Significant effects of second KK particles on LKP dark matter physics Mitsuru Kakizaki (ICRR, Univ. of Tokyo & Bonn Univ.) August 29, 2005 @ Bonn Univ. Collaborated with Shigeki Matsumoto (KEK) Yoshio Sato (Saitama U. & Munich, Tech. U.) Masato Senami (ICRR) Refs: PRD 71 (2005) 123522 [hep-ph/0502059] hep-ph/0508283

1. Motivation Recent observation of cosmic microwave background anisotropies by WMAP: Non-baryonic cold dark matter [http://map.gsfc.nasa.gov] 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

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

2. Universal extra dimensions [Appelquist, Cheng, Dobrescu, PRD67 (2000) 035002] 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

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

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 036005 (2002)] August 29, 2005 Mitsuru Kakizaki

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

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

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

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

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

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

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

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

Backup slides August 29, 2005 Mitsuru Kakizaki

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

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

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

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