# Performance of a continuously rotating half-wave plate on the POLARBEAR telescope [IMA]

A continuously rotating half-wave plate (CRHWP) is a promising tool to improve the sensitivity to large angular scales in cosmic microwave background (CMB) polarization measurements. With a CRHWP, single detectors can measure all three of the Stokes parameters, $I$, $Q$ and $U$, thereby avoiding the set of systematic errors that can be introduced by mismatches in the properties of orthogonal detector pairs. We focus on the implementation of CRHWPs in large aperture telescopes (i.e. the primary mirror is larger than the current maximum half-wave plate diameter of $\sim$0.5 m), where the CRHWP can be placed between the primary mirror and focal plane. In this configuration, one needs to address the intensity to polarization ($I{\rightarrow}P$) leakage of the optics, which becomes a source of 1/f noise and also causes differential gain systematics that arise from CMB temperature fluctuations. In this paper, we present the performance of a CRHWP installed in the POLARBEAR experiment, which employs a Gregorian telescope with a 2.5 m primary illumination pattern. The CRHWP is placed near the prime focus between the primary and secondary mirrors. We find that the $I{\rightarrow}P$ leakage is larger than the expectation from the physical properties of our primary mirror, resulting in a 1/f knee of 100 mHz. The excess leakage could be due to imperfections in the detector system, i.e. detector non-linearity in the responsivity and time-constant. We demonstrate, however, that by subtracting the leakage correlated with the intensity signal, the 1/f noise knee frequency is reduced to 32 mHz ($\ell \sim$39 for our scan strategy), which is sufficient to probe the primordial B-mode signal. We also discuss methods for further noise subtraction in future projects where the precise temperature control of instrumental components and the leakage reduction will play a key role.

S. Takakura, M. Aguilar, Y. Akiba, et. al.
Fri, 24 Feb 17
4/50

Comments: 27 pages, 5 figures, 3 tables, to be submitted to JCAP

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# Evolution of linear wave dark matter perturbations in the radiation-dominant era [CEA]

Linear perturbations of the wave dark matter, or $\psi$ dark matter ($\psi$DM), of particle mass $\sim 10^{-22}$eV in the radiation-dominant era are analyzed, and the matter power spectrum at the photon-matter equality is obtained. We identify four phases of evolution for $\psi$DM perturbations, where the dynamics can be vastly different from the counterparts of cold dark matter (CDM). While in late stages after mass oscillation long-wave $\psi$DM perturbations are almost identical to CDM perturbations, some subtle differences remain, let alone intermediate-to-short waves that bear no resemblance with those of CDM throughout the whole evolutionary history. The dissimilarity is due to quantum mechanical effects which lead to severe mode suppression. We also discuss the axion model with a cosine field potential. The power spectrum of axion models are generally almost identical to those of $\psi$DM, but in the extreme case when the initial axion angle is near the field potential top, this axion model predicts a higher spectral cutoff than $\psi$DM, which is equivalent to having a higher particle mass for $\psi$DM.

U. Zhang and T. Chiueh
Fri, 24 Feb 17
7/50

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# Quantum Circuit Cosmology: The Expansion of the Universe Since the First Qubit [CL]

We consider cosmological evolution from the perspective of quantum information. We present a quantum circuit model for the expansion of a comoving region of space, in which initially-unentangled ancilla qubits become entangled as expansion proceeds. We apply this model to the comoving region that now coincides with our Hubble volume, taking the number of entangled degrees of freedom in this region to be proportional to the de Sitter entropy. The quantum circuit model is applicable for at most 140 $e$-folds of inflationary and post-inflationary expansion: we argue that no geometric description was possible before the time $t_1$ when our comoving region was one Planck length across, and contained one pair of entangled degrees of freedom. This approach could provide a framework for modeling the initial state of inflationary perturbations.

N. Bao, C. Cao, S. Carroll, et. al.
Fri, 24 Feb 17
11/50

Comments: 12 pages, 1 figure. Including appendix

# The cool core state of Planck SZ-selected clusters versus X-ray selected samples: evidence for cool core bias [CEA]

We characterized the population of galaxy clusters detected with the SZ effect with Planck, by measuring the cool core state of the objects in a well-defined subsample of the Planck catalogue. We used as indicator the concentration parameter Santos et al. (2008). The fraction of cool core clusters is $29 \pm 4 \%$ and does not show significant indications of evolution in the redshift range covered by our sample. We compare the distribution of the concentration parameter in the Planck sample with the one of the X-ray selected sample MACS (Mann & Ebeling, 2011): the distributions are significantly different and the cool core fraction in MACS is much higher ($59 \pm 5 \%$). Since X-ray selected samples are known to be biased towards cool cores due to the presence of their prominent surface brightness peak, we simulated the impact of the “cool core bias” following Eckert et al. (2011). We found that it plays a large role in the difference between the fractions of cool cores in the two samples. We examined other selection effects that could in principle bias SZ-surveys against cool cores but we found that their impact is not sufficient to explain the difference between Planck and MACS. The population of X-ray under-luminous objects, which are found in SZ-surveys but missing in X-ray samples (Planck Collaboration 2016), could possibly contribute to the difference, as we found most of them to be non cool cores, but this hypothesis deserves further investigation.

