Death and serious injury from dark matter

A few years ago, I wrote a blog post about a paper published on the subject of dark matter as a potential cancer-causing agent.  Today, a related paper was published on the potential of "macros" -- dark matter object of macroscopic size (or weight) that could cause death or serious injury in humans, in the form a bullet-like wounds.  The apparent absence of such dark matter deaths is then used to put limits on the actual occurrence of such forms of dark matter.  

The paper is published open access in Physics Letters B, here.

First papers published in our Frontiers special topic

Last year, some colleagues (Lu Guo (郭璐), Denis Lacroix, Cédric Simenel, Nicolas Schunck) and I started organising and co-editing a special topic in the Frontiers in Physics journal on "Advances in Time-dependent Methods for Nuclear Structure and Dynamics".  We hoped to get a fairly broad snapshot of the current active work in the area, and a review of important problems.  I'm pleased to say that the first couple of papers have recently been published:

• Collective Inertial Masses in Nuclear Reactions,  Kai Wen and Takashi Nakatsukasa,  Front. Phys. 8, 16 (2020) describes a problem in going from a fully microscopic picture of nuclei (in which you treat each proton and neutron as an individual entity, and keep track of how they are evolving) to a collective picture (in which you characterise the whole nucleus in terms of a few parameters, such as its position, size, deformation).  One can derive collective equations of motion from the more complicated microscopic picture, thus providing a sure footing, but there is always a difficulty of how to deal with the mass in the kinetic energy term.  This paper discusses a particular method to derive these masses from the underlying microscopic theory, and that the results are consistent in the limit of several test cases, as well as showing interesting results for alpha-alpha scattering.

• Time-dependent Approaches to Open Quantum Systems, Maasaki Tokeida, and Kouichi Hagino, Front. Phys. 8, 8 (2020) discusses the problem of describing a quantum system that interacts with its environment, or a quantum system which can lose particles - an "open quantum system".  The loss, or dissipation, of energy, or of particles, or information can be a complicated (and complex in the mathematical sense, for that matter) thing to describe, and the authors develop and present two methods to describe systems which lose information to the environment, using a time-dependent approach, and show how each can be applied to the nuclear physics case of a heavy-ion collision.

There are several more papers to come, and I'm looking forward to reading them all, and having them as a useful collection of papers for everyone working in the field.  The picture is from the Wen and Nakatsukasa paper, showing snapshots of a calculation of and alpha+alpha reaction

Hyperfine school

I've been off work sick for a few days with the lurgy.  Ugh.  Ah well, these things happen, and it is winter flu season after all.  It's also exam marking season, and I'm back in at work with lots of marking to do which I had planned to get done earlier in the week.  

I also have an email that I thought I'd share here.  It's from a MOOC (free, online, university-level course) on hyperfine interactions; those interactions between electrons and nuclei that give rise to tiny splittings of atomic energy levels.  From the point of view of nuclear physics, they're useful because they give us a probe of nuclear properties, using theory that is quite well understood (and so relatively model-independent)

It looks very interesting, and great that Ghent University are providing the material, and support, for this course.  I don't know what textbook (if any) they use, but I include a picture of me reading the book I found most useful on the subject as an undergraduate. I paste the whole email from the course organisers below, for those interested in taking part which can be done starting next week in a supported way, or any time, in a totally self-study way:

On 12 February 2020, a new edition of http://www.hyperfinecourse.org will start. It is a free open online course about the physics of hyperfine interactions and experimental methods based thereupon. You can take this course self-paced at any time of the year, or - if you start on Feb 12 or before - you can take it in sync with students at Ghent University. In the latter case, you can ask questions and get feedback just as these students do.

The course is scheduled for 12 weeks, and requires about 5 hours of work per week. Emphasis is on conceptual understanding, less on mathematical derivations. The level is advanced bachelor or (early) master. A general science background at bachelor level is the expected entry level.

