# Cosmic Flows (and other novelties on Large Scales)

COVID-19 information for PI Residents and Visitors

Conference Date:
Monday, August 10, 2015 (All day) to Wednesday, August 12, 2015 (All day)
Scientific Areas:
Cosmology

Observational cosmology has undergone a renaissance over the past couple of decades, in large part thanks to the incredible success of the Cosmic Microwave Background (CMB) anisotropy surveys. However, as CMB surveys are (nearly) exhausting their potential, the attention is shifting to the next frontier, i.e. the Large Scale Structure (LSS) of our Universe. Several probes of LSS, such as kinematic Sunyaev Zeldovich measurements, velocity fields, and 21cm surveys are now coming of age, while galaxy and weak lensing surveys are reaching their maturity. The aim of this workshop is to bring together young researchers and experts in the field, in order to identify the most significant scientific questions and their most promising observational probes that will shape the agenda for observational cosmology over the next decade.

Sponsorship for this workshop has been provided by:

• Yacine Ali-Haimoud, John Hopkins University
• Marcelo Alvarez, CITA
• Florian Beutler, University of California, Berkeley
• Neal Dalal, University of Illinois, Urbana-Champaign
• Hume Feldman, University of Kansas
• Michael Hudson, University of Waterloo
• Derek Inman, University of Toronto
• Matthew McQuinn, University of Washington
• Mubdi Rahman, Johns Hopkins University
• Emmanuel Schaan, Princeton University
• Leonardo Senatore, Stanford University
• Sarah Shandera, Pennsylvania State University & Perimeter Institute
• Richard Shaw, University of British Columbia
• Kris Sigurdson, Univrsity of British Columbia
• Anze Slosar, Brookhaven National Laboratory
• Richard Woodard, University of Florida
• Haoran Yu, Canadian Institute for Theoretical Astrophysics
• Matias Zaldarriaga, Institute for Advanced Study
• Hong-Ming Zhu, Chinese Academy of Sciences, Beijing
• Marcelo Alvarez, CITA
• Niayesh Afshordi, Perimeter Institute & University of Waterloo
• Yacine Ali-Haimoud, John Hopkins University
• Anita Bahmanya, CITA
• Phil Berger, CITA
• Florian Beutler, University of California, Berkeley
• Dick Bond, CITA
• Cliff Burgess, Perimeter Institute & McMaster University
• Neal Dalal, University of Illinois, Urbana-Champaign
• Hume Feldman, University of Kansas
• Daniel Guariento, Perimeter Institute
• Zhiqi Huang, CITA
• Michael Hudson, University of Waterloo
• Derek Inman, CITA
• Matthew Johnson, Perimeter Institute & York University
• Mansour Karami, Perimeter Institute
• Connor Liam, CITA
• David Marsh, Perimeter Institute
• John Moffat, Perimeter Institute
• Matthew McQuinn, University of Washington
• Chiamaka Okoli Nwosu, Perimeter Institute
• Ue-Li Pen, Perimeter Institute & CITA
• Mubdi Rahman, Johns Hopkins University
• Mehdi Saravani, Perimeter Institute
• Emmanuel Schaan, Princeton University
• Erik Scnhetter, Perimeter Institute
• Leonardo Senatore, Stanford University
• Sarah Shandera, Pennsylvania State University & Perimeter Institute
• Richard Shaw, University of British Columbia
• Kris Sigurdson, Univrsity of British Columbia
• Dana Simard, CITA
• Anze Slosar, Brookhaven National Laboratory
• Kendrick Smith, Perimeter Institute
• George Stein, CITA
• Alexandra Terrana, York University
• Alexander van Engelen, CITA
• Richard Woodard, University of Florida
• Haoran Yu, Canadian Institute for Theoretical Astrophysics
• Matias Zaldarriaga, Institute for Advanced Study
• Hong-Ming Zhu, Chinese Academy of Sciences, Beijing

Schedule is Subject to Change

Monday, August 10, 2015

 Time Event Location 8:30 – 9:15am Registration Reception 9:15 – 9:30am Welcome and Opening Remarks Bob Room 9:30 – 10:10am Neal Dalal, University of Illinois at Urbana-ChampaignStructure formation with hot particles Bob Room 10:10 – 10:40am Coffee Break Bistro – 1st Floor 10:40 – 11:20am Matt McQuinn, University of WashingtonThe thermal history of the IGM Bob Room 11:20 – 12:00pm Emmanuel Schaan, Princeton UniversityProbing cosmic flows through the kinematic Sunyaev Zel'dovich effect Bob Room 12:00 – 2:00pm Lunch Bistro – 2nd Floor 2:00 – 2:40pm Haoran Yu, CITATianNu: simulating the neutrino sky Bob Room 2:40 – 3:20pm Derek Inman, University of TorontoPrecision reconstruction of the cold dark matter-neutrinorelative velocity. Bob Room 3:20 – 3:50pm Coffee Break Bistro – 1st Floor 3:50 – 4:30pm Sarah Shandera, Pennsylvania State UniversityCMB Anomalies and Non-Gaussianity Bob Room 4:30 - 5:10pm Hume Feldman, University of KansasFunny Thing Happened on the Way to Convergence. Bob Room

