Transcript Signatures of large eXtra Dimensions

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
Outline
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Motivation: why eXtra dimensions
Models with eXtra dimensions ADD & RS
Observable signatures for eXtra dimensions
Summary
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
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: ...
The ADD - model
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•
•
•
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
V
1 1

Newton´s law:
m m 2p r

V
1
1
 d  2 d 1  m2  M d 2 Rd
p
f
m Mf r
Gravitons in accelerator experiments
• excitations of gravitons look on the brane like
massive
2
d
particles:  A A  (      i  i )  (      ni2 )  0
i 1
nmax
R
R
• From phase space one finds with
that the cross section
for graviton production for example in (ee  G)
d 2
2


behaves like: d ~ m p  s   2
s
dt
s  M f 
• Measurement via energy loss:
Black holes in accelerator
experiments
• Modification of Newton´s law at distances smaller than R
leads to increase of the Schwarzschild radius RH
RH 
2M
38

2

10
m2p
1  2 M
fm  RH (d ) 
M f  d  1 M f




 d 1
 d 2 104 fm
• Particles that get closer than RH form a horizon.
up to  109 black holes
might be produced at LHC
per year.
LXDs in Astrophysics
Strongest constraints on size of eXtra dimensions from
supernova and neutron star observations:
• Observed neutrino flux from SN1987a
M f d 2 84 TeV , M f d 3 7 TeV
• Non observed flux of decay products of massive
gravitons from SN and neutron stars
M f d 2 500 TeV ,
Hannestad & Raffelt 2002
M f d 3 30 TeV
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
k  k ( p)  p /   a2 p 2  a3 p3  ...
• with minimal possible compton wavelength
c  L f  1/ M f
• this changes basic quantum mechanics
   p 2  
ˆ
[ xˆi , k j ]  i ij  xp  1 
2 
M 2f 
Observation of minimal length
• Modification of SM cross sections at high energies
• Modification of the gyromagnetic moment of electrons
and myons.
a  ( g  2) / 2  (116592030 80) 1011
 M f  577 GeV
independent of number of eXtra dimensions
Harbach et al. 2004
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