Tags: #physics

Each of the two searchable webpages has a link to the other, as well as to the source data. The webpages are self-contained with all the data included in the html file, which contains the javascript code for the searches and the CSS for styling.

The original purpose in doing this was because many of the submissions were not on the arXiv, and I wanted to see what else was available and also so the PDF file link were all on one page. In addition, though, the search feature has been very useful.

The webpages are coded with simple html and javascript (javascript must be enabled to view the data). The webpage search input box shows the syntax:

Use * for AND search, : keyword1*keyword2

Use | for OR search: keyword1|keyword2

For NOT, use — (2 hyphens) after 1st keyword: keyword1—keyword2

¹APC: Activity, Project, or State of the Profession Consideration

HashTags: #astrophysics #cosmology #physics

January 2020: In new paper arXiv: 2001.09213, the MCP reports an updated $H_0$ value of 73.9 ± 3.0 based on improved distance measurements for 4 of the 6 systems they previously reported on. MCP researchers Braatz, Pesce, Condon, Reid, et al teamed up with SH0ES team members Scolnic and Riess for this paper. Here is a clip of Figure 1 from the paper. Additional details in this reddit thread.

July 2019: video and slides of a presentation by Mark Reid at the KITP-UCSB conference Tensions between the Early and the Late Universe on July 16, 2019: H0: NGC 4258 and the Megamaser Cosmology Project -—

This post is about the paper Science with the ngVLA: H2O Megamaser Cosmology, which was posted on the arXiv preprint server in Oct. 2018.

What's This About? A recent comment by one of the people I regularly follow (who writes excellent posts on astronomy/cosmology topics) mentioned this NRAO key project as providing direct geometric measurements of the Hubble Constant (H_0) independent of the Cosmic Microwave Background (CMB) and standard candle methods. The megamaser method gives angular diameter distances to water megamasers¹ in the nuclear regions of host active galaxies within ~0.1 pc of the SMBH. The galaxies are typically well into the Hubble flow at between 50 – 200 Mpc distance. This slide compares the distances to various studied megamasers to those for Cepheids. As indicated in the slide, these megamaser distances can be used to calibrate other distance methods.

Not being familiar with this MCP project but finding it of interest, I've tried to integrate and summarize some reading on it into this mini-overview, non-expert's report.

What Are They? These H₂O megamasers being studied are a special type of astrophysical maser originating in a flat accretion disk, with warm (~400 K) dense gas clouds, in Keplerian motion orbiting the SMBHs of host active galaxies. They produce stimulated coherent emission at 22 GHz from collisionally excited transitions between rotational energy levels of ortho-states of water². Typical rotation velocities are ~500 km s^-1. Megamasers have a large isotropic luminosity, typically 10³ solar luminosities. A radio continuum background source is needed to provide the radiation that's amplified by the maser.

What facilities are currently involved? “The MCP uses the most sensitive suite of telescopes working today at 22 GHz, including the GBT for surveys and spectral monitoring observations, and the High Sensitivity Array (the VLBA, GBT, VLA, and 100-m Effelsberg telescope) to map maser disk systems.” [quote source]

What's Involved in Measuring the Distances? Multiple steps, e.g.: (1) survey with the GBT to identify the rare, edge-on disk megamasers needed for this method (this maximizes the gain length as described in footnote¹ references), (2) image the sub-parsec disks with the High Sensitivity Array, (3) with the GBT, monitor spectral drifts in maser lines (red vs blue shifting) from centripetal accelerations of the clouds as they orbit the central BH, (4) VLBI observations for rotation curve mapping, and (5) modeling the disk dynamics. Basically, the distance to the galaxy is measured by comparing the observed angular radius of the maser's orbit to its measured linear distance from the black hole (see this visual slide and further informational details in footnote¹).

Current Status: The most complete set of H_0 results I've seen the MCP report is 67.6 ±4.0, a 6% measurement. The individual 6 measurements are shown in this slide, which also shows the distances in Mpc. A comment indicates they expect to improve the measurement to < 4%. (I've also seen a ±3% goal in several of their papers). In the slide, two of the results are shown in prep, which may explain the difference from the 69.3 ±4.2 result from their latest paper 1810.06686 which reports only 4 results.

