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A Hitchhiker’s Guide to the Swampland

Posted in Maynooth, The Universe and Stuff with tags , , , , , on September 5, 2025 by telescoper

A very comprehensive review article has appeared on arXiv with the title Hitchhiker’s Guide to the Swampland: The Cosmologist’s Handbook to the string-theoretical Swampland Programme by Kay Lehnert (who just happens to be my PhD student). The paper is 170 pages long and contains over 1,800 references, which gives some idea of what a large field this is and how much work Kay has put into writing it!

This is Figure 3 from Kays paper. If you would like to know more of what it is about, turn to page 50…

The abstract reads

String theory has strong implications for cosmology: it tells us that we cannot have a cosmological constant, that single-field slow-roll inflation is ruled out, and that black holes decay. We elucidate the origin of these statements within the string-theoretical swampland programme. The swampland programme is generating a growing body of insights that have yet to be incorporated into cosmological models. Taking a cosmologist’s perspective, we highlight the relevance of swampland conjectures to black holes, dark matter, dark energy, and inflation, including their implications for scalar fields such as quintessence and axions. Our goal is to inspire cosmological model builders to examine the compatibility of effective field theories with quantum gravitational UV completions and to address outstanding cosmological tensions such as the Hubble tension. This comprehensive literature review presents clear definitions, cosmological implications, and the current status – including evidence and counterexamples – of the following swampland conjectures: the anti-de Sitter distance conjecture (AdSDC), the completeness conjecture (CC), the cobordism conjecture, the de Sitter conjecture (dSC), the swampland distance conjecture (SDC), the emergence proposal (EP), the Festina Lente Bound (FLB), the finite number of massless fields conjecture (or finite flux vacua conjecture (FFV)), the no global symmetries conjecture, the no non-supersymmetric theories conjecture, the non-negative null energy condition conjecture, the positive Gauss-Bonnet term conjecture, the species scale conjecture, the gravitino swampland conjecture (GSC), the tadpole conjecture, the tameness conjecture, the trans-Planckian censorship conjecture (tPCC/TCC), the unique geodesic conjecture, and the weak gravity conjecture (WGC), including the repulsive force conjecture (RFC).

This is essentially the literature review part of Kay’s thesis; the aim of his research is to study the implications of the string-theoretical swampland programme for cosmology. He’s particularly interested in the predictions string theory makes regarding inflation, dark energy, and dark matter, and the impact this has on the Hubble tension. The point of writing this review was to suggest projects that might be undertaken to bring string theory into the realm of testability, thus suppling material for the rest of Kay’s thesis, but I think it is also a very good guide for cosmologists of all types to what the swampland conjectures are and what they do and do not say about the Universe we actually live in.

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Government of Ireland Postgraduate Scholarships & Postdoctoral Fellowships

Posted in Biographical, Maynooth with tags , , on August 31, 2025 by telescoper
Close Up of Highlighting Specific Word Research in a Dictionary

While I remember, and before I get caught up in start-of-term things, I thought I would pass on news that two calls administered by Research Ireland will open on September 11th. These are the Government of Ireland Postgraduate Scholarships and the Government of Ireland Postdoctoral Fellowships. These are open to applications from candidates anywhere in the world.

You can find information about the Postgraduate Scholarships here and the Postdoctoral Fellowships here. The postdoctoral positions are for one or two years; postgraduate positions are for 2 years (Research Masters) or 4 years (PhD).

The application deadline is 23rd October 2025 and positions of both types are to start on 1st September 2026. You will need to contact possible supervisors at your planned host institute in advance of application so there isn’t much time.

Anyone interested in applying to hold one of these positions in Maynooth is welcome to contact me privately for advice or assistance. Given my rapidly approaching retirement, however, I am not able to act as nominated supervisor for postgraduate positions. I would happily support an applicant for a postdoctoral fellowship in the area of cosmology. There are of course many other potential supervisors both at Maynooth and elsewhere.

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It’s That Time of Year Again

Posted in Biographical, Education, Maynooth with tags , , , on August 31, 2025 by telescoper

Today is the last day of August, which, according to my calculations, means that tomorrow is the first day of September. Last week the kids started to go back to school and some of course started for the first time. I think the schools vary in the timetable for new arrivals and returning students, but they’re basically all operating fully from tomorrow, Monday 1st September.

