Fields

[richardings]

How are all the fields linked?

at the LHC, two particles collide, why do they change the higgs field and produce a higgs particle?

 

 

[elfmotat]

Field excitations are called "particles." So, we get particles from fields by definition. Some fields are coupled to each other in various ways. For example the photon field and the electron field are coupled.

[BluePhaze]

Field excitations are called "particles." So, we get particles from fields by definition. Some fields are coupled to each other in various ways. For example the photon field and the electron field are coupled.

Does that mean massless particles' corresponding fields aren't coupled to the Higgs field? And if it does, I presume you couldn't get a Higgs particle out of a massless particle collision, right?

Edited March 23, 2013 by BluePhaze

[beefpatty]

Does that mean massless particles' corresponding fields aren't coupled to the Higgs field? And if it does, I presume you couldn't get a Higgs particle out of a massless particle collision, right?

 

Yes but you can get around that by say, two photons interacting and creating massive bosons (or fermions) which then interact to form a Higgs. The reverse process (Higgs -> bosons/fermions -> photons) I believe is one of the main channels they investigated to discover the Higgs.

 

Here's a helpful link: http://www.hep.lu.se/atlas/thesis/egede/thesis-node17.html

Edited March 25, 2013 by beefpatty

[BluePhaze]

thanks for the link, beefpatty That's quite interesting.

I think it's explained in the link but I don't think I get it, so, is it easier to get a Higgs from a massless or massive collision?

I'm guessing it's easier to get a Higgs from massive collisions, but maybe the fields' coupling isn't all that influences on the probabilities of it appearing or not...

Edited March 25, 2013 by BluePhaze

[beefpatty]

 

I'm guessing it's easier to get a Higgs from massive collisions, but maybe the fields' coupling isn't all that influences on the probabilities of it appearing or not...

 

I'm pretty sure you're correct, although I haven't studied that area of particle physics too in depth yet. The link says the branching ratio for [math]H \rightarrow \gamma\gamma[/math] is less than 0.3%, which means only that many are produced on average from a Higgs decay (depending on the mass of the Higgs).

[richardings]

So how do we know which fields are coupled? is it just some complex maths or is there another explanation?

 

How many fundamental fields are there in all?

For example you could say that there is a field for everything, but say i look at some supposed 'temperature field' (the temperature at each point in space-time),

you could say that that's just the energies of the fundamental particles in the region, and then you are looking at a different field (spacetime itself?).

 

so my question is do all fields root from a select few of fundamental field like the particles?

[elfmotat]

So how do we know which fields are coupled? is it just some complex maths or is there another explanation?

 

 

Some were figured out by analogy with classical physics, some by guesswork, and some by symmetries that the particular theory should have, etc. For example, in the Lorenz gauge the classical Maxwell's equations which describe the electromagnetic field are: [math]\square A^\mu=j^\mu[/math], where [math]A^\mu[/math] is the electromagnetic four-potential, and [math]j^\mu[/math] is the current density. When [math]A^\mu[/math] is quantized it becomes the photon field, i.e. the field whose excitations are photons. There's also a field which describes electrons, called the Dirac field [math]\psi[/math]. It turns out there's a conserved quantity made up from the Dirac field which acts like a current density: [math]j^\mu =-e\bar{\psi} \gamma^\mu \psi [/math]. If we make the assumption that the photon field couples to the Dirac field in exactly the same way that the Dirac field couples to the photon field, we can write, by the using the current-density relation above, the coupled photon-Dirac Lagrangian:

 

[math]\mathcal{L}_{QED} = \bar{\psi} (i\gamma^\mu \partial_\mu -m)\psi -e\bar{\psi} \gamma^\mu \psi A_\mu -\frac{1}{4}F_{\mu \nu} F^{\mu \nu}[/math]

 

I put the subscript "QED" there because this Lagrangian turns out to be exactly what describes Quantum Electrodynamics. Now, there are other ways of adding interaction terms, such as adding higher order powers of a field to its own Lagrangian. This describes a field which self-interacts. There are many things you can add, and some of them turn out to be interesting and physically meaningful.

 

How many fundamental fields are there in all?

For example you could say that there is a field for everything, but say i look at some supposed 'temperature field' (the temperature at each point in space-time),

you could say that that's just the energies of the fundamental particles in the region, and then you are looking at a different field (spacetime itself?).

 

so my question is do all fields root from a select few of fundamental field like the particles?

 

There are a lot of fields, one for each type of particle pretty much. I'm not sure what you're talking about with the temperature thing, but it's not clear whether or not there is some "unified field" from which everything else is an offspring at this point. The electromagnetic force and the weak force were successfully unified into the electroweak force, so that's a bit of success.

[richardings]

cool, thanks elfmotat, thats a bit mathematically dense for me, but i think i understand it!

really interesting actually