Tuesday, August 11, 2015

 Time Event Location 9:30 – 10:10am Richard Woodard, University of FloridaFine Tuning May Not Be Enough Bob Room 10:10 – 10:40am Coffee Break Bistro – 1st Floor 10:40 – 11:20am Kris Sigurdson, University of British ColumbiaTBA Bob Room 11:20 – 12:00pm Mubdi Rahman, Johns Hopkins UniversityClustering Redshifts: A New Era of Distance Measurement Bob Room 12:00 – 2:00pm Lunch Bistro – 2nd Floor 2:00 – 2:40pm Matias Zaldarriaga, Institute for Advanced StudyTBA Bob Room 2:40 – 3:20pm Hong-Ming Zhu,National Astronomical Observatories of China, BeijingCosmological measurement of neutrino masses from relative velocities Bob Room 3:20 – 3:25pm Conference Photo TBA 3:25 – 3:50pm Coffee Break Bistro – 1st Floor 3:50 – 4:30pm Anze Slosar, Brookhaven National LaboratoryBiasing in the Lyman-alpha forest Bob Room 4:30 - 5:10pm Marcelo Alvarez, CITALarge-Scale Flows During Reionization and their Detectability via Cross-correlations Bob Room 6:30 - 8:30pm Banquet Bistro – 2nd Floor

Wednesday, August 12, 2015

 Time Event Location 9:30 – 10:10am Florian Beutler, University of California, BerkeleyCosmic Flows with the Baryon Oscillation Spectroscopic Survey (BOSS) Bob Room 10:10 – 10:40am Coffee Break Bistro – 1st Floor 10:40 – 11:20am Richard Shaw,  University of British ColumbiaProbing Dark Energy with the Canadian Hydrogen Intensity Mapping Experiment (CHIME) Bob Room 11:20 – 12:00pm Yacine Ali-Haimoud, Johns Hopkins University21cm fluctuations in the dark ages and cosmic heat flows Bob Room 12:00 – 2:00pm Lunch Bistro – 2nd Floor 2:00 – 3:00pm ColloquiumLeonardo Senatore, Stanford UniversityThe Effective Field Theory of Large Scale Structures Theatre 3:00 – 3:30pm Coffee Break Bistro – 1st Floor 3:30 - 4:10pm Discussion Bob Room 4:10 – 5:30pm Mike Hudson, University of WaterlooChallenges and Prospects in Large-Scale Structure and Flows: Summary and Discussion Bob Room

Yacine Ali-Haimoud, Johns Hopkins University

21cm fluctuations in the dark ages and cosmic heat flows

The spin-flip transition in neutral hydrogen may be used to probe large-scale structure at high redshifts, before the first luminous objects formed. The huge number of modes potentially accessible make this a very promising avenue. I will discuss several key unknowns that could be measured with high-redshift 21cm surveys: primordial non-gaussianity, the primordial small-scale power spectrum, and dark-matter-baryon interactions. I will close by discussing CMB spectral distortions, another promising probe of early Universe physics, and illustrate how they can be used to test dark-matter interactions with standard model particles.

Marcelo Alvarez, CITA

Large-Scale Flows During Reionization and their Detectability via Cross-correlations

New results on the observational signatures of large-scale flows during reionization, using new simulations and analytical methods, will be presented. A preliminary analysis will be described, indicating that cross-correlation of diffuse radiation with tracers of the large scale matter fluctuations can in principle provide new constraints on the timing and duration of reionization, via peculiar velocities.

Florian Beutler, University of California, Berkeley

Cosmic Flows with the Baryon Oscillation Spectroscopic Survey (BOSS)

I will present results from the SDSS-III BOSS-DR11 analysis. In this talk I will focus on the analysis of the power spectrum multipoles, which allows to constrain the growth of structure through redshift-space distortions. Such measurements can be used to test GR and measure the sum of the neutrino masses. Beside RSD we also constrain the geometry of the Universe through the Alcock-Paczynski effect and Baryon Acoustic Oscillations.

