S-Track Stabilization of Heterotic de Sitter Vacua

We present a new mechanism, the S-Track, to stabilize the volume modulus S in heterotic M-theory flux compactifications along with the orbifold-size T besides complex structure and vector bundle moduli stabilization. The key dynamical ingredient which makes the volume modulus stabilization possible, is M5-instantons arising from M5-branes wrapping the whole Calabi-Yau slice. These are natural in heterotic M-theory where the warping shrinks the Calabi-Yau volume along S^1/Z_2. Combined with H-flux, open M2-instantons and hidden sector gaugino condensation it leads to a superpotential W which stabilizes S similar like a racetrack but without the need for multi gaugino condensation. Moreover, W contains two competing non-perturbative effects which stabilize T. We analyze the potential and superpotentials to show that it leads to heterotic de Sitter vacua with broken supersymmetry through non-vanishing F-terms.Comment: 16 pages, 2 figures; final PRD versio

Understanding Educators’ Perceptions of Mindfulness on Students’ Academic Skills, Behavior, and Overall Well-Being

Research indicates that academic performance and social and emotional well-being are fundamentally interrelated (Schonert-Reichl, Oberle, Lawlor, Abbott, Thomson, Oberlander, & Diamond, 2015). Given that 13-20% of children in the United States experience social and emotional challenges, schools are required to attend to the social, emotional, and behavioral needs of students (Maynard, Solis, Miller, & Brendel, 2017). However, students are often unequipped with the skills to effectively cope with stress and resort to behaviors that cause emotional, mental, and physical suffering, all of which thwart the learning process (Schonert-Reichl et al., 2015). Schools warrant interventions that support the whole student, given the increase in mental health statistics (Meiklejohn, Phillips, Freedman, Griffin, Biegel, Roach, Frank, Burke, Pinger, Soloway, Isberg, Sibinga, Grossman, & Saltzman, 2012). Given that the stakes for student success and well-being are high, many schools have integrated mindfulness practices within classrooms. This study sought to understand the efficacy of mindfulness programs in the K-12 education setting, specifically educators’ perceptions of mindfulness on students’ academic skills, behavior, and well-being. This qualitative study involved semi-structured interviews with ten participants from schools in Massachusetts and Rhode Island. The findings indicate that mindfulness is successful when applied both indirectly and directly, is adaptable within class structures and transitional periods, is practiced using a variety of techniques, and supports a diverse student climate. However, while there is little to no data to support the effects of mindfulness on academics, this study does suggest that mindfulness can be an effective means of supporting students’ behavior and well-being. Further research measuring the effects of mindfulness on academic skills is needed

New sum rules for nucleon and trinucleon total photoproduction cross-sections

Two new sum rules are derived relating Dirac radii and anomalous magnetic moments of the considered strongly interacting fermions with the convergent integral over a difference of the total proton and neutron, as well as $He^3$ and $H^3$, photoproduction cross-sections.Comment: 1 eps figure. Contribution presented at the PHOTON'03, April 7-11, 2003, Frascati (Roma), Ital

Perspectives on Pfaffians of Heterotic World-sheet Instantons

To fix the bundle moduli of a heterotic compactification one has to understand the Pfaffian one-loop prefactor of the classical instanton contribution. For compactifications on elliptically fibered Calabi-Yau spaces X this can be made explicit for spectral bundles and world-sheet instantons supported on rational base curves b: one can express the Pfaffian in a closed algebraic form as a polynomial, or it may be understood as a theta-function expression. We elucidate the connection between these two points of view via the respective perception of the relevant spectral curve, related to its extrinsic geometry in the ambient space (the elliptic surface in X over b) or to its intrinsic geometry as abstract Riemann surface. We identify, within a conceptual description, general vanishing loci of the Pfaffian, and derive bounds on the vanishing order, relevant to solutions of W=dW=0.Comment: 40 pages; minor changes, discussion section 1.1 adde

Interference in Bohmian Mechanics with Complex Action

In recent years, intensive effort has gone into developing numerical tools for exact quantum mechanical calculations that are based on Bohmian mechanics. As part of this effort we have recently developed as alternative formulation of Bohmian mechanics in which the quantum action, S, is taken to be complex [JCP {125}, 231103 (2006)]. In the alternative formulation there is a significant reduction in the magnitude of the quantum force as compared with the conventional Bohmian formulation, at the price of propagating complex trajectories. In this paper we show that Bohmian mechanics with complex action is able to overcome the main computational limitation of conventional Bohmian methods -- the propagation of wavefunctions once nodes set in. In the vicinity of nodes, the quantum force in conventional Bohmian formulations exhibits rapid oscillations that pose severe difficulties for existing numerical schemes. We show that within complex Bohmian mechanics, multiple complex initial conditions can lead to the same real final position, allowing for the description of nodes as a sum of the contribution from two or more crossing trajectories. The idea is illustrated on the reflection amplitude from a one-dimensional Eckart barrier. We believe that trajectory crossing, although in contradiction to the conventional Bohmian trajectory interpretation, provides an important new tool for dealing with the nodal problem in Bohmian methods

On the Heterotic World-sheet Instanton Superpotential and its individual Contributions

