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      Hunting for Statistical Anisotropy in Tensor Modes with B-mode Observations

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          Abstract

          We investigate a possibility of constraining statistical anisotropies of the primordial tensor perturbations by using future observations for the Cosmic Microwave Background (CMB) B-mode polarization. By parameterizing a statistically-anisotropic tensor power spectrum as \(P_h ({\boldsymbol{k}}) = P_h (k) \sum_n g_n \cos^n \theta_{\boldsymbol{k}}\), where \(\theta_{\boldsymbol{k}}\) is an angle of the direction of \(\hat{k}={\boldsymbol{k}}/k\) from a preferred direction, we find that it would be possible for future B-mode observations such as CMB-S4 to detect the tensor statistical anisotropy at the level of \(g_n \sim {\mathcal O} (0.1)\).

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          Planck 2015 results. XX. Constraints on inflation

          Planck Collaboration, P. A. R. Ade, N. Aghanim … (2015)
          We present the implications for cosmic inflation of the Planck measurements of the cosmic microwave background (CMB) anisotropies in both temperature and polarization based on the full Planck survey. The Planck full mission temperature data and a first release of polarization data on large angular scales measure the spectral index of curvature perturbations to be \(n_\mathrm{s} = 0.968 \pm 0.006\) and tightly constrain its scale dependence to \(d n_s/d \ln k =-0.003 \pm 0.007\) when combined with the Planck lensing likelihood. When the high-\(\ell\) polarization data is included, the results are consistent and uncertainties are reduced. The upper bound on the tensor-to-scalar ratio is \(r_{0.002} < 0.11\) (95% CL), consistent with the B-mode polarization constraint \(r< 0.12\) (95% CL) obtained from a joint BICEP2/Keck Array and Planck analysis. These results imply that \(V(\phi) \propto \phi^2\) and natural inflation are now disfavoured compared to models predicting a smaller tensor-to-scalar ratio, such as \(R^2\) inflation. Three independent methods reconstructing the primordial power spectrum are investigated. The Planck data are consistent with adiabatic primordial perturbations. We investigate inflationary models producing an anisotropic modulation of the primordial curvature power spectrum as well as generalized models of inflation not governed by a scalar field with a canonical kinetic term. The 2015 results are consistent with the 2013 analysis based on the nominal mission data.
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            BICEP2 / Keck Array VI: Improved Constraints On Cosmology and Foregrounds When Adding 95 GHz Data From Keck Array

            , , … (2016)
            We present results from an analysis of all data taken by the BICEP2 & Keck Array CMB polarization experiments up to and including the 2014 observing season. This includes the first Keck Array observations at 95 GHz. The maps reach a depth of 50 nK deg in Stokes \(Q\) and \(U\) in the 150 GHz band and 127 nK deg in the 95 GHz band. We take auto- and cross-spectra between these maps and publicly available maps from WMAP and Planck at frequencies from 23 GHz to 353 GHz. An excess over lensed-LCDM is detected at modest significance in the 95x150 \(BB\) spectrum, and is consistent with the dust contribution expected from our previous work. No significant evidence for synchrotron emission is found in spectra such as 23x95, or for correlation between the dust and synchrotron sky patterns in spectra such as 23x353. We take the likelihood of all the spectra for a multi-component model including lensed-LCDM, dust, synchrotron and a possible contribution from inflationary gravitational waves (as parametrized by the tensor-to-scalar ratio \(r\)), using priors on the frequency spectral behaviors of dust and synchrotron emission from previous analyses of WMAP and Planck data in other regions of the sky. This analysis yields an upper limit \(r_{0.05}<0.09\) at 95% confidence, which is robust to variations explored in analysis and priors. Combining these \(B\)-mode results with the (more model-dependent) constraints from Planck analysis of CMB temperature plus BAO and other data, yields a combined limit \(r_{0.05}<0.07\) at 95% confidence. These are the strongest constraints to date on inflationary gravitational waves.
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              Mission design of LiteBIRD

              T Morishima, N Katayama, Y Inoue … (2013)
              LiteBIRD is a next-generation satellite mission to measure the polarization of the cosmic microwave background (CMB) radiation. On large angular scales the B-mode polarization of the CMB carries the imprint of primordial gravitational waves, and its precise measurement would provide a powerful probe of the epoch of inflation. The goal of LiteBIRD is to achieve a measurement of the characterizing tensor to scalar ratio \(r\) to an uncertainty of \(\delta r=0.001\). In order to achieve this goal we will employ a kilo-pixel superconducting detector array on a cryogenically cooled sub-Kelvin focal plane with an optical system at a temperature of 4~K. We are currently considering two detector array options; transition edge sensor (TES) bolometers and microwave kinetic inductance detectors (MKID). In this paper we give an overview of LiteBIRD and describe a TES-based polarimeter designed to achieve the target sensitivity of 2~\(\mu\)K\(\cdot\)arcmin over the frequency range 50 to 320~GHz.
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                Author and article information

                Journal
                Publication date Created: 24 August 2018
                Article
                ArXiV ID: 1808.08044
                SO-VID: cad415db-80a9-4ef8-88b2-e41fc534be85
                License:

                http://arxiv.org/licenses/nonexclusive-distrib/1.0/

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                Custom metadata
                Report No RUP-18-26
                Comments 7 pages
                Categories astro-ph.CO

                ScienceOpen disciplines: Cosmology & Extragalactic astrophysics
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                ScienceOpen disciplines: Cosmology & Extragalactic astrophysics

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