8 Oct 07Feng 1 THE SEARCH FOR DARK MATTER Jonathan Feng University of California, Irvine 8 October 2007 CSULB Colloquium Graphic: N. Graf

8 Oct 07Feng 2 WHAT IS THE UNIVERSE MADE OF? An age old question, but… Recently there have been remarkable advances in our understanding of the Universe on the largest scales We live in interesting times: for the first time in history, we have a complete inventory of the Universe

8 Oct 07Feng 3 Remarkable agreement Dark Matter: 23% ± 4% Dark Energy: 73% ± 4% [Baryons: 4% ± 0.4% Neutrinos: ~0.5%] Remarkable precision (~10%) Remarkable results The Inventory

8 Oct 07Feng 4 Historical Precedent Eratosthenes measured the size of the Earth in 200 B.C. Remarkable precision (~10%) Remarkable result But just the first step in centuries of exploration Alexandria Syene

8 Oct 07Feng 5 Dark Matter Questions What particle forms dark matter? What is its mass? What is its spin? What are its other quantum numbers and interactions? Is dark matter composed of one particle species or many? How and when was it produced? Why does  DM have the observed value? How is dark matter distributed now? What is its role in structure formation? Is it absolutely stable?

8 Oct 07Feng 6 Known DM properties DARK MATTER Not baryonic DM: precise, unambiguous evidence for new particles Not hot Not short-lived

8 Oct 07Feng 7 Dark Matter Candidates The Wild, Wild West of particle physics: axions, warm gravitinos, neutralinos, Kaluza-Klein particles, Q balls, wimpzillas, self-interacting particles, self-annihilating particles, fuzzy dark matter, superWIMPs,… Masses and interaction strengths span many, many orders of magnitude But independent of cosmology, new particles are required to understand the weak force

8 Oct 07Feng 8 Naturalness and the Weak Scale m h ~ 100 GeV,  ~ GeV  cancellation of 1 part in At M weak ~ 100 GeV we expect new particles: supersymmetry, extra dimensions, something! Classical =+ = − Quantum e L e R

8 Oct 07Feng 9 THE “WIMP MIRACLE” (1) Initially, new particle is in thermal equilibrium:  ↔  f f (2) Universe cools: N = N EQ ~ e  m/T (3)  s “freeze out”: N ~ const (1) (2) (3)

8 Oct 07Feng 10 The amount of dark matter left over is inversely proportional to the strength of annihilation:  DM ~ 1/  A v  What’s the constant of proportionality? Impose a natural relation:     k  2 /m 2 DOE/NSF HEPAP Subpanel (2005) Remarkable “coincidence”: cosmology alone also tells us we should explore the weak scale [band width from k = 0.5 – 2, S and P wave]

8 Oct 07Feng 11 STABILITY DM must be stable Problems ↕ Discrete symmetry ↕ Stability In many theories, dark matter is easier to explain than no dark matter New Particle States Standard Model Particles Stable

8 Oct 07Feng 12 DARK MATTER CANDIDATES There are two classes of candidates that explain the “coincidence” and naturally give the right amount of dark matter: WIMPs: weakly-interacting massive particles SuperWIMPs: superweakly-interacting massive particles

8 Oct 07Feng 13 WIMPs from Supersymmetry The classic WIMP: neutralinos predicted by supersymmetry Goldberg (1983); Ellis et al. (1983) Supersymmetry: extends rotations/boosts/translations, string theory, unification of forces,… For every known particle X, predicts a partner particle X̃ Neutralino   (  ̃, Z̃, H̃ u, H̃ d ) Particle physics alone   is lightest supersymmetric particle, stable, mass ~ 100 GeV. All the right properties for WIMP dark matter!

8 Oct 07Feng 14  DM = 23% ± 4% stringently constrains models Feng, Matchev, Wilczek (2003) Focus point region Co-annihilation region Bulk region Yellow: pre-WMAP Red: post-WMAP Too much dark matter Cosmology excludes many possibilities, favors certain regions

8 Oct 07Feng 15 WIMPs from Extra Dimensions Garden hose Extra spatial dimensions could be curled up into small circles. Particles moving in extra dimensions appear as a set of copies of normal particles. mass 1/R 2/R 3/R 4/R 0 … Servant, Tait (2002) Cheng, Feng, Matchev (2002) DM

8 Oct 07Feng 16 WIMP Detection: No-Lose Theorem   f  f f Annihilation Correct relic density  Efficient annihilation then  Efficient annihilation now  Efficient scattering now  f  f f Scattering Crossing symmetry

8 Oct 07Feng 17 DIRECT DETECTION WIMP essentials: v ~ c Kinetic energy ~ 100 keV Local density ~ 1 / liter Detected by recoils off ultra-sensitive underground detectors WIMP

