Bulletin of the American Physical Society
APS April Meeting 2018
Volume 63, Number 4
Saturday–Tuesday, April 14–17, 2018; Columbus, Ohio
Session U15: Cosmic Microwave Background and More |
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Sponsoring Units: DAP Chair: Barbara Ryden, Ohio State University Room: B230-231 |
Monday, April 16, 2018 3:30PM - 3:42PM |
U15.00001: GreenPol Ari Kaplan, Philip Lubin, Peter Meinhold, Nic Rupert, Hans Kristian Eriksen, Ingunn Kathrine Wehus, Unni Fuskeland, Pavel Naselsky, Per Rex Christensen, Sebastian Domenico von Hausegger, Hao Liu Measurements of the polarization of the Cosmic Microwave Background (CMB) provide an excellent probe of the inflationary era of the early universe, as tensor mode gravitational waves produced during inflation can lead to polarization signals in the CMB. It has become clear recently that galactic foreground emission will be the fundamental limit to studies of CMB polarization. There is a huge effort underway to study these modes in the CMB, however most current experiments focus on high frequencies, where galactic dust is dominant. Because this emission is more complex than was expected, current data is insufficient to be certain which frequencies will be best for separating foregrounds from tensor mode signals. It's therefore necessary to investigate lower frequency foregrounds as well in order to be confident in any measurement of the tensor modes. GreenPol plans to map the low frequency galactic polarization emission at Summit Station in Greenland from 10-44 GHz for 50{\%} of the sky at various elevation angles. This summer we will deploy to Greenland to map the sky at 10 GHz using a 2.2 meter off-axis Gregorian telescope with a reflection half wave plate at its focus, with plans for higher frequency measurements in the future. [Preview Abstract] |
Monday, April 16, 2018 3:42PM - 3:54PM |
U15.00002: SPT-3G: An Upgraded Cosmic Microwave Background Receiver for the South Pole Telescope Joshua Sobrin The 10-meter South Pole Telescope (SPT) surveys the cosmic microwave background (CMB) with arcminute resolution. In early 2017, the SPT was upgraded with a new receiver, SPT-3G, offering improved sensitivity to the temperature and polarization anisotropies of the CMB. Newly implemented optics, detector, and readout technologies have yielded a low-noise, high-resolution camera with impressive throughput and sensitivity across multiple frequency bands (95, 150, and 220 GHz). SPT-3G is undertaking a 4-year 1500 deg$^{2}$ survey designed to measure the CMB with unprecedented sensitivity on arcminute angular scales. These measurements will improve cosmological constraints, including the energy scale of inflation, the sum of neutrino masses, and the dark energy equation of state. I will summarize the design principles of the receiver and report on the on-sky performance of the integrated instrument. [Preview Abstract] |
Monday, April 16, 2018 3:54PM - 4:06PM |
U15.00003: CMB Data Analysis and Selection for POLARBEAR-2 Raymond Tat Observations of the cosmic microwave background (CMB) B-mode polarization provide useful measurements of inflation and large-scale gravitational lensing. The POLARBEAR-2 (PB2) experiment is a ground-based telescope designed to measure this polarization. In order to mitigate the effects of low-frequency noise due to fluctuations in atmospheric emission, we modulate the polarization entering the PB2 camera using a rapidly-rotating half-wave plate (HWP). By then demodulating this signal, we can greatly suppress low-frequency noise in the demodulated data as demonstrated by the Atacama B-mode Search, as well as by POLARBEAR, the predecessor of PB2. Further, in order to more effectively process the CMB data collected from PB2, we investigate various methods of data analysis. We implement filters for detecting jumps and glitches in the transition-edge sensor (TES) timestreams, as well as set up a web site to allow collaborators to easily examine PB2 data. We demonstrate this software using data from POLARBEAR. We also perform a preliminary analysis of several supervised and unsupervised machine learning algorithms for use in CMB data selection and find that shallow neural networks yield the highest classification accuracy. [Preview Abstract] |
Monday, April 16, 2018 4:06PM - 4:18PM |
U15.00004: Cosmological analysis pipelines through Neural Networks Nesar Ramachandra Potential avenues of deep learning applications for astrophysical analyses are currently being investigated. Majority of these frameworks are geared towards astronomical image studies, in anticipation of large amount of observational data from future sky surveys. The role of Neural Networks, however, may have wider impact on our understanding of our Universe. Some of these applications include emulators of cosmological functions, astrophysical parameter inference models and uncertainty quantification. We present application of one such neural network architecture, a Variational Autoencoder (VAE) in dimensionality reduction of cosmological data. We illustrate that a nonlinear encoding of information from VAE coupled with Gaussian Processes can be used for fast and accurate emulation of cosmic microwave background power spectrum. [Preview Abstract] |
