July 28, 20.
Hi, I'm Julia Yeomans. I'm head of Theoretical Physics.
Thank you very much for coming today. We really appreciate the support at this time of term.
Having you here makes us remember how lucky we are to be doing this exciting research and we're really looking forward to telling you about it.
So it's a very nice to see people in person. I think it's the first one we've held in person and in person interactions work much better.
Things are pretty much back to normal in the Beecroft now.
And what we've remembered, what we realised due to the pandemic,
is how important it is to be interacting with each other on a daily basis and at random moments.
It's been a little bit of a struggle sometimes getting the new graduate students back in because
they used to being undergraduates where it's fine to sit in your room and get your work done.
That just doesn't work with research.
We need them popping into each other's offices to help each other and having random moments over coffee where they're chatting to each other.
And that's how ideas are formulated. And what we've been very lucky to have is the Beecroft Building.
It's made an enormous difference. It's built in a beautiful way so that people can interact with each other.
We have the best blackboards in Oxford and probably in the world.
We have the little pods where people can go. It's sort of like a hamster run and there's lots of little places for them.
It really has made a difference in terms of interactions.
So we're lucky. I would going to say something very brief about various Wickham professors.
First of all, we have ready piles sought here that she was given when he was made several of piles.
If you want to come and have a look. And just in case anyone in the audience gets uppity, we've got to have them.
Oxford is a bit of a. It likes its traditions.
And you've heard the joke about how many Oxford dons it takes to change a light bulb.
Change? So a new welcome.
Professor Shivaji Sundy has been a breath of fresh air with lots of new ideas.
Shivaji is here. If you could get up and say hello. Shivaji is from Princeton and he's distinguished by many things, in particular the EPS.
You're a physics prize. It's been great having him here.
And in particular, we have set up with the funding that Shivaji brought, the Leverhulme International Professorship.
We've set up Leverhulme Pyle's fellowships, which are for the best postdocs we can we can appoint.
And we've been very, very lucky this year to be able to appoint Andy and George and Francesco to want to stand
up a wave to people who are doing a great job getting us all talking to each other.
So that's made a big difference. Another Wickham professor was Wallace LAMB.
He was Wickham professor around 1960, and in his honour, we're starting a set of LAMB lectures next summer.
And in particular, we have been lucky enough to attract Professor Madhavan Mahadevan from Harvard.
Maha Works is professor of both applied maths and evolutionary biology, and he applies the ideas of mathematics to bio physics.
And so please put in your diary the date of June the 10th, where Maha will be giving a public lecture,
probably a slightly different format from this morning's of their article Physics, but you might be interested in that.
We're very pleased to be able to host him then.
Anyway. On with the business of today. We're going to tell you about actions.
Nobody quite knows what they are. But we're going to do our best. And we're going to start with Professor Joe Conlon.
And thank you very much to Joe, who is running admissions at the same time as doing this, which is really quite a challenge.
Joe's going to talk about the Axion, how angles became particles.
Okay. Thank you very much. Judy. So Judy said not sure.
Access. I will I will tell you one thing either actions,
which is the actions are one of the most beautiful wide ranging and interesting topics in certainly in threats to particle
physics for something which also a seed will tell you in the second talk extends over to condensed matter physics.
They are they're not just a very nice originally idea with some very nice theory behind their
empirical consequences can span the almost the entire gamut of ranges applications from black holes,
which I think John Doe might talk about astrophysics experiments in the lab.
So they are a very active, one of the most active areas in particle physics in a way to look for new physics beyond the standard model.
And they have also got lots of beautiful theory attached.
So it is very much from a physicist theorists, from a theoretical physicist point of view, a double win.
Okay, so I'm going to talk, introduce myself and I'm going to start talking at axioms or see how an angle became a particle.
So we happening second on a condensed matter physics and John Charles,
we'll be talking more then about further searches for axioms those I'll ask questions but any impertinent questions.
I'm glad to see that there is something appropriate left here on the desk for me for me to deal with such questions.
Okay. So axioms, four angles, particles.
Right. So the search for you,
physics to understand the laws of nature goes back goes back a long way using many different different different forms of technology.
And if you're a particle physicist,
one of the fundamental questions you would phrase this as is we write down internal physics in terms of the growth engines.
You know, in a very simple sense, we want the Lagrangian for this world.
We want the Lagrangian for. To describe nature.
And we know that this contains the standard model.
