No abstract

No abstract

If supersymmetry exists at low energies, it is necessary to understand why the squark spectrum exhibits sufficient degeneracy to suppress flavor changing neutral currents. In this note, we point out that gauged horizontal symmetries can yield realistic quark mass matrices, while at the same time giving just barely enough squark degeneracy to account for neutral K-meson phenomenology. This approach suggests likely patterns for squark masses, and indicates that there could be significant supersymmetric contributions to B −B and D −D mixing and CP -violation in the K and B systems.

One possible solution to the strong CP problem is that CP is an exact symmetry, spontaneously broken at some scale. Some years ago, Nelson and Barr suggested a mechanism for obtaining θ = 0 at tree level in this framework, and showed that radiative corrections were small in some non-supersymmetric models. Further investigations suggested that the same could be true in supersymmetric theories.In this note, we show that such solutions assume extraordinarily high degrees of degeneracy among squark masses and among other supersymmetry breaking parameters. We argue, using naturalness as well as expectations from string theory, that this is not very plausible.

We explore the influence of an anomalous chromomagnetic moment n on the production characteristics of top quark pairs at the Fermilab Tevatron with a center-of-mass energy of & = 1.8TeV. We find that for top quarks in the 175 GeV mass range, present measurements are probing values of n of order 0.25. We discuss a class of technicolor models with techniscalars which may produce such large values of n in conjunction with the generation of mt. For n's in this range we find that significant enhancements in both the qq, gg -+ t f production cross sections are obtained.Once sufficient statistics have been accumulated and QCD uncertainties are under control, future high precision measurements at the Fermilab Tevatron will eventually be sensitive to values of K with magnitudes smaller than --0.1.PACS number(s): 14.65. Ha, 12.60.Jv, 12.60.Nz, 14.70.Dj The discovery of the top quark a t the Fermilab Tevatron by the Collider Detector at Fermilab (CDF) and DO Collaborations [1,2] in the mass range anticipated by precision electroweak data [3] represents a great triumph for the standard model (SM). Once more data become avail-\ ,

Adding singlet neutrinos to the standard model spectrum in general gives rise to Z-induced flavor-changing neutral currents. We study the impact of these currents on matter-induced neutrino oscillations in the sun and in supernovae. While the effects for solar neutrinos are negligible, dramatic effects are possible for supernova neutrinos.

The compact 3T MRI system has been in continuous operation at the Mayo Clinic since March 2016. To date, over 200 patient studies have been completed, including 96 comparison studies with a clinical 3T whole-body MRI. The increased gradient performance has reliably resulted in consistently improved image quality.

Purpose To develop a highly efficient magnetic field gradient coil for head imaging that achieves 200 mT/m and 500 T/m/s on each axis using a standard 1 MVA gradient driver in clinical whole‐body 3.0T MR magnet. Methods A 42‐cm inner diameter head‐gradient used the available 89‐ to 91‐cm warm bore space in a whole‐body 3.0T magnet by increasing the radial separation between the primary and the shield coil windings to 18.6 cm. This required the removal of the standard whole‐body gradient and radiofrequency coils. To achieve a coil efficiency ~4× that of whole‐body gradients, a double‐layer primary coil design with asymmetric x‐y axes, and symmetric z‐axis was used. The use of all‐hollow conductor with direct fluid cooling of the gradient coil enabled ≥50 kW of total heat dissipation. Results This design achieved a coil efficiency of 0.32 mT/m/A, allowing 200 mT/m and 500 T/m/s for a 620 A/1500 V driver. The gradient coil yielded substantially reduced echo spacing, and minimum repetition time and echo time. In high b = 10,000 s/mm2 diffusion, echo time (TE) < 50 ms was achieved (>50% reduction compared with whole‐body gradients). The gradient coil passed the American College of Radiology tests for gradient linearity and distortion, and met acoustic requirements for nonsignificant risk operation. Conclusions Ultra‐high gradient coil performance was achieved for head imaging without substantial increases in gradient driver power in a whole‐body 3.0T magnet after removing the standard gradient coil. As such, any clinical whole‐body 3.0T MR system could be upgraded with 3‐4× improvement in gradient performance for brain imaging.