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July 28, 20.

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Hi, I'm Julia Yeomans. I'm head of Theoretical Physics.

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Thank you very much for coming today. We really appreciate the support at this time of term.

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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.

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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.

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Things are pretty much back to normal in the Beecroft now.

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And what we've remembered, what we realised due to the pandemic,

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is how important it is to be interacting with each other on a daily basis and at random moments.

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It's been a little bit of a struggle sometimes getting the new graduate students back in because

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they used to being undergraduates where it's fine to sit in your room and get your work done.

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That just doesn't work with research.

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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.

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And that's how ideas are formulated. And what we've been very lucky to have is the Beecroft Building.

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It's made an enormous difference. It's built in a beautiful way so that people can interact with each other.

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We have the best blackboards in Oxford and probably in the world.

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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.

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It really has made a difference in terms of interactions.

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So we're lucky. I would going to say something very brief about various Wickham professors.

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First of all, we have ready piles sought here that she was given when he was made several of piles.

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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.

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Oxford is a bit of a. It likes its traditions.

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And you've heard the joke about how many Oxford dons it takes to change a light bulb.

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Change? So a new welcome.

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Professor Shivaji Sundy has been a breath of fresh air with lots of new ideas.

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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.

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You're a physics prize. It's been great having him here.

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And in particular, we have set up with the funding that Shivaji brought, the Leverhulme International Professorship.

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We've set up Leverhulme Pyle's fellowships, which are for the best postdocs we can we can appoint.

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And we've been very, very lucky this year to be able to appoint Andy and George and Francesco to want to stand

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up a wave to people who are doing a great job getting us all talking to each other.

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So that's made a big difference. Another Wickham professor was Wallace LAMB.

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He was Wickham professor around 1960, and in his honour, we're starting a set of LAMB lectures next summer.

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And in particular, we have been lucky enough to attract Professor Madhavan Mahadevan from Harvard.

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Maha Works is professor of both applied maths and evolutionary biology, and he applies the ideas of mathematics to bio physics.

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And so please put in your diary the date of June the 10th, where Maha will be giving a public lecture,

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probably a slightly different format from this morning's of their article Physics, but you might be interested in that.

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We're very pleased to be able to host him then.

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Anyway. On with the business of today. We're going to tell you about actions.

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Nobody quite knows what they are. But we're going to do our best. And we're going to start with Professor Joe Conlon.

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And thank you very much to Joe, who is running admissions at the same time as doing this, which is really quite a challenge.

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Joe's going to talk about the Axion, how angles became particles.

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Okay. Thank you very much. Judy. So Judy said not sure.

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Access. I will I will tell you one thing either actions,

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which is the actions are one of the most beautiful wide ranging and interesting topics in certainly in threats to particle

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physics for something which also a seed will tell you in the second talk extends over to condensed matter physics.

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They are they're not just a very nice originally idea with some very nice theory behind their

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empirical consequences can span the almost the entire gamut of ranges applications from black holes,

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which I think John Doe might talk about astrophysics experiments in the lab.

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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.

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And they have also got lots of beautiful theory attached.

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So it is very much from a physicist theorists, from a theoretical physicist point of view, a double win.

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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.

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So we happening second on a condensed matter physics and John Charles,

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we'll be talking more then about further searches for axioms those I'll ask questions but any impertinent questions.

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I'm glad to see that there is something appropriate left here on the desk for me for me to deal with such questions.

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Okay. So axioms, four angles, particles.

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Right. So the search for you,

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physics to understand the laws of nature goes back goes back a long way using many different different different forms of technology.

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And if you're a particle physicist,

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one of the fundamental questions you would phrase this as is we write down internal physics in terms of the growth engines.

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You know, in a very simple sense, we want the Lagrangian for this world.

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We want the Lagrangian for. To describe nature.

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And we know that this contains the standard model.

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We know that this contains general relativity. What else is in there?

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So what new particles, interactions or forces may lie beyond our current knowledge?

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Now, there are many ways you can push this. You can push this, if you like, in the direction of kind of quantum gravity.

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But this is not what this is about. This is about.

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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.

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And it leads us to see how this suggests of a new possible type of particle and then how we might look for this.

