Thursday, March 17, 2005

Of Colliders and Cosmology

I'm now into my second day of blogging and must say that I am surprised and delighted by the supportive and encouraging comments I've been receiving. Thanks to all who dropped by.

This afternoon I'm headed to California to take part in the International Linear Collider Workshop (LCWS2005) at Stanford University. The ILC is a proposal for the next large particle-smashing machine after the imminent (2007) turn-on of the Large Hadron Collider (LHC) in Geneva. I and my counterparts from Europe (Wim de Boer) and Asia (Nobuchika Okada) are co-conveners of the Cosmological Connections group, which is organizing three sessions of talks about the connections between extending our understanding of the universe and improving our knowledge about particle physics. The connections are many and I may devote a later post to a detailed description. Since I have to pack, feed the cats, call a cab and perform a host of other chores before then, I'll just give a quick summary here.

The main connection is to the search for dark matter. There is overwhelming evidence that the universe contains matter of a type other than that which we see forming galaxies, stars, planets and us (called baryons). In fact, the evidence shows that there is five times more of this so-called dark matter in the universe than there are baryons. It is observed indirectly through many different cosmological methods and, indeed, is the reason that galaxies are able to form the way they do. However, so far we have not been able to determine what the particles that make up the dark matter are. There is a good reason for this. The reason the dark matter is not seen glowing along with much of the rest of the material in galaxies is that it does not experience electromagnetism, the force of nature that leads to light. We think that dark matter particles must be only weakly interacting (electromagnetism is quite a strong force) and a consequence of this is that it is hard to get them to do anything measureable to material on Earth in order to betray their presence.

There are two ways to get around this. one is to build very sensitive detectors to measure even the smallest effects of dark matter on normal matter. After all, if there is five times more dark matter than baryons around, there should be lots passing through the Earth all the time as our solar system orbits the galaxy. There are many people devoted to these efforts and there are reasons to think that success is lurking in the not too distant future. The second way is, rather than waiting for cosmological dark matter to hit something in your detector, to smash particles together hard enough to create some of it all for yourself. If one can do this, then one would be able to measure its properties (its mass and the strengths of its interactions) and study how it fits into the overall structure of particle physics. This is where our colliders are indispensible.

With my friend Jonathan Feng from U.C. Irvine, I co-Chair the Working Group on Cosmology and the Linear Collider subgroup of the American Linear Collider Physics Group. With Marco Battaglia, Norman Graf and Michael Peskin we will, in the next month or so, complete a long document detailing this and other connections between colliders and cosmology. When this is completed I'll try to post a more comprehensive discussion of the topic.

I'm hoping to post a few times from the conference if I can demonstrate the self control required not to sprint out into the sunshine as soon as the sessions are over.
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