1,361 research outputs found
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 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
or 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
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 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 is vanishingly small. In addition, for \alpha
\gsim 10^{-52} and normal hierarchy, resonant enhancement of
results in nontrivial energy dependent effects on the survival
probability. We perform a complete three generation analysis, and obtain
constraints on through a global fit to the solar neutrino and KamLAND
data. We get the limits and
when is much smaller than our
distance from the galactic center. With larger , the collective LR
potential due to all the electrons in the galaxy becomes significant and the
constraints on 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
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 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 at LEP-200 with total final luminosity of .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 ,
where 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 decay
The first limit on the branching ratio of the electric charge-nonconserving
invisible muon decay 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 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 -decays and appears to reveal the first manifestations of electroweak radiative corrections. In fact, these data differ, at the level of , from their electroweak Born values, while they agree, to within , with the theoretical values which take the electroweak radiative corrections into account. Previous data were within in agreement with both sets of values
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
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
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