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

Transcription

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

2 Dark Matter The dawn (mid-morning?) of precision cosmology: Ω DM = 0.23 ± 0.04 Ω total = 1.02 ± 0.02 Ω baryon = ± 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 17 March 2003 MIT Feng 2

3 WIMPs Weakly-interacting particles with weak-scale masses decouple with Ω DM ~ 0.1; this is remarkable [Cf. quarks with natural Ω 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) 17 March 2003 MIT Feng 3

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

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

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 17 March 2003 MIT Feng 6

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 µν + G µ5 + G 55 Kaluza: virtually unsurpassed formal unity...which could not amount to the mere alluring play of a capricious accident. 17 March 2003 MIT Feng 7

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: good bad New solution 17 March 2003 MIT Feng 8

9 Compactify on S 1 /Z 2 instead (orbifold); require Unwanted scalar is projected out: good bad Similar projection on fermions chiral 4D theory, Very simple (requires UV completion at Λ >> R 1 ) Appelquist, Cheng, Dobrescu (2001) 17 March 2003 MIT Feng 9

10 KK-Parity An immediate consequence: conserved KK-parity ( 1) KK Interactions require an even number of odd KK modes 1 st KK modes must be pair-produced at colliders Macesanu, McMullen, Nandi (2002) weak bounds: R 1 > 200 GeV Appelquist, Yee (2002) LKP (lightest KK particle) is stable dark matter! 17 March 2003 MIT Feng 10

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 1 > few TeV from f f V µ1 f f No concrete dark matter candidate everything in bulk (Universal Extra D) No localization mechanism required Natural dark matter candidate LKP _ 17 March 2003 MIT Feng 11

12 UED and SUSY Similarities: Superpartners KK partners R-parity KK-parity LSP LKP Bino dark matter B 1 dark matter Sneutrino dark matter ν 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 17 March 2003 MIT Feng 12

13 Minimal UED KK Spectrum tree-level R 1 = 500 GeV loop-level R 1 = 500 GeV Cheng, Matchev, Schmaltz (2002) 17 March 2003 MIT Feng 13

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) 17 March 2003 MIT Feng 14

15 Co-annihilation But degeneracy coannihilations important Co-annihilation processes: Dot: 3 generations Dash: 1 generation 1% degeneracy 5% degeneracy Preferred m B 1: l 1 lowers it, q 1 raises it; 100s of GeV to few TeV possible Servant, Tait (2002) 17 March 2003 MIT Feng 15

16 B 1 Dark Matter Detection Direct Detection t-channel h exchange s- and u-channel B 1 q q 1 B 1 q σ scalar σ spin s-channel enhanced by B 1 -q 1 degeneracy Cheng, Feng, Matchev (2002) Constructive interference: lower bounds on σ scalar, σ spin 17 March 2003 MIT Feng 16

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), χχ f f is chirality suppressed B 1 B 1 f f isn t; generically true for bosons 17 March 2003 MIT Feng 17

18 Positrons Moskalenko, Strong (1999) Here f i (E 0 ) ~ δ(e 0 m B 1), and the peak is not erased by propagation (cf. χχ W + W e + ν e ν) AMS will have e + /e separation at 1 TeV and see ~1000 e + above 500 GeV Cheng, Feng, Matchev (2002) 17 March 2003 MIT Feng 18

19 Muon flux is Muons from Neutrinos Ritz, Seckel (1988) Jungman, Kamionkowski, Griest (1995) B 1 B 1 ν ν is also unsuppressed, gives hard neutrinos, enhanced µ flux Cheng, Feng, Matchev (2002) Hooper, Kribs (2002) Bertone, Servant, Sigl (2002) degeneracy Discovery reach 17 March 2003 MIT Feng 19

20 Gamma Rays B 1 B 1 γ γ is loopsuppressed, but light quark fragmentation gives hardest photons, so absence of chirality suppression helps again _ Integrated photon flux ( J = 500) Results sensitive to halo clumpiness; choose moderate value Bergstrom, Ullio, Buckley (1998) Cheng, Feng, Matchev (2002) 17 March 2003 MIT Feng 20

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 ~ <F>/M Pl, unknown O(1) coefficients determine ordering. The gravitino may be the LSP. These possibilities are very similar; consider in parallel. 17 March 2003 MIT Feng 21

22 superwimps Suppose LKP is G 1. If NLKP is B 1, B 1 freezes out with the usual desired Ω, then decays much later via B 1 γ G 1 m swimp = 0.1, 0.3, 1 TeV (from below) G 1 inherits the desired Ω, retains all WIMP virtues BUT: G 1 is superweaklyinteracting, and so undetectable by all dark matter searches gravitino graviton Only possible signal is in WIMP superwimp decays Feng, Rajaraman, Takayama (2003) 17 March 2003 MIT Feng 22

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

24 CMB Late decays may also destroy black-body spectrum of CMB Excluded regions (above CMB contours) Again get weak constraints for early decays, when e γ e γ e X e X γ e γ e γ γ are all effective gravitino graviton superwimp DM: m SWIMP as indicated m WIMP, m SWIMP τ, ε γ Feng, Rajaraman, Takayama (2003) Ω SWIMP = Ω DM abundance Y SWIMP 17 March 2003 MIT Feng 24

25 superwimp Dark Matter gravitino graviton Feng, Rajaraman, Takayama (2003) Weak-scale superwimps are viable cold dark matter 17 March 2003 MIT Feng 25

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

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

28 Conclusions Guiding principles: well-motivated particle physics naturally correct Ω DM WIMPs from Extra Dimensions B 1 : qualitatively new signals Many other candidates to investigate superwimps WIMPs SUSY Extra D 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! 17 March 2003 MIT Feng 28