Signatures of Large eXtra Dimensions

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
The Standard Model (SM)
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)
• ...

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

• 3d 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 Newtons 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 Newtons law at distances
  smaller than R
• leads to increase of the Schwarzschild radius
• Particles that get closer than RH 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 dont
  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

12
(No Transcript)