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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.

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You, you are you all familiar with. Then this is the Higgs boson.

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So this is the most recent fundamental particle discovered discovered at the LHC.

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And this is your what you might think of as the classic model of looking for new particles.

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You get something which is really energetic.

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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.

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So this is how the Higgs was discovered. The LHC operates is the the highest controlled energies that we have anywhere,

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offering a centre of mass energy around about 14 tera tera electron volts.

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And by colliding protons together, famously, the LHC discovered the Higgs particle, a new particle extending our knowledge of nature.

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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,

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so it's rather expensive, but they will sell you their this coffee mug.

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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

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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?

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Oh, okay. So, so, so the first time in the negotiation, you see what I see is the kinetic terms for the gauge fails.

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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.

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And then in the last part, you've got the potential, the connected term and the potential for the Higgs.

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There is one other term you could write down. There's a term which is renormalisation, which is perfectly fine.

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There is no reason not to write it down there, no reason not to include it in this Lagrangian.

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And the third concern coffee mug is hiding this from you this time that you don't include it.

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And this term is the term where from which axioms sprang.

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So the term written down here is another way of putting together the.

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The field strengths for the field. So if you the simplest version of this, which is electromagnetism,

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then that all this term reduces to be that combination of if you knew alpha beta eight,

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the ones that co-produces to age of the electric field with the magnetic field,

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whereas the kinetic terms are really e squared and, and B, but this is the term that stern don't tell you about.

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I mean, I just want to sort of think about. How you look for new particles?

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What are the obstructions to finding new physics?

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So the classic obstruction, which is the obstruction involving the Higgs, is we do not have enough energy to make a new particle.

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The past exists. It interacts relatively strongly as with the sort of strong force of the animal electromagnetic

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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.

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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.

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So that is the classic particle physics. Yeah. So how you search for new particles?

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But. There is another almost orthogonal frontier.

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If you have particles which have no energetic cost to make them.

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The actual mass of such a particle is, say, a trillionth of that of the massive electron.

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So there's almost no energy cost to actually make them. But they interact extremely feebly.

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Extremely weakly with our standard model. Think.

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Think neutrinos except a billion times.

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It is less interacting than neutrinos. And as you know, neutrinos will kind of stream through the entire earth without interacting.

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So imagine a set of particles which are extremely weakly interacting that are very light.

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There's no energy costs. There's no energy problem with making them.

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It's the fact they are so weakly interacting is the issue.

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And this is the frontier particle physics, the action set in.

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It's the weak coupling frontier. You don't need to build an electron to look for these.

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But the problem is that they're very weakly interacting, which means the techniques you would use to look for them are different from.

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Allows us to look for the Higgs. So as you will be familiar, one of the great things,

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the physics is that the same equations have the same solutions and the same equations crop up in so many different areas of physics.

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So I start talking about the Higgs. The Higgs mechanism first came up in condensed matter and condensed matter physics.

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And if you look at this picture, this is a picture that used for searching for the Higgs.

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But what you will see, in effect, is actually the Higgs mechanism is already in those magnets, because superconductivity,

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as a condensed matter phenomenon, also uses the Higgs, what we call the Higgs, make up the Anderson Higgs mechanism.

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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.

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And so we'll talk about the condensed matter sides of this in the talk after.

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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.

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It is not like a particularly fancy or elevated or cultural town compared to Oxford.

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But I will make the point that Didcot has a road named after after Higgs.

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It has a road named after Dirac. And it is also and this is only appreciated by true connoisseurs of theoretical physics.

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It has a road named after Tom Kibble. So I'm not going to talk about axioms and Axion like particles.

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So where does the vaccine story start from? So it starts from understanding the strong force.

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So if you at the top I've written the Lagrangian which describes the strong force quantum climate dynamics.

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Now. I will tell you that.

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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.

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And in the middle you've got this extra term that CERN was does not put on their coffee mug.

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This term. Is not. Experimentally neutral if you think about what you know about the neutron.

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So change the neutron. Now. You probably know that the neutron consists of an up coke and two jam corks.

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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.

