1. Signatures of Large eXtra Dimensions LXD-Group ITP Frankfurt Marcus Bleicher, Sabine Hossenfelder (Tucson), Stefan Hofmann (Stockholm), Lars Gerland (TelAviv), Kerstin Paech, Jörg Ruppert, Christoph Rahmede, Sascha Vogel, Horst Stöcker, Benjamin Koch

2. Outline Motivation: why eXtra dimensions Models with eXtra dimensions ADD & RS Observable signatures for eXtra dimensions Summary

3. Very successfull effective quantum-field-theory of electroweak and strong interactions Problems: Gravitation missing why is gravitation so weak (hierarchy problem) quantisation of gravity Too many parameters to be really fundamental Why Higgs so light (finetuning problem)... The Standard Model (SM) LXDs

4. Large eXtra Dimensions Models with extra dimensions: Arkani-Hamed, Dimopoulos & Dvali (ADD) Randall & Sundrum (RS) Universal Extra Dimensions (UXD) All contain one or more eXtra dimensions that are compactified on a radius that is so small that it could not be observed up to now. * Large means large compared to Planck length:...

5. The ADD - model 3+d spacelike dimensions d dimensions on d-torus with radii R all standard model fields live only in 4-dim. spacetime (brane) only gravity propagates in all dimensions (bulk) This leads to a modification of Newton´s law:

6. Gravitons in accelerator experiments excitations of gravitons look on the brane like massive particles: From phase space one finds with that the cross section for graviton production for example in behaves like: Measurement via energy loss:

7. Black holes in accelerator experiments Modification of Newton´s law at distances smaller than R leads to increase of the Schwarzschild radius Particles that get closer than R H form a horizon. up to black holes might be produced at LHC per year.

8. LXDs in Astrophysics Strongest constraints on size of eXtra dimensions from supernova and neutron star observations: Observed neutrino flux from SN1987a Non observed flux of decay products of massive gravitons from SN and neutron stars Hannestad & Raffelt 2002

9. Minimal length Higher dimensional space-time and the existence of a minimal length scale are intrinsic features of string theory and quantum gravity Minimal length can be modeled by setting with minimal possible compton wavelength this changes basic quantum mechanics

10. Observation of minimal length Modification of SM cross sections at high energies Modification of the gyromagnetic moment of electrons and myons. independent of number of eXtra dimensions Harbach et al. 2004

11. Summary Soon we might be able to look behind the SM Simple models like LXD + minimal length don´t claim to a TOE......but provide useful basis to probe general features of spacetime like - value of new scale - number and size of eXtra dimensions - existence of minimal length Model yields predictions for astro- & collider-physics May help to learn about - structure of quantum gravity - mechanism of unification