Invisibles Workshop 2013
The Invisible Cloak of Constraints in Physics
Lumley Castle is a beautiful place, filled with stone corridors and tapestries, medieval art and happy staff. The Invisibles Conference held here in July 2013 highlighted the parameters involved in the search for Dark Matter. I was graciously invited to attend talks at the end of the week, missing the days devoted to Neutrinos, but finding myself sailing instead into a sea of conflicting ideas as to what constitutes Dark Matter and what it should look like.
Thursday morning began with an assertion that being unstable in vacuum (i.e. deep space) could be due to a relationship with the Truth (Top) Quark, and that Supersymmetry would be the route to stabilisation. Breakage of SUSY (supersymmetry) happens in the Higgs field, the first speaker told us, and gives rise to quantum loop problems. And loop cancellation requires additional particles to be added to the existing, overpopulated Zoo. On the Dark Matter trail, SUSY "hasn't been seen, and should have shown up by now," he said.
New Physics and what it should look like was a topic touched upon by many speakers, with debates raging over what dark matter particles might be. A popular contender seems to be the WIMP (weakly interactive massive particle) but vanilla Wimps apparently produce embarrassingly large couplings, which would seem to go against the grain of Dark Matter. Sacha liked Axions, also an oft-mentioned candidate. Hidden gauge bosuns were proposed too, but they rely on stability from SUSY. A 'minimal approach' might be that Dark Matter allows for gauge interactions only, but across a wide range of particles, giving it freedom to interact with all of them. The speaker on this was seeming to indicate that such freedom would include freedom from SUSY, but when I asked him later if this were the case, he said it didn't.
A welcome change of pace arrived in the form of Neil, who opened with the fact that it had taken 50 years to find Higgs, and there were wide anomalies over what Dark Matter should look like (compared with Higgs which had been a reasonably straightforward picture). He surmised 3 categories in Dark Matter theory - Reasonable, Weird, and Crazy, going on to discuss a slide which showed a matrix of factors related to each category. 1984, he said, was a Utopia year for SUSY, but times have changed. "We now see positron excesses at high energies and a general increase in the appearance of antimatter - does this signal DM [Dark Matter], or is it all too good to be true?"
Naive exclusions, he said, were commonly imposed on what after all represents a potentially vast rate of exchange, and questions were correspondingly needed - what if assumptions were relaxed or broadened? The positron, he suggested, widened the understanding of Dark Matter models, but the homely affair with light WIMPs demonstrated the limits of 'exclusion plots' as a tool for further stretching of cosy boundaries.
After coffee we were brought back to ground state in exploring constraints with spin vector couplings - worth noting that spin dependence is weaker than spin independence, a clear signal that Dark Matter doesn't have any desire to be constrained. We could steal from SUSY jet objects, said the speaker, and we could look at the coupling of Dark Matter to Quarks. What fraction of events would be sufficient to probe the UV transition? I pricked up ears. UV transition? What part did light have to play on the Dark Matter trail? We could look for the light mediators directly, said the speaker, or we could look for the "available, observable, invisible signature".
Lunch was a sparklingly wonderful affair, with delicious food which spanked the pants off a 4-star Michelin meal I'd been treated to elsewhere some weeks before. I talked briefly to some participants and asked one, "does Dark Matter have to rely on symmetry?" Obsession with symmetry seems to know no bounds and whilst one speaker had suggested that dark forces could cover a wide range of particle scales, he confirmed nevertheless that symmetry had to be part of the equation. A young man from Southampton standing in the food queue shook his head slowly and said, "no", inspiring a certainty that this dark substance was going to break many rulebooks before it would allow itself to be identified.
The afternoon sessions kicked off. And while diagrams vaguely resembling breaching whales appeared on the Powerpoint projections, it was said that the background data cannot be explained. I harked back to Cryodet II, when the hunt for neutrino identities was still crashing around in the thicket, and no sooner had I thought this than the speaker told us that the first signals had been detected at Gran Sasso (where Cryodet II took place). There are, and were back then, many more experiments worldwide, and many more synchronicities to follow.
Solar winds, meanwhile, could affect mass calculations, and make WIMPs look heavier than they really are. Aggressive contenders in the Dark Matter line-up, WIMPs appear time and again as seductively cosy candidates. But, warned the speaker, parametising in bins has limitations. Without applying fixed scales, he said, data construction works better. There was a question from the floor as to whether parametisation was flexible enough. And another queried that as the Sagittarius stream appeared to be passing clean through our solar system, would it be likely to affect us? I was busily asking myself of the many potential ways in which these invisible entites, energies and associated forces could be affecting us directly. The next day, I came pretty close to finding out.
Lots of toys around to play with in the hunt for Dark Matter, hence Powerpoint pictures of satellites and ground telescopes, allowing astrophysics to cover a lot of intergalactic ground. With Fermi bubbles shining through our galaxy, charged particles, Gamma rays and astro neutrinos, Dark Matter clustering can be charted from halo distributions but considerable uncertainties remain. The challenge, it was said, is in looking for an uncertain signal in an uncertain background, making a search for a needle in a haystack a walk in the park by comparison. Dwarf galaxies as prime Dark Matter candidates? Light ratios there are low, but gamma ray lines are considered a 'smoking gun' - Earth's atmosphere itself presents a gamma ray 'ring' haloed from the energies abundant in outer space. New experiments "often reveal residual backgrounds". It's very challenging to quantify the exact properties of residuals.