M. Rossetti, F. Gastaldello, D. Eckert, et. al.
Fri, 24 Feb 17
16/50

Comments: Accepted for publication in MNRAS

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# Detection of an Optical Counterpart to the ALFALFA Ultra-compact High Velocity Cloud AGC 249525 [GA]

We report on the detection at $>$98% confidence of an optical counterpart to AGC 249525, an Ultra-Compact High Velocity Cloud (UCHVC) discovered by the ALFALFA blind neutral hydrogen survey. UCHVCs are compact, isolated HI clouds with properties consistent with their being nearby low-mass galaxies, but without identified counterparts in extant optical surveys. Analysis of the resolved stellar sources in deep $g$- and $i$-band imaging from the WIYN pODI camera reveals a clustering of possible Red Giant Branch stars associated with AGC 249525 at a distance of 1.64$\pm$0.45 Mpc. Matching our optical detection with the HI synthesis map of AGC 249525 from Adams et al. (2016) shows that the stellar overdensity is exactly coincident with the highest-density HI contour from that study. Combining our optical photometry and the HI properties of this object yields an absolute magnitude of $-7.1 \leq M_V \leq -4.5$, a stellar mass between $2.2\pm0.6\times10^4 M_{\odot}$ and $3.6\pm1.0\times10^5 M_{\odot}$, and an HI to stellar mass ratio between 9 and 144. This object has stellar properties within the observed range of gas-poor Ultra-Faint Dwarfs in the Local Group, but is gas-dominated.

W. Janesh, K. Rhode, J. Salzer, et. al.
Fri, 24 Feb 17
24/50

Comments: 9 pages, 4 figures; accepted to ApJL

# Large-Scale Clustering as a Probe of the Origin and the Host Environment of Fast Radio Bursts [CEA]

We propose to use degree-scale angular clustering of fast radio bursts (FRBs) to identify their origin and the host galaxy population. We study the information content in auto-correlation of the angular positions and dispersion measures (DM) and in cross-correlation with galaxies. We show that the cross-correlation with Sloan Digital Sky Survey (SDSS) galaxies will place stringent constraints on the mean physical quantities associated with FRBs. If ~10,000 FRBs are detected with <deg resolution in the SDSS field, the clustering analysis can constrain the global abundance of free electrons at $z<1$, the bias factor of FRB host galaxies, and the mean near-source dispersion measure, with fractional errors (with a $68\%$ confidence level) of $\sim5 \%, \sim 20 \%$, and $\sim70 \%$, respectively. The delay time distribution of FRB sources can be also determined by combining the clustering and the probability distribution function of dispersion measure. Our approach will be complementary to high-resolution ($\ll {\rm deg}$) event localization using e.g., VLA and VLBI for identifying the origin of FRBs and the source environment. We strongly encourage future observational programs such as CHIME, UTMOST, HIRAX to survey FRBs in the SDSS field.

M. Shirasaki, K. Kashiyama and N. Yoshida
Fri, 24 Feb 17
25/50

Comments: 14 pages, 8 figures, 2 tables, To be submitted to Phys. Rev. D

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# The nightmare scenario: measuring the stochastic gravitational-wave background from stalling massive black-hole binaries with pulsar-timing arrays [GA]

Massive black-hole binaries, formed when galaxies merge, are among the primary sources of gravitational waves targeted by ongoing Pulsar Timing Array (PTA) experiments and the upcoming space-based LISA interferometer. However, their formation and merger rates are still highly uncertain. Recent upper limits on the stochastic gravitational-wave background obtained by PTAs are starting being in marginal tension with theoretical models for the pairing and orbital evolution of these systems. This tension can be resolved by assuming that these binaries are more eccentric or interact more strongly with the environment (gas and stars) than expected, or by accounting for possible selection biases in the construction of the theoretical models. However, another (pessimistic) possibility is that these binaries do not merge at all, but stall at large ($\sim$ pc) separations. We explore this extreme scenario by using a galaxy-formation semi-analytic model including massive black holes (isolated and in binaries), and show that future generations of PTAs will detect the stochastic gravitational-wave background from the massive black-hole binary population within $10-15$ years of observations, even in the “nightmare scenario” in which all binaries stall at the hardening radius. Moreover, we argue that this scenario is too pessimistic, because our model predicts the existence of a sub-population of binaries with small mass ratios ($q \lesssim 10^{-3}$) that should merge within a Hubble time simply as a result of gravitational-wave emission. This sub-population will be observable with large signal-to-noise ratios by future PTAs thanks to next-generation radiotelescopes such as SKA or FAST, and possibly by LISA.

I. Dvorkin and E. Barausse
Fri, 24 Feb 17
30/50