1,195 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
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
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
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
Trialogue on the number of fundamental constants
This paper consists of three separate articles on the number of fundamental
dimensionful constants in physics. We started our debate in summer 1992 on the
terrace of the famous CERN cafeteria. In the summer of 2001 we returned to the
subject to find that our views still diverged and decided to explain our
current positions. LBO develops the traditional approach with three constants,
GV argues in favor of at most two (within superstring theory), while MJD
advocates zero.Comment: Version appearing in JHEP; 31 pages late
Dirac neutrino magnetic moment and the shock wave revival in a supernova explosion
The process of the two-step conversion of the neutrino helicity, , is analysed in the supernova conditions, where the first
stage is realized due to the interaction of the neutrino magnetic moment with
the plasma electrons and protons in the supernova core. The second stage is
caused by the neutrino resonant spin-flip in a magnetic field of the supernova
envelope. Given the neutrino magnetic moment within the interval , and with the existence of the
magnetic field at the scale G between the neutrinosphere and the
shock-wave stagnation region, it is shown that an additional energy of the
order of erg can be injected into this region during the typical time
of the shock-wave stagnation. This energy could be sufficient for stumulation
of the damped shock wave.Comment: 6 pages, LaTeX, 2 PS figures, based on the talk presented by N.V.
Mikheev at the XV International Seminar Quarks'2008, Sergiev Posad, Moscow
Region, May 23-29, 2008, to appear in the Proceeding
Mass of the higgs versus fourth generation masses
The predicted value of the higgs mass is analyzed assuming the
existence of the fourth generation of leptons () and quarks ().
The steep and flat directions are found in the five-dimensional parameter
space: , , , , . The LEPTOP fit of the precision
electroweak data is compatible (in particular) with GeV, GeV, GeV, GeV, and GeV. The quality of fits drastically improves when the data on b- and
c-quark asymmetries and new NuTeV data on deep inelastic scattering are
ignored.Comment: 8 pages, 4 figure
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