Upcoming and Previous Seminars (Past months or Previous years)

Note that if the talk's pdf or ppt is available after the talk, you can get it by clicking on the talk title.

Physics/Astronomy C290C Cosmology and Cosmology-BCCP Seminar
The Physics/Astronomy C290C series consists of the Cosmology-BCCP LBNL-Physics-Astronomy Cosmology seminars held Tuesdays 1:10-2:00 pm via ZOOM.
Please mail Joanne Cohn if you need the ZOOM login information (before 1 pm for sure, and the earlier the better), or to add to this list or to suggest speakers.

This seminar is intended for BCCP members and Berkeley graduate students pursuing their dissertation research in cosmology. Other LBL, Berkeley Astronomy and and Berkeley Physics Department members are welcome.

Speaker/Visitor Info is here.

BOSS and Nyx
(Image by C. Stark)

Note that there are also other talks which might be of interest, including:

June 2021
June 3, Thursday
4 pm (LBL RPM)
Julien Guy, LBL
The Dark Energy Spectroscopic Instrument (DESI): start of the five year survey.
The Dark Energy Spectroscopic Instrument (DESI) started its main survey on May 14. Over 5 years, it will measure the spectra and redshifts of about 30 millions galaxies and quasars over 14,000 square degrees. This 3D map will be used to reconstruct the expansion history of the universe up to z=3.5, and measure the growth rate of structure in the redshift range 0.7-1.6 with unequaled precision (< 1.5% per redshift bin of 0.1). The start of the survey marks the end of a successful survey validation period during which more than one million cosmological redshifts were measured. This data set, along with many commissioning studies, has demonstrated the project meets its science requirements written many years ago. I will present how we have validated the target selection, the instrument performance, the spectroscopic pipeline, operations, and the survey strategy.
June 8, Tuesday
1:10 pm (BCCP/Cosmology)--postponed April talk
Alexandra Amon, SLAC/Stanford
The Dark Energy Survey Year 3 Results from Weak Lensing and Clustering
I will present the cosmological weak lensing and clustering results from the Dark Energy Survey (DES) using its first three years of data taken using the Dark Energy Camera on the 4m Blanco telescope at CTIO. This analysis spans the full DES footprint, more than 4000 sq. deg. of sky, with the final shear catalogue containing more than 100 million galaxies, constituting the most powerful weak lensing dataset to date. The comparison of DES cosmological constraints on dark matter and dark energy from WL and LSS in the low-redshift Universe to CMB constraints provides an unprecedented test of the standard cosmological model, across high and low redshift. These DES results from the low-redshift Universe are consistent with those from the cosmic microwave background (CMB) and support the standard cosmological model, LCDM. I will mention the main challenges that our analysis is susceptible to, and the summarise the DES-Year 3 approach to account for these and deliver robust cosmological constraints.

Past Months

July 2020
July 9, Thursday
4 pm (RPM LBL)
Kyle Dawson, Utah By ZOOM
“The Completed SDSS-IV extended Baryon Oscillation Spectroscopic Survey: Cosmological Implications from two Decades of Spectroscopic Surveys at the Apache Point observatory”
The Extended Baryon Oscillation Spectroscopic Survey (eBOSS) concluded observations of the cosmic distance scale and the growth of structure in February, 2019. The three dimensional clustering in all samples from the Sloan Digital Sky Survey (SDSS) was used to make 15 distinct, high precision measurements of Baryon Acoustic Oscillations (BAO) to an effective redshift z<2.4 and six measurements of redshift space distortions (RSD) to z<1.5. With this redshift coverage and sensitivity, the SDSS experiment is unparalleled in its ability to explore models of dark energy. Using available cosmological samples, we provide new constraints on the cosmological model with an emphasis on the role of the final BAO and RSD clustering measurements in advancing the cosmological model. In this talk, I will give a brief overview of the BAO and RSD measurements and present the highlights of the advances in modeling dark energy, the local expansion rate, tests of general relativity, neutrino masses, and the overall cosmological model.
Results webpages:

September 2020
Sep 1, Tuesday
1:10 pm (BCCP/Cosmology)
Elisa Chisari, Leiden
Cosmology and galaxy evolution from galaxy shapes
Two phenomena contribute to correlating galaxy shapes across the Universe: the deviation of photons from a straight path due to the spacetime curvature ("gravitational lensing”), and tidal interactions (“intrinsic alignments”). Modelling both accurately is crucial to obtaining unbiased constraints on the cosmological model from forthcoming surveys, particularly in the context of elucidating the origin of accelerated expansion of the Universe. In this talk, I will cover recent advances in our understanding of the intrinsic alignments of galaxies. While these alignments are typically regarded as a contaminant to weak gravitational lensing, I will also discuss how they might become a cosmological and galaxy evolution probe of their own in the near future.
Sep 2, Wednesday
12 noon (sharp, LBL DESI group lunch)
Anand Raichoor, newly arriving