We know that this contains general relativity. What else is in there?
So what new particles, interactions or forces may lie beyond our current knowledge?
Now, there are many ways you can push this. You can push this, if you like, in the direction of kind of quantum gravity.
But this is not what this is about. This is about.
This talk is going to start going to be sort of coming from what the standard model coming from one particular problem with the standard model.
And it leads us to see how this suggests of a new possible type of particle and then how we might look for this.
So let's just first off, you may be less familiar with that scene. So let's start with maybe a new particle that's you.
You, you are you all familiar with. Then this is the Higgs boson.
So this is the most recent fundamental particle discovered discovered at the LHC.
And this is your what you might think of as the classic model of looking for new particles.
You get something which is really energetic.
You get to the highest energies you possibly can and you collide things together and you try and see what new particles you can discover.
So this is how the Higgs was discovered. The LHC operates is the the highest controlled energies that we have anywhere,
offering a centre of mass energy around about 14 tera tera electron volts.
And by colliding protons together, famously, the LHC discovered the Higgs particle, a new particle extending our knowledge of nature.
So if you go to sir and I do recommend you go SEN, I have a gift shop and all the prices are in Swiss francs,
so it's rather expensive, but they will sell you their this coffee mug.
And what they claim on this coffee mug is that this is this is the Lagrangian of the standard model and you've got a slightly simplified
but that you have terms if you look at this and I think it is if I might ask you this is the point or is this completely forbidden?
Oh, okay. So, so, so the first time in the negotiation, you see what I see is the kinetic terms for the gauge fails.
The second term is where you've got the presence of the Permian as the third term of the interaction of the Higgs and the fermions.
And then in the last part, you've got the potential, the connected term and the potential for the Higgs.
There is one other term you could write down. There's a term which is renormalisation, which is perfectly fine.
There is no reason not to write it down there, no reason not to include it in this Lagrangian.
And the third concern coffee mug is hiding this from you this time that you don't include it.
And this term is the term where from which axioms sprang.
So the term written down here is another way of putting together the.
The field strengths for the field. So if you the simplest version of this, which is electromagnetism,
then that all this term reduces to be that combination of if you knew alpha beta eight,
the ones that co-produces to age of the electric field with the magnetic field,
whereas the kinetic terms are really e squared and, and B, but this is the term that stern don't tell you about.
I mean, I just want to sort of think about. How you look for new particles?
What are the obstructions to finding new physics?
So the classic obstruction, which is the obstruction involving the Higgs, is we do not have enough energy to make a new particle.
The past exists. It interacts relatively strongly as with the sort of strong force of the animal electromagnetic
field it interacts with somewhat under some of the forces we are very familiar with. But we simply do not have enough energy to make it.
And so the way we need to build a large accelerator in order to send software that's collide stuff together to make this new particle.
So that is the classic particle physics. Yeah. So how you search for new particles?
But. There is another almost orthogonal frontier.
If you have particles which have no energetic cost to make them.
The actual mass of such a particle is, say, a trillionth of that of the massive electron.
So there's almost no energy cost to actually make them. But they interact extremely feebly.
Extremely weakly with our standard model. Think.
Think neutrinos except a billion times.
It is less interacting than neutrinos. And as you know, neutrinos will kind of stream through the entire earth without interacting.
So imagine a set of particles which are extremely weakly interacting that are very light.
There's no energy costs. There's no energy problem with making them.
It's the fact they are so weakly interacting is the issue.
And this is the frontier particle physics, the action set in.
It's the weak coupling frontier. You don't need to build an electron to look for these.
But the problem is that they're very weakly interacting, which means the techniques you would use to look for them are different from.
Allows us to look for the Higgs. So as you will be familiar, one of the great things,
the physics is that the same equations have the same solutions and the same equations crop up in so many different areas of physics.
So I start talking about the Higgs. The Higgs mechanism first came up in condensed matter and condensed matter physics.
And if you look at this picture, this is a picture that used for searching for the Higgs.
But what you will see, in effect, is actually the Higgs mechanism is already in those magnets, because superconductivity,
as a condensed matter phenomenon, also uses the Higgs, what we call the Higgs, make up the Anderson Higgs mechanism.
So. Similar equations can crop up in many different areas of physics and axioms in terms of will also can also appear in condensed matter physics.
And so we'll talk about the condensed matter sides of this in the talk after.
