B. Pontecorvo

Neutrino astronomy and lepton charge

Abstract It is shown that lepton nonconservation might lead to a decrease in the number of detectable solar neutrinos at the earth surface, because of νe←νμ oscillations, similar to K o ← K o oscillations. Equations are presented describing such oscillations for the case when there exist only four neutrino states.

Lepton mixing and neutrino oscillations

Abstract The present article is a review of phenomena connected with neutrino oscillations. Mixing of two neutrinos (Majorana as well as Dirac) with masses m1 and m2 is considered in detail. It is shown that the hypothesis of lepton mixing is not in contradiction with the existing data if |m12−m22| ⪅ 1 (eV)2. Possible experiments designed to reveal neutrino oscillations at reactor, meson factory and high energy accelerator facilities are considered. In such experiments oscillation might be found if |m 1 2 −m 2 2 | ⪆ 0.01 (eV) 2 . The possibilities of searching for oscillations by experiments on cosmic ray neutrinos and especially on solar neutrinos are discussed in detail. The last experiments have an incredible high sensitivity from the point of view of testing the lepton mixing hypothesis (oscillation effects might be observable if |m 1 2 −m 2 2 | ⪆ 10 −12 (eV) 2 ). The “solar neutrino puzzle” is also discussed from the point of view of lepton mixing. Neutrino oscillations are considered then in the case where in nature there exist N ⩾ 2 neutrino types. In conclusion the case of heavy lepton mixing is considered. It is shown that in a concrete scheme with right-handed currents, the probabilities of such processes as μ → eγ, μ → 3e etc. can be close to existing experimental upper limits, provided the heavy lepton masses are of an order of a few GeV, whereas the probabilities of the above processes are entirely negligible if only neutrinos are mixed.

Lepton mixing, μ → e + γ decay and neutrino oscillations

Abstract The μ → e γ decay is investigated in a gauge theory with lepton mixing under the assumption that in nature there exist heavy leptons. It is shown that for lepton masses of the order of a few GeV the μ → e γ decay probability may well be close to its experimentally determined upper limit. The relation between such a decay process and neutrino oscillations is briefly considered.

On the νe + e → νe + e process

Abstract The scattering of antineutrinos by electrons is considered under different assumptions about the ν e − e -interaction. The recoil electron spectra are calculated for the practical case where the antineutrino source is an uranium reactor. It is shown that even rough measurements of the electron spectrum would allow to draw important conclusions about the nature of the interaction.

Quark-lepton analogy and neutrino oscillations

Abstract A theory of the weak interactions of leptons which is analogous to that of the weak interaction of the four quarks is considered. Mixing of neutrinos (with finite masses) is introduced and arguments are given in favour of maximum mixing. Physical consequences of the theory are discussed with emphasis on neutrino oscillations.

On the ν - ν interaction

Abstract A new hypothetical interaction between neutrinos is considered. It is shown that even relatively strong ν e - ν e , ν μ - ν μ and ν e - ν μ interactions are not in contradiction with existing data and upper limits for the corresponding interaction constant are obtained. New experiments are suggested which might give information on ν - ν interactions.

Neutrino oscillations in new mixing schemes with either Dirac or Majorana masses

Abstract Neutrino oscillations with either Dirac or Majorana mass terms are considered in new mixing schemes requiring an even number of charged leptons. It is shown that the investigation of oscillations may allow one to distinguish Dirac and Majorana mass eigenvalues.

On the anti-nu/e + e --> anti-nu/e + e process

Abstract The scattering of antineutrinos by electrons is considered under different assumptions about the ν e − e -interaction. The recoil electron spectra are calculated for the practical case where the antineutrino source is an uranium reactor. It is shown that even rough measurements of the electron spectrum would allow to draw important conclusions about the nature of the interaction.

Majorana and dirac masses, neutrino oscillations and the number of charged leptons

Abstract A new scheme of lepton mixing is proposed in which the number of charged leptons, as well as the number of neutrino types, must e even. Dirac and Majorana masses coexist and a “hierarchy” of different oscillation types is quite natural (for example υ e ⇌ υ μ oscillations might be suppressed with respect to υ e ⇌ υ τ oscillations).

Search for radioactive superdense nuclei

Abstract The results of an experimental search for new long-lived particles performed at Serpukhov discussed in terms of the possible existence of superdense nuclei. The upper limits of cross sections for the production of radiactive superdense nuclei in collisions of high energy protons with normal nuclei are presented.