Post on 05-Jan-2016
description
J.W. Ustron 2009
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UN
B. GrzadkowskiJ.W
- cosmology
J.W. Ustron 2009
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UVcompletion
Basic idea
New type of physics such that
• It is conformally invariant in the IR• Asymptotically free in the UV• It interacts weakly with the SM
Standard Standard ModelModel
Banks-Zaks (BZ) phase
Asymptotically free
Unparticle (U) phase
Conformally invariant
New New physicsphysics
HeavyMediators
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UV completion
BZ phase
Unparticle phase
The history of unparticles is dark and unknown but it is nevertheless divided by theoreticians into three periods
The first about which we know nothing
The second about which we know almost as much as about the first
And the third which succeeded the first two
(with apologies to A. Averchenko)
The new physics sector has two relevant scales:
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To make calculations one needs:
Rather unique collider signatures
No experimental motivation whatsoever
Can be used to understand how unusual types of new physics can affect cosmic evolution
That follows from conformal invariance
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Thermodynamics
Conformal invariance:
• has a non-trivial IR zero at g=g*
• The trace of the energy momentum tensor vanishes in the IR g
g*
g
g*
= anomalous dimension of F2
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) For available models gNP » 100
In the UV: asymptotically free ) / T4 to leading order
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SM-NP interactions Equilibrium, freeze-out and thaw-in
Standard approach: use the Boltzmann equation
Equilibrium as long as > H
= H at T = Tf
Less standard approach: use the Kubo equation … yields the same result … but does not need to introduce the unparticle distribution function
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NP
SM
SM’
NP’
Energy = ESM
4-momentum=KSM
Energy = ENP
4-momentum=KNP
Energy = E4 mom. = K
Energy = E’SM
4-momentum=K’SM
Energy = E’NP
4-momentum=K’NP
Energy = E’4 mom. = K’
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Only need a order of magnitude estimate for :
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dSM + dNP > 4.5 ) freeze-outdSM + dNP < 4.5 ) thaw-in
> H: coupled< H: decoupled' H ) T = Tf
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SN-NP coupling/decoupling
Blue: Tf 2 U phase
Red: SM-NP coupled
No-color: Tf < v
We assume that SP and NP were in equillibrium as T ! 1
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Unparticle effects on BBN
If SM-NP were in equilibrium and then decoupled, TSM and TNP can be related using entropy conservation:
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If SM-NP remain in equilibrium during BBN: gIR < 0.3
NP contribution to mimics that of additional ’s
So unparticle models should exhibit conformal invariance with a small number of RDF in the IR.
Unaware of an explicit model with this property
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Comments
Strongly coupled new physics can lead to /H » Tn (n positive or negative) ) A variety o freeze-out and thaw-in scenarios are viable ) BBN generates strong constraints on the NP.
Even for the “normal” decoupling scenarios (n>0) the BBN constraint is significant: gIR < 20, while the models available have gIR > 100
Unparticle models also suffer from potential theoretical problems: the coupling to the SM necessarily breaks conformal invariance.
If this effect is strong the above arguments do not apply … but then the experimental signatures are particle-like