Theory of Z boson decays

The precision data on Z boson decays from LEP-I and SLC colliders are compared with the predictions based on the Minimal Standard Theory. The Born approximation of the theory is based on three most accurately known observables: G_mu -- the four fermion coupling constant of muon decay, m_Z -- the mass of the Z boson, and alpha(m_Z) -- the value of the running fine structure constant at the scale of m_Z. The electroweak loop corrections are expressed, in addition, in terms of the masses of higgs, m_H, of the top and bottom quarks, m_t and m_b, and of the strong interaction constant alpha_s(m_Z). The main emphasis of the review is focused on the one-electroweak-loop approximation. Two electroweak loops have been calculated in the literature only partly. Possible manifestations of new physics are briefly discussed.Comment: 80 pages, 16 figures, accepted in Reports on Progress in Physic

Electroweak radiative corrections in Z boson decays

Contribution to A.D.Sakharov memorial volume. A detailed review of the electroweak radiative corrections to the Z-boson decays in the framework of the Minimal Standard Modelm (MSM) is presented. After a short historical introduction we describe the optimal parametrization of the MSM, especially of the Born approximation, and derive expressions for the one-loop electroweak corrections. Finally a global fit of all relevant experimental data is performed, resulting in fitted values of the top-quark mass, m_t, and strong coupling constant /alpha_s. Allowed range for the value of the Higgs mass, m_H, is discussed. Various details of calculations are described in 16 appendices.Comment: 98 pages,21 EPS and PS figures,uses epsf.sty, separate file with the tared, compressed and uuencoded figures is awailable at http://wwwtheor.itep.ru/~vysotsky/figures.u

Do neutrino oscillations allow an extra phenomenological parameter?

The quantity $\xi$ introduced recently in the phenomenological description of neutrino oscillations is in fact not a free parameter, but a fixed number.Comment: 2 pages, LaTeX 2e style articl

Constraints on flavor-dependent long range forces from solar neutrinos and KamLAND

Flavor-dependent long range (LR) leptonic forces, like those mediated by the $L_e-L_\mu$ or $L_e -L_\tau$ gauge bosons, constitute a minimal extension of the standard model that preserves its renormalizability. We study the impact of such interactions on the solar neutrino oscillations when the interaction range $R_{LR}$ is much larger than the Earth-Sun distance. The LR potential can dominate over the standard charged current potential inside the Sun in spite of strong constraints on the coupling $\alpha$ of the LR force coming from the atmospheric neutrino data and laboratory search for new forces. We demonstrate that the solar and atmospheric neutrino mass scales do not get trivially decoupled even if $\theta_{13}$ is vanishingly small. In addition, for \alpha \gsim 10^{-52} and normal hierarchy, resonant enhancement of $\theta_{13}$ results in nontrivial energy dependent effects on the $\nu_e$ survival probability. We perform a complete three generation analysis, and obtain constraints on $\alpha$ through a global fit to the solar neutrino and KamLAND data. We get the $3\sigma$ limits $\alpha_{e\mu} < 3.4 \times 10^{-53}$ and $\alpha_{e\tau} < 2.5 \times 10^{-53}$ when $R_{LR}$ is much smaller than our distance from the galactic center. With larger $R_{LR}$, the collective LR potential due to all the electrons in the galaxy becomes significant and the constraints on $\alpha$ become stronger by upto two orders of magnitude.Comment: 25 pages, 7 figure

Precision measurements, extra generations and heavy neutrino

The existence of extra chiral generations with all fermions heavier than $M_Z$ is strongly disfavored by the precision electroweak data. The exclusion of one additional generation of heavy fermions in SUSY extension of Standard Model is less forbidden if chargino and neutralino have low degenerate masses with $\Delta m \simeq 1$ GeV. However the data are fitted nicely even by a few extra generations, if one allows neutral leptons to have masses close to 50 GeV. Such heavy neutrino can be searched in the reaction $e^+ e^- \to N\bar{N}\gamma$ at LEP-200 with total final luminosity of $2600 pb^{-1}$.Comment: 5 pages, 6 figures, Proceedings ICHEP2000 Osaka conferenc

On the search for 50 GeV neutrinos

Using the computer code CompHEP we estimate the number of events and the background, at LEP II and TESLA, for the reaction $e^+ e^- \to N\bar{N}\gamma$, where $N$ is a hypothetical Dirac neutrino with mass of the order of 50 GeV.Comment: Standard LaTeX, 9 pages, 2 tables, 3 figure

Limit on the electric charge-nonconserving μ+→invisible\mu^+ \to invisible decay

The first limit on the branching ratio of the electric charge-nonconserving invisible muon decay $Br(\mu^+ \to invisible) < 5.2 \times 10^{-3}$ is obtained from the recently reported results on new determination of the Fermi constant from muon decays. The results of a feasibility study of a new proposed experiment for a sensitive search for this decay mode at the level of a few parts in 10^{11} are presented. Constrains on the $\tau \to invisible$ decay rate are discussed. These leptonic charge-nonconserving processes may hold in four-dimensional world in models with infinite extra dimensions, thus making their searches complementary to collider experiments probing new physics.Comment: 5 pages, 2 Figure, to appear in PR

First evidence for electroweak radiative corrections from the new precision data

The analysis of the newest data on the leptonic Z-decays and m.sub(W) appears to reveal the first manifestations of electroweak radiative corrections. In fact, these data differ, at the level of 2.sigma., from their electroweak Born values, while they agree, to within 1.sigma., with the theoretical values which take the electroweak radiative corrections into account. Previous data were within 1.sigma. in agreement with both sets of values.The analysis of the newest data on the leptonic $Z$-decays and $m_W$ appears to reveal the first manifestations of electroweak radiative corrections. In fact, these data differ, at the level of $2\sigma$, from their electroweak Born values, while they agree, to within $1\sigma$, with the theoretical values which take the electroweak radiative corrections into account. Previous data were within $1\sigma$ in agreement with both sets of values

Interplay of gravitation and linear superposition of different mass eigenstates

The interplay of gravitation and the quantum-mechanical principle of linear superposition induces a new set of neutrino oscillation phases. These ensure that the flavor-oscillation clocks, inherent in the phenomenon of neutrino oscillations, redshift precisely as required by Einstein's theory of gravitation. The physical observability of these phases in the context of the solar neutrino anomaly, type-II supernovae, and certain atomic systems is briefly discussed

Constraints on the variability of quark masses from nuclear binding

Based on recent work on nuclear binding, we update and extend the anthropic constraints on the light quark masses, with results that are more tightly constrained than previously obtained. We find that heavy nuclei would fall apart (because the attractive nuclear central potential becomes too weak) if the sum of the light quark masses m_u+m_d would exceed their physical values by 64% (at 95% confidence level). We summarize the anthropic constraints that follow from requiring the existence both of heavy atoms and of hydrogen. With the additional assumption that the quark Yukawa couplings do not vary, these constraints provide a remarkably tight anthropic window for the Higgs vacuum expectation value: 0.39 < v/v_physical < 1.64.Comment: 21 pages, 7 figure