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This thesis concerns itself with low-momentum-transfer processes in high-energy particle collisions. These processes cannot be described in the framework of the fundamental theory of quantum chromodynamics (QCD), but rely on a pre-QCD approach, the Regge theory. Several models containing various degrees of complexity have been proposed within this framework, some of which have been developed and studied in this thesis. All models have been implemented in a numerical simulation (a Monte Carlo event generator), which allows forprecise predictions of several types of particle collisions at various energies.Paper I: A model for hard diffractive events in pp collisions is proposed. It is based on evaluating a probability for diffraction, but employs an additional dynamical choice of survival of the proposed diffractive events. This dynamical description is the first of its kind and offers an explanation of earlier discrepancies between data and theory.Paper II: Existing models are reviewed and new ones developed for all components of the pp cross section; the total, elastic and diffractive cross sections. The models are implemented in the event generator Pythia 8, thus offering improved predictions for these collisions at LHC energies.Paper III: In this work the model for hard diffraction is extended to photoproduction. The dynamical survival effect is by construction only present in a subset of these collisions and thus puts forward an explanation of the discrepancies between data and theory of hard diffractive dijet events in the photoproduction regime.Paper IV: Here a new model for intial state evolution is implemented and studied in Pythia 8. This model opens up for asymmetrical matter distributions within the colliding particles, and consequences because of these asymmetries are studied within ep, pp, pA and AA collisions. Predictions for the color fluctuations in the crosssections in eA collisions are presented as a first step towards a complete description of elec

The accuracy of geomagnetic field models was studied in this report. The first-order model (a dipole model) of International Geomagnetic Reference Field (IGRF) has so far been used in wheel unloading etc. of Earth orbiting satellites. The maximum errors in the dipole model reach about 30 deg. Since magnetic sensors are used as a main sensor of the attitude control system of a piggyback satellite, the error of 30 deg is not acceptable. In this study, the accuracy improvement of geomagnetic field models was investigated by using higher-order IGRF models. The maximum errors were found to be 16.4 deg with the second-order model, 6.4 deg with the third-order model, and 3.5 deg with the fourth-order model, indicating the improving trend of the accuracy with the increasing order of models. Improvement in the accuracy by models with orders higher than five was not so appreciable as expected from the increase in the amount of computation. Therefore, the use of the third-order or fourth-order model of IGRF1995 was recommended as the geomagnetic field model of a piggyback satellite., 本資料では地磁場モデルの誤差検討を行う。これまで地磁場モデルとしては、国際標準地磁気モデル(IGRF)の1次モデル(ダイポールモデル)が、地球周回衛星のホイールアンローディングなどに使用されてきた。ダイポールモデルはモデルの誤差が最大30度前後となる。ピギーバック衛星では、磁気センサを姿勢制御系のメインセンサとして使用するため、30度の誤差は許容できない。ここではIGRFの高次モデルを使用することにより、地磁場モデルの精度向上を検討した。その結果、2次モデルを使用すると最大誤差は16.4度、3次モデルでは6.4度、4次モデルでは3.5度とモデルの精度が向上する。また、5次以上では計算量の増加に対し、精度向上があまり望めない。したがって、ピギーバック衛星では地磁場モデルとして、IGRF1995の3次または4次モデルを使用することが望ましい。