Weekly Group Meeting schedule

Zoom link (every week): https://harvard.zoom.us/j/99548956115?pwd=cGkvcDB5ZlZ2T2N0cjZkQnM2Wi8yZz09

or

Meeting time: 0900-1000 Boston time Fridays

Instructions: Claim a block of 15minutes to discuss, with the group:

issues you are having
victories you have won
foes you have defeated
Anything you like

You can claim more than 1 10- or 15- minute block, but please yield that time if many people have things to discuss. Note - the last time block is only 10 minutes to provide us 5 minutes to wrap up.

Advocate for quadnotch

Meeting Friday, Feb 23

Time	Person	Brief description of purpose
11-11:05	Stubbs Urbach	Lab announcements and safety information/etc (EVERY WEEK) Announcements: MIT & Harvard joint AI workshop last week, arXiv search tool.
11:05 to 11:30	all	roundtable discussion
11:30 to 11:45	Elana	Updates on CBP + CBP calibration system

Friday Feb 25, 2022 at 8:30 am

2021/03/09

Group Journal Club

date	paper	who?
Friday Sept 17	H_o paper linked below	Sasha
Friday Sept 24	continuation of H_o paper	Sasha
Friday Oct 1	1) The Atacama Cosmology Telescope: Constraints on Pre-Recombination Early Dark Energy https://arxiv.org/abs/2109.04451 2) Dark Energy at early times and ACT: a larger Hubble constant without late-time priors https://arxiv.org/abs/2109.06229	Dillon
Friday Oct 8	What makes the Universe accelerate? A review on what dark energy could be and how to test it DE review	Elana
Friday Oct 22	Anomalous gravity constraints from asteroid orbital precessions	Eske
Friday Nov 19	First two chapters of decadal survey	Elana
Friday Dec 3	Chapters 5, 6, 7 of the decadal survey	Sasha
Fri Mar 4	Sec 3.5 Unveiling the Universe with Emerging Cosmological Probes	Brodi
Fri Sept 23	Introduction to astronomical photometry. Read pages 101-108 of this document: wrccd22oct06.pdf Look here: https://photutils.readthedocs.io/en/stable/getting_started.html read this: Schechter_1993_PASP_105_1342.pdf	Chris
Journal Club articles, topic (Green means we've done that paper)	arXiv or link	PDF	abstract
Ho	https://arxiv.org/abs/2109.01161	HoBuyersGuide.pdf	Since the expansion of the universe was first established by Edwin Hubble and Georges Lemaitre about a century ago, the Hubble constant H0 which measures its rate has been of great interest to astronomers. Besides being interesting in its own right, few properties of the universe can be deduced without it. In the last decade a significant gap has emerged between different methods of measuring it, some anchored in the nearby universe, others at cosmological distances. The SH0ES team has found H0=73.2±1.3 km sec−1 Mpc−1 locally, whereas the value found for the early universe by the Planck Collaboration is H0=67.4±0.5 km sec−1 Mpc−1 from measurements of the cosmic microwave background. Is this gap a sign that the well-established ΛCDM cosmological model is somehow incomplete? Or are there unknown systematics? And more practically, how should humble astronomers pick between competing claims if they need to assume a value for a certain purpose? In this article, we review results and what changes to the cosmological model could be needed to accommodate them all. For astronomers in a hurry, we provide a buyer's guide to the results, and make recommendations.
Anthropic bound on the cosmological constant	https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.59.2607	WeinbergLambda1987.pdf	In recent cosmological models, there is an "anthropic" upper bound on the cosmological constant Λ. It is argued here that in universes that do not recollapse, the only such bound on Λ is that it should not be so large as to prevent the formation of gravitationally bound states. It turns out that the bound is quite large. A cosmological constant that is within 1 or 2 orders of magnitude of its upper bound would help with the missing-mass and age problems, but may be ruled out by galaxy number counts. If so, one may conclude that anthropic considerations do not explain the smallness of the cosmological constant.
What makes the Universe accelerate? A review on what dark energy could be and how to test it	DE review	Brax_2018_Rep._Prog._Phys._81_016902.pdf	Explaining the origin of the acceleration of the expansion of the Universe remains as challenging as ever. In this review, we present different approaches from dark energy to modified gravity. We also emphasize the quantum nature of the problem and the need for an explanation which should violate Weinberg's no go theorem. This might involve a self-tuning mechanism or the acausal sequestering of the vacuum energy. Laboratory tests of the coupling to matter of nearly massless scalar fields, which could be one of the features required to explain the cosmic acceleration, are also reviewed.
