119462460
Probing the structure of the cold dark matter halo using ancient mica
Mica can store (for {gt}1thinspGyr) etchable tracks caused by atoms recoiling from WIMPs. Ancient mica is a directional detector despite the complex motions it makes with respect to the WIMP {open_quotes}wind.{close_quotes} We can exploit the properties of directionality and long integration time to probe for structure in the dark matter halo of our galaxy. We compute a sample of possible signals in mica for a plausible model of halo structure. {copyright} {ital 1998} {ital The American Physical Society}
28559917
Measurement of cross sections for charge pickup by relativistic holmium ions on heavy targets.
We have measured the cross section for nuclear charge pickup by relativistic holmium on several targets of larger atomic number than have been studied previously. We find that although measurements made with most of the targets are consistent with a peripheral geometric scaling, one target, silver, shows an anomalously high cross section.
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.
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.
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.
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.
53329243
A sufficient condition for de Sitter vacua in type IIB string theory
A bstractWe derive a sufficient condition for realizing meta-stable de Sitter vacua with small positive cosmological constant within type IIB string theory flux compactifications with spontaneously broken supersymmetry. There are a number of ‘lamp post’ construc-tions of de Sitter vacua in type IIB string theory and supergravity. We show that one of them — the method of ‘Kähler uplifting’ by F-terms from an interplay between non-perturbative effects and the leading α′-correction — allows for a more general parametric understanding of the existence of de Sitter vacua. The result is a condition on the values of the flux induced superpotential and the topological data of the Calabi-Yau compactification, which guarantees the existence of a meta-stable de Sitter vacuum if met. Our analysis explicitly includes the stabilization of all moduli, i.e. the Kähler, dilaton and complex structure moduli, by the interplay of the leading perturbative and non-perturbative effects at parametrically large volume.
119235337
Drifting oscillations in axion monodromy
We study the pattern of oscillations in the primordial power spectrum in axion monodromy inflation, accounting for drifts in the oscillation period that can be important for comparing to cosmological data. In these models the potential energy has a monomial form over a super-Planckian field range, with superimposed modulations whose size is model-dependent. The amplitude and frequency of the modulations are set by the expectation values of moduli fields. We show that during the course of inflation, the diminishing energy density can induce slow adjustments of the moduli, changing the modulations. We provide templates capturing the effects of drifting moduli, as well as drifts arising in effective field theory models based on softly broken discrete shift symmetries, and we estimate the precision required to detect a drifting period. A non-drifting template suffices over a wide range of parameters, but for the highest frequencies of interest, or for sufficiently strong drift, it is necessary to include parameters characterizing the change in frequency over the e-folds visible in the CMB. We use these templates to perform a preliminary search for drifting oscillations in a part of the parameter space in the Planck nominal mission data.
119209436
Metastable electroweak vacuum: Implications for inflation
Abstract Within the Standard Model, the current Higgs and top quark data favor metastability of the electroweak vacuum, although the uncertainties are still significant. The true vacuum is many orders of magnitude deeper than ours and the barrier separating the two is tiny compared to the depth of the well. This raises a cosmological question: how did the Higgs field get trapped in the shallow minimum and why did it stay there during inflation? The Higgs initial conditions before inflation must be fine-tuned to about one part in 10 8 in order for the Higgs field to end up in the right vacuum. In this Letter, we show that these problems can be resolved if there is a small positive coupling between the Higgs and the inflaton.
