Boris Kayser

Constraints from neutrino oscillation experiments on the effective Majorana mass in neutrinoless double beta decay

Abstract We determine the possible values of the effective Majorana neutrino mass |〈m〉|=| ∑ j U ej 2 m j | in the different phenomenologically viable three and four-neutrino scenarios. The quantities U αj ( α = e , μ , τ ,…) denote the elements of the neutrino mixing matrix and the Majorana neutrino masses m j ( j =1,2,3,…) are ordered as m 1 2 Assuming m 1 ≪ m 3 in the three-neutrino case and m 1 ≪ m 4 in the four-neutrino case, we discuss, in particular, how constraints on |〈 m 〉| depend on the mixing angle relevant in solar neutrino oscillations and on the three mass-squared differences obtained from the analyses of the solar, atmospheric and LSND data. If neutrinoless double β -decay proceeds via the mechanism involving |〈 m 〉|, conclusions about neutrinoless double β -decay can be drawn. If one of the two viable four-neutrino schemes (Scheme A) is realized in nature, |〈 m 〉| can be as large as 1 eV and neutrinoless double β -decay could possibly be discovered in the near future. In this case a Majorana CP phase of the mixing matrix U could be determined. In the other four-neutrino scheme (Scheme B) there is an upper bound on |〈 m 〉| of the order of 10 −2 eV. In the case of three-neutrino mixing the same is true if the neutrino mass spectrum is hierarchical, however, if there exist two quasi-degenerate neutrinos and the first neutrino has a much smaller mass, values of |〈 m 〉| as large as ∼0.1 eV are possible.

Determining theCP-violating phase γ

The weak phase γ is conventionally probed by theBs→ρ0 mode. The predicted rate is tiny. Even if aBs→ρ0Ks rate difference could be established, it would not be clear that sin 2γ had been measured, because amplitudes with other weak phases may contribute significantly. Non-CP eigenstates, such asBs→Ds±K∓, have a two-fold advantage overBs→ρ0Ks. Their rates are orders of magnitude above that forBs→ρ0Ks, and they probe theCP-violating phase γ, without any contamination from other weak phases. Detailed time-dependent studies of non-CP eigenstates remove possible final-state phases and extract the weak phase γ.

Fate of the sterile neutrino

Abstract In light of recent Super-Kamiokande data and global fits that seem to exclude both pure ν μ → ν s oscillations of atmospheric neutrinos and pure ν e → ν s oscillations of solar neutrinos (where ν s is a sterile neutrino), we reconsider four-neutrino models to explain the LSND, atmospheric, and solar neutrino oscillation indications. We argue that the solar data, with the exception of the 37 Cl results, are suggestive of ν e → ν s oscillations that average to a probability of approximately 1 2 . In this interpretation, with two pairs of nearly degenerate mass eigenstates separated by order 1 eV, the day-night asymmetry, seasonal dependence, and energy dependence for 8 B neutrinos should be small. Alternatively, we find that four-neutrino models with one mass eigenstate widely separated from the others (and with small sterile mixings to active neutrinos) may now be acceptable in light of recently updated LSND results; the 37 Cl data can be accommodated in this model. For each scenario, we present simple four-neutrino mixing matrices that fit the stated criterion and discuss future tests.

Are neutrons always left-handed?

Abstract We explore the possibility of using neutral weak interactions to see whether neutrinos may flip their helicity. Experiments ranging from low-energy neutrino-nucleus scattering to high-energy inclusive reactions are discussed as tests for the presence of helicity-flipping scalar, pseudoscalar and tensor interactions.

NEUTRINO MASS AND OSCILLATION

▪ Abstract The question of neutrino mass is one of the major riddles in particle physics. Recently, strong evidence that neutrinos have nonzero masses has been found. Though tiny, these masses could be large enough to contribute significantly to the mass density of the universe. The evidence for nonvanishing neutrino masses is based on the apparent observation of neutrino oscillation—the transformation of a neutrino from one type or “flavor” to another. We explain the physics of neutrino oscillation and review and weigh the evidence that it actually occurs in nature. We discuss the constraints on neutrino mass from cosmology and from experiments with negative results. After presenting illustrative neutrino mass spectra suggested by the present data, we consider how experiments in the near and distant future can further illuminate the nature of neutrinos and their masses.

DETERMINING THE QUARK MIXING MATRIX FROM CP-VIOLATING ASYMMETRIES

If the standard model explanation of

EPR experiments without “collapse of the wavefunction”

\mathrm{CP}

B decay CP asymmetries, discrete ambiguities and new physics

violation is correct, then measurements of

The role of the vacuum insertion approximation in calculating CP asymmetries in B decays

\mathrm{CP}

Neutrino mass, mixing, and oscillation

-violating asymmetries in