1. WIMPs and superWIMPs Jonathan Feng UC Irvine MIT Particle Theory Seminar 17 March 2003

2. MITFeng 2 Dark Matter The dawn (mid-morning?) of precision cosmology:  DM = 0.23  0.04  total = 1.02  0.02  baryon = 0.044  0.004 t 0 = 13.7  0.2 Gyr WMAP (2003) We live in interesting times: We know how much dark matter there is We have no idea what it is Our best evidence for new particle physics

3. 17 March 2003MITFeng 3 WIMPs Weakly-interacting particles with weak-scale masses decouple with  DM ~ 0.1; this is remarkable [Cf. quarks with natural  B ~10 -11 ] Either –a devious coincidence, or –a strong, fundamental, and completely cosmological motivation for new physics at the electroweak scale Jungman, Kamionkowski, Griest (1995)

4. 17 March 2003MITFeng 4 Outline Explore new possibilities for particle dark matter Guiding principles: –Must be well-motivated from particle physics viewpoint –Must naturally produce desired  DM (this is all we know!) WIMPs superWIMPs SUSYExtra D FRT* CFM* *Cheng, Feng, Matchev (2002) *Feng, Rajaraman, Takayama (2003)

5. 17 March 2003MITFeng 5 SUSY WIMPs Feng, Matchev, Wilczek (2000) Relic density regions and gaugino-ness (%) Neutralinos: fermionic partners of , Z, W 0, h 0  DM ~ 0.1 in much of parameter space Requirements: high supersymmetry breaking scale (supergravity) R-parity conservation

6. 17 March 2003MITFeng 6 SUSY WIMP Detection Particle probes Direct DM detection Indirect DM detection Astrophysical and particle searches are promising: many possible DM signals before 2007 This is generally true of WIMPs: undetectable  weak interactions  weak annihilation  too much relic density

7. 17 March 2003MITFeng 7 Extra D WIMPs 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.”

8. 17 March 2003MITFeng 8 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: New solution… good bad

9. 17 March 2003MITFeng 9 Compactify on S 1 /Z 2 instead (orbifold); require Unwanted scalar is projected out: Similar projection on fermions  chiral 4D theory, … Very simple (requires UV completion at  R  ) Appelquist, Cheng, Dobrescu (2001) good bad

10. 17 March 2003MITFeng 10 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)

11. 17 March 2003MITFeng 11 Other Extra D 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 (Universal Extra D) –No localization mechanism required –Natural dark matter candidate – LKP __

12. 17 March 2003MITFeng 12 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

13. 17 March 2003MITFeng 13 Minimal UED KK Spectrum Cheng, Matchev, Schmaltz (2002) loop-level R  = 500 GeV tree-level R  = 500 GeV

14. 17 March 2003MITFeng 14 Extra D WIMPs LKP is nearly pure B 1 in minimal model (more generally, a B 1 -W 1 mixture) Relic density: Annihilation through Preferred mass range ~ 1 TeV, variations from co-annihilations Servant, Tait (2002)

15. 17 March 2003MITFeng 15 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)

16. 17 March 2003MITFeng 16 s-channel enhanced by B 1 -q 1 degeneracy Constructive interference: lower bounds on  scalar,  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

17. 17 March 2003MITFeng 17 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

18. 17 March 2003MITFeng 18 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)

19. 17 March 2003MITFeng 19 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

20. 17 March 2003MITFeng 20 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) _

21. 17 March 2003MITFeng 21 What about KK gravitons? G 1 may be the LKP. In fact, loop contributions, typically positive, are negligible for G 1. For that matter, what about gravitinos in SUSY? In supergravity, m 3/2 ~ m 0 ~ M 1/2 ~ /M Pl, unknown O(1) coefficients determine ordering. The gravitino may be the LSP. These possibilities are very similar; consider in parallel.

22. 17 March 2003MITFeng 22 superWIMPs Suppose LKP is G 1. If NLKP is B 1, B 1 freezes out with the usual desired , then decays much later via B 1   G 1 G 1 inherits the desired  retains all WIMP virtues BUT: G 1 is superweakly- interacting, and so undetectable by all dark matter searches Only possible signal is in WIMP  superWIMP decays Feng, Rajaraman, Takayama (2003) gravitino graviton m sWIMP = 0.1, 0.3, 1 TeV (from below)

23. 17 March 2003MITFeng 23 BBN Excluded Regions (shaded) Late decays may destroy BBN light element abundance predictions  typically quickly thermalize, BBN constrains total energy release  X =   n SWIMP / n BG Constraints weak for early decays: universe is hot,  BG  e + e  suppresses spectrum at energies above nuclear thresholds Cyburt, Ellis, Fields, Olive (2002)

24. 17 March 2003MITFeng 24 CMB gravitinograviton m SWIMP as indicated Excluded regions (above CMB contours) Late decays may also destroy black-body spectrum of CMB Again get weak constraints for early decays, when e    e   e  X   e  X  e    e   are all effective superWIMP DM: m WIMP, m SWIMP  ,    SWIMP =  DM  abundance Y SWIMP Feng, Rajaraman, Takayama (2003)

25. 17 March 2003MITFeng 25 superWIMP Dark Matter gravitinograviton Weak-scale superWIMPs are viable cold dark matter Feng, Rajaraman, Takayama (2003)

26. 17 March 2003MITFeng 26 Is it testable? BBN versus CMB baryometry is a powerful probe Cyburt, Fields, Olive (2003)Fields, Sarkar, PDG (2002) WMAP  D =  CMB but 7 Li is low

27. 17 March 2003MITFeng 27 7 Li low 4 He low D low D high 10 5 s 3 10 5 s 10 6 s 3 10 6 s 10 7 s  X and  10 -8 GeV 3 10 -9 GeV 10 -9 GeV 3 10 -10 GeV 10 -10 GeV Feng, Rajaraman, Takayama (2003)Cyburt, Ellis, Fields, Olive (2002)

28. 17 March 2003MITFeng 28 Conclusions Guiding principles: –well-motivated particle physics –naturally correct  DM WIMPs from Extra Dimensions –B 1 : qualitatively new signals –Many other candidates to investigate superWIMPs: gravitinos/gravitons naturally yield desired thermal relic density, but are inaccessible to all conventional searches –Bino NLSP : BBN, CMB signals –Many other NLSP candidates to investigate Escape from the tyranny of neutralino dark matter! WIMPs superWIMPs SUSYExtra D