A simple technique for combining simplified models and its application to direct stop production

The results of many LHC searches for supersymmetric particles are interpreted using simplified models, in which one fixes the masses and couplings of most sparticles then scans over a few remaining masses of interest. We present a new technique for combining multiple simplified models (that requires no additional simulation) thereby highlighting the utility and limitations of simplified models in general, and demonstrating a simple way of improving LHC search strategies. The technique is used to derive limits on the stop mass that are model independent, modulo some reasonably generic assumptions which are quantified precisely. We find that current ATLAS and CMS results exclude stop masses up to 340 GeV for neutralino masses up to 120 GeV, provided that the total branching ratio into channels other than top-neutralino and bottom-chargino is small, and that there is no mass difference smaller than 10 GeV in the mass spectrum. In deriving these limits we place upper bounds on the branching ratios for complete stop pair decay processes for many values of the stop, neutralino and chargino masses. These are available with this paper.Comment: 25 pages, data included in source. V3: new content added, version accepted for publicatio

Collider constraints on tuning in composite Higgs models

Two potential sources of tuning exist in composite Higgs models: one comes from keeping the Higgs VEV below the compositeness scale and one comes from keeping the Higgs light after constraints on the top partner masses are applied. We construct a measure that determines whether these tunings are independent or not and combines them appropriately. We perform a comprehensive scan of the parameter space for three explicit models and report the minimum tuning values compatible with existing collider constraints. Tuning values are given as functions of resonance masses and deviations to the Higgs couplings so the effect of future constraints can easily be quantified. The current minimum tuning in the minimal model is 2.5-5% and will be decreased to around 0.8-3.3% if no top partners are observed over the lifetime of the LHC.Comment: 31 pages, 18 figures. Comments and references added for v2, accepted for publication in JHE

UV descriptions of composite Higgs models without elementary scalars

We consider four-dimensional UV descriptions of composite Higgs models without elementary scalars, in which four-fermion interactions are introduced to an underlying gauge theory like in the gauged NJL model. When the anomalous dimension of the fermion bilinear is large, these interactions drive the spontaneous global symmetry breaking in the model, with the Higgs identified as a Nambu-Goldstone boson. The UV descriptions support composite top partner operators, also with large anomalous dimensions, thereby providing an explicit realisation of the idea of partial compositeness. In particular, the composite SO(6)/SO(5) model can be described by an Sp gauge theory with four flavours of fermion, together with a vector-like pair of fermions transforming in the antisymmetric representation and charged under SU(3) colour. These fermions confine to produce both the Higgs and top partner bound states. Our methods can also be applied to different coset groups, suggesting that four-fermion operators can describe the underlying UV dynamics of other composite Higgs models.Comment: 28 pages. V2: references added, version accepted for publicatio

Degrees of Metastability in Gauge Mediated Supersymmetry Breaking

This thesis consists of an investigation into supersymmetry and its breaking. Emphasis is placed on the question of metastability and the role of non-topological solitons in the hidden sector. A desirable feature in models employing direct gauge mediation is that of tree level metastability, in order to generate large enough gaugino masses. An explicit realisation of this idea is constructed via a simple deformation of SQCD that is well motivated and needs no fine tuning. Any viable metastable supersymmetry breaking vacuum must also be stable enough to survive until the present day. Non-topological solitons, or Q-balls, are supported in all such vacua where there is a conserved, global U(1) symmetry and no massless, charged scalars. It is shown that for a broad class of models Q-balls are extremely influential on the vacuum lifetime and make seemingly viable vacua catastrophically short lived. Even when there is no effect on vacuum stability flat directions charged under an R-symmetry are a ubiquitous feature of O’Raifeartaigh models. Non-topological solitons associated with this symmetry, R-balls, are likely to form through the fragmentation of a condensate. Their cosmology is studied and it is found that they can have significant observable effects, from acting as a good dark matter candidate to providing the primary source of reheating in the early universe

Natural gauge mediation with a bino NLSP at the LHC

Natural models of supersymmetry with a gravitino LSP provide distinctive signatures at the LHC. For a neutralino NLSP, sparticles can decay to two high energy photons plus missing energy. We use the ATLAS diphoton search with 4.8 fb^{-1} of data to place limits in both the stop-gluino and neutralino-chargino mass planes for this scenario. If the neutralino is heavier than 50 GeV, the lightest stop must be heavier than 580 GeV, the gluino heavier than 1100 GeV and charginos must be heavier than approximately 300-470 GeV. This provides the first nontrivial constraints in natural gauge mediation models with a neutralino NLSP decaying to photons, and implies a fine tuning of at least a few percent in such models.Comment: 10 pages, 3 figures; v2: updated figure 3, version published in PR

On the technology of a beet sugar factory, for working up the produce of five hundred acres of beet.

In tracing the history of any great enterprise,it will rarely appear that success has been attained all at once, but in most instances the progress gained has been slow and gradual;and it has generally been found to be a work of time to wear down prejudices, alter the course of habitual thought and practice, as well as to overcome that vis inertiae which is opposed to all innovation and change. The cultivation of the White or Silesian Beet, with its many attendant advantages in relation to agriculture, and as a sugar-producing root, has proved no exception to this ordinary experience. In support of this, it may be well, before passing on to the particular object of this paper, to draw attention to what has been done towards the establishment of the important industry now under consideration

Timor leste collaborative project: a short report

This report discusses findings from a small-scale scoping study, which is part of a larger curriculum project—a collaborative venture between staff from the Universidade Nacional Timor Lorosa'e (UNTL) and a New Zealand university. The aim of the wider project is to develop a context-sensitive English language curriculum for students at UNTL who are undergoing pre-service training to be teachers of English as a foreign language in local secondary schools. (Details of the institutional and linguistic context are provided in the appendix.) According to Norton (2000), investment by learners is a key factor in the successful implementation of a new curriculum: "if learners invest in a second language, they do so with the understanding that they will acquire a wider range of symbolic and material resources, which will increase their value in the social world" (Norton, 2000, pp. 165-166). Thus, when designing the curriculum, it is important to ensure that the students will not only understand how to use the specific learning tasks but that it also expands their repertoire of skills and knowledge for application in their subsequent professional and social lives. The report begins by outlining the history and objectives of the project before explaining the specific research questions posed for the scoping study. The means of collecting data will be outlined and examples of the participants' attitudes will be presented based on open-ended questionnaire responses. These findings will be discussed in terms of how they might lead to the design of a curriculum which is internationally-framed and context-sensitive in terms both of its content and implementation. The report will conclude with the further steps that are being taken to move the project to its next phase