736 research outputs found
On the Holomorphic Structure of a Low Energy Supersymmetric Wilson Effective Action
The Wilson (exact) renormalization group equations are used to determine the
evolution of a general low energy N=1 supersymmetric action containing a U(1)
gauge vector multiplet and a neutral chiral multiplet. The effective theory
evolves towards satisfying a fixed relation where the K\"ahler potential and
effective gauge coupling are obtained from a N=2 supersymmetric holomorphic
prepotential.Comment: 10 pages, LaTe
The supercharge and superconformal symmetry for N=1 supersymmetric quantum mechanics
The superspace Lagrangian formulation of N=1 supersymmetric quantum mechanics
is presented. The general Lagrangian constructed out of chiral and antichiral
supercoordinates containing up to two derivatives and with a canonically
normalized kinetic energy term describes the motion of a nonrelativistic spin
1/2 particle with Land\'e g-factor 2 moving in two spatial dimensions under the
influence of a static but spatially dependent magnetic field. Noether's theorem
is derived for the general case and is used to construct superspace dependent
charges whose lowest components give the superconformal generators. The
supercoordinate of charges containing an R symmetry charge, the supersymmetry
charges and the Hamiltonian are combined to form a supercharge supercoordinate.
Superconformal Ward identities for the quantum effective action are derived
from the conservation equations and the source of potential symmetry breaking
terms are identified.Comment: 59 pages, LaTe
Stability of Fine Tuned Hierarchies in Strongly Coupled Chiral Models
A fine tuned hierarchy between a strongly coupled high energy compositeness
scale and a much lower chiral symmetry breaking scale is a requisite ingredient
in many models of dynamical electroweak symmetry breaking. Using a
nonperturbative continuous Wilson renormalization group equation approach, we
explore the stability of such a hierarchy against quantum fluctuations.Comment: 14,PURD-TH-94-1
Holographic Walking Technicolor and Stability of Techni-Branes
Techni-fermions are added as stacks of D7-anti-D7 techni-branes within the
framework of a holographic technicolor model that has been proposed as a
realization of walking technicolor. The stability of the embedding of these
branes is determined. When a sufficiently low bulk cut-off is provided the
fluctuations remain small. For a longer walking region, as would be required in
any realistic model of electroweak symmetry breaking, a larger bulk cut-off is
needed and in this case the oscillations destabilize.Comment: Latex, 25 pages, 10 figure
Electron Exchange Coupling for Single Donor Solid-State Qubits
Inter-valley interference between degenerate conduction band minima has been
shown to lead to oscillations in the exchange energy between neighbouring
phosphorus donor electron states in silicon \cite{Koiller02,Koiller02A}. These
same effects lead to an extreme sensitivity of the exchange energy on the
relative orientation of the donor atoms, an issue of crucial importance in the
construction silicon-based spin quantum computers. In this article we calculate
the donor electron exchange coupling as a function of donor position
incorporating the full Bloch structure of the Kohn-Luttinger electron
wavefunctions. It is found that due to the rapidly oscillating nature of the
terms they produce, the periodic part of the Bloch functions can be safely
ignored in the Heitler-London integrals as was done by Koiller et. al. [Phys.
Rev. Lett. 88,027903(2002),Phys. Rev. B. 66,115201(2002)], significantly
reducing the complexity of calculations.
