Well, if day two was the long day, day three was the short one. There

were no plenary sessions, just a short moring parallel session, then

excursions in the afternoon. It was a very nice day to be out on the

Irish countryside, so that was very nice.

Day four had the plenary sessions I was most interested in, a close

collaborator, Quentin Mason, started off the day talking about lattice

perturbaiton theory, which is what I do. Quentin has completed the

two-loop calculation of the light quark mass, which allows for a much

more accurate determination. Quentin also reviewed the determination

of the strong coupling constand, which I've covered in a previous

post.

Next up was Zoltan Ligeti, who reveiwed progress in heavy quark

physics from a non-lattice perspective. There's been lots of activity

on this front over the past few years, with the development of a new

expansion, the Soft Colinear Expansion. This theory is complicated

enough that I won't even try to explain it.

Finally, another collaborator, Masataka Okamoto, gave a very nice

overview of the status of lattice calculations of the CKM matrix.

This the the matrix which tells you how the various types (or

flavours) of quarks interact in the standard model. It has nine

entries (not all of them are independent) most of which can be

computed from lattice QCD + an experimental result. Masataka has done

a large amount of work, both doing many of the calculations himself,

and collecting everything into a coherent picture.

In the standerd model, the CKM matrix is unitary. If you accept that

assumption, the Masataka has produced a complete determination of the

CKM matrix from lattice QCD, experimental measurements, and the

unitarity of the matrix. Of course, it would be nice to test the

unitarity, from just theory+experiment with no extra assumption. In

that case, you can check row by row in the matrix. Masataka showed

how one row is completly determined without assuming unitarity. And

in that row, the matrix is unitary, up to the errors. It will be a

big challenge to repeat this for the other two rows.

## Friday, July 29, 2005

## Wednesday, July 27, 2005

### Lattice 2005, day two

Hello again from Dublin. Day two of Lattice 2005 was the "busy" day,

with three plenary sessions, a parallel session, and the poster

session all in one day. Twelve solid hours of physics, which is

rather tiring, particularly since I was presenting a poster. As such,

today's update of the Plenary sessions will be brief.

The morning started off with a talk by Herbert Neuberger on simulations

of large N field theory. As discovered by 't Hooft, SU(N) gauge

theory simplifies as you take the limit N -> infinity. However, this

is hard to do in Lattice QCD, as you would need infinite sized

matrices. However, there are techniques for attacking the problem.

Neuberger reviewed the interesting phase structure you see in this

system. The lattice version of large N QCD has 6 different phases.

Next up was Simon Catterall, who reviewed his work on Lattice

supersymmetry. In the early days of both supersymmetry and lattice

QCD, it wasn't thought possible to put a supersymetric theory on the

lattice without badly breaking the supersymmetry. However in recent

years, a few different methods have been discovered. The basic idea

is you construct a continuum theory with lots of supersymmetry and

arrange things such that when you put the theory on the lattice, a

remmenant of the supersymmetry remains. Simon reviewed his method for

doing this, and briefly touched on some of the possible applications

of these methods.

After a coffee break, the sessions shifted in focus a little bit.

Chris Dawson reviewed the state of Kaon Phenomenology on the lattice.

The focus here is on kaon decays, which are hard to do in lattice

QCD. For example, a kaon can decay into two pions. This is extremely

hard to compute, since pions are very large, it's hard to fit two of

them inside your finite lattice box.

We swapped last names for the next talk, Chris Dawson became Chris

Michael, who gave a lively review of the state of hadronic decays on

the lattice. The people I work with are interested in doing very high

precision calculations. This is good, however, it limits you to a

small number of thing you can calculate. However lattice QCD can, in

principle, calculate many many more interesting strong interaction

processes. Chris gave an update of the state of some of these

calculations, which are very very hard to do. You have an unstable

particle in the intitial state, two or more hadrons in the final

state, and a transition at some point between. I

with three plenary sessions, a parallel session, and the poster

session all in one day. Twelve solid hours of physics, which is

rather tiring, particularly since I was presenting a poster. As such,

today's update of the Plenary sessions will be brief.

The morning started off with a talk by Herbert Neuberger on simulations

of large N field theory. As discovered by 't Hooft, SU(N) gauge

theory simplifies as you take the limit N -> infinity. However, this

is hard to do in Lattice QCD, as you would need infinite sized

matrices. However, there are techniques for attacking the problem.

Neuberger reviewed the interesting phase structure you see in this

system. The lattice version of large N QCD has 6 different phases.

