New Time!
CCAPP Cosmology Lunch meets on Thursdays at 1:00 pm in the Price Place (PRB M2005).

The small-scale structure problems of the universe can be solved by self-interacting dark matter that becomes strongly interacting at low energy. A particularly predictive model for the self-interactions is resonant short-range interactions with an S-wave scattering length that is much larger than the range. The velocity dependence of the cross section in such a model provides an excellent fit to selfinteraction cross sections inferred from dark-matter halos of galaxies and clusters of galaxies if the dark-matter mass is about 19 GeV and the scattering length is about 17 fm. Such a model makes definite predictions for the few-body physics of weakly bound clusters of the dark-matter particles. The formation of the two-body bound cluster is a bottleneck for the formation of larger bound clusters. We calculate the production of two-body bound clusters by three-body recombination in the early universe under the assumption that the dark matter particles are identical bosons, which is the most favorable case. If the dark-matter mass is 19 GeV and the scattering length is 17 fm, the fraction of dark matter in the form of two-body bound clusters can increase by as much as 4 orders of magnitude when the dark-matter temperature falls below the binding energy, but its present value remains less than 10−6 . The present fraction can be increased to as large as 10−3 by relaxing the constraints from small-scale structure and decreasing the mass of the dark matter particle. 

June 28,  2018

June 5,  2018

  • Visitor talk: Alice Pisani, Title: Constraining Cosmology with Cosmic Voids

Cosmic voids, the emptiest regions in the Universe, are an increasingly active sector of galaxy clustering analysis. In this talk I will explain why voids are interesting tools for cosmology and what kind of void-related observables we can focus on. I will discuss the treatment of systematics and present some recent methods and results. Finally I will discuss what we can expect from current and upcoming surveys in term of constraining power.

In this talk I will give an overview of the Physics of the Accelerating Universe Survey (PAUS): a unique combination of a large field-of-view and 40 narrow-band (NB) filters (12.5nm FWHM) that span the wavelength range from 450nm to 850nm and that was commissioned successfully in June 2015 on the WHT. This exquisite wavelength sampling results in photometric redshifts with a precision that approaches that of spectroscopic measurements, while being able to cover large areas of sky. I will present the current photometric redshift performance comparing to the zCOSMOS spectroscopic sample and the new photo-z template-based code that we have developed to estimate photometric redshifts for a narrow band photometric survey.

April 26,  2018

April 19,  2018
  • Xiao might talk about constraints on sub-lunar mass range for primordial black holes if time permits it.
  • Visitor talk, Sten Delos: Constraining the primordial power spectrum using minihalos

    Abstract: Ultracompact minihalos (UCMHs) have attracted considerable interest as a probe of the primordial power spectrum at small scales.  However, previous treatments assumed that halos collapsing at early times possess an extremely steep r^-9/4 density profile.  We recently found that UCMHs actually develop shallower r^-3/2 or r^-1 inner profiles depending on the shape of the power spectrum, but these halos are still highly concentrated due to their early formation.  I will discuss these results and the factors that set the inner density profile of a dark matter halo.  I will also outline the process of deriving power spectrum constraints in this revised picture.  Since the formalism can now include halos that collapse at any time, our preliminary revised constraints turn out to be stronger than prior constraints from UCMHs.

April 5,  2018
  • Visitor talk, Lucas Seco: Probing Dark Matter Self-Interactions with Disk Galaxies

    Abstract: Self-interacting Dark Matter (SIDM) has been proposed as a way to help reconcile small scale astrophysical observations with CDM predictions. We use N-body simulations to study the effect of SIDM on the morphology of disk galaxies falling into galaxy clusters. An effective drag force arises from dark matter scatterings and leads to offsets of the stellar disk with respect to its surrounding halo, causing distortions in the disk. We show that potentially observable warps, asymmetries, and thickening of the disk occur in simulations with currently allowed cross-sections. With further analysis of the potential systematic uncertainties of these novel probes, we believe it could be possible to constrain SIDM cross-sections with current and future observations.

March 29,  2018

March 22,  2018

March 15,  2018
                Abstract: A robust measurement of galaxy clustering relies on our understanding of imaging systematics such as Galactic Extinction, and how they introduce fluctuations in galaxy density. In this talk we will present the idea of using Artificial Neural Networks in modeling the dependence of galaxy density on imaging systematics. This method could be used for systematic mitigation and therefore is beneficial to ongoing and future galaxy surveys such as eBOSS and DESI.

February 15,  2018
  • Daniel Martens on using BOSS data to analyze intrinsic alignment effects on redshift space distortion parameters.

