Towards a formal description of the collapse approach to the inflationary origin of the seeds of cosmic structure

Inflation plays a central role in our current understanding of the universe. According to the standard viewpoint, the homogeneous and isotropic mode of the inflaton field drove an early phase of nearly exponential expansion of the universe, while the quantum fluctuations (uncertainties) of the other modes gave rise to the seeds of cosmic structure. However, if we accept that the accelerated expansion led the universe into an essentially homogeneous and isotropic space-time, with the state of all the matter fields in their vacuum (except for the zero mode of the inflaton field), we can not escape the conclusion that the state of the universe as a whole would remain always homogeneous and isotropic. It was recently proposed in [A. Perez, H. Sahlmann and D. Sudarsky, "On the quantum origin of the seeds of cosmic structure," Class. Quant. Grav. 23, 2317-2354 (2006)] that a collapse (representing physics beyond the established paradigm, and presumably associated with a quantum-gravity effect a la Penrose) of the state function of the inflaton field might be the missing element, and thus would be responsible for the emergence of the primordial inhomogeneities. Here we will discuss a formalism that relies strongly on quantum field theory on curved space-times, and within which we can implement a detailed description of such a process. The picture that emerges clarifies many aspects of the problem, and is conceptually quite transparent. Nonetheless, we will find that the results lead us to argue that the resulting picture is not fully compatible with a purely geometric description of space-time.Comment: 53 pages, no figures. Revision to match the published versio

The Magnus expansion and some of its applications

Approximate resolution of linear systems of differential equations with varying coefficients is a recurrent problem shared by a number of scientific and engineering areas, ranging from Quantum Mechanics to Control Theory. When formulated in operator or matrix form, the Magnus expansion furnishes an elegant setting to built up approximate exponential representations of the solution of the system. It provides a power series expansion for the corresponding exponent and is sometimes referred to as Time-Dependent Exponential Perturbation Theory. Every Magnus approximant corresponds in Perturbation Theory to a partial re-summation of infinite terms with the important additional property of preserving at any order certain symmetries of the exact solution. The goal of this review is threefold. First, to collect a number of developments scattered through half a century of scientific literature on Magnus expansion. They concern the methods for the generation of terms in the expansion, estimates of the radius of convergence of the series, generalizations and related non-perturbative expansions. Second, to provide a bridge with its implementation as generator of especial purpose numerical integration methods, a field of intense activity during the last decade. Third, to illustrate with examples the kind of results one can expect from Magnus expansion in comparison with those from both perturbative schemes and standard numerical integrators. We buttress this issue with a revision of the wide range of physical applications found by Magnus expansion in the literature.Comment: Report on the Magnus expansion for differential equations and its applications to several physical problem

Detector Description and Performance for the First Coincidence Observations between LIGO and GEO

For 17 days in August and September 2002, the LIGO and GEO interferometer gravitational wave detectors were operated in coincidence to produce their first data for scientific analysis. Although the detectors were still far from their design sensitivity levels, the data can be used to place better upper limits on the flux of gravitational waves incident on the earth than previous direct measurements. This paper describes the instruments and the data in some detail, as a companion to analysis papers based on the first data.Comment: 41 pages, 9 figures 17 Sept 03: author list amended, minor editorial change

Modular software for flow cytometry and sorting: the LACEL system

We present an overview of the software for a flexible data acquisition system for multiple flow cytometers. Together with the hardware, which is discussed in a companion paper, the LACEL (Los Alamos Cell Analysis) system provides the capability to acquire data on up to 8 parameters and control bidirectional sorting based on up to 4 parameters for each direction. The two major software modules include a user interface which accepts commands and displays frequency distributions, and a data acquisition module which communicates with the hardware, moves incoming data to mass storage and generates the frequency distributions for each data parameter

New methodlogy for measuring damage to respiratory tract cells using flow-system cell-analysis techniques

Automated flow-system cell-analysis techniques provide a new method for determining damage to respiratory tract cells in humans exposed by inhalation of environmental pollutants such as from the production of synthetic fuels from coal and oil shale. This paper describes results of preliminary experiments designed to develop flow-system instrumentation methods for measuring biological damage to respiratory tract cells using the Syrian hamster as a model. Hamster respiratory tract cell samples were obtained by lavaging the lungs with normal saline. Cell samples stained with fluorescent dyes specific for various biochemical parameters were analyzed in liquid suspension as they flowed through a chamber intersecting a laser beam of exciting light. Sensors measured fluorescence and light-scatter optical signals on a cell-by-cell basis. Cellular parameters proportional to optical signals (e.g., cell size, DNA content, enzymatic esterase activity, nuclear and cytoplasmic diameter) were displayed as frequency distribution histograms. Basic operating features of this technology are presented, along with representative examples of results which illustrate the initial flow-system characterization of normal exfoliated respiratory tract cells