225 research outputs found
Neutrino-nucleus interactions in the T2K experiment
We present a study of neutrino-nucleus interactions at the T2K experiment
based on the GiBUU transport model. The aim of T2K is to measure
appearance and , but it will also be able to do a precise
measurement of disappearance. The former requires a good
understanding of production while the latter is closely connected with
a good understanding of quasielastic scattering. For both processes we
investigate the influence of nuclear effects and particular final-state
interactions on the expected event rates taking into account the T2K detector
setup.Comment: v3: matches version to be published in Phys. Rev.
Eta electroproduction on nuclei in the nucleon resonance region
We investigate eta electroproduction on nuclei for Q^2=2.4 and 3.6 GeV^2 in
the framework of a coupled-channel BUU transport model. We analyze the
importance of final state interactions and side feeding and compare with
findings drawn from eta photoproduction. It is shown that in contrast to
photoproduction the influence of etas stemming from secondary processes becomes
important at high Q^2.Comment: 5 pages, 5 figure
Interactions of multi-quark states in the chromodielectric model
We investigate 4-quark () systems as well as multi-quark
states with a large number of quarks and anti-quarks using the chromodielectric
model. In the former type of systems the flux distribution and the
corresponding energy of such systems for planar and non-planar geometries are
studied. From the comparison to the case of two independent -strings
we deduce the interaction potential between two strings. We find an attraction
between strings and a characteristic string flip if there are two degenerate
string combinations between the four particles. The interaction shows no strong
Van-der-Waals forces and the long range behavior of the potential is well
described by a Yukawa potential, which might be confirmed in future lattice
calculations. The multi-quark states develop an inhomogeneous porous structure
even for particle densities large compared to nuclear matter constituent quark
densities. We present first results of the dependence of the system on the
particle density pointing towards a percolation type of transition from a
hadronic matter phase to a quark matter phase. The critical energy density is
found at .Comment: 19 pages, 40 eps-figures, RevTex 4, v2: typos correcte
Strangeness production in antiproton-nucleus collisions
Antiproton annihilations on nuclei provide a very interesting way to study
the behaviour of strange particles in the nuclear medium. In low energy annihilations, the hyperons are produced mostly by strangeness exchange
mechanisms. Thus, hyperon production in interactions is very
sensitive to the properties of the antikaon-nucleon interaction in nuclear
medium. Within the Giessen Boltzmann-Uehling-Uhlenbeck transport model (GiBUU),
we analyse the experimental data on and production in collisions at GeV/c. A satisfactory overall agreement is
reached, except for the production in Ne collisions at
MeV/c, where we obtain substantially larger
production rate. We also study the hyperon production, important in view
of the forthcoming experiments at FAIR and J-PARC.Comment: 8 pages, 4 figures, invited talk given by A.B. Larionov at the 10th
International Conference on Low Energy Antiproton Physics (LEAP2011),
Vancouver, Canada, Apr 27 - May 1, 2011, Hyperfine Interact. in pres
Production of Eta-Mesons in Collisions of Nucleons and Delta-Resonances
We calculate the cross section for the production of -mesons via
\mbox{} in a relativistic One-Boson-Exchange-Model.
Using this cross section we then determine the probability for the production
of an -meson by a -resonance moving in nuclear matter. The result
is compared to prescriptions in BUU-calculations in which \et-production
proceeds both through a direct channel and through the sequential process
.Comment: revised version: large parts have been rewritten, there are two new
figures. A discusion of effects of multi-body reactions of the intermediate
pion on our results has been adde
Realistic Interactions and Dilepton production off pp-collisions
We present a model for dilepton production of proton-proton collisions using
a realist T-matrix that by incorporating Delta-isobar degrees of freedom fits
the NN-scattering data up to 2 GeV. The results we find differ in details from
earlier work that use less sophisticated interactions but the overall agreement
with these calculations is good.Comment: 11 pages Revtex, 2 postscript figures include
Nuclear Flow in Consistent Boltzmann Algorithm Models
We investigate the stochastic Direct Simulation Monte Carlo method (DSMC) for
numerically solving the collision-term in heavy-ion transport theories of the
Boltzmann-Uehling-Uhlenbeck (BUU) type. The first major modification we
consider is changes in the collision rates due to excluded volume and
shadowing/screening effects (Enskog theory). The second effect studied by us is
the inclusion of an additional advection term. These modifications ensure a
non-vanishing second virial and change the equation of state for the scattering
process from that of an ideal gas to that of a hard-sphere gas. We analyse the
effect of these modifications on the calculated value of directed nuclear
collective flow in heavy ion collisions, and find that the flow slightly
increases.Comment: 12 pages, REVTeX, figures available in PostScript from the authors
upon reques
Nonminimal isotropic cosmological model with Yang-Mills and Higgs fields
We establish a nonminimal Einstein-Yang-Mills-Higgs model, which contains six
coupling parameters. First three parameters relate to the nonminimal coupling
of non-Abelian gauge field and gravity field, two parameters describe the
so-called derivative nonminimal coupling of scalar multiplet with gravity
field, and the sixth parameter introduces the standard coupling of scalar field
with Ricci scalar. The formulated six-parameter nonminimal
Einstein-Yang-Mills-Higgs model is applied to cosmology. We show that there
exists a unique exact cosmological solution of the de Sitter type for a special
choice of the coupling parameters. The nonminimally extended Yang-Mills and
Higgs equations are satisfied for arbitrary gauge and scalar fields, when the
coupling parameters are specifically related to the curvature constant of the
isotropic spacetime. Basing on this special exact solution we discuss the
problem of a hidden anisotropy of the Yang-Mills field, and give an explicit
example, when the nonminimal coupling effectively screens the anisotropy
induced by the Yang-Mills field and thus restores the isotropy of the model.Comment: 15 pages, revised version accepted to Int. J. Mod. Phys. D, typos
correcte
Topological effects in the thermal properties of knotted polymer rings
The topological effects on the thermal properties of several knot
configurations are investigated using Monte Carlo simulations. In order to
check if the topology of the knots is preserved during the thermal fluctuations
we propose a method that allows very fast calculations and can be easily
applied to arbitrarily complex knots. As an application, the specific energy
and heat capacity of the trefoil, the figure-eight and the knots are
calculated at different temperatures and for different lengths. Short-range
repulsive interactions between the monomers are assumed. The knots
configurations are generated on a three-dimensional cubic lattice and sampled
by means of the Wang-Landau algorithm and of the pivot method. The obtained
results show that the topological effects play a key role for short-length
polymers. Three temperature regimes of the growth rate of the internal energy
of the system are distinguished.Comment: 7 pages, 12 figures, LaTeX + RevTeX. With respect to the first
version, in the second version the text has been improved and all figures are
now in black and whit
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