# Andreas Braun

# Andreas Braun

Research Assistant

I am a researcher working in the string theory group at the Rudolf Peierls Centre for theoretical physics. I am working on dualities of string and field theories, as well as compactifications of string theory and the question how string theory is related to observed physics.

My upbringing as a student has been as a theoretical particle physicist. As things go, I first got involved with string theory and then with the mathematics needed to make progress.

In slightly technical terms, I have worked a lot on F-theory, which is very elegant geometrization of the self-duality of type IIB string theory. This works by replacing the complexified string coupling of type IIB string theory by a elliptic curve (i.e. a torus) and nicely ties together M-Theory, type IIB string theory and heterotic E8 x E8 string theory. A basic introduction can be found here http://people.sissa.it/~cecotti/FNOTES10.pdf

Although this is great fun in its own right and has led to many insights, F-Theory provides an interesting starting point for 'string phenomenology'. This concerns the question how we should think about string theory in relation to the known low energy physics as described by the Standard Models of particle physics and cosmology. A review of why F-theory is interesting for string phenomenology can be found here http://arxiv.org/abs/1009.3497.

Although String Theory is a very beautiful theory which seems to be unique as a 10 dimensional theory, it is presently unclear how we should think about it in relation to our four-dimensional world. An obvious way to go is to consider solutions of string theory which effectively look four-dimensional below a certain energy scale. One of the fundamental problems of String Theory is that there is a huge number of options to do this. Although opinions on what this means differ wildly, it is fair to say that many things about this 'landscape' are poorly understood. Here are a few questions:

-- Can we find a solution of String Theory which perfectly reproduces observed physics ?

-- Is the set of effectively four-dimensional solutions even finite ?

-- Is (a well-defined subset of) every consistent four-dimensional theory an effective description of some string theory compactification ?

-- Are there universal features (maybe in some well-defined subset) ?

-- Are there correlations between (desirable) features ?

-- What has cosmological evolution to say about this ?

In more technical terms, one of the main themes of my own research are F-Theory solutions which include 'fluxes'. These are (quantized) background values for fields other than the metric which cannot simply decay away. They give, however, potentials influencing shapes and sizes of extra dimensions. See http://arxiv.org/abs/1107.5337

I really like K3 surfaces, as their geometry provides a starting point for many beautiful things in String Theory. Here is a visualization: https://www.maths.ox.ac.uk/node/14678/quartic-surfaces/kummer-surfaces

Here are some lectures I have given on how to use the open-source mathematics software SAGE to do computations with Calabi-Yau manifolds http://www.mth.kcl.ac.uk/~ss299/GGI/scheduleSchool.html

I like music a lot and often listen to resonance.fm while working. If I had to pick one, my favourite movie would be 'Night on Earth' by Jim Jarmusch, but it is hard to choose. I am a Linux fanboy. My favourite colour is blue. In the late summer, I like to hunt for wild mushrooms but won't tell you where to find them (secret of the trade). I swam in the Themse. I like cacti and coriander. We live in a pretty big universe with many interesting things to discover.