We address issues of fabrication and calculate the expected exchange coupling
between neighbouring donors that have been implanted into the silicon substrate
using an 15keV ion beam in the so-called 'top down' fabrication scheme for a
Kane solid-state quantum computer. In addition we calculate the exchange
coupling as a function of the voltage bias on control gates used to manipulate
the electron wavefunctions and implement quantum logic operations in the Kane
proposal, and find that these gate biases can be used to both increase and
decrease the magnitude of the exchange coupling between neighbouring donor
electrons. The zero-bias results reconfirm those previously obtained by
Koiller.Comment: 10 Pages, 8 Figures. To appear in Physical Review
Wilson Renormalization Group Analysis of Theories with Scalars and Fermions
The continuous block spin (Wilson) renormalization group equation governing
the scale dependence of the action is constructed for theories containing
scalars and fermions. A locally approximated form of this equation detailing
the structure of a generalized effective potential is numerically analyzed. The
role of the irrelevant operators in the nonperturbative renormalization group
running is elucidated and a comparison with the 1-loop perturbative results is
drawn. Focusing on the spontaneously broken phase of a model possessing a
discrete symmetry forbidding an explicit fermion mass term, mass bounds on both
the scalar and fermion degrees of freedom are established. The effect of the
generalized Yukawa coupling on the scalar mass upper bound is emphasized.Comment: 40, PURD-TH-92-
Road exposure and the detectability of birds in field surveys
Road ecology, the study of the impacts of roads and their traffic on wildlife, including birds, is a rapidly growing field, with research showing effects on local avian population densities up to several kilometres from a road. However, in most studies, the effects of roads on the detectability of birds by surveyors are not accounted for. This could be a significant source of error in estimates of the impacts of roads on birds and could also affect other studies of bird populations. Using road density, traffic volume and bird count data from across Great Britain, we assess the relationships between roads and detectability of a range of bird species. Of 51 species analysed, the detectability of 36 was significantly associated with road exposure, in most cases inversely. Across the range of road exposure recorded for each species, the mean positive change in detectability was 52% and the mean negative change was 36%, with the strongest negative associations found in smaller-bodied species and those for which aural cues are more important in detection. These associations between road exposure and detectability could be caused by a reduction in surveyorsâ abilities to hear birds or by changes in birdsâ behaviour, making them harder or easier to detect. We suggest that future studies of the impacts of roads on populations of birds or other taxa, and other studies using survey data from road-exposed areas, should account for the potential impacts of roads on detectability.The BBS is jointly funded by the BTO, JNCC and RSPB. Stuart Newson is supported by the BTOâs Young Scientistsâ Programme. Sophia C. Cooke is funded by the Natural Environment Research Council
Detecting new microRNAs in human osteoarthritic chondrocytes identifies miR-3085 as a human, chondrocyte-selective, microRNA
Objective: To use deep sequencing to identify novel microRNAs in human osteoarthritic cartilage which have a functional role in chondrocyte phenotype or function. Design: A small RNA library was prepared from human osteoarthritic primary chondrocytes using in-house adaptors and analysed by Illumina sequencing. Novel candidate microRNAs were validated by northern blot and qRT-PCR. Expression was measured in cartilage models. Targets of novel candidates were identified by microarray and computational analysis, validated using 3â-UTR-luciferase reporter plasmids. Protein levels were assessed by western blot and functional analysis by cell adhesion. Results: We identified 990 known microRNAs and 1621 potential novel microRNAs in human osteoarthritic chondrocytes, 60 of the latter were expressed in all samples assayed. MicroRNA-140-3p was the most highly expressed microRNA in osteoarthritic cartilage. Sixteen novel candidate microRNAs were analysed further, of which 6 remained after northern blot analysis. Three novel microRNAs were regulated across models of chondrogenesis, chondrocyte differentiation or cartilage injury. One sequence (novel #11), annotated in rodents as microRNA-3085-3p, was preferentially expressed in cartilage, dependent on chondrocyte differentiation and, in man, is located in an intron of the cartilage-expressed gene CRTAC-1. This microRNA was shown to target the ITGA5 gene directly (which encodes integrin alpha5) and inhibited adhesion to fibronectin (dependent on alpha5beta1 integrin). Conclusion: Deep sequencing has uncovered many potential microRNA candidates expressed in human cartilage. At least three of these show potential functional interest in cartilage homeostasis and osteoarthritis. Particularly, novel #11 (microRNA-3085-3p) which has been identified for the first time in man
Empirical investigation of extreme single-particle behavior of nuclear quadrupole moments in highly collective AâŒ150 superdeformed bands
The intrinsic quadrupole moment Q0 of superdeformed rotational bands in AâŒ150 nuclei depends on the associated single-particle configuration. We have derived an empirical formula based on the additivity of effective quadrupole moments of single-particle orbitals that describes existing measurements from 142Sm to 152Dy. To further test the formula, the predicted Q0 moments for two superdeformed bands in 146Gd of 14.05eb were confronted with a new measurement yielding 13.9±0.4eb and 13.9 ± 0.3eb, respectively. This excellent agreement provides empirical evidence of extreme single-particle behavior in highly deformed, collective systems
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