Universities start back a little later, though this also varies. In Maynooth, Orientation Week (for new students) begins on September 15th, and lectures commence for all years on September 22nd, which happens to be the day of the Autumnal Equinox. My first lecture of the new academic year is on that day. I don’t know how many students I’ll have in my class yet. It’s a 4th-year class, and those students don’t register for modules until Friday 12th September, at the end of a week that begins with new students starting to enrol on Monday 8th September.

The first week of September will therefore be a bit quieter in the University than in the local schools. Next week sees a number of conferring ceremonies at which students who completed their studies with the examinations in May will receive their degrees. That includes a number of Physics students, who will graduate on Wednesday 3rd September. Unfortunately, when I tried to register to attend the ceremony, a few weeks ago, I was unable to because it was booked up so I’ll have to send my congratulations virtually. In any case, Conferring ceremonies at Maynooth are not what they used to be. Instead of the atmospheric surroundings of the Aula Maxima, they are now held in the soulless environnment of a lecture theatre. Instead of a nice buffet reception afterwards the graduates used to get, they now get a cup of tea in a paper cup and (if they’re lucky) a very small Danish pastry. It’s quite embarrassing actually. I wouldn’t be surprised if, in future, graduands were told to being their own sandwiches and a thermos flask. Anyway, a PhD student of mine will attend a conferring ceremony at the end of October. I’ll have to ensure I register on time for that one as I will be reading out the title of her thesis. Our first cohort of MSc students will graduate then too.

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Primordial Black Holes in Cosmological Simulations – Update

Posted in Maynooth, The Universe and Stuff with tags , , on August 28, 2025 by telescoper

Just time for a quick update about a paper that I posted about at the start of the summer, when it appeared on arXiv. At that time it had already gained a bit of traction in the media, e.g. here. Well, the paper is now published in the Open Journal of Astrophysics. Obviously, as an author I was conflicted so not involved in the editorial process.

Here is the overlay:

For those of you not in the field, there is currently a big mystery about how galaxies we have found at high redshift with JWST managed to acquire massive black holes so early in the Universe’s evolution. Black holes can grow quickly in a dense environment by accreting mass onto an initial seed, but what are the seeds? In this paper we investigate the possibility that they were primordial black holes. These form directly from fluctuations in the early Universe, as opposed to astrophysical black holes which form from stellar collapse. We don’t know exactly what mass primordial black holes would have nor how numerous they would be, but this paper uses high-resolution numerical experiments to investigate their effects if they do exist.

Here’s a pretty picture which is a zoom into 200 pc of the full simulation. I think 10pc counts as high resolution for a cosmological simulation! The blue circle shows the most massive PBH in the simulation, the green circle shows its nearest neighbour. The colour scale represents the number-density of dark matter particles.

For more details, read the paper!

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A Day of Offerings

Posted in Education, Maynooth with tags , , , , , , , on August 27, 2025 by telescoper

Today (27th August) is the day that students across Ireland receive offers of places at Third-Level Institutions to start next month. The offers for all courses and all institutions are available on the official CAO website here; they are also widely available elsewhere, including this searchable list.

The official numbers for Maynooth are here. Minimum points required for Maynooth’s – and indeed Ireland’s – most important course, MH206 Theoretical Physics and Mathematics, are 520 this year, up a little from 513 last year. MH204 Physics with Astrophysics is 385, up two points on last year’s 383. MH201 General Science (of which Physics is a part) is on 352 points, up two from 350 last year. Just for comparison, the points for these courses from 10 years ago were: MH206 550; MH204 480; and MH201 435, all significantly higher than this year.

Maynooth’s biggest course (by student numbers) – and indeed the biggest course in Ireland reckoned that way – is the Omnibus Arts programme MH101 which has an entry level this year of just 300 CAO points. Ten years ago it was 390.

It seems the first-round entry points for most courses at Maynooth have not changed dramatically despite the reduction in Leaving Certificate grades this year after several years of artificial inflation over the Covid-19 years. Leaving Certificate results are just one factor in determining the CAO points for a particular course at a particular Institution. Overall the picture is rather complex. Across Ireland, points are up for about 50% of courses and down for about 42%. The CAO points needed for a course is largely a matter of demand versus capacity rather than academic performance. For the last few years Maynooth University has been recruiting more and more students, putting pressure on accommodation, teaching loads and campus space. This strategy will prevent any significant rise in CAO points for the foreseeable future. This is probably happening to some extent across the sector, though Maynooth has a more urgent need for more students: to pay for the legions of new managers it has appointed. Two new €100K managerial jobs have been advertised so far this week…

All this just concerns the first round of offers so things may change significantly over the next week or two. Students now have to decide whether to accept their first-round offer or try to change course. They have until next week to do this. Departments won’t know how many new students they have for a while yet.

