Cosmological parameter inference with Bayesian statistics

Bayesian statistics and Markov Chain Monte Carlo (MCMC) algorithms have found their place in the field of Cosmology. They have become important mathematical and numerical tools, especially in parameter estimation and model comparison. In this paper, we review some fundamental concepts to understand Bayesian statistics and then introduce MCMC algorithms and samplers that allow us to perform the parameter inference procedure. We also introduce a general description of the standard cosmological model, known as the $\Lambda$CDM model, along with several alternatives, and current datasets coming from astrophysical and cosmological observations. Finally, with the tools acquired, we use an MCMC algorithm implemented in python to test several cosmological models and find out the combination of parameters that best describes the Universe.Comment: 30 pages, 17 figures, 5 tables; accepted for publication in Universe; references adde

Stealth Acceleration and Modified Gravity

We show how to construct consistent braneworld models which exhibit late time acceleration. Unlike self-acceleration, which has a de Sitter vacuum state, our models have the standard Minkowski vacuum and accelerate only in the presence of matter, which we dub ``stealth-acceleration''. We use an effective action for the brane which includes an induced gravity term, and allow for an asymmetric set-up. We study the linear stability of flat brane vacua and find the regions of parameter space where the set-up is stable. The 4-dimensional graviton is only quasi-localised in this set-up and as a result gravity is modified at late times. One of the two regions is strongly coupled and the scalar mode is eaten up by an extra symmetry that arises in this limit. Having filtered the well-defined theories we then focus on their cosmology. When the graviton is quasi-localised we find two main examples of acceleration. In each case, we provide an illustrative model and compare it to LambdaCDM.Comment: 32 pages, 5 figure

mm-Wave DRW Antenna Phase Centre Determination

This document presents an approach to the phase centre determination of a dielectric rod waveguide (DRW) antenna by means of measurements obtained with a planar measuring system at millimeter wave lengths. Phase centre determination by the least squares fit technique is described in this document for different DRW antennas (silicon and sapphire). Results at different operating frequencies are offered

Implementing Problem Resolution Models in Remedy

This paper defines the concept of Problem Resolution Model (PRM) and describes the current implementation made by the User Support unit at CERN. One of the main challenges of User Support services in any High Energy Physics institute/organization is to address solving of the computing-relatedproblems faced by their researchers. The User Support group at CERN is the IT unit in charge of modeling the operations of the Help Desk and acts as asecond level support to some of the support lines whose problems are receptioned at the Help Desk. The motivation behind the use of a PRM is to provide well defined procedures and methods to react in an efficient way to a request for solving a problem,providing advice, information etc. A PRM is materialized on a workflow which has a set of defined states in which a problem can be. Problems move from onestate to another according to actions as decided by the person who is handling them. A PRM can be implemented by a computer application, generallyreferred to as Problem Reporting Management System (PRMS). Through this application problems can be effectively guided through the states of theworkflow by applying actions on them. This automatic handling improves problem resolution times and provides flexible incorporation of the problems inthe workflow (either by email, the helpdesk operator etc.). It also provides registration and accounting of problems including the creation of a knowledgebase, reporting, performance measurement, etc. For such implementation we have used Remedy, which is the current choice of the IT Division at CERN fora PRMS. Remedy is an specialized development system to create PRM applications. We have developed a complete Remedy application to implement theUser Support PRM. Also, we have created complementary tools for reporting, statistics, backups, etc. The aim of this paper is to explain all these concepts and the main issues behind their implementation

Integrating autonomous Problem Resolution Models with Remedy

This paper briefly defines the concept of Problem Resolution Model and shows possible approaches to the issues which may arise when integrating various PRMs to present a consistent view to the end user, despite of the peculiarities of each physical implementation. Integration refers to various autonomous PRMs having to interact as problems pass from one to another in the resolution flow. This process should be transparent to the user and internally there must be a way to track in which stage of the resolution process any problem is. This means addressing two different issues. On one side PRMs which are to be integrated need to comply with certain interface standards. These standards must ensure that problems exchanged between them can always be traced. On the other side problems owned by different PRMs should be presented to the end user under a homogeneous view. This means having an uniform criteria for automatic notification messages, a single reference point (www) where users can query the status of problems regardless who owns them , etc. Remedy is a specialized development system designed to implement PRMs and it is the current choice of IT Division for such a system. When integrating Remedy based PRMs system there are some difficulties arising which are intrinsic to Remedy's design. In this paper we describe our assessment of those difficulties and their Remedy specific implementational implications