Neal Dalal, University of Illinois at Urbana-Champaign

Structure formation with hot particles

I will describe a novel method for simulating nonlinear structure formation in cosmologies that have hot or warm collisionless species.  After introducing the method, I will show results of our simulations for universes with massive neutrinos, and warm dark matter simulations.

Hume Feldman, University of Kansas

Funny Thing Happened on the Way to Convergence.

Modeling the cosmic velocity field, and especially estimating its lowest order moment, the bulk flow, has been a popular pursuit among aficionados in the cosmological community for three decades now. Other than estimating the magnitude and direction of the flow, one of the main difficulties has been defining the scale of flow detected.  There is a nearly universal agreement as to the direction of the flow, however, there is some disagreements regarding the magnitude and scale of the flow.  We developed and applied the Minimal Variance (MV) formalism to optimize and clearly define the scale of a particular analysis, using the width of the survey window function as a proxy for scale. Comparing the MV ideal window function to any analysis window function gives an unbiased estimate to the survey width (or scale) and thus provides a method to directly compare various results. Further, I will introduce a new estimator of the peculiar velocity from redshift and distance estimates. This estimator results in peculiar velocity estimates that are statistically unbiased and have Gaussian distributed errors. The adoption of the new estimator significantly improves the accuracy and validity of studies of the large-scale peculiar velocity field and eliminates potential systematic biases, thus helping to bring peculiar velocity analysis into the era of precision cosmology. I will discuss the method, compare various recent analyses and show that the disagreements are not as significant as they appear.

Michael Hudson, University of Waterloo

Challenges and Prospects in Large-Scale Structure and Flows: Summary and Discussion

I will summarize the current state of the field, review the novel ideas and results presented at the meeting, raise some challenges and future prospects, all the while still leave lots of time for discussion.

Derek Inman, University of Toronto

Precision reconstruction of the cold dark matter-neutrino relative velocity.

Neutrinos occur in great number throughout the Universe, yet remain poorly understood due to their weak interactions with other matter. In particular, individual neutrino masses remain an elusive property for particle physicists and cosmologists abound. Recently, it has been proposed that individual neutrino masses may be constrained from observations of neutrino wakes that result from the relative flow between cold dark matter (CDM) and neutrinos. The only required knowledge for such a detection is the relative velocity field between CDM and neutrinos. However, since neither CDM nor neutrinos are directly observable, their relative flow must be obtained by indirect means. We modify the cosmology code, CUBEP3M, to simulate neutrino N-body particles alongside CDM. We find the result that the relative velocity field can be obtained accurately by applying linear transformations to the halo density field. Assuming prior knowledge of the halo bias, we find that the reconstructed relative velocities are highly correlated with the simulated ones, with correlation coefficients of 0.94, 0.93, 0.92 and 0.88 for neutrinos of mass 0.05, 0.1, 0.2 and 0.4 eV, respectively. We confirm that the relative velocity field reconstructed from large-scale structure observations, such as galaxy or 21 cm surveys, can be accurate in direction and, with appropriate scaling, magnitude.

Matt McQuinn, University of Washington

The thermal history of the IGM

In standard models, the unshocked IGM is heated predominantly by photoionization.  I will show that this model works remarkably well at reproducing recent IGM temperature measurements spanning 1.5<z<5, allowing little room for extra sources of heat.

At z>5, O(1) fluctuations in the opacity of the Lyman-alpha forest are see on 100 Mpc scales, which previous models have had difficulty explaining.  I will describe what I think is the most natural explanation for these fluctuations, an explanation that has significant implications for the process of reionization.

Mubdi Rahman, Johns Hopkins University

Clustering Redshifts: A New Era of Distance Measurement

The measurement of distance has long been a fundamental challenge in astrophysics. We have developed a method of inferring distances to astrophysical sources using spatial cross-correlations with galaxies of known redshift.  These “clustering redshifts” are robust to problems plaguing other distance estimates and require only knowledge of the on-sky position of the sources.  We have verified the method with sources with spectroscopic redshifts, demonstrating accuracies exceeding those required for many cosmological probes. Using this technique, we have explored the SDSS photometric galaxies, characterizing their distances and discovering entirely unidentified populations within. Clustering redshifts are proving their potential in the era of large scale surveys, such as LSST and DES, and will be a new tool in unlocking the third dimension of astronomical observations from the radio to the X-ray.

