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 .
in room 131 Campbell Hall. . Please don't bring your lunch (it is hard to keep this room clean; this is a change).
Please mail Joanne Cohn 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. If the talk is on ZOOM, members of the Berkeley Astronomy/Physics and Cosmology communities can email Joanne Cohn for information.

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:

January 2023
Jan. 17, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Misha Ivanov, IAS
131 Campbell
Probing Cosmic Inflation and Dark Matter with Galaxy Surveys 
The distribution of galaxies on large scales is a sensitive probe of cosmological physics. In particular, the structure of this distribution depends on properties of dark matter and the dynamics of the early universe. Understanding this dependence, however, is a challenging task because the observed galaxy distribution is modulated by a variety of non-linear effects. I will present new theoretical tools that have allowed for a systematic analytic description of these effects. These tools play a central role in a new program of extracting cosmological information from galaxy surveys. I will share some results of this program from several independent analyses of the public data from the Baryon acoustic Oscillation Spectroscopic Survey. These results include new limits on non-linear interactions during cosmic inflation, parity violation in the cosmological initial conditions, and novel constraints on non-minimal dark matter models. 
Jan. 24, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Jordan Mirocha, JPL
131 Campbell
A new era in studies of the cosmic dawn: constraints from galaxy surveys, redshifted 21-cm signals, and the extragalactic background light
Our knowledge of the high redshift Universe has grown considerably in the last decade, thanks in large part to galaxy surveys conducted with Hubble, Planck's constraints on the CMB optical depth, and dedicated ground-based studies of Lyman-alpha emitters and quasars. Several groups have shown that relatively simple galaxy formation models, in which star formation is assumed to be inflow-driven and feedback-regulated, are able to satisfy all of these measurements without much tuning. However, the first wave of constraints from the James Webb Space Telescope pose a clear challenge to this simple picture of high-z galaxy evolution. In this talk, I will summarize the most surprising aspects of these early JWST constraints and explore several potential solutions. Then, I'll describe a suite of complementary constraints of the high-z Universe, including HERA's limits on the 21-cm power spectrum at >100 MHz and the 78 MHz absorption trough detected in the sky-averaged spectrum by EDGES in 2018, and how to understand these measurements in the context of Hubble (and now JWST) galaxy surveys. Finally, I will briefly discuss the near-future prospects for validating 21-cm measurements in cross-correlation with Roman's high-latitude survey (late 2020s), and what we can expect to learn about the high-z Universe from NASA's upcoming SPHEREx mission (2025 launch).
Jan. 31, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Enrique Paillas, Waterloo
131 Campbell
Unveiling ΛCDM with summary statistics beyond the power spectrum
Large-scale structure encodes secrets about the underlying nature of the Cosmos, including its expansion history and the rate at which structure grows. Two-point statistics, such as the galaxy power spectrum, provide a complete statistical description for Gaussian density fields. However, the late-time density field we observe at small scales is highly non-Gaussian due to non-linear gravitational evolution, and higher-order summary statistics are required to capture all of the information. I will discuss different ways in which we can decode this information, focusing on novel clustering techniques that are currently being applied in BOSS and DESI.

February 2023
Feb. 7, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Brant Robertson, UC Santa Cruz
131 Campbell
First Results on the Earliest Galaxies from the JADES/NIRCam Program
The JWST Advanced Deep Extragalactic Survey (JADES) is a collaboration of the NIRCam and NIRSpec GTO teams pooling over 750 hours of JWST time to conduct an ambitious study of galaxy evolution in the Great Observatories Origins Deep Survey GOODS-S and GOODS-N fields. Here, we report on exciting first results from the JADES/NIRCam observations about discoveries in the distant (z>10) universe that provide new insight into the process of early galaxy formation and cosmic reionization. We discuss how our new constraints on star formation and galaxy growth at the very earliest times will revise our picture for how the first galaxies form and evolve.
Feb. 7, Tuesday
4:00 pm (LBL RPM)
Steve Choi , Cornell
LBL 50-5132 plus ZOOM
“Probing Fundamental Physics by Mapping the Millimeter and Submillimeter Sky”
Cosmology has transformed from a field of speculation to precision science as a result of a wealth of data from sensitive instruments. In particular, precise observations of the cosmic microwave background (CMB) have revolutionized our understanding of the Universe. Despite the success of the standard model of cosmology (ΛCDM) in describing much of the cosmos with just six parameters, many fundamental questions remain unresolved. Are there primordial gravitational waves? Are there new light relic particles? How will the current cosmological tensions be resolved? Improved mapping of the millimeter and submillimeter sky will help address these questions. I will highlight recent results from the Atacama Cosmology Telescope (ACT), and describe how the new ACT maps will advance our understanding of the Universe beyond Planck. I will also present recent progress on CCAT-prime and Simons Observatory that are paving the way for CMB-S4 in pursuit of next-generation cosmology.
Feb. 9, Thursday
12:30 pm (Astronomy Colloquium)
Joel Leja, Penn State
131 Campbell
Powered by Rainbows, Stars, and Machines: A Rapid and Inexorable AI Revolution in Galaxy Evolution
What is the story of galaxy formation -- when, where, and how did these vast cosmic ecosystems assemble? How did they build-up their heavy elements, assemble their stellar populations, and grow their supermassive black holes? Armed with ultra-deep, ultra-broad photometric and spectroscopic surveys of the universe, we are in a better position to answer these questions than ever before. Yet these new data breathe new life into long-standing challenges in extragalactic observations: how do we simultaneously model all of these processes at once? In this talk I present recent progress made using the high-dimensional modeling of galaxy SEDs and galaxy populations. By including flexible, model-agnostic prescriptions for the complex physical processes in galaxies, we have produced qualitatively new and quantitatively distinct solutions for simple galaxy properties. These new solutions solve old problems, for example different measurements of the cosmic star formation rate density, or discrepancies between galaxy star formation rates and halo mass accretion rates. However, to date these models have only been applied to small samples due to their high computational requirements. I will present rapidly accelerating research into machine learning techniques which dramatically speed up inference, by factors of thousands to millions. I end by describing the near future where lightning-fast ML-powered inference techniques and massive large-scale surveys promise to open up entirely new research directions in extragalactic astronomy -- for example, modeling the formation histories of tens millions of galaxies simultaneously, using unresolved galaxies as laboratories for exotic phases of stellar evolution, and accurately modeling their complex spatial structures.
