Limits on the Size of Extra Dimensions and the String Scale.pdf

a r X i v : h e p - p h / 0 1 0 8 1 7 4 v 1 2 2 A u g 2 0 0 1 ETH-TH/01-11 CERN-TH/2001-204 LIMITS ON THE SIZE OF EXTRA DIMENSIONS AND THE STRING SCALE ? I. Antoniadis 1,2 and K. Benakli 1,3 1 CERN Theory Division CH-1211, Gene?ve 23, Switzerland 3 Theoretical Physics, ETH Zurich, Switzerland Abstract We give a brief summary of present bounds on the size of possible extra-dimensions as well as the string scale from collider experiments. ? Based on talks given by I.A. at La Thuile2001 and by K.B. at Moriond2001 . 2 On leave of absence from CPHT, Ecole Polytechnique, UMR du CNRS 7644 1 Introduction Although the standard model has been experimentally verified to an impressive precision level, it remains unsatisfactory in some of its theoretical aspects. The major one concerns dealing with the quantum effects of gravity. The renormalization procedure which allows to extract finite predictions for processes involving the three other fundamental forces fails when gravitational interactions are taken into account. String theory stands here as only known consistent framework to incorporate these effects. There, known fundamental particles are “point-like”only because the experimental energies are too small to excite the string oscillation modes so only the center of mass motion is perceived. In addition to these heavy oscillation modes, strings have new degrees of freedom that often take the classical geometry description of propagation in extra dimensions and thus provide a compelling reason for the latter. This raises important questions: Is it possible that our world has more dimensions than the one that we are aware of? If so, why don’t we see the other dimensions? Is there a way to detect them?. Answering these questions has attracted a lot of efforts lately as it has became clear that not only these extra-dimensions might be there, but also they could be just at the border of the energy domain at reach to near future experiments. This is because, within our prese