The day closed with a Discussion session, and when Topic 1 appeared on the screen I couldn't resist raising a hand. The question popped on Powerpoint was, "How do we get out of this mess?" I volunteered a possible solution. "Given that there's a lot of concentration on constraints and constant parameters, how about pushing the boundaries a bit more and thinking right outside the box?" A few of the scientists around me quietly voiced various thoughts of their own.
Friday kicked off with Dark Operators. There is still a lot of argument over whether Higgs is vanilla.
Terms of spin polarisation are not projected out in physical observables. Spin - a property of quantum particles to dance about in given ways, commonly known as spin-up or spin-down, plus a number quotient - half or one, or sometimes even three-quarters. The width of a Higgs particle is unmeasurable by the Large Hardon Collider, and as this is the most advanced piece of kit available to date I'd guess measuring the width is likely to remain a task beyond the wit of man, but why worry? Width, surely, isn't everything. A light Higgs is very narrow - no telling how narrow, of course. If Dark states are initially light, they must of course stay light, a curse lifted possibly by neutrino portal operators, and it was a pleasant relief to me that as the day wore on the neutrino made more shows on stage while the girth of God particles disappeared into the wings.
WIMPs came back in the second talk, coming under the Normal range of possible Dark Matter models. The speaker was rightly concerned that over the past 15 years, models have grown in abundance, and to have any chance of satisfying that abundance, "some technical naturalness is required". He added, "Let us get rid of dark force or extra mediator concepts, or maybe make them very heavy." A light version of a Dark Matter field could kill off a Higgs boson quite easily.
A Powerpoint slide said, "You think gravitino Dark Matter is depressing, so can be WIMPs," of which there are two types - Secluded and Unsecluded. And if Dark Matter carries no charge it will be difficult to detect, so he proposed an extra-near detector setup might be the answer. New toys to order.
I wrote in my notebook, "Carbon excitation with energy release," because we are carbon units, so anything to do with Carbon could well have something to do with us, but the moment was gone before I could add to that comment. The next speaker spoke more about constraints, the strongest being from Xenon-10 but these are also the most uncertain (that trade-off again - the more you seek to constrain something the more uncertain your outcomes are likely to be). He finished with an ear-pricking speculation - that a Dark Matter beam on top of a neutrino beam is an interesting possibility.
Lecture 3 was about WISPy Cold Dark Matter. Like others before him, this speaker had a pie chart on his Powerpoint which showed a big percentage of Dark Matter and Energy beside a piddling slice of ordinary matter and neutrinos (I wondered where photons fitted in but didn't ask). He vouchsafed that Dark Matter doesn't radiate and only weakly interacts, it has to be cold and it has to be bosonic. (A WISPy thing in physics is a Weakly Interacting Sub-eV Particle which means it doesn't communicate with other things very much and is too small to be easily measured.)
String Theory, he said, needs extra dimensions, which must compactify so that shape and size deformations conform to fields connected to the fundamental scale. I sighed. So much conformity and compactification. But then he spoke about hidden photons - the quantum partners of standard photons - and that photons might oscillate between the two. The question arising in my mind by now was whether this didn't in itself imply a likely relationship between 'Ordinary' Matter and Dark Matter, but I didn't voice the point.
Carlos Frenk then delivered a lively presentation with a riveting show of intergalactic simulations. He ruled out neutrinos as likely candidates, as they would be 'too hot', while ruling in the sterile neutrino. Two Dark Matter propagating models whirled around the projector screen, the Cold version being very gauze-like and full of widely dispersing filaments, much as you'd see if you pulled apart a piece of pillow filling. The warm version was quite different - it seemed to flow in an almost liquefied fashion. The warm version was smooth, streaming and had fewer self-bound structures in it. But, he asked, was warm Dark Matter "too small to succeed?" And was cold Dark Matter ruled out by the abundance of 'massive satellites' (solar structures)? There was a question from the floor - whether Dark Matter was likely to be a single particle, or a more complicated affair?
At lunch, served out on the fabulous lawn due to a wedding takeover of the banqueting hall, I found myself seated at a table where discussion turned to the shifting nature of Dark inputs according to various spacial positions. I asked whether this could not suggest some visible effects on Earth as we moved around the solar system. The woman holding court at the table turned to her contemporaries in considering the best analogy to offer (an ignorant unscientific interloper), and began to explain about the listing of ships against the wind. I understood what she was saying, I explained in turn, but wondered whether perhaps Dark influence might be responsible for the repetitive weather patterns we see according to the position of the sun at certain hours, when for instance over the course of a few days we would see that the weather sets its clock according to the position of the sun - something I saw no harm in mentioning it at the al fresco dinner table. Talk of the weather is after all a standard English safety zone. Or so I thought. I was to be proved wrong.
