Dark matter research (Edinburgh conf. this week)

[Martin]

Severian mentioned this on another thread

Dark matter is an issue.

Very true. The 5th International Workshop on the Identification of Dark Matter[/url'] is on in Edinburgh next week.

 

May be worth having a thread about current search going on for dark matter and efforts to map the presumed dark matter in clusters of galaxies by observing gravitational lensing of light coming from still further galaxies----from ones "behind" the cluster from our viewpoint.

 

I went to the Edinburgh conference site and downloaded the programme.

It did not mean a lot to me. there is obviously a huge amount of activity in observational astronomy around the dark matter thing.

 

Also at Edinburgh they will be having a talk by Alain Blanchard who has some somewhat novel ideas. Also there are to be talks about dark energy.

the astronomy boat is rocking so much these days it can get uncomfortable just trying to watch it.

 

Is anyone (Severian?) going to attend the Edinburgh conference?

 

Notice that on the evening of Monday September 6 they will not be having any talks because they have planned a

 

Reception at Scottish Whisky Heritage Centre

 

the Scots understand the idea of heritage.

[Martin]

Severian tells us he will be at the Edinburgh conference on dark matter...

 

[edit: just learned that Severian gave one of the plenary talks there on Thursday, yesterday!]

 

interesting all the different things dark matter might turn out to be, and

various ways people are contriving to look for evidence about it with colliders (e.g. LHC) and by astrophysics instruments

[Alexa]

Hi Martin,

 

I have no information about the conf. at Edinbourgh, but here you have the last article on space. com

September 14

Dark Matter Draws Galaxies onto Collision Course

 

A nearby cluster of galaxies is being pulled around by an underlying superstructure of mysterious dark matter, according to new evidence from NASA's Chandra X-ray Observatory.

Scientists don't know what dark matter is, but they think most of the universe is made of the stuff, because there isn't enough regular matter to account for the gravity that binds galaxies. The dark matter is thought to be concentrated in long filaments. Where the filaments intersect, regular matter clumps and galaxy clusters form.

A Chandra survey of the Fornax galaxy cluster revealed a vast, swept-back cloud of hot gas near the center of the cluster. The hot gas cloud, which is several hundred thousand light years in length, is moving rapidly through a larger, less dense cloud of gas, astronomers suspect. Other observations suggest an unseen, large structure is collapsing and drawing everything toward a common center of gravity.

 

"At a relatively nearby distance of about 60 million light-years, the Fornax cluster represents a crucial laboratory for studying the interplay of galaxies, hot gas and dark matter as the cluster evolves." said Caleb Scharf of Columbia University in New York. "What we are seeing could be associated directly with the intergalactic gas surrounding a very large scale structure that stretches over millions of light years."

 

Scientists don't know what dark matter is made of and they've never seen it. But indirect observations like this help them constrain its properties.

 

The infalling galaxy group is about 3 million light-years from the cluster core, so any collision will be a few billion years off. The findings were presented last week at an American Astronomical Society meeting in New Orleans.

 

-- SPACE.com Staff

[Severian]

Unfortunately I could not go to all of the conference because I am in the middle of moving house. So I was just there for the day of my talk. The transparancies for the talks are on the web site too. If you want an introductory overview, I would recommend the talks of the first day, and in particular Keith Olive and Leszek Roszkowski.

 

You should be aware though that DM researchers have a bad habit of placing exculsions at 2 sigma. The WMAP data then rules out a lot of the models for DM. This is very unfair in my opinion, since 2 sigma is far too low. Saying a model is ruled out to 2 sigma is only saying that it is ruled out to 95.45% confidence. Statistically, you would expect a correct model to be 'ruled out' one in 20 measurements!

 

In contrast, in particle physics exclusions (ruling something out) is done at 3 sigma (99.73%), and discovery (definitively saying something has been discovered) is announced with a 5 sigma (99.9943%) confidence.

 

Changing the exclusion limits on the plots from 2 to 3 sigma would make a substantial difference.

[Martin]

... The transparancies for the talks are on the web site too. If you want an introductory overview' date=' I would recommend the talks of the first day, and in particular Keith Olive and Leszek Roszkowski.

...[/quote']

 

Hi Severian and Alexa,

I went looking for the transparencies but didnt find them yet,

however in looking I came across the transparencies for a related

symposium held this month at Sheffield

http://www.shef.ac.uk/physics/idm2004.html

 

---quote---

New Trends in Particle Physics and Cosmology

Sheffield, 1st-3rd September 2004

 

Scanned lectures now available.

The Astro-Particle Theory and Cosmology group at the University of Sheffield and the Institute for Particle Physics Phenomenology (University of Durham) are holding an advanced Summer Institute on "New Trends in Particle Physics and Cosmology" ...

