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 $\nu_e$ appearance and $\theta_{13}$, but it will also be able to do a precise measurement of $\nu_\mu$ disappearance. The former requires a good understanding of $\pi^0$ 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 ($qq\bar{q}\bar{q}$) 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 $q\bar{q}$-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 $\epsilon_c = 1.2 GeV/fm^3$.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 $\bar p$ annihilations, the hyperons are produced mostly by strangeness exchange mechanisms. Thus, hyperon production in $\bar p A$ 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 $\Lambda$ and $K^0_S$ production in $\bar p A$ collisions at $p_{\rm lab}=0.2-4$ GeV/c. A satisfactory overall agreement is reached, except for the $K^0_S$ production in $\bar p+^{20}$Ne collisions at $p_{\rm lab}=608$ MeV/c, where we obtain substantially larger $K^0_S$ production rate. We also study the $\Xi$ 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 $\eta$-mesons via \mbox{$\Delta N \to N N \eta$} in a relativistic One-Boson-Exchange-Model. Using this cross section we then determine the probability for the production of an $\eta$-meson by a $\Delta$-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 $\Delta \to N \pi ; \pi N \to N \eta$.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 $8_1$ 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