Sep 8, Tuesday
1:10 pm (BCCP/Cosmology)
Omar Darwish, Cambridge
Reconstructing cosmic mass with new CMB lensing methods
Current and future high significance CMB lensing-galaxy cross-correlations will soon precisely probe the growth of structure and provide powerful tests for parameter tensions, non-Gaussianity, and modifications to LCDM and gravity. However, such cross-correlations are sensitive to CMB foreground contamination, and the resulting biases represent an important challenge for cosmological analyses. In the first part of this talk, I will describe new CMB lensing cross-correlation measurements and new techniques to mitigate foreground effects in lensing maps. In particular, I will present a tSZ cleaned cross-spectrum between Atacama Cosmology Telescope lensing and BOSS galaxies using a modified version of the standard quadratic estimator that retains most of the signal-to-noise. I will also discuss work on upcoming correlations with Advanced ACT CMB lensing maps (which can reach up to 100 sigma significance) and on further improvements to foreground mitigation. In the second part of this talk, I will turn to the three-dimensional large scale structure of the Universe probed by galaxy surveys. I will show how we can reconstruct the large-scale density field from galaxy modes using CMB lensing-inspired methods and use this reconstruction to improve constraints on local non-Gaussianity.
Sep 10, Thursday
4 pm (LBL)
Yacine Ali-Haimoud, NYU
"Hunting for Dark Matter in the Early Universe"
It is now well established that the dominant part of non-relativistic matter in the Universe is some substance which appears to be oblivious to any force but gravity. The nature of this dark matter remains a nagging puzzle, and several candidates remain in the running. For instance, dark matter might be a new particle, as light as an electron, which might weakly interact with standard particles. Or it could be partly made of primordial black holes as massive as many Suns, born in the very early Universe from the gravitational collapse of enhanced primordial fluctuations. In this talk, I will describe how one can try and tease out some of the properties of dark matter from the Cosmic Microwave Background (CMB), both through its frequency spectrum, and its angular fluctuations. After reviewing the basic physics underlying the CMB, I will highlight how it can constrain interacting particles and primordial black holes. If time allows, I will discuss what LIGO may be able to tell us about primordial-black holes.
Sep 15, Tuesday
1:10 pm (BCCP/Cosmology)
Ethan Nadler, Stanford/SLAC
The Faintest Galaxies and Their Dark Matter Halos
As luminous tracers of the smallest dark matter halos, ultra-faint dwarf galaxies offer a unique window into the physics of galaxy formation and dark matter. Our census of these extremely faint systems has drastically improved in recent years as a result of detailed searches in deep photometric datasets, including those from the Dark Energy Survey. In this talk, we describe recent advances in our understanding of these systems, focusing on their implications for 1) the galaxy--halo connection, reionization physics, and high-redshift galaxy formation, and 2) the microphysical properties of dark matter. We show that the lack of a cutoff in the observed abundance of ultra-faint galaxies yields among the strongest astrophysical constraints to date on the warmth, Standard Model couplings, and de Broglie wavelength of dark matter, and we discuss the implications of these constraints for particle models including sterile neutrinos and ultra-light axions.
Sep 16, Wednesday
12 noon (sharp, LBL DESI group lunch)
Andres Salcedo, OSU
Cosmological Forecasting with Cluster Cross-Correlations and Constraining Galaxy Assembly Bias in SDSS
Cluster weak lensing is a sensitive probe of cosmology, particularly the amplitude of matter clustering and matter density parameter. The main nuisance parameter in a cluster weak lensing cosmological analysis is the scatter between the true halo mass and the relevant cluster observable. We show that combining cluster weak lensing with the projected cluster-galaxy cross-correlation function and galaxy auto correlation function can break the degeneracy between cosmology and the cluster mass-observable relation to achieve tight, percent level constraints on the amplitude of matter clustering. For our fiducial scenario of combining these three observables measured over 0.3 - 30.0 Mpc/h, for clusters at z = 0.35-0.55, we forecast a 1.4% constraint on the amplitude of matter clustering while marginalizing over the scatter in the cluster mass-observable relation and all HOD parameters. I will present these and other results on cluster cosmology in the first section of the talk. In the second section of the talk I will discuss work on the connection between the properties and bias of haloes with their proximity to massive neighbors and more recent work on constraining the level of galaxy assembly bias in SDSS.
Sep 22, Tuesday
1:10 pm (BCCP/Cosmology)
Shivam Pandey, Penn
Precise constraints on cosmology and gas physics: small scales modeling using DES, ACT and Planck
Small scale correlations between the tracers of large scale structure (LSS) carry the majority of the information but are challenging to model due to complex astrophysics. The correlations constructed out of galaxy positions, galaxy shear, and Sunyaev-Zeldovich effect can be used to constrain these processes. The first half of the talk will be focussed on describing galaxy clustering and galaxy-galaxy lensing correlations down to scales of 4Mpc/h using an effective perturbation theory model. I will describe the validation of the model using the DES-like simulations and its applications to the imminent cosmology results from DES Year 3 data. The second half will focus on describing the cross-correlations between shear/galaxy-positions from DES Year 3 data with the Compton-y maps from ACT and Planck. I will describe the constraints on the evolution of the average thermal energy of the Universe, preliminary constraints on the pressure profile, and comparison with hydrodynamical simulations.
Sep 24, Thursday
4 pm (LBL RPM)
Vivian Miranda, Arizona
The Connected Universe: Relating Early, Intermediate and Late Universe with cosmological data
The standard model of cosmology is built upon a series of propositions on how the early, intermediate, and late epochs of the Universe behave. In particular, it predicts that dark energy and dark matter currently pervades the cosmos. Understanding the properties of the dark sector is plausibly the biggest challenge in theoretical physics. There is, however, a broad assumption in cosmology that the Universe in its earlier stages is fully understood and that discrepancies between the standard model of cosmology and current data are suggestive of distinct dark energy properties. Uncertainties on this hypothesis's validity are not usually taken into account when forecasting survey capabilities, even though our investigations might be obfuscated if the intermediate and early Universe did behave abnormally. In this colloquium, I propose a program to investigate dark energy and earlier aspects of our Universe simultaneously, through space missions in the 2020s in combination with ground-based observatories. This program will help guide the strategy for the future Rubin and Roman supernovae and weak lensing surveys. My investigations on how properties of the early and intermediate Universe affect inferences on dark energy (and vice-versa) will also support community understanding of how future missions can be employed to test some of the core hypotheses of the standard model of cosmology.
Sep 29, Tuesday
1:10 pm (BCCP/Cosmology)
Chun-Hao To, Stanford
Cosmological constraints from a joint analysis of cluster abundances, galaxy correlations, and weak gravitational lensing in Dark Energy Survey
Three cosmic tracer fields are measured from imaging surveys: galaxy density, weak gravitation lensing shear, and cluster density. The joint analysis of the auto and cross correlations of the first two fields, often referred to as the 3x2pt analysis, has become a popular and competitive cosmological test of the standard cosmological model. The abundances and spatial distributions of galaxy clusters, which are associated with the highest peaks in the matter density field, provide another powerful probe of cosmic structure formation and evolution; thus, the combination of cluster abundances and 3x2pt analysis is expected to yield precise cosmological constraints. In the first part of the talk, I will present a novel multi-probe cluster cosmology analysis, which focuses exclusively on large scales. This new cluster cosmology analysis yields competitive cosmological constraints while being robust against several systematics. I will describe the extensive validation of the measurements, modeling, and inferences using N-body simulations populated with galaxies. In the second part of the talk, I will present cosmological constraints from the first joint analysis of cluster abundances and auto/cross correlations of all three cosmic tracer fields measured from the first year of the Dark Energy Survey (DESY1). The talk will be concluded by a discussion on the implication of the result, potential improvements, and expected constraining powers in the up-coming DESY3 analysis and future wide imaging surveys.