Monday, April 16, 2018 4:18PM - 4:30PM |
U15.00005: Cosmological constraints from lensing ratios Judit Prat Marti In this talk, measurements of lensing ratios involving galaxy lensing and CMB lensing using data from the Dark Energy Survey (DES), the South Pole Telescope (SPT) and Planck are presented. These ratios between lensing-galaxy two-point functions are defined in such a way that the dependency on the galaxy power spectrum cancels and therefore do not rely on assumptions about the galaxy bias and the matter power spectrum, while still being sensitive to the geometry of the Universe. The use of lensing ratios involving CMB lensing as a geometrical probe was first proposed in Das \& Spergel (2009) and the first measurements were recently presented in Miyatake et al. (2017). In this work, using data from the first year of observations of the Dark Energy Survey (DES Y1), for the first time we use a set of lens galaxies obtained from a photometric survey. Also, we perform a complete cosmological analysis to obtain parameter constraints from the lensing ratio and joint constraints with other cosmological probes. [Preview Abstract] |
Monday, April 16, 2018 4:30PM - 4:42PM |
U15.00006: Exploring circular polarization in the CMB due to conventional sources of cosmic birefringence Paulo Montero-Camacho, Christopher Hirata The circular polarization of the cosmic microwave background (CMB) is usually taken to be zero since it is not generated by Thomson scattering. Here we explore the actual level of circular polarization in the CMB generated by conventional cosmological sources of birefringence. We consider two classes of mechanisms for birefringence. One is alignment of the matter to produce an anisotropic susceptibility tensor: the hydrogen spins can be aligned either by density perturbations or CMB anisotropies themselves. The other is anisotropy of the radiation field coupled to the non-linear response of the medium to electromagnetic fields: this can occur either via photon-photon scattering (non-linear response of the vacuum); atomic hyperpolarizability (non-linear response of neutral atoms); and plasma delay (non-linear response of free electrons). The strongest effect comes from photon-photon scattering from recombination at a level of $ \sim 10^{-13} \ \textup{K}$. Our results are consistent with a negligible circular polarization of the CMB in comparison with the linear polarization or the sensitivity of current and near-term experiments. [Preview Abstract] |
Monday, April 16, 2018 4:42PM - 4:54PM |
U15.00007: Self-interactions of a highly degenerate quantum scalar field Sankha Subhra Chakrabarty, Seishi Enomoto, Yaqi Han, Pierre Sikivie, Elisa Todarello We develop a formalism to describe how the quantum mechanical evolution of a highly degenerate scalar field differs from its classical counterpart. We apply the formalism to homogeneous condensate with attractive 4-point contact interactions. In classical description, the condensate persists forever. But, in quantum evolution, parametric resonance causes the quanta to jump out of the condensate in pairs. Modes with wave-vectors less than a critical value become populated. We calculate the time-scale over which the homogeneous condensate gets depleted and the classical description becomes invalid. [Preview Abstract] |
Monday, April 16, 2018 4:54PM - 5:06PM |
U15.00008: Baryogenesis via Post-Inflationary Relaxation of the Higgs Vacuum Expectation Value Lauren Pearce In the Standard Model with a Higgs boson of mass 125 Gev, the Higgs potential becomes relatively flat at large scales. Consequently, during an inflationary epoch the Higgs field vacuum expectation value (VEV) $\sqrt{\left<\phi^2\right>}$ generically becomes large due to fluctuations in this potential. As the Hubble parameter decreases during reheating, this VEV will relax to its equilibrium value. This out-of-equilibrium epoch provides novel opportunities for baryogenesis. We consider an effective operator of dimension six, $\phi^2 F \tilde{F}\slash\Lambda^2$, which couples the Higgs field to the SU(2) gauge fields. This can be rewritten in the form $(\partial_\mu \phi^2)j_{B+L}^\mu\slash\Lambda^2$, which biases the production of leptons and/or baryons during the Higgs relaxation epoch, provided that a baryon-number-violating or lepton-number-violating process occurs. As a minimal example, we introduce lepton-number-violating Majorana masses in the neutrino sector. To emphasize the novelty of this scenario, the right handed neutrinos are kept sufficiently heavy to suppress thermal leptogenesis. In addition to describing the relevant parameter space, if time permits I will also discuss potentially observable signatures, particularly regarding the cosmic infrared background [Preview Abstract] |
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