8 Oct 07Feng 18 FUTURE DIRECT DETECTION mSUGRA Focus Point Region

8 Oct 07Feng 19 Indirect Detection Dark Matter Madlibs! Dark matter annihilates in ________________ to a place __________, which are detected by _____________. some particles an experiment

8 Oct 07Feng 20 Dark Matter annihilates in the galactic center to a place photons, which are detected by Cerenkov telescopes. some particles an experiment HESS Telescope Array in Namibia

8 Oct 07Feng 21 Dark Matter annihilates in the center of the Sun to a place neutrinos, which are detected by AMANDA, IceCube. some particles an experiment   (km -2 yr -1 ) AMANDA in the Antarctic Ice

8 Oct 07Feng 22 IDENTIFYING WIMPS If WIMPs contribute significantly to dark matter, we will see signals before the end of the decade: Direct dark matter searches Indirect dark matter searches Tevatron at Fermilab Large Hadron Collider at CERN (2008)

8 Oct 07Feng 23 What then? Cosmology can’t discover SUSY Particle colliders can’t discover DM Lifetime > 10  7 s  s ?

8 Oct 07Feng 24 THE EXAMPLE OF BBN Nuclear physics  light element abundance predictions Compare to light element abundance observations Agreement  we understand the universe back to T ~ 1 MeV t ~ 1 sec

8 Oct 07Feng 25 DARK MATTER ANALOGUE (1) (2) (3) Particle physics  dark matter abundance prediction Compare to dark matter abundance observation How well can we do? American Linear Collider Cosmology Subgroup

8 Oct 07Feng 26 Contributions to Neutralino WIMP Annihilation

8 Oct 07Feng 27 WMAP (current) Planck (~2010) LHC (“best case scenario”) ILC LCC1 RELIC DENSITY DETERMINATIONS % level comparison of predicted  hep with observed  cosmo ALCPG Cosmology Subgroup

8 Oct 07Feng 28 IDENTIFYING DARK MATTER Are  hep and  cosmo identical? Congratulations! You’ve discovered the identity of dark matter and extended our understanding of the Universe to T=10 GeV, t=1 ns (Cf. BBN at T=1 MeV, t=1 s) Yes Calculate the new  hep Can you discover another particle that contributes to DM? Which is bigger? No  hep  cosmo Does it account for the rest of DM? Yes No Did you make a mistake? Does it decay? Can you identify a source of entropy production? No Yes No Yes Can this be resolved with some wacky cosmology? Yes No Are you sure? Yes Think about the cosmological constant problem No

8 Oct 07Feng 29 DIRECT DETECTION IMPLICATIONS Current Sensitivity Near Future Future Theoretical Predictions Baer, Balazs, Belyaev, O’Farrill (2003) LHC + ILC   m < 1 GeV,  < 10% Comparison tells us about local dark matter density and velocity profiles

8 Oct 07Feng 30 HESS COLLIDERS ELIMINATE PARTICLE PHYSICS UNCERTAINTIES, ALLOW ONE TO PROBE ASTROPHYSICAL DISTRIBUTIONS Particle Physics Astro- Physics Halo profiles are poorly understood, controversial near the galactic center INDIRECT DETECTION IMPLICATIONS

8 Oct 07Feng 31 SuperWIMP Dark Matter All of these signals rely on DM having weak force interactions. Is this required? Strictly speaking, no – the only required DM interactions are gravitational (much weaker than weak). But the relic density “coincidence” strongly prefers weak interactions. Is there an exception to this rule? Feng, Rajaraman, Takayama (2003)

8 Oct 07Feng 32 Consider supersymmetry: Gravitons  gravitinos G̃ What if the G̃ is the lightest superpartner? WIMPs freeze out as usual But then all WIMPs decay to gravitinos (after ~ month!) No-Lose Theorem: Loophole Gravitinos naturally inherit the right density, but interact only gravitationally – they are “superWIMPs” G̃G̃ WIMP ≈

8 Oct 07Feng 33 SuperWIMP Detection SuperWIMPs evade all particle dark matter searches. “Dark Matter may be Undetectable” But cosmology is complementary: Superweak interactions  very late decays l ̃ → G̃ l  observable consequences: Galaxy formation Cold dark matter (WIMPs) seeds structure formation. Simulations of galaxies indicate more central mass than observed – cold dark matter may be too cold. SuperWIMPs are produced warm, could resolve this problem. Kaplinghat (2005) Cembranos, Feng, Rajaraman, Takayama (2005)

8 Oct 07Feng 34 Big Bang Nucleosynthesis 4 He, D, 3 He, 7 Li, … abundances determined by BBN at ~ 1 to 100 s Late decays may modify these predictions (may be good!) CMB The CMB spectrum is black body Late decays may produce observable distortions Fixsen et al. (1996) Particle Data Group ( 2004)

8 Oct 07Feng 35 