Next up was Simon Catterall, who reviewed his work on Lattice

supersymmetry. In the early days of both supersymmetry and lattice

QCD, it wasn't thought possible to put a supersymetric theory on the

lattice without badly breaking the supersymmetry. However in recent

years, a few different methods have been discovered. The basic idea

is you construct a continuum theory with lots of supersymmetry and

arrange things such that when you put the theory on the lattice, a

remmenant of the supersymmetry remains. Simon reviewed his method for

doing this, and briefly touched on some of the possible applications

of these methods.

After a coffee break, the sessions shifted in focus a little bit.

Chris Dawson reviewed the state of Kaon Phenomenology on the lattice.

The focus here is on kaon decays, which are hard to do in lattice

QCD. For example, a kaon can decay into two pions. This is extremely

hard to compute, since pions are very large, it's hard to fit two of

them inside your finite lattice box.

We swapped last names for the next talk, Chris Dawson became Chris

Michael, who gave a lively review of the state of hadronic decays on

the lattice. The people I work with are interested in doing very high

precision calculations. This is good, however, it limits you to a

small number of thing you can calculate. However lattice QCD can, in

principle, calculate many many more interesting strong interaction

processes. Chris gave an update of the state of some of these

calculations, which are very very hard to do. You have an unstable

particle in the intitial state, two or more hadrons in the final

state, and a transition at some point between. I

Labels:
conferences

## Tuesday, July 26, 2005

### Lattice 2005, day one

Hello from Dublin. As promised, I'm going to try to deliver daily

reports from the plenary sessions. Unfortunately, getting wireless

internet access in the conference room has proved problematic, so

it'll have to be after the fact reports, rather than live blog

updates. These comments are subjective, and I can cover every talk,

so that's that.

After the usual introductory speechs the conference got off to a bang

with a talk by Julius Kuti, from the University of California San

Deigo. The topic was Lattice QCD and String Theory, which is a

growing field. There is a lot of interesting problems in the field,

from more abstract things to practical things. Julius spent most of

his talk on a practical goal, namely using lattice QCD simulations to

understand effective string models of QCD.

In some sense this is a return to the orgins of string theory. The

original idea was to model the gluon field connecting two quarks as a

peice of relativistic string. The naive application of this idea

didn't work, and so string theory went off in a totally different

direction. However, with all the things that have been learned about

it, effective (four dimensional) string models can now be

constructed. And lattice QCD is the ideal tool to test these models

against. There are some issues, as there always are, but the results

here were promising, and offer a lot of new territory to explore.

Next up was one of the best field theorists in the world, Martin

Luscher. He talked about effeciently simulating a certain type of

dynamical fermions (Wilson quarks, for the experts) much more

effeciently than they've been done before.

His idea was to split the lattice up into smaller hypercubic blocks,

about 0.5 fm on a side. Then you split your update algorithim into

three parts,

gluon part + inside block quark part + block boundry part

Now, in the standard way of doing things, all of these parts are

computed the same number of times (say 2000 times per lattice

point). What Luscher (and his collaborators) do is take advantage of

the physics of the system to drastically reduce the number of times

you have to compute the block boundry part, which is the most

expensive bit. The essential bit of physics is that the correlation

between points on the boundry, and points deep inside the cube is very

weak. This means you don't have to compute it's effects nearly as

often as when you compute the gluon effects.

As Luscher mentioned, comparing computer algorithms is a tricky

business, however his simulations with this new method seem to be a

factor of ten or more faster than comperable simulations with the

standard methods.

In the second plenary session we had a talk by Jim Napolitano, who is

an experimentalist working on the CLEO-C experiment. CLEO-C is

currently studying D meson physics in great detail at the CESR

accelertor at Cornell. One of the main motivations for CLEO-C is to

test lattice QCD predictions in the charm system, so that results in

the B meson system can be confidently predicted. Jim ran over a

number of new results from CLEO including the leptonic decay constant

fD, and the masses of two new mesons, the h_c and the \Upsilon(1D).

These measurements are very tough, they involve looking for rare

raditive transitions in decays of highly excited mesons. The reason

that the can be done at all is because CLEO has very good control over

the initial state. Basically, they're colliding electrons and

positrons right on top of a charm anti-charm quark resonance. This

resonance decays to a pair of D mesons, almost at rest. In most

cases, both D's decay in a shower of crap (pions, kaons, etc). But

sometimes one decays into a shower of crap, and one does something

rare. When this happens you're happy, because, from the shower of

crap you can learn everything about one of the D's that decayed. And

sinc the total momentum is nearly zero, conservation of momentum tells

you that it's the same for the D that decayed in a rare way. With

that information, and the final state of the rare decay, you can very

accurately reconstruct what happened. As usual, listening to an

experimental talk made me glad I'm in theory. What they do is really

hard :)

So there's lots going on here. I'll update tomorrow with the next

round of talks.

reports from the plenary sessions. Unfortunately, getting wireless

internet access in the conference room has proved problematic, so

it'll have to be after the fact reports, rather than live blog

updates. These comments are subjective, and I can cover every talk,

so that's that.

