1. Interacting Dark Energy
Xinmin Zhang
Institute of High Energy Physics
Beijing
June 18, 2004

2.   * Recent years Cosmology made big progress
 
* 4%: Particles in the standard model
but why no antimatter?
* Understanding the Dark Sector: Challenges to particle physics
Dark Matter:
Favored candidates:
Axion
Neutralino
Thermal Production & Non-thermal Production
For ex: consider a model with extra UB-L(1)
UB-L(1) broken neutrino masses & cosmic string
String loop decay
Jeannerot,
Brandenberger
&Zhang, Jan. 1999

3. Thermal production Non-thermal 1，
2, enhancing the parameter space
3, cold dark matter warm dark matter
Weak interactions
“stronger” interactions

4. CDM: “Nagging Problems”
Prediction of cuspy dark halos
Apparent prediction of too much substructures
thermal
Non-thermal
Astrophysical explanations
Lin, Huang, Zhang & Brandenberger,
Particle physics PRL (2001)

5. Dark Energy: * Negative pressure: 
* Smoothly distributed, (almost ) not clustering
Candidates:
* Cosmological constant (or vacuum Energy)
But: , cosmological problem!
* Dynamical Field: Quintessence, K-essence, Phantom etc

6. Outline of this talk on Interacting DE
Very briefly review on the current constraints on Dark Energy
A model of unifying and
In the framework of Quintessence, introducing coupling:
A model of neutrinos with varying masses
Since the scale of DE,
Only comparable with mν, interesting to speculate on the possible
connection betweens the two:
Interaction between the neutrino and DE:
A model of DE and DM:
SUSY fermionic partner of Quintessence,Quintessino as DM particle
Summary
(Feng, Wang and Zhang)
(Li, Feng Wang and Zhang)
(Gu, Wang and Zhang)
(Bi, Li and Zhang)

7. Constraints on the Dark Energy
A quantity characterizing the property of Dark Energy:
Equation of state: w(Z)=P/ρ
For example :
* Vacuum Energy: w=-1
* Quintessence:
* Phantom:
Model independent analysis with the following parameterization：
1，w(z)=w_0 + w_1* z
2，w(z)=w_1 + w_a*z/(1+z)
(E.Linder)
Using the recent 157 Supernova data published by Riess et al.
astro-ph/ )
* Within 2 σ, the cosmological constant fits well the data
* Data mildly favors a running of the W across -1

8. Feng, Wang &
Zhang
Astro-ph/
Huterer & Cooray
Astro-ph/

9. If the running of w(Z), especially a transition across –1, confirmed
in the future, big challenge to the model building
* Vacuum : w=-1
* Quintessence:
* Phantom:
A new scenanio of Dark Energy : Quintom (Zhang et al.)
For ex:
single scalar:
multi-scalar:

10. * Interacting with neutrinos: mass varying neutrino
Interacting Quintessence
* If Quintessence –like scalar field responsible for the current
acceleration of the Universe ,expected also to interact with the
matter directly. Open new possibilities for the detection.
* Direct coupling with ordinary matter
Constraint from the limits on the long-range force
* Interaction with derivative
Goldstone theorem: Spin-dependent force
a unified model of DE and Baryo(Lepto)genesis
Quintessino as DM
* Interacting with DM (Peebles et al )
* Interacting with neutrinos: mass varying neutrino

11. Quintessential Baryogenesis
M.Li, X.Wang, B.Feng, X. Zhang PRD65, (2002);
M.Li & X. Zhang， PLB573,20 (2003)
In thermo equilibrium 
Cohen & Kaplan
The value of depends on the model of Quintessence

12. If B-violation is due to electroweak sphalerons TD about 100 GeV
model：
Albrecht & Skordis
PRL84,2076(2000)
Solution:
Tracking
Decoupling T：
If B-violation is due to electroweak sphalerons TD about 100 GeV
requires

13. Quintessential leptogenesis & neutrino mass limits
Similarly:
TD determined by
where
which gives
and
for degenerate neutrino masses:
defining
Cosmological limits give
WMAP:
SDSS:

14. Minimal model of Baryogenesis
* In the Quintessence as Dark Energy scenario, this is the minimal model for Baryogenesis in the sense that no extra particle beyond the standard model is introduced .
* In ΛCDM model,
with f(R): function of Ricci scalar,
If ,
Einstein equation give:
so, in radiation dominant Universe,
We propose , so
generating nB/s naturally!
Davoudiasl,Kitano,Kribs
Murayama and Steinhardt
H.Li, M.Li,X.Zhang

15. Mass varying Neutrinos
Motivations:
smaller than any scale in the particle Physics, however
comparable with neutrino masses
Any connection between the two?
Neutrino interacting with the Dark Energy
In the Quintessence-like models for Dark Energy:
Possible couplings:
Or in the see-saw model:
Implication for Leptogenesis!

16. Where, Corresponding the formula for the neutrino
mass upper limit now is:
Where,

17. Including the back reaction
Bi,Feng,Li,and
Zhang, in preparation
R.Fordon, A.Nelson and N. Weiner consider a case with δ, c=0
R. D. Peccei hep-ph/

18. Quintessino As Dark Matter
If susying the Quintessence:
Quintessence: Q
Squintessence: σq
Quintessino:
(X. Bi, M. Li
and Zhang)
Similar to : Axion, Saxion, Axino
Majoron, Smajoron, Majorino
(R. Mohapatra and Zhang)
If is lighter than , could serve as Dark matter
Susying the following interaction
(H: SU(2) doublet)
gives
gives
* Prediction: long-lived charged particle:

19. Summary Dark Energy Interaction with I. for Baryo(Lepto)genesis
II. neutrino: mass varying
Implication in Leptogenesis
Cosmological limits needs check
III. SUSY: Quintessino as Dark matter
(Bi, Gu, Wang and Zhang)
The Dynamics of the Dark sector might be very rich!
( remember that for the 4% sector, the dynamics is already very rich)

20. Thanks !