123231936
Higher-Dimension Operators in Higher-Dimensional Field Theories
The present thesis investigates effects of higher-dimension operators in higher-dimensional field theories. 1-loop power corrections to the gauge couplings in 5d and 6d are studied. They become calculable in the case of a softly broken grand unified theory (GUT) combined with minimal symmetry assumptions. Using the analysis of the exact quantum effective action of supersymmetric gauge theories in 5d, these power corrections are demonstrated to be the effect of higher-dimension operators. They can be unambiguously determined within 5d low-energy effective field theory. Thus, large and quantitatively controlled power-law contributions to gauge couplings arise naturally and can, in the most extreme case, lead to calculable TeV-scale power law unification. A simple 5d SU(5) model with one massless 10 in the bulk is identified where the power-law effect is exactly MSSM-like. In compactifications of 10d type IIB supergravity higher-dimension operators are an important ingredient for the stabilization of the moduli. Their cosmological impact in stabilized string vacua is analyzed and a model of inflation is constructed where these operators are essential. This model can accommodate the WMAP data of the cosmic microwave background (CMB) with a spectral index of the density fluctuations ns = 0.93. Zusammenfassung Die vorliegende Arbeit untersucht Effekte von Operatoren höherer Massendimension in höherdimensionalen Feldtheorien. Zunächst werden 1-Loop-Potenzkorrekturen zu den Eichkopplungen in 5d und 6d analysiert. Diese werden im Falle weicher Brechung einer GUT und minimaler Symmetrieannahmen berechenbar. Die Potenzkorrekturen werden dann mittels Analyse der exakten quanten-effektiven Wirkung supersymmetrischer Eichtheorien in 5d auf die Effekte von Operatoren höherer Massendimension zurückgeführt. Diese Operatoren sind durch die Eigenschaften der 5d effektiven Feldtheorie eindeutig bestimmt. Damit ergibt sich, daß diese Quantenkorrekturen zu den Eichkopplungen berechenbare ’Power-Law’Vereinigung an der TeV-Skala ermöglichen. Es wird ein einfaches 5d SU(5) GUT Modell mit einer Materie-10 im 5d ’Bulk’ beschrieben, in dem die Quantenkorrekturen exakt die Vereinigung der Eichkopplungen im MSSM imitieren. Operatoren höherer Massendimension sind in Kompaktifizierungen der 10d Typ IIB Supergravitation ein wichtiger Faktor bei der Modulistabilisierung. Die kosmologischen Implikationen dieser Operatoren werden untersucht und es wird ein Inflationsmodell konstruiert, das essentiell auf ihrer Gegenwart beruht. Dieses Modell mit einem spektralen Index der Dichtefluktuationen von ns = 0.93 ist mit den WMAP-Daten des kosmischen Mikrowellenhintergrunds verträglich.
53529659
Heterotic moduli stabilisation
A bstractWe perform a systematic analysis of moduli stabilisation for weakly coupled heterotic string theory compactified on internal manifolds which are smooth Calabi-Yau three-folds up to α′ effects. We first review how to stabilise all the geometric and gauge bundle moduli in a supersymmetric way by including fractional fluxes, the requirement of a holomorphic gauge bundle, D-terms, higher order perturbative contributions to the superpotential as well as non-perturbative and threshold effects. We then show that the inclusion of α′ corrections to the Kähler potential leads to new stable Minkowski (or de Sitter) vacua where the complex structure moduli and the dilaton are fixed supersymmetrically at leading order, while the stabilisation of the Kähler moduli at a lower scale leads to spontaneous breaking supersymmetry. The minimum lies at moderately large volumes of all the geometric moduli, at perturbative values of the string coupling and at the right phenomenological value of the GUT gauge coupling. We also provide a dynamical derivation of anisotropic compactifications with stabilised moduli which allow for perturbative gauge coupling unification around 1016 GeV. The value of the gravitino mass can be anywhere between the GUT and the TeV scale depending on the stabilisation of the complex structure moduli. In general, these are fixed by turning on background fluxes, leading to a gravitino mass around the GUT scale since the heterotic three-form flux does not contain enough freedom to tune the superpotential to small values. Moreover accommodating the observed value of the cosmological constant is a challenge. Low-energy supersymmetry could instead be obtained by focusing on particular Calabi-Yau constructions where the gauge bundle is holomorphic only at a point-like sub-locus of complex structure moduli space, or situations with a small number of complex structure moduli (like orbifold models), since in these cases one may fix all the moduli without turning on any quantised background flux. However obtaining the right value of the cosmological constant is even more of a challenge in these cases. Another option would be to focus on compactifications on non-complex manifolds, since these allow for new geometric fluxes which could be used to tune the superpotential as well as the cosmological constant, even if the moduli space of these manifolds is presently only poorly understood.