Archive for Shaun Hotchkiss

Cosmology Talks: Julien Lesgourgues on Neutrino Masses

Posted in The Universe and Stuff with tags , , , on April 3, 2020 by telescoper

If you are missing your regular seminar experience because of the Coronavirus lockdown, Shaun Hotchkiss has set up a YouTube channel just for you!

The channel features technical talks rather than popular expositions so it won’t be everyone’s cup of tea but for those seriously interested in cosmology at a research level they should prove interesting.

Here’s an example in which Julien Lesgourgues talks about (not measuring neutrino masses with cosmological data.

Article of the Day!

Posted in The Universe and Stuff with tags , , , , , , on July 31, 2013 by telescoper

Back in the office today, the heatwave having given way to grey drizzle and cool breezes (at least for the time being). I’ve got stacks of paperwork to catch up on, but fortunately I’ve got time to post a quick congratulatory message to Ian Harrison, who is author of today’s NASA ADS Article of the Day! Ian is a PhD student in the School of Physics & Astronomy at Cardiff University and was supervised by me until I abandoned ship to come here to Sussex earlier this year; he’s got a postdoctoral research position lined up in the Midlands (Manchester) when he finishes his thesis. The other author, Shaun Hotchkiss, is coming to Sussex as a postdoctoral researcher in October.

Anyway, the paper is a nice one, called A consistent approach to falsifying ΛCDM with rare galaxy clusters. Here’s the abstract:

We consider methods with which to answer the question “is any observed galaxy cluster too unusual for ΛCDM?” After emphasising that many previous attempts to answer this question will overestimate the confidence level at which ΛCDM can be ruled out, we outline a consistent approach to these rare clusters, which allows the question to be answered. We define three statistical measures, each of which are sensitive to changes in cluster populations arising from different modifications to the cosmological model. We also use these properties to define the “equivalent mass at redshift zero” for a cluster — the mass of an equally unusual cluster today. This quantity is independent of the observational survey in which the cluster was found, which makes it an ideal proxy for ranking the relative unusualness of clusters detected by different surveys. These methods are then used on a comprehensive sample of observed galaxy clusters and we confirm that all are less than 2σ deviations from the ΛCDM expectation. Whereas we have only applied our method to galaxy clusters, it is applicable to any isolated, collapsed, halo. As motivation for future surveys, we also calculate where in the mass redshift plane the rarest halo is most likely to be found, giving information as to which objects might be the most fruitful in the search for new physics.

In case you’re wondering, the rather Popperian nature of the title is not the reason why I’m not among the authors. I’m just not the sort of supervisor who feels he should always be an author of papers done by his research students even when they had the idea and did all the work themselves. From what I’ve heard talking to others, we’re a dying breed!