353 research outputs found
Quasi-fixed point scenario in the modified NMSSM
The simplest extension of the MSSM that does not contradict LEP II
experimental bound on the lightest Higgs boson mass at is the
modified Next-to-Minimal Supersymmetric Standard Model (MNSSM). We investigate
the renormalization of Yukawa couplings and soft SUSY breaking terms in this
model. The possibility of -quark and -lepton Yukawa coupling
unification at the Grand Unification scale is studied. The particle
spectrum is analysed in the vicinity of the quasi-fixed point where the
solutions of renormalization group equations are concentrated at the
electroweak scale.Comment: 19 pages, 3 figures, LaTeX2
Infrared quasi-fixed solutions in the NMSSM
The considerable part of the parameter space in the MSSM corresponding to the
infrared quasi fixed point scenario is almost excluded by LEP II bounds on the
lightest Higgs boson mass. In the NMSSM the mass of the lightest Higgs boson
reaches its maximum value in the strong Yukawa coupling limit when Yukawa
couplings are essentially larger than gauge ones at the Grand Unification
scale. In this limit the solutions of the renormalisation group equations are
attracted to the infrared and Hill type effective fixed lines or surfaces in
the Yukawa coupling parameter space. They are concentrated in the vicinity of
quasi fixed points for . However the solutions are attracted
to such points rather weakly. For this reason when all the
solutions of the renormalisation group equations are gathered near a line in
the Hill type effective surface. In the paper the approximate solutions for the
NMSSM Yukawa couplings are given. The possibility of --quark and
--lepton Yukawa coupling unification at the scale is also
discussed.Comment: 32 pages, 8 figures included, LaTeX 2
Resonance-like coherent production of a pion pair in the reaction in the GeV region
The reaction was studied at 0.8-2.0 GeV proton
beam energies with the ANKE magnetic spectrometer at the COSY synchrotron
storage ring. The proton-deuteron pairs emerging with high momenta, 0.6-1.8
GeV/, were detected at small angles with respect to the proton beam.
Distribution over the reaction missing mass reveals a local enhancement
near the threshold of the pion pair production specific for the so-called ABC
effect. The enhancement has a structure of a narrow bump placed above a smooth
continuum. The invariant mass of the system in this enhancement
region exhibits a resonance-like peak at GeV/
with the width GeV/. A possible interpretation of
these features is discussed.Comment: 14 pages, 16 figures, submitted to Eur. Phys. J. A. v2: Added
references [42,43] in section IV.A. v3: revised version according to referee
remarks v4: revised version according to referee remark
and coupling constants in QCD sum rules
The coupling constants and
are calculated in the framework of
three-point QCD sum rules. The correlation functions responsible for these
coupling constants are evaluated considering contributions of both and
mesons as off-shell states, but in the absence of radiative
corrections. The results, and are
obtained for the considered strong coupling constants.Comment: 13 Pages and 11 Figure
The heavy baryons in the nonperturbative string approach
We present some piloting calculations of the short-range correlation
coefficients for the light and heavy baryons and masses of the doubly heavy
baryons and () in the framework of the
simple approximation within the nonperturbative QCD approach.Comment: 21 pages; to appear in Phys. Atom. Nuc
First measurements of spin correlations in the np -> d pi^0 reaction
The transverse spin correlations Axx and Ayy in the np-> d pi^0 reaction have
been measured for the first time in quasi-free kinematics at the COSY-ANKE
facility using a polarised deuteron beam incident on a polarised hydrogen cell
target. The results obtained for neutron energies close to 353 MeV and 600 MeV
are in good agreement with the partial wave analysis of data on the
isospin-related pp-> d pi^+ reaction, though the present results cover also the
small-angle region, which was largely absent from these data
Higgs bosons in the simplest SUSY models
Nowadays in the MSSM the moderate values of are almost excluded
by LEP II lower bound on the lightest Higgs boson mass. In the Next-to-Minimal
Supersymmetric Standard Model the theoretical upper bound on it increases and
reaches maximal value in the strong Yukawa coupling limit when all solutions of
renormalization group equations are concentrated near the quasi-fixed point.
For calculation of Higgs boson spectrum the perturbation theory method can be
applied. We investigate the particle spectrum in the framework of the modified
NMSSM which leads to the self-consistent solution in the strong Yukawa coupling
limit. This model allows one to get GeV at values of
. In the investigated model the lightest Higgs boson mass
does not exceed GeV. The upper bound on the lightest CP-even
Higgs boson mass in more complicated supersymmetric models is also discussed.Comment: 27 pages, 5 figures included, LaTeX 2e. Plenary talk at the
Conference of RAS Nuclear Physics Department 2000 in ITEP, Moscow, Russia; to
appear in Phys. Atom. Nuc
Measurement of the analyzing powers in pd elastic and pn quasi-elastic scattering at small angles
The analyzing powers in proton-deuteron elastic and proton-neutron
quasi-elastic scattering have been measured at small angles using a polarized
proton beam at the COSY storage ring incident on an unpolarized deuterium
target. The data were taken at 796MeV and five higher energies from 1600MeV to
2400MeV. The analyzing power in pd elastic scattering was studied by detecting
the low energy recoil deuteron in telescopes placed symmetrically in the COSY
plane to the left and right of the beam whereas for pn quasi-elastic scattering
a low energy proton was registered in one of the telescopes in coincidence with
a fast scattered proton measured in the ANKE magnetic spectrometer. Though the
experiment explores new domains, the results are consistent with the limited
published information.Comment: 10 pages with 8 figure
Coherent pion production in proton-deuteron collisions
Values of the proton analysing power in the
reactions at 350-360~MeV
per nucleon were obtained by using a polarised proton beam incident on a
deuterium cluster-jet target and with a polarised deuteron beam incident on a
target cell filled with polarised hydrogen. These results have a much larger
angular coverage than existing data. First measurements are also presented of
the deuteron vector analysing power and the deuteron-proton spin correlations.
Data were also obtained on the deuteron-proton spin correlation and proton
analysing power at small angles at 600~MeV per nucleon, though the angular
coverage at this energy was much more restricted even when using a deuteron
beam. By combining the extrapolated values of the spin correlations to the
forward or backward directions with published measurements of the deuteron
tensor analysing powers, the relative phases between the two non-vanishing
amplitudes were evaluated.Comment: 5 pages, 5 figure
Measurement of the analysing power in proton-proton elastic scattering at small angles
The proton analysing power in elastic scattering has been measured
at small angles at COSY-ANKE at 796 MeV and five other beam energies between
1.6 and 2.4 GeV using a polarised proton beam. The asymmetries obtained by
detecting the fast proton in the ANKE forward detector or the slow recoil
proton in a silicon tracking telescope are completely consistent. Although the
analysing power results agree well with the many published data at 796 MeV, and
also with the most recent partial wave solution at this energy, the ANKE data
at the higher energies lie well above the predictions of this solution at small
angles. An updated phase shift analysis that uses the ANKE results together
with the World data leads to a much better description of these new
measurements.Comment: 5 pages, 3 figure
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