3,503 research outputs found
Long-Lived Neutralino NLSPs
We investigate the collider signatures of heavy, long-lived, neutral
particles that decay to charged particles plus missing energy. Specifically, we
focus on the case of a neutralino NLSP decaying to Z and gravitino within the
context of General Gauge Mediation. We show that a combination of searches
using the inner detector and the muon spectrometer yields a wide range of
potential early LHC discoveries for NLSP lifetimes ranging from 10^(-1)-10^5
mm. We further show that events from Z(l+l-) can be used for detailed kinematic
reconstruction, leading to accurate determinations of the neutralino mass and
lifetime. In particular, we examine the prospects for detailed event study at
ATLAS using the ECAL (making use of its timing and pointing capabilities)
together with the TRT, or using the muon spectrometer alone. Finally, we also
demonstrate that there is a region in parameter space where the Tevatron could
potentially discover new physics in the delayed Z(l+l-)+MET channel. While our
discussion centers on gauge mediation, many of the results apply to any
scenario with a long-lived neutral particle decaying to charged particles.Comment: 31 pages, 12 figure
Phenomenology of the Littlest Higgs with T-Parity
Little Higgs models offer an interesting approach to weakly coupled
electroweak symmetry breaking without fine tuning. The original little Higgs
models were plagued by strong constraints from electroweak precision data which
required a fine tuning to be reintroduced. An economical solution to this
problem is to introduce a discrete symmetry (analogous to R-parity of SUSY)
called T-parity. T-parity not only eliminates most constraints from electroweak
precision data, but it also leads to a promising dark matter candidate. In this
paper we investigate the dark matter candidate in the littlest Higgs model with
T-parity. We find bounds on the symmetry breaking scale f as a function of the
Higgs mass by calculating the relic density. We begin the study of the LHC
phenomenology of the littlest Higgs model with T-parity. We find that the model
offers an interesting collider signature that has a generic missing energy
signal which could "fake" SUSY at the LHC. We also investigate the properties
of the heavy partner of the top quark which is common to all littlest Higgs
models, and how its properties are modified with the introduction of T-parity.
We include an appendix with a list of Feynman rules specific to the littlest
Higgs with T-parity to facilitate further study.Comment: 32 pages, 8 figures; dark matter bounds revised; comphep model files
made publicly available at http://www.lns.cornell.edu/public/theory/tparity
General Neutralino NLSPs at the Early LHC
Gauge mediated supersymmetry breaking (GMSB) is a theoretically
well-motivated framework with rich and varied collider phenomenology. In this
paper, we study the Tevatron limits and LHC discovery potential for a wide
class of GMSB scenarios in which the next-to-lightest superpartner (NLSP) is a
promptly-decaying neutralino. These scenarios give rise to signatures involving
hard photons, 's, 's, jets and/or higgses, plus missing energy. In order
to characterize these signatures, we define a small number of minimal spectra,
in the context of General Gauge Mediation, which are parameterized by the mass
of the NLSP and the gluino. Using these minimal spectra, we determine the most
promising discovery channels for general neutralino NLSPs. We find that the
2010 dataset can already cover new ground with strong production for all NLSP
types. With the upcoming 2011-2012 dataset, we find that the LHC will also have
sensitivity to direct electroweak production of neutralino NLSPs.Comment: 26 page
Surface energy and stability of stress-driven discommensurate surface structures
A method is presented to obtain {\it ab initio} upper and lower bounds to
surface energies of stress-driven discommensurate surface structures, possibly
non-periodic or exhibiting very large unit cells. The instability of the
stressed, commensurate parent of the discommensurate structure sets an upper
bound to its surface energy; a lower bound is defined by the surface energy of
an ideally commensurate but laterally strained hypothetical surface system. The
surface energies of the phases of the Si(111):Ga and Ge(111):Ga systems and the
energies of the discommensurations are determined within eV.Comment: 4 pages RevTeX. 2 Figures not included. Ask for a hard copy (through
regular mail) to [email protected]
Natural Supersymmetry at the LHC
If the minimal supersymmetric standard model is the solution to the hierarchy
problem, the scalar top quark (stop) and the Higgsino should weigh around the
electroweak scale such as 200 GeV. A low messenger scale, which results in a
light gravitino, is also suggested to suppress the quantum corrections to the
Higgs mass parameters. Therefore the minimal model for natural supersymmetry is
a system with stop/Higgsino/gravitino whereas other superparticles are heavy.
