423 research outputs found
On the production of a lepton pair in the collision of ultrarelativistic neutral particle with nonzero magnetic moment with nuclei
Explicit formulas which describe muon pair production in reaction through neutrino magnetic moment are obtained and used to
derive in the leading approximation cross section of muon pair production in
-scattering due to neutrino magnetic moment. This cross section appears
to be proportional to . Comparison with experimental data on
tridents production provides an upper bound , which is approximately two orders of magnitude weaker than that from
elastic scattering data.Comment: 9 pages, 4 figures, numerical estimates are improve
Extra quark-lepton generations and precision measurements
The existence of extra chiral generations with all fermions heavier than M_Z
is strongly disfavoured by the precision electroweak data. However the data are
fitted nicely even by a few extra generations, if one allows neutral leptons to
have masses close to 50 GeV. The data allow inclusion of one additional
generation of heavy fermions in SUSY extension of Standard Model if chargino
and neutralino have masses close to 60 GeV with \Delta m =~ 1 GeV.Comment: 14 pages, 5 figure
Seiberg Duality and e+ e- Experiments
Seiberg duality in supersymmetric gauge theories is the claim that two
different theories describe the same physics in the infrared limit. However,
one cannot easily work out physical quantities in strongly coupled theories and
hence it has been difficult to compare the physics of the electric and magnetic
theories. In order to gain more insight into the equivalence of two theories,
we study the ``e+ e-'' cross sections into ``hadrons'' for both theories in the
superconformal window. We describe a technique which allows us to compute the
cross sections exactly in the infrared limit. They are indeed equal in the
low-energy limit and the equality is guaranteed because of the anomaly matching
condition. The ultraviolet behavior of the total ``e+ e-'' cross section is
different for the two theories. We comment on proposed non-supersymmetric
dualities. We also analyze the agreement of the ``\gamma\gamma'' and ``WW''
scattering amplitudes in both theories, and in particular try to understand if
their equivalence can be explained by the anomaly matching condition.Comment: 24 pages, 2 figures, uses psfi
Inclusive Semi-leptonic B Decays to order 1/m_b^4
We give a systematic way to compute higher orders in the 1/m_b expansion in
inclusive semi-leptonic decays at tree level. We reproduce the known 1/m_b^3
terms and compute the 1/m_b^4 terms at tree level. The appearing
non-perturbative parameters and the impact on the determination of V_{cb} are
discussed.Comment: 23 pages, 3 figures, uses phystex.st
Higgs potential bounds on extra quark-lepton generations
We consider the bounds for the values of higgs mass and of the mass of
the extra quarks and leptons derived from the stability of vacuum
and from the absence of Landau pole in Higgs potential. We find that in the
case of the absence of new physics up to the GUT scale the bounds for the mass
of the 4th generation are so restrictive that the negative result of CDF search
for extra quarks closes the window for fourth generation. In the case of the
absence of new physics up to GeV we get weaker but still nontrivial
bounds on and as well.Comment: 7pp, LaTeX, uses epsf, 5 figures, PS file available at
http://venus.itep.ru/preprints/1995/95058.ps.g
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
The strength of small-instanton amplitudes in gauge theories with compact extra dimensions
We study instanton effects in theories with compact extra dimensions. We
perform an instanton calculation in a 5d theory on a circle of radius R, with
gauge, scalar, and fermion fields in the bulk of the extra dimension. We show
that, depending on the matter content, instantons of size rho << R can dominate
the amplitude. Using deconstruction as an ultraviolet definition of the theory
allows us to show, in a controlled approximation, that for a small number of
bulk fermions, the amplitude for small size instantons exponentially grows as
e^{O(1)R/rho}.Comment: Title modified, references added, typos corrected. Version to appear
in JHEP. 24 pages, 1 figur
The Minimal Supersymmetric Fat Higgs Model
We present a calculable supersymmetric theory of a composite ``fat'' Higgs
boson. Electroweak symmetry is broken dynamically through a new gauge
interaction that becomes strong at an intermediate scale. The Higgs mass can
easily be 200-450 GeV along with the superpartner masses, solving the
supersymmetric little hierarchy problem. We explicitly verify that the model is
consistent with precision electroweak data without fine-tuning. Gauge coupling
unification can be maintained despite the inherently strong dynamics involved
in electroweak symmetry breaking. Supersymmetrizing the Standard Model
therefore does not imply a light Higgs mass, contrary to the lore in the
literature. The Higgs sector of the minimal Fat Higgs model has a mass spectrum
that is distinctly different from the Minimal Supersymmetric Standard Model.Comment: 13 pages, 5 figures, REVTe
Symmetries, Large Leptonic Mixing and a Fourth Generation
We show that large leptonic mixing occurs most naturally in the framework of
the Sandard Model just by adding a fourth generation. One can then construct a
small discrete symmetry, instead of the large ,
which requires that the neutrino as well as the charged lepton mass matrices be
proportional to a democratic mass matrix, where all entries are
equal to unity. Without considering the see-saw mechanism, or other more
elaborate extensions of the SM, and contrary to the case with only 3
generations, large leptonic mixing is obtained when the symmetry is broken.Comment: 6 pages, ReVTeX, no figure
Determination of the magnetic susceptibility of the quark condensate using radiative heavy meson decays
We use a light-cone sum rule (LCSR) analysis of the branching ratios of
radiative meson decays to contrain the value of the magnetic susceptibility of
the quark condensate . For the first time, we use a complete set of
three-particle distribution amplitudes that enables us to give a consistent
prediction for the branching ratios. Furthermore we will make use of a very
recent update of several non-perturbative parameters. Our final result for
(assuming asymptotic wave
functions) agrees with the currently used value of .Comment: 21 pages, 4 figures, references adde
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