The Linear Collider and the Rest of the Universe Jonathan Feng University of California, Irvine ALCPG Victoria Meeting 28 July 2004

ALCPG Victoria MeetingFeng 2 I. RECENT PROGRESS II. OPEN PROBLEMS III. OPPORTUNITIES FOR THE LINEAR COLLIDER

28 July 2004ALCPG Victoria MeetingFeng 3 RECENT PROGRESS What is the Universe made of? Recently there have been remarkable advances in our understanding of the Universe on the largest scales We live at a privileged time: we now have a complete census of the Universe

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28 July 2004ALCPG Victoria MeetingFeng 5 Hubble (1929) “Supernovae” Rubin, Ford, Thonnard (1978) Allen, Schmidt, Fabian (2002) “Clusters” Then Now Constrains  M Constrains     M

28 July 2004ALCPG Victoria MeetingFeng 6 Cosmic Microwave Background Then Now Constrains     M

28 July 2004ALCPG Victoria MeetingFeng 7 These three agree: Dark Matter: 23 ± 4% Dark Energy: 73 ± 4% Baryons: 4 ± 0.4% [Neutrinos: 0.5%] Two must be wrong to change this conclusion Stunning progress (cf.1998)

28 July 2004ALCPG Victoria MeetingFeng 8 earth, air, fire, water baryons, s, dark matter, dark energy A less charitable view

28 July 2004ALCPG Victoria MeetingFeng 9 OPEN PROBLEMS DARK MATTER What are dark matter and dark energy? These problems appear to be completely different No known particles contribute Probably tied to M weak ~ 100 GeV Several compelling solutions DARK ENERGY All known particles contribute Probably tied to M Planck ~ GeV No compelling solutions

28 July 2004ALCPG Victoria MeetingFeng 10 Known DM properties Dark Matter Non-baryonic Cold Stable DM: precise, unambiguous evidence for new physics

28 July 2004ALCPG Victoria MeetingFeng 11 Dark Matter Candidates The Wild, Wild West of particle physics: axions, warm gravitinos, neutralinos, Kaluza-Klein particles, Q balls, wimpzillas, superWIMPs, self-interacting particles, self- annihilating particles, branons… Masses and interaction strengths span many orders of magnitude But independent of cosmology, we expect new particles: electroweak symmetry breaking

28 July 2004ALCPG Victoria MeetingFeng 12 The Problem with Electroweak Symmetry Breaking m h ~ 100 GeV,  ~ GeV  cancellation to 1 part in We expect new physics (supersymmetry, extra dimensions, something!) at M weak Classical =+ = − Quantum e L e R

28 July 2004ALCPG Victoria MeetingFeng 13 Thermal Relic DM Particles (1) Initially, DM is in thermal equilibrium:  ↔  f f (2) Universe cools: N = N EQ ~ e  m/T (3)  s “freeze out”: N ~ const (1) (2) (3)

28 July 2004ALCPG Victoria MeetingFeng 14 Final N fixed by annihilation cross section:  DM ~ 0.1 (  weak /   ) Just right if   ~  weak : remarkable! Domestic diva Martha Stewart sells ImClone stock – the next day, stock plummets Coincidences? Maybe, but worth serious investigation! Exponential drop Freeze out

28 July 2004ALCPG Victoria MeetingFeng 15 Dark Energy Minimal case: vacuum energy p = w  Energy density  ~ R  3(1+w) Matter:  M ~ R  3 w = 0 Radiation:  R ~ R  4 w = ⅓ Vacuum energy:   ~ constant w = -1   ≈ 0.7    ~ (meV) 4

28 July 2004ALCPG Victoria MeetingFeng 16 All Fields Contribute to  Quantum mechanics: ½ ħ     k   m  Quantum field theory: ∫ E d 3 k ( ½ ħ  ) ~ E 4, where E is the energy scale where the theory breaks down We expect (M Planck ) 4 ~   (M SUSY ) 4 ~   (M GUT ) 4 ~   (M weak ) 4 ~  

