1,850 research outputs found
Freeform three-mirror anastigmatic large-aperture telescope and receiver optics for CMB-S4
Get PDFCMB-S4, the next-generation ground-based cosmic microwave background (CMB)
observatory, will provide detailed maps of the CMB at millimeter wavelengths to
dramatically advance our understanding of the origin and evolution of the
universe. CMB-S4 will deploy large and small aperture telescopes with hundreds
of thousands of detectors to observe the CMB at arcminute and degree
resolutions at millimeter wavelengths. Inflationary science benefits from a
deep delensing survey at arcminute resolutions capable of observing a large
field of view at millimeter wavelengths. This kind of survey acts as a
complement to a degree angular resolution survey. The delensing survey requires
a nearly uniform distribution of cameras per frequency band across the focal
plane. We present a large-throughput, large-aperture (5-meter diameter)
freeform three-mirror anastigmatic telescope and an array of 85 cameras for CMB
observations at arcminute resolutions, which meets the needs of the delensing
survey of CMB-S4. A detailed prescription of this three-mirror telescope and
cameras is provided, with a series of numerical calculations that indicate
expected optical performance and mechanical tolerance
CMB-S4: Forecasting Constraints on Primordial Gravitational Waves
Get PDFInternational audienceCMB-S4—the next-generation ground-based cosmic microwave background (CMB) experiment—is set to significantly advance the sensitivity of CMB measurements and enhance our understanding of the origin and evolution of the universe. Among the science cases pursued with CMB-S4, the quest for detecting primordial gravitational waves is a central driver of the experimental design. This work details the development of a forecasting framework that includes a power-spectrum-based semianalytic projection tool, targeted explicitly toward optimizing constraints on the tensor-to-scalar ratio, r, in the presence of Galactic foregrounds and gravitational lensing of the CMB. This framework is unique in its direct use of information from the achieved performance of current Stage 2–3 CMB experiments to robustly forecast the science reach of upcoming CMB-polarization endeavors. The methodology allows for rapid iteration over experimental configurations and offers a flexible way to optimize the design of future experiments, given a desired scientific goal. To form a closed-loop process, we couple this semianalytic tool with map-based validation studies, which allow for the injection of additional complexity and verification of our forecasts with several independent analysis methods. We document multiple rounds of forecasts for CMB-S4 using this process and the resulting establishment of the current reference design of the primordial gravitational-wave component of the Stage-4 experiment, optimized to achieve our science goals of detecting primordial gravitational waves for r > 0.003 at greater than 5σ, or in the absence of a detection, of reaching an upper limit of r < 0.001 at 95% CL
The SPIDER CMB Polarimeter
Get PDFSPIDER is a balloon-borne millimeter-wave telescope designed to study the polarization of the Cosmic Microwave Background (CMB). SPIDER will map 10% of the full sky with degree-scale beams to search for the distinctive inflationary gravitational wave signal on angular scales between 1 degree and 10 degrees, thereby probing the energy scale of inflation. In its first flight, SPIDER will field 2,400 antenna-coupled bolometers split between two bands centered at 93 GHz and 148 GHz. Slot antenna arrays, band defining microstrip filters and superconducting bolometers are all fabricated photolithographically on a shared silicon substrate. SPIDER's detectors are split amongst six monochromatic on-axis refractors in a shared helium-cooled cryostat. This thesis reviews the design of SPIDER and its antenna-coupled bolometers, and details the currently achieved performance of SPIDER's receivers
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CMB-S4: Forecasting Constraints on Primordial Gravitational Waves
Get PDFCMB-S4---the next-generation ground-based cosmic microwave background (CMB)
experiment---is set to significantly advance the sensitivity of CMB
measurements and enhance our understanding of the origin and evolution of the
Universe, from the highest energies at the dawn of time through the growth of
structure to the present day. Among the science cases pursued with CMB-S4, the
quest for detecting primordial gravitational waves is a central driver of the
experimental design. This work details the development of a forecasting
framework that includes a power-spectrum-based semi-analytic projection tool,
targeted explicitly towards optimizing constraints on the tensor-to-scalar
ratio, , in the presence of Galactic foregrounds and gravitational lensing
of the CMB. This framework is unique in its direct use of information from the
achieved performance of current Stage 2--3 CMB experiments to robustly forecast
the science reach of upcoming CMB-polarization endeavors. The methodology
allows for rapid iteration over experimental configurations and offers a
flexible way to optimize the design of future experiments given a desired