Emmanuel Schaan, Princeton University

Probing cosmic flows through the kinematic Sunyaev Zel'dovich effect

Beyond its primary fluctuations, the cosmic microwave background (CMB) contains a wealth of information on the large-scale structure of the universe, which it illuminates as a backlight. The baryon momentum field is thus imprinted on the CMB through the kinematic Sunyaev-Zel'dovich (kSZ) effect. Current small-scale high-sensitivity CMB experiments make this effect detectable, providing a unique handle on peculiar velocities and baryon physics.
I will report a significant detection of the kSZ effect, obtained by combining CMB intensity data with peculiar velocities reconstructed from the galaxy number density field. I will present the prospects for localizing the missing baryons, constraining baryon physics inside galaxy clusters, and measuring the growth rate of structure from the kSZ effect. I will finally explore the possibility of measuring velocities across the line of sight through the CMB moving lens effect.

Leonardo Senatore, Stanford University

The Effective Field Theory of Large Scale Structures

After the completion of the Planck satellite, the next most important experiments in cosmology will be about mapping the Large Scale Structures of the Universe. In order to continue to make progress in our understanding of the early universe, it is essential to develop a precise understanding of this system. The Effective Filed Theory of Large Scale Structures provides a novel framework to analytically compute the clustering of the Large Scale Structures in the weakly non-linear regime in a consistent and reliable way. The theory that describes the long wavelength fluctuations is obtained after integrating out the strongly-coupled, short-distance modes, and adding suitable operators that allow us to correctly reconstruct the effect of short distance fluctuations at long distances. By using techniques that originate in the particle physics context, a few observables have been computed so far, and the results are extremely promising. I will discuss the formalism, the main results so far, and the potential implications for next generation experiments.

Sarah Shandera, Pennsylvania State University

CMB Anomalies and Non-Gaussianity

When the primordial fluctuations are non-Gaussian and inflation lasts longer than the minimum number of e-folds, the likelihood that we observe mild deviations from isotropy increases. I will present a single framework that encompasses many of the most promising scenarios for generating a hemispherical power asymmetry. This framework allows a comparison of the observational evidence for various models, including some with a natural connection between large scale power suppression and power asymmetry.

Richard Shaw, University of British Columbia

Probing Dark Energy with the Canadian Hydrogen Intensity Mapping Experiment (CHIME)

CHIME will use the 21cm emission line of neutral hydrogen to map large-scale
structure between redshifts of 0.8 and 2.5. By measuring BAO we will place
constraints on the dark energy equation of state as it begins to dominate the
expansion of the Universe, particularly at redshifts poorly probed by current
BAO surveys.

In this talk I will introduce CHIME, a transit radio interferometer designed
specifically for this purpose. I will discuss its goals and describe the
powerful new analysis techniques we have developed to confront the many
challenges of such observations, in particular removal of astrophysical
foregrounds which are six orders of magnitude larger than the 21cm signal. A
smaller 40m x 37m pathfinder telescope is currently operating at the DRAO in
Penticton, BC, and the construction of the full-sized 80m x 100m instrument
commenced in early 2015. I will report on current progress, and the lessons

Anze Slosar, Brookhaven National Laboratory

Biasing in the Lyman-alpha forest

I'll present a series of numerical experiments to test simple analytical predictions for large-scale Lyman-alpha forest bias parameters. Despite relying on second-order SPT, some of the predictions are surprisingly accurate, especially if thermal broadening is not taken into account. I'll also discuss details of using filtered and squared small-scale fields as robust tracers of large-scale structure that might be useful for non-Gaussianity measurements.

Richard Woodward, University of Florida

Fine Tuning May Not Be Enough

This talk is based on arXiv:1506.07306, with Shun-Pei Miao. We argue that the fine tuning problems of scalar-driven inflation may be worse than is commonly believed. The reason is that reheating requires the inflaton to be coupled to other matter fields whose vacuum fluctuations alter the inflaton potential. The usual response has been that even more fine-tuning of the classical potential $V(\varphi)$ can repair any damage done in this way. We point out that the effective potential in de Sitter background actually depends in a complicated way upon the dimensionless combination of $\varphi/H$. We also show that the factors of $H$ which occur in de Sitter do not even correspond to local functionals of the metric for general geometries, nor are they Planck-suppressed.

Haoran Yu, CITA

TianNu: simulating the neutrino sky

Hong-Ming Zhu, National Astronomical Observatories of China, Beijing

Cosmological measurement of neutrino masses from relative velocities

Present day streaming motions of neutrinos relative to dark matter and baryons are several hundred km/s, comparable with their thermal velocity dispersion. This results in a unique dipole anisotropic distortion of the matter-neutrino cross power spectrum, which is observable through the dipole distortion in the cross correlation of different galaxy populations. Such a dipole vanishes if not for this relative velocity and so it is a clean signature for neutrino mass. We estimate the size of this effect and find that current and future galaxy surveys may be sensitive to these signature distortions.