Feb. 9, Thursday
4:00 pm (LBL RPM)
Sara Simon , Fermilab
LBL 50-5132 plus ZOOM
“Probing Fundamental Physics by Mapping the Millimeter and Submillimeter Sky”
The cosmic microwave background (CMB) provides an unparalleled opportunity to advance our understanding of the fundamental physics of the universe. Recent and ongoing experiments have contributed to our understanding of neutrinos, dark energy, and dark matter through measurements of large-scale structure imprinted on the CMB and constrained the conditions in the early universe, tightly restricting inflationary and other cosmological models through measurements of CMB polarization. Next-generation CMB experiments like CMB-S4 will further constrain the sum of the neutrino masses and the number of relativistic species, expand our understanding of dark energy and dark matter, and set new constraints on cosmological models describing the first moments of the universe. The polarization in the CMB is faint, so future experiments must be at least an order of magnitude more sensitive than current experiments. These unprecedented levels of sensitivity require improved systematic mitigation via modeling and novel calibration techniques. I will give an overview of the science achievable with these next-generation experiments and the advances in technology that are critical for its this leap in performance.
Feb. 14, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Lloyd Knox, Davis
131 Campbell
Searching for Cosmological Model Solutions to the Hubble Constant Problem
Distances to redshifts much less than 1, as determined by Cepheid-calibrated supernovae, are significantly less than predicted by LCDM when calibrated with other highly-informative cosmological observations such as CMB temperature and polarization maps. This 5 sigma discrepancy might be due to an as-yet-discovered systematic error or a failure of LCDM. In this talk I'll present a scaling transformation that leaves all dimensionless cosmological observables (such as CMB maps) unchanged, while boosting all relevant rates (including the expansion rate). I'll also describe our search for a viable cosmological model that can exploit this transformation. To date, these efforts run into conflicts with observed helium abundances and also with the standard theory of big bang nucleosynthesis. Time permitting, I'll also have some brief remarks on our search for ``early dark energy'' solutions and modified-recombination solutions to the Hubble constant problem.
Feb. 16, Thursday
4 pm (RPM seminar)
Clara Verges, Harvard
LBL 50-5132
A window on the Universe with the next-generation of millimeter-wave telescopes
Cosmology has experienced a considerable surge in the past thirty years, and is now well established as a precision science. While the standard cosmological model provides an effective description of the observed Universe, many fundamental questions remain unresolved. From shedding light on the very first fractions of second after the Big Bang to unveiling the dark Universe and looking for exotic physics, the Cosmic Microwave Background continues to be a unique probe for fundamental physics. The next generation of CMB polarisation observatories, embodied by CMB-Stage 4 for ground observations, will explore this window into the Universe in an unprecedented way, enabling breakthrough science. I will review how current experiments such as the BICEP/Keck telescopes pave the way for this next stage by developing efficient technologies and observing strategies, and by sharpening constraints on theoretical models. I will then discuss the technological challenges that the CMB community must meet to ensure the scientific success of future experiments.
Feb. 21, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Andrei Cuceu, OSU
131 Campbell
New constraints on the cosmic expansion rate at redshift 2.3 from the Lyman-α forest
The Lyman-alpha (Lya) forest is currently one of the most powerful probes of large-scale structure at high redshift (z > 2). This is made possible by large spectroscopic surveys that measure hundreds of thousands of quasar spectra, such as the Baryon Oscillation Spectroscopic Survey (BOSS) and its successor, extended BOSS (eBOSS). Over the last decade, 3D correlations of the Lya forest have only been used to measure the baryon acoustic oscillations (BAO) feature. However, these correlations contain cosmological information beyond the BAO peak position, which can be extracted when fitting their full shapes. In this talk, I will present the first such analysis, where we obtain some of this untapped information through the Alcock-Paczynski effect. I will start with an overview of the Lya forest and how it is currently being used for cosmology, and introduce the different sources of cosmological information present, including the Alcock-Paczynski effect. After that, I will present our analysis of the Lya correlation functions measured from synthetic data and from the real BOSS and eBOSS data. Our measurement delivers a factor of two improvement in constraining power compared to BAO analyses. I will then show how BAO and Alcock-Paczynski measurements can help constrain the Hubble constant and dark energy, and discuss the cosmological constraints derived from our measurement. Finally, I will show forecasts of full-shape Lya forest measurements with the on-going Dark Energy Spectroscopic Instrument (DESI).
Feb. 28, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Colin Hill, Columbia/CCA
131 Campbell
Searching for Cosmological Concordance with New Physics in the Dark Sector: Hints and Challenges
I will discuss recent and ongoing work focused on attempts to restore concordance amongst cosmological data sets, motivated by discrepancies between some measurements of the cosmic expansion rate (H_0) and the matter clustering amplitude (S_8). Particular attention will be paid to models invoking new physics in the high-redshift universe, including quasi-accelerating early dark energy models (and extensions thereof, featuring EDE-dark matter interactions) and generalized decaying particle scenarios. In particular, I will discuss constraints on these models derived using the latest CMB measurements from the Atacama Cosmology Telescope (ACT) and from the Planck satellite, amongst other data sets. I will present new constraints on canonical EDE models derived from previously-unconsidered late-universe data sets, which effectively eliminate the viability of this scenario to resolve the Hubble tension. Finally, I will highlight new, extremely precise neural-network-based emulators for Boltzmann codes that we have trained in recent months (and will release shortly), which enable Stage-IV-level cosmological parameter inference to be performed in minutes on a laptop.