October 2020
Oct 6, Tuesday
1:10 pm (BCCP/Cosmology)
Christina Kreisch, Princeton
Constraining Elusive Neutrino Properties Near and Far
Neutrinos remain an elusive component of the standard model, and constraining the sum of neutrino masses is a prominent goal in cosmology. But what if there are additional properties of this mysterious particle beyond the standard model? New physics in the neutrino sector might be necessary to address anomalies between different neutrino oscillation experiments. Intriguingly, it also offers a possible solution to the discrepant cosmological measurements of H_0. I will discuss our paper in which we delay the onset of neutrino free-streaming until close to the epoch of matter-radiation equality by introducing neutrino self-interactions in the presence of a non-vanishing sum of neutrino masses. Our analysis shows that it is possible to find radically different cosmological models that nonetheless provide excellent fits to the data, hence providing an impetus to thoroughly explore alternate cosmological scenarios. I will then discuss a large scale structure probe—cosmic voids—that can help us put constraints on the sum of neutrino masses. How neutrinos impact the scale at which voids cluster and the void correlation is sensitive to the tracers. The interplay of these neutrino signatures in the void abundance and clustering leaves a distinct fingerprint that could be detected with observations and potentially help break degeneracies between different cosmological parameters.
Oct 13, Tuesday
1:10 pm (BCCP/Cosmology)
Zack Li, Princeton
Discovery from Millimeter-Wave Surveys in the Next Five Years
We're producing some exciting data with high-resolution ground-based observations at 27 - 280 GHz, from experiments like ACT, SPT, and (soon) SO. I'll discuss CMB data analysis and how these experiments will probe dark matter physics. I'll also talk about the astrophysics one can learn from these experiments, since they double as deep surveys of radio galaxies and Galactic dust, in both temperature and polarization.
Oct 14, Wednesday
12 noon (sharp, LBL DESI group lunch)
Sihan (Sandy) Yuan, Harvard
Evidence for Galaxy Assembly bias in BOSS CMASS redshift-space 2PCF
We find the BOSS CMASS redshift-space 2PCF at small scale rejects the standard 5-parameter HOD, and strongly favors an extended HOD that incorporates both a concentration-based assembly bias and an environment-based assembly bias. The combination of the two assembly bias dependencies also seemingly alleviates the galaxy-galaxy lensing tension by predicting the lensing signal to within 1sigma of the observation. We suggest that the lensing tension can at least be partially explained by the lack of flexible galaxy-halo connection models and the lack of constraining power in the projected 2PCF.
Oct 15, Thursday
4 pm (LBL RPM)
Andrej Obuljen, Waterloo
Anisotropic assembly bias in theory, simulations and BOSS data
Clustering of matter on large scales provides an important source of information on key cosmological parameters. To extract this information we need to understand the relation between the tracers we observe and the underlying matter field. The clustering strength of halos and galaxies on large scales is linearly biased compared to the matter clustering. This linear bias mainly depends on halo mass and redshifts, though selections based on other scalar halo properties (age, spin, concentration etc.) show additional bias dependences — called assembly bias. Furthermore, non-scalar halo properties: shapes, velocity dispersion and angular momentum, are correlated with the large-scale tidal field. Selection effects that couple to these non-scalar halo properties can produce anisotropic clustering even in real-space and act as a contaminant to redshift-space distortion measurements, through an anisotropic assembly bias (AB). I will discuss our recent results on studying the halo AB using a large number of numerical simulations. Then I will present the first detection of the galaxy anisotropic assembly bias in BOSS DR12 galaxies. Finally, I will show other consequences and future prospects.
Oct 20, Tuesday
1:10 pm (BCCP/Cosmology)
Stephon Alexander, Brown
The Story of a Halo: Cosmic Inflation, Dark Genesis and Superfluid Halos
All matter, visible and dark, had to originate from some mysterious event in the early universe-baryogenesis and dark-genesis. This necessary physics goes beyond our standard cosmology and standard model of particle physics. In this colloquium I provide a pedagogical introduction to cosmic inflation, baryogenesis and argue the necessity of Chern-Simons theory in collaboration with the quantum dynamics of cosmic inflation (but not limited to it) to explain the coincidence between the density of dark and visible matter. A surprise regarding quantum coherence in halos awaits as a result.
Oct 21, Wednesday
12 noon (sharp, LBL DESI group lunch)
Ellen Hang, ROE
Clustering in the Legacy Survey and its imprint on the CMB
Large Scale Structures can leave various imprints on the Cosmic Microwave Background. Two main features come from the spatial and temporal perturbations of the CMB photon trajectory due to LSS: weak lensing and the Integrated Sachs-Wolfe effect. I will give a summary of our paper "Galaxy clustering in Legacy Survey and its imprint on the CMB" (arXiv: 2010.00466), where we use the Legacy Imaging Survey to extract cosmological information from the above effects in the redshift range 0 < z < 0.8. The Legacy Survey, covering about a third of the sky area and containing tens of millions of galaxies, is excellent for the purpose of cross-correlation study, although a difficulty is to obtain robust redshift distribution for those galaxies given very limited photometric bands. In this study, we use our own method to find competitive photometric redshifts using colour information and construct galaxy density maps in four tomographic redshift slices. These maps are cross-correlated in angular space with the Planck 2018 lensing convergence and temperature maps. By comparing our measurements with theoretical predictions from the standard Lambda-CDM model assuming Planck 2018 Cosmology, we find that interestingly the lensing amplitude is lower than expected, consistent with the recently announced weak lensing results from the KiDS Survey. This may add to the existing tension in the Omega_m-sigma_8 parameter space.
Oct 27, Tuesday
1:10 pm (BCCP/Cosmology)
Johannes Lange, UCSC
On the Cosmological Interpretation of Non-Linear Scales in BOSS and Beyond
The distribution of galaxies and matter in the Universe encodes a wealth of information about galaxies and cosmology. Particularly, measurements on non-linear scales are impacted by both galaxy physics and cosmology, making a cosmological interpretation more difficult. At the same time, measurements on non-linear have a higher precision than measurements on larger linear and quasi-linear scales. In this talk, I will present new, more robust analysis techniques for the cosmological study of non-linear scales. Additionally, I will discuss new cosmological interpretations of the non-linear and highly non-linear matter and galaxy distribution in the Baryon Oscillation Spectroscopic Survey (BOSS) LOWZ galaxy sample. Specifically, I will present new constraints on the growth-rate of the Universe via the study of the redshift-space galaxy correlation function. Additionally, I will discuss new findings on the mass and scale dependence of the galaxy-galaxy lensing tension with respect to CMB constraints. Finally, I will outline future directions in the study of non-linear scales.