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So if you are asked to estimate the electric dipole moment of the neutron,

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the measure of how much the there's more charge or one side of the neutron than the other side of the neutron.

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You would you have take your rough estimate of taking the charges of these quarks and multiplying them by the size of the neutron?

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And you would say that you would expect there to be an electron an electron dipole moment for the neutron.

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Maybe my maybe my units. So they.

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So you would expect that to be an election type of moment of the of the neutral.

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But when the elected department is measured, the bounds on this are smaller by a factor of about ten to the ten.

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Then the value of the estimate site, because this is made up of three charged objects.

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So you expect that to be a bit more charge on one side than the other.

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So this is called the strong CP problem and it is one of the clear and well-defined problems

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of the standard model that you have something sort of like you'd expect it to have,

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and the actual measured value is smaller by a factor of around a billion.

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The origin of this is coming from this angle tab. Now this term violates charge parity or CPA.

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And you couldn't work out using the quantum mechanics of the quantum field theory.

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The strong force that this will give you is terms equivalent to the electric dipole moment of the neutron.

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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.

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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.

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It's one of the things we don't know about. We don't know the answer to why.

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It's the measured electric dipole moment of the neutron. Effectively zero.

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Right now, something that is not is not immediately obvious from this the ranch.

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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.

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And what I mean by an angle really is you take it to two pi.

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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.

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But let me just try and give you a very brief idea so that even if you have some sort of quantum mechanics,

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you have this idea of the following path integral. You integrate over all possible, possible quantities used by all possible field configurations,

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and you weight this by each of the I of the each of the all of the action.

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And the point is that what happens with this anger is that you end up with something which is topologically, topologically quantised.

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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.

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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.

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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.

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And so in theatregoers between zero and two part, you were always exactly where you back.

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And some very nice mathematics for those of you who are. Mathematically inclined.

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This relates to something called the a TSE Singer Index Theorem about why that is is quantised.

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But. So in the pure standard model, this is an angle.

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It's just an angle fixed. So value it is what it is.

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The action arises from saying, let us suppose that this angle is not fixed,

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this this angle and this angle, and that this wrong in the lagoon to this animal is not fixed.

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It can be dynamical. It can be something a field, it can have a potential, it can roll along or potentially it can move.

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So the angle, the non-dominant angle is promoted for dynamical field, and that field is the action.

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And if people in particle physics want to be specific, they will call it the Q seed action.

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To be specific, this is the associated to this particular term in the standard model and not to possible generalisations of it.

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When this. Angle is promoted to a field.

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Then because fields have mass dimension one, there also needs to be a there's a mass, an extra mass scale.

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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.

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Weakly interacting. This actually is. And.

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One of the fundamental insights of.

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Field theory across particle physics, across condensed matter physics, that is that fields correspond to particles that when you quantised fields,

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that what particles are how particles should be interpreted is as the quantum excitation, the minimal quantum excitation of a field.

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So if there is one kind of. Theoretical statement I want you to remember from my talk.

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It is that you know what is. An accident.

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What is the car accident? There is an angle.

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Into the growth engine of the standard model. When that angle is promoted to a dynamical field.

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The quantum excitations, the minimal quantum excitations of that field all correspond to axioms.

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In the way that the minimal quantum excitations of the electron field correspond to electrons

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in the minimal quantum excitations of the electromagnetic field corresponding to photons.

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There is another. Point is we appreciate and actions because actions involve angles.

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The minimal quantum excitation because the mean is because of the angles.

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This means that when you shift the action by two pi or 2.5, once it becomes dimensional.

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The. Potential must return to itself.

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And so what this means is that if you are a religious any kind of little bit familiarity with.

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Filter it. Yeah. You would like a mass time if you want to write a mass term for the action.

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An ordinary mastcam by itself. The sorts of problems you write down in ordinary kind of perturbation theory.

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When you have the natural kind of mass, you'd write down that this is actually by itself on its own.

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This is forbidden because such a term is not periodic under.

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So if you use it for the action. So this is not periodic.

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That does not have an Anglo dependence and anglo dependencies are not whole, are not easy to get.