No one will have looked at Higgs the last point at the Higgs. I just want to make a post about why the town I live in did not many people think did.
It is not like a particularly fancy or elevated or cultural town compared to Oxford.
But I will make the point that Didcot has a road named after after Higgs.
It has a road named after Dirac. And it is also and this is only appreciated by true connoisseurs of theoretical physics.
It has a road named after Tom Kibble. So I'm not going to talk about axioms and Axion like particles.
So where does the vaccine story start from? So it starts from understanding the strong force.
So if you at the top I've written the Lagrangian which describes the strong force quantum climate dynamics.
Now. I will tell you that.
So the first time in that negotiation on the left, over the left of the kinetic terms for the gluons on the right, you've got the mass of the corks.
And in the middle you've got this extra term that CERN was does not put on their coffee mug.
This term. Is not. Experimentally neutral if you think about what you know about the neutron.
So change the neutron. Now. You probably know that the neutron consists of an up coke and two jam corks.
And if so, if you were asked to see this is electrically neutral, but it's made up of three objects which themselves have charge.
So if you are asked to estimate the electric dipole moment of the neutron,
the measure of how much the there's more charge or one side of the neutron than the other side of the neutron.
You would you have take your rough estimate of taking the charges of these quarks and multiplying them by the size of the neutron?
And you would say that you would expect there to be an electron an electron dipole moment for the neutron.
Maybe my maybe my units. So they.
So you would expect that to be an election type of moment of the of the neutral.
But when the elected department is measured, the bounds on this are smaller by a factor of about ten to the ten.
Then the value of the estimate site, because this is made up of three charged objects.
So you expect that to be a bit more charge on one side than the other.
So this is called the strong CP problem and it is one of the clear and well-defined problems
of the standard model that you have something sort of like you'd expect it to have,
and the actual measured value is smaller by a factor of around a billion.
The origin of this is coming from this angle tab. Now this term violates charge parity or CPA.
And you couldn't work out using the quantum mechanics of the quantum field theory.
The strong force that this will give you is terms equivalent to the electric dipole moment of the neutron.
So if the typical values of this angle, you overshoot the measured value of the electric dipole moment by a factor of around a million.
And this is the strong CP problem. And this problem has it is one of the kind of major open problems with the standard model.
It's one of the things we don't know about. We don't know the answer to why.
It's the measured electric dipole moment of the neutron. Effectively zero.
Right now, something that is not is not immediately obvious from this the ranch.
But I was so I was saying it as a true fact. An in-flight is a true fact is that this is an angle.
And what I mean by an angle really is you take it to two pi.
The physics are complete is completely equivalent. The full reasons to the full reasons to understand this are kind of a bit a bit hard.
But let me just try and give you a very brief idea so that even if you have some sort of quantum mechanics,
you have this idea of the following path integral. You integrate over all possible, possible quantities used by all possible field configurations,
and you weight this by each of the I of the each of the all of the action.
And the point is that what happens with this anger is that you end up with something which is topologically, topologically quantised.
And so this term ends up giving something that looks like basically e to the only and feature where n has to be an integer.
And so when you do the pulse integral, you integrate it for all possible field configurations you can have and of course what you end up with.
So the states is the same. I'm just going to state is that you have this kind of topological part which looks like each of the iron feature.
And so in theatregoers between zero and two part, you were always exactly where you back.
And some very nice mathematics for those of you who are. Mathematically inclined.
This relates to something called the a TSE Singer Index Theorem about why that is is quantised.
But. So in the pure standard model, this is an angle.
It's just an angle fixed. So value it is what it is.
The action arises from saying, let us suppose that this angle is not fixed,
this this angle and this angle, and that this wrong in the lagoon to this animal is not fixed.
It can be dynamical. It can be something a field, it can have a potential, it can roll along or potentially it can move.
So the angle, the non-dominant angle is promoted for dynamical field, and that field is the action.
And if people in particle physics want to be specific, they will call it the Q seed action.
To be specific, this is the associated to this particular term in the standard model and not to possible generalisations of it.
When this. Angle is promoted to a field.
Then because fields have mass dimension one, there also needs to be a there's a mass, an extra mass scale.
So if those of you who are there's a mass scale, which is the FIA, which is a measure of how weakly interacting they are.
Weakly interacting. This actually is. And.
One of the fundamental insights of.
Field theory across particle physics, across condensed matter physics, that is that fields correspond to particles that when you quantised fields,
that what particles are how particles should be interpreted is as the quantum excitation, the minimal quantum excitation of a field.
