Session S9: Cosmic Microwave Background

Uniformity of CMB as a non-inflationary geometrical effect

The conventional LambdaCDM cosmological model supplemented by the inflation concept explains the Universe evolution well. However, there are still a few concerns: New Planck data impose a non-trivial constraint on the shape of the inflation potential, which excludes many inflationary models; the dark matter is not detected directly; and the dark energy is not described theoretically on a satisfactory level. Within the FLRW formalism we consider a model of the closed Universe (with the spherical spatial topology), filled with the additional perfect fluid with the constant parameter -1/3 in the linear equation of state (which may be called quintessence). We compare this model with the standard LambdaCDM and answer the following question: can this additional fluid lead to light traveling between the antipodal points during the current age of the Universe? This possibility could strongly affect the inflation scenario which may completely lose its necessity. This work is supported by NSF CREST (HRD-0833184) and NASA (NNX09AV07A).   

Constraining light WIMPs and neutrinos with BBN and the CMB

Cosmology constrains the properties of light ($< 10$ MeV, roughly) particle species mainly through their effects on the expansion rate of the universe at early times. The sensitivity of cosmic microwave background (CMB) observations to the expansion rate up to recombination is now comparable to that of big bang nucleosynthesis (BBN) during the first few minutes of the universe. While CMB observations do not currently favor neutrino-like particles beyond the standard model, the signal could be hidden if ``light WIMPs'' with MeV-scale masses were in thermal equilibrium in the early universe. Light WIMPs affect BBN through modified expansion rates and heating of photons or neutrinos, so light-element observations break the CMB degeneracy between neutrinos and light WIMPs. We describe joint analyses of BBN and CMB data that constrain simultaneously light WIMPs and extra neutrinos, finding that one extra neutrino species is allowed, the standard-model expansion rate is disfavored, and any WIMP mass must be greater than an MeV.   

Rees-Sciama signatures from evolving dark matter halos in the cosmic microwave background

Photons in the cosmic microwave background (CMB) radiation receive an extra blueshift in their energies as they traverse slowly-growing dark matter halos. This Rees-Sciama effect arises from the time-dependent gravitational potentials generated by the subsequent accretion of dark matter flows onto collapsed halo cores. Studies of the Rees-Sciama contributions to the stochastic anisotropies in the CMB from large scale linear or quasi-linear perturbations have been previously conducted, but in this work we focus on non-perturbative, collapsed halos. We calculate the magnitude of this effect for a spherical symmetric halo model of self-similarity, and demonstrate a projected profile of this signature on the sky as a function of the impact parameter of the line of sight. Its typical angular size is larger than that of the halo's virialized core, which provides a possible avenue to separate Rees-Sciama signatures from scattering signatures of Sunyaev-Zeldovich effects. We argue that this effect can be potentially utilized not only to probe the dynamics of dark matter halos, but also to measure cosmological parameters such as $H(z)$ and $\Omega_{\Lambda}(z)$.   

Cosmology with CMB measurements from ACTPol: current status and future constraints

Measurements of the polarization of the Cosmic Microwave Backround (CMB) contain important information complementary to the temperature anisotropies. The ACTPol polarization sensitive receiver for the Atacama Cosmology Telescope (ACT) is measuring CMB polarization from arcminute to degree scales. These data will improve constraints on cosmological parameters, in particular on neutrino mass, dark energy and inflationary models. One of the unique advantages of ACTPol is its ability to overlap with several large scale structure surveys, allowing cross-correlation studies that will achieve even stronger constraints on the cosmological parameters. Additional science is enabled by the combination of high sensitivity and arcminute resolution, such as surveys of galaxy clusters and new probes of dark energy via the thermal and kinematic Sunyaev-Zel'dovich (SZ) effects. Beyond ACTPol is the stage III Advanced ACTPol project, which offers greater sensitivity and frequency coverage than ACTPol. I will discuss ACTPol constraints and projections achievable with the Advanced ACTPol experiment. I will focus in particular on neutrino mass and on dark energy constraints from measurements of galaxy clusters peculiar velocities made by combining SZ effect measurements with galaxy surveys data.   

ACTPol: Status and preliminary CMB polarization results from the Atacama Cosmology Telescope

The Atacama Cosmology Telescope Polarimeter (ACTPol) is a polarization sensitive upgrade for the Atacama Cosmology Telescope, located at an elevation of 5190 m on Cerro Toco in Chile. In summer 2013, ACTPol achieved first light with one third of the final detector configuration. The remaining two thirds of the detector array will be installed during spring 2014, enabling full sensitivity, high resolution, observations at both 90 GHz and 150 GHz. Using approximately 3,000 transition-edge sensor bolometers, ACTPol will enable measurements of small angular scale polarization anisotropies in the Cosmic Microwave Background (CMB). I will present a status update for the ACTPol receiver and some preliminary results. ACTPol measurements will allow us to probe the spectral index of inflation as well as to constrain early dark energy and the sum of neutrino masses.   