March 2023
Mar 2, Thursday
12:30 pm (Astronomy Colloquium)
Dan Stark, Arizona
131 Campbell
Galaxies and Cosmic Reionization: New Insights from JWST and Ground-Based Telescopes
Over the past few months, deep infrared images and spectra from JWST have pushed the cosmic frontier back to just 300 million years after the Big Bang, delivering the first large sample of galaxies at redshifts 7 < z< 15. Sometime in this redshift window the hydrogen in the intergalactic medium transitioned from mostly neutral to ionized. The emergence of the first detailed JWST and ground-based spectra of z>7 galaxies have begun to sharpen our understanding of this process of reionization, while also providing a glimpse of the physical nature of early galaxies. The spectral features we are detecting at z>7 are unlike what has been seen at lower redshifts, revealing a metal poor population of galaxies with bursty star formation histories. In this talk, I will review the latest progress in our understanding of reionization and early galaxies, then discuss several of the surprises that have emerged in the first datasets from JWST.
Mar. 7, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Marcello Musso, Salamanca
131 Campbell
The Energy Minimisation Principle: Linking protohalo counts and shapes to anisotropic infall
In most analytical models of large scale structures, protohaloes (the initial regions from which DM haloes form) are associated with peaks of the smoothed initial density field. Although qualitatively correct, this picture suffers from a number of drawbacks. After a broad introduction to the topic, I will describe how this approach can be improved using local minima of the mean energy instead. Physically, these are points where the local velocity field converges, a dynamic condition conducive to the formation of high density regions. Furthermore, whereas the smoothing is usually done within spheres, the energy principle can be used to identify non-spherical Lagrangian regions, solving for the shapes that minimize the energy at fixed volume. The resulting shapes are in excellent agreement with N-body simulations, and can be useful to improve analytical predictions of the halo mass function, the acquisition of angular momentum, intrinsic alignments and assembly bias.
Mar 9, Thursday
12:30 pm (Astronomy Colloquium)
Caitlin Casey, Austin
131 Campbell
Formed too Fast: Massive Galaxies at Cosmic Dawn
The pace of galaxy growth in the early Universe offers one of the strongest and most accessible tests of the Lambda-CDM cosmological framework. A growing number of surprisingly massive galaxies are now being found in the first billion years after the Big Bang that push the limits of theoretical predictions. Unusually bright high-redshift galaxies discovered by JWST challenge our most fundamental models of how fast stars form. Massive dusty starbursts found with ALMA are requiring new explanations about early dust production. The spatial distribution of massive galaxies within large scale structure may be more highly clustered than expected, which would impact the timescale and uniformity of reionization — the last major phase change of the Universe from a neutral to ionized medium. I will present an overview of large, multi-wavelength observational campaigns I am leading to place the first comprehensive constraints on the rarest, most massive galaxies to emerge at z>6 and the impact they in turn have on our interpretations of the early Universe. These efforts unite the unprecedented sensitivity of JWST together with ALMA and Keck to address fundamental challenges of massive galaxy formation using several independent tests and tracers. Looking ahead, the next generation of facilities under development — ngVLA, the TMT, Roman, and future NASA probes — will definitively establish the story of when and how the first galaxies assembled.
Mar. 14, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Sunil Simha, UCSC
131 Campbell
Searching for the source of excess extragalactic DM of FRBs
Fast radio burst (FRB) dispersion measures (DMs) from radio observations record the presence of ionized baryons that are otherwise invisible to effectively all other techniques. Therefore, with FRBs, we may resolve the matter distribution in the cosmic web to offer unique constraints on our cosmological paradigm. The number of FRBs localized to their host galaxies has steadily increased to tens of FRB sightlines. Thus motivated, we have designed the FLIMFLAM survey to obtain redshifts of the foreground galaxies proximal to FRB sightlines to estimate the FRB DM independently. For a few sightlines, we have already obtained spectra of hundreds of field galaxies using the AAT/AAOmega and the Keck/LRIS and DEIMOS spectrographs. The survey aims to study ~30 sightlines to produce < 10 % constraints on key parameters describing baryonic distribution in the universe. These include the fractions of baryons in the diffuse IGM and the CGM of galaxies. Our sample continues to grow, and preliminary analysis is underway. Meanwhile, a handful of these sightlines are interesting as they exhibit a significantly high excess in extragalactic DM (i.e., the DM from outside the Milky Way) compared to the mean value expected at their host redshifts from the Macquart Relation. In this talk, I will present the results of our latest work, where we leverage the data collected for the FLIMFLAM survey to constrain the contribution of the foreground cosmic web to their DM excess.
Mar. 21, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Daniela Galárraga-Espinosa, MPIA
131 Campbell
Filaments: from the large-scale structure to the CGM
Matter in the Universe is assembled under the action of gravity to form a gigantic network of nodes, filaments, walls, and voids, called the cosmic web. This structure is mainly set by the dynamics of dark matter (DM), which forms the skeleton onto which baryonic matter is accreted. While the denser cosmic structures (clusters of galaxies) have been thoroughly studied, because of their lower densities and complex morphologies, the properties of cosmic filaments are still poorly known. I will present a comprehensive study of cosmic filaments today, detected from the galaxy distribution of recent large-scale hydro-dynamical simulations. The radial distribution of DM, gas, and galaxies around these structures will be analysed, together with some gas properties such as temperature, pressure, and baryon fraction. I will show that filaments of different lengths do not have the same physical properties, and I will focus on the characterisation of the two extreme populations: the short and long ones. Short filaments are denser, puffier, and hotter than the long ones. They trace denser environments in the cosmic web (e.g. close to clusters of galaxies). On the contrary, the long population is thinner, and often embedded in under-dense regions of the web.
In the second part of my talk, I will zoom into the scales of the circum-galactic medium (CGM) of TNG50 at z=2, and assess the impact of the smaller-scale filaments (or streams) on galaxy star-formation. By performing an analysis of ~3000 central galaxies, I will show that the number of streams connected to haloes enhances the sSFR of galaxy at their centres, especially for the case of low mass galaxies. In order to study the influence of the larger scales, the galaxies will be then split according to their location in different cosmic web environments. We will see that, at fixed mass and local density, the sSFR enhancement is the most significant for galaxies in cosmic filaments with respect to those in voids and walls, hinting at the importance of the large-scale matter reservoirs and of the anisotropic tidal field for understanding galaxy evolution.