So if there is one kind of. Theoretical statement I want you to remember from my talk.
It is that you know what is. An accident.
What is the car accident? There is an angle.
Into the growth engine of the standard model. When that angle is promoted to a dynamical field.
The quantum excitations, the minimal quantum excitations of that field all correspond to axioms.
In the way that the minimal quantum excitations of the electron field correspond to electrons
in the minimal quantum excitations of the electromagnetic field corresponding to photons.
There is another. Point is we appreciate and actions because actions involve angles.
The minimal quantum excitation because the mean is because of the angles.
This means that when you shift the action by two pi or 2.5, once it becomes dimensional.
The. Potential must return to itself.
And so what this means is that if you are a religious any kind of little bit familiarity with.
Filter it. Yeah. You would like a mass time if you want to write a mass term for the action.
An ordinary mastcam by itself. The sorts of problems you write down in ordinary kind of perturbation theory.
When you have the natural kind of mass, you'd write down that this is actually by itself on its own.
This is forbidden because such a term is not periodic under.
So if you use it for the action. So this is not periodic.
That does not have an Anglo dependence and anglo dependencies are not whole, are not easy to get.
And the only way you can get them is through highly suppressed processes called non perturb active processes, process outside,
perturbations the outside, the normal thing we say classical small quantum correction second order quantum correction, third order correction.
The non perturbed physics is highly suppressed. And this is what means that vaccines as particles are naturally extremely light.
They are extremely light and they remain extremely light.
So is this the accident that you would expect to get in the standard model if the axial solution of the strong C.P problem is true,
this has a mass of ten below less than ten to the minus three electron volts.
There's a source of preferred range which is a pretty about ten to the minus three electron volts and ten to the minus six electron volts.
But it could be lighter and think how light this is. There is no you know, you slice it, this is tiny, tiny, tiny amounts of energy.
It is not hard to have to have the energy to prove such actions.
What they. The problem is that they also weakly coupling, they interact extremely weakly with ah, ordinary matter.
So this is the kind of. Where they come from.
They come from the the standard model. And they are one of the main targets for particle physics.
Right. So I'm not going to try to talk about string theory, but I am by profession a string theorists.
So I will say another good reason for thinking about axioms is whenever you try and do
string theory and relate ten dimensional string theory to four dimensional physics,
then you almost always get a plenitude of axioms in the low energy.
Well, things that are very similar tracks and so very similar behaviour to the Q associated strongly to the standard model.
So this is from my perspective, another reason to go look for axioms as a possible extension of the standard model.
Right. So now I'm now I'm just moving on to actually talking about how one actually looks for vaccines.
Actual searches for vaccines in the search for vaccines.
So I've talked about the vaccine arising from the particular coupling to the strong force.
Most of the searches for accidents or for axiom like particles rely on a very related but slightly different coupling.
So they relate. They use what is the same form of the coupling, but applying for electromagnetism rather than for the the strong force.
So you might not even notice the difference between these two these two terms I've written down.
What if you want to kind of see what the difference is? You can see if you look at the upper one,
the upper one has this extra index a this is a sign that this is running over all the different generations of the strong force.
This is all over all the different fields.
The shows in the strong force, the lower one is the straight coupling to electromagnetism and electromagnetism alone.
The coupling to electromagnetism. Is perhaps easier to.
Conceive of because we can write you how you want.
We're more familiar with electromagnetism and you can write out what this term in the Lagrangian engine looks like.
And what it looks like is a coupling of the axiom fails to e dot b.
And then the term G is is the what is the coupling constant.
So this is a measuring of the strength of the interaction. The larger g would be the larger the coupling of the.
The action or the action like particle to electromagnetism, the smaller gas,
the weaker the coupling and the most aspects, the harder it is to find this this action.
I would you just clear up a bit of nomenclature?
So in particle physics, people talk about both axioms and Axion like particles.
Often the word vaccine is used.
For the particle which couples to the strong force. Axiom like particle.
Is used for something that does not have the coupling to the strong force.
It's very similar in many ways, but the judge just has this coupling to electromagnetism.
The. Q The axiom. The axiom can couple both to the strong force and to electromagnetism.
But we also a lot of searches are also for what would actually like particles,
which would be a similar particle, which just couples to the to electromagnetism.
