Stephon Alexander

Away in Trinidad and Tobago

So I'm here at the University of the West Indies in Trinidad and Tobago.  There are actually three lovely campuses across the Caribbean; Jamaica , Barbados and Trinidad.  There is a physics department in all campuses and I'm here to give to talks.  The first one is going to be a public lecture which overviews the field of cosmology and the second will be a technical talk on the interface between cosmology and quantum gravity/string theory.

Trinidad is absolutely beautiful and the people here know how to enjoy life (they call it Lyming or fetting)

I've gotten some time to hike to the marvelous waterfalls and the secluded crystal clear warm bays of the northern coast.   I also saw a giant leatherback turtle lay her eggs!!!

Hey Clifford,  I'm staying with my aunt in Buen Intento road (coincidence??)

Thinking Thinking

Its sunny and breezy out here in San Fran. Although I'm tempted to go out for a run, I've been here for last couple hours thinking about cutoffs in field theory and its effect on cosmology. Marvin Weinstein (see my previous post on him) and I got in a fight the other day (typical Bronx versus Brooklyn brawl).

Marvin: So whaddya want to do, what are your trying to get at and don't gimme no bullshit

Stephon: I've been telling you that non-perturbative effects like gravitational instantons can be induced during inflation to kill the cosmological constant!

Marvin: You didnt solve a damn thing.

Stephon: Where you going with that Marv, my starting point is no different than Woodards. I say lets start with a huge cosmological constant, space-time will naturally be in a de Sitter phase. Now we have to
ask, by what dynamics is it killed. . .

Marvin: Yeah, except that its infinite. Not even Woodard solves that! Look, I'm a simple man-if you put in cutoffs then you have a very non trivial problem, nobody talks about it but its there o.k?

Stephon: So why don't you write it up! Didn't you and Ratin in your recent paper on Quantum de Sitter cover that ? see: http://arXiv.org/abs/hep-th/0312249

Marvin: Its there but not explicit-Look, I only write things up when I have something to say, I don't waste paper.

Stephon: So whaddya you want me to do? No one knows what to do with cutoffs in a dynamical space-time -especially non compact ones, I mean Jacobson and his students are currently studying this. I tried ok? See you next week ol man

-So the battle continues, Me, Marvin and the rest of the species trying to understand why Lambda_cc is small and positive today!

Hi Clifford-I'm just lost in a calculation

I just got great news that Willie Merrell, a young string theorist (graduate student of Jim Gates), earned the prestigious KITP Graduate Fellowship http://www.itp.ucsb.edu/activities/grad_fellows/. Great job Willie-I'm expecting great things from you!

So lately I've been a bit underground struggling over a calculation that is quite horrendous. What am I trying to calculate? Let me try to explain the physics. So there is this embarrising problem in theoretical physics, the cosmological constant problem (nowadays called the Dark Energy Problem). Its just a damn hard problem. I dedicated two blog entries to explaining the problem. My basic insight into a potential resolution of the problem is to use some wisdom from quantum mechanics of many body systems. Imagine that the cosmological constant is very large from the zero point motion of everything in the universe. Naturally, space-time will undergo inflation (we call this the de Sitter phase). But the de Sitter phase will also undergo quantum fluctuations as well and will generate quantum ripples of space-time (we call these gravity waves). Now imagine that these gravity waves are interacting with fermion. If the interaction is attractive then these fermions can form a bound state and possibly transform into a boson.
If it does this then there will be something that condensed matter physicst call a Gap. What is a Gap? The Gap is a quantity that seperates two ground states; the false ground state which was unstable and the true ground state which has a lower energy.

I am trying to calculate this gap in the context of inflation. It involves some high tech quantum field theory and a two loop graviton fermion calculation. Because the problem is time dependent I have to go back to the drawing board and figure out how to do two loop calculations in de Sitter space.

Otherwise, I'm reading Carlo Rovelli's new book on Quantum Gravity by Cambridge University Press. It is a very clear and beautifully written graduate level text book on the Canonical (non-perturbative) approach to Quantum Gravity (Loop Quantum Gravity).

I've also been thinking hard about the model independent axion in string theory and particle phenomenology. In particluar, I have been reading Witten's beautiful paper on Worldsheet corrections via D-instantons. This paper points out the worldsheet origin of the Green-Schwarz anomaly cancelling mechanism in 10D Supergravity. Deep stuff and it might be connected to Loop Quantum Gravity (but I'll save this idea once it is completely (mathematically) complete)

And one more thing. Hi Clifford!! In case you all don't know Clifford Johnson, he's basically my tough love uncle of physics and a badd arse String Theorist.