November 2020
Nov 3, Tuesday
1:10 pm (BCCP/Cosmology)
NO Talk

Nov 10, Tuesday
1:10 pm (BCCP/Cosmology)
Ana Diaz Rivero, Harvard
Flow-based likelihoods for non-Gaussian inference
We investigate the use of data-driven likelihoods to bypass a key assumption made in many scientific analyses, which is that the true likelihood of the data is Gaussian. In particular, we suggest using the optimization targets of flow-based generative models, a class of models that can capture complex distributions by transforming a simple base distribution through layers of nonlinearities. We call these flow-based likelihoods (FBL). We analyze the accuracy and precision of the reconstructed likelihoods on mock Gaussian data, and show that simply gauging the quality of samples drawn from the trained model is not a sufficient indicator that the true likelihood has been learned. We nevertheless demonstrate that the likelihood can be reconstructed to a precision equal to that of sampling error due to a finite sample size. We then apply FBLs to mock weak lensing convergence power spectra, a cosmological observable that is significantly non-Gaussian (NG). We find that the FBL captures the NG signatures in the data extremely well, while other commonly-used data-driven likelihoods, such as Gaussian mixture models and independent component analysis, fail to do so. This suggests that works that have found small posterior shifts in NG data with data-driven likelihoods such as these could be underestimating the impact of non-Gaussianity in parameter constraints. By introducing a suite of tests that can capture different levels of NG in the data, we show that the success or failure of traditional data-driven likelihoods can be tied back to the structure of the NG in the data. Unlike other methods, the flexibility of the FBL makes it successful at tackling different types of NG simultaneously. Because of this, and consequently their likely applicability across datasets and domains, we encourage their use for inference when sufficient mock data are available for training.
Nov 17, Tuesday
1:10 pm (BCCP/Cosmology)
Jahmour Givans, OSU
Modeling of the Lyman-alpha forest and weak lensing detector systematics
The Lyman-alpha forest is the primary cosmological tracer in the post-reionization Universe at 2 < z < 6. Many attempts have been made to model the Lyman-alpha flux fluctuation power spectrum using perturbation theory, but most of these either only model large (linear) scales or rely on fitting functions to capture small-scale (nonlinear) behavior. In the first part of this talk, I will present my work on using perturbation theory to model flux fluctuations at second order. I then show how this model refines our understanding of the importance of one BAO systematic, namely, early Universe streaming velocity between dark matter and baryons. In the second part of this talk, I will discuss my work on modeling infrared detector effects that are sources of systematics for Roman Space Telescope flight candidates. I then show how well our modeling performs against data and explain what it means for future weak lensing measurements.
Nov 18, Wednesday
12 pm (DESI talk)
Justin Myles, Stanford
Leveraging Spectroscopy for Photometric Galaxy Survey Science
Large photometric galaxy surveys enable a broad range of science applications in astrophysics and cosmology, but suffer from challenges arising from the difficulty in constraining galaxy redshift. I will discuss two projects that leverage spectroscopic observations for a small subset of galaxies observed in wide field surveys to improve the utility of photometric datasets for cosmological experiments. First, I will show results using archival spectroscopy of redMaPPer galaxy clusters to measure the impact of projection effects on these clusters and comment on how this measurement relates to the DES Year 1 cluster cosmology results. Second, I will show the new methodology of and preliminary results for the DES Year 3 weak lensing source galaxy redshift calibration. Finally, I will discuss future applications of DESI data for these science goals, including active spare fiber proposals.
Nov 20, Friday
10 am INPA "double feature" (2x 30 min talks)
Anton Baleato Lizancos (Cambridge), and Utkarsh Giri (Perimeter Institute of Theoretical Physics)
“Understanding biases to CMB lensing and delensing on the road to precision science” (Anton)
For cosmologists, CMB lensing can be both a blessing and a nuisance. It's a nuisance because it generates spurious B-mode polarisation which obscures the highly-sought-after signal from inflationary gravitational waves, but it's a blessing because it can be used to reconstruct maps of the projected matter distribution of the Universe, from which any physics affecting the growth of cosmic structure can be constrained. In this talk, I will focus on systematics that need to be addressed in order to harness the full statistical power of upcoming CMB experiments and make progress in both of these exciting areas. In the first part of my talk, I will briefly review the ways in which extragalactic emission from galaxies and clusters can bias CMB lensing reconstruction power spectra and cross-correlations with other tracers of the matter distribution. I will then present ongoing work on a novel approach where we model these biases analytically as a function of experimental characteristics, enabling improved physical insight, a quantification of theoretical uncertainties and potentially opening the door to improved mitigation methods. In the second part of the talk, I will explain how the lensing contamination to CMB B-modes can be removed — what is known as delensing — in order to facilitate searches for inflationary gravitational waves, and describe limitations of the commonly-used "template" approach to delensing. I will then briefly summarize preparatory efforts to delens data from the upcoming Simons Observatory. Finally, I will conclude by discussing biases affecting the procedure (and how to mitigate them) when lensing is reconstructed internally from the CMB itself, and in the alternative scenario where the CIB is used as a tracer of the matter.