And is this Lagrangian is simple. It involves relatively well-understood physics, electromagnetism.
It is a very attractive target to think about how you could constrain and discover such particles.
And I will now move on to describing one way to look at such cultures.
A lot of ways to look for vaccines and the one I'm going to talk about.
It's like this. So involves the idea that if you have this coupling.
I bet you let me write you up on the board. It's that important to a a doll.
Baby G. That you can turn on magnetic fields, you can build big magnets, you can either build big magnets,
or you can go and find places where there are magnetic fields, for example, in astrophysics.
And so this term, the P term, has an expectation value that has a background.
And because you know that the electro electromagnetic field originates from photons, what you then have is a coupling.
The background of a magnetic field. You have a coupling between the actions and the photons.
Actions. Couple of photons. Photons coupled to axons.
And this means that accidents can turn into photons, and photons can turn interactions in the background of a magnetic field.
And this is the way we're going to use to describe a search for axons.
So this coupling. So some of you may know about Serena physics.
Now I know about neutrino oscillations, the way that different species of neutrinos can oscillate into one another.
As they pass through the sun, as they pass through space.
The physics of axons and photons in background magnetic fields is extremely similar to the physics of neutrino oscillations.
In fact, written the right way the mathematics turns out to be.
Identical. The axiom can oscillate into a photon and the photon can oscillate into an action.
You may also know that the. The when people study neutrino oscillations, neutrinos being close in mass is kind of quite important to oscillations.
And the same is true here. With the when the the fact that the action is very light.
Is it close to the mass of the photon? And you might be thinking, well, but photon of the photon is exactly massless.
The photon is only ever really exactly massless.
On theorists blackboards in the bit in the Beecroft building.
Because in any real environment, even in deepest empty space, there is some density of free electrons.
And this means that even, you know, you put yourself in space, you know, you have thousands, tens of thousands of light years in the next galaxy.
There is still an electron density. There is still a plasma frequency.
And as you may recall, from electromagnetic electromagnetism causes in the presence of a plasma, the photon develops an effective mass.
So even in very deep space, the photon has an effective mass, which might be like and I just give you an order of the magnitude.
So in the sort of galactic environment,
the effective mass of the proton of the of the photon is going to come in about something like ten to the -11 electron volts.
This is a sort of mass that we're going to get in typical astrophysics in astrophysical environments.
And this is very relevant for looking at when you're looking at axons, converting into photons.
So just to draw up the analogy to neutrino oscillations, if some of you have no neutrino stations, so there's flavour,
all I can say is a mass like in states, the mass like it states the elegant states of the Hamiltonian.
But the flavour all I can states that the way things are produced and flavour I can say is oscillate between one another.
While the massive logging sites would kind of continue as they also with neutrinos,
you have different flavours of neutrino which oscillate through another one with axons and photons.
The axon and the photon are correspond to the.
Flavour I can states which can oscillate with with one another.
What? Okay. So let me give you the formula for a simplified version of the formula, but it's a very beautiful formula for the conversion,
the rate of conversion, the probability of conversion between an accident and a photon.
So what we have here, I've been doing it a little bit on the board is we have a transverse magnetic field bay which extends over a distance.
L And we are sending let's say we send a photon through this or an axis.
So what we are asking is after this has been through this, what if we then measure the quantum mechanical state at the other end?
What is the probability? What is the probability of.
The function is converted into an action. Or alternatively, what is the probability that the action has converted to a photon?
And so this formula is given at the top. It goes as the square of the magnetic field.
The square of the length and the square of the of the coupling.
And as a factor of a quarter, to give you an idea of just some numbers on this,
let me just give you some and the low part of this slide, I've kind of put some numbers in.
So this is for a coupling between vaccines and photons, which is roughly where the observed limits are.
So if you look at the magnitude of this. This is around nine orders of magnitude weaker than sort of weak interactions.
This interaction strength between accents with photons. I've put a magnetic field of a micro gauss might gauss might create.
These are the units used in astrophysics for astrophysical magnetic fields.
This corresponds about ten to the minus ten Tesla and I put a length of one killer parsec, which is again, this is an astrophysical lens scale.
This is anticipating the application I'm going to use, which is a measure of kind of roughly what length you might get in astrophysics.
A coherent magnetic field, roughly pointing the same way for.
And one nice thing you get so you can say is actually the numbers is that this number is not large, this conversion probability.
But we are we are kind of it's not ten to the -100 either.