SPTpol Measurement of E and B-mode CMB Polarization

The South Pole Telescope Polarimeter (SPTpol) began observations of the cosmic microwave background (CMB) in February 2012. The instrument features dual polarization transition edge sensor bolometers in two bands, 588 pixels (1176 bolometers) at 150 GHz and 180 pixels (360 bolometers) at 95 GHz. During the first year of observations SPTpol covered a 100 square degree patch of sky, which led to the first detection of lensing B modes. This field has now been mapped in polarization to a depth of 9$\mu$K-arcmin at 150 GHz and 19$\mu$K-arcmin at 95 GHz. Measurements of CMB polarization anisotropy will provide cosmological information that cannot be obtained with temperature measurements alone. Measuring even parity modes, E modes, will lead to tighter parameter constraints and tests of the $\Lambda$CDM model. Measuring odd parity modes, B modes, will give us important information on two fronts. At small angular scales lensing B modes will provide powerful constraints on the sum of the neutrino masses, while at larger angular scales B modes produced by gravitational waves may confirm inflation and probe its energy scale. Here we will present the SPTpol E and B mode measurements and the cosmological implications.   

The E and B EXperiment: EBEX

We report on the status of the E and B Experiment (EBEX) a balloon-borne polarimeter designed to measure the polarization of the cosmic microwave background radiation. The instrument employs a 1.5 meter Gregorian Mizuguchi-Dragone telescope providing 8 arc-minute resolution at three bands centered on 150, 250, and 410 GHz. A continuously rotating achromatic half wave plate, mounted on a superconducting magnetic bearing, and a polarizing grid give EBEX polarimetric capabilities. Radiation is detected with a kilo-pixel array of transition edge sensor (TES) bolometers that are cooled to 0.25 K. The detectors are readout using SQUID current amplifiers and a digital frequency-domain multiplexing system in which 16 detectors are readout simultaneously with two wires. EBEX is the first instrument to implement TESs and such readout system on board a balloon-borne platform. EBEX was launched from the Antarctic in December 2012 on an 11-day long-duration balloon flight. This presentation will provide an overview of the instrument and discuss the flight and status of the data analysis.   

Detection of gravitational lensing of the Cosmic Microwave Background polarization by the POLARBEAR experiment

We report the direct detection of gravitational lensing of the Cosmic Microwave Background polarization. We present maps of 30 square degrees of the sky measured to a depth of 6 microK*arcminute at 150 GHz. To detect the non-Gaussian signature of gravitational lensing, we measure the 4-point correlation functions EEEB and EBEB where E and B describe E-mode and B-mode maps. We reject the null hypotheses at 4.2 sigma significance, including the contribution of systematic errors, using the combination of these two 4-point correlation functions. Further, we measure a lensing amplitude normalized to LCDM of 1.06 $+$/-0.47(stat) $+$0.32/-0.27(sys) consistent with the current standard cosmological model. This result gives a measurement of the amplitude of matter fluctuations in the Universe with 26{\%} error. Measurements of gravitational lensing of the Cosmic Microwave Background have great potential as a probe of structure formation, the behavior of Dark Energy, and the sum of the masses of neutrinos through their role as hot Dark Matter.   

Relic neutrinos: Physically consistent treatment of effective number of neutrinos and neutrino mass

It is well known that the effective number of cosmic neutrinos, $N_\nu$, is larger than the standard model number of neutrino flavors $N^f_\nu=3$ due a small flow of entropy into neutrinos from $e\pm$ annihilation. Observational bounds from both BBN and the CMB suggest a value of $N_\nu$ that is larger than the current theoretical prediction of $N_\nu=3.046$. We show in a model independent way how $N_\nu$ relates to the neutrino kinetic freeze-out temperature, $T_k$, which we treat as parameter. We derive the relations that must hold between $N_\nu$, the photon to neutrino temperature ratio, the neutrino fugacity, and $T_k$. Our results imply that measurement of neutrino reheating, as characterized by $N_\nu$, amounts to the determination of $T_k$. We follow the free streaming neutrinos down to a temperature on the order of the neutrino mass and determine how the cosmic neutrino properties i.e. energy density, pressure, particle density, depend in a physically consistent way on both neutrino mass and $N_\nu$. We continue down to the present day temperature and characterize the neutrino distribution in this regime as well. See arXiv:1212.6943, PRD in press.