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.
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.
117774283
Antarctic muon and neutrino detector array
116901571
Ultrahigh-energy neutrino astrophysics with AMANDA
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.
34007176
Just enough inflation: power spectrum modifications at large scales
We show that models of `just enough' inflation, where the slow-roll evolution lasted only 50- 60 e-foldings, feature modifications of the CMB power spectrum at large angular scales. We perform a systematic analytic analysis in the limit of a sudden transition between any possible non-slow-roll background evolution and the final stage of slow-roll inflation. We find a high degree of universality since most common backgrounds like fast-roll evolution, matter or radiation-dominance give rise to a power loss at large angular scales and a peak together with an oscillatory behaviour at scales around the value of the Hubble parameter at the beginning of slow-roll inflation. Depending on the value of the equation of state parameter, different pre-inflationary epochs lead instead to an enhancement of power at low l, and so seem disfavoured by recent observational hints for a lack of CMB power at l 40. We also comment on the importance of initial conditions and the possibility to have multiple pre-inflationary stages.
53318340
The overshoot problem in inflation after tunneling
We show the absence of the usual parametrically large overshoot problem of small-field inflation if initiated by a Coleman-De Luccia (CDL) tunneling transition from an earlier vacuum in the limit of small inflationary scale compared to the tunneling scale. For low-power monomial exit potentials V() ~ n , n < 4, we derive an expression for the amount of overshoot. This is bounded from above by the width of the steep barrier traversed after emerging from tunneling and before reaching a slow-roll region of the potential. For n ≥ 4 we show that overshooting is entirely absent. We extend this result through binomials to a general potential written as a series expansion, and to the case of arbitrary finite initial speed of the inflaton. This places the phase space of initial conditions for small-field and large-field inflation on the same footing in a landscape of string theory vacua populated via CDL tunneling.
53343041
Finding all flux vacua in an explicit example
A bstractWe explicitly construct all supersymmetric flux vacua of a particular Calabi-Yau compactification of type IIB string theory for a small number of flux carrying cycles and a given D3-brane tadpole. The analysis is performed in the large complex structure region by using the polynomial homotopy continuation method, which allows to find all stationary points of the polynomial equations that characterize the supersymmetric vacuum solutions. The number of vacua as a function of the D3 tadpole is in agreement with statistical studies in the literature. We calculate the available tuning of the cosmological constant from fluxes and extrapolate to scenarios with a larger number of flux carrying cycles. We also verify the range of scales for the moduli and gravitino masses recently found for a single explicit flux choice giving a Kähler uplifted de Sitter vacuum in the same construction.
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.
17808521
Simple Exercises to Flatten your Potential
We show how backreaction of the inflaton potential energy on heavy scalar fields can flatten the inflationary potential, as the heavy fields adjust to their most energetically favorable configuration. This mechanism operates in previous UV-complete examples of axion monodromy inflation - flattening a would-be quadratic potential to one linear in the inflaton field - but occurs more generally, and we illustrate the effect with several examples. Special choices of compactification minimizing backreaction may realize chaotic inflation with a quadratic potential, but we argue that a flatter potential such as power-law inflation V({phi}) {proportional_to} {phi}{sup p} with p < 2 is a more generic option at sufficiently large values of {phi}.