Mar. 28, Tuesday
No seminar-spring break

April 2023
Apr. 4, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Elena de la Hoz, UCB
131 Campbell
Improvements in low-frequency foreground modeling for future primordial B-mode searches
Primordial gravitational waves, whose detection would constitute compelling evidence of inflation, are expected to be measurable through their imprint on the polarized CMB. However, this detection entails many experimental and data analysis challenges since it is relatively faint compared to other B-mode sources, e.g., astrophysical foregrounds, lensed E- to B-modes, and systematic errors. Optimal characterization of the foregrounds is mandatory to reach the sensitivity targeted by future CMB experiments and rule out false detections. In this talk, I present the latest improvements in the synchrotron's modeling on the Northern Hemisphere obtained using the final QUIJOTE-MFI data with data from WMAP and Planck. Moreover, I outline current efforts toward measuring the low-frequency sky (6-20 GHz) from the Southern Hemisphere with ELFS-S.
Apr. 5, Wednesday
2 pm (Particle theory seminar)
Keir Rogers, Toronto
LBL 50A-5132
"Searching for the fundamental nature of dark matter in the cosmic large-scale structure"
The fundamental nature of dark matter (DM) so far eludes direct detection experiments, but it has left its imprint in the large-scale structure (LSS) of the Universe. I will present a search using cosmic microwave background (CMB) and galaxy surveys for ultra-light DM particle candidates called axions that are well motivated from high energy theory. In combining these datasets, I will discuss how the presence of axions can improve consistency between these probes and, in particular, help alleviate the S_8 cosmological parameter tension (the discrepancy in the amplitude of density fluctuations as inferred from CMB and galaxy data). I will then present complementary searches for ultra-light and light (sub-GeV) DM using a LSS probe called the Lyman-alpha forest. By combining complementary large- and small-scale structure probes, I will demonstrate how current and forthcoming cosmological data will systematically test the nature of DM. In order to model novel DM physics accurately and efficiently in CMB and LSS probes, I will present new machine learning approaches using neural network "emulators" to accelerate DM parameter inference from days to seconds and active learning to reduce massively the computational expense.
Apr. 7, Friday
12 noon (INPA)
Noah Sailer, UCB
LBL 50A-5132
Accurate cosmology from CMB lensing and galaxy surveys
Joint analyses of CMB lensing and spectroscopically-calibrated galaxies have the ability to measure the evolution of matter fluctuations out to high redshifts without the complications of photometric redshift uncertainties and intrinsic alignments. These measurements are rapidly becoming one of the more powerful tools in a cosmologist’s toolkit, enabling precise (and accurate) inference of cosmological parameters and potential deviations from ΛCDM. While cross-correlations are typically more robust against systematic effects, correlated systematics arising from (extra)galactic foreground contamination and masking induce significant biases if not properly accounted for. I will discuss progress towards mitigating these effects, the implementation of these methods in an ongoing cross-correlation analysis of DESI luminous red galaxies and CMB lensing from ACT, and the prospects of future analyses with Stage-V spectroscopy and CMB-S4.
Apr. 11, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Elisabeth Krause, Arizona
131 Campbell
Weak Lensing without Shape Noise
Weak gravitational lensing imprints a coherent distortion onto the observed shapes of distant galaxies. At the image level, this gravitational shear is degenerate with the intrinsic shape of galaxies, and the weak lensing signal-to-noise from an individual galaxy is of order 0.01. I will describe Kinematic Lensing, a new technique combining imaging and galaxy kinematics to measure weak lensing with signal-to-noise of order one per galaxy.
Apr. 18, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Zarija Lukic, LBL
131 Campbell
Simulations and modeling of the intergalactic medium for DESI and beyond
Performing controlled experiments is not a viable approach in cosmology, making simulations and modeling — the ability to create "virtual universes" — one of the key aspects of scientific inference. Sky surveys like DESI effectively pose an inverse problem, where the measurement result is obtained and one tries to infer the values of parameters which characterize the underlying physical system — the evolving Universe. The difficulty here is that producing each virtual universe in principle requires an extremely expensive numerical simulation carried out at high fidelity. In this talk I will review ongoing simulations and modeling efforts in LBL's Computational Cosmology Center which focuses on the intergalactic medium and Lyman alpha forest. Broadly, the effort I will cover in the talk consists of three coordinated components: (1) developing physics-based simulation capability based on our Nyx code; (2) augmenting physical simulations with data-driven generative models; and (3) enabling inference with a limited number of simulations via surrogate modeling.
Apr. 25, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Koki Kakiichi, UCSB
131 Campbell
Photometric IGM Tomography Across Cosmic Time
The art of cosmography, i.e. map-making of the Universe, is essential for progress in astronomy. In this talk, I present a new technique to map the large-scale structure of the intergalactic medium (IGM) using ultra-deep Subaru/HSC narrow-band imaging. This so-called “photometric IGM tomography” detects faint Lyman-alpha forest transmission along all background galaxies photometrically, allowing us to reconstruct the tomographic map of HI at high redshifts from z~4 to 6. Using the publicly available HSC data, I demonstrate the proof-of-concept and present the first co-spatial, large-scale map of the cosmic web of both galaxies and the IGM at z~5 in the COSMOS field. By analyzing the IGM tomographic map with theory/numerical simulations, I discuss the physical implications of the result on the source of reionization, escape fractions and ionizing capabilities of galaxies, and the radiative growth history of supermassive black holes. I conclude by discussing how this technique could be improved further by using the data from JWST.

May 2023
May 2, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Gerrit Farren, Cambridge
131 Campbell
"Cosmology from CMB lensing cross-correlations with galaxy clustering from unWISE"
I will present work on measuring cosmology, in particular structure growth, using cross-correlations between CMB lensing reconstructions and galaxy clustering from the unWISE galaxy catalog. My talk will focus on highlighting the improvements we have made to the modelling and analysis pipeline compared to previous work on the cross-correlation between Planck lensing and unWISE by some of my collaborators (Krolewski et al. 2021). I will show, for the first time publicly, the results from our reanalysis of Planck lensing x unWISE which yields highly competitive constraints on structure growth. Finally, I will present an outlook to our most recent work on performing a comparable analysis with the upcoming Atacama Cosmology Telescope Data Release 6 lensing reconstruction.
