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High energy particle collisions involve complex physics, beyond analytical control. Instead, Monte Carlo event generators like Pythia have been used to simulate particle collisions since decades. A study of the production of heavy quarks (namely, charm and bottom) is presented for two different scenarios: lepton (e+e−) and hadron (pp) collisions. Electron- positron collisions at the Z0 resonance a
In this thesis a method for decomposing QCD colour structures into multiplet bases is described. The method is applicable for any number of gluons and quarks. To achieve the decomposition requires the knowledge of group theoretical weights, so-called Wigner 3j and 6j coefficients. The number of required coefficients have been calculated for up to 12 external gluons, and been shown to scale well in
In this thesis, we consider a 2-Higgs-doublet model with a gauged Froggatt-Nielsen mechanism as an extension of the standard model. We assume that (i) the theory at the electroweak scale is the low energy limit of a theory defined at a scale $\Lambda_{FN}$ (ii) the Yukawa couplings at $\Lambda_{FN}$ are generated by the Froggatt-Nielsen mechanism. The first assumption is enforced by requiring that
The Einstein-Hilbert Lagrangian for gravity is non-renormalizable at loop level. However, it can be treated in the effective field theory framework which means that gravity as an effective theory can be renormalized when a proper expansion of the effective Lagrangian is made. At the same time, the Feynman rules for gravity are very complicated, although the resulting amplitudes do not have the sam
The black hole information paradox is of central importance in the study of quantum gravity. The paradox states that quantum fields surrounding a black hole behave in ways that run into conflict with the unitarity of quantum mechanical time evolution. In the course of the past two years, new theoretical discoveries have made progress towards the paradox’s resolution, suggesting that unitarity can
In this thesis we investigate the properties of a specific two Higgs Doublet Model (2HDM) that can be used to explain the data on B->Dtu and B->D*tu, which deviate from the Standard Model (SM) by 3.4 sigma. The 2HDM is the simplest extension of the Standard model scalar sector. Phenomenologically it is very rich with 4 new Higgs bosons: 2 neutral and an electromagnetic charged pair. The 2HDMs exhi
This thesis gives an introduction to the basic formalism of one-dimensional supersymmetric quantum mechanics. The factorization of a Hamiltonian is used to create a supersymmetric partner Hamiltonian. The connections between the energy spectra and wave functions of these partner Hamiltonians are deduced and examined for the case of broken and unbroken supersymmetry. An extension to hierarchies of
5 februari 2026 15:15 till 17:00 | Open lecture with Associate Professor Wako Asato, Kyoto University Asian welfare regimes have historically taken the form of liberal familialist welfare regimes characterized by a heavy reliance on migrant care workers. While this arrangement is often interpreted as a mere extension of familialism, it is more accurately understood as a process through which Confu
https://www.lu.se/evenemang/global-care-chains-and-migration-east-asia-pain-and-gain-temporariness - 2026-05-06
A feedback neural network approach to communication routing problems is developed, with emphasis on Multiple Shortest Path problems, with several requests for transmissions between distinct start- and endnodes. The basic ingredients are a set of Potts neurons for each request,with interactions designed to minimize path lengths and to prevent overloading of network arcs. The topological nature of
The unfolding behavior of ubiquitin under the influence of a stretching force recently was investigated experimentally by single-molecule constant-force methods. Many observed unfolding traces had a simple two-state character, whereas others showed clear evidence of intermediate states. Here, we use Monte Carlo simulations to investigate the force-induced unfolding of ubiquitin at the atomic level
The 16 - 22 amino-acid fragment of the beta-amyloid peptide associated with the Alzheimer's disease, Abeta, is capable of forming amyloid fibrils. Here we study the aggregation mechanism of Abeta(16-22) peptides by unbiased thermodynamic simulations at the atomic level for systems of one, three, and six Abeta(16-22) peptides. We find that the isolated Abeta(16-22) peptide is mainly a random coil i
A third workshop on small-x physics, within the Small-x Collaboration, was held in Hamburg in May 2004 with the aim of overviewing recent theoretical progress in this area and summarizing the experimental status.
We present a flexible and efficient program package written in C++, PROFASI, for simulating protein folding and aggregation. The systems are modeled using an all-atom description of the protein chains with only torsional degrees of freedom, and implicit water. The program package has a modular structure that makes the interaction potential easy to modify. The currently implemented potential is abl
Divergent-light halos are produced when light from nearby light sources is scattered by ice crystals in the atmosphere. We present a theory of divergent-light halos leading to an improved algorithm for the simulation of such halos. Contrary to the algorithm that we presented earlier for simulating such halos, the new algorithm includes a mathematically rigorous weighting of the events. The compute
A simplified interaction potential for protein folding studies at the atomic level is discussed and tested on a set of peptides with; 20 residues each. The test set contains both alpha-helical ( Trp cage, F-s) and beta-sheet ( GB1p, GB1m2, GB1m3, Betanova, LLM) peptides. The model, which is entirely sequence-based, is able to fold these different peptides for one and the same choice of model param
We compute the energy levels of an SU(2) Yang-Mills field in perturbation theory to order g2, for a box of finite size and symmetric twist m=(1, 1, 1). A cubic-invariant spectrum results, with almost degenerate E++ and T2 ++ levels. Various suggestions for further MC measurements are made.
We study the thermodynamic behavior of a simple off-lattice model for protein folding. The model is two dimensional and has two different "amino acids." Using numerical simulations of all chains containing eight or ten monomers, we examine the sequence dependence at a fixed temperature. It is shown that only a few of the chains exist in unique folded state at this temperature, and the energy level
We develop the hybrid Monte Carlo method for simulations of single off-lattice polymer chains. We discuss implementation and choice of simulation parameters in some detail. The performance of the algorithm is tested on models for homopolymers with short- or long-range self-repulsion, using chains with 16≤N≤512 monomers. Without excessive fine tuning, we find that the computational cost grows as N2