After the usual introductory speechs the conference got off to a bang

with a talk by Julius Kuti, from the University of California San

Deigo. The topic was Lattice QCD and String Theory, which is a

growing field. There is a lot of interesting problems in the field,

from more abstract things to practical things. Julius spent most of

his talk on a practical goal, namely using lattice QCD simulations to

understand effective string models of QCD.

In some sense this is a return to the orgins of string theory. The

original idea was to model the gluon field connecting two quarks as a

peice of relativistic string. The naive application of this idea

didn't work, and so string theory went off in a totally different

direction. However, with all the things that have been learned about

it, effective (four dimensional) string models can now be

constructed. And lattice QCD is the ideal tool to test these models

against. There are some issues, as there always are, but the results

here were promising, and offer a lot of new territory to explore.

Next up was one of the best field theorists in the world, Martin

Luscher. He talked about effeciently simulating a certain type of

dynamical fermions (Wilson quarks, for the experts) much more

effeciently than they've been done before.

His idea was to split the lattice up into smaller hypercubic blocks,

about 0.5 fm on a side. Then you split your update algorithim into

three parts,

gluon part + inside block quark part + block boundry part

Now, in the standard way of doing things, all of these parts are

computed the same number of times (say 2000 times per lattice

point). What Luscher (and his collaborators) do is take advantage of

the physics of the system to drastically reduce the number of times

you have to compute the block boundry part, which is the most

expensive bit. The essential bit of physics is that the correlation

between points on the boundry, and points deep inside the cube is very

weak. This means you don't have to compute it's effects nearly as

often as when you compute the gluon effects.

As Luscher mentioned, comparing computer algorithms is a tricky

business, however his simulations with this new method seem to be a

factor of ten or more faster than comperable simulations with the

standard methods.

In the second plenary session we had a talk by Jim Napolitano, who is

an experimentalist working on the CLEO-C experiment. CLEO-C is

currently studying D meson physics in great detail at the CESR

accelertor at Cornell. One of the main motivations for CLEO-C is to

test lattice QCD predictions in the charm system, so that results in

the B meson system can be confidently predicted. Jim ran over a

number of new results from CLEO including the leptonic decay constant

fD, and the masses of two new mesons, the h_c and the \Upsilon(1D).

These measurements are very tough, they involve looking for rare

raditive transitions in decays of highly excited mesons. The reason

that the can be done at all is because CLEO has very good control over

the initial state. Basically, they're colliding electrons and

positrons right on top of a charm anti-charm quark resonance. This

resonance decays to a pair of D mesons, almost at rest. In most

cases, both D's decay in a shower of crap (pions, kaons, etc). But

sometimes one decays into a shower of crap, and one does something

rare. When this happens you're happy, because, from the shower of

crap you can learn everything about one of the D's that decayed. And

sinc the total momentum is nearly zero, conservation of momentum tells

you that it's the same for the D that decayed in a rare way. With

that information, and the final state of the rare decay, you can very

accurately reconstruct what happened. As usual, listening to an

experimental talk made me glad I'm in theory. What they do is really

hard :)

So there's lots going on here. I'll update tomorrow with the next

round of talks.

Labels:
conferences

## Tuesday, July 19, 2005

### Update

Been a while since I posted an update, so I thought I'd check in. The physics blog world is abuzz with the creation of a new physics group blog cosmic variance which features Sean Carroll, Mark Trodden, JoAnne Hewett, Clifford Johnson, and Risa Wechsler. A nice mix of cosmology, particle phenomenology and string theory.

I've been busy calculating, and preparing for Lattice 2005, which is the big annual conference for lattice field theory. This year it's being held at Trinity college in Dublin. They have wireless around, so I should be able to liveblog at least some of the sessions. I'm also going to try to post nightly updates.

An amusing note, the built in spellchecker for blogger flags "blog" and "liveblog" as spelling errors.

I've been busy calculating, and preparing for Lattice 2005, which is the big annual conference for lattice field theory. This year it's being held at Trinity college in Dublin. They have wireless around, so I should be able to liveblog at least some of the sessions. I'm also going to try to post nightly updates.

An amusing note, the built in spellchecker for blogger flags "blog" and "liveblog" as spelling errors.

Labels:
blogs,
conferences

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