May 18, Thursday
4 pm (RPM)
Frank Qu, Cambridge
LBL 50A-5132
Cosmology from high-precision CMB lensing measurements with the Atacama Cosmology Telescope
The cosmic microwave background provides a unique backlight for illuminating the growth of structures in our universe. Measuring the arcminute-scale lensing deflections experienced by the CMB photons as they travel to our telescopes enables the mapping of the matter distribution to very high redshifts. This lensing signal provides a clean window for constraining fundamental physics, such as the sum of neutrino masses, and enables powerful tests of the standard cosmological model via comparison of high-precision measurements of structure growth at late times with early-time predictions.

June 2023
June 2, Friday
12 noon INPA seminar (LBL)
Roohi Dalal, Princeton
LBL 50-5132
Cosmology and Systematics from Hyper Suprime-Cam Year 3 Data
The Hyper Suprime-Cam (HSC) survey is the deepest Stage III weak lensing experiment, going to ~26 mag with exquisite seeing. The depth and image quality achieved by HSC allow us to probe cosmology using weak lensing upto high redshifts, and these analyses serve as important preparatory studies for the next generation of weak lensing surveys. I will discuss our constraints on cosmological parameters using weak lensing cosmic shear power spectra measured from the Year 3 shear catalog of HSC, covering 416 square degrees of the northern sky. After giving a brief overview of our cosmological analysis, and our new constraint on the S8 parameter, I will focus on systematics that have been important and distinguishing factors in our analysis, including photometric redshift uncertainties, systematics from higher order PSF moments, and uncertainties in the modeling of baryonic feedback. I will show that we have made a number of conservative choices to ensure that our analysis is robust to these systematics and share some lessons learned that will enable future surveys to hopefully no longer be limited by such systematics.

Past Months

August 2022
Aug 30, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
group intro
131 Campbell Hall

September 2022
Sep 2, Friday
12 noon (LBL INPA talk)
Zhelei Xu, MIT
Speaker will be on zoom, at LBL can also watch in LBL 50-5132
Precision Cosmology: from CMB and 21cm
Over the past decades, observations of the cosmic microwave background (CMB) have established the standard cosmological model. In the future, 21cm signals from neutral hydrogen have great potential for cosmological and astrophysical studies. In this talk, I will review the previous CMB observations and how it established the ΛCDM cosmology model. Then I will discuss the instrumentation and calibration of the Cosmology Large Angular Scale Surveyor (CLASS) and the Simons Observatory (SO). At the end, I will discuss how we can use the 21cm observation as a powerful probe to study cosmology and introduce our novel mapping method for 21cm interferometric data.
Sep 6, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Marco Gatti, Penn
131 Campbell
Weak Lensing Non-Gaussian Statistics in the era of precision Cosmology
In recent years, non-Gaussian statistics have been growing in popularity as powerful tools for efficiently extracting cosmological information from current weak lensing data. Their use can improve constraints on cosmological parameters over standard two-point statistics, can additionally help discriminate between general relativity and modified gravity theories, and can help to self-calibrate astrophysical and observational nuisance parameters.
During this seminar, I will discuss the current state-of-the-art in weak lensing non-Gaussian analyses. I will show the constraints on cosmological parameters from two independent analyses using non-Gaussian statistics applied to the first three years of data (Y3) of the Dark Energy Survey (DES): moments and peaks. I will further describe promising techniques that are soon to be applied to data (wavelet-based methods), and discuss the main challenges ahead in view of stage IV surveys.
Sep 13, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Dylan Jow, Toronto
131 Campbell
Wave-optics in astrophysical lensing: unlocking the potential of the coherent sky
The lensing of coherent sources, such as FRBs, pulsars, and gravitational waves, has the potential to be a powerful cosmological and astrophysical probe. In particular, with the abundance of FRB data we are set to obtain, gravitationally lensed FRBs may be used to constrain compact dark matter over a wide range of masses, as well as probe cosmic expansion in real time. However, the theory of wave optics needed to describe the lensing of coherent sources is underdeveloped. In addition, scattering due to plasma along the line of sight may limit the sensitivity of gravitationally lensed FRBs as a cosmological probe. We will discuss advancements in the theory of wave optics as applicable to astrophysical lensing (plasma and gravitational), in particular the application of Picard-Lefschetz theory for the evaluation of the Kirchoff diffraction integral. We will also describe progress in understanding the origin of pulsar scintillation due to scattering in the ISM and its implications for modeling FRB scattering. Time permitted, we will briefly discuss the application of these techniques to gravitational wave lensing.
Sep 16, Friday
12 noon (INPA)
Yuuki Omori, Chicago
Constraining cosmology and astrophysics using the combination of CMB x LSS, and understanding biases in cross-correlation measurements
Cross-correlation measurements between CMB and LSS observables is becoming an increasingly popular approach to constrain cosmology and astrophysics. Since CMB and LSS surveys have different experimental systematic effects, cross-correlation measurements are known to be minimally impacted by these effects. However, what is often disregarded are the astrophysical systematic effects, which are present in both CMB and LSS data, which contaminate cross-correlation measurements. In the first part of the talk, I will present the recent results from the DESxSPT 6x2pt analysis, and discuss how we mitigated such biases. In the second part of the talk, I will present a new simulation suite that has both CMB and LSS observables that can be used to study these biases.
Sep 19, Monday
4:15 pm (Physics Colloquium)
Michael Turner, U Chicago
Physics North Lecture Hall 1
Cosmology: What we know, what we don’t know and what we don’t know we don’t know
For most of the last century cosmology was the province of astronomers (mostly in California) and concerned itself with galaxies in an expanding universe. Beginning around 1980, ideas from particle physics began to enter cosmology, focussed on events that took place during the first microsecond. Circa 2000, with the discovery of cosmic acceleration/dark energy and precision measurements of CMB anisotropy the current paradigm — LambdaCDM emerged, revealing deep connections between particle physics and cosmology. According to LCDM, the gravity of particle dark matter holds all structures together, the repulsive gravity of dark energy is speeding up the expansion and the quantum seeds for galaxies arose during a very early burst of accelerated expansion (inflation). Cosmology solved? Not exactly, we have no direct evidence for the dark matter particle; we don’t understand dark energy; and have no standard model for inflation (or evidence to support it). And our aspirations are even higher. Great time to be a cosmologist.
