Dan Hooper Theoretical Astrophysics Group dhooper@fnal

1. Kaluza-Klein Dark Matter Dan Hooper Theoretical Astrophysics Group dhooper@fnal.gov Exotic Physics with Neutrino Telescopes Workshop, Uppsala Sweden September 20, 2006

2. Dark Matter • Evidence from a wide range of astrophysical observations including rotation curves, CMB, lensing, clusters, BBN, SN1a, large scale structure

3. NASA/Chandra Press Release, August 21, 2006

4. Dark Matter • Evidence from a wide range of astrophysical observations including rotation curves, CMB, lensing, clusters, BBN, SN1a, large scale structure • Each observes dark matter through its gravitational influence • Still no (reliable) observations of dark matter’s electroweak interactions (or other non-gravitational interactions) • Still no (reliable) indications of dark matter’s particle nature

5. The Dark Matter Candidate Zoo Axions, Neutralinos,Gravitinos, Axinos, Kaluza-Klein Photons, Kaluza-Klein Neutrinos, Heavy Fourth Generation Neutrinos, Mirror Photons, Mirror Nuclei, Stable States in Little Higgs Theories, WIMPzillas, Cryptons, Sterile Neutrinos, Sneutrinos, Light Scalars, Q-Balls, D-Matter, Brane World Dark Matter, Primordial Black Holes, …

6. Weakly Interacting Massive Particles (WIMPs) • As a result of the thermal freeze-out process, a relic density of WIMPs is left behind: •  h2 ~ xF / <v> • For a particle with a GeV-TeV mass, to obtain a thermal abundance equal to the observed dark matter density, we need an annihilation cross section of <v> ~ pb • Generic weak interaction yields: • <v> ~ 2 (100 GeV)-2 ~ pb

7. Weakly Interacting Massive Particles (WIMPs) • As a result of the thermal freeze-out process, a relic density of WIMPs is left behind: •  h2 ~ xF / <v> • For a particle with a GeV-TeV mass, to obtain a thermal abundance equal to the observed dark matter density, we need an annihilation cross section of <v> ~ pb • Generic weak interaction yields: • <v> ~ 2 (100 GeV)-2 ~ pb Numerical coincidence? Or an indication that dark matter originates from EW physics?

8. Supersymmetry • Perhaps the most theoretically appealing (certainly the most well studied) extension of the Standard Model • Natural solution to hierarchy problem (stabilizes quadradic divergences to Higgs mass) • Restores unification of couplings • Vital ingredient of string theory • Naturally provides a compelling candidate for dark matter

9. Supersymmetry • Perhaps the most theoretically appealing (certainly the most well studied) extension of the Standard Model • Natural solution to hierarchy problem (stabilizes quadradic divergences to Higgs mass) • Restores unification of couplings • Vital ingredient of string theory • Naturally provides a compelling candidate for dark matter

10. Universal Extra Dimensions • All SM particles allowed to travel around extra dimension(s) with size ~TeV-1 • Particles moving around extra dimensions appear as heavy versions of SM particles (Kaluza-Klein modes) • The lightest Kaluza-Klein particle can be stable, weakly interacting and a suitable candidate for dark matter

11. The UED Spectrum • At tree level, KK masses given by: Radiative Corrections SM mass Extra-Dimensional Momentum

12. The UED Spectrum • At tree level, KK masses given by: Radiative Corrections SM mass Extra-Dimensional Momentum Largest Contribution: Leads to Quasi-Dengerate KK Spectrum

13. The UED Spectrum • The radiative corrections as calculated by Cheng, Matchev and Schmaltz lead to a KK spectrum resembling: Cheng, Matchev and Schmaltz, PRD, hep-ph/0204342

14. Kaluza-Klein Dark Matter • In a model with a simple circular compactification, the KK-number of a particle would represent the amount of momentum it had in the extra dimension • If KK-number is a conserved quantity, then an isolated KK state could not decay into (zero mode) SM particles • Therefore the lightest Kalzua-Klein particle (LKP) would be unable to decay and would be stable

15. Kaluza-Klein Dark Matter • Any realistic model cannot be so simple, however • To allow for the existence of chiral fermions, the extra dimension must be orbifolded (in 5-D, S1/Z2) • For example: • KK-number conservation is broken, but KK-parity remains • KK-parity insures that first level KK states can only be produced or destroyed in pairs (much like R-parity) • Leads to stable LKP

16. Kaluza-Klein Dark Matter • But which state is the LKP? • To be a suitable candidate for dark matter, LKP should be electrically neutral and not colored: • KK photon • KK Z • KK Higgs • KK neutrino • KK graviton

17. Kaluza-Klein Dark Matter • But which state is the LKP? • To be a suitable candidate for dark matter, LKP should be electrically neutral and not colored: • KK photon • KK Z • KK Higgs • KK neutrino • KK graviton Large zero mode mass contribution

18. Kaluza-Klein Dark Matter • But which state is the LKP? • To be a suitable candidate for dark matter, LKP should be electrically neutral and not colored: • KK photon • KK Z • KK Higgs • KK neutrino • KK graviton Large zero mode mass contribution Excluded by direct detection

19. Kaluza-Klein Dark Matter • But which state is the LKP? • To be a suitable candidate for dark matter, LKP should be electrically neutral and not colored: • KK photon • KK Z • KK Higgs • KK neutrino • KK graviton Large zero mode mass contribution Excluded by direct detection Not a WIMP (although still a possibility for dark matter)

20. Kaluza-Klein Dark Matter • But which state is the LKP? • To be a suitable candidate for dark matter, LKP should be electrically neutral and not colored: • KK photon • KK Z • KK Higgs • KK neutrino • KK graviton Focus on KK photon and Z Large zero mode mass contribution Excluded by direct detection Not a WIMP (although still a possibility for dark matter)

