Thesis (Ph. D.)--Ohio State University, 2006. / Title from first page of PDF file. Includes bibliographical references (p. 111-116).

The geometry of non-conformal supersymmetric non-linear sigma models in one and two dimensions are reviewed. Transformations of the Osp(1|2) subgroup of the superconformal group are derived and then used in finding geometrical constraints on the target space of an N=(1,1) sigma model reduced to an N=1 sigma model.

This master’s thesis investigates the relationship between supersymmetry and integrability in quantum mechanics. This is done by finding a suitable way to systematically add more supersymmetry to the system. Adding more super- symmetry will give constraints on the potential which will lead to an integrable system. A possible way to explore the integrability of supersymmetric quantum mechanics was introduced in a paper by Crombrugghe and Rittenberg in 1983, their method has been used as well as another approach based on expanding a N = 1 system by introducing complex structures. N = 3 or more supersymmetry is shown to give an integrable system.

A search for rare B0 s -> µ+µ- and B0d -> µ+µ- decays has been performed in pp collisions at sqroot(s) = 1.96 TeV using 364 pb-1 of data collected by the CDF II experiment at the Fermilab Tevatron Collider. The rate of each decay is sensitive to contributions from physics beyond the Standard Model (SM). No events pass the optimized selection requirements, consistent with the SM expectation. The resulting upper limits on the branching ratios are B(B0s -> µ+µ-) < 1.5 x 10-7 and B(B0d -> µ+µ-) < 3.8 x 10-8 at the 90% confidence level. The limits are used to exclude some parameter space for several supersymmetric models.

Ten-dimensional superstring theory (or the conjectured nonperturbative Mtheory in eleven dimensions) is the most promising candidate for a consistent quantum theory of gravity capable of unifying all known forces of nature. An important question concerning these fundamental theories is how they compactify to lower dimensions and how to obtain a real four dimensional world? In this dissertation we present new avenues for M/string theory to reduce to lower dimensions as well as to four dimensions. For example, we show that by performing a generalized Kaluza-Klein IR reduction on the low-energy field theory of the heterotic string, the resulting lower dimensional theory compactifies spontaneously on S3 to give rise to (Minkowski)6 spacetime. Furthermore, a generalized reduction of M-theory on K3 × IR compacti- fies spontaneously on S2 to give rise to a (Minkowski)4 spacetime. The generalized Kaluza-Klein reduction gauges the Cremmer-Julia type global symmetry and the homogeneous rescaling symmetry of the supergravity equations of motion by giving the higher dimensional fields an additional dependence on the circle coordinate. We apply the generalized reduction scheme to half-maximal supergravities which are obtained from the heterotic string (or the NS-NS sector of the type-II string) compactified on a (10 − D)-dimensional torus truncated to the pure supergravity multiplet. This gives rise to new gauged supergravities in diverse dimensions with supersymmetric Minkowski × sphere vacua.Since two large extra dimensions have received much attention recently, we make a detailed study of the gauged D = 6, N = (1, 1) supergravity. In particular, we show that this theory allows for a consistent sphere reduction on S2 to give rise to D = 4, N = 2 supergravity coupled to a vector multiplet which can further be truncated to N = 1 supergravity with a chiral multiplet. We also investigate pp-waves in AdS backgrounds, i.e. pp-waves as solutions of gauged supergravities with AdS vacua. These solutions generically preserve 1 4 of the supersymmetry. We demonstrate supernumerary supersymmetries for both purely gravitational pp-waves and pp-waves supported by fields strengths. These new backgrounds provide interesting novel features of the supersymmetry enhancement for the dual conformal field theory in the infinite-momentum frame.

published_or_final_version / Physics / Doctoral / Doctor of Philosophy

A search for evidence of supersymmetry with a three lepton and missing transverse energy signature is presented. This signature is a possible final state from the associated production of a chargino and a neutralino, two particles predicted by supersymmetry. The study is performed on 2.06 fb⁻¹ of 7 TeV center of mass energy proton-proton collisions, recorded with the ATLAS experiment at the Large Hadron Collider in 2011. A multivariate analysis is utilized, implementing a boosted decision tree classifier using lepton p(T), missing transverse energy, dilepton mass, and the razor variable R as inputs. No significant excess over the Standard Model prediction is observed, and upper limits are placed on the cross section times branching ratio of simplified models across a mass parameter space.

No description available.

Searches of supersymmetry at the LHC have put stringent constraints on the strong production of squarks and gluinos. Current results exclude colored particles with masses up to roughly 1 TeV. To fully explore the discovery potential of the LHC, we study the challenging signals that are hidden by Standard Model backgrounds but with masses accessible by the LHC. These particles include the sleptons with a weak production cross section, and stops that are hidden by large top-antitop backgrounds. In this dissertation, I explore the collider phenomenology of sleptons and stops at the LHC. Sleptons can be produced at the LHC either through cascade decay or via Drell-Yan pair production. For the cascade decay, we studied neutralino-chargino associated production, with the subsequent decay through on shell sleptons resulting in a trilepton plus missing transverse energy signal. The invariant mass from the neutralino decay has a distinctive triangle shape with a sharp kinematic cutoff. We utilized this feature and obtained the effective cross section that is needed for a 5-sigma discovery of sleptons. We apply these results to the MSSM and find a discovery reach for left-handed sleptons which extends beyond the reach expected in usual Drell-Yan studies. Slepton pair production searches on the other hand, have limited reach at the LHC. The slepton decay branching fractions, however, depend on the composition of the lightest supersymmetric particle (LSP). We extend the experimental analysis for data collected thus far to include different scenarios for the composition of the LSP. We find that the LHC slepton reach is enhanced up to a factor of 2 for a non-Bino-LSP. We present the 95% C.L. exclusion limits and 5-sigma discovery reach for sleptons at the 8 and 14 TeV LHC considering Bino-, Wino-, or Higgsino-like LSPs. Current stop searches at the LHC focus on signals with top-antitop plus missing transverse energy. However, in many regions of SUSY parameter space, these decay modes are not dominant, leading to weakened experimental limits on stops. We identify stop decays that can have significant branching fractions to new final states resulting in new signal channels to observe. We investigate stop pair production by considering the channel of stop to top-higgs-LSP and stop to bottom-W-LSP leading to a signal of 4 b-jets, 2 jets, 1 lepton and missing transverse energy. We present the 95% C.L. exclusion limits and 5-sigma discovery reach for stops at the 14 TeV LHC.

A search for Supersymmetry is presented. The search is done with final states containing jets, missing transverse energy and no leptons, using 4.7 fb-1 of proton-proton collisions at sqrt(s)=7 TeV recorded by the ATLAS detector at the Large Hadron Collider. The analysis is carried out using new kinematic variables in two distinct signal regions with and without b-jet tagging. No significant excess above the Standard Model background expectation is observed, and limits are set on the Supersymmetry models. The results are interpreted as limits on the minimal supergravity framework, as well as a simplified Supersymmetry model of Gluino pair-production