Supernova clustering	https://arxiv.org/abs/2109.02651	SN_Clustering.pdf	The new generation of wide-field time-domain surveys has made it feasible to study the clustering of supernova (SN) host galaxies in the large-scale structure (LSS) for the first time. We investigate the LSS environment of SN populations, using 106 dark matter density realisations with a resolution of ∼ 3.8 Mpc, constrained by the 2M++ galaxy survey. We limit our analysis to redshift z<0.036, using samples of 498 thermonuclear and 782 core-collapse SNe from the Zwicky Transient Facility's Bright Transient Survey and Census of the Local Universe catalogues. We detect clustering of SNe with high significance; the observed clustering of the two SNe populations is consistent with each other. Further, the clustering of SN hosts is consistent with that of the Sloan Digital Sky Survey (SDSS) Baryon Oscillation Spectroscopic Survey (BOSS) DR12 spectroscopic galaxy sample in the same redshift range. Using a tidal shear classifier, we classify the LSS into voids, sheets, filaments and knots. We find that both SNe and SDSS galaxies are predominantly found in sheets and filaments. SNe are significantly under-represented in voids and over-represented in knots compared to the volume fraction in these structures. This work opens the potential for using forthcoming wide-field deep SN surveys as a complementary LSS probe.
Anomalous gravity constraints from asteroid orbital precessions	https://arxiv.org/abs/2107.04038	AsteroidYukawa.pdf	We study for the first time the possibility of probing long-range fifth forces utilizing asteroid astrometric data, via the fifth force-induced orbital precession. We examine nine Near-Earth Object (NEO) asteroids whose orbital trajectories are accurately determined via optical and radar astrometry. Focusing on a Yukawa-type potential mediated by a new gauge field (dark photon) or a baryon-coupled scalar, we estimate the sensitivity reach for the fifth-force coupling strength and mediator mass in the mass range m≃10−21−10−15eV. Our estimated sensitivity is comparable to leading limits from torsion balance experiments, potentially exceeding these in a specific mass range. The fifth forced-induced precession increases with the orbital semi-major axis in the small m limit, motivating the study of objects further away from the Sun. We discuss future exciting prospects for extending our study to more than a million asteroids (including NEOs, main-belt asteroids, Hildas, and Jupiter Trojans), as well as trans-Neptunian objects and exoplanets.
Lensed type Ia SN	https://www.nature.com/articles/s41550-021-01450-9	RodneyLensedSN2021 NatureComment.pdf	When the light from a distant object passes very near to a foreground galaxy or cluster, gravitational lensing can cause it to appear as multiple images on the sky¹. If the source is variable, it can be used to constrain the cosmic expansion rate² and dark energy models³. Achieving these cosmological goals requires many lensed transients with precise time-delay measurements⁴. Lensed supernovae are attractive for this purpose because they have relatively simple photometric behaviour, with well-understood light curve shapes and colours—in contrast to the stochastic variation of quasars. Here we report the discovery of a multiply imaged supernova, AT 2016jka (‘SN Requiem’). It appeared in an evolved galaxy at redshift 1.95, gravitationally lensed by a foreground galaxy cluster⁵. It is probably a type Ia supernova—the explosion of a low-mass stellar remnant, whose light curve can be used to measure cosmic distances. In archival Hubble Space Telescope imaging, three lensed images of the supernova are detected with relative time delays of <200 d. We predict that a fourth image will appear close to the cluster core in the year 2037 ± 2. Observation of the fourth image could provide a time-delay precision of ~7 d, <1% of the extraordinary 20 yr baseline. The supernova classification and the predicted reappearance time could be improved with further lens modelling and a comprehensive analysis of systematic uncertainties.