For supersymmetric heterotic string compactifications on a Calabi-Yau threefold $X$ endowed with a vector bundle $V$ the world-sheet superpotential $W$ is a sum of contributions from isolated rational curves \C in $X$; the individual contribution is given by an exponential in the K\"ahler class of the curve times a prefactor given essentially by the Pfaffian which depends on the moduli of $V$ and the complex structure moduli of $X$. Solutions of $DW=0$ (or even of $DW=W=0$) can arise either by nontrivial cancellations between the individual terms in the summation over all contributing curves or because each of these terms is zero already individually. Concerning the latter case conditions on the moduli making a single Pfaffian vanish (for special moduli values) have been investigated. However, even if corresponding moduli - fulfilling these constraints - for the individual contribution of one curve are known it is not at all clear whether {\em one} choice of moduli exists which fulfills the corresponding constraints {\em for all contributing curves simultaneously}. Clearly this will in general happen only if the conditions on the 'individual zeroes' had already a conceptual origin which allows them to fit together consistently. We show that this happens for a class of cases. In the special case of spectral cover bundles we show that a relevant solution set has an interesting location in moduli space and is related to transitions which change the generation number.Comment: 47 page

Effects of Instructions and Stimulus Representation on Selective Learning in Children

Selective learning patterns of children were investigated using incidental learning methodology. Since incidental, in contrast to intentional learning occurs in the absence of instructions which prepare the subject for later retention tests, a subject has relatively more freedom to choose to attend to and learn only a portion of the presented information (thus exercising selectivity). Previous research suggested that selectivity seemed to increase or decrease with development in relation to different incidental learning paradigms. For studies in which incidental stimuli were presented without a concurrent intentional task (Type 1) incidental learning increased with age indicating decreased selectivity. For studies in which incidental stimuli were presented with a simultaneous intentional task (Type 2) incidental learning remained stable or decreased with age, while concurrent intentional learning increased, indicating increased selectivity. The purpose of the present study was to delineate developmental processes associated with these seemingly divergent trends. In addition, children\u27s selective learning of stimuli corresponding to different developmental levels of cognitive representation had been seriously neglected in the literature. Most investigations employed unrelated stimuli which necessitated rote processes for recall. It was also the purpose of this study to determine the influence of stimulus representation upon children\u27s selective learning. Based upon theory (development of conceptual representation) and empirical trends, it was hypothesized that older children are more flexible in exercising selectivity than younger children. Thus, learning patterns of older but not younger children were expected to be significantly modified by instructional and stimulus variation. To test this hypothesis, a three-way factorial design was employed. The factors were: (a) type of instruction (Type 1 vs. 2), (b) stimulus representation (conceptually-, perceptually- or unrelated), and (c) developmental level (first- and sixth-graders). Subjects were 168 white, middle class children who were randomly assigned to experimental conditions. An equal number of first- and sixth-grade girls and boys were employed. Eight pairs of colored pictures were presented in each condition. The same stimuli were used in all conditions, but were paired conceptually, perceptually or in unrelated manner. In the Type 1 condition subjects were instructed to look at the pictures but were not informed that they would receive later retention tasks. In the Type 2 condition subjects were instructed to look at all stimuli and to remember the top member of each pair for later retention. Free recall and matching of pairs tasks were administered following stimulus exposure to determine the influence of instructions and stimulus representation on learning. Results revealed that selective learning patterns of both age groups were significantly and similarly modified by instructions and stimuli. Incidental learning was significantly superior for subjects in Type 1 compared to those in Type 2 conditions, while learning of the top (intentional—Type 2) stimulus was significantly superior for subjects in Type 2 compared to those in Type 1 conditions. Relative proportions of intentional (top) to total stimulus recall were not significantly different between the grades. Matching performance of subjects in perceptual conditions was significantly superior to that of subjects in conceptual conditions, whose matching was significantly superior to that of subjects in unrelated stimulus conditions. Developmental differences were related to the level rather than the pattern of retention. Type 1 instructions enhanced sixth-graders’ free recall of incidental stimuli and pairs to a significantly greater extent than for first-graders, while Type 2 conditions enhanced first-graders\u27 total stimulus recall to a significantly greater degree than for sixth-graders. Selectivity did not increase or decrease with age but was related to experimental conditions for all subjects. The resulting developmental differences indicated that relatively nonstructured conditions enhanced older subjects\u27 recall to a greater extent relative to younger subjects, while younger subjects\u27 recall was facilitated by relatively structured conditions compared to older subjects. Production deficiency and/or retrieval inefficiencies of younger relative to older children are processes advanced to explain the developmental differences. The similarity of younger and older children\u27s use of representation is discussed, as well as the influence of Type 1 and 2 designs on selective learning patterns. A definition of selectivity which accounts for components rather than total amount of learning is proposed

Cooling Torsional Nanomechanical Vibration by Spin-Orbit Interactions

We propose and study a spin-orbit interaction based mechanism to actively cool down the torsional vibration of a nanomechanical resonator made by semiconductor materials. We show that the spin-orbit interactions of electrons can induce a coherent coupling between the electron spins and the torsional modes of nanomechanical vibration. This coherent coupling leads to an active cooling for the torsional modes via the dynamical thermalization of the resonator and the spin ensemble.Comment: 4 pages, 3 figure