provided the Dirac phase δ is very close to maximal (±π/ 2). In the case of a normal neutrino mass spectrum, i.e. when m₁ = 0, the agreement of our model with the data is imperfect — the reactor mixing angle θ₁₃ is too small in our model. Minimal leptogenesis is not an option in our model due to the vanishing elements in the Yukawa-coupling matrices.

The origin of highest energy cosmic rays remains unresolved. High-energy neutrinos may provide the clues to fundamental phenomena such as the origin of cosmic rays or dark matter in the Universe. The IceCube Neutrino Observatory, a km scale neutrino detector, has come into full operation in 2011. At the highest energy levels, prototypes of a new experiment, the Askaryan Radio Array, have been deployed and are being tested. We report on the status, first results and prospects of the experimental neutrino searches under way and planned at the South Pole.

The Micromegas detectors have been gaining importance as reliable options in their implementation to Time Projection Chambers (TPCs) in experiments searching for Rare Events mainly due to their demonstrated good performance regarding low background levels, energy and time resolution, gain and stability of operation. In the present paper, we will briefly review the latest developments carried out within the T-REX project of detector R&D, and the performance achieved in the context of several experiments: the CAST solar axion search experiment, the NEXT experiment of double beta decay and the MIMAC dark matter directional search.

The Gran Sasso National Laboratory of INFN (LNGS) is the largest underground laboratory for astroparticle physics in the world. Located in Italy between the cities of L'Aquila and Teramo, 120 km far from Rome, is a research infrastructure mainly dedicated to astroparticle and neutrino physics. It offers the most advanced underground facility in terms of dimensions, complexity and completeness of its infrastructures. LNGS is one of the four national laboratories run by the Istituto Nazionale di Fisica Nucleare (INFN).

The scientific program at LNGS is mainly focused on astroparticle, particle and nuclear physics. The laboratory presently hosts many experiments as well as R&D activities, including world-leading research in the fields of solar neutrinos, accelerator neutrinos (CNGS neutrino beam from CERN to Gran Sasso), dark matter (DM), neutrinoless double beta decay (2β0ν) and nuclear cross-section of astrophysical interest. Associate sciences like earth physics, biology and fundamental physics complement the activities. The laboratory is operated as an international science facility and hosts experiments whose scientific merit is assessed by an international advisory Scientific Committee.

A review of the main experiments carried out at LNGS will be given, together with the most recent and relevant scientific results achieved.

We investigate the possibility of expressing the charged leptons and neutrino mass matrices as linear combinations of elements of a single finite group. Constraints imposed on the resulting mixing matrix by current data restrict the group types, but allow a nonzero value for the θ₁₃ mixing angle.