28 July 2004ALCPG Victoria MeetingFeng 17 One Approach   ~ M Pl 4   = 0   ~ m 4, (M W 2 /M Pl ) 4,... ?? Small numbers ↔ broken symmetry

28 July 2004ALCPG Victoria MeetingFeng 18 Another Approach   ~ M Pl 4 Many, densely spaced vacua (string landscape, many universes, etc.) Anthropic principle: -1 <   < 100 Weinberg (1989)

28 July 2004ALCPG Victoria MeetingFeng 19 Two very different approaches There are others, but none is especially compelling Dark energy: the black body radiation problem of the 21 st century? Ways forward: –Discover a fundamental scalar particle (Higgs would be nice) –(M weak ) 4 ~   : map out the EW potential –(M SUSY ) 4 ~   : understand SUSY breaking –(M GUT ) 4 ~   : extrapolate to GUT scale –(M Planck ) 4 ~   : …

28 July 2004ALCPG Victoria MeetingFeng 20 Prospects Dark Energy Constrain w, w’ Riess et al. (2004) Dark Matter Constrain m,  Many other cosmological and astrophysical probes, but they are unlikely to lead to fundamental understandings of dark matter and dark energy

28 July 2004ALCPG Victoria MeetingFeng 21 OPPORTUNITIES FOR THE LINEAR COLLIDER Detailed and exhaustive exploration of the weak scale is required to determine its contributions to dark matter This is true on general grounds: –EWSB  new particles at ~ TeV –Constraints  conservation laws  new stable particle –Relic density “coincidence”  new stable particle with significant  DM Peskin (2004)

28 July 2004ALCPG Victoria MeetingFeng 22 Supersymmetry –Superpartners –R-parity –Neutralino  with significant  DM Goldberg (1983) Universal Extra Dimensions –Kaluza-Klein partners –KK-parity Appelquist, Cheng, Dobrescu (2000) –Lightest KK particle with significant  DM Servant, Tait (2002) Branes –Brane fluctuations –Brane-parity –Branons with significant  DM Cembranos, Dobado, Maroto (2003) Examples

28 July 2004ALCPG Victoria MeetingFeng 23 Supersymmetry Cosmology excludes much of parameter space (   too big) Pre-WMAPPost-WMAP Cosmology focuses attention on particular regions (   just right) Focus Point Region Co-annihilation Region Excluded Regions of  

28 July 2004ALCPG Victoria MeetingFeng 24 Co-annihilation Region If other superpartners are nearly degenerate with the  LSP, they can help it annihilate Requires similar e –m/T for  and  ̃, so (roughly)  m < T ~ m  /25 Motivates theoretical studies of co-annihilation effects, and experimental studies of  ̃ →   with  m ~ few GeV Gondolo, Edsjo, Ullio, Bergstrom, Schelke, Baltz (2002) Nauenberg et al. Ellis, Olive, Santoso, Spanos (2003)Dutta, Kamon Baer, Belyaev, Kruovnickas, Tata (2003) Battaglia et al. Belanger, Boudjema, Cottrant, Pukhov, Semenov (2004)...   ̃̃   Griest, Seckel (1986)

28 July 2004ALCPG Victoria MeetingFeng 25 Focus Point Region Relic density can also be reduced if  has significant Higgsino component to enhance Feng, Matchev, Wilczek (2000) Baer, Belyaev, Krupovnickas, Tata (2003) Motivates SUSY with multi-TeV g̃, q̃, l ̃  ± /  0 highly degenerate Such SUSY would be missed at LHC, discovered at LC

28 July 2004ALCPG Victoria MeetingFeng 26 Collider Inputs Weak-scale Parameters  Annihilation  N Interaction Relic Density Indirect DetectionDirect Detection Astrophysical and Cosmological Inputs Synergy Particle Physics ↔ Cosmology : Freeze out at T = 10 GeV, t = s [Nuclear Physics ↔ Astrophysics : BBN at T = 1 MeV, t = 1 s]