In Extragalactic maser surveys [1802.04727] they report: “With respect to 22 GHz H₂O masers, we note that the MCP is close to completion. We can expect a final Hubble constant deduced from this survey with an uncertainty of only a few percent during the next one or two years.” (page 9) Their latest paper says their final results will be based on distances to 9 megamasers. Surveys of 3000 galaxies were necessary to identify those 9 (AGNs are required with a maser disk suitable for measurement and with an edge-on view).

What's Their Future Plan? A recent 5-page paper details their plans involving the next-generation Very Large Array: H2O Megamaser Cosmology with the ngVLA [1810.06686]. Their ultimate goal is a 1% measurement, which will (1) require a survey to identify additional megamasers – their forecast is that ngVLA can discover ~30 times more sources than the GBT, and (2) the ngVLA must have certain design features as outlined in section 6 of the paper.

An overview document on the ngVLA shows it's timeline as initiating early science in 2028 and full operations in 2034.

Are There Other Study Results from MCP? Besides its primary mission for H_0 measurements, MCP results to date include the “gold standard” most accurate method for extragalactic BH masses, (e.g., see 1801.06332), and also precise BH masses in relatively low-mass systems where the BH masses have been difficult to measure – this has important implications for galaxy evolution (e.g., see 1007.2851).

What are some other MCP references? An interesting set of slides from an NRAO presentation is Water Megamasers in Galaxies, which I recommend. The Megamaser Cosmology Project has a wiki page here.

Footnotes: ¹ For a good reference on the distance measurement techniques, see Braatz et al, Measuring the Hubble constant with observations of water-vapor megamasers. For a nice summary graphic of this geometric distance technique, see this. Also the wikipedia page has a short summary here.

² See this for a graphic showing various rotational energy level transitions of water. Also see this graphic. The particular transition of interest for megamaser study is 6₁,₆ –> 5₂,₃. For more complete data on these transitions, see Table 6 in 1510.06182. Other transitions of ortho-H20 such as at 183 GHz are also candidates, but 22 GHz is the most studied currently, and is directed at ortho-H20 rather than para-H2O: “we consider only transitions between ortho-states because these are the states for which the most extensive collisional data have been calculated, and because in a hot plasma the abundance of ortho-water will exceed that of para-water by a factor 3.” Note: these two water states “are not connected by radiative or collisional transitions.” Neufeld and Melnick 1987 ApJ 322,266. Two other good sources on the transition details is Astrophysical masers and The Physics of Water Masers observable with ALMA and SOFIA [1510.06182].

Tags: #cosmology #H0 #physics

Planck Length: PhysicsForums article

Cosmology: Sean Carroll on True Facts About Cosmology (or, Misconceptions Skewered) | Inflationary Misconceptions and the Basics of Cosmological Horizons | Inflation Balloon Analogy Misconceptions | Expanding Confusion: common misconceptions of cosmological horizons and the superluminal expansion of the Universe, by Davis and Lineweaver |

Quantum Mechanics: reddit thread

Statistics: Statistical tests, P values, confidence intervals, and power: a guide to misinterpretations

Physics: reddit thread

Hashtags: #physics #cosmology

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 opportunities^2a. The project is described as the “the first of its kind and the only one^2b 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 neutrinos^2a. The anticipated energy resolution is ∼0.05eV, “an order of magnitude beyond the original target and the highest resolution of any calorimeter.” [source]

This paper was reviewed prior to release at an international conference⁶ of principal collaborators in Nov 2018. Chris Tully leads the experimental effort⁷. A 2016 article about him and this project is here.

I searched for a project website but did not find one. For supplemental details on this project, there's a video of a Chris Tully talk. Tully gives an indication of the magnitude of the effort at this point near the end of the talk⁹. Slides from another of his talks are here.