“Exploring kSZ velocity reconstruction with N-body simulations and the halo model” (Utkarsh)
KSZ velocity reconstruction is a recently proposed method for mapping the largest-scale modes of the universe, by applying a quadratic estimator v̂ to the small-scale CMB and a galaxy catalog. We implement kSZ velocity reconstruction in an N-body simulation pipeline and explore its properties. We find that the reconstruction noise can be larger than the analytic prediction which is usually assumed. We revisit the analytic prediction and find additional noise terms that explain the discrepancy. The new terms are obtained from a six-point halo model calculation, and are analogous to the N(1) and N(3/2) biases in CMB lensing. We implement an MCMC pipeline which estimates fNL from N-body kSZ simulations and show that it recovers unbiased estimates of fNL, with statistical errors consistent with a Fisher matrix forecast. Overall, these results confirm that kSZ velocity reconstruction will be a powerful probe of cosmology in the near future, but new terms should be included in the noise power spectrum.
Nov 20, Friday
12 pm (INPA)
Liang Dai,UCB
A New Window Into the Universe: Gravitational Waves From Compact Binary Coalescence
Detection of chirping gravitational waves (GWs) at ground-based laser interferometry observatories LIGO and Virgo have uncovered a population of compact binary mergers. Forthcoming observing runs with upgraded sensitivity and more observatories joining the network will tremendously increase the number of source systems, which will shed light on their astrophysical origin and enable to exploit those events as cosmological probes. I will present independent efforts by the IAS group to analyze the publicly available LIGO/Virgo data and report newly discovered GW events in addition to what experimental collaborations have reported. I will highlight several original and crucial data analysis methodologies we have developed for template matching, noise characterization and parameter estimation. In addition, I will give outlook on gravitational lensing of cosmological GW sources as expected from forthcoming observations and envisage its applications. I will explain our new findings of how wave propagation effects, measurable with GWs but unfeasible with usual electromagnetic sources, can allow extraction of unique information to reconstruct the lens or to probe non-luminous sub-galactic dark matter structures, thereby deepening our understanding of the matter distribution in the Universe.
Nov 24
1:10 pm (BCCP/Cosmology)

December 2020
Dec 1, Tuesday
1:10 pm (BCCP/Cosmology)
Yun-Ting Cheng, Caltech
Cosmology and Astrophysics with Intensity Mapping
Intensity mapping (IM) has emerged as a promising tool to study the high redshift universe and the faint, diffuse extragalactic populations. Without resolving individual galaxies, IM measures the integrated light from all sources and uses that to statistically probe the emission properties of the sources as well as the underlying large-scale structure they trace. In this talk, I will cover several topics on intensity mapping technique. First, I will introduce line intensity mapping (LIM), which probes the 3D large-scale structure of the universe, and a [C II] LIM experiment, TIME, that I am currently working on. Next I will talk about two recent projects on studying extragalactic background light (EBL), the aggregate emission from all extragalactic sources throughout cosmic time. I will present our latest stacking analysis results on probing the extended stellar halo with CIBER, a sounding rocket experiment that measures the near-IR EBL. Finally, I will conclude with future outlook for IM using SPHEREx, an upcoming all-sky near-infrared spectro-imaging survey.
Dec 16, Wednesday
12 noon (sharp, LBL DESI group lunch)
Mehdi Rezaie, OSU
Robust Measurements of the Large-Scale Clustering of Galaxies and Quasars
Wide-area galaxy surveys, such as the Rubin Observatory and DESI, along with high-resolution CMB experiments, such as the Simons Observatory and CMB-S4, will provide a massive amount of data to probe the initial conditions of the Universe. However, observational systematics pose a multifaceted challenge as galaxy surveys aim at probing sparser and fainter samples out to higher redshifts. Standard treatment methods are limited by their assumptions of linearity and improving them is a crucial step for the full exploitation of galaxy clustering and CMB lensing in the era of DESI and CMB-S4. In this talk, I will present a novel cleaning approach for galaxy clustering measurements. I will give a summary of our paper "Improving galaxy clustering measurements with deep learning: analysis of the DECaLS DR7 data" MNRAS (2020), where the method has been developed, validated, and applied to the photometric data from the DESI Legacy Imaging Surveys Data Release 7 and simulations. Then, I will elaborate on how we have enhanced the method to unlock a robust measurement of the local-type primordial non-Gaussianity with the final sample of spectroscopic quasars from eBOSS.