February 8,  2018

February 1,  2018

November 1,  2017

Sep 27,  2017

Sep 20,  2017

Jul 19,  2017

Jul 12,  2017

Jul 05,  2017

Jun 28,  2017

Jun 21,  2017

Jun 7,  2017

May 31,  2017

May, 17  2017
May, 11  2017
  • Scottez et al., 2017,, "Testing the accuracy of clustering redshift with simulations"
  • Masters et al., 2017,, "The Complete Calibration of the Color-Redshift Relation (C3R2) Survey: Survey Overview and Data Release 1"
  • Keck Array 2017,, "BICEP2 / Keck Array IX: New Bounds on Anisotropies of CMB Polarization Rotation and Implications for Axion-Like Particles and Primordial Magnetic Fields"
April, 19  2017

April, 5  2017

March, 29  2017
  • Speaker: Alex Mead
  • "Is the spherical-collapse model of halo formation useful?"
  • Abstract: I will discuss differences in non-linear structure formation between cosmological models that are designed so as to share a linear-theory power spectrum at redshift zero, but that differ in their growth histories. Simulations of these cosmologies are seen to share a large-scale structure skeleton, but differ in the details of their halo populations. I will demonstrate that these differences can be largely understood via the cosmology dependence of spherical-collapse-model predictions for the formation times and average densities of the haloes. This fact can then be used to generate per-cent level accurate non-linear matter power spectra for a range of dark energy models.

March, 22  2017

March, 8  2017
March, 1  2017
  • Dvorkin & Barausse, 2017,, "The nightmare scenario: measuring the stochastic gravitational-wave background from stalling massive black-hole binaries with pulsar-timing arrays"
  • Masui et al., 2017,, "Two- and Three-dimensional Probes of Parity in Primordial Gravity Waves"
  • Hopkins et al., 2017,, "FIRE-2 Simulations: Physics versus Numerics in Galaxy Formation"
  • Inayoshi et al. 2017,, "Identifying stellar binary black hole formation channels from the imprint of their center-of-mass acceleration in their gravitational wave signal"
  • Shirasaki et al. 2017,, "Large-Scale Clustering as a Probe of the Origin and the Host Environment of Fast Radio Bursts"
  • Bao et al, 2017,, "Quantum Circuit Cosmology: The Expansion of the Universe Since the First Qubit"
  • Dai & Venumadhav, 2017,, "On the waveforms of gravitationally lensed gravitational waves"
  • Our Ami Choi will discuss ways in which overlapping wide-area surveys can be leveraged to investigate photometric redshift bias and shear multiplicative measurement bias based on various combinations of lensing and clustering cross-correlations from spectroscopic, photometric and CMB surveys such as CFHTLenS, RCSLenS, KiDS, BOSS, WiggleZ, and Planck.
February, 22  2017

February, 15  2017
February, 08  2017
  • Guest speaker: David Cinabro, "Search For Type Ia Supernova NUV-Optical Subclasses"
February, 01  2017
  • Local speaker: Ashely Ross, "Things to consider when planning a large-scale structure survey and how this relates to BOSS, eBOSS, DESI, and DES”
  • Abbott et al., 2017,, "First Search for Gravitational Waves from Known Pulsars with Advanced LIGO"
  • Klypin et al., 2017,, "Dark Matter Statistics for Large Galaxy Catalogs: Power Spectra and Covariance Matrices"
January, 25  2017
  • Speaker: Susmita Adhikari, "Outskirts of Dark Matter Halos"
  • Speaker: Kaze Wong, "Advanced LIGO lensing rate predictions"
January, 11  2017

December, 14  2016

December, 1  2016

November, 17 2016

    Special talk: 
    Michael Wilson
    University of Edinburgh
    "Geometric and growth rate tests of gravity with the linearised galaxy distribution"

    This talk will outline the consistency of the VIPERS PDR-2 census of the galaxy distribution at z=0.8 with the expansion history and linear growth rate predicted by General Relativity and a Planck (2015) cosmology.  These may be inferred from the observed anisotropy of the galaxy power spectrum, which is sensitive to both the coherent infall of galaxies towards clusters (outflow from voids) and the assumption of an expansion history differing from the true one.
    I will then present the results of including a simple density transform prior to the analysis; this tackles the principal cause of non-linearity by down-weighting the most massive structures and extends the validity of theoretical models.  Moreover, this weighting would amplify signatures of modified gravity in ‘shielded’ models and represents a higher-order statistic, which contains information beyond that available to the power spectrum.
    Finally, the final data release of the VIPERS spectroscopic survey will be on Nov 18th (  I will detail the characteristics of the survey and describe the breadth of the accompanying clustering analyses.

November, 10  2016

November, 3  2016

October, 27 2016

    Special talk: 
    Patrick Breysse
    John Hopkins University
    "High-Redshift Astrophysics Using Every Photon"

    Large galaxy surveys have dramatically improved our understanding of the complex processes which govern gas dynamics and star formation in the nearby universe. However, we know far less about the most distant galaxies, as existing high-redshift observations can only detect the very brightest sources. Intensity mapping surveys provide a promising tool to access this poorly-studied population. By observing emission lines with low angular resolution, these surveys can make use of every photon in a target line to study faint emitters which are inaccessible using traditional techniques. With upcoming carbon monoxide experiments in mind, I will demonstrate how an intensity map can be used to measure the luminosity function of a galaxy population, and in turn how these measurements will allow us to place robust constraints on the cosmic star formation history. I will then show how cross-correlating CO isotopologue lines will make it possible to study gas dynamics within the earliest galaxies in unprecedented detail.

October, 20  2016

October, 6  2016

September, 29  2016

September, 22  2016

September, 15  2016

September, 8  2016

September, 1  2016