Thermal Conductivity of Thermally-Isolating Polymeric and Composite Structural Support Materials Between 0.3 and 4 K

We present measurements of the low-temperature thermal conductivity of a number of polymeric and composite materials from 0.3 to 4 K. The materials measured are Vespel SP-1, Vespel SP-22, unfilled PEEK, 30% carbon fiber-filled PEEK, 30% glass-filled PEEK, carbon fiber Graphlite composite rod, Torlon 4301, G-10/FR-4 fiberglass, pultruded fiberglass composite, Macor ceramic, and graphite rod. These materials have moderate to high elastic moduli making them useful for thermally-isolating structural supports.Comment: Accepted for publication in the journal Cryogenic

SPIDER: Probing the Early Universe with a Suborbital Polarimeter

We evaluate the ability of SPIDER, a balloon-borne polarimeter, to detect a divergence-free polarization pattern ("B-modes") in the Cosmic Microwave Background (CMB). In the inflationary scenario, the amplitude of this signal is proportional to that of the primordial scalar perturbations through the tensor-to-scalar ratio r. We show that the expected level of systematic error in the SPIDER instrument is significantly below the amplitude of an interesting cosmological signal with r=0.03. We present a scanning strategy that enables us to minimize uncertainty in the reconstruction of the Stokes parameters used to characterize the CMB, while accessing a relatively wide range of angular scales. Evaluating the amplitude of the polarized Galactic emission in the SPIDER field, we conclude that the polarized emission from interstellar dust is as bright or brighter than the cosmological signal at all SPIDER frequencies (90 GHz, 150 GHz, and 280 GHz), a situation similar to that found in the "Southern Hole." We show that two ~20-day flights of the SPIDER instrument can constrain the amplitude of the B-mode signal to r<0.03 (99% CL) even when foreground contamination is taken into account. In the absence of foregrounds, the same limit can be reached after one 20-day flight.Comment: 29 pages, 8 figures, 4 tables; v2: matches published version, flight schedule updated, two typos fixed in Table 2, references and minor clarifications added, results unchange

First Results from the Arcminute Cosmology Bolometer Array Receiver

We review the first science results from the Arcminute Cosmology Bolometer Array Receiver (ACBAR); a multifrequency millimeter-wave receiver optimized for observations of the Cosmic Microwave Background (CMB) and the Sunyaev-Zel'dovich (SZ) effect in clusters of galaxies. ACBAR was installed on the 2 m Viper telescope at the South Pole in January 2001 and the results presented here incorporate data through July 2002. We present the power spectrum of the CMB at 150 GHz over the range \ell = 150 - 3000 measured by ACBAR as well as estimates for the values of the cosmological parameters within the context of Lambda-CDM models. We find that the inclusion of Omega_Lambda greatly improves the fit to the power spectrum. We also observe a slight excess of small-scale anisotropy at 150 GHz; if interpreted as power from the SZ effect of unresolved clusters, the measured signal is consistent with CBI and BIMA within the context of the SZ power spectrum models tested.Comment: To be published in the proceedings of "The Cosmic Microwave Background and its Polarization", New Astronomy Reviews, (eds. S. Hanany and K.A. Olive). 10 pages, 2 figure

Cosmological Constraints on Decaying Dark Matter

We present a complete analysis of the cosmological constraints on decaying dark matter. Previous analyses have used the cosmic microwave background and Type Ia supernova. We have updated them with the latest data as well as extended the analysis with the inclusion of Lyman-$\alpha$ forest, large scale structure and weak lensing observations. Astrophysical constraints are not considered in the present paper. The bounds on the lifetime of decaying dark matter are dominated by either the late-time integrated Sachs-Wolfe effect for the scenario with weak reionization, or CMB polarization observations when there is significant reionization. For the respective scenarios, the lifetimes for decaying dark matter are $\Gamma^{-1} \gtrsim 100$ Gyr and $(f \Gamma) ^{-1} \gtrsim 5.3 \times 10^8$ Gyr (at 95.4% confidence level), where the phenomenological parameter $f$ is the fraction of the decay energy deposited in baryonic gas. This allows us to constrain particle physics models with dark matter candidates through investigation of dark matter decays into Standard Model particles via effective operators. For decaying dark matter of $\sim 100$ GeV mass, we found that the size of the coupling constant in the effective dimension-4 operators responsible for dark matter decay has to generically be $\lesssim 10^{-22}$. We have also explored the implications of our analysis for representative models in theories of gauge-mediated supersymmetry breaking, minimal supergravity and little Higgs.Comment: 29 pages, 6 figures. Added references and corrected typos as well as grammatical oversight

A Determination of the Hubble Constant Using Measurements of X-Ray Emission and the Sunyaev-Zeldovich Effect at Millimeter Wavelengths in the Cluster Abell 1835

We present a determination of the Hubble constant and central electron density in the cluster Abell 1835 (z = 0.2523) from measurements of X-ray emission and millimeter-wave observations of the Sunyaev-Zeldovich (S-Z) effect with the Sunyaev-Zeldovich Infrared Experiment (SuZIE) multifrequency array receiver. Abell 1835 is a well studied cluster in the X-ray with a large central cooling flow. Using a combination of data from ROSAT PSPC and HRI images and millimeter wave measurements we fit a King model to the emission from the ionized gas around Abell 1835 with θ0 = 022 ± 002 and β = 0.58 ± 0.02. Assuming the cluster gas to be isothermal with a temperature of 9.8 keV, we find a y-parameter of 4.9 ± 0.6 × 10-4 and a peculiar velocity of 500 ± 1000 km s-1 from measurements at three frequencies, 145, 221, and 279 GHz. Combining the S-Z measurements with X-ray data, we determine a value for the Hubble constant of H0 = 59 km s-1 Mpc-1 and a central electron density for Abell 1835 of ne0 = 5.64 × 10-2 cm-3 assuming a standard cosmology with Ωm = 1 and ΩΛ = 0. The error in the determination of the Hubble constant is dominated by the uncertainty in the temperature of the X-ray emitting cluster gas

In-flight gain monitoring of SPIDER's transition-edge sensor arrays

International audienceExperiments deploying large arrays of transition-edge sensors (TESs) often require a robust method to monitor gain variations with minimal loss of observing time. We propose a sensitive and non-intrusive method for monitoring variations in TES responsivity using small square waves applied to the TES bias. We construct an estimator for a TES's small-signal power response from its electrical response that is exact in the limit of strong electrothermal feedback. We discuss the application and validation of this method using flight data from SPIDER, a balloon-borne telescope that observes the polarization of the cosmic microwave background with more than 2000 TESs. This method may prove useful for future balloon- and space-based instruments, where observing time and ground control bandwidth are limited