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And the only way you can get them is through highly suppressed processes called non perturb active processes, process outside,

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perturbations the outside, the normal thing we say classical small quantum correction second order quantum correction, third order correction.

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The non perturbed physics is highly suppressed. And this is what means that vaccines as particles are naturally extremely light.

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They are extremely light and they remain extremely light.

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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,

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this has a mass of ten below less than ten to the minus three electron volts.

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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.

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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.

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It is not hard to have to have the energy to prove such actions.

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What they. The problem is that they also weakly coupling, they interact extremely weakly with ah, ordinary matter.

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So this is the kind of. Where they come from.

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They come from the the standard model. And they are one of the main targets for particle physics.

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Right. So I'm not going to try to talk about string theory, but I am by profession a string theorists.

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So I will say another good reason for thinking about axioms is whenever you try and do

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string theory and relate ten dimensional string theory to four dimensional physics,

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then you almost always get a plenitude of axioms in the low energy.

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Well, things that are very similar tracks and so very similar behaviour to the Q associated strongly to the standard model.

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So this is from my perspective, another reason to go look for axioms as a possible extension of the standard model.

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Right. So now I'm now I'm just moving on to actually talking about how one actually looks for vaccines.

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Actual searches for vaccines in the search for vaccines.

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So I've talked about the vaccine arising from the particular coupling to the strong force.

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Most of the searches for accidents or for axiom like particles rely on a very related but slightly different coupling.

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So they relate. They use what is the same form of the coupling, but applying for electromagnetism rather than for the the strong force.

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So you might not even notice the difference between these two these two terms I've written down.

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What if you want to kind of see what the difference is? You can see if you look at the upper one,

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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.

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This is all over all the different fields.

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The shows in the strong force, the lower one is the straight coupling to electromagnetism and electromagnetism alone.

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The coupling to electromagnetism. Is perhaps easier to.

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Conceive of because we can write you how you want.

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We're more familiar with electromagnetism and you can write out what this term in the Lagrangian engine looks like.

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And what it looks like is a coupling of the axiom fails to e dot b.

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And then the term G is is the what is the coupling constant.

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So this is a measuring of the strength of the interaction. The larger g would be the larger the coupling of the.

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The action or the action like particle to electromagnetism, the smaller gas,

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the weaker the coupling and the most aspects, the harder it is to find this this action.

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I would you just clear up a bit of nomenclature?

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So in particle physics, people talk about both axioms and Axion like particles.

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Often the word vaccine is used.

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For the particle which couples to the strong force. Axiom like particle.

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Is used for something that does not have the coupling to the strong force.

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It's very similar in many ways, but the judge just has this coupling to electromagnetism.

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The. Q The axiom. The axiom can couple both to the strong force and to electromagnetism.

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But we also a lot of searches are also for what would actually like particles,

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which would be a similar particle, which just couples to the to electromagnetism.

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And is this Lagrangian is simple. It involves relatively well-understood physics, electromagnetism.

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It is a very attractive target to think about how you could constrain and discover such particles.

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And I will now move on to describing one way to look at such cultures.

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A lot of ways to look for vaccines and the one I'm going to talk about.

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It's like this. So involves the idea that if you have this coupling.

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I bet you let me write you up on the board. It's that important to a a doll.

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Baby G. That you can turn on magnetic fields, you can build big magnets, you can either build big magnets,

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or you can go and find places where there are magnetic fields, for example, in astrophysics.

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And so this term, the P term, has an expectation value that has a background.

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And because you know that the electro electromagnetic field originates from photons, what you then have is a coupling.

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The background of a magnetic field. You have a coupling between the actions and the photons.

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Actions. Couple of photons. Photons coupled to axons.

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And this means that accidents can turn into photons, and photons can turn interactions in the background of a magnetic field.

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And this is the way we're going to use to describe a search for axons.

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So this coupling. So some of you may know about Serena physics.

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Now I know about neutrino oscillations, the way that different species of neutrinos can oscillate into one another.

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As they pass through the sun, as they pass through space.

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The physics of axons and photons in background magnetic fields is extremely similar to the physics of neutrino oscillations.

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In fact, written the right way the mathematics turns out to be.