The eventual plans are for a world-wide array of detectors to reach discovery sensitivity for the CNB. The number and deployment will depend on the next phase of PTOLEMY developments after the 3-year study described in the two papers. ___ Note: page numbers in the footnotes refer to pages in the PDF, not page numbers as shown on the page footer

¹ The acronym stands for the PonTecorvo Observatory for Light, Early-universe Massive-neutrino Yield. Originally the facilities were at Princeton, with the leading P and T stand for Princeton Tritium but that was changed with the move to LNGS. (I'm not clear on whether the move is planned or actually underway or even completed. I found nothing online about that.) The meeting room for the recent conference⁶ was in the Pontecorvo Room at LNGS. Chris Tully has a humorous anecdote about his renaming dilemma in this video clip.

^2a Broader capabilities or potential opportunities include (1) MeV dark matter searches which are anticipated to begin at the end of 2019 with data collection through 2020 [1808.01892, pg6], (2) checking the neutrino mass hierarchy “from a different and independent approach than oscillation experiments” (pg20), (3) measuring the standard neutrino absolute mass scale (pg20), (4) determining the neutrino mass ordering (pg12), and (5) checking for the “scenario of an extra sterile neutrino with mass in the eV range coupled to the active states via oscillations” (see section 6 beginning on pg 15). There's a discussion on pg7 about the capture event count rate being different (~double) for non-relativistic Majorana neutrinos vs Dirac, along with a discussion of whether the experiment could distinguish between the two cases (characterized as “difficult to achieve”).

^2b “Despite the demanding technological issues in dealing with a large tritium mass, as well as in achieving high energy resolutions (which, however, are not so far from present values), we note that there are no other feasible approaches to directly unveil the CNB. The only other plausible one, the Stodolsky effect, is much more challenging to be detected, if not simply impossible, if cosmological neutrinos have zero (or exceedingly small) chemical potential.” (pg20)

³ Neutrinos decoupled ~1 second after the end of inflation, being in thermal equilibrium prior to that. [neutrino decoupling] In contrast, photons did not begin freely streaming until ~380,000 years later, prior to that they were constantly scattered by free electrons until the universe cooled enough for neutral atoms to form.

⁴ For more in-depth details on ³H beta decay and NCB, see [pg12 in PTOLEMY: A Proposal for Thermal Relic Detection of Massive Neutrinos and Directional Detection of MeV Dark Matter 1808.01892, slides 4 – 6 in footnote⁸, and footnote⁵. Wikipedia also has a quickie overview.

⁵ For more details on NCB, see Measuring anisotropies in the cosmic neutrino background (PhysRevD.90.073006)

⁶ The International Conference on Cosmic Neutrino Background Detection and Dark Matter Searches with PTOLEMY. Slides and materials from that conference are available at the link.

⁷ Tully and Marcello Messina are the spokespersons at the top of the project's organization chart.⁸ (slide 39 in footnote 8)

⁸ See slides from Messina's talk at the 2018 conference event⁶ site: The PTOLEMY project – from an idea to a real experiment for detecting Cosmological Relic Neutrinos.

⁹ “I remember giving a talk at Stony Brook a couple years back and a good colleague of mine Paul Grannis said 'look, your experiment involves atomic physics, nuclear physics, condensed matter physics, cosmology particle physics, you know, you and what army is going to take on this.' And you know if anything maybe my role is to show that there's something worth fighting for but I think that I see you know around the world there's a growing and growing larger number of people who are interested in tackling these problems and so I wouldn't be surprised that you see a lot of these observatories springing up. I think that this idea of starting with the light Dark Matter scattering is a very promising way to get that going.”

Tags: #cosmology #neutrinos #physics

The graphic below is from Planck 2018 results. XVI. Cosmological parameters, Table 1 on page 14.

This next graphic is from the Wikipedia Lambda-CDM article, which is based on the Planck 2015 results.

The graphic below is from a talk by Marius Millea, slide 19 of The Planck satellite and cosmic concordance. He discusses this graphic in a video starting at 10 mins into the talk. For some additional info, see another of his talks, The Planck Value of H0 (and other ΛCDM Parameters). Also, see additional talk materials by Marius.

The graphic below is from [1611.00036] The DESI Experiment Part I: Science,Targeting, and Survey Design Search, Table 2.2, page 18:

Tags: #cosmology #physics