174 research outputs found
Measuring Slepton Masses and Mixings at the LHC
Flavor physics may help us understand theories beyond the standard model. In
the context of supersymmetry, if we can measure the masses and mixings of
sleptons and squarks, we may learn something about supersymmetry and
supersymmetry breaking. Here we consider a hybrid gauge-gravity supersymmetric
model in which the observed masses and mixings of the standard model leptons
are explained by a U(1) x U(1) flavor symmetry. In the supersymmetric sector,
the charged sleptons have reasonably large flavor mixings, and the lightest is
metastable. As a result, supersymmetric events are characterized not by missing
energy, but by heavy metastable charged particles. Many supersymmetric events
are therefore fully reconstructible, and we can reconstruct most of the charged
sleptons by working up the long supersymmetric decay chains. We obtain
promising results for both masses and mixings, and conclude that, given a
favorable model, precise measurements at the LHC may help shed light not only
on new physics, but also on the standard model flavor parameters.Comment: 24 pages; v2: fixed a typo in our computer program that led to some
miscalculated branching ratios, various clarifications and minor
improvements, conclusions unchanged, published versio
Interpreting a 1 fb^-1 ATLAS Search in the Minimal Anomaly Mediated Supersymmetry Breaking Model
Recent LHC data significantly extend the exclusion limits for supersymmetric
particles, particularly in the jets plus missing transverse momentum channels.
The most recent such data have so far been interpreted by the experiment in
only two different supersymmetry breaking models: the constrained minimal
supersymmetric standard model (CMSSM) and a simplified model with only squarks
and gluinos and massless neutralinos. We compare kinematical distributions of
supersymmetric signal events predicted by the CMSSM and anomaly mediated
supersymmetry breaking (mAMSB) before calculating exclusion limits in mAMSB. We
obtain a lower limit of 900 GeV on squark and gluino masses at the 95%
confidence level for the equal mass limit, tan(beta)=10 and mu>0.Comment: 18 pages, 11 figure
Supersymmetric Monojets at the Large Hadron Collider
Supersymmetric monojets may be produced at the Large Hadron Collider by the
process qg -> squark neutralino_1 -> q neutralino_1 neutralino_1, leading to a
jet recoiling against missing transverse momentum. We discuss the feasibility
and utility of the supersymmetric monojet signal. In particular, we examine the
possible precision with which one can ascertain the neutralino_1-squark-quark
coupling via the rate for monojet events. Such a coupling contains information
on the composition of the neutralino_1 and helps bound dark matter direct
detection cross-sections and the dark matter relic density of the neutralino_1.
It also provides a check of the supersymmetric relation between gauge couplings
and gaugino-quark-squark couplings.Comment: 46 pages, 10 figures. The appendix has been rewritten to correct an
error that appears in all previous versions of the appendix. This error has
no effect on the results in the main body of the pape
MFV Reductions of MSSM Parameter Space
The 100+ free parameters of the minimal supersymmetric standard model (MSSM)
make it computationally difficult to compare systematically with data,
motivating the study of specific parameter reductions such as the cMSSM and
pMSSM. Here we instead study the reductions of parameter space implied by using
minimal flavour violation (MFV) to organise the R-parity conserving MSSM, with
a view towards systematically building in constraints on flavour-violating
physics. Within this framework the space of parameters is reduced by expanding
soft supersymmetry-breaking terms in powers of the Cabibbo angle, leading to a
24-, 30- or 42-parameter framework (which we call MSSM-24, MSSM-30, and MSSM-42
respectively), depending on the order kept in the expansion. We provide a
Bayesian global fit to data of the MSSM-30 parameter set to show that this is
manageable with current tools. We compare the MFV reductions to the
19-parameter pMSSM choice and show that the pMSSM is not contained as a subset.
