3,402 research outputs found
A New Avenue to Charged Higgs Discovery in Multi-Higgs Models
Current searches for the charged Higgs at the LHC focus only on the
, , and final states. Instead, we consider the process where is a heavy neutral Higgs boson,
is a charged Higgs boson, and is a light Higgs boson, with mass
either below or above the threshold. The cross-section for this
process is typically large when kinematically open since
can be the dominant decay mode of the charged Higgs. The final state we
consider has two leptons and missing energy from the doubly leptonic decay of
the and possibly additional jets; it is therefore constrained by
existing SM Higgs searches in the channel. We extract these
constraints on the cross-section for this process as a function of the masses
of the particles involved. We also apply our results specifically to a type-II
two Higgs doublet model with an extra Standard-Model-singlet and obtain new and
powerful constraints on and . We point out that a
slightly modified version of this search, with more dedicated cuts, could be
used to possibly discover the charged Higgs, either with existing data or in
the future.Comment: 38 pages, 14 figure
Limits on Vectorlike Leptons from Searches for Anomalous Production of Multi-Lepton Events
We consider extensions of the Standard Model by vectorlike leptons and set
limits on a new charged lepton, , using the ATLAS search for anomalous
production of multi-lepton events. It is assumed that only one Standard Model
lepton, namely the muon, dominantly mixes with vectorlike leptons resulting in
possible decays , , and
. We derive generally applicable limits on the new
lepton treating the branching ratios for these processes as free variables. We
further interpret the general limits in two scenarios with
originating predominantly from either the doublet or the
singlet. The doublet case is more constrained as a result of larger production
cross-section and extra production processes and
in addition to , where is a new neutral state accompanying
. We find that some combinations of branching ratios are poorly
constrained, whereas some are constrained up to masses of more than 500 GeV. In
the doublet case, assuming BR, all masses below
about 300 GeV are ruled out. Even if this condition is relaxed and additional
decay modes, and , are allowed,
below the Higgs threshold still almost all of the parameter space (of
independent branching ratios) is ruled out. Nevertheless, even assuming the
maximal production cross-section, which coincides with the doublet case, the
new charged lepton can still be as light as the LEP-II limit allows. We discuss
several possible improvements of current experimental analyses that would
dramatically reduce the allowed parameter space, even with current data.Comment: 24 pages, 11 figure
E6SSM vs MSSM gluino phenomenology
The E6SSM is a promising model based on the group E6, assumed to be broken at
the GUT scale, leading to the group SU(3)\times SU(2)\times U(1)\times U(1)' at
the TeV scale. It gives a solution to the MSSM {\mu}-problem without
introducing massless axions, gauge anomalies or cosmological domain walls. The
model contains three families of complete 27s of E6, giving a richer
phenomenology than the MSSM. The E6SSM generically predicts gluino cascade
decay chains which are about 2 steps longer than the MSSM's due to the presence
of several light neutralino states. This implies less missing (and more
visible) transverse momentum in collider experiments and kinematical
distributions such as M_eff are different. Scans of parameter space and MC
analysis suggest that current SUSY search strategies and exclusion limits have
to be reconsidered.Comment: Presented at the 2011 Hadron Collider Physics symposium (HCP-2011),
Paris, France, November 14-18 2011, 3 pages, 7 figure
Robust control design with real parameter uncertainty using absolute stability theory
The purpose of this thesis is to investigate an extension of mu theory for robust control design by considering systems with linear and nonlinear real parameter uncertainties. In the process, explicit connections are made between mixed mu and absolute stability theory. In particular, it is shown that the upper bounds for mixed mu are a generalization of results from absolute stability theory. Both state space and frequency domain criteria are developed for several nonlinearities and stability multipliers using the wealth of literature on absolute stability theory and the concepts of supply rates and storage functions. The state space conditions are expressed in terms of Riccati equations and parameter-dependent Lyapunov functions. For controller synthesis, these stability conditions are used to form an overbound of the H2 performance objective. A geometric interpretation of the equivalent frequency domain criteria in terms of off-axis circles clarifies the important role of the multiplier and shows that both the magnitude and phase of the uncertainty are considered. A numerical algorithm is developed to design robust controllers that minimize the bound on an H2 cost functional and satisfy an analysis test based on the Popov stability multiplier. The controller and multiplier coefficients are optimized simultaneously, which avoids the iteration and curve-fitting procedures required by the D-K procedure of mu synthesis. Several benchmark problems and experiments on the Middeck Active Control Experiment at M.I.T. demonstrate that these controllers achieve good robust performance and guaranteed stability bounds
Variance of sums in arithmetic progressions of arithmetic functions associated with higher degree <i>0</i>-functions in F<sub><i>q</i></sub>[<i>t</i>]
We compute the variances of sums in arithmetic progressions of generalised -divisor functions related to certain -functions in q[], in the limit as q → ∞. This is achieved by making use of recently established equidistribution results for the associated Frobenius conjugacy classes. The variances are thus expressed, when q → ∞, in terms of matrix integrals, which may be evaluated. Our results extend those obtained previously in the special case corresponding to the usual -divisor function, when the -function in question has degree one. They illustrate the role played by the degree of the -functions; in particular, we find qualitatively new behaviour when the degree exceeds one. Our calculations apply, for example, to elliptic curves defined over q[], and we illustrate them by examining in some detail the generalised -divisor functions associated with the Legendre curve
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Building a Community of Practice: A Case Study of Introductory College Chemistry Students
Engagement in active learning and learning communities is important for persistence of STEM students early in their academic programs. Colleges and universities have an ongoing call to facilitate active learning techniques, yet large group, lecture-based instruction is still the prominent method of instruction. This qualitative case study examines interviews and classroom observations of undergraduate chemistry students enrolled at a primarily undergraduate institution. Critical educational elements were identified for chemistry students participating in a redesigned, introductory course which included a collaborative peer-lead learning experience. The participants engaged in required, weekly sessions structured around community building and active learning. The data were framed through a community of practice (CoP) framework, and emergent themes were centered on the following components: mutual engagement, joint enterprise, and shared repertoire. Findings show participant engagement created opportunities for collaboration beyond the required, weekly sessions, which included forming study groups and seeking assistance from chemistry tutors. Participants also shared study techniques based on a mutual understanding that effective learning required routine practice. Implications for STEM departments and researchers about implementing research-based curriculum are discussed
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