Monte Carlo simulations of physics beyond the standard model

The Large Hadron Collider, currently under construction at CERN, will give direct access to physics at the TeV scale for the first time. The lack of certainty over the type of physics that will be revealed has produced a wealth of ideas for so-called Beyond the Standard Model physics, all with the aim of solving the problems possessed by the Standard Model. The oldest and most well studied is supersymmetry but new ideas based on extra dimensions and collective symmetry breaking have been proposed more recently. In order to study these models most effectively, we argue that they must be implemented within the framework of a Monte Carlo event generator so that their signals can be studied in a real world setting. In this thesis we develop a general approach for the simulation of new physics models with the aim of reducing the effort in implementing a new model into the Herwig++ event generator. The approach is based upon the external spin structures of production and decay matrix elements so that the amount of information required to input a new model is simply a set of Feynman rules and mass spectrum. The first method uses an on-shell approximation throughout but this is later refined to include the effects of finite widths, as these are found to be important when processes occur close to threshold. In all of the discussions regarding our new approach we make specific reference to two models of new physics, the Minimal Supersymmetrie Standard Model and the Minimal Universal Extra Dimensions model. Our general matrix elements and approach to finite widths are all demonstrated and tested using examples from these two models. The concluding discussion makes use of a third model, the Littlest Higgs model with T-parity, such that signals from the three models are compared and contrasted using the general framework developed here

An Investigation of the Neurophysiological Correspondents of Learning and Memory in Two Forebrain Regions of the Day-Old Chick

Spontaneous bursting (5 or more spikes of 200-450mV amplitude at 400Hz) occurs in many areas of chick forebrain. Day-old chicks trained on a one-trial passive avoidance task show a bilateral increase of up to 350% in bursting following training in one of these areas: the intermediate medial hyperstriatum ventrale, or IMHV (Mason & Rose, 1987; 1988). An investigation was carried out into the time course and lateralization of this change in bursting activity following the training of day-old chicks on a passive avoidance task. Chicks were trained to either avoid a bead coated with the bitter-tasting substance methylanthranilate (M-birds) or were trained to peck a water coated bead (W-birds). Bursting was recorded sequentially from the IMHV of both hemispheres at 8 time points over the period 1 to 9 hours post-test. The results indicate that there are significant differences in bursting activity recorded from M-birds only during the period 3-7hr posttest, when compared to W-birds. Between 6-7hr posttest there are significant differences in the burst firing patterns of the right IMHV of M-birds compared to the left. At other time points tested there are no significant differences between hemispheres. No between hemisphere differences are evident in W-birds. Multi-unit recordings were made from the lobus parolfactorius (LPO), another forebrain structure to show changes in biochemistry and morphology following passive avoidance training. M-birds showed a higher incidence of bursting when compared to W-birds over the period 1-10hr posttest. No lateralization of bursting was seen in either group at any time posttest. In a further experiment, chicks trained to avoid the methylanthranilate coated bead were subjected to subconvulsive electroshock 5min posttraining. This procedure was used to test whether the training-induced increase in bursting in the LPO was a direct correlate of memory formation for the task. This electroshock treatment produced two groups of birds: one group that avoided the bead (remembered the task) and another that pecked the bead (forgot the task). Multi-unit recordings from the LPO of these two groups revealed that the group that avoided the bead had a significantly higher mean burst-frequency when compared to the group that pecked the bead, indicating that increased bursting in the LPO following training is directly associated with recall for the task. These results are similar to those of Mason and Rose (1988) who showed that amnesia abolished a training-induced enhancement of bursting in the IMHV. The effects of pretraining bilateral LPO lesions on IMHV bursting activity were examined. The IMHV of four groups of birds was recorded ftom following training: two groups of M-birds, one with LPO lesions the other with sham LPO lesions and two similarly treated groups of W-birds. A significant increase in overall IMHV bursting activity was observed in sham-lesioned M-birds when compared to sham-lesioned W-birds. However, no significant difference in bursting activity was seen between lesioned M-birds and lesioned W-birds. There was a trend towards a higher overall level of bursting in lesioned W-birds, when compared to sham-lesioned W-birds. These results are discussed with reference to previous electrophysiological studies concerning the role of burst-firing patterns in models of learning and memory

Episodic-Like Memory for What-Where-Which Occasion is Selectively Impaired in the 3xTgAD Mouse Model of Alzheimer’s Disease