January 2021
Jan 12, Tuesday
4:00 pm (LBL RPM)
Digvijay Wadekar, NYU
“Accelerating analysis of cosmological surveys with novel analytic methods and machine learning”
In order to infer cosmological parameters from data of upcoming surveys like DESI, we will use summary statistics such as the power spectrum. An accurate estimate of their covariance matrix is crucial for the inference analysis. The traditional process of obtaining the covariance involves thousands of expensive mock simulations. I will present a novel analytic approach to calculate the covariance which is faster by more than four orders of magnitude. I will demonstrate the validation of our analytic approach with an analysis of the BOSS DR12 data and also show that it helps reduce the systematic error budget of cosmological constraints, thus making our approach useful for upcoming high-precision surveys like the Rubin observatory and DESI.
In the second part of my talk, I will present machine learning methods to emulate expensive hydrodynamical simulations and make cheap and accurate synthetic catalogs, which are needed for modeling non-linear scales in galaxy and line intensity mapping surveys.
Jan 14, Thursday
4:00 pm (LBL RPM)
Nandita Khetan, Gran Sasso
“Cosmology in the multi-messenger era”
The talk will present my PhD project research which focuses on advancing the standardization of various transients to be used as cosmological probes and the evaluation of the Hubble constant (H0). With SN Ia, I will present interesting results coming from a recent work where I used an alternate way to calibrate SN Ia based on the surface brightness fluctuations (SBF) method. Besides SNe Ia, I explored other exotic/new transients like Superluminous supernovae, Kilonovae and Gravitational waves as distance indicators. In particular, I worked on SLSNe in rest frame UV wavelengths to find peak luminosity correlations with light curve properties. I participated in a project exploring KNe as a standard candle to perform independent measurements of H0. I am currently working on the prospects of calibrating SNe Ia with GW distances measured from future GW detectors. I will briefly present these cosmological probes and discuss their future perspectives.
Jan 19, Tuesday
1:10 pm (LBL RPM and BCCP/Cosmology)
Sihan (Sandy) Yuan, Harvard
Tackling the challenges of galaxy-dark matter connection modeling and secondary bias
Modeling galaxy-dark matter connection is essential in deriving unbiased cosmological constraints from galaxy clustering observations. We show that a more physically motivated galaxy-dark matter incorporating secondary biases can result in more accurate predictions of galaxy clustering, and that it significantly reduces the tension in galaxy lensing. We further present progress in building a galaxy-dark matter connection framework that is rich in features and highly efficient in evaluation, enabling more robust cosmological analyses with upcoming DESI data.
Jan 22, Friday
12:00 pm (LBL RPM INPA)
Tucker Elleflot, UCSD
Multiplexed Readout of Transition Edge Sensors for CMB Polarization Experiments
The polarization of the Cosmic Microwave Background (CMB) provides a valuable means to study the very early universe and high energy physics beyond the standard model. Remarkable experimental progress has been made on this front in the past decade. Modern experiments employ as many as O(10,000) Transition Edge Sensor (TES) bolometers and highly multiplexed readout systems, all operating below the photon noise level. My research has focused on the development of the sensors and multiplexing systems for CMB experiments. I will first describe my contributions to TES characterization for the POLARBEAR-2 experiment, emphasizing a specific systematic effect created by the multiplexing system. Next I will discuss my current research: taking the lessons learned from POLARBEAR-2 to develop an even higher performance multiplexing system for the next generation of CMB experiments such as CMB-S4 and LiteBIRD. I will end by noting potential applications of this work to dark matter direct detection experiments using TES calorimeters.
Jan 26, Tuesday
1:10 pm (LBL RPM and BCCP/Cosmology)
Noah Weaverdyck, Michigan
Controlling Systematics in Large-Scale Structure Surveys
Large-scale structure (LSS) surveys have exploded in size over the last few decades, cataloguing the locations and shapes of hundreds of millions of galaxies. The unprecedented precision enabled by such datasets puts extraordinary demands on the control of systematic errors. In this talk, I will discuss how extracting information from LSS surveys is complicated by systematics that enter the survey selection function, outline several approaches to address these systematics, and highlight important lessons for upcoming surveys.
Jan 29, Friday
12:00 pm (LBL RPM and INPA)
Joe DeRose, UCB/UCSC
“Models of the Non-Linear Universe for Precision Cosmology”
Imaging and redshift surveys of galaxies and high resolution observations of the CMB promise to shed light on the physical nature of dark matter and dark energy in the coming decade. One of the main factors limiting the precision and accuracy of cosmological constraints coming from these measurements will be our understanding of how non-linear structure forms in our universe. In this talk I will present a roadmap for leveraging cosmological simulations to improve this understanding. First, I will discuss recent progress on combining perturbative models of structure formation with N-body simulations in order to obtain highly optimized predictions for real-space galaxy clustering and weak lensing, and describe how similar models might be used to confront a variety of observations. I will then show how realistic models of galaxy formation and evolution combined with contemporary machine learning techniques can be used as robustness tests for complex cosmological analyses, with case studies from the Dark Energy Survey and the Dark Energy Spectroscopic Instrument.

