暗黒物質対消滅起源のガンマ線

1. 暗黒物質対消滅起源のガンマ線 久野純治　(東京大学宇宙線研究所） 研究会「CANGAROO望遠鏡によるガンマ線天文学の新展開」 日時：　２００３年１２月１１日（木）-１２日（金） 場所：　京都大学 基礎物理学研究所 湯川記念館3F 大講演室

2. 1, Introduction Evidence of cold dark matter Fit to the WMAP , CBI, ACBAR, 2dFGRS and Lyman α forest data 2dFGRSv.s. N-body simulation for Large-scale structure formation What is this dark matter?

3. Candidate of dark matter • MACHO (almost excluded) Microlensing Wide binaries • Neutrino (Not cold) It might be hot dark matter, thus • Unknown stable particle Relics in the early hot universe. WIMP (Weakly interacting massive particle) (Cold) SUSY particle, Kaluza-Klein particle, Wimpzilla,,, Axion (Cold) (Chaname et al)

4. SUSY dark matter • Solves hierarchy problem • SUSY GUTs • Light Higgs boson • Lightest SUSY particle(LSP) is stable due to R parity. SM particles; even, SUSY particles; odd 　→ Dark Matter

5. Nature of LSP • It depends on the SUSY breaking mechanism Neutralino ; Bino -like or Higgsino -like in supergravity Wino -like in the anomaly mediation Gravitino in the gauge mediation • Direct search for DM　ｂｙ the nucleus elastic scattering Dirac neutrino (sneutrino) mass > 100TEV Dark matter should be Majorana fermion or real scalar if it has weak charge.

6. DM genesis • Thermal abundance is blocked when Smaller may mean larger annihilation rate. Notice co-annihilation may enhances cross section when SUSY particles masses are degenerate. (Nath et al)

7. Non-thermal production DM is produced after by non-thermal process. (for example, ) In this case, the larger annihilation rate, such as in Higgsino-like or Wino-like case, is favored.

8. Detection of DM • Direct detection by elastic scattering with nucleus. DAMA, EDELWEISS, CDMS, Zeplin, …… • Indirect detection of neutrinos, antiproton, positron, and gamma ray from DM annihilation in our Galaxy, Sun, or Eearh. • Collider experiment LHC starts on 07’. It determine mass and properties of the DM candidate.

9. 2, Dark matter distribution • N-body simulation provides universal cuspy profile for the halo DM density distributon (Navarro, Frenk & White, 96,97). Navarro, Frenk &White Moore

10. High resolution N body simulation • Large N and small time stepsize are required. Recent simulation observed deviation from the universal profile for Time evolution (Figures;Fukushige and Makino)

11. Cusp/Core problem • Rotation curve measure ment of Low Surface-brightness Galaxies by HI and Halpha. Data prefer soft cores . Early suspicion on observation; beaming, pointing error, small sample, inconsistency among observations, etc. de Blok(2003): These problems no more exit.

12. Measurement of gravitational lense constrains DM profile for clusters. Sand et al show Objection :Ellipticity (Dalal et al) • A little good news. for large radius is favored. (CL0024+11654, Kneib et al)

13. Our galaxy • Our galaxy is High surface-brightness galaxy. (Baryon rich, Bar, BH ) It is difficult to say something, especially DM profile around the galactic center. http://www.astronomynotes.com/ismnotes/rotcurv2-big.gif

14. 3, Gamma ray from DM annihilationin Galactic center • Gamma ray from DM annihilation line spectrum: continuum spectrum: • Merit and Demerit Merit: Characteristic spectrum, e.g. line. Sensitive to heavier DM Demerit: Cross section depends on DM proparties. Sensitive to DM halo profile.

15. Gamma ray flux

16. Galactic Halo profile • Dependence on DM profile is huge. In the following, I take the moderate value, that is

17. DM annihilation cross section • Annihilation cross section to fermions is suppressed by the fermion mass due to the S wave annihilation. Sizable cross section to continum gammais expected when • Cross section depends on propaties of the DM. Case 1:Bino-like DM. Interaction is very weak. MSUGRA + thermal production favor this. Case 2: Higgsino or Wino DM. These have SU(2) weak charge.

18. Bino-like DM • Line spectrum. Sensitive to slepton mass. • Continuum spectrum MSUGRA simulation by Feng et al.

19. Higgsino or Wino DM • They have SU(2) weak charge and acompany with SU(2) partner, those are chargino, When they are heavier than W boson mass, the masses are degenerate. • Annihiration cross section to 2 gamma’s is independent of the DM mass at the leading order. This means that line gamma search is sensitive to heavier DM. However, this behavior is strange since

20. Non-relativistic effects • DM is highly non-relativistic . Thus, the cross section is sensitive to existence of bound state under Yukawa potential induced by W exchange. Wino-like Higgsino-like Leading order cal. Zero energy resonance enhances the cross section. Bound state W-exchanged Yukawa potential

21. Line spectrum ( ). Wino-like Higgsino-like

22. Continuum spectrum ( ) Wino-like Higgsino-like Photon energy (GeV) The shaded regions correspond to S> BG. There are already some regions constrained by the EGRET.

23. (Cesarini et al) EGLET Gamma ray spectrum from Galactic center observed by EGLET is not well fit to the standard explanation of diffused gamma, It might come from DM annihilation.

24. 4, Summary • After WMAP measurement, DM search is very important subject. Gamma from DM annihilation is sensitive to relatively heavier DM, and it has different dependence from other DM searches. • Will gamma from DM annihilation at Galactic center be observed or not ? Or, can we discriminate particle physics models or astronomical models? At present, it is hard to answer them, because gamma ray signal depend on detail of both models. • If DM candidate is discovered at new collider (LHC?) or DM-like gamma ray is observed, DM astronomy will be started.