And this is giving a sign that this is something we can do some interesting physics with.
From a theoretical point of view, I will also point out one really cool feature of this formula.
And that's the L Squared. So why is this really cool?
Is that if you are thinking about something converting or interacting with something else?
So sent me walking through the next stage saying What's the probability of me bumping into something that if I take my glasses off,
you would expect this probability to go as let's you know, you would say that the longer I walk, the more chances I would bump into something.
And you would expect the probability of me bumping into something to go as the length that I have.
What? And so it would in classical physics.
The cool thing about the Dylan squared is this is a quantum mechanical process.
So what's actually happening is that as I move going forward, the amplitude for me to bump something in something is growing as length.
But then the probability of the conversion is growing as squared because in quantum
mechanics we need to square the amplitude to get something which is involves probabilities.
And this is where one of the to me, one of the really cool ideas that aspects of Axion physics are is in the sort of application I'm talking about.
The length is coming in here is is going to parsecs.
So when we're kind of talking about how you search for axioms,
we are talking about using effects that would be kind of quantum mechanically coherent or length scales of 12 parsecs.
Yeah, because we normally think about atoms, but here we are thinking about quantum effects working on telepathic scales.
Right. So let me tell you. So this is some work. I did work it a few years ago.
We get some very nice patterns which should be kind of further improved by the people since.
So what's the search strategy? So the idea is what we're going to do is how are we going to look for actions?
We're going to look for photons from and look at photons from an astrophysical source.
Photons pass through an astrophysical magnetic field. There's a chance that they'll convert to axioms.
And so what we will then try and look for is would we see the the absence of these of these factions?
Would we see this kind of the fact that some of the photons have converged axons and yep.
Using this, or in practice using the absence of this effect, we can bound the coupling between the photon field and the action field.
So this is what we do is we're going from an agent,
central agent of what is called the Perseus Cluster of galaxies, which is this great big fat cluster of galaxies,
a great big fat galaxy at the centre with an even a great big fat at the centre of it, which is about 70 megaparsec away.
And we're going to be looking at X-ray photons travelling from there to to us.
But so the search strategy is to send photons from A to B will pick up the photons.
Right. To be there's a magnetic field in between the two. The magnetic field leads to axial photon conversion.
And if the coupling was strong enough, the photon spectrum would show modulations compared to the source spectrum.
And this is what we are looking for. And in practice, from the absence of these modulations, we are going to band the.
The acting company. Right now.
How do you look for something that is this is the the the picture of what we want to do, folks.
What's going next is the how do you look for something that you can't see in the photo soundtracks?
If you can't see them, how would you tell that? They're originally photos?
They're already. So this is where this is slightly kind of take you because this just in some sense, this is a matter of how the numbers work out.
But let me show you what the kind of result is, because then you can appreciate why this is why this is possible.
So you may recall that with things like neutrino oscillations, you get these 30 sort of sinusoidal oscillations.
And when you look in detail at conversion between photons and axons, the conversion rate has this kind of approximately sinusoidal form in energy.
So on this plot. Down here.
So this is sort of for astrophysical parameters. For electron density.
It fails an X-ray energy. This is an illustration.
This is the conversion, probably from a weak value of coupling to make it manifest.
But this is what the convert sort of conversion properties would look like.
They have this kind of sinus structure that is sort of quasi sinusoidal in energy.
And so if you think about then the effects of what would survive is that you have kind of one minus this.
So what the action is capable of doing would be imprinting this kind of sinusoidal structure on an X-ray photon spectrum.
And I basically I know of no possible astrophysical way that you could you could ever kind of mimic
this sort of these sorts of sinusoidal oscillations on the on a kind of a spectrum of X-ray photons.
So this is why we're using X-rays and this is why the of of what we're looking for.
Okay. So this is what we are looking at. For what?
This is the Perseus cluster of galaxies and right in the centre of the Perseus clusters of galaxies is this,
which is the large central galaxy and right at the centre is the large set to AGM.
So this is blasting out photons, but all these folks will then have to traverse first the galaxy itself and
then the entire cluster medium of the Perseus cluster before they get to us.
And this region is magnetised and passing through this Magnetised region, there is a chance that such photons will convert into interactions.
So when we were looking at this, this slide is slightly more technical, so you kind of skip it, if you will.
This is just a measure of what we were kind of the models we were using.