This is the list of topics covered:

the nucleus
the physics framework (classical/quantum)
electric monopole shift
magnetic hyperfine interaction
electric quadrupole interaction
+++
laser spectroscopy
Mössbauer spectroscopy
synchrotron radiation methods
nuclear magnetic resonance (NMR, a.k.a. MRI)
nuclear quadrupole resonance (NQR)
ENDOR (Electron Nuclear DOuble Resonance)
electron paramagnetic resonance (EPR)
low-temperature nuclear orientation (LTNO)
NMR on oriented nuclei (NMR/ON)
perturbed angular correlation spectroscopy (PAC)

Students get every week a set of videos, with associated tasks. Reports are submitted 24 hours before the weekly feedback webinar. During this weekly webinar, common problems encountered in the tasks are discussed, and questions raised by students during the past week are addressed. The webinars are livestreamed and recorded for later use.

If you want to offer this course as a formal course to students at your place, please get in touch and we’ll see how this can be organized.

Feel free to have a look at http://www.hyperfinecourse.org. A short registration is required (temporarily or permanent, as you wish), after which you have access to all material.

You receive this one-time email because you are known to be interested in hyperfine interactions, or because you have been previously registered as a student in this course.

Yours sincerely,
Stefaan Cottenier
Ghent University
Belgium

Brexit Day

I'm feeling pretty sad today that we are leaving the EU.  At 2300 this evening we will no longer be a member state.  So long, EU.  It was good while it lasted.

picture credit:  It's from this page in the Daily Express "Brexit POLL: Should it be illegal to fly the EU flag from UK public buildings.  VOTE HERE!" (I voted no)

Historical reminiscences on Skyrmions

There's a new paper on the arXiv today by Ian Aitchison, giving an historical account of the development of Skyrme's nonlinear field theory for nucleons and nuclei.  It explains some of the motivations - in terms of a desire to consider boson fields as more basic than fermion fields, with the latter being derived from the former; a desire not to have point-like particles; and a desire for conservation to arise from structural properties of an object rather than a symmetry.  In that last point he was apparently (as explained in the paper) inspired by William Thompson (Lord Kelvin), who was much enthralled by vortices in liquids and the emergence of a conserved quantity (Wirbelbewegung) and who came up with a vortex theory of atoms as a result.

The paper is quite informal, so I'd say it's fairly accessible to interested physicists, but with parenthetical remarks in it like "(this is essentially a consequence of the hedgehog ansatz)" it's clearly not quite targeted at the lay-person.  An enjoyable read for me to start the day with before getting on with marking assignments.  

Here's a picture from the paper, of a machine to make smoke rings to study the vortices that so interested Kelvin.  

Happy Birthday Gran!

I've just walked to the post office on campus to send off a card, written by my kids and also signed by me, to wish my grandmother a happy 90th birthday.  That happens on Sunday, so I hope my second-class stamp will get it there by then. 

Not only has my grandmother reached a major decadal milestone (or is about to), but all her 5 siblings are alive and well.  I don't think they are all getting together for the birthday, as far as I know, and I can never keep track of who is and isn't talking to whom in my family, but I hope that I inherited the relevant genetic traits from her to keep me fit, active, and mentally with-it to such an age.  

I am currently 45, so around the age my grandmother was when I was born.  Funny to think that the grandmother I remember from my earliest years was only in her late-40s - an age which seems relatively young to me, now that I am there!

The picture was taken 2 years ago; the last time I visited her in Troon.  That's my second daughter, Alba, posing next to her.  For a sense of scale, If I were standing on the other side of my grandmother, our three heights would form roughly a straight line.

Happy birthday Gran!

Paul-Henri Heenen 1947–2019

I received the latest copy of Nuclear Physics News today and was saddened to read of the death of Paul-Henri Heenen.  I knew Paul-Henri mainly through his work on building the Generator Coordinate Method on top of the nuclear mean-field to give a rather complete model of nuclear structure starting from an effective interaction and giving results at the bulk level (nuclear masses, sizes, and shapes) and spectroscopic level (details of excited state energies and transition rates) all in one picture.  I cite his review, co-authored with Michael Bender and P.-G. Reinhard in practically every paper I write. 

I met Paul-Henri many times at different conferernces and meetings.  I was particualrly struck by his humility when discussing his work, partly because it is an all-too-rare trait.  Despite the fact that his work was heroic in its sophistication and completeness, he was honest about the deficiencies.  Many people I know are quick to point out only the good points of their own work, and the bad points of others'. 

RIP Paul-Henri.  The picture is taken from the defi.eu website.