1. Significant effects of second KK particles on LKP dark matter physics
Mitsuru Kakizaki (ICRR, Univ. of Tokyo & Bonn Univ.)
August 29, Bonn Univ.
Collaborated with
Shigeki Matsumoto (KEK)
Yoshio Sato (Saitama U. & Munich, Tech. U.)
Masato Senami (ICRR)
Refs:
PRD 71 (2005) [hep-ph/ ]
hep-ph/

2. 1. Motivation
Recent observation of cosmic microwave background anisotropies by WMAP:
Non-baryonic cold dark matter [
What is the constituent of dark matter?
Weakly interacting massive particles are good candidates:
Lightest supersymmetric particle (LSP) in supersymmetric (SUSY) models
Lightest Kaluza-Klein particle (LKP) in universal extra dimension models
etc.
Today’s topic
August 29, 2005
Mitsuru Kakizaki

3. Outline
In universal extra dimension (UED) models, Kaluza-Klein (KK) dark matter physics is drastically affected by second KK particles
Reevaluation of relic density of KK dark matter including coannihilation and resonance effects Dark matter particle mass consistent with WMAP increases
Motivation
Universal extra dimensions (UEDs)
Relic abundance of KK dark matter
Resonant KK dark matter annihilation
Summary
New
August 29, 2005
Mitsuru Kakizaki

4. 2. Universal extra dimensions
[Appelquist, Cheng, Dobrescu, PRD67 (2000) ]
Idea: All SM particles propagate compact spatial extra dimensions
Dispersion relation:
Momentum along the extra dimension  Mass in four-dimensional viewpoint
Mass spectrum for
For compactification with radius ,
is quantized
Momentum conservation in the extra dimension
Conservation of KK number in each vertex
August 29, 2005
Mitsuru Kakizaki

5. The LKP is a good candidate of dark matter
Minimal UED model
In order to obtain chiral fermions at zeroth KK level, the extra dimension is compactified on an orbifold
Conservation of KK parity [+ (--) for even (odd) ]
The lightest KK particle (LKP) is stable
c.f. R-parity and LSP
The LKP is a good candidate of dark matter
Only two new parameters in minimal UED model:
: Size of extra dimension
: Cutoff scale
Constraints from electroweak measurements are weak:
August 29, 2005
Mitsuru Kakizaki

6. Mass spectra of KK states
1-loop corrected mass spectrum of the first KK level
KK modes are degenerate in mass at each KK level:
Radiative corrections relax the degeneracy
Lightest KK Particle (LKP): Next to LKP: SU(2)L singlet leptons:
: Cutoff scale
[From Cheng, Matchev, Schmaltz, PRD (2002)]
August 29, 2005
Mitsuru Kakizaki

7. 3. Relic abundance of KK dark matter
Co-moving number density
3. Relic abundance of KK dark matter
Decoupling
Increasing
Thermal equilibrium
Generic picture
Dark matter was at thermal equilibrium in the early universe
After the annihilation rate dropped below the expansion rate, the number density per comoving volume is almost fixed
Relic abundance of LKP dark matter
[Servant, Tait, Nucl.Phys.B650 (2003)391]
3 flavors
Without coannihilation
Including coannihilation
Only tree level diagrams are considered
August 29, 2005
Mitsuru Kakizaki

8. 4. Resonant KK dark matter annihilation
New
4. Resonant KK dark matter annihilation
Dark matter is non-relativistic in the early universe
(The incident energy of two LKPs)
(Mass of 2nd KK modes)
Mass splitting:
The annihilation cross section for the LKP is enhanced due to the resonance by s-channel 2nd KK Higgs boson at loop level
August 29, 2005
Mitsuru Kakizaki

9. Thermal average of annihilation cross section for LKP
Smaller The averaged cross section becomes maximum at later time and has larger maximum value
August 29, 2005
Mitsuru Kakizaki

10. Relic abundance of LKP (without coannihilation)
The resonant annihilation by effectively reduces the number density of dark matter
The resonance effect raises the LKP mass consistent with the WMAP data
2nd KK modes play an important role in calculation of the relic density of the LKP dark matter
August 29, 2005
Mitsuru Kakizaki

11. Coannihilation with NLKP
We can systematically survey effects of 2nd KK resonances:
-resonance in : sizable
-resonance in : relatively small
No second KK resonance in
Evolution of dark matter abundance
[Three flavors: ]
The number density gradually decreases even after decoupling
August 29, 2005
Mitsuru Kakizaki

12. Allowed mass region For Tree level result Including resonance
August 29, 2005
Mitsuru Kakizaki

13. Allowed mass region For Tree level result Including resonance
Contour plot of mass splitting
Allowed mass region
For
Tree level result
Including resonance
August 29, 2005
Mitsuru Kakizaki

14. 5. Summary UED models provide a viable dark matter candidate:
The lightest Kaluza-Klein particle (LKP)
(Mass of 2nd KK particles)
(Mass of 1st KK particles)
Resonant annihilation
We evaluated the relic abundance of the LKP dark matter including the coannihilation and resonance effects
The LKP mass consistent with WMAP is sizably raised due to the s-channel second KK resonance
August 29, 2005
Mitsuru Kakizaki

15. Backup slides
August 29, 2005
Mitsuru Kakizaki

16. Positron experiments
The HEAT experiment indicated an excess in the positron flux:
Unnatural dark matter substructure is required to match the HEAT data in SUSY models
[Hooper, Taylor, Kribs (2004)]
KK dark matter may explain the excess
[Hooper, Kribs (2004)]
Future experiments (PAMELA, AMS-02, …) will confirm or exclude the positron excess
August 29, 2005
Mitsuru Kakizaki

17. Mass splitting in minimal UED
Contour plot of mass splitting
Radiative corrections to 2nd KK Higgs boson mass:
-0.5 %
Mass splitting:
Small
Resonance by
is realized in the minimal UED for a large parameter region
August 29, 2005
Mitsuru Kakizaki

18. Resonances in coannihilation
We can systematically survey possible resonances:
-resonance in : sizable
-resonance in : relatively small
No second KK resonance in
Dark matter abundance
[Three flavors: ]
In generic
Effective annihilation
Tree
Tree
WMAP
WMAP
Tree + Res.
Tree + Res.
August 29, 2005
Mitsuru Kakizaki

19. Including coannihilation
The LKP is nearly degenerate with the SU(2)L singlet leptons
Coannihilation effect is important
Annihilation cross sections
The allowed LKP mass region is lowered due to coannihilation effect
c.f. SUSY models: coannihilation effect raises the allowed LSP mass
August 29, 2005
Mitsuru Kakizaki