scientific goal. To form a closed-loop process, we couple this semi-analytic
tool with map-based validation studies, which allow for the injection of
additional complexity and verification of our forecasts with several
independent analysis methods. We document multiple rounds of forecasts for
CMB-S4 using this process and the resulting establishment of the current
reference design of the primordial gravitational-wave component of the Stage-4
experiment, optimized to achieve our science goals of detecting primordial
gravitational waves for r > 0.003 at greater than , or, in the
absence of a detection, of reaching an upper limit of r < 0.001 at CL
CMB-S4: Forecasting Constraints on Primordial Gravitational Waves
Get PDFCMB-S4---the next-generation ground-based cosmic microwave background (CMB)
experiment---is set to significantly advance the sensitivity of CMB
measurements and enhance our understanding of the origin and evolution of the
Universe, from the highest energies at the dawn of time through the growth of
structure to the present day. Among the science cases pursued with CMB-S4, the
quest for detecting primordial gravitational waves is a central driver of the
experimental design. This work details the development of a forecasting
framework that includes a power-spectrum-based semi-analytic projection tool,
targeted explicitly towards optimizing constraints on the tensor-to-scalar
ratio, , in the presence of Galactic foregrounds and gravitational lensing
of the CMB. This framework is unique in its direct use of information from the
achieved performance of current Stage 2--3 CMB experiments to robustly forecast
the science reach of upcoming CMB-polarization endeavors. The methodology
allows for rapid iteration over experimental configurations and offers a
flexible way to optimize the design of future experiments given a desired
scientific goal. To form a closed-loop process, we couple this semi-analytic
tool with map-based validation studies, which allow for the injection of
additional complexity and verification of our forecasts with several
independent analysis methods. We document multiple rounds of forecasts for
CMB-S4 using this process and the resulting establishment of the current
reference design of the primordial gravitational-wave component of the Stage-4
experiment, optimized to achieve our science goals of detecting primordial
gravitational waves for at greater than , or, in the
absence of a detection, of reaching an upper limit of at CL.Comment: 24 pages, 8 figures, 9 tables, submitted to ApJ. arXiv admin note:
text overlap with arXiv:1907.0447
The intrinsic B-mode polarisation of the cosmic microwave background
Get PDFAbstract. We estimate the B-polarisation induced in the Cosmic Microwave Background by the non-linear evolution of density perturbations. Using the second-order Boltzmann code SONG, our analysis incorporates, for the first time, all physical effects at recombination. We also include novel contributions from the redshift part of the Boltzmann equation and from the bolometric definition of the temperature in the presence of polarisation. The remaining line-of-sight terms (lensing and time-delay) have previously been studied and must be calculated non-perturbatively. The intrinsic B-mode polarisation is present independent of the initial conditions and might contaminate the signal from primordial gravitational waves. We find this contamination to be comparable to a primordial tensor-to-scalar ratio of r ' 10−7 at the angular scale ` ' 100, where the primordial signal peaks, and r ' 5 × 10−5 at ` ' 700, where the intrinsic signal peaks. Therefore, we conclude that the intrinsic B-polarisation from second-order effects is not likely to contaminate future searches of primordial gravitational waves.ar X i
Observation of Cosmic Microwave Background Polarization with BICEP
Get PDFBackground Imaging of Cosmic Extragalactic Polarization (BICEP) is a bolometric polarimeter that has been optimized to target the B-mode of the cosmic microwave background (CMB) polarization at degree angular scales, which is a sensitive probe of the energy scale of inflation. The instrument's focal plane comprises 49 pairs of polarization-sensitive bolometers operating at 100 and 150 GHz, and the 25-cm aperture refractive optics provide degree-scale resolution over a 17 degree instantaneous field of view. The compact design enables sufficient control of instrumental polarization systematics to attain a projected final sensitivity corresponding to a tensor-to-scalar ratio of 0.1. This thesis describes the design, performance, and preliminary science results from BICEP, which has been observing the CMB from the South Pole since January 2006. After the first two seasons of operation, the EE, TE, and TT power spectra are measured with high precision at 30 < ell < 300, and BB is consistent with zero. BICEP has also observed the Galactic plane, and polarized emission is mapped with high signal-to-noise
Planck 2018 results: VII. Isotropy and statistics of the CMB