February 2021
Feb 2, Tuesday
1:10 pm (LBL RPM BCCP/Cosmology)
Anton Baleato Lizancos, Cambridge
Fundamental Physics with CMB Lensing and Delensing: the Good, the Bad and the Systematics
Gravitational lensing of CMB photons by the matter distribution of the Universe can be both a blessing and nuisance. It's a blessing because of the way it can be harnessed to map the structures responsible for the deflections, and from this, constrain any physics affecting the growth of cosmic structure, such as the sum of the neutrino masses or dark matter. But lensing is also a nuisance because it generates B-mode polarization which obscures the highly-sought-after primordial signal associated with gravitational waves generated during cosmic inflation, our most accessible portal to physics near the GUT scale. In this talk, I will focus on key systematic effects that need to be controlled in order to harness the full potential of the Simons Observatory (SO), CMB-S4, and other upcoming experiments to make progress in these exciting areas.
In the first part of my talk, I will briefly review the ways in which emission from galaxies and clusters can bias power spectra and cross-correlations of CMB lensing reconstructions, and describe our ongoing efforts to understand these biases analytically. Then, in the second part, I will explain how the lensing contamination to CMB B-modes can be removed — what is known as delensing — and discuss our recent findings regarding the performance of different delensing methods. I will also summarize preparatory work to delens SO data, and highlight biases to watch out for (and how to mitigate them) when the matter proxy used for delensing is either the cosmic infrared background or a lensing reconstruction derived from the CMB itself.
Feb. 5, Friday
12:00 pm (INPA)
Zack Li, Princeton
Enabling New Views of the Early Universe from the Atacama in the Next Five Years
We're producing some exciting Cosmic Microwave Background data with high-resolution, ground-based observations at 27 - 280 GHz, from experiments like ACT, SPT, and (soon) SO and CMB-S4. I'll discuss present and future challenges for CMB data analysis, and show results from integrating Planck data analysis with the Simons Observatory power spectrum pipeline. I'll also talk about prospects for these surveys to use the early Universe to detect the particle nature of dark matter, and briefly introduce a theory code intended for machine learning.
Feb 9, Tuesday
1:10 pm (BCCP/Cosmology)
Niall Jeffrey, ENS
High-dimensional likelihood-free inference: weak gravitational lensing
In many cosmological inference problems, the likelihood is unknown or intractable, which necessitates approximations and assumptions that can lead to incorrect inference of cosmological models and parameters. Likelihood-free inference methods can rigorously estimate posterior distributions using forward modelling of mock data with arbitrary non-linear summary statistics. I will present the first likelihood-free cosmological inference with galaxy weak lensing data using neural data compression of Dark Energy Survey (DES) SV map summary statistics. We explore combinations of the power spectra, peak counts, and higher-order statistics of the lensing mass map using deep convolutional networks. I will discuss extending likelihood-free inference to high-dimension, presenting "marginal flows" and "Moment Networks". Many cosmological inference problems can be cast in this framework, and I will introduce preliminary applications in galaxy weak lensing and the CMB analysis with phase-harmonic generative foregrounds. [ArXiv:2009.08459 & 2011.05991]
Feb 16, Tuesday
1:10 pm (BCCP/Cosmology)
Kazuyuki Akitsu, IPMU
The intrinsic alignment as a new cosmological probe
Upcoming galaxy imaging surveys will measure billions and billions of galaxy shapes to probe the weak lensing effect. However, observed galaxy shapes are affected by not only lensing but also surrounding matter distribution around galaxies, known as the intrinsic alignment (IA). Although the IA has been considered as a contaminant to the weak lensing signal, the IA itself potentially has a wealth of cosmological information given that it has a physical origin. In order to use the IA as a precision cosmological tool, it is important to understand the relation between the alignment strength and the underlying matter distribution, which is an analogous to the galaxy bias but less investigated than it. I will present the dependence of the alignment strength on halo mass and redshift obtained from a tidal separate universe simulation, which is an extension to the separate universe simulation. We also found the secondary dependence of the alignment strength on halo concentration, which can be regarded as“shape assembly bias”. Finally I will discuss the IA can probe the angular-dependent primordial non-Gaussianity (PNG) of local type, which cannot be explored by number density tracers. Using N-body simulations, we demonstrate the angular-dependent PNG induces the scale-dependent bias in the IA, just as the angular-independent PNG leads to the scale-dependent bias in the galaxy number density correlation. Through this scale-dependent bias in the IA, future galaxy surveys are potentially capable of constraining the angular-dependent PNG better than CMB experiments.
Feb 23, Tuesday
1:10 pm (BCCP/Cosmology)
Ian McCarthy, Liverpool
The structure (and substructures) of dark matter haloes
In this two-part talk I will address two pressing questions concerning the nature of dark matter haloes: i) what is the sensitivity of dark halo structure to the initial conditions of the universe?; and ii) how can we distinguish between a scenario where low-mass dark matter substructures (e.g., in the Milky Way) are absent vs. one where they are just not efficient at forming stars?
In terms of the first question, nearly three decades of work based on cosmological N-body simulations suggests that dark matter haloes have a self-similar form, with the density distribution being reasonably well represented by an NFW form and the phase-space profile being a nearly pure power law. The apparent insensitivity of this result to (some) variations in the initial conditions and to the expansion history of the universe suggest that it may be an attractor solution that is generic to CDM-based cosmologies. However, using a new suite of simulations we will show that, in fact, the structure of dark matter haloes retains a clear memory of the initial conditions of the universe and that the NFW form and power law phase space profiles are only (approximately) true for "CMB-normalised" cosmologies. In principle, this means we can extract information about the primordial power spectrum from the observed structure of dark haloes.
In the second part of the talk, we propose a new method for detecting the presence of substructures orbiting galaxies like the Milky Way, namely via the fluctuations they source in the circumgalactic medium (CGM). In short, the CGM is gravitationally compressed in the presence of dark substructures, leading to a local enhancement in density and temperature. We calculate the magnitude of this effect using a variety of tools (of varying sophistication) and propose observational methods for extracting this information.