Sep 20, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Gabriela Sato-Polito, JHU
131 Campbell
"Cosmology and astrophysics with the extragalactic light: background and fluctuations"
The aggregate light emitted by all extragalactic sources can be measured either as an absolute intensity or through its spatial fluctuations; these are known as line-intensity mapping (LIM) when a particular line transition is targeted. I will discuss how these measurements can be used both to learn about galaxy evolution and to investigate the presence of more speculative sources of radiation, such as decaying dark matter. I will also discuss the prospects of LIM as a probe of large-scale structure in a multi-tracer context, focusing on the joint information across different line transitions and across different tracers, such as galaxies and CMB foregrounds.
Sep 27, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Nick Kokron, Stanford
131 Campbell
Structure formation at the juncture of simulations and perturbation theory
A key challenge for the next decade of survey cosmology is ensuring that the models for summary statistics they measure, such as galaxy clustering and lensing, are sufficiently accurate in light of the high degree of precision of these measurements. A recently proposed class of models, hybrid effective field theory (hybrid EFT), combines perturbation theory-based descriptions of the tracer--matter connection with the nonlinear dark matter distributions produced by cosmological N-body simulations. I will show how hybrid EFT promises to be a powerful model for describing the two-point statistics of clustering and lensing to small scales at high accuracy. I will proceed to survey recent developments in this juncture between simulations and perturbation theory that show their combination is mutually beneficial beyond just modelling two-point statistics.

October 2022
Oct 4, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Justin Myles, Stanford
131 Campbell
Novel Methods to Leverage Spectroscopic Overlap of Imaging Surveys
Large galaxy imaging surveys promise to deliver extraordinary datasets to answer open questions about cosmology, but these surveys suffer from challenges arising from the difficulty in constraining galaxy redshift. I will discuss three projects that leverage spectroscopic observations of small, well selected subsets of galaxies observed in imaging surveys to improve the utility of photometric datasets for cosmological experiments. First, I will describe the new methodology used for the Dark Energy Survey Year 3 weak lensing source galaxy redshift calibration and the resulting DES Y3 cosmology constraints. Second, I will present a novel algorithm for accurately propagating redshift distribution uncertainties. Third, 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 Y1 cluster cosmology results. To conclude, I will discuss promising paths forward involving spectroscopy and multi-wavelength observations to make the most use of forthcoming surveys.
Oct 6, Thursday
3:30 pm (Astronomy Colloquium)
Caitlin Casey, UT Austin
1 Physics North
The Rarest Galaxies in the First Billion Years
The rarest galaxies assembled early in the Universe’s history (z>6) pose unique problems for galaxy formation and evolution in a Lambda-CDM universe. I will present several legacy-class, mutliwavelength observational campaigns aimed at characterizing a range of such galaxies — massive dust obscured galaxies, quasars, and extremely UV-bright Lyman-break galaxies. In particular I will share recent results from the MORA Survey (Mapping Obscuration to Reionization with ALMA, a 50+ hour 2mm survey), constructed to identify the most highly obscured, massive (M_ISM>10^11Msun) star-forming galaxies beyond z>4 that are the likely progenitors of the first quiescent systems. This is complemented in the rest-frame ultraviolet with the WERLS Program (the Webb Epoch of Reionization Lyman-alpha Survey), a 29-night NASA Keck survey which will construct the first spatial maps of ionized bubbles in legacy JWST survey fields using UV-bright galaxies (M_UV < -20). Lastly, I will highlight early results from JWST on the search for ultra high-redshift, massive galaxies at z=10-17. These discoveries are setting the stage for the 218-hour COSMOS-Web JWST Cycle 1 GO program. Covering over 0.5deg^2 to "deep field" sensitivity, COSMOS-Web will eliminate uncertainty from cosmic variance at z>6, enabling the first robust mapping of large-scale structure during the Epoch of Reionization. Together these campaigns will provide important and diverse observational tests of Lambda-CDM at the earliest epochs of the Universe.
Oct 7, Friday
12 noon (INPA, LBL)
Jeff Cooke, Swinburne
LBL 50-5132
Wide-Field Imager and the future direction of the Keck Observatory
The Keck Wide-Field Imager (KWFI) is a 1 degree diameter field of view wide-field optical imager for Keck that will be the most powerful wide-field imager in the world for the foreseeable future. KWFI has extreme sensitivity from 10000A down to 3000A that will enable new science from the high redshift Universe, to time-domain science, to the local Universe and the solar system that cannot be done on any other existing or planned telescope for decades. We have now entered into the era of next-generation facilities, including JWST and NASA Roman space telescope, the Cherenkov Telescope Array, the Square Kilometre Array, LIGO/Virgo/KAGRA, Subaru Prime Focus Spectrograph, Maunakea Spectroscopic Explorer, and 30m-class telescopes, with larger, more sensitive facilities in planning for the next decades, such as the Cosmic Explorer, LISA, LUVOIR, and others. In this talk, I will discuss how KWFI's extremely deep, wide-field imaging is vital for nearly all science cases for these facilities (many are billion-dollar facilities) operating at all wavelengths and how it will greatly extend their reach. KWFI will excel at targeted science programs, which make up the bulk of all Keck community science. I will discuss the status and continued progress of KWFI and development of a deployable secondary mirror to enable new science and fast imaging and spectroscopy capability in the same night.
Oct 11, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Neal Dalal, Perimeter
131 Campbell
Galaxies in the axiverse
Ultra-light bosons are well-motivated dark matter candidates with interesting phenomenology on galactic scales. In particular, wavelike behaviour of dark matter in the so-called “fuzzy” regime can help relieve potential problems for standard cold dark matter in galaxies, by producing central cores and suppressing the abundance of low-mass satellites. I will describe observational signatures of this wavelike behaviour, and will show how the smallest galaxies may be used to constrain ultra-light dark matter particle masses.
