1. WIMPs and superWIMPs from Extra Dimensions Jonathan Feng UC Irvine Johns Hopkins Theory Seminar 31 January 2003

2. Johns HopkinsFeng 2 Dark Matter Our best evidence for new particle physics We live in interesting times –we know how much there is (  DM = 0.25 +/- 0.04) –but not what it is (non-baryonic, cold) WIMPs are attractive –predicted in many particle theories (EWSB) –naturally give thermal relic density  DM ~  (1) –  DM < 1     f f not small   f    f not small, so testable: promising for direct, indirect detection

3. 31 January 2003Johns HopkinsFeng 3 Candidates from Particle Physics Supersymmetry –Neutralinos – partners of , Z, W, h –Requirements: high supersymmetry-breaking scale (supergravity) R-parity conservation Extra Dimensions –Kaluza-Klein particles – partners of , Z, W, h, G ,… –Requirements: universal extra dimensions Cheng, Feng, Matchev (2002) Feng, Rajaraman, Takayama

4. 31 January 2003Johns HopkinsFeng 4 Universal Extra Dimensions Kaluza (1921) and Klein (1926) considered D=5, with 5 th dimension compactified on circle S 1 of radius R: D=5 gravity  D=4 gravity + EM + scalar G MN  G  + G  5 + G 55 Kaluza: “virtually unsurpassed formal unity...which could not amount to the mere alluring play of a capricious accident.”

5. 31 January 2003Johns HopkinsFeng 5 Problem: gravity is weak Solution: introduce extra 5D fields: G MN, V M, etc. New problem: many extra 4D fields; some with mass n/R, but some are massless! E.g., 5D gauge field: A new solution… good bad

6. 31 January 2003Johns HopkinsFeng 6 Compactify on S 1 /Z 2 instead (orbifold); require Unwanted scalar is projected out: Similar projection on fermions  4D chiral theory, … Very simple (requires UV completion at  R  ) Appelquist, Cheng, Dobrescu (2001) good bad

7. 31 January 2003Johns HopkinsFeng 7 KK-Parity An immediate consequence: conserved KK-parity  KK Interactions require an even number of odd KK modes 1 st KK modes must be pair-produced at colliders weak bounds: R  > 200 GeV LKP (lightest KK particle) is stable – dark matter Appelquist, Yee (2002) Macesanu, McMullen, Nandi (2002) Kolb, Slansky (1984) Saito (1987)

8. 31 January 2003Johns HopkinsFeng 8 Other Extra Dimension Models SM on brane; gravity in bulk (brane world) –Requires localization mechanism –No concrete dark matter candidate fermions on brane; bosons and gravity in bulk –Requires localization mechanism –R  > few TeV from f f  V  1  f f –No concrete dark matter candidate everything in bulk (UED) –No localization mechanism required –Natural dark matter candidate – LKP __

9. 31 January 2003Johns HopkinsFeng 9 UED and SUSY Similarities: Superpartners  KK partners R-parity  KK-parity LSP  LKP Bino dark matter  B 1 dark matter Sneutrino dark matter  1 dark matter... Not surprising: SUSY is also an extra (fermionic) dimension theory Differences: KK modes highly degenerate, split by EWSB and loops Fermions  Bosons

10. 31 January 2003Johns HopkinsFeng 10 Minimal UED KK Spectrum Cheng, Matchev, Schmaltz (2002) loop-level R  = 500 GeV tree-level R  = 500 GeV

11. 31 January 2003Johns HopkinsFeng 11 B 1 WIMP Dark Matter LKP is nearly pure B 1 in minimal model (more generally, a B 1 -W 1 mixture) Relic density: Annihilation through Servant, Tait (2002)

12. 31 January 2003Johns HopkinsFeng 12 Co-annihilation But degeneracy  co- annihilations important Co-annihilation processes: Preferred m B 1 : l 1 lowers it, q 1 raises it; 100s of GeV to few TeV possible Dot: 3 generations Dash: 1 generation 1% degeneracy 5% degeneracy Servant, Tait (2002)

13. 31 January 2003Johns HopkinsFeng 13 s-channel enhanced by B 1 -q 1 degeneracy Constructive interference: lower bound on both  scalar and  spin B 1 Dark Matter Detection Direct Detection Cheng, Feng, Matchev (2002) t-channel h exchange s- and u-channel B 1 q  q 1  B 1 q  scalar  spin

14. 31 January 2003Johns HopkinsFeng 14 B 1 Dark Matter Detection Indirect Detection: –Positrons from the galactic halo –Muons from neutrinos from the Sun and Earth –Gamma rays from the galactic center All rely on annihilation, very different from SUSY –For neutralinos (Majorana fermions),    f f is chirality suppressed –B 1 B 1  f f isn’t; generically true for bosons

15. 31 January 2003Johns HopkinsFeng 15 Positrons Cheng, Feng, Matchev (2002) Here f i (E 0 ) ~  (E 0  m B 1 ), and the peak is not erased by propagation (cf.    W + W    e   e  ) AMS will have e  /e  separation at 1 TeV and see ~1000 e  above 500 GeV Moskalenko, Strong (1999)

16. 31 January 2003Johns HopkinsFeng 16 Muons from Neutrinos Cheng, Feng, Matchev (2002) Hooper, Kribs (2002) Bertone, Servant, Sigl (2002) Muon flux is B 1 B 1   is also unsuppressed, gives hard neutrinos, enhanced  flux Ritz, Seckel (1988) Jungman, Kamionkowski, Griest (1995) Discovery reach degeneracy

17. 31 January 2003Johns HopkinsFeng 17 Gamma Rays Cheng, Feng, Matchev (2002) B 1 B 1   is loop- suppressed, but light quark fragmentation gives hardest photons, so absence of chirality suppression helps again Results sensitive to halo clumpiness; choose moderate value Bergstrom, Ullio, Buckley (1998) Integrated photon flux ( J = 500) _

18. 31 January 2003Johns HopkinsFeng 18 superWIMPs What about the KK graviton? LKP may be 1 st KK graviton G 1 If NLKP is B 1, B 1 freezes out, then decays much later via B 1   G 1 G 1 is a superWIMP: retains all WIMP virtues, but is undetectable by conventional dark matter searches (Gravitino is another possible superWIMP) Feng, Rajaraman, Takayama gravitino graviton m sWIMP = 0.1, 0.3, 1, 3 TeV (from below)

19. 31 January 2003Johns HopkinsFeng 19 BBN and CMB gravitinograviton m sWIMP as indicated m sWIMP Y sWIMP (GeV) Late decays may destroy BBN successes or distort CMB Both constraints may be satisfied Possible signals in diffuse photon flux

20. 31 January 2003Johns HopkinsFeng 20 Conclusions Extra Dimensions yield natural dark matter candidates Several novel features: –s-channel enhancements from degeneracy –Annihilation not chirality suppressed Direct detection,  from, e +, and  rays, may all push sensitivity beyond collider reach superWIMPs: graviton (and gravitino) DM naturally yields desired thermal relic density, but is inaccessible to all conventional searches Much work to be done: 1, h 1 WIMPs, many other possible NLKPs in superWIMP scenarios, etc. DM from extra dimensions – escape from the tyranny of neutralino dark matter!