---end quote---

 

this link was at the Edinburgh site. I have bolded some phrases that remind me of what I see as a shift going on in HEP----high energy physics which used to be so "accelerator-centered" is turning its attention on the sky more and more, or so it seems.

[Martin]

Well I found the Edinburgh talks, mostly in PDF it says (although often with original powerpoint as an option too)

in the obvious place at the main site. dont know how I missed it earlier.

 

----sample of what is available for download----

 

......

Non-baryonic dark matter: theory

....

....

Keith Olive

SUSY Dark Matter

 

Leszek Roszkowski

Supersymmetric WIMPs

 

Mario Gómez

CP phases and neutralino relic density

 

Ana Teixeira

Theoretical predictions for direct detection of neutralino dark matter in the NMSSN

........

........

 

Microlensing and dark matter

 

Andy Taylor

Probing the dark universe with weak gravitational lensing

Original Powerpoint

 

Wyn Evans

The End of the MACHO Era

 

Alan McConnachie

A bird's eye view of M31 and its satellites

 

Philippe Jetzer

Microlensing events towards LMC and M31

 

Klaus Eitel

Direct measurements of the neutrino mass

-----end of sample----

 

 

I saw a few talks (three maybe) on the subject of dark energy.

so it was touched on as well. but there are literally scores of talks

on dark matter, the main focus.

[Severian]

I have bolded some phrases that remind me of what I see as a shift going on in HEP----high energy physics which used to be so "accelerator-centered" is turning its attention on the sky more and more' date=' or so it seems.[/quote']

 

The reason for that is rather obvious. LEP has now switched off since the same tunnel is to be used for the LHC. So until the LHC switches on in 2007, there is not really any collider data coming in (the Tevatron is having problems with its luminosity), whereas the astro experiments are still taking data.

 

It will all shift round again in 2007.

[Martin]

I can picture it coming round again quite smartly when LHC fires up

in 2007, though I think the present period of high "astroparticle" interest will leave a residue as well.

 

what do you see as the main issues that might surface then (with LHC running)? I have heard talk of:

SUSY found/not found

electroweak symmetry breaking

 

Can you help me (us?) get my expectations in better focus?

[Severian]

You pretty much have it already.

 

The big question is how we break the electroweak symmetry. Most people seem to be expecting the Higgs boson but it is not clear if it will be the minimal Higgs model or something a little more complicated.

 

The problem is that fermion mass terms in a Lagrangian always look like [math]m \bar \psi_R \psi_L[/math] so they basically mix left (L) and right ® handed particles. But in our very good theory of electroweak interaction, left and right handed fermions are in different representations. This is analagous to the left-handed particle being a vector in SU(2) space while the right handed is a scalar.

 

As you all know (I hope) a scalar times a vector is a vector and not an invariant - it changes with your coordinate system. So the mass term above is not allowed in our theory, at a fundamental level.

 

The only way that it can be put in is to add another SU(2) vector 'H' to make an invariant: [math]Y \bar \psi_R H \psi_L[/math]. Then the (dot) product of two vectors is a scalar, times a scalar is another scalar and therefore the term is SU(2) symmetric and allowed (Y is just a coupling constant). Then one has to imagine that 'H' does not oscillate about zero but oscillates about a finite value 'v'. Then the dynamics of H 'breaks the SU(2) symmetry': we shift H to its minimum [math]H \to H_0 + v[/math] and we are left with [math]Y v \bar \psi_R \psi_L+\bar \psi_R H_0 \psi_L[/math]. Now H₀ oscillates around zero as usual and we have given a mass to the fermion of [math]m=Y v[/math].

 

As you probably realised, H is the 'Higgs boson'. The difficulty is that this is pretty much the only way to do this. Any theory of electroweak symmetry breaking has to provide a fermion mass, so any theory is going to have to provide an SU(2) vector to balance the mass term out. It may be that the new vector is not fundamental, but they all have it. So in technicolor models, for example, the vector is a techniquark bound state.

 

Therefore everyone with any sense expects to see a 'Higgs boson like particle' at the LHC. The real question will be: what is it really? That will take a few years to sort out I imagine.

 

Of course, if they find supersymmetry (susy), the Higgs mechanism for breaking electroweak is pretty much a given since it is so intimately linked to the Higgs mechanism. There are prently of different variations of Higgs mechanism to sort out then though.

 

If susy is there it will be really easy to see. The challenge then is to measure all the masses and couplings of the new particles and try to figure out some mechanism for breaking supersymmetry. This would most likely provide a GUT model too.

 

If susy is not there, the Higgs mechanism becomes a little bit uncomfortable. Quantum corrections to the Higgs boson mass become very large and it is hard to get a physically reasonable theory. In that case, I would imagine there would be some other mechanism like Strongly Interacting Ws or Large Extra Dimensions. The latter would be nice because it might mean that we could probe gravity at the LHC too....