Year 2017-2018

August 23, 2018

- O'Connel et al., Large Covariance Matrices: Accurate Models Without Mocks
- Mukherjee et al., Beyond the classical distance-redshift test: cross-correlating redshift-free standard candles and sirens with redshift surveys

August 16, 2018

- Hall & Taylor, A Bayesian method for combining theoretical and simulated covariance matrices for large-scale structure surveys
- Sanchez & Bernstein, Redshift inference from the combination of galaxy colors and clustering in a hierarchical Bayesian model
- Walther et al., New Constraints on IGM Thermal Evolution from the Lyα Forest Power Spectrum
- Katz et al., Femtolensing by Dark Matter Revisited

July 19, 2018

- Planck 18 results: Akrami et al., Planck 2018 results. I. Overview and the cosmological legacy of Planck
- Aghanim et al., Planck 2018 results. VI. Cosmological parameters
- Aghanim et al., Planck 2018 results. VIII. Gravitational lensing
- Akrami et al., Planck 2018 results. X. Constraints on inflation
- Talk by Denise Schmitz on Time evolution of intrinsic alignments of galaxies

Abstract:

Intrinsic alignments (IA), correlations between the intrinsic shapes and orientations of galaxies on the sky, are both a significant systematic in weak lensing and a probe of the effect of large-scale structure on galactic structure and angular momentum. In the era of precision cosmology, it is thus especially important to model IA with high accuracy. Efforts to use cosmological perturbation theory to model the dependence of IA on the large-scale structure have thus far been relatively successful; however, extant models do not consistently account for time evolution. In particular, advection of galaxies due to peculiar velocities alters the impact of IA, because galaxy positions when observed are generally different from their positions at the epoch when IA is believed to be set. In this work, we evolve the galaxy IA from the time of galaxy formation to the time at which they are observed, including the effects of this advection, and show how this process naturally leads to a dependence of IA on the velocity shear. We calculate the galaxy-galaxy-IA bispectrum to tree level (in the linear matter density) in terms of the evolved IA coefficients. We then discuss the implications for weak lensing systematics as well as for studies of galaxy formation and evolution. We find that considering advection introduces nonlocality into the bispectrum, and that the degree of nonlocality represents the memory of a galaxy's path from the time of its formation to the time of observation. We discuss how this result can be used to constrain the redshift at which IA is determined and provide Fisher estimation for the relevant measurements using the example of SDSS-BOSS.

July 5, 2018

- Leistedt et al., Hierarchical modeling and statistical calibration for photometric redshifts
- Talk by prof. Braaten on Production of dark-matter bound states in the early universe by three-body recombination

Abstract:

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

- Mooley et al., Superluminal motion of a relativistic jet in the neutron star merger GW17081
- Hotokezaka et al., A Hubble constant measurement from superluminal motion of the jet in GW170817

June 14, 2018

- Adhikari et al., Splashback in galaxy clusters as a probe of cosmic expansion and gravity.
- Adhikari et al., Splashback in accreting dark matter halos
- Beane et al., Extracting bias using the cross-bispectrum: An EOR and 21 cm-[CII]-[CII] case study
- Chiba et al., Reconstructing f(R) gravity from the spectral index

June 5, 2018

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

Abstract:

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.

May 24, 2018

May 10, 2018

- Modi et al., Cosmological Reconstruction From Galaxy Light: Neural Network Based Light-Matter Connection
- Visitor talk: Alex Alarcon, Title: PAU Survey: Overview and current photo-z results

Abstract:

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.

May 3, 2018

- Castorina et al., Primordial non-Gaussianities and zero bias tracers of the Large Scale Structure
- Riess et al., Milky Way Cepheid Standards for Measuring Cosmic Distances and Application to Gaia DR2: Implications for the Hubble Constant

April 26, 2018

- Jenna will talk about her research.
- Feng et al., Exploring the posterior surface of the large scale structure reconstruction

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

- Hektor et al., Constraining Primordial Black Holes with the EDGES 21-cm Absorption Signal
- MacCrann et al., DES Y1 Results: Validating cosmological parameter estimation using simulated Dark Energy Surveys
- Baumann et al., First Measurement of Neutrinos in the BAO Spectrum
- Xiao will talk about constraints on sub-lunar mass range for primordial black holes.

March 22, 2018

- Montero-Camacho et al., Exploring circular polarization in the CMB due to conventional sources of cosmic birefringence

March 15, 2018

- Montero-Camacho et al., Exploring circular polarization in the CMB due to conventional sources of cosmic birefringence

Mehdi Rezaie talk: Mitigating Systematic Errors in Galaxy Surveys with Artificial Intelligence.

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.

March 8, 2018