Electric Dipole Moments in the Generic Supersymmetric Standard Model

The generic supersymmetric standard model is a model built from a supersymmetrized standard model field spectrum the gauge symmetries only. The popular minimal supersymmetric standard model differs from the generic version in having R-parity imposed by hand. We review an efficient formulation of the model and some of the recently obtained interesting phenomenological features, focusing on one-loop contributions to fermion electric dipole moments.Comment: 1+7 pages Revtex 3 figures incoporated; talk at NANP'0

Variations in structure and tectonics along the Mid-Atlantic Ridge, 23⁰N and 26⁰N

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution June 1990The variation in the depth and width of the median valley along the Mid-Atlantic Ridge (MAR) suggests that the formation of ocean crust at slow spreading centers is not a simple two-dimensional process in which crustal accretion occurs uniformly both along the ridge axis and with time. Rather, it has been proposed that the ridge axis can be divided into a number of distinct segments or spreading cells. This thesis investigates the segmentation model by studying the variability in the structure and tectonics within spreading cells at 23°N and 26°N along the MAR. The results support the segmentation model in which accretion varies along the ridge, evolving as independent spreading cells or segments, with different portions of the ridge system being in different stages of volcanic and tectonic evolution. Chapter 2 presents an overview of morphologic and tectonic variations along a 100- km-length of the MAR south of the Kane Fracture Zone (MARK area). Sea MARC.I side scan sonar data and multi-beam Sea Beam bathymetry are used to document the distribution of crustal magmatism and extensional tectonism near 23°N. The data indicate a complex median valley composed by two distinct en echelon spreading cells which overlap in a discordant zone that lacks a well-developed rift valley or neovolcanic zone. The northern cell, immediately south of the fracture zone, is dominated by a large constructional volcanic ridge and is associated with active high-temperature hydrothermal activity. In contrast, the southern cell is characterized by a NNE-trending band of small fissured and faulted volcanos that are built upon relatively old, fissured and sediment-covered lavas; this cell is inferred to be in a predominantly extensional phase with only small, isolated volcanic eruptions. Despite the complexity of the MARK area, volcanic and tectonic activity appears to be confined to the 10-17 km wide inner rift valley. Small-offset normal faulting along near-vertical planes begins within a few kilometers of the ridge axis and appears to be largely completed by the time the crust moves out of the median valley. Mass-wasting and gullying of scarp faces, and sedimentation which buries low-relief seafloor features, are the major geological processes occurring outside the rift valley. In Chapters 3 and 4, the microearthquake characteristics and P wave velocity structure beneath the median valley of the Mid-Atlantic Ridge near 26°N are studied; this ridge segment is characterized by a large high-temperature hydrothermal field situated within the inner floor at the along-axis high. Chapter 3 explores the tectonic variations within the crust as evidenced from the distribution and source mechanisms of microearthquakes observed by a network of seven ocean bottom hydrophones and two ocean bottom seismometers over a three week period in 1985. Hypocenters were determined for 189 earthquakes, with good resolution of focal depth obtained for 105 events. Almost all events occurred at depths between 3 and 7 km beneath the seafloor, with earthquakes occurring at shallower depths beneath the along-axis high (<4 km). The distribution of hypocenters and the diversity of faulting associated with earthquakes beneath the inner floor and walls suggests a spatially variable tectonic state for the ridge segment at 26°N. These variations are presumably a signature of lateral heterogeneity in the depth region over which brittle failure occurs, and are a consequence of along-axis changes in the thermal structure and state of stress. We suggest that at present the hydrothermal activity and deposition of massive sulfides is being sustained by heat generated by a recent magmatic intrusion. A consequence of this scenario is that thermal stresses play a dominant role in controlling the distribution of earthquakes and nature of faulting. Such a hypothesis is consistent with an apparent lack of seismicity beneath the hydrothermal field, the location of hypocenters around the low velocity zone (Chapter 4), attenuation of P wave energy to instruments atop the high (Chapter 4), the higher b-values associated with the along-axis high region, and the occurrence of high-angle (or very low angle) normal faulting and reverse faulting, as well as the variability in nodal plane orientations, associated with inner floor events beneath the along-axis high