And of course,
it's not a single it's not this isn't like an electric magnet where you have a single magnet that you turn on for a certain length and then a note.
Yeah. What you have is you have kind of a multi there's a multi scale thing.
There are many different domains simultaneously. There's a full spectrum of different power on different scales.
So the sort of the very clean plot I showed you.
Here is going to get sort of we get distorted by some of the realisation the magnetic field is in the fact you've got many,
many different domains, one after the other. Right.
So this is Chandra. So this is the it's I think it's still operating, which is this is this is the long standing X-ray telescope,
which has lots of publicly available data, because it's been used to observe lots and lots of astrophysical sources for a long time.
And so what we're doing is this is thing we're passing the folks,
the photons are passing through the magnetic field and then they are converting into.
Some were converted to axioms. And the idea is that this which I'm going to blow up on the next one.
So this is a completely simulated many possible realisation of the matrix of each one with different give a different spectrum.
But the general idea is new. You get these sorts of questions.
The soil structure in the spectrum and that if the structure was large enough, you would see it.
And there's no possible way of mimicking such structure using.
Use it using astrophysics. Okay.
So this would be this is a simulated survival probability for assessing for certain value of the X, in fact, from coupling.
This is a pure survival probability. So if we can evolve it with the detector resolution, this is what we would, then this is a more realistic one,
given you have an actual real x ray x ray detector, an x ray, actual real x ray telescope with actual real electronics on board.
So this is the sort of thing we are looking for to search for the vaccines.
So so this is this is from a few days ago.
So this is an astrophysics plot. And yeah, so obviously there are lots of astrophysical uncertainties.
But the point isn't so much the astrophysical is this is the point that, yes,
access the normal astrophysical model clearly fits the data to within about 10%.
And the subtleties with the text, there are subtleties with those.
But what is clear is that you rule out. Any coupling that would be strong enough to give, say, 25% modulations on the spectrum.
Any sort of quasi sinusoidal oscillations at the level of 25% are ruled out.
And this then converts into a bound on the coupling on the interaction between a hypothetical Axion like particle and electromagnetism.
So this kid, then? Yeah. So this.
This data can then be used to constrain the coupling of such a hypothetical vaccine like
particle with electromagnetism at a level that is 1 billion times weaker than the weak scale.
So remember that with neutrinos, the characteristic interaction strength is the weak scale,
and we know how weakly interacting neutrinos are by looking at something like the X-ray
spectrum of an energy and you can constrain such a hypothetical possible at the Axion,
you constrain its coupling strength to be weaker than about 1 billion times weaker than the neutrino.
And so this part shows the balance that we put on this extended all the people have since done this with with better data they've.
The data I kind of showed you was just kind of general operating mode.
They were got a long exposure with a a mode that gives you kind of very precise energy resolution,
which in turn gives you much, which in turn to give you much better context.
These constraints have all been have all been improved since then.
But this is the section of one of the ways that you could look for axioms.
This is an astrophysical search involving looking at.
X-ray telescopes and X-ray data coming from far off astrophysical sources.
And this will again prove proof again when the next thing know which is the next large modern.
X ray telescope is launched hopefully sometime towards the end of this decade.
And the estimate is that this will give a further factor of ten improvement on the coupling strength between such Axion like particles and photons.
Okay. So we're now coming to the end. Of my talk.
We've got two more brilliant talks to come. Right.
The first point is that axioms axioms originated from an angle in the standard model.
When the angle is promoted to dynamical field.
And Quantised the elementary quantum excitations of that field turn into a particle.
And that particle is the axiom. The Q axiom.
Such actions are naturally extremely light to lessen the trillionth of the massive electron and extremely weakly coupled.
Yeah. Far, far more weekly couple than than the week scale. As you will hear further out.
So you hear in John's talk, you will hear more about the many different ways that accents can manifest themselves in.
You can look for actions in the lab and in other astrophysical environments and other things.
Instead you'll hear from Sid. You will hear about how such accidents as in the same way that the fundamental Higgs scale of the standard model.
You also have the same physics in in condensed matter.
You will hear about some of the same physics. The same equations appear in condensed matter.
I talked about one best way to look for axioms involving some of my own research looking
for action like particles involving X-ray astrophysics and looking at the spectra of ions.
This will be improved in the future. But one thing I hope I have conveyed is the actions of this setting of having
both beautiful theory and lots of really fun observational physics behind them.
That's the end of my talk. Thank you very much.