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Identical. The axiom can oscillate into a photon and the photon can oscillate into an action.

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You may also know that the. The when people study neutrino oscillations, neutrinos being close in mass is kind of quite important to oscillations.

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And the same is true here. With the when the the fact that the action is very light.

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Is it close to the mass of the photon? And you might be thinking, well, but photon of the photon is exactly massless.

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The photon is only ever really exactly massless.

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On theorists blackboards in the bit in the Beecroft building.

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Because in any real environment, even in deepest empty space, there is some density of free electrons.

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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.

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There is still an electron density. There is still a plasma frequency.

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And as you may recall, from electromagnetic electromagnetism causes in the presence of a plasma, the photon develops an effective mass.

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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.

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So in the sort of galactic environment,

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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.

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This is a sort of mass that we're going to get in typical astrophysics in astrophysical environments.

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And this is very relevant for looking at when you're looking at axons, converting into photons.

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So just to draw up the analogy to neutrino oscillations, if some of you have no neutrino stations, so there's flavour,

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all I can say is a mass like in states, the mass like it states the elegant states of the Hamiltonian.

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But the flavour all I can states that the way things are produced and flavour I can say is oscillate between one another.

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While the massive logging sites would kind of continue as they also with neutrinos,

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you have different flavours of neutrino which oscillate through another one with axons and photons.

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The axon and the photon are correspond to the.

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Flavour I can states which can oscillate with with one another.

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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,

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the rate of conversion, the probability of conversion between an accident and a photon.

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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.

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L And we are sending let's say we send a photon through this or an axis.

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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?

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What is the probability? What is the probability of.

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The function is converted into an action. Or alternatively, what is the probability that the action has converted to a photon?

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And so this formula is given at the top. It goes as the square of the magnetic field.

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The square of the length and the square of the of the coupling.

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And as a factor of a quarter, to give you an idea of just some numbers on this,

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let me just give you some and the low part of this slide, I've kind of put some numbers in.

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So this is for a coupling between vaccines and photons, which is roughly where the observed limits are.

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So if you look at the magnitude of this. This is around nine orders of magnitude weaker than sort of weak interactions.

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This interaction strength between accents with photons. I've put a magnetic field of a micro gauss might gauss might create.

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These are the units used in astrophysics for astrophysical magnetic fields.

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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.

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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.

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A coherent magnetic field, roughly pointing the same way for.

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And one nice thing you get so you can say is actually the numbers is that this number is not large, this conversion probability.

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But we are we are kind of it's not ten to the -100 either.

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And this is giving a sign that this is something we can do some interesting physics with.

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From a theoretical point of view, I will also point out one really cool feature of this formula.

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And that's the L Squared. So why is this really cool?

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Is that if you are thinking about something converting or interacting with something else?

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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,

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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.

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And you would expect the probability of me bumping into something to go as the length that I have.

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What? And so it would in classical physics.

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The cool thing about the Dylan squared is this is a quantum mechanical process.

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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.

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But then the probability of the conversion is growing as squared because in quantum

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mechanics we need to square the amplitude to get something which is involves probabilities.

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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.

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The length is coming in here is is going to parsecs.

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So when we're kind of talking about how you search for axioms,

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we are talking about using effects that would be kind of quantum mechanically coherent or length scales of 12 parsecs.

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Yeah, because we normally think about atoms, but here we are thinking about quantum effects working on telepathic scales.

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Right. So let me tell you. So this is some work. I did work it a few years ago.

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We get some very nice patterns which should be kind of further improved by the people since.

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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?

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We're going to look for photons from and look at photons from an astrophysical source.

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Photons pass through an astrophysical magnetic field. There's a chance that they'll convert to axioms.

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And so what we will then try and look for is would we see the the absence of these of these factions?

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Would we see this kind of the fact that some of the photons have converged axons and yep.

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Using this, or in practice using the absence of this effect, we can bound the coupling between the photon field and the action field.

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So this is what we do is we're going from an agent,

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central agent of what is called the Perseus Cluster of galaxies, which is this great big fat cluster of galaxies,

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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.

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And we're going to be looking at X-ray photons travelling from there to to us.

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But so the search strategy is to send photons from A to B will pick up the photons.