Episodic memory loss is a defining feature of early-stage Alzheimer’s disease (AD). A test of episodic-like memory for the rat, the What-Where-Which occasion task (WWWhich), requires the association of object, location, and contextual information to form an integrated memory for an event. The WWWhich task cannot be solved by use of non-episodic information such as object familiarity and is dependent on hippocampal integrity. Thus, it provides an ideal tool with which to test capacity for episodic-like memory in the 3xTg murine model for AD. As this model captures much of the human AD phenotype, we hypothesized that these mice would show a deficit in the WWWhich episodic-like memory task. To test the specificity of any episodic-like deficit, we also examined whether mice could perform components of the WWWhich task that do not require episodic-like memory. These included object (Novel Object Recognition), location (Object Location Task, What-Where task), and contextual (What-Which) memory, as well as another three-component task that can be solved without reliance on episodic recall (What-Where-When; WWWhen). The results demonstrate for the first time that control 129sv/c57bl6 mice could form WWWhich episodic-like memories, wherea, 3xTgAD mice at 6 months of age were impaired. Importantly, while 3xTgAD mice showed some deficit on spatial component tasks, they were unimpaired in the more complex WWWhen combination task (which includes a spatial component and is open to non-episodic solutions). These results strongly suggest that AD pathology centered on the hippocampal formation mediates a specific deficit for WWWhich episodic-like memory in the 3xTgAD model

Synthetic studies on pterin glycosides: the first synthesis of 2′-O-(α-d-glucopyranosyl)biopterin

L-Rhamnose was led, in a 14-step-sequence, to N2-(N,N-dimethylaminomethylene)-1′-O-(4-methoxybenzyl)-3-[2-(4-nitrophenyl)ethyl]biopterin (23), an appropriately protected precursor for 2′-O-glycosylation, while 4,6-di-O-acetyl-2,3-di-O-(4-methoxybenzyl)-α-d-glucopyranosyl bromide (32), a novel glycosyl donor, was efficiently prepared from d-glucose in 8 steps. The first synthesis of 2′-O-(α-d-glucopyranosyl)biopterin (2a) was achieved by treatment of the key intermediate 23 with 32 in the presence of silver triflate and tetramethylurea, followed by successive removal of the protecting groups

New Physics backgrounds to the H -> WW search at the LHC?

The searches for H -> WW events at the LHC use data driven techniques for estimating the q qbar -> WW background, by normalizing the background cross section to data in a control region. We investigate the possibility that new physics sources which mainly contribute to the control region lead to an overestimate of Standard Model backgrounds to the Higgs boson signal and, thus, to an underestimate of the H -> WW signal. A supersymmetric scenario with heavy squarks and gluinos but charginos in the 200 to 300 GeV region and somewhat lighter sleptons can lead to such a situation.Comment: 13 pages, 3 figures, 1 table. v2: matches version published in PL

HERWIG 6.4 Release Note

A new release of the Monte Carlo program HERWIG (version 6.4) is now available. The main new features are: spin correlations between the production and decay of heavy fermions, i.e. top quarks, tau leptons and SUSY particles; polarization effects in SUSY production processes in lepton-lepton collisions; an interface to TAUOLA for tau decays; MSSM Higgs processes in lepton-lepton collisions

Herwig++ 2.1 Release Note

A new release of the Monte Carlo program Herwig++ (version 2.1) is now available. This version includes a number of significant improvements including: an eikonal multiple parton-parton scattering model of the underlying event; the inclusion of Beyond the Standard Model (BSM) physics; and a new hadronic decay model tuned to LEP data. This version of the program is now fully ready for the simulation of events in hadron-hadron collisions

Constraining compressed supersymmetry using leptonic signatures

We study the impact of the multi-lepton searches at the LHC on supersymmetric models with compressed mass spectra. For such models the acceptances of the usual search strategies are significantly reduced due to requirement of large effective mass and missing E_T. On the other hand, lepton searches do have much lower thresholds for missing E_T and p_T of the final state objects. Therefore, if a model with a compressed mass spectrum allows for multi-lepton final states, one could derive constraints using multi-lepton searches. For a class of simplified models we study the exclusion limits using ATLAS multi-lepton search analyses for the final states containing 2-4 electrons or muons with a total integrated luminosity of 1-2/fb at \sqrt{s}=7 TeV. We also modify those analyses by imposing additional cuts, so that their sensitivity to compressed supersymmetric models increase. Using the original and modified analyses, we show that the exclusion limits can be competitive with jet plus missing E_T searches, providing exclusion limits up to gluino masses of 1 TeV. We also analyse the efficiencies for several classes of events coming from different intermediate state particles. This allows us to assess exclusion limits in similar class of models with different cross sections and branching ratios without requiring a Monte Carlo simulation.Comment: 18 pages, 5 figure

Herwig++ Status Report

Herwig++ is the successor of the event generator HERWIG. In its present version 2.2.1 it provides a program for full LHC event generation which is superior to the previous program in many respects. We briefly summarize its features and describe present work and some future plans