244 research outputs found
Top quark rare decays in the standard model and beyond
Theoretical predictions for the top quark rare decays are reviewed within and
beyond the standard model. Expectations at the CERN Large Hadron Collider are
discussed.Comment: 7 pages, 2 figures. Published in *Moscow 1999, High energy physics
and quantum field theory* 224-230. A few references adde
Lepton Spectra and the B Polarization at LEP
I review the present state of knowledge on lepton energy spectra in the
inclusive semileptonic decay of beauty hadrons, as a means to measure b
polarization effects on the Z peak. Charged-lepton as well as neutrino spectra
are considered.Comment: 15 pages + 5 figs (available upon request), LaTex, preprint Rome
University "La Sapienza" n.1009, March 199
Testing Effective Yukawa Couplings in Higgs Searches at the Tevatron and LHC
We explore the possibility that, while the Higgs mechanism provides masses to
the weak-gauge bosons at the electroweak scale as in the standard model,
fermion masses are generated by an unknown mechanism at a higher energy scale.
At low energies, the standard model can then be regarded as an effective field
theory, where fermion masses explicitly break the electroweak SU(2)_L \times
U(1)_Y gauge symmetry. If \Lambda is the renormalization scale where the
renormalized Yukawa couplings vanish, then at energies lower than \Lambda,
effective Yukawa couplings will be radiatively induced by nonzero fermion
masses. In this scenario, Higgs-boson decays into photons and weak gauge-bosons
pairs are in general quite enhanced for a light Higgs. However, depending on
\Lambda, a substantial decay rate into b \bar{b} can arise, that can be of the
same order as, or larger than, the enhanced H\to gamma gamma rate. A new
framework for Higgs searches at hadron colliders is outlined, vector-boson
fusion becoming the dominant production mechanism at the CERN LHC, with an
important role also played by the WH/ZH associated production. A detailed
analysis of the Higgs branching fractions and their implications in Higgs
searches is provided, versus the energy scale \Lambda.Comment: 35 pages, 10 figures, 5 tables, Fig.[10] corrected, 1 new reference
adde
Ultrahigh energy neutrinos scattering off relic light neutrinos to explain UHECR above GZK cut off and thin blazars
UHE neutrinos may transfer highest cosmic-rays energies overcoming
BBR and radio-waves opacities (the GZK cut off) from most distant
AGN sources at the age of the Universe. These UHE might scatter onto
those (light and cosmological) relic neutrinos clustered around our galactic
halo or nearby neutrino hot dark halo clustered around the AGN blazar and its
jets. The branched chain reactions from a primordial nucleon (via photo
production of pions and decay to UHE neutrinos) toward the consequent beam dump
scattering on galactic relic neutrinos is at least three order of magnitude
more efficient than any known neutrino interactions with Earth atmosphere or
direct nucleon propagation. Therefore the rarest cosmic rays (as the 320 EeV
event) might be originated at far distances (as Seyfert
galaxy MCG 8-11-11); its corresponding UHE radiation power is in agreement with
the observed one in MeV gamma energies. The final chain products observed on
Earth by the Fly's Eye and AGASA detectors might be mainly neutron and
anti-neutrons and delayed, protons and anti-protons at symmetric off-axis
angles. These hadronic products are most probably secondaries of or
pair productions and might be consistent with the last AGASA discoveries
of doublets and one triplet event.Comment: 4 pages, 1 figure.To be presented at the 26th ICRC Conference
1999,Salt Lak
Higgs boson plus photon production at the LHC: a clean probe of the b-quark parton densities
Higgs boson production in association with a high pT photon at the CERN Large
Hadron Collider is analyzed, in the framework of the MSSM model, for the
heavier neutral Higgs bosons. The request of an additional photon in the
exclusive Higgs boson final state selects b-quark pairs among the possible
initial partonic states, since gluon-gluon initial states are not allowed by
C-parity conservation. Hence, the measurement of cross sections for neutral
Higgs boson plus photon production can provide a clean probe of the b-quark
density in the proton as well as of the b-quark Yukawa coupling. The
suppression of the production rates by the b-quark electromagnetic coupling can
be compensated by the enhanced Higgs boson Yukawa coupling to b's in the large
tan(beta) regime. The Higgs boson decay into a tau-lepton pair is considered,
and irreducible backgrounds with corresponding signal significances are
evaluated.Comment: 10 pages, 4 figures, a few comments and 3 references added at the
end. To appear in Physical Review
- …