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Right. To be there's a magnetic field in between the two. The magnetic field leads to axial photon conversion.

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And if the coupling was strong enough, the photon spectrum would show modulations compared to the source spectrum.

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And this is what we are looking for. And in practice, from the absence of these modulations, we are going to band the.

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The acting company. Right now.

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How do you look for something that is this is the the the picture of what we want to do, folks.

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What's going next is the how do you look for something that you can't see in the photo soundtracks?

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If you can't see them, how would you tell that? They're originally photos?

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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.

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But let me show you what the kind of result is, because then you can appreciate why this is why this is possible.

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So you may recall that with things like neutrino oscillations, you get these 30 sort of sinusoidal oscillations.

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And when you look in detail at conversion between photons and axons, the conversion rate has this kind of approximately sinusoidal form in energy.

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So on this plot. Down here.

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So this is sort of for astrophysical parameters. For electron density.

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It fails an X-ray energy. This is an illustration.

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This is the conversion, probably from a weak value of coupling to make it manifest.

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But this is what the convert sort of conversion properties would look like.

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They have this kind of sinus structure that is sort of quasi sinusoidal in energy.

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And so if you think about then the effects of what would survive is that you have kind of one minus this.

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So what the action is capable of doing would be imprinting this kind of sinusoidal structure on an X-ray photon spectrum.

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And I basically I know of no possible astrophysical way that you could you could ever kind of mimic

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this sort of these sorts of sinusoidal oscillations on the on a kind of a spectrum of X-ray photons.

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So this is why we're using X-rays and this is why the of of what we're looking for.

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Okay. So this is what we are looking at. For what?

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This is the Perseus cluster of galaxies and right in the centre of the Perseus clusters of galaxies is this,

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which is the large central galaxy and right at the centre is the large set to AGM.

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So this is blasting out photons, but all these folks will then have to traverse first the galaxy itself and

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then the entire cluster medium of the Perseus cluster before they get to us.

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And this region is magnetised and passing through this Magnetised region, there is a chance that such photons will convert into interactions.

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So when we were looking at this, this slide is slightly more technical, so you kind of skip it, if you will.

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This is just a measure of what we were kind of the models we were using.

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And of course,

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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.

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Yeah. What you have is you have kind of a multi there's a multi scale thing.

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There are many different domains simultaneously. There's a full spectrum of different power on different scales.

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So the sort of the very clean plot I showed you.

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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,

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many different domains, one after the other. Right.

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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,

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which has lots of publicly available data, because it's been used to observe lots and lots of astrophysical sources for a long time.

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And so what we're doing is this is thing we're passing the folks,

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the photons are passing through the magnetic field and then they are converting into.

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Some were converted to axioms. And the idea is that this which I'm going to blow up on the next one.

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So this is a completely simulated many possible realisation of the matrix of each one with different give a different spectrum.

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But the general idea is new. You get these sorts of questions.

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The soil structure in the spectrum and that if the structure was large enough, you would see it.

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And there's no possible way of mimicking such structure using.

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Use it using astrophysics. Okay.

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So this would be this is a simulated survival probability for assessing for certain value of the X, in fact, from coupling.

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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,

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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.

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So this is the sort of thing we are looking for to search for the vaccines.

389
00:43:40,040 --> 00:43:43,070
So so this is this is from a few days ago.

390
00:43:43,410 --> 00:43:48,860
So this is an astrophysics plot. And yeah, so obviously there are lots of astrophysical uncertainties.

391
00:43:49,880 --> 00:43:53,650
But the point isn't so much the astrophysical is this is the point that, yes,

392
00:43:53,650 --> 00:43:58,160
access the normal astrophysical model clearly fits the data to within about 10%.

393
00:43:59,190 --> 00:44:02,580
And the subtleties with the text, there are subtleties with those.

394
00:44:02,670 --> 00:44:12,300
But what is clear is that you rule out. Any coupling that would be strong enough to give, say, 25% modulations on the spectrum.

395
00:44:12,750 --> 00:44:17,760
Any sort of quasi sinusoidal oscillations at the level of 25% are ruled out.

