I had in mind to create a list of recent papers I found of interest that also had an author's talk available and in some cases a review. But after starting this post, I realized it's really so much better to have this data input into the recently initiated and excellent ResearchSeminars.org site, which has great listing and filtering capabilities and is becoming widely used. So I volunteered to the organizers of two cosmology talk series to input their data: Cosmology Talks on youtube hosted by Shaun Hotchkiss and CosmoConβ on youtube, aka Cosmology from Home. The target audience for these are researchers in the field. Now at the Research Seminars site, both Cosmology Talks and CosmoConβ are listed with all their current talks. Also, the Cosmology Talks series includes indexed links to the times of major sections of each talk as a convenience and helpful reference feature.
This paper [arxiv: 1902.03261] is a current status review on improving systematics1 in SNe Ia distance measurements by combining optical with near-infrared (NIR) photometry. Though initially being done at low redshifts (z <= 0.04), there are plans to extend this work to higher redshifts2. The paper is authored by some of the more noted researchers in this area, e.g., Arturo Avelino and Robert Kirshner3. My goal here is a top-level summary, so that if you don't read the paper you'll hopefully get the gist of it, while also including helpful supplemental info. In a few cases, I added some font bolding for emphasis.
“This is significant for supernova cosmology because, along with photometric-calibration uncertainties, uncertain dust [extinction](https://en.wikipedia.org/wiki/Extinction_(astronomy) estimates and the intrinsic variability of SN Ia colors present challenging and important systematic problems for dark energy measurements. (pg2)”
“Recent work has demonstrated that SN Ia in the NIR are more nearly standard candles, even before correction for light curve (LC) shape or host galaxy dust reddening... Overall, a substantial body of evidence indicates that rest-frame LCs of SN Ia in NIR are both better standard candles than at optical wavelengths and less sensitive to the confounding effects of dust. When NIR data are combined with UBV RI photometry, this yields accurate and precise distance estimates. (pg2)”
New developments since this post was originally created:
This is about two recent papers with the premise that H0 tension resolution could come from new physics at early times before recombination.
The first paper, Sounds Discordant: Classical Distance Ladder & ΛCDM-based Determinations of the Cosmological Sound Horizon [arxiv:1811.00537] is based on looking at the tension in terms of the sound horizon rs. They cite several advantages of doing so: (1) “added insensitivity to extreme changes in the cosmology at z < 0.1, since one does not need to extrapolate to z = 0”, (2) “the ΛCDM predictions for the sound horizon are more robust than those for H0”, (3) “as with the inverse distance ladder, this approach clarifies that reconciliation can not be delivered by altering cosmology at z < 1”, (4) “it serves to clarify that the reconciliation of distance ladder, BAO, and CMB observations via a cosmological solution is likely to include a change to the cosmological model in the two decades of scale factor evolution prior to recombination”, and (5) “σ(rs)/rs from CMB data, assuming ΛCDM, is four times smaller than the σ(H0)/H0 from the same data and assumed model.”
Subject paper: Measuring the Duration of Last Scattering, by Boryana Hadzhiyska and David N. Spergel
General Background:
A very common simplification one hears is that the cosmic microwave background (CMB) photons began freely streaming ~380k yrs after the big bang at redshift ~1090 when the universe cooled sufficiently for neutral hydrogen atoms to form and Thomson scattering no longer impeded the free flow of photons. What's rarely mentioned in science media articles is that what's called the surface of last scatter, when individual CMB photons decoupled and began freely traveling, has a thickness (or depth) layer to it. This thickness has been compared to the skin on an apple1. Though the term 'last scattering surface' is commonly used, it's more accurately characterized as a 'last scattering layer'2 due to its width. The layer is opaque and has been compared to a fog bank on Earth.3
Slides from talk by Chris Tully at the Opening New Windows to the Universe forum at Brookhaven National Labs on 2021-11-03: PTOLEMY: Relic Neutrino Detection
New developments since this post was originally created: Cosmologist Sunny Vagnozzi shares some updated info on the PTOLEMY project status in a short thread here. He also mentions that he is collaborating on a paper about PTOLEMY with Stefano Gariazzo that will soon (as of March 2020) be posted on the arXiv.
-—
This is about paper 1902.05508, posted to the arXiv on 2/14/2019.
I was mostly unfamiliar with this groundbreaking project so this new paper provided a reading-up opportunity, leading to these general overview notes. I added the bolding for emphasis.
The PTOLEMY project1 aims to directly detect relic neutrinos from the cosmic neutrino background (CNB or CνB), along with a impressive broader set of capabilities or opportunities2a. The project is described as the “the first of its kind and the only one2b conceived that can look directly at the image of the Universe encoded in neutrino background produced in the first second after the Big Bang”.3 (pg2) Achieving the project's goal “would profoundly confront and extend the sensitivity of precision cosmology data.”(pg5) This paper addresses the theoretical aspects of the project, its physics goals, and an outline of the project's scope of work to be done in the next three years. An earlier paper 1808.01892 gives more details on three phases of the project: proof-of-principle demonstrator, scalable prototype realization and tests, and full detector construction.
The technology is based on neutrino capture on beta decaying nuclei (NCB)5, with tritium (3H) determined as the best choice. The capture results in a tiny boost of energy to the electrons emitted in tritium decay, so there'll be a peak in the electron spectrum above the β-decay endpoint4. The planned target is ∼100g of tritium atomically bound to a radio-pure graphene substrate (they refer to it as “tritiated graphene”). They expect ∼10 CνB capture events per year, depending on the mass hierarchy and the Dirac versus Majorana nature of the neutrinos; the rate is half as large for non-relativistic Dirac neutrinos2a. The anticipated energy resolution is ∼0.05eV, “an order of magnitude beyond the original target and the highest resolution of any calorimeter.” [source]