March 2021
Mar 2, Tuesday
1:10 pm (BCCP/Cosmology)
Alex Hall, Edinburgh
Density and transverse velocity in the local Universe as probes of cosmology
I will discuss two novel probes of the large-scale matter distribution, and how they may be used to improve the scientific exploitation of upcoming dark energy surveys. In the first part of the talk I will discuss the prospects of using precision astrometry (from, e.g. Gaia) to measure the transverse velocities of galaxies at cosmological distances in real time. I will describe a new CMB-inspired statistical formalism which allows noisy proper motion measurements to be stacked over the full sky, and discuss the various sources of bias and variance which one must account for to measure cosmological parameters this way. In the second part of the talk I will discuss the ways in which our local environment affects measurements of large-scale structure, and examine a recent claim that our own local density fluctuation biases weak lensing power spectra at a level significant for Stage-IV surveys. I will describe recent progress in computing conditional statistics in cosmology, present the implied biases, and discuss how our local density may be used as a consistency test of cosmological models.
Mar 9, Tuesday
1:10 pm (BCCP/Cosmology)
Solene Chabanier, LBL
Neutrino cosmology with the Lya forest
Neutral hydrogen in the Intergalactic Medium (IGM) produces a collection of Lya absorptions, called the Lya forest, seen in the spectra of background objects. According to the common paradigm, neutral hydrogen in the IGM evolves from primordial density fluctuations in a low density and photo-ionized environment. It therefore acts as a direct tracer of dark matter. However, it also implies that temperature and density are tightly coupled, giving rise to degeneracies between parameters describing either cosmology or the IGM thermal history. The Lya forest 1D power spectrum (P1D) is sensitive to clustering on small scales, and as such to the smoothing scale of relativistic particles. It has been used to put the strongest constraints on the sum of the neutrino masses. To infer cosmological constraints and to test our models at the percent level accuracy, the measurements need to be compared to state-of-the-art hydrodynamical simulations. We also need to refine our understanding of the impact of galactic feedbacks on the IGM temperature.
I will present the analysis that leads to the most recent SDSS P1D measurement. As the current uncertainties are at the percent level, and will even shrink further in the DESI era, the P1D becomes sensitive to complex mechanical effects known as AGN feedback. I will present the realization and analysis of the Horizon suite of simulations, among which Horizon-AGN and Extreme-Horizon, to evaluate the impact of AGN feedback on the P1D and prevent degeneracies with neutrino effects to give the the most up-to-date constraints on the mass of active neutrinos. Finally, I will present unexpected results from the Extreme-Horizon simulation on the formation of massive compact galaxies at high redshifts.
Mar 11, Thursday
4 pm (LBL RPM)
David Weinberg, OSU
“Cosmology Past, Present, and Future”
I will give a broad overview of the current state of observational cosmology, with historical context and an eye to the future. Developments over the past three decades have led to a standard cosmological scenario that is remarkably successful at explaining a wide array of high precision measurements. However, this scenario leaves several big questions at best partially answered. What is dark matter? Why is the expansion of the universe accelerating? What is the physics of inflation and the origin of the universe? I will discuss observational tensions that hint at cracks within the standard model, and I will discuss ongoing and upcoming experimental efforts that aim at order-of-magnitude increases in measurement precision with the hope of revealing vital new clues about the physics of the cosmos.
Mar 16, Tuesday
1:10 pm (BCCP/Cosmology)
Henry Grasshorn Gebhardt, JPL
“SuperFaB: a fabulous code for Spherical Fourier-Bessel decomposition”
The spherical Fourier-Bessel (SFB) decomposition is a natural choice for the radial/angular separation that allows optimal extraction of cosmological information from large volume galaxy surveys. In this talk, I will develop intuition for the SFB power spectrum and introduce a SFB power spectrum estimator that allows the measurement of the largest angular and radial modes with the next generation of galaxy surveys. The code measures the pseudo-SFB power spectrum, and takes into account mask, selection function, pixel window, and shot noise. By imposing boundary conditions at the minimum and maximum radius encompassing the survey volume, the estimator does not suffer from the numerical instabilities that have proven challenging in the past. The estimator is demonstrated on simplified Roman-like, SPHEREx -like, and Euclid -like mask and selection functions. For intuition and validation, I also explore the SFB power spectrum in the Limber approximation.
Mar 23, Tuesday
spring break, no talk

Mar 30, Tuesday
1:10 pm (BCCP/Cosmology)
George Efstathiou, Cambridge
Planck, LCDM & H0

April 2021
Apr 6, Tuesday
1:10 pm (BCCP/Cosmology)
Apr 13, Tuesday
1:10 pm (BCCP/Cosmology)
Alice Pisani, Princeton
Unraveling the Universe with cosmic voids
Modern surveys provide access to high-quality measurements on large areas of the sky, sampling the galaxy distribution in detail also in the emptiest regions, voids. Void cosmology is becoming an increasingly active sector of galaxy clustering analysis: by measuring void properties, such as density profiles or void number counts, it is possible to constrain cosmological parameters. Cosmic voids are particularly sensitive to the properties of dark energy and neutrinos, and are a powerful tool to test modifications of the laws of general relativity. Studying voids provides a novel perspective to unravel the unsolved mysteries of our Universe.
In this talk I introduce cosmic voids as a tool for cosmology, I present recent results—with a particular focus on the advantages of calibration-free approaches—and I discuss future developments in the field.
Apr 20, Tuesday
1:10 pm (BCCP/Cosmology)
CANCELLED: Satya Gontcho A Gontcho, LBL
May 25, Tuesday
12:30 pm (LBL RPM)
Valerie Domcke, CERN
"Cosmology with Axion-Like Particles"
Axion-like particles may play a key role in early universe cosmology. They are naturally equipped with the right properties to explain cosmic inflation, can dynamically explain the smallness of the electroweak scale, may be involved in the generation of the matter antimatter asymmetry and are promising dark matter candidates. In this talk I discuss a generic but previously overlooked particle particle production mechanism, resulting in the dual production of gauge fields and fermions induced by axion-like particles. I will discuss how this crucially impacts all of the cosmological scenarios mentioned above and may be probed with upcoming gravitational wave detectors.

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