and the volcano. In Chapter 4, we report results from the explosive refraction line and from the tomographic inversion of P wave travel time residuals for seismic velocity structure in the vicinity of the hydrothermal field. The twcrdimensional along-axis P wave structure beneath the inner floor indicates that young oceanic crust cannot be adequately characterized by a simple, laterally homogeneous velocity structure, but that one-dimensional StruGtures are at least locally valid (at 5-10 km length scales). The shallowmost crust (upper 1-2 km) beneath an axial volcano and the along-axis high is characterized by significantly higher velocities (by more than 1 km/s) than are associated with the upper crust in the deepest portions of the median valley. The variation is inferred to be a consequence of more recent magmatic and volcanic activity in the along-axis high region, as compared with the alongaxis deep where tectonic fissuring has created a highly porous crust characterized by lower seafloor velocities. The crust beneath the along-axis deep appears to be typical of normal young oceanic crust, with a mantle velocity of 8.25 krn/s observed at 5 k:m depth. A low velocity zone centered beneath the along-axis high and extending under an axial volcano is imaged from 3 to 5 km depth (7.2 km/s to 6.0 km/s); the velocity decrease is required to satisfy the travel time residual data and to explain the severe attenuation in compressional wave energy to instruments atop the along-axis high. The presence of an active high-temperature hydrothermal field atop the along-axis high, together with the observations of lower P wave velocities, the absence of microearthquake activity greater than 4 km in depth, and the propagation of S waves through the crust beneath the volcano and along-axis high (Chapter 3), suggest that the volume corresponds to a region of hot rock with no seismically-resolvable pockets of partial melt. The shallow velocity gradients describing the low velocity volume(<0.6 s-l) appear to be a corrunon characteristic of inferred zones of magmatic intrusion on the MAR. Comparison of the depth to the velocity inversion with the depths determined in other seismic studies at locally high regions along the MAR, the Juan de Fuca Ridge, and the East Pacific Rise reveals a correlation between lid thickness and spreading rate, suggesting that the amount of magma available at each location is spatially variable, or that the differences in lid thickness are describing the temporal evolution of magmatic intrusions beneath mid-ocean ridges. In Chapter 5, the first direct measurement of upper mantle P- and S-wave delay times beneath an oceanic spreading center is presented. Two independent estimates of the epicenters and origin times are made for each of two earthquakes in a 1985 earthquake swarm near 25°50'N on the Mid-Atlantic Ridge using local and teleseismic arrival time data. Comparison indicates a 14-20 km northward bias in the epicenters teleseismically located using a Herrin [1968] Earth model. The bias is due to departures of the actual velocity structure from that implicit in the travel time tables used for the locations, combined with unbalanced station distribution. The comparison of origin times for the best-located event, after correction for the epicentral bias and for an oceanic crustal thickness, shows there to be only slightly lower velocities than a Herrin [1968] upper mantle; the P-wave delay is +0.3 ± 0.9 s (+0.2 ± 0.9 sand -2.4 ± 0.9 s relative to the isotropic Preliminary Earth Reference Model (PREM) and the Jeffreys-Bullen [1940] (JB) travel time tables, respectively). The lack of a resolvable P-wave delay suggests that the Herrin [1968] model is a good approximation to the average upper mantle velocity beneath this segment of the MAR. Measurement of the S-wave delay for the same MAR swarm event shows there to be a positive delay (+3.1 ± 2.0 s), or larger travel times and slower velocities compared to the JB S-wave tables (+ 3.9 ± 2.0 s relative to the isotropic PREM S-wave model). In contrast to the larger P-wave delays found in other MAR studies, the lack of a significant seismic anomaly near 26°N indicates that sizeable regions of low velocity material do not presently exist in the upper few hundred kilometers of mantle beneath this section of the ridge. This evidence argues for substantial along-axis variations in the active upwel~ng of mantle material along the slowly-spreading Mid-Atlantic Ridge. In order to explain the observation of a smaller than expected P wave delay in a region where the S delay suggests significant temperature anomalies (low velocities), we propose a model for mantle upwelling in which the decrease in travel time is due to an anisotropic P wave structure (fast direction vertical); the anisotropy results from the reorientation of olivine crystals parallel to the ascending flow and balances the travel time delay due to a region of low velocities.This thesis was funded in part by grants EAR-8407798, EAR-8407745, and EAR- 8817173 from the National Science Foundation