396
00:44:18,690 --> 00:44:29,670
And this then converts into a bound on the coupling on the interaction between a hypothetical Axion like particle and electromagnetism.

397
00:44:34,320 --> 00:44:37,680
So this kid, then? Yeah. So this.

398
00:44:39,200 --> 00:44:44,839
This data can then be used to constrain the coupling of such a hypothetical vaccine like

399
00:44:44,840 --> 00:44:51,140
particle with electromagnetism at a level that is 1 billion times weaker than the weak scale.

400
00:44:51,500 --> 00:44:56,450
So remember that with neutrinos, the characteristic interaction strength is the weak scale,

401
00:44:57,230 --> 00:45:02,150
and we know how weakly interacting neutrinos are by looking at something like the X-ray

402
00:45:02,150 --> 00:45:06,410
spectrum of an energy and you can constrain such a hypothetical possible at the Axion,

403
00:45:06,560 --> 00:45:13,820
you constrain its coupling strength to be weaker than about 1 billion times weaker than the neutrino.

404
00:45:18,090 --> 00:45:25,830
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.

405
00:45:26,860 --> 00:45:30,310
The data I kind of showed you was just kind of general operating mode.

406
00:45:30,940 --> 00:45:36,850
They were got a long exposure with a a mode that gives you kind of very precise energy resolution,

407
00:45:37,360 --> 00:45:40,380
which in turn gives you much, which in turn to give you much better context.

408
00:45:40,390 --> 00:45:44,830
These constraints have all been have all been improved since then.

409
00:45:46,650 --> 00:45:51,000
But this is the section of one of the ways that you could look for axioms.

410
00:45:51,270 --> 00:45:54,510
This is an astrophysical search involving looking at.

411
00:45:55,700 --> 00:46:00,830
X-ray telescopes and X-ray data coming from far off astrophysical sources.

412
00:46:05,550 --> 00:46:14,910
And this will again prove proof again when the next thing know which is the next large modern.

413
00:46:16,050 --> 00:46:20,910
X ray telescope is launched hopefully sometime towards the end of this decade.

414
00:46:21,060 --> 00:46:29,340
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.

415
00:46:32,500 --> 00:46:37,360
Okay. So we're now coming to the end. Of my talk.

416
00:46:38,050 --> 00:46:41,320
We've got two more brilliant talks to come. Right.

417
00:46:41,430 --> 00:46:46,230
The first point is that axioms axioms originated from an angle in the standard model.

418
00:46:48,160 --> 00:46:51,250
When the angle is promoted to dynamical field.

419
00:46:52,410 --> 00:46:58,709
And Quantised the elementary quantum excitations of that field turn into a particle.

420
00:46:58,710 --> 00:47:01,410
And that particle is the axiom. The Q axiom.

421
00:47:03,340 --> 00:47:10,200
Such actions are naturally extremely light to lessen the trillionth of the massive electron and extremely weakly coupled.

422
00:47:11,220 --> 00:47:19,360
Yeah. Far, far more weekly couple than than the week scale. As you will hear further out.

423
00:47:19,840 --> 00:47:25,450
So you hear in John's talk, you will hear more about the many different ways that accents can manifest themselves in.

424
00:47:26,660 --> 00:47:32,050
You can look for actions in the lab and in other astrophysical environments and other things.

425
00:47:32,350 --> 00:47:40,750
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.

426
00:47:40,960 --> 00:47:44,740
You also have the same physics in in condensed matter.

427
00:47:44,750 --> 00:47:48,550
You will hear about some of the same physics. The same equations appear in condensed matter.

428
00:47:49,570 --> 00:47:54,040
I talked about one best way to look for axioms involving some of my own research looking

429
00:47:54,040 --> 00:48:00,100
for action like particles involving X-ray astrophysics and looking at the spectra of ions.

430
00:48:00,460 --> 00:48:09,100
This will be improved in the future. But one thing I hope I have conveyed is the actions of this setting of having

431
00:48:09,550 --> 00:48:16,350
both beautiful theory and lots of really fun observational physics behind them.

432
00:48:16,790 --> 00:48:18,400
That's the end of my talk. Thank you very much.