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Michele Maio's Web Page

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My main interest is String Theory in its generality. Currently, I am working on how to make contact with the real world and more in details on developing new conformal field theory tools that can then be used in several directions, from model building to brane boundary states.
For more detailed information, please check the links.

My studies in Theoretical Physics started at the University of Bologna and continued in Amsterdam, first within the UvA String Theory Group and then the Nikhef Theory Group.

String Theory is an exciting subject. It brings new ideas and opens unexpected, maybe disturbing at first, ways of looking at the world. The starting point is to consider tiny strings instead of pointlike particles as main constituents of matter. The spectrum of closed strings contains the graviton, while open strings give rise to all kinds of gauge fields. Consistent open string theories also require higher dimensional objects, called branes. Hence, String Theory could represent the framework where gauge theories and gravity are described simultaneously.

Experimental verifications are still missing, but there are reasons why it is worth pursuing the research on the subject. In fact, String Theory is very interesting by itself. As a mere theory, it has pushed forward many mathematical areas. Some examples are: Conformal Field Theory, which has a lot of applications in Condensed Matter Physics; mirror symmetry in the context of Calabi-Yau manifolds, which was discovered within String Theory and has then developed as a distinct field in Mathematics.
As a physical theory, it has also some merits. For example, it is possible to derive the correct black hole entropy. Moreover, the web of dualities connecting all the various string theories gives insights for a more fundamental physical theory, which is unfortunately mostly an empty box at the moment.

String theory, in its full geometrical approach, is known to predict the existence of ten spacetimes dimensions. However only four are directly observable to current experiments. The explanation of why we do not see the extra six spatial dimensions is an old problem. A more generic approach allows to get rid of the extra space from the start and leads to four dimensional string theories. It is based on conformal field theories (CFT's for short) and does not always have a geometric interpretation. In these recent years we have developed new tools in CFT which are immediately applicable to string theory phenomenology and allow to build new 4d models. Some of these models are different from what we experience in accelerators, but some others are very similar to the standard model of particle physics. These new tools are however not fully generic, but apply only to a subset, still rather large and important, of all the possible situations one can have. We wish to complete the full study during the next few years. In a bit more technical words, we have considered the permutation orbifold of two identical CFT's and used it to build 4d strings. Using this formalism, we have been able to construct models with three families. The number three seems however not special, since the number of families changes in different models. One can then ask the question of why our world is as it is ans why, in the landscape of all the possibilities, it should be just this particular one.

Currently, most research is focused on making connections with experiments, either exploiting gauge/string dualities or looking for appropriate (flux?) compactifications of the small internal manifold.
String Theory is an exciting field and it is now the right time for conceptual breakthroughs, needed in order for the whole subject to progress and maybe give predictions. Especially in this period, pressure from experiments is starting to show itself among theorists: soon new data will clarify the direction to follow, with the consequence that we will all get new valuable insights from them, but also in such a way that it would make the theory less independent from observation. It is then really the time to hurry.

Immediately connected with this discussion, the most obvious topic to start with is Supersymmetry: it is going to be crucial in the near future, when the LHC will produce the first results, providing new ideas for physics beyond the standard model. Supersymmetry might be discovered already at the TeV scale and, since we would still like to think of the physics at those energies in terms of a gauge theory, then we should consider supersymmetric gauge theories as the relevant descriptions of physics, where new symmetries appear (e.g. R symmetry) that are subsequently broken and new dualities (e.g. Seiberg duality) relate different regions of the parameter space.

Cosmology is in a similar position: with the Planck satellite in orbit at the Lagrangian point L2 taking data, more detailed information will come over the cosmic radiation and hence over the Universe immediately after the Big Bang. We know by now that our Universe is in good approximation flat and probably destined to undergo a cold and infinite expansion, but many other urgent problems are still far from being solved. For example, why do we need such a small cosmological constant? Or how did inflation (or any other similar mechanism) happen? What did the Universe look like at the Big Bang epoque? Crucial questions, but all with unsatisfactory answers.

There is still at least one more subject that deserves its own space: the gauge/gravity duality, that started as the AdS/CFT correspondence, but has then been generalized to many other situations (holography). It does look very surprising that a theory with gravity is equivalent to a gauge theory without gravity living in one dimension less, but in many instances it seems that Nature works exactly this way: we just need to know what theory is defined at the boundary to reconstruct the full gravitational theory in the bulk. It is as if all the relevant degrees of freedom lived on the boundaries. At the end of the day, maybe that's why the entropy of a black hole scales with its area!

The message here should be that there are many directions worth being explored. Actually, they must be explored, in order to acquire a full knowledge of modern Theoretical Physics and to be able to make connections between apparently unrelated fields, because only in this way real scientific progress can be made. Apparently String Theory has already given us a prediction: the impossibility of deriving the correct vacuum, which should in turn be picked from a moltiplicity of possibilities. This is often referred to as the landscape problem.

Of course, there is still a lot of work to do...

This page is still under construction.