Thermal Relic Density of LKP Dark Matter and Indirect Detection Using Positrons

1. LC physics study meeting ( UED II ) Shigeki Matsumoto (KEK, Theory) LKP (Lightest Kaluza-Klein Particle) Dark matter physics ○ Thermal Relic Density of LKP DM ○ Indirect detection of LKP DM using positrons in CR

2. Dark Matter Abundance Results from recent cosmological observation Mean density of matter and baryon Existence of non-baryonic (cold) dark matter = Beyond SM Physics Constituent of dark matter

3. LKP dark matter Candidate of non-baryonic dark matter • Lightest Supersymmetric particle (LSP) in SUSY • Lightest Kaluza-Klein particle (LKP) in UED LKP is stable KK parity [ + (-) for even (odd) KK particle ] c.f. The LSP stabilized by R-parity in SUSY models The LKP is a good candidate of dark matter In the minimal UED, the LKP is

4. Cosmic Relic density in Thermal Relic Scenario DM density per comoving volume Dark matter is in thermal equilibrium in the early universe After the annihilation rate becomes smaller than the expansion rate, the DM number density per comoving volume is fixed Increasing Freeze-out Relic density The relic density is determined only by the annihilation cross section. WMAP observation Constraint parameter region of models.

5. LKP dark matter annihilation (Self annihilation) [Servant, Tait (2002)] @ tree level Model parameters in UED 1/R(= m), mh, Λ, Annihilation cross section depends on 1/R, when 1/R is larger than electroweak scale In addition to the annihilating processes, the co-annihilation processes are also important !! (when there is a particle whose mass is degenerated with DM)

6. LKP dark matter annihilation (co-annihilation) In the LKP DM case, the 1st excited KK modes of right-handed leptons are highly degenerated with the LKP. Co-annihilation processes Self annihilation processes for 1st KK of right-handed leptons

7. Effect of co-annihilation on the DM abundance Simplest situation of co-annihilation using the toy model Characters appearing in the processes: DM, DM’ If we do not consider the co-annihilation process, Non-including Case !! If we include co-annihilation process Effective annihilation cross section LSP case LKP case

8. 2nd KK resonance in LKP DM annihilation [Kakizaki, SM, sato, senami (2005)] 2nd KK resonance in the LKP DM annihilation The LKP annihilates non-relativisticaly, some 1-loop diagrams in which 2nd KK Propagate in the s-channel significantly contribute to the annihilation cross section. The mass difference between mh(2) and 2m depends on the higgs mass. This amplitude has a sensitivity in higgs mass and cut-off Λ

9. Thermal Relics of LKP dark matter [Servant, Tait (2002); Kakizaki, SM, sato, senami (2005)] Parameter regions consistent with WMAP observation The LKP DM mass consistent with WMAP is 500 GeV ~ 800 GeV

10. Positron excess in HEAT measurement Dark matter search • For investigating nature • of dark matter, • Direct detection • Indirect detection using Annihilation Annihilation positrons Solar system Annihilation Indirect detection using positrons Positrons from the DM annihilation is observed as the positron excess in CR when the annihilation rate is large enough. Galactic halo

11. Anomaly in positron fraction J.J.beatty,etc(2004) It is difficult to explain the anomaly by usual “LSP dark matter” (Bino-like dark matter) due to “helicity suppression” Background LKP dark matter can (B(1) dark mtter) explain the anomaly