Planck 2015 cosmological results
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The concordance cosmological model (aka ΛCMD) is more successfull than ever at surviving observationnal tests. Cosmic microwave background (CMB) properties have become one of the key observables for measuring its parameters, as well as looking for evidence for its extensions. This talk will give a summary of the recent cosmological results presented by the Planck collaboration, which results from the full mission temperature and polarization analysis, with an emphasis on CMB properties as extracted from our 2015 data release.Keywords:
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Cosmic background radiation
We introduce the 'wedge diagram', an intuitive way to illustrate how cosmological models with a classical (non-singular) bounce generically resolve fundamental problems in cosmology. These include the well-known horizon, flatness, and inhomogeneity problems; the small tensor-to-scalar ratio observed in the cosmic microwave background; the low entropy at the beginning of a hot, expanding phase; and the avoidance of quantum runaway. The same diagrammatic approach can be used to compare with other cosmological scenarios.
Flatness (cosmology)
Diagrammatic reasoning
Cosmic background radiation
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A Cosmological Coherence Principle (CCP) is proposed, meaning each well-defined phenomena is mono-frequency. When applied to the steady-state critical cosmology, with scale factor exp(t/T_U), the CCP leads to three independent formula for T_U compatible with the so-called Universe age 13.80(4) Gyr, estimated by the recent Planck's mission, so refuting the Primordial Big Bang model, in favor of the Vibrating Universe model with frequency 10^103 Hz and pseudo-period T_U. The matter density is simply shown to be 3/10 and the baryonic one (3/10)²/2 = 0.0450.
Cosmological principle
Scale factor (cosmology)
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We conduct a pseudo- C ℓ analysis of the tomographic cross-correlation between 1000 deg 2 of weak-lensing data from the Kilo-Degree Survey (KiDS-1000) and the thermal Sunyaev–Zeldovich (tSZ) effect measured by Planck and the Atacama Cosmology Telescope (ACT). Using HM X , a halo-model-based approach that consistently models the gas, star, and dark matter components, we are able to derive constraints on both cosmology and baryon feedback for the first time from these data, marginalising over redshift uncertainties, intrinsic alignment of galaxies, and contamination by the cosmic infrared background (CIB). We find our results to be insensitive to the CIB, while intrinsic alignment provides a small but significant contribution to the lensing–tSZ cross-correlation. The cosmological constraints are consistent with those of other low-redshift probes and prefer strong baryon feedback. The inferred amplitude of the lensing–tSZ cross-correlation signal, which scales as σ 8 (Ω m /0.3) 0.2 , is low by ∼2 σ compared to the primary cosmic microwave background constraints by Planck . The lensing–tSZ measurements are then combined with pseudo- C ℓ measurements of KiDS-1000 cosmic shear into a novel joint analysis, accounting for the full cross-covariance between the probes, providing tight cosmological constraints by breaking parameter degeneracies inherent to both probes. The joint analysis gives an improvement of 40% on the constraint of S 8 = σ 8 Ω m /0.3 over cosmic shear alone, while providing constraints on baryon feedback consistent with hydrodynamical simulations, demonstrating the potential of such joint analyses with baryonic tracers such as the tSZ effect. We discuss remaining modelling challenges that need to be addressed if these baryonic probes are to be included in future precision-cosmology analyses.
South Pole Telescope
Cosmic background radiation
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Several ground, balloon and space based experiments have recently provided detailed maps of the Cosmic Microwave Background. We review the status of the observations and their implications for the current cosmological model. Then we focus on unresolved issues and on the research still to be done to really achieve concordance cosmology, with particular attention to what can be done
Observational cosmology
Cosmic background radiation
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The Cosmic Microwave Background (CMB) temperature and polarization anisotropy measurements from the Planck mission have provided a strong confirmation of the Lambda Cold Dark Matter (LCDM) model of structure formation. However, there are a few interesting tensions with other cosmological probes that leave the door open to possible extensions to LCDM. I will review some interesting extended cosmological scenarios, in order to find a new concordance model that could explain and relieve tensions in current cosmological data.
Cold dark matter
Structure formation
Observational cosmology
Cosmic background radiation
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The cosmic microwave background (CMB) radiation provides a means to test the standard model of cosmology and determine its parameters with precision. Cosmology has made a great step forward with the observations and discoveries of the COBE satellite. These were followed with a series of observations and progress via ballon-borne and ground-based instrumentation. Now NASA and ESA have selected and approved new space missions: MAP and COBRAS/SAMBA (now named Planck) which may nearly reach the full potential of CMB observations.
Observational cosmology
Cosmic background radiation
Instrumentation
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Mirror dark matter interacting with ordinary matter via photon-mirror photon kinetic mixing can explain the DAMA, CoGeNT and CRESST-II direct detection experiments. This explanation requires kinetic mixing of strength ϵ∼10−9. Such kinetic mixing will have important implications for early Universe cosmology. We calculate the additional relativistic energy density at recombination, δNeff[CMB]. We also calculate the effects for big bang nucleosynthesis, δNeff[BBN]. Current hints that both δNeff[CMB] and δNeff[BBN] are non-zero and positive can be accommodated within this framework if ϵ≈few×10−9. In the near future, measurements from the Planck mission will either confirm these hints or constrain ϵ≲10−9.
Big Bang nucleosynthesis
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Since the publication of the results of the Planck satellite mission in 2013, the local and early Universes have been considered to be in tension in respect of the determination of amplitude of the matter density spatial fluctuations ( σ 8 ) and the amount of matter present in the Universe (Ω m ). This tension can be seen as a lack of massive galaxy clusters in the local Universe compared to the prediction inferred from Planck cosmic microwave background (CMB) best-fitting cosmology. In the present analysis we perform the first detection of the cross-correlation between X-rays and CMB weak lensing at 9.1 σ . We next combine thermal Sunyaev–Zel’dovich effect, X-rays, and weak-lensing angular auto- and cross-correlation power spectra to determine the galaxy cluster hydrostatic mass bias. We derive (1 − b H ) = 0.71 ± 0.07. Considering these constraints, we observe that estimations of σ 8 in the local Universe are consistent with Planck CMB best-fitting cosmology. However, these results are in clear tension with the output of hydrodynamical simulations that favor (1 − b H )> 0.8.
Cosmic background radiation
Cold dark matter
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Cosmological inflation is the dominating paradigm to account for observations of the Cosmic Microwave Background (CMB). In this thesis, we study the phenomenology of a class of particularly well motivated models of inflation, known under the generic name of hybrid models. They are characterised by a transition from a valley to a hilltop shaped potential. In particular, we study three limiting regimes of the simplest realisation, hybrid inflation, constraining its parameter space using observational bounds on the spectral index and the non-gaussianity of the primordial perturbations. We find that the model is highly constrained by observations, with large part of the parameter space either ruled out by a blue spectral index ($n_s>1$) or by a large non-gaussianity parameter $f_{rm NL}$, two quantities measured with precision by PLANCK. However, there exists regions in parameter space leading to interesting phenomenology compatibly with observational bounds. Also, a version of hybrid inflation with a third light scalar field at horizon crossing is derived from the supersymmetry framework. We find that the model can generate observables within observational bounds.
Spectral index
Cosmic background radiation
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