28 July 2004ALCPG Victoria MeetingFeng 27 DM at Colliders: No-Lose Theorem Correct relic density  efficient annihilation then  Efficient production now   f f Annihilation ¯   f f Production ¯

28 July 2004ALCPG Victoria MeetingFeng 28 No-Lose Theorem: Loophole G̃ not LSP Assumption of most of literature SM LSP G̃G̃ G̃ LSP Completely different cosmology and phenomenology SM NLSP G̃G̃ SUSY predicts gravitinos: mass ~ M W, couplings ~ M W /M Pl

28 July 2004ALCPG Victoria MeetingFeng 29 Assume gravitino is LSP. Early universe behaves as usual, WIMP freezes out with desired thermal relic density A year passes…then all WIMPs decay to gravitinos WIMP ≈G̃G̃ Gravitinos become dark matter, naturally inherit the right density, but are seemingly impossible to produce at colliders M Pl 2 /M W 3 ~ year

28 July 2004ALCPG Victoria MeetingFeng 30 SuperWIMPs Gravitinos are superweakly-interacting massive particles – “superWIMPs” all interactions are suppressed by M W /M Pl ~ 10  16 Are there any observable consequences?

28 July 2004ALCPG Victoria MeetingFeng 31 Big Bang Nucleosynthesis Late decays,  ̃ →  G̃,… modify light element abundances Fields, Sarkar, PDG (2002) After WMAP  D =  CMB Independent 7 Li measurements are all low by factor of 3: 7 Li is now a serious problem Jedamzik (2004)

28 July 2004ALCPG Victoria MeetingFeng 32 Consider  ̃ → G̃  (others similar) Its impact depends on –Decay time  –Energy release  EM Grid: Predictions for m G̃ = 100 GeV – 3 TeV (top to bottom)  m = 600 GeV – 100 GeV (left to right) Effects on BBN Feng, Rajaraman, Takayama (2003) SuperWIMP DM naturally explains 7 Li !

28 July 2004ALCPG Victoria MeetingFeng 33 Collider Phenomenology Each SUSY event produces 2 metastable sleptons Spectacular signature: highly-ionizing charged tracks Current bound (LEP): m l̃ > 99 GeV Tevatron Run II reach: m l̃ ~ 150 GeV LHC reach: m l̃ ~ 700 GeV in 1 year Buchmuller, Hamaguchi, Ratz, Yanagida (2004) Feng, Su, Takayama (2004) Ellis, Olive, Santoso, Spanos (2004) … Drees, Tata (1990) Goity, Kossler, Sher (1993) Feng, Moroi (1996) Hoffman, Stuart et al. (1997) Acosta (2002)

28 July 2004ALCPG Victoria MeetingFeng 34 Slepton Trapping Sleptons live a year, so can be trapped then moved to a quiet environment to observe decays LHC: 10 6 sleptons/yr possible, but most are fast. By optimizing trap location and shape, can catch ~100/yr in 1000 m 3 we. LC: tune beam energy to produce slow sleptons, can catch ~1000/yr in 1000 m 3 we. Feng, Smith Slepton trap Reservoir

28 July 2004ALCPG Victoria MeetingFeng 35 Measuring m G̃ and M * Decay width to G̃ : Measurement of   m G̃   G̃. SuperWIMP contribution to dark matter  F. Supersymmetry breaking scale, dark energy  Early universe (BBN, CMB) in the lab Measurement of  and E l  m G̃ and M *  Precise test of supergravity: gravitino is graviton partner  Measurement of G Newton on fundamental particle scale  Probes gravitational interaction in particle experiment

28 July 2004ALCPG Victoria MeetingFeng 36 CONCLUSIONS IMPRESSIVE RECENT PROGRESS FUNDAMENTAL OPEN PROBLEMS EXTRAORDINARY OPPORTUNITIES FOR THE LINEAR COLLIDER