Afternoon sessions opened with Vanilla Cosmology, on which I took few notes because vanilla is not my strongest subject. But the speaker eloquently described a slowly rolling scalar field, with 'stretched quantum fluctuations', in which entropy had produced from a hot, swirling thermal plasma soup an abundance of Higgs-like particles. I had to smile - the newest particle to hit the discovery charts had quickly made its way, it seemed, to the top of the Dark Matter candidacy jar. Phase transition on the universal scale, she said, started with hybrid inflation, through to cosmic strings, to leptogenesis and ultimately Dark Matter, suggesting that Dark Matter had somehow made a late appearance in the cosmic order. I wondered if this were so, and how one would know, since nobody has ever seen it.
Christof Wetterich gave what I thought to be one of the best talks of all, introducing a new term to the gathering - the Cosmon field. This field, he explained, is similar to the electric field but has no 'direction'. He spoke of the neutrino evolving into a non-relativistic particle late in the timeline of the Universe and bringing with it an energy density not much smaller than that believed to arise from Dark Matter, to which Neutrinos, he purported, can have a substantial coupling potential. There would be, he said, strong bounds on atom-cosmon couplings, shown from tests of equivalence principles and time variation, but no such bounds apply to neutrino couplings. A cosmon-mediated attractive force would have a similar scale to gravity, while growing neutrinos can change cosmon evolution, and growing neutrino mass triggers a transition to almost static Dark Energy. A 'stopped' scalar field, he said, mimics a Constant! I found myself nodding. More smoking guns in the woodpile. Cosmic events. says Christof, trigger changes in cosmon evolution.
The last session put the cosmological constant under further investigation. Once more we saw lots of finely-tuned cosmic pies varying from the pies thrown onto screens before. The speaker mentioned a "Quintessence-Cosmon slowing rolling scalar field" with negligible couplings to matter. And during a warning of loop systems, I noticed Amendola's name in the corner, there among the list of credited scientists investigating Dark Energy-coupled models. (Luca Amendola is distantly related to Tony Amendola, whose quote is on the Home page.) "Is the Universe non-flat," the speaker asked? "Have we been duped by a fake W (or Z)?" I laughed silently. If it turned out that the W particle was fake, I'd be first to congratulate Carlo Rubbia on winning a Nobel Prize for intergalactic deception.
As I made my way out of the hall I was stopped in my tracks by a large young man who told me the organiser wanted to see me. I was pleased, as I'd wanted to chat with her about what I was doing, and why. But I was struck dumb by what I found to be the reality of that present moment. In hindsight I blamed those conversations on the weather.
"I don't want any of this Conference making its way into any book you might write," she said vociferously. "This is a public event, but those attending it are scientists, and I'm very uncomfortable with what's been said here and feel misled by your emails."
My emails had explained truthfully that I'd had a conversation with a scientist speaking at this event, and he had suggested I contact her to see if I could sit in on some of the talks. My website, clearly citing the nature of my interest, was linked as a postscript and also appeared on subsequent coupled mailings confirming the time of my likely arrival. I'd made no suggestion that I was other than what I am, so this accusation really took me aback. More was to come.
She told me that the scientist concerned had no recollection of any conversations with me. I happily allowed her to march me off for a confrontation with said scientist and put it to him that we had spoken, he was happy to refer me to the organisers of two conferences back-to-back in Durham, and both organisers on hearing from me had shown no reservation in inviting me along. He remembered.
"If it's in the public domain," he said lightly to Angry Organiser, "then surely she can use it?"
He seemed almost as taken aback as I was.
Apologising for offending anyone, on the grounds that I had no intention of putting anybody's back up, I rested my case. She said she'd have to think about it. Apparently some of the things I'd said over lunch were 'inappropriate', and questions I'd raised from the floor were "not the sort of questions scientists want to be asked."
Scientists seated in lofty branches can be over-protective of their craft, and resentful of observation from the ground. No wonder Brian Cox so rigorously shunned any wider interpretation of the Uncertainty Principle. Any wider interpretation of anything held within the jaws of scientific parlance is apparently taboo. Well, I'd still like to think that everyone can enjoy their own version of Light.
On Saturday I took off into Durham City to complete a life-tick by visiting the cathedral. I'd seen pictures, and had a burning desire to see the real thing, having a suspicion that a lot of the artwork and architecture had a pre-Masonic sniff about it. But when I walked in, all these things vanished from mind. I stood there, awestruck, and began to cry silently. A woman wearing a lilac cassock stood nearby. She smiled.
"It's just a bit too much," I sniffed an embarrased explanation. "Always wanted to see this place and now ... well, you know..."
"Where have you come from?" she asked gently.
"About five hours south. I'm here for a Dark Matter conference."
The encounter launched up a gear with a rush of unexpected energy and the lady excitedly told me that her husband was most interested in dark matter, had given a sermon on the subject only a few days ago, and if I were to see him here - he would love to speak with me....
I gave her my card. Later a call came through on the mobile as I sat outside my tent watching children play, and was delighted to find that her husband had actually tracked me down. The next evening we talked about the emerging role of Dark Matter in the scheme of universal intellect. No Gods or God particles. The Universe really has no need of anything beyond its own systems of factuality.