We study the LHC signatures of the minimal system and discuss the discovery
potential and methods for the mass measurements.Comment: 19 pages, 6 figures, 1 tabl
Bandgap properties of two-dimensional low-index photonic crystals
We study the bandgap properties of two-dimensional photonic crystals created
by a lattice of rods or holes conformed in a symmetric or asymmetric triangular
structure. Using the plane-wave analysis, we calculate a minimum value of the
refractive index contrast for opening both partial and full two-dimensional
spectral gaps for both TM and TE polarized waves. We also analyze the effect of
ellipticity of rods and holes and their orientation on the threshold value and
the relative size of the bandgap.Comment: 5 pages, 6 figures, App. Phys. B. styl
Human-modified landscapes provide key foraging areas for a threatened flying mammal : the grey-headed flying-fox
Urban expansion is a major threat to natural ecosystems but also creates novel opportunities that adaptable species can exploit. The grey-headed flying-fox (Pteropus poliocephalus) is a threatened, highly mobile species of bat that is increasingly found in human-dominated landscapes, leading to many management and conservation challenges. Flying-fox urbanisation is thought to be a result of diminishing natural foraging habitat or increasing urban food resources, or both. However, little is known about landscape utilisation of flying-foxes in human-modified areas, and how this may differ in natural areas. Here we examine positional data from 98 satellite-tracked P. poliocephalus for up to 5 years in urban and nonurban environments, in relation to vegetation data and published indices of foraging habitat quality. Our findings indicate that human-modified foraging landscapes sustain a large proportion of the P. poliocephalus population year-round. When individuals roosted in nonurban and minor-urban areas, they relied primarily on wet and dry sclerophyll forest, forested wetlands, and rainforest for foraging, and preferentially visited foraging habitat designated as high-quality. However, our results highlight the importance of human-modified foraging habitats throughout the species’ range, and particularly for individuals that roosted in major-urban environments. The exact plant species that exist in human-modified habitats are largely undocumented; however, where this information was available, foraging by P. poliocephalus was associated with different dominant plant species depending on whether individuals roosted in ‘urban’ or ‘non-urban’ areas. Overall, our results demonstrate clear differences in urban- and non-urban landscape utilisation by foraging P. poliocephalus. However, further research is needed to understand the exact foraging resources used, particularly in human-modified habitats, and hence what attracts flying-foxes to urban areas. Such information could be used to modify the urban foraging landscape, to assist long-term habitat management programs aimed at minimising human-wildlife conflict and maximising resource availability within and outside of urban environments
Pain severity predicts depressive symptoms over and above individual illnesses and multimorbidity in older adults.
BACKGROUND: Multi-morbidity in older adults is commonly associated with depressed mood. Similarly, subjective reports of pain are also associated with both physical illness and increased depressive symptoms. However, whether pain independently contributes to the experience of depression in older people with multi-morbidity has not been studied. METHODS: In this study, participants were 1281 consecutive older adults presenting to one of 19 primary care services in Australia (recruitment rate = 75%). Participants were asked to indicate the presence of a number of common chronic illnesses, to rate their current pain severity and to complete the Geriatric Depression Scale. RESULTS: Results confirmed that the number of medical illnesses reported was strongly associated with depressive symptoms. Twenty-six percent of participants with multi-morbidity scored in the clinical range for depressive symptoms in comparison to 15% of participants with no illnesses or a single illness. In regression analyses, the presence of chronic pain (t = 5.969, p < 0.0005), diabetes (t = 4.309, p < 0.0005), respiratory (t = 3.720, p < 0.0005) or neurological illness (t = 2.701, p = 0.007) were all independent contributors to depressive symptoms. Even when controlling for each individual illness, and the overall number of illnesses (t = 2.207, p = 0.028), pain severity remained an independent predictor of depressed mood (F change = 28.866, p < 0.0005, t = 5.373, p < 0.0005). CONCLUSIONS: Physicians should consider screening for mood problems amongst those with multi-morbidity, particularly those who experience pain
Photonic band structure of highly deformable, self-assembling systems
We calculate the photonic band structure at normal incidence of highly
deformable, self-assembling systems - cholesteric elastomers subjected to
external stress. Cholesterics display brilliant reflection and lasing owing to
gaps in their photonic band structure. The band structure of cholesteric
elastomers varies sensitively with strain, showing new gaps opening up and
shifting in frequency. A novel prediction of a total band gap is made, and is
expected to occur in the vicinity of the previously observed de Vries bandgap,
which is only for one polarisation
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