20546508
Elemental Compositions of Comet 81P/Wild 2 Samples Collected by Stardust
We measured the elemental compositions of material from 23 particles in aerogel and from residue in seven craters in aluminum foil that was collected during passage of the Stardust spacecraft through the coma of comet 81P/Wild 2. These particles are chemically heterogeneous at the largest size scale analyzed (∼180 ng). The mean elemental composition of this Wild 2 material is consistent with the CI meteorite composition, which is thought to represent the bulk composition of the solar system, for the elements Mg, Si, Mn, Fe, and Ni to 35%, and for Ca and Ti to 60%. The elements Cu, Zn, and Ga appear enriched in this Wild 2 material, which suggests that the CI meteorites may not represent the solar system composition for these moderately volatile minor elements.
118008749
AMANDA: Antarctic Muon And Neutrino Detector Array
Enormous detectors with unprecedented sensitivity will be required to search for astrophysical sources of neutrinos. If the transparency of deep polar ice is similar to that measured in the laboratory, then AMANDA (Antarctic Muon And Neutrino Detector Array) may be the most cost-effective way to reach the detector volumes required to search for astrophysical sources of high energy neutrinos or WIMP annihilation within the sun.
20884449
UNIQUE SIGNATURE OF DARK MATTER IN ANCIENT MICA
Mica can store (for >1 Gy) etchable tracks caused by atoms recoiling from WIMPs. Because a background from fission neutrons will eventually limit this technique, a unique signature for WIMPs in ancient mica is needed. Our motion around the center of the Galaxy causes WIMPs, unlike neutrons, to enter the mica from a preferred direction on the sky. Mica is a directional detector and despite the complex rotations that natural mica crystals make with respect to this WIMP ``wind,'' there is a substantial dependence of etch pit density on present day mica orientation.
73628788
Energy loss of relativistic heavy ions in matter
Abstract We have investigated the theory of energy loss of charged particles in matter due to ionization of the medium, integrating the work of other authors over several decades. We describe the most important corrections to standard energy-loss formulae. We compare our calculations to an improved measurement of the range of 1 A GeV U ions and to other codes and tabulations. We show that calculations based on the theory of ionization energy loss are at least as accurate as tabulations extrapolated from empirical data for the stopping of uranium ions in matter. We have made available the computer code resulting from our investigations.
18611958
Aerogel keystones: Extraction of complete hypervelocity impact events from aerogel collectors
In January 2006, the Stardust mission will return the first samples from a solid solar system body beyond the Moon and the first samples of contemporary interstellar dust ever collected. Although sophisticated laboratory instruments exist for the analysis of Stardust samples, techniques for the recovery of particles and particle residues from aerogel collectors remain primitive. Here, we describe our recent progress in developing techniques for extracting small volumes of aerogel, which we have called "keystones," which completely contain particle impacts but minimize the damage to the surrounding aerogel collector. These keystones can be fixed to custom-designed micromachined silicon fixtures (so called "microforklifts"). In this configuration, the samples are self-supporting, which can be advantageous in situations where interference from a supporting substrate is undesirable. The keystones may also be extracted and placed onto a substrate without a fixture. We have also demonstrated the capability of homologously crushing these unmounted keystones for analysis techniques that demand flat samples.
116901571
Ultrahigh-energy neutrino astrophysics with AMANDA
15943987
De Sitter string vacua from perturbative Kähler corrections and consistent D-terms
We present a new way to construct de Sitter vacua in type IIB flux compactifications, in which moduli stabilization and D-term uplifting can be combined in a manner consistent with the supergravity constraints. Here, the closed string fluxes fix the dilaton and the complex structure moduli while perturbative quantum corrections to the Kahler potential stabilize the volume Kahler modulus in an AdS4-vacuum. Then, the presence of magnetized D7-branes in this setup provide supersymmetric D-terms in a fully consistent way which uplift the AdS4-vacuum to a metastable dS-minimum.
53489520
An exact tunneling solution in a simple realistic landscape
We present an analytical solution for the tunneling process in a piecewise linear and quadratic potential which does not make use of the thin-wall approximation. A quadratic potential allows for the smooth attachment of various slopes exiting into the final minimum of a realistic potential. Our tunneling solution thus serves as a realistic approximation to situations such as populating a landscape of slow-roll inflationary regions by tunneling, and it is valid for all regimes of the barrier parameters. We comment briefly on the inclusion of gravity.
14328805
Gravity Waves and Linear Inflation from Axion Monodromy
Wrapped branes in string compactifications introduce a monodromy that extends the field range of individual closed-string axions to beyond the Planck scale. Furthermore, approximate shift symmetries of the system naturally control corrections to the axion potential. This suggests a general mechanism for chaotic inflation driven by monodromy-extended closed-string axions. We systematically analyze this possibility and show that the mechanism is compatible with moduli stabilization and can be realized in many types of compactifications, including warped Calabi-Yau manifolds and more general Ricci-curved spaces. In this broad class of models, the potential is linear in the canonical inflaton field, predicting a tensor to scalar ratio r{approx_equal}0.07 accessible to upcoming cosmic microwave background observations.
119221927
Building an explicit de Sitter
A bstractWe construct an explicit example of a de Sitter vacuum in type IIB string theory that realizes the proposal of Kähler uplifting. As the large volume limit in this method depends on the rank of the largest condensing gauge group we carry out a scan of gauge group ranks over the Kreuzer-Skarke set of toric Calabi-Yau threefolds. We find large numbers of models with the largest gauge group factor easily exceeding a rank of one hundred. We construct a global model with Kähler uplifting on a two-parameter model on $ \mathbb{CP}_{11169}^4 $, by an explicit analysis from both the type IIB and F-theory point of view. The explicitness of the construction lies in the realization of a D7 brane configuration, gauge flux and RR and NS flux choices, such that all known consistency conditions are met and the geometric moduli are stabilized in a metastable de Sitter vacuum with spontaneous GUT scale supersymmetry breaking driven by an F-term of the Kähler moduli.
6609921
Monodromy in the CMB : Gravity waves and string inflation
We present a simple mechanism for obtaining large-field inflation, and hence a gravitational wave signature, from string theory compactified on twisted tori. For nil manifolds, we obtain a leading inflationary potential proportional to {phi}{sup 2/3} in terms of the canonically normalized field {phi}, yielding predictions for the tilt of the power spectrum and the tensor-to-scalar ratio, n{sub s}{approx_equal}0.98 and r{approx_equal}0.04 with 60 e-foldings of inflation; we note also the possibility of a variant with a candidate inflaton potential proportional to {phi}{sup 2/5}. The basic mechanism involved in extending the field range--monodromy in D-branes as they move in circles on the manifold--arises in a more general class of compactifications, though our methods for controlling the corrections to the slow-roll parameters require additional symmetries.