21. Kaluza-Klein Dark Matter • In the SM, the photon and Z are mixtures of the B and W3: • At the first KK level, this mixing matrix is modified as: • So, the two states, B(1) and W3(1), mix only very slightly, leading to the lightest KK state being a nearly pure B(1) (couples to fermions and Higgs proportional to their hypercharge)

22. Relic Abundance • KKDM annihilates efficiently to fermion pairs: Leads to measured abundance of dark matter for mKK~850-900 GeV Servant and Tait, NJP, hep-ph/0209262

23. Relic Abundance • Other first level states, such as KK leptons, are expected to be important • Quasi-degenerate KK leptons can be somewhat long lived, and freeze-out quasi-independently of the LKP • When these states decay, they enhance the density of LKPs • Opposite to result typically found for SUSY coannihilation Servant and Tait, NJP, hep-ph/0209262

24. Relic Abundance • Coannihilations with KK quarks and KK gluons have been shown to deplete the LKP density • Depending on the details of the UED spectrum, measured dark matter density could be produced for mKK in the range of roughly 500 GeV to 3 TeV Burnell and Kribs, PRD, hep-ph/0509118; Kong and Matchev, JHEP, hep-ph/0509119

25. Astrophysical Probes of Particle Dark Matter • Direct Detection -Momentum transfer to detector through elastic scattering • Indirect Detection -Observation of annihilation products (, , e+, p, etc.)

26. Direct Detection • KKDM-nuclei elastic scattering can occur through Higgs and KK-quark exchange diagrams: Servant and Tait, NJP, hep-ph/0209262; Cheng, Feng and Matchev, PRL, hep-ph/0207125

27. Direct Detection • KKDM-nuclei elastic scattering varies with LKP mass, KK-quark masses and Higgs mass: KK quark-LKP mass splitting Servant and Tait, NJP, hep-ph/0209262

29. Direct Detection • Current Status: Zeplin, Edelweiss DAMA CDMS KKDM

30. Direct Detection • Near-Future Prospects: Zeplin, Edelweiss DAMA SUSY Models CDMS CDMS 2007 Projection KKDM

31. Direct Detection • Long-Term Prospects: Zeplin, Edelweiss DAMA CDMS Super-CDMS, Zeplin-Max

32. Indirect Detection With Neutrinos • KKDM elastically scatters with nuclei in the Sun, becoming gravitationally bound • As WIMPs accumulate in the Sun’s core, they annihilate at an increasing rate • After ~Gyr, annihilation rate typically reaches equlibrium with capture rate, generating a potentially observable flux of high-energy neutrinos

33. Indirect Detection With Neutrinos • Muon neutrinos from the Sun interacting via charged current produce energetic muons • Kilometer-scale neutrino telescope IceCube currently under construction at South Pole

34. Indirect Detection With Neutrinos • Rate observed at IceCube depends primarily on the KKDM capture rate in the Sun (the elastic scattering cross section) • The reach of neutrino telescopes is, therefore, expected to be tied to that of direct detection experiments

35. Indirect Detection With Neutrinos • Important Caveat: WIMPs scatter with nuclei in the Sun through both spin-independent and spin-dependent scattering • Sensitivity of direct detection to spin-dependent scattering is currently very weak (~1 pb for SD, compared to 10-6 pb for SI) Much larger than spin-independent cross section Fractional KK quark mass splitting G. Kribs and Hooper, PRD, hep-ph/02008261; F. Halzen and Hooper, PRD, hep-ph/0510048

36. Indirect Detection With Neutrinos High rates in neutrino telescopes result from large spin-dependent scattering cross section with protons and annihilations to tau pairs (20-25%) and neutrino pairs (2-4%) Approximate IceCube Sensitivity Kribs and Hooper, PRD, hep-ph/02008261; Halzen and Hooper, PRD, hep-ph/0510048

37. Indirect Detection with Anti-Matter and Gamma-Rays

38. Indirect Detection with Positrons The Cosmic Positron Spectrum Annihilations to e+e- (and +-, +-) generate distinctive hard spectrum with edge UED Case SUSY case (gauge bosons, heavy quarks) background (mDM=300 GeV, BF=5, moderate propagation)

39. Indirect Detection with Gamma-Rays The Gamma-Ray Annihilation Spectrum Kaluza-Klein dark matter particles produce harder spectrum due to 20-25% annihilation to tau pairs, and final state radiation Total, including ’s and FSR Quark fragmentation alone (SUSY-like) Including ’s

40. Summary • Models with Universal Extra Dimensions are a simple and attractive extension of the Standard Model • Naturally include a stable, weakly interacting particle suitable as a dark matter candidate

41. Summary • Direct detection difficult in these models, requiring ton-scale detectors (perhaps ~10 years away) • Indirect detection is promising for a variety of reasons: • 1) Annihilations to light fermions leads to distinctive features/high fluxes in neutrinos, positrons and gamma-rays • 2) Large spin-dependent elastic scattering cross section • 3) Quasi-independent freeze-out of various KK states can lead to an enhanced relic abundance, and corresponding annihilation rate

42. Summary • Direct and indirect detection of dark matter can provide additional information on physics beyond the Standard Model (UED, SUSY, or whatever) • In many cases, dark matter measurements can break degeneracies between various models and regions of parameter space • Astrophysical probes of dark matter can fill in some of the gaps in our post-LHC/pre-ILC understanding of the TeV scale

43. CMS DZERO ANTA ZEPLIN A T L S RES H E S I C E C U B E CDF D M S VERITAS M A G I C GLAST I C E A M E L A P M S Let’s use all of the tools we have to solve the puzzles of the terascale!