Oct 18, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Molly Wolfson, UCSB
131 Campbell
Constraining the mean free path of ionizing photons at z > 5 from the Lyman-α forest flux auto-correlation function
Lyman-α (Lyα) forest transmission towards high-z quasars contains information on the state of the universe just after the epoch of reionization. Fluctuations in Lyα forest transmission are partially sourced from spatial fluctuations in the ultraviolet background (UVB), where the level of UVB fluctuations are set by the mean free path of ionizing photons (λmfp). The auto-correlation function of Lyα forest flux characterizes the strength and scale of transmission fluctuations and, as we show, is thus sensitive to λmfp. Recent measurements of λmfp at z ~ 6 suggest a rapid evolution of λmfp at z > 5.0 which would leave a signature in the evolution of the auto-correlation function. We modeled mock Lyα forest data with properties similar to the XQR-30 extended data set at z > 5. For an ideal data set, where the data matches the model for λmfp = 9.0 cMpc at z = 6.0, we recover λmfp = 12 + 6 - 3 cMpc. This precision is comparable to direct measurements of λmfp from the stacking of quasar spectra beyond the Lyman limit. We find that the distribution of mock values of the auto-correlation function is highly non-Gaussian for high-z, which should caution work with other statistics of the high-z Lyα forest against making this assumption. We use a rigorous statistical method to pass an inference test, however future work on non-Gaussian methods will enable higher precision measurements.
Oct 25, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Mike Chapman, Perimeter/Waterloo
131 Campbell
Isolating the linear signal in small scale RSD
The nature of dark energy and the accelerated expansion of the Universe remains one of the most compelling problems in modern physics. Measurements of f\sigma_8 from galaxy clustering provide a unique test of theories of dark energy and modified gravity that seek to explain this acceleration. I will present my recently published measurement of the growth rate from small scale clustering in the eBOSS luminous red galaxy sample, where I use a galaxy clustering emulator with an independent velocity scaling parameter to measure f\sigma_8 and parameterize deviations from LCDM. My measurement provides a significant improvement in uncertainty over the more conventional RSD analysis of the same sample, and finds some tension with the expectation for a LCDM universe with Planck 2018 cosmology. I will then present new work I’ve done to improve my model and isolate the linear signal in the small scale clustering, providing a more robust result and more accurate interpretation of the growth rate measurement. I will give a preview of my results with the new model, and explain why small scale RSD measurements with DESI have the potential to reveal a significant new tension in the standard model of cosmology.

November 2022
Nov 1, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Cyndia Yu, Stanford
131 Campbell
Cosmology with Large-Scale CMB Polarization
The cosmic microwave background (CMB) has been key to building and validating our current Standard Model of Cosmology. As information from CMB temperature becomes limited by cosmic variance, polarization data is increasingly key to breaking degeneracies and probing new physics. The large angular scale polarization features in particular are a sensitive probe of cosmic inflation through the “B-mode” polarization. Beyond primordial B-modes, large-scale polarization features probe other beyond Standard Model phenomena such as early dark energy and dark matter. I will discuss the constraints obtained by current experiments as well as efforts to build next-generation observatories, which will deploy over an order of magnitude more polarization-sensitive detectors to enable ever more sensitive measurements.
Nov 3, Thursday
4 pm (LBL RPM)
Hee-Jong Seo, LBNL
LBL 50A-5132
Accelerating Universe through DESI
One of the most intriguing questions in physics today is the nature of dark energy that is responsible for the accelerated expansion of the Universe. Three-dimensional maps of galaxies from spectroscopic galaxy surveys provide a giant laboratory to test the nature of the Universe, including dark energy, in a way that is complementary to other cosmic surveys. DESI, being the largest galaxy redshift survey up to date, is currently preparing for the first-year cosmology analysis release in Summer 2023, In this talk, among the key science goals of DESI, I want to focus on the studies of two accelerated expansion phases of the Universe using DESI, one today due to dark energy and the other, cosmic inflation right after the Big Bang. For the former, I will show the first Baryon Acoustic Oscillation detection result using only the first two months of the DESI data. For the latter, I will discuss how we can fight the observational systematics using neural networks and derive a tight constraint on inflation using the DESI Legacy survey.
Nov 8, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Frank Qu, Cambridge
131 Campbell
Testing fundamental physics with high resolution CMB lensing mass maps
Dark matter not only provides the invisible scaffolding from which the birth of galaxies takes place, but by studying its distribution in our universe we can infer a great deal of information regarding the growth of structure and cosmic expansion. Measuring the gravitational lensing of the CMB allows the mapping of all the matter distribution (for which the majority is dark matter) to very high redshifts. New observations with the Atacama Cosmology Telescope will allow CMB lensing to be determined at the ~2% level. This high signal-to-noise lensing spectrum will translate into a few percent determination of sigma_8, hence providing a robust test of low amplitudes reported by galaxy lensing surveys and one of the tightest constraints on the sum of neutrino masses. This measurement also sets the foundation for ground-based high-resolution lensing covering a large fraction of the sky.
In the first part of my talk, I will explore the implications of our measurement in the context of structure growth and discuss in detail the novel methods used to tackle key systematics affecting precision lensing related to atmospheric noise and extragalactic foregrounds. I will also highlight some of the main null tests from our comprehensive test suite used to deliver this robust state of the art lensing measurements. For the second part of my talk, I will explore the prospects of using CMB lensing as a probe of the high-redshift structure only by ‘delensing’ the low redshift content of CMB lensing using correlated tracers like galaxy surveys, resulting in a map of high-redshift structure alone. This opens up a window to explore cosmological periods uncharted by other probes, enabling measurements of structure growth and providing rigorous confrontations between theory and observations within a redshift range where little information is otherwise available.