Update: Thursday 28th August. Here is the traditional  Irish Times First Round Offers supplement.

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Blu Tack Art

Posted in Art, Maynooth with tags , , on August 26, 2025 by telescoper

My attention was drawn today to this scuplture which is currently on display in the Department of Physics at Maynooth University. The artist and subject are unknown (to me) and the work is not dated, but the material is clearly Blu Tack, a putty-like pressure-sensitive adhesive commonly used to attach lightweight objects to walls, doors or other dry surfaces.

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Five Years at Home in Maynooth

Posted in Biographical, Covid-19, Maynooth with tags , , , , on August 26, 2025 by telescoper

I’ve received a number of bills and renewal notices of various kinds over the last few weeks, indicating the anniversary of me completing the purchase of, and moving into, my house in Maynooth. In fact it was five years ago today that I wrote a blog post occasioned by the fact that I’d collected the keys to this property, though it wasn’t until the following weekend that I actually stayed overnight here for the first time.

I was very lucky to be able to able to buy this property in what turned out to be a short window in the Covid-19 lockdown restrictions in the Summer of 2020. There were plans to return to on-campus teaching in September with drastic restrictions on the number of students in each venue. That plan was subsequently changed and then changed again to move almost all teaching back online, and then again to move again into a “Level 5” lockdown.

I was Head of Department back then. My memories of that time were immense levels of stress and frustration, constantly having to change our teaching arrangements with very little support from the University as well as shouldering a full teaching load. In order for the institution to carry on functioning, all teaching and support staff to do huge amounts of unpaid overtime while the institution built up a massive financial surplus. I could say more about the callous indifference to staff and students alike shown at that time by one particular member of The Management, but I think I had better save it for when I’ve retired.

Given the enormous workload I had then, it was to be almost another year before I had time to collect most of my belongings from my house in Cardiff and longer still before I managed to sell it and pay off the mortgage I took out to buy my house here. All this was much more complicated than I expected when I moved to Ireland!

Anyway, many of the things I’d planned to do when I moved here still aren’t done. I bought some old furniture from the previous owner with the intention of replacing it with new, for example, but I somehow never got round to that. Nor have I replaced the old windows, gutters, etc, yet…

One thing I have done is change the refuse collection. When I moved in I took over a contract with  Bord na Móna (literally “The Turf Board”), a company set up in 1946 to supply peat as a form of fuel but now diversified into other activities such as collecting and disposing waste. Over the last year the service provided by this company has degenerated to the point of complete unreliability. When I looked around for a replacement I found that Bord na Móna was also significantly more expensive than its competitors. Earlier this summer, therefore, I swtiched to a company called Greyhound which so far seems much better organized and is about 2/3 the price. That meant I had two sets of wheelie bins cluttering up my garden for about two months until Bord na Móna got around to removing theirs.

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Moving On

Posted in Education, Maynooth with tags , , , , , , , on August 22, 2025 by telescoper

Last week I wrote a post about the loose ends of the academic year, one of which concerned my PhD student Aoibhinn, who passed her viva voce examination way back in May, who had to submit a bound copy of the thesis to the relevant office by September 6th so that her degree could be ratified by Faculty and Academic Council. She has now done that, and in the process kindly made me an extra copy of the Authorized Version to put on my shelf:

It will be easy to find on my shelf because it’s a different colour from the others. Aoibhinn will be off to Germany for a postdoctoral fellowship after her conferring ceremony in October.

In subsequent post I mentioned a plethora of meetings to take place this week, all of which went off without much incident. The various Departmental Examination Boards did their business and students will receive their results on September 5th. Students involved in these will be moving on in various ways: some will be graduating, some progressing to the next year of their course and others – though not very many at all – will be leaving without qualifying.

Meanwhile, elsewhere in Ireland, students in the Class of 25 have today been receiving their school Leaving Certificate results. As expected, the proportion at the highest grade (H1) is down significantly compared 2024. On the other hand, the total number of students taking  Leaving Certificate examinations is significantly higher  than last year. You can find all the national statistics here.