extinction in type Ia photometry	https://arxiv.org/abs/2004.10206	SNExtinction.pdf	The use of Type Ia Supernovae (SNe Ia) as cosmological tools has motivated significant effort to: understand what drives the intrinsic scatter of SN Ia distance modulus residuals after standardization, characterize the distribution of SN Ia colors, and explain why properties of the host galaxies of the SNe correlate with SN Ia distance modulus residuals. We use a compiled sample of ∼1450 spectroscopically confirmed, photometric light-curves of SN Ia and propose a solution to these three problems simultaneously that also explains an empirical 11σ detection of the dependence of Hubble residual scatter on SN Ia color. We introduce a physical model of color where intrinsic SN Ia colors with a relatively weak correlation with luminosity are combined with extrinsic dust-like colors (E(B−V)) with a wide range of extinction parameter values (RV). This model captures the observed trends of Hubble residual scatter and indicates that the dominant component of SN Ia intrinsic scatter is from variation in RV. We also find that the recovered E(B−V) and RV distributions differ based on global host-galaxy stellar mass and this explains the observed correlation (γ) between mass and Hubble residuals seen in past analyses as well as an observed 4.5σ dependence of γ on SN Ia color. This finding removes any need to prescribe different intrinsic luminosities to different progenitor systems. Finally we measure biases in the equation-of-state of dark energy (w) up to \|Δw\|=0.04 by replacing previous models of SN color with our dust-based model; this bias is larger than any systematic uncertainty in previous SN Ia cosmological analyses.
Are Type Ia Supernovae in Restframe H Brighter in More Massive Galaxies?	https://arxiv.org/abs/2006.13803	2006.13803.pdf	We analyze 143 Type Ia supernovae (SNeIa) observed in H band (1.6-1.8 μm) and find SNeIa are intrinsically brighter in H-band with increasing host galaxy stellar mass. We find SNeIa in galaxies more massive than 1010.43M⊙ are 0.13±0.04 mag brighter in H than SNeIa in less massive galaxies. The same set of SNeIa observed at optical wavelengths, after width-color-luminosity corrections, exhibit a 0.10±0.03 mag offset in the Hubble residuals. We observe an outlier population (\|ΔHmax\|>0.5 mag) in the H band and show that removing the outlier population moves the mass threshold to 1010.65M⊙ and reduces the step in H band to 0.08±0.04 mag, but the equivalent optical mass step is increased to 0.13±0.04 mag. We conclude the outliers do not drive the brightness--host-mass correlation. Less massive galaxies preferentially host more higher-stretch SNeIa, which are intrinsically brighter and bluer. It is only after correction for width-luminosity and color-luminosity relationships that SNeIa have brighter optical Hubble residuals in more massive galaxies. Thus finding SNeIa are intrinsically brighter in H in more massive galaxies is an opposite correlation to the intrinsic (pre-width-luminosity correction) optical brightness. If dust and the treatment of intrinsic color variation were the main driver of the host galaxy mass correlation, we would not expect a correlation of brighter H-band SNeIa in more massive galaxies.
Impact of axions on the Cassiopea A neutron star cooling.	https://arxiv.org/abs/2105.14745	2105.14745.pdf	The observed anomalous steady decrease in surface temperature of the supernova remnant Cassiopeia A (Cas A), which was reported about ten years ago, has generated much debate. Several exotic cooling scenarios have been proposed using non-standard assumptions about the physics and evolution of this neutron star (NS). At present, significant corrections have been made to the observational data, which make it possible to numerically simulate the Cas A NS cooling process in the framework of the scenario of minimal neutrino cooling. If there is an additional source of cooling, such as axion emission, the steepness of the Cas A NS surface temperature drop will increase with the growth of the axion-nucleon interaction strength. This makes it possible to limit the minimum value of the axion decay constant fa using the condition that the NS surface temperature should be within the 99% confidence interval obtained from the observational data. Two types of axion models are considered: the Kim-Shifman-Weinstein-Zakharov – KSVZ model and the Dean-FischlerSrednitsky-Zhitnitsky –DFSZ model. The above criterion gives a lower limit on the axion decay constant, fa > 3 × 107 GeV and fa > 4.5 × 108 GeV for KSVZ and DFSZ axions, respectively.