Nov 11, Friday
12 noon (INPA seminar)
Peter Craig, UCB
Effects of Microlensing on Time Delay Measurements from Strongly Lensed Supernovae
Strongly lensed supernovae are highly valuable cosmological probes, sensitive to both the Hubble constant and the distribution of dark matter. Measuring time delays in strong lensing systems allows for independent measurements of the Hubble constant, providing a mechanism to resolve the current Hubble tension. These time delays are also sensitive to the dark matter substructures located along the line of sight. Microlensing effects from stars in the lensing galaxy can contaminate measurements of the time delays, making some methods for measuring time delays unreliable. We consider methods for measuring time delays with both Type Ia and Type II-P supernovae by simulating spectra in microlensing systems. Both types of supernovae may be effectively used to measure the Hubble constant, especially with the number of detections that are expected with LSST and the Roman Space Telescope. These measurements can also be used to constrain the properties of dark matter substructure given a sufficient number of systems. We’ve also been working on understanding the local distributions of dark matter using an “acceleration ladder” built using local direct acceleration measurements combined with dynamical constraints on the Milky Way potential.
CANCELLED Nov 15, Tuesday
1:10 pm (BCCP/Cosmology Seminar)
Jordan Mirocha, JPL
131 Campbell
Nov 15, Wednesday
12 noon (INPA seminar)
Nickolas Kokron, Stanford
LBL-50A-5132 and Zoom
Pen-and-Paper Meets Supercomputing: Building Accurate Models for Cosmological Surveys
Stage-IV cosmological surveys are poised to revolutionize our understanding of the Universe. The vast data sets collected by surveys like DESI, Rubin and CMB-S4 will be orders of magnitude more powerful than their precursors from the last decade and will significantly sharpen our understanding of unknown properties of the Universe. These include the properties of dark energy, the masses of neutrinos and the fundamental nature of the primordial fluctuations in the early Universe. However, the statistical uncertainties of upcoming observations are so small that models for the statistics we measure are not yet accurate enough to analyze their whole datasets. I will introduce a program of research dedicated to addressing the challenge of accurately modeling these data and making our cosmological surveys the most powerful they can be. This program is underpinned by a fruitful marriage of traditionally disparate techniques — supercomputer simulations and pen-and-paper calculations — to describe the growth and evolution of large-scale structure in the Universe. I will show that their combination is more powerful than the sum of its parts and will play a key role in extracting the most amount of information from DESI and its cross-correlations with weak and CMB lensing surveys in the coming future.
Nov 29, Tuesday
1:10 pm (LBL RPM and BCCP/Cosmology Seminar)
Kate Storey-Fisher, NYU
131 Campbell and ZOOM
Galaxy Clustering with Emulation and Equivariant Machine Learning
There is significant untapped cosmological information in the clustering of galaxies, particularly at small scales. I will discuss two projects aimed at this. In the Aemulus project we take an emulation approach, populating dark matter only cosmological simulations with a simple galaxy–halo connection model and training machine learning (ML) emulators to predict clustering statistics. I will show that incorporating beyond-standard statistics sensitive to the local environment aids in constraining galaxy bias parameters and increases the precision on recovered cosmological parameters.
To account for uncertainties in galaxy formation, we require improved models of the galaxy–halo connection. I will present a new equivariant ML approach to learning the relationship between dark matter halo and galaxy properties in cosmological simulations. Our approach explicitly respects physical symmetries by describing halos in terms of a large set of invariant dimensionless scalars. I will show that this results in precise predictions of galaxy properties. These frameworks will be critical for the analysis of upcoming spectroscopic surveys.

December 2022
Dec. 14, Wednesday
12 Noon (INPA)
Justin Myles, Stanford
LBL 50A-5132 and Zoom
The Treachery of (Galaxy) Images
Large galaxy imaging surveys promise to deliver extraordinary datasets to answer open questions about cosmology, but these surveys suffer from challenges arising from the difficulty in constraining galaxy redshift. I will discuss methods to leverage spectroscopic observations of small, well selected subsets of galaxies observed in imaging surveys to improve the utility of these datasets for cosmological experiments. First, I will describe the methodology used for the Dark Energy Survey Year 3 weak lensing source galaxy redshift calibration and the resulting DES Y3 cosmology constraints, with emphasis on a novel algorithm for accurately propagating redshift distribution uncertainties used in this analysis. Second, 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 Y1 cluster cosmology results. Third, I will discuss promising paths forward involving DESI observations to make the most use of forthcoming imaging surveys. In summary, this talk will discuss how to make the most use of DESI in concert with other multi-wavelength surveys.
Dec. 15, Thursday
4 pm (RPM)
Edmond Chaussidon, Saclay
LBL 50A-5132 and Zoom
Measuring the primordial non-gaussianity with DESI
 Inflation can be strongly characterized with a precise measurement of primordial non-gaussianity (PNG), typically on the order of unity, to allow a detection that will rule out the single-field models. Through the tiny imprint left at large scales on the matter power spectrum by local PNG, known as the scale-dependent bias, the state-of-the-art multi-fiber spectroscopic instrument DESI (Dark Energy Spectroscopic Instrument) is expected to obtain similar accuracy to Planck and reach, in the future, the sensitivity allowing a PNG detection of the order of unity with more advanced methods.  First, I will present the Quasar (QSO) sample of DESI, which is the most suitable tracer to measure the PNG. In particular, I will introduce the QSO target selection used in DESI and the spectroscopic pipeline to collect the redshift. Then, I will review various observational effects that could contaminate the measurement of PNG and how to address them. Finally, I will give a forecast for the first data release of DESI in January 2024 and give some potential improvements to reach the desired sensitivity of the order of unity.
Dec. 16, Friday
12 Noon (RPM & INPA)
Kevin Fanning, Ohio State
LBL 50A-5132 and Zoom
Excitement and Challenges with Multiplexed Spectroscopic Galaxy Surveys
The ongoing Dark Energy Spectroscopic Instrument (DESI) Survey is collecting galaxy redshifts at an astounding rate. Analysis from this new data promises exciting new constraints on big cosmological problems such as dark energy models and primordial non-gaussianity along with a measurement of the sum of the neutrino masses. Key technologies including the robotic focal plane system help enable nearly 5,000 simultaneous spectra with on average 2 minutes between exposures. In this talk I will describe some of the challenges encountered optimizing the DESI instrument for science results. Furthermore, I will discuss some of the impact the focal plane and fiber assignment algorithms have on galaxy clustering data and some novel mitigations I am exploring to resolve this problem. Finally, I will conclude with a look to the future and how we can engage in current efforts to build on the success of DESI.

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