Electronic excitation spectrum of metallic carbon nanotubes

We have studied the discrete electronic spectrum of closed metallic nanotube quantum dots. At low temperatures, the stability diagrams show a very regular four-fold pattern that allows for the determination of the electron addition and excitation energies. The measured nanotube spectra are in excellent agreement with theoretical predictions based on the nanotube band structure. Our results permit the complete identification of the electron quantum states in nanotube quantum dots.Comment: 4 pages, 3 figure

Phonon self-energy corrections to non-zero wavevector phonon modes in single-layer graphene

Phonon self-energy corrections have mostly been studied theoretically and experimentally for phonon modes with zone-center (q = 0) wave-vectors. Here, gate-modulated Raman scattering is used to study phonons of a single layer of graphene (1LG) in the frequency range from 2350 to 2750 cm-1, which shows the G* and the G'-band features originating from a double-resonant Raman process with q \not= 0. The observed phonon renormalization effects are different from what is observed for the zone-center q = 0 case. To explain our experimental findings, we explored the phonon self-energy for the phonons with non-zero wave-vectors (q \not= 0) in 1LG in which the frequencies and decay widths are expected to behave oppositely to the behavior observed in the corresponding zone-center q = 0 processes. Within this framework, we resolve the identification of the phonon modes contributing to the G* Raman feature at 2450 cm-1 to include the iTO+LA combination modes with q \not= 0 and the 2iTO overtone modes with q = 0, showing both to be associated with wave-vectors near the high symmetry point K in the Brillouin zone

Gradient projection newton algorithm for sparse collaborative learning

Exploring the relationship among multiple sets of data from one same group enables practitioners to make better decisions in medical science and engineering. In this paper, we propose a sparse collaborative learning (SCL) model, an optimization with double-sparsity constraints, to process the problem with two sets of data and a shared response variable. It is capable of dealing with the classification problems or the regression problems dependent on the discreteness of the response variable as well as exploring the relationship between two datasets simultaneously. To solve SCL, we first present some necessary and sufficient optimality conditions and then design a gradient projection Newton algorithm which has proven to converge to a unique locally optimal solution globally with at least a quadratic convergence rate. Finally, the reported numerical experiments illustrate the efficiency of the proposed method

Robust two-stage stochastic linear programs with moment constraints

We consider the two-stage stochastic linear programming model, in which the recourse function is a worst case expected value over a set of probabilistic distributions. These distributions share the same first- and second-order moments. By using duality of semi-infinite programming and assuming knowledge on extreme points of the dual polyhedron of the constraints, we show that a deterministic equivalence of the two-stage problem is a second-order cone optimization problem. Numerical examples are presented to show non-conservativeness and computational advantage of this approach

Evolution equations of curvature tensors along the hyperbolic geometric flow

We consider the hyperbolic geometric flow $\frac{\partial^2}{\partial t^2}g(t)=-2Ric_{g(t)}$ introduced by Kong and Liu [KL]. When the Riemannian metric evolve, then so does its curvature. Using the techniques and ideas of S.Brendle [Br,BS], we derive evolution equations for the Levi-Civita connection and the curvature tensors along the hyperbolic geometric flow. The method and results are computed and written in global tensor form, different from the local normal coordinate method in [DKL1]. In addition, we further show that any solution to the hyperbolic geometric flow that develops a singularity in finite time has unbounded Ricci curvature.Comment: 15 page