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

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

Non-local quantum correlations and detection processes in QFT

Quantum detection processes in QFT must play a key role in the description of quantum field correlations, such as the appearance of entanglement, and of causal effects. We consider the detection in the case of a simple QFT model with a suitable interaction to exact treatment, consisting of a quantum scalar field coupled linearly to a classical scalar source. We then evaluate the response function to the field quanta of two-level point-like quantum model detectors, and analyze the effects of the approximation adopted in standard detection theory. We show that the use of the RWA, that characterizes the Glauber detection model, leads in the detector response to non-local terms corresponding to an instantaneously spreading of source effects over the whole space. Other detector models, obtained with non-standard or the no-application of RWA, give instead local responses to field quanta, apart from source independent vacuum contribution linked to preexisting correlations of zero-point field.Comment: 23 page

Flavor Asymmetry of the Nucleon Sea: Consequences for Dilepton Production

Parton distributions derived from a chiral quark model that generates an excess of down quarks and antiquarks in the proton's sea satisfactorily describe the measured yields of muon pairs produced in proton-nucleus collisions. Comparison of dilepton yields from hydrogen and deuterium targets promises greater sensitivity to the predicted flavor asymmetry.Comment: 11 pages, REVTEX, (Three PostScript figures available by anonymous ftp from fnth06.fnal.gov in directory /pub/Fermilab-Pub/92.264.) FERMILAB-PUB-92/264--T LBL-3298

Nucleon-Quarkonium Elastic Scattering and the Gluon Contribution to Nucleon Spin

It is shown that the amplitude for the scattering of a heavy quarkonium system from a nucleon near threshold is completely determined by the fraction of angular momentum, as well as linear momentum, carried by gluons in the nucleon. A form for the quarkonium-nucleon non-relativistic potential is derived.Comment: 4 pages, no figures. Author's e-mail: [email protected]

Effective s- and p-Wave Contact Interactions in Trapped Degenerate Fermi Gases

The structure and stability of dilute degenerate Fermi gases trapped in an external potential is discussed with special emphasis on the influence of s- and p-wave interactions. In a first step an Effective Contact Interaction for all partial waves is derived, which reproduces the energy spectrum of the full potential within a mean-field model space. Using the s- and p-wave part the energy density of the multi-component Fermi gas is calculated in Thomas-Fermi approximation. On this basis the stability of the one- and two-component Fermi gas against mean-field induced collapse is investigated. Explicit stability conditions in terms of density and total particle number are given. For the single-component system attractive p-wave interactions limit the density of the gas. In the two-component case a subtle competition of s- and p-wave interactions occurs and gives rise to a rich variety of phenomena. A repulsive p-wave part, for example, can stabilize a two-component system that would otherwise collapse due to an attractive s-wave interaction. It is concluded that the p-wave interaction may have important influence on the structure of degenerate Fermi gases and should not be discarded from the outset.Comment: 18 pages, 11 figures (using RevTEX4

Graduate Quantum Mechanics Reform

We address four main areas in which graduate quantum mechanics education can be improved: course content, textbook, teaching methods, and assessment tools. We report on a three year longitudinal study at the Colorado School of Mines using innovations in all these areas. In particular, we have modified the content of the course to reflect progress in the field in the last 50 years, used textbooks that include such content, incorporated a variety of teaching techniques based on physics education research, and used a variety of assessment tools to study the effectiveness of these reforms. We present a new assessment tool, the Graduate Quantum Mechanics Conceptual Survey, and further testing of a previously developed assessment tool, the Quantum Mechanics Conceptual Survey. We find that graduate students respond well to research-based techniques that have been tested mainly in introductory courses, and that they learn much of the new content introduced in each version of the course. We also find that students' ability to answer conceptual questions about graduate quantum mechanics is highly correlated with their ability to solve calculational problems on the same topics. In contrast, we find that students' understanding of basic undergraduate quantum mechanics concepts at the modern physics level is not improved by instruction at the graduate level.Comment: accepted to American Journal of Physic

Model Analysis of the ep→ep′π+π−ep \to ep'\pi^+\pi^- Electroproduction Reaction on the Proton

Recent CLAS data on the $p\pi^+\pi^-$ electroproduction off protons at 1.3$<$W$<$1.57 GeV and 0.25$<$$Q^{2}$$<$0.6 GeV$^{2}$ have been analyzed using a meson-baryon phenomenological model. By fitting nine 1-fold differential cross section data for each $W$ and $Q^{2}$ bin, the charged double pion electroproduction mechanisms are identified from their manifestations in the observables. We have extracted the cross sections from amplitudes of each of the considered isobar channels as well as from their coherent sum. We also obtained non-resonant partial wave amplitudes of all contributing isobar channels which could be useful for advancing a complete coupled-channel analysis of all meson electroproduction data.Comment: Experiment Numbers: E93-006, E94-005 Group: Hall