S. Ostapchenko

Quark-Gluon String Model and EAS Simulation Problems at Ultra-High Energies

The reliability of model calculations is of considerable significance because at energies above those attained by accelerators only model predictions enable us to extract primary cosmic ray characteristics. Different phenomenological models based on the quark-gluon picture of hadron interactions are of use now as a foundation for experimental data analysis at energies > 10 15 eV. In this paper we consider the present status of quark-gluon string (QGS) model with allowance made for semihard processes and (in the framework of so advanced model) discuss experimental data obtained at energies 10 15 ÷ 10 19 eV. In doing so we assume mass composition following from the diffusion notions of cosmic ray propagation through the Galaxy. Some general problems of EAS simulation and among them the simulation of electron-photon cascades are also discussed.

KASCADE measurements of energy spectra for elemental groups of cosmic rays: Results and open problems

Abstract A composition analysis of KASCADE air shower data is performed by means of unfolding the two-dimensional frequency spectrum of electron and muon numbers. Aim of the analysis is the determination of energy spectra for elemental groups representing the chemical composition of primary cosmic rays. Since such an analysis depends crucially on simulations of air showers the two different hadronic interaction models QGSJet and SIBYLL are used for their generation. The resulting primary energy spectra show that the knee in the all particle spectrum is due to a steepening of the spectra of light elements but, also, that neither of the two simulation sets is able to describe the measured data consistently over the whole energy range with discrepancies appearing in different energy regions.

QGSJET-II: Towards reliable description of very high energy hadronic interactions

Since a number of years the QGSJET model has been successfully used by different groups in the field of high energy cosmic rays. Current work is devoted to the first general update of the model. The key improvement is connected to an account for non-linear interaction effects which are of crucial importance for reliable model extrapolation into the ultra-high energy domain. The proposed formalism allows to obtain a consistent description of hadron-hadron cross sections and hadron structure functions and to treat non-linear effects explicitly in individual hadronic and nuclear collisions. Other ameliorations concern the treatment of low mass diffraction, employment of realistic nuclear density profiles, and re-calibration of model parameters using a wider set of accelerator data.

Detection and imaging of atmospheric radio flashes from cosmic ray air showers.

The nature of ultrahigh-energy cosmic rays (UHECRs) at energies >1020 eV remains a mystery. They are likely to be of extragalactic origin, but should be absorbed within ∼50 Mpc through interactions with the cosmic microwave background. As there are no sufficiently powerful accelerators within this distance from the Galaxy, explanations for UHECRs range from unusual astrophysical sources to exotic string physics. Also unclear is whether UHECRs consist of protons, heavy nuclei, neutrinos or γ-rays. To resolve these questions, larger detectors with higher duty cycles and which combine multiple detection techniques are needed. Radio emission from UHECRs, on the other hand, is unaffected by attenuation, has a high duty cycle, gives calorimetric measurements and provides high directional accuracy. Here we report the detection of radio flashes from cosmic-ray air showers using low-cost digital radio receivers. We show that the radiation can be understood in terms of the geosynchrotron effect. Our results show that it should be possible to determine the nature and composition of UHECRs with combined radio and particle detectors, and to detect the ultrahigh-energy neutrinos expected from flavour mixing.

Nonlinear screening effects in high energy hadronic interactions

Nonlinear effects in hadronic interactions are treated by means of enhanced Pomeron diagrams, assuming that Pomeron-Pomeron coupling is dominated by soft partonic processes. It is shown that the approach allows to resolve a seeming contradiction between realistic parton momentum distributions, measured in deep inelastic scattering experiments, and the energy behavior of total proton-proton cross section. Also a general consistency with both soft and hard diffraction data is demonstrated. An important feature of the proposed scheme is that the contribution of semihard processes to the interaction eikonal contains a significant nonfactorizable part. On the other hand, the approach preserves the QCD factorization picture for inclusive high-

Parton-based Gribov–Regge theory

{p}_{t}

Lower limit on the strength and filling factor of extragalactic magnetic fields

jet production.

One-dimensional hybrid approach to extensive air shower simulation

Abstract We present a new parton model approach for hadron–hadron interactions and, in particular, for the initial stage of nuclear collisions at very high energies (RHIC, LHC and beyond). The most important aspect of our approach is a self-consistent treatment, using the same formalism for calculating cross sections and particle production, based on an effective, QCD-inspired field theory, where many of the inconsistencies of presently used models will be avoided. In addition, we provide a unified treatment of soft and hard scattering, such that there is no fundamental cutoff parameter any more defining an artificial border between soft and hard scattering. Our approach cures some of the main deficiencies of two of the standard procedures currently used: the Gribov–Regge theory and the eikonalized parton model. There, cross section calculations and particle production cannot be treated in a consistent way using a common formalism. In particular, energy conservation is taken care of in case of particle production, but not concerning cross section calculations. In addition, hard contributions depend crucially on some cutoff, being divergent for the cutoff being zero. Finally, in case of several elementary scatterings, they are not treated on the same level: the first collision is always treated differently from the subsequent ones. All these problems are solved in our new approach. For testing purposes, we make very detailed studies of electron–positron annihilation and lepton–nucleon scattering before applying our approach to proton–proton and nucleus–nucleus collisions. In order to keep a clean picture, we do not consider secondary interactions. We provide a very transparent extrapolation of the physics of more elementary interactions towards nucleus–nucleus scattering, without considering any nuclear effects due to final state interactions. In this sense we consider our model a realistic and consistent approach to describe the initial stage of nuclear collisions.

Restricting UHECRs and cosmogenic neutrinos with Fermi-LAT

High energy photons from blazars can initiate electromagnetic pair cascades interacting with the extragalactic photon background. The charged component of such cascades is deflected and delayed by extragalactic magnetic fields (EGMF), reducing thereby the observed point-like flux and leading potentially to multi degree images in the GeV energy range. We calculate the fluence of 1ES 0229+200 as seen by Fermi-LAT for different EGMF profiles using a Monte Carlo simulation for the cascade development. The non-observation of 1ES 0229+200 by Fermi-LAT suggests that the EGMF fills at least 60% of space with fields stronger than O(10 − 10)G for life times of TeV activity of O(10 − 10) yr. Thus the (non-) observation of GeV extensions around TeV blazars probes the EGMF in voids and puts strong constraints on the origin of EGMFs: Either EGMFs were generated in a space filling manner (e.g. primordially) or EGMFs produced locally (e.g. by galaxies) have to be efficiently transported to fill a significant volume fraction, as e.g. by galactic outflows. Subject headings: magnetic fields: origin – magnetic fields: extragalactic – gamma rays: galaxies – galaxies: active

Ankle-like feature in the energy spectrum of light elements of cosmic rays observed with KASCADE-Grande

Abstract An efficient scheme for one-dimensional extensive air shower simulation and its implementation in the program conex are presented. Explicit Monte Carlo simulation of the high-energy part of hadronic and electro-magnetic cascades in the atmosphere is combined with a numeric solution of cascade equations for smaller energy sub-showers to obtain accurate shower predictions. The developed scheme allows us to calculate not only observables related to the number of particles (shower size) but also ionization energy deposit profiles which are needed for the interpretation of data of experiments employing the fluorescence light technique. We discuss in detail the basic algorithms developed and illustrate the power of the method. It is shown that Monte Carlo, numerical, and hybrid air shower calculations give consistent results which agree very well with those obtained within the corsika program.