The MSSM-30 analysis favours a relatively lighter TeV-scale pseudoscalar Higgs
boson and with multi-TeV sparticles.Comment: 2nd version, minor comments and references added, accepted for
publication in JHE
Stress analysis in a layered aortic arch model under pulsatile blood flow
BACKGROUND: Many cardiovascular diseases, such as aortic dissection, frequently occur on the aortic arch and fluid-structure interactions play an important role in the cardiovascular system. Mechanical stress is crucial in the functioning of the cardiovascular system; therefore, stress analysis is a useful tool for understanding vascular pathophysiology. The present study is concerned with the stress distribution in a layered aortic arch model with interaction between pulsatile flow and the wall of the blood vessel. METHODS: A three-dimensional (3D) layered aortic arch model was constructed based on the aortic wall structure and arch shape. The complex mechanical interaction between pulsatile blood flow and wall dynamics in the aortic arch model was simulated by means of computational loose coupling fluid-structure interaction analyses. RESULTS: The results showed the variations of mechanical stress along the outer wall of the arch during the cardiac cycle. Variations of circumferential stress are very similar to variations of pressure. Composite stress in the aortic wall plane is high at the ascending portion of the arch and along the top of the arch, and is higher in the media than in the intima and adventitia across the wall thickness. CONCLUSION: Our analysis indicates that circumferential stress in the aortic wall is directly associated with blood pressure, supporting the clinical importance of blood pressure control. High stress in the aortic wall could be a risk factor in aortic dissections. Our numerical layered aortic model may prove useful for biomechanical analyses and for studying the pathogeneses of aortic dissection
Emotional Fuzzy Sliding-Mode Control for Unknown Nonlinear Systems
[[abstract]]The brain emotional learning model can be implemented with a simple hardware and processor; however, the learning model cannot model the qualitative aspects of human knowledge. To solve this problem, a fuzzy-based emotional learning model (FELM) with structure and parameter learning is proposed. The membership functions and fuzzy rules can be learned through the derived learning scheme. Further, an emotional fuzzy sliding-mode control (EFSMC) system, which does not need the plant model, is proposed for unknown nonlinear systems. The EFSMC system is applied to an inverted pendulum and a chaotic synchronization. The simulation results with the use of EFSMC system demonstrate the feasibility of FELM learning procedure. The main contributions of this paper are (1) the FELM varies its structure dynamically with a simple computation; (2) the parameter learning imitates the role of emotions in mammalians brain; (3) by combining the advantage of nonsingular terminal sliding-mode control, the EFSMC system provides very high precision and finite-time control performance; (4) the system analysis is given in the sense of the gradient descent method.[[notice]]補正完
Search for squarks and gluinos with the ATLAS detector in final states with jets and missing transverse momentum using √s=8 TeV proton-proton collision data
A search for squarks and gluinos in final states containing high-p T jets, missing transverse momentum and no electrons or muons is presented. The data were recorded in 2012 by the ATLAS experiment in s√=8 TeV proton-proton collisions at the Large Hadron Collider, with a total integrated luminosity of 20.3 fb−1. Results are interpreted in a variety of simplified and specific supersymmetry-breaking models assuming that R-parity is conserved and that the lightest neutralino is the lightest supersymmetric particle. An exclusion limit at the 95% confidence level on the mass of the gluino is set at 1330 GeV for a simplified model incorporating only a gluino and the lightest neutralino. For a simplified model involving the strong production of first- and second-generation squarks, squark masses below 850 GeV (440 GeV) are excluded for a massless lightest neutralino, assuming mass degenerate (single light-flavour) squarks. In mSUGRA/CMSSM models with tan β = 30, A 0 = −2m 0 and μ > 0, squarks and gluinos of equal mass are excluded for masses below 1700 GeV. Additional limits are set for non-universal Higgs mass models with gaugino mediation and for simplified models involving the pair production of gluinos, each decaying to a top squark and a top quark, with the top squark decaying to a charm quark and a neutralino. These limits extend the region of supersymmetric parameter space excluded by previous searches with the ATLAS detector
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