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Signatures of Large eXtra Dimensions
• LXD-Group ITP FrankfurtMarcus Bleicher, Sabine Hossenfelder (Tucson), Stefan Hofmann (Stockholm), Lars Gerland (TelAviv), Kerstin Paech, Jörg Ruppert, Christoph Rahmede, Sascha Vogel,
Horst Stöcker, Benjamin Koch
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Outline
• Motivation: why eXtra dimensions
• Models with eXtra dimensions ADD & RS
• Observable signatures for eXtra dimensions
• Summary
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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
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Large eXtra DimensionsModels 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: ...
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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:rmm
V
p
112
12
11dd
f rMm
V ddfp RMm 22
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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:
0)()(1
2
2
d
i
ii
iA
A
R
n
R
ns max
2
22
~
d
f
p
M
s
s
m
dt
d
)( Gee
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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 RH form a horizon. up to black holes might be produced at LHC per year.
HR
fmM
M
dMdRfm
m
MR d
d
ffH
pH
42
1
382
101
21)(102
2
910
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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
TeVMTeVM dfdf 7,84 32
TeVMTeVM dfdf 30,500 32
Hannestad & Raffelt 2002
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Minimal lengthHigher dimensional space-time and the existence ofa minimal length scale are intrinsic features of string theory and quantum gravity
• Minimal length can be modeled by setting
.../)( 33
22 papappkk
• with minimal possible compton wavelength
• this changes basic quantum mechanics
ffc ML /1
2
2
12
]ˆ,ˆ[f
ijji M
ppxikx
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Observation of minimal length
• Modification of SM cross sections at high energies
• Modification of the gyromagnetic moment of electrons
and myons. 1110)80116592030(2/)2( ga
GeVM f 577
independent of number of eXtra dimensions
Harbach et al. 2004
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SummarySoon 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
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