No full textFunding Information: ★ Corresponding authors: A. J. Banday, e-mail: [email protected]; K. M. Górski, e-mail: [email protected]; E. Martínez-González, e-mail: [email protected]; P. Vielva, e-mail: [email protected] 1 Planck (http://www.esa.int/Planck) is a project of the European Space Agency (ESA) with instruments provided by two scientific consortia funded by ESA member states and led by Principal Investigators from France and Italy, telescope reflectors provided through a collaboration between ESA and a scientific consortium led and funded by Denmark, and additional contributions from NASA (USA). Funding Information: Acknowledgements. The Planck Collaboration acknowledges the support of: ESA; CNES, and CNRS/INSU-IN2P3-INP (France); ASI, CNR, and INAF (Italy); NASA and DoE (USA); STFC and UKSA (UK); CSIC, MINECO, JA, and RES (Spain); Tekes, AoF, and CSC (Finland); DLR and MPG (Germany); CSA (Canada); DTU Space (Denmark); SER/SSO (Switzerland); RCN (Norway); SFI (Ireland); FCT/MCTES (Portugal); ERC and PRACE (EU). A description of the Planck Collaboration and a list of its members, indicating which technical or scientific activities they have been involved in, can be found at http://www.cosmos.esa.int/web/planck/ planck-collaboration. This work has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement numbers 687312, 776282, and 772253. Publisher Copyright: © Planck Collaboration 2020.Analysis of the Planck 2018 data set indicates that the statistical properties of the cosmic microwave background (CMB) temperature anisotropies are in excellent agreement with previous studies using the 2013 and 2015 data releases. In particular, they are consistent with the Gaussian predictions of the ΛCDM cosmological model, yet also confirm the presence of several so-called "anomalies"on large angular scales. The novelty of the current study, however, lies in being a first attempt at a comprehensive analysis of the statistics of the polarization signal over all angular scales, using either maps of the Stokes parameters, Q and U, or the E-mode signal derived from these using a new methodology (which we describe in an appendix). Although remarkable progress has been made in reducing the systematic effects that contaminated the 2015 polarization maps on large angular scales, it is still the case that residual systematics (and our ability to simulate them) can limit some tests of non-Gaussianity and isotropy. However, a detailed set of null tests applied to the maps indicates that these issues do not dominate the analysis on intermediate and large angular scales (i.e., ℓ 400). In this regime, no unambiguous detections of cosmological non-Gaussianity, or of anomalies corresponding to those seen in temperature, are claimed. Notably, the stacking of CMB polarization signals centred on the positions of temperature hot and cold spots exhibits excellent agreement with the ΛCDM cosmological model, and also gives a clear indication of how Planck provides state-of-the-art measurements of CMB temperature and polarization on degree scales.Peer reviewe
QCD equation of state and dark matter
No full textThe QCD equation of state is not often discussed in cosmology. However, the relic density of
weakly interacting massive particles (WIMPs) depends on the entropy and the expansion rate of
the Universe when they freeze out, at a temperature in the range 400 MeV – 40GeV, where QCD
corrections are still important. We use recent analytic and lattice calculations of the QCD pressure
to produce a new equation of state suitable for use in relic density calculations. As an example,
we show that relic densities calculated by the dark matter package DarkSUSY receive corrections
of several per cent, within the observational accuracy of the Planck CMB mission, due for launch
in 2007
Recovering the CMB Signal with Machine Learning
Get PDFThe cosmic microwave background (CMB), carrying the inhomogeneous information
of the very early universe, is of great significance for understanding the
origin and evolution of our universe. However, observational CMB maps contain
serious foreground contaminations from several sources, such as galactic
synchrotron and thermal dust emissions. Here, we build a deep convolutional
neural network (CNN) to recover the tiny CMB signal from various huge
foreground contaminations. Focusing on the CMB temperature fluctuations, we
find that the CNN model can successfully recover the CMB temperature maps with
high accuracy, and that the deviation of the recovered power spectrum
is smaller than the cosmic variance at . We then apply this method to
the current Planck observation, and find that the recovered CMB is quite
consistent with that disclosed by the Planck collaboration, which indicates
that the CNN method can provide a promising approach to the component
separation of CMB observations. Furthermore, we test the CNN method with
simulated CMB polarization maps based on the CMB-S4 experiment. The result
shows that both the EE and BB power spectra can be recovered with high
accuracy. Therefore, this method will be helpful for the detection of
primordial gravitational waves in current and future CMB experiments. The CNN
is designed to analyze two-dimensional images, thus this method is not only
able to process full-sky maps, but also partial-sky maps. Therefore, it can
also be used for other similar experiments, such as radio surveys like the
Square Kilometer Array.Comment: 20 pages, 25 figures, and 3 tables, updated citations in section 1.
The code repository is available at https://github.com/Guo-Jian-Wang/cmbNNC
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