67 research outputs found
Simulating Calibration and Beam Systematics for a Future CMB Space Mission with the TOAST Package
We address in this work the instrumental systematic errors that can
potentially affect the forthcoming and future Cosmic Microwave Background
experiments aimed at observing its polarized emission. In particular, we focus
on the systematics induced by the beam and calibration, which are considered
the major sources of leakage from total intensity measurements to polarization.
We simulated synthetic data sets with Time-Ordered Astrophysics Scalable Tools,
a publicly available simulation and data analysis package. We also propose a
mitigation technique aiming at reducing the leakage by means of a template
fitting approach. This technique has shown promising results reducing the
leakage by 2 orders of magnitude at the power spectrum level when applied to a
realistic simulated data set of the LiteBIRD satellite mission
Numerical Methods in Cosmological Global Texture Simulations
Numerical simulations of the evolution of a global topological defect field
have two characteristic length scales --- one macrophysical, of order the field
correlation length, and the other microphysical, of order the field width. The
situation currently of most interest to particle cosmologists involves the
behaviour of a GUT-scale defect field at the epoch of decoupling, where the
ratio of these scales is typically of order . Such a ratio is
unrealisable in numerical work, and we consider the approximations which may be
employed to deal with this. Focusing on the case of global texture we outline
the implementation of the associated algorithms, and in particular note the
subtleties involved in handling texture unwinding events. Comparing the results
in each approach then establishes that, subject to certain constraints on the
minimum grid resolution, the methods described are both robust and consistent
with one another.Comment: LaTeX, IMPERIAL/TP/93-94/2
On The Absence Of Open Strings In A Lattice-Free Simulation Of Cosmic String Formation
Lattice-based string formation algorithms can, at least in principle, be
reduced to the study of the statistics of the corresponding aperiodic random
walk. Since in three or more dimensions such walks are transient this approach
necessarily generates a population of open strings. To investigate whether open
strings are an artefact of the lattice we develop an alternative lattice-free
simulation of string formation. Replacing the lattice with a graph generated by
a minimal dynamical model of a first order phase transition we obtain results
consistent with the hypothesis that the energy density in string is due to a
scale-invariant Brownian distribution of closed loops alone.Comment: 9 pages ReVTeX, 1 Postscript figure, minor changes for publicatio
Making Maps Of The Cosmic Microwave Background: The MAXIMA Example
This work describes Cosmic Microwave Background (CMB) data analysis
algorithms and their implementations, developed to produce a pixelized map of
the sky and a corresponding pixel-pixel noise correlation matrix from time
ordered data for a CMB mapping experiment. We discuss in turn algorithms for
estimating noise properties from the time ordered data, techniques for
manipulating the time ordered data, and a number of variants of the maximum
likelihood map-making procedure. We pay particular attention to issues
pertinent to real CMB data, and present ways of incorporating them within the
framework of maximum likelihood map-making. Making a map of the sky is shown to
be not only an intermediate step rendering an image of the sky, but also an
important diagnostic stage, when tests for and/or removal of systematic effects
can efficiently be performed. The case under study is the MAXIMA data set.
However, the methods discussed are expected to be applicable to the analysis of
other current and forthcoming CMB experiments.Comment: Replaced to match the published version, only minor change
Thermal Phase Mixing During First Order Phase Transitions
The dynamics of first order phase transitions are studied in the context of
(3+1)-dimensional scalar field theories. Particular attention is paid to the
question of quantifying the strength of the transition, and how `weak' and
`strong' transitions have different dynamics. We propose a model with two
available low temperature phases separated by an energy barrier so that one of
them becomes metastable below the critical temperature . The system is
initially prepared in this phase and is coupled to a thermal bath.
Investigating the system at its critical temperature, we find that `strong'
transitions are characterized by the system remaining localized within its
initial phase, while `weak' transitions are characterized by considerable phase
mixing. Always at , we argue that the two regimes are themselves separated
by a (second order) phase transition, with an order parameter given by the
fractional population difference between the two phases and a control parameter
given by the strength of the scalar field's quartic self-coupling constant. We
obtain a Ginzburg-like criterion to distinguish between `weak' and `strong'
transitions, in agreement with previous results in (2+1)-dimensions.Comment: 28 pages RevTeX, 9 postscript figures, IMPERIAL/TP/93-94/58,
DART-HEP-94/0
Stochastic Production Of Kink-Antikink Pairs In The Presence Of An Oscillating Background
We numerically investigate the production of kink-antikink pairs in a
dimensional field theory subject to white noise and periodic driving.
The twin effects of noise and periodic driving acting in conjunction lead to
considerable enhancement in the kink density compared to the thermal
equilibrium value, for low dissipation coefficients and for a specific range of
frequencies of the oscillating background. The dependence of the kink-density
on the temperature of the heat bath, the amplitude of the oscillating
background and value of the dissipation coefficient is also investigated. An
interesting feature of our result is that kink-antikink production occurs even
though the system always remains in the broken symmetry phase.Comment: Revtex, 21 pages including 7 figures; more references adde
CMB-S4 Science Book, First Edition
This book lays out the scientific goals to be addressed by the
next-generation ground-based cosmic microwave background experiment, CMB-S4,
envisioned to consist of dedicated telescopes at the South Pole, the high
Chilean Atacama plateau and possibly a northern hemisphere site, all equipped
with new superconducting cameras. CMB-S4 will dramatically advance cosmological
studies by crossing critical thresholds in the search for the B-mode
polarization signature of primordial gravitational waves, in the determination
of the number and masses of the neutrinos, in the search for evidence of new
light relics, in constraining the nature of dark energy, and in testing general
relativity on large scales
Recommended from our members
Inflation and Dark Energy from spectroscopy at z > 2
The expansion of the Universe is understood to have accelerated during two
epochs: in its very first moments during a period of Inflation and much more
recently, at z < 1, when Dark Energy is hypothesized to drive cosmic
acceleration. The undiscovered mechanisms behind these two epochs represent
some of the most important open problems in fundamental physics. The large
cosmological volume at 2 < z < 5, together with the ability to efficiently
target high- galaxies with known techniques, enables large gains in the
study of Inflation and Dark Energy. A future spectroscopic survey can test the
Gaussianity of the initial conditions up to a factor of ~50 better than our
current bounds, crossing the crucial theoretical threshold of
of order unity that separates single field and
multi-field models. Simultaneously, it can measure the fraction of Dark Energy
at the percent level up to , thus serving as an unprecedented test of
the standard model and opening up a tremendous discovery space
Science from an Ultra-Deep, High-Resolution Millimeter-Wave Survey
Opening up a new window of millimeter-wave observations that span frequency
bands in the range of 30 to 500 GHz, survey half the sky, and are both an order
of magnitude deeper (about 0.5 uK-arcmin) and of higher-resolution (about 10
arcseconds) than currently funded surveys would yield an enormous gain in
understanding of both fundamental physics and astrophysics. In particular, such
a survey would allow for major advances in measuring the distribution of dark
matter and gas on small-scales, and yield needed insight on 1.) dark matter
particle properties, 2.) the evolution of gas and galaxies, 3.) new light
particle species, 4.) the epoch of inflation, and 5.) the census of bodies
orbiting in the outer Solar System.Comment: 5 pages + references; Submitted to the Astro2020 call for science
white paper
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