Can Stubbs kill MOND?	https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.161302	PhysRevLett.127.161302.pdf	We propose a relativistic gravitational theory leading to modified Newtonian dynamics, a paradigm that explains the observed universal galactic acceleration scale and related phenomenology. We discuss phenomenological requirements leading to its construction and demonstrate its agreement with the observed cosmic microwave background and matter power spectra on linear cosmological scales. We show that its action expanded to second order is free of ghost instabilities and discuss its possible embedding in a more fundamental theory.
A standard siren measurement of the Hubble constant using gravitational wave events from the first three LIGO/Virgo observing runs and the DESI Legacy Survey	https://arxiv.org/abs/2111.06445	https://arxiv.org/pdf/2111.06445.pdf	We present a new constraint on the Hubble constant H0 using a sample of well-localized gravitational wave (GW) events detected during the first three LIGO/Virgo observing runs as dark standard sirens. In the case of dark standard sirens, a unique host galaxy is not identified, and the redshift information comes from the distribution of potential host galaxies. From the third LIGO/Virgo observing run detections, we add the asymmetric-mass binary black hole GW190412, the high-confidence GW candidates S191204r, S200129m, and S200311bg to the sample of dark standard sirens analyzed. Our sample contains the top 20% (based on localization) GW events and candidates to date with significant coverage by the Dark Energy Spectroscopic Instrument (DESI) Legacy Survey. We combine the H0 posterior for eight dark siren events, finding H0=79.8+19.1−12.8 km s−1 Mpc−1 (68% Highest Density Interval) for a prior in H0 uniform between [20,140] km s−1 Mpc−1. This result shows that a combination of 8 well-localized dark sirens combined with an appropriate galaxy catalog is able to provide an H0 constraint that is competitive (∼20% versus 18% precision) with a single bright standard siren analysis (i.e. assuming the electromagnetic counterpart) using GW170817. When combining the posterior with that from GW170817, we obtain H0=72.77+11.0−7.55 km s−1 Mpc−1. This result is broadly consistent with recent H0 estimates from both the Cosmic Microwave Background and Supernovae.
Searching for TESS Photometric Variability of Possible JWST Spectrophotometric Standard Stars	https://arxiv.org/abs/2201.03670	2201.03670.pdf	We use data from the Transiting Exoplanet Survey Satellite (TESS) to search for, and set limits on, optical to near-infrared photometric variability of the well-vetted, candidate James Webb Space Telescope (JWST) spectrophotometric standards. Our search of 37 of these candidate standards has revealed measurable periodic variability in 15 stars. The majority of those show variability that is less than half a percent; however, four stars are observed to vary photometrically, from minimum to maximum flux, by more than 1% (the G dwarf HD 38949 and three fainter A dwarfs). Variability of this size would likely impact the error budget in the spectrophotometric calibration of the science instruments aboard JWST. For the 22 candidate standards with no detected variability, we report upper limits on the observed changes in flux. Despite some systematic noise, all stars brighter than 12 magnitude in the TESS band show a 3 sigma upper limit on the total change in brightness of less than half a percent on time scales between an hour and multiple weeks, empirically establishing their suitability as spectrophotometric standards. We further discuss the value and limits of high-cadence, high-precision photometric monitoring with TESS as a tool to vet the suitability of stars to act as spectrophotometric standards.
Directional Variations of Cosmological Parameters from the Planck CMB Data	https://arxiv.org/abs/2201.03799	2201.03799.pdf	Recent observations suggest that there are violations of the isotropy of the universe at large scales, an important part of the cosmological principle. In this paper, we use the Cosmic Microwave Background (CMB) data to search for spatial variations of the cosmological parameters in the ΛCDM model. We fit the Planck temperature angular power spectrum TTℓ for 48 different half-skies, centering on 48 different directions, to search for directional dependences of the standard cosmological parameters. There are 3(2)σ-level directional variations in Ωbh2, Ωch2, ns, 100θMC, and H0 (τ and ln(1010As)). Furthermore, the directional distributions of the parameters follow a dipole form to good approximation. The Bayes factor between the isotropic and anisotropic hypotheses is 0.0041, strongly disfavouring the former. The best-fit dipole axes for Ωbh2, Ωch2, ns, 100θMC, and Ase−2τ all generally align with the mean direction of V≡(b=−5.6+17.0∘−17.4,l=48.8+14.3∘−14.4), which is roughly perpendicular to the dipole of the variation in fine structure constant, and is about 45∘ to the directions of the CMB kinematic dipole, CMB parity asymmetry, and polarization of QSOs. Our results suggest either significant violation of the cosmological principle, or previously unknown systematic errors in the standard CMB analysis.
