251 research outputs found
Equation of state of hadronic matter with dibaryons in an effective quark model
The equation of state of symmetric nuclear matter with the inclusion of
non-strange dibaryons is studied. We pay special attention to the existence of
a dibaryon condensate at zero temperature. These calculations have been
performed in an extended quark-meson coupling model with density-dependent
parameters, which takes into account the finite size of nucleons and dibaryons.
A first-order phase-transition to pure dibaryon matter has been found. The
corresponding critical density is strongly dependent on the value of the
dibaryon mass. The density behavior of the nucleon and dibaryon effective
masses and confining volumes have also been discussed.Comment: 9 pages, LaTex, 3 Postscript figures, a misprint correcte
Grand unified theory constrained supersymmetry and neutrinoless double beta decay
We analyze the contributions to the neutrinoless double decay
(-decay) coming from the Grand Unified Theory (GUT) constrained
Minimal Supersymmetric Standard Model (MSSM) with trilinear R-parity breaking.
We discuss the importance of two-nucleon and pion-exchange realizations of the
quark-level -decay transitions. In this context, the questions
of reliability of the calculated relevant nuclear matrix elements within the
Renormalized Quasiparticle Random Phase Approximation (pn-RQRPA) for several
medium and heavy open-shell nuclei are addressed. The importance of gluino and
neutralino contributions to -decay is also analyzed. We review
the present experiments and deduce limits on the trilinear R-parity breaking
parameter from the non-observability of -decay
for different GUT constrained SUSY scenarios. In addition, a detailed study of
limits on the MSSM parameter space coming from the processes
by using the recent CLEO and OPAL results is performed. Some studies in respect
to the future -decay project GENIUS are also presented.Comment: 29 pages, 8 figure
Properties of hyperons in chiral perturbation theory
The development of chiral perturbation theory in hyperon phenomenology has
been troubled due to power-counting subtleties and to a possible slow
convergence. Furthermore, the presence of baryon-resonances, e.g. the
lowest-lying decuplet, complicates the approach, and the inclusion of their
effects may become necessary. Recently, we have shown that a fairly good
convergence is possible using a renormalization prescription of the
loop-divergencies which recovers the power counting, is covariant and
consistent with analyticity. Moreover, we have systematically incorporated the
decuplet resonances taking care of both power-counting and
problems. A model-independent understanding of diferent properties including
the magnetic moments of the baryon-octet, the electromagnetic structure of the
decuplet resonances and the hyperon vector coupling , has been
successfully achieved within this approach. We will briefly review these
developments and stress the important role they play for an accurate
determination of the Cabibbo-Kobayashi-Maskawa matrix element from
hyperon semileptonic decay data.Comment: To appear in HypX Proceeding
Data Acquisition and Analysis of the 76Ge Double Beta Experiment in Gran Sasso 1990-2003
Data acquisition in a long running underground experiment has its specific
experimental challenges, concerning data acquisition, stability of the
experiment and background reduction. These problems are addressed here for the
HEIDELBERG-MOSCOW experiment, which collected data in the period August 1990 -
May 2003. The measurement and the analysis of the data is presented. The duty
cycle of the experiment was ~80%, the collected statistics is 71.7 kgy. The
background achieved in the energy region of the Q value for double beta decay
is 0.11 events/kg y keV. The two-neutrino accompanied half-life is determined
on the basis of more than 100 000 events. The confidence level for the
neutrinoless signal has been improved to a 4 sigma level.Comment: Full version (50 pages, 36 figures, 9 tables), zipped ps file (size
~21MB or pdf format (size ~26MB), can be found in
http://www.mpi-hd.mpg.de/non_acc/super.html (corrected typos) In press in NIM
A, 200
Unification of gauge couplings and the tau neutrino mass in Supergravity without R-parity
Minimal R-parity violating supergravity predicts a value for
smaller than in the case with conserved R-parity, and therefore closer to the
experimental world average. We show that the R-parity violating effect on the
prediction comes from the larger two-loop b-quark Yukawa contribution
to the renormalization group evolution of the gauge couplings which
characterizes R-parity violating supergravity. The effect is correlated to the
tau neutrino mass and is sensitive to the initial conditions on the soft
supersymmetry breaking parameters at the unification scale. We show how a few
percent effect on may naturally occur even with tau neutrino
masses as small as indicated by the simplest neutrino oscillation
interpretation of the atmospheric neutrino data from Super-Kamiokande.Comment: Latex, 21 pages including 2 figure
Off shell behaviour of the in medium nucleon-nucleon cross section
The properties of nucleon-nucleon scattering inside dense nuclear matter are
investigated. We use the relativistic Brueckner-Hartree-Fock model to determine
on-shell and half off-shell in-medium transition amplitudes and cross sections.
At finite densities the on-shell cross sections are generally suppressed. This
reduction is, however, less pronounced than found in previous works. In the
case that the outgoing momenta are allowed to be off energy shell the
amplitudes show a strong variation with momentum. This description allows to
determine in-medium cross sections beyond the quasi-particle approximation
accounting thereby for the finite width which nucleons acquire in the dense
nuclear medium. For reasonable choices of the in-medium nuclear spectral width,
i.e. MeV, the resulting total cross sections are, however,
reduced by not more than about 25% compared to the on-shell values. Off-shell
effect are generally more pronounced at large nuclear matter densities.Comment: 31 pages Revtex, 12 figures, typos corrected, to appear in Phys. Rev.
Limits on R-parity non-conservation in MSSM with gauge mediated supersymmetry breaking from the neutrinoless double beta decay
The R-parity non-conservation phenomenology within the minimal supersymmetric
standard model with gauge mediated supersymmetry breaking has been studied. New
constraints on the lepton number violating constant were
imposed by non-observability of the neutrinoless double beta decay. We find
that depends strongly on the effective supersymmetry
breaking scale only and deduce limits which are much stronger than
those previously found in literature.Comment: 6 pages, 1 figur
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