How these nationwide effects  will work their way through to undergraduate admissions at Maynooth remains to be seen. Applicants will get offers through the CAO system next week; the points required by each higher education institution should be available online on Wednesday 27th. The Irish Times traditionally publishes a pull-out supplement showing all the offers for all courses at all universities across the sector the following day, i.e. on Thursday 28th September.

By the end of next week, therefore, we’ll have some sort of an idea how many students we will have entering the University in September 2025 and can begin moving on to the next academic year. One thing I’ve already got sorted out – way ahead of previous years – is my teaching timetable for Semester 1. Usually I’ve been happy if I had this before the first week of term! My new timetable makes Tuesdays and Thursdays my heaviest teaching days, but gives me Wednesday free for research and other things that I’ve started planning already.

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The Week Ahead

Posted in Education, Maynooth with tags , , , , , on August 17, 2025 by telescoper

Another weekend is almost over so, after spending most of this afternoon in the garden, I’ve retreated indoors to look at my calendar for the forthcoming week. I find a plethora of Examination Board meetings, one (tomorrow) for our Masters students who did their presentations on Friday and two for undergraduates who took repeat examinations in August (one for Mathematical Physics and one for Engineering, as I happen to have been teaching Engineering Mathematics this year). The two undergraduate boards are both on Thursday. All three of these should be relatively brief, but you never know…

There is another meeting tomorrow, Monday, about organizing our computational physics teaching for the new academic year. The merger of theoretical and experimental physics has given us the chance to coordinate the different computational modules offered by the two previous departments, but we need to make sure the teaching rooms are big enough and the computers have the correct software, etc. Fortunately I’m not actually teaching Computational Physics again until Semester 2 but we have to get it sorted in time for other modules happening in Semester 1.

In between Monday and Thursday I have two whole days with no meetings and no grading to do. I might be able to get on with some research, or at least with writing up some research I’ve already done.

Friday is a big day for the Irish higher education system, in that it’s the day students get their Leaving Certificate results. This year the grade inflation introduced during the pandemic is supposed to begin to unwind, but none of us outside the examination system knows how this will be achieved or what the results will be. If I had to bet I’d say that the CAO points needed for most courses at Maynooth will go down substantially, partly because of the deflation mentioned previously but also because The Management has decided that the University has to recruit more and more students and will drop entry standards as low as it needs to in order to meet its targets.

I don’t know how many students we will end up with for Academic Year 2025/6 but I do know that I will have retired before most of them complete their course. I used to find it a bit scary thinking about retirement, but not any more.

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Presentation Day

Posted in Education, mathematics, Maynooth with tags , , , on August 15, 2025 by telescoper

Today was the day of the last component of our MSc in Theoretical Physics and Mathematics here in Maynooth. The students handed in their dissertations on Monday and today they all gave presentations about their work. Listening to them all was very enjoyable, actually, as they were on a range of different topics, some purely mathematical, some statistical, and some more obviously physics. Moreover, they were all very good.

I often worry that assessing presentations is much more subjective than written work in physics and mathematics. In the event, however, we usually find good consistency in the scores awarded by staff in attendance. 

It also occurred to me during today’s presentations that we may make more use of such assessments to deal with the encroaching use of AI in project dissertations. One can get a good idea if someone has actually done and understood the work if they can present it in person and answer questions. That is, after all, the main reason we do viva voce examinations at PhD level.

Listening to talk after talk in a long session can be quite wearying – conferences are usually set up like that and they’re not often useful or interesting – but today’s session was fun. Not so much for the students I suppose, as there were a few signs of nerves. When all the talks were over the students trouped off en masse (presumably to the pub) as that was the end of their course. The staff remained behind to agree a set of marks and combine them with the other components of assessment, i.e. the marks for the dissertation. The examination board meets early next week, after which the final results will go forward to the University.

It was great to see the students all completing their course successfully, especially because it is (I think) such a demanding one. My only sadness is that we won’t see them until the conferring ceremonies in October. The Masters students have been regularly present in the Department throughout the whole year and I’ve had quite a lot of interest chats with them. I saw my own project student even more frequently, once a week for almost a year. We have to banish such thoughts now, though, as our thoughts turn to next year’s intake.

I don’t think any of the MSc students will read this – for all I know they’re still in the pub! – but in any case I’d like to say congratulations to them all and wish them all the very best for the future. They’ve earned it!

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