Unveiling the Universe with Emerging Cosmological Probes	https://arxiv.org/pdf/2201.07241.pdf		The detection of the accelerated expansion of the Universe has been one of the major breakthroughs in modern cosmology. Several cosmological probes (Cosmic Microwave Background, Supernovae Type Ia, Baryon Acoustic Oscillations) have been studied in depth to better understand the nature of the mechanism driving this acceleration, and they are being currently pushed to their limits, obtaining remarkable constraints that allowed us to shape the standard cosmological model. In parallel to that, however, the percent precision achieved has recently revealed apparent tensions between measurements obtained from different methods. These are either indicating some unaccounted systematic effects, or are pointing toward new physics. Following the development of CMB, SNe, and BAO cosmology, it is critical to extend our selection of cosmological probes. Novel probes can be exploited to validate results, control or mitigate systematic effects, and, most importantly, to increase the accuracy and robustness of our results. This review is meant to provide a state-of-art benchmark of the latest advances in emerging “beyond-standard” cosmological probes. We present how several different methods can become a key resource for observational cosmology. In particular, we review cosmic chronometers, quasars, gamma-ray bursts, standard sirens, lensing time-delay with galaxies and clusters, cosmic voids, neutral hydrogen intensity mapping, surface brightness fluctuations, secular redshift drift, and clustering of standard candles. The review describes the method, systematics, and results of each probe in a homogeneous way, giving the reader a clear picture of the available innovative methods that have been introduced in recent years and how to apply them. The review also discusses the potential synergies and complementarities between the various probes, exploring how they will contribute to the future of modern cosmology.
Galaxy Void catalog from SDSS	https://arxiv.org/abs/2202.01226	2202.01226.pdf	We produce several public void catalogs using a volume-limited subsample of the Sloan Digital Sky Survey Data Release 7 (SDSS DR7). Using new implementations of three different void-finding algorithms, VoidFinder and two ZOBOV-based algorithms (VIDE and REVOLVER), we identify 1159, 534, and 518 cosmic voids with radii >10 Mpc/h, respectively, out to a redshift of z = 0.114. We compute effective radii and centers for all voids and find none with an effective radius >54 Mpc/h. The median void effective radius is 15-17 Mpc/h for all three algorithms. We extract and discuss several properties of the void populations, including radial density profiles, the volume fraction of the catalog contained within voids, and the fraction of galaxies contained within voids. Using 64 mock galaxy catalogs created from the Horizon Run 4 N-body simulation, we compare simulated and observed void properties and find good agreement between the SDSS~DR7 and mock catalog results.
Hints of FLRW Breakdown from Supernovae	https://arxiv.org/abs/2106.02532		A 10% difference in the scale for the Hubble parameter constitutes a clear problem for cosmology. Here, considering angular distribution of Type Ia supernovae (SN) within the Pantheon compilation and working within flat ΛCDM cosmology, we observe a correlation between higher H0 and the CMB dipole direction, confirming our previous results for strongly-lensed quasars \cite{Krishnan:2021dyb}. Concretely, we record a ∼1 km/s/Mpc variation in H0 at antipodal points on the sky within the Pantheon sample, which is evident in the Low zsubsample (z≲0.075) and gets enhanced by higher redshift SN. Our work raises the possibility that we may be at the precision required to probe anisotropic Hubble expansions, while providing a concrete prediction for future inferences of H0.

Weekly Group Meeting schedule

Group Journal Club

Anthropic bound on the cosmological constant