## Discussion

Wednesday Aug 12, 2015
Speaker(s):
Scientific Areas:

## The Effective Field Theory of Large Scale Structures

Wednesday Aug 12, 2015
Speaker(s):

After the completion of the Planck satellite, the next most important experiments in cosmology will be about mapping the Large Scale Structures of the Universe. In order to continue to make progress in our understanding of the early universe, it is essential to develop a precise understanding of this system. The Effective Filed Theory of Large Scale Structures provides a novel framework to analytically compute the clustering of the Large Scale Structures in the weakly non-linear regime in a consistent and reliable way.

Scientific Areas:

## 21cm fluctuations in the dark ages and cosmic heat flows

Wednesday Aug 12, 2015
Speaker(s):

The spin-flip transition in neutral hydrogen may be used to probe large-scale structure at high redshifts, before the first luminous objects formed. The huge number of modes potentially accessible make this a very promising avenue. I will discuss several key unknowns that could be measured with high-redshift 21cm surveys: primordial non-gaussianity, the primordial small-scale power spectrum, and dark-matter-baryon interactions.

Scientific Areas:

## Probing Dark Energy with the Canadian Hydrogen Intensity Mapping Experiment (CHIME)

Wednesday Aug 12, 2015
Speaker(s):

CHIME will use the 21cm emission line of neutral hydrogen to map large-scale
structure between redshifts of 0.8 and 2.5. By measuring BAO we will place
constraints on the dark energy equation of state as it begins to dominate the
expansion of the Universe, particularly at redshifts poorly probed by current
BAO surveys.

Scientific Areas:

## Cosmic Flows with the Baryon Oscillation Spectroscopic Survey (BOSS)

Wednesday Aug 12, 2015
Speaker(s):

I will present results from the SDSS-III BOSS-DR11 analysis. In this talk I will focus on the analysis of the power spectrum multipoles, which allows to constrain the growth of structure through redshift-space distortions. Such measurements can be used to test GR and measure the sum of the neutrino masses. Beside RSD we also constrain the geometry of the Universe through the Alcock-Paczynski effect and Baryon Acoustic Oscillations.

Scientific Areas:

## Large-Scale Flows During Reionization and their Detectability via Cross-correlations

Tuesday Aug 11, 2015
Speaker(s):

New results on the observational signatures of large-scale flows during reionization, using new simulations and analytical methods, will be presented. A preliminary analysis will be described, indicating that cross-correlation of diffuse radiation with tracers of the large scale matter fluctuations can in principle provide new constraints on the timing and duration of reionization, via peculiar velocities.

Scientific Areas:

## Biasing in the Lyman-alpha forest

Tuesday Aug 11, 2015
Speaker(s):

I'll present a series of numerical experiments to test simple analytical predictions for large-scale Lyman-alpha forest bias parameters. Despite relying on second-order SPT, some of the predictions are surprisingly accurate, especially if thermal broadening is not taken into account. I'll also discuss details of using filtered and squared small-scale fields as robust tracers of large-scale structure that might be useful for non-Gaussianity measurements.

Scientific Areas:

## Cosmological measurement of neutrino masses from relative velocities

Tuesday Aug 11, 2015
Speaker(s):

Present day streaming motions of neutrinos relative to dark matter and baryons are several hundred km/s, comparable with their thermal velocity dispersion. This results in a unique dipole anisotropic distortion of the matter-neutrino cross power spectrum, which is observable through the dipole distortion in the cross correlation of different galaxy populations. Such a dipole vanishes if not for this relative velocity and so it is a clean signature for neutrino mass.

Scientific Areas:

## TBA

Tuesday Aug 11, 2015
Speaker(s):

TBA

Scientific Areas:

## Clustering Redshifts: A New Era of Distance Measurement

Tuesday Aug 11, 2015
Speaker(s):

The measurement of distance has long been a fundamental challenge in astrophysics. We have developed a method of inferring distances to astrophysical sources using spatial cross-correlations with galaxies of known redshift. These “clustering redshifts” are robust to problems plaguing other distance estimates and require only knowledge of the on-sky position of the sources. We have verified the method with sources with spectroscopic redshifts, demonstrating accuracies exceeding those required for many cosmological probes.

Scientific Areas:

## Pages

Scientific Organizers:

• Niayesh Afshordi, Perimeter Institute & University of Waterloo
• Matthew Johnson, Perimeter Institute & York University
• Ue-Li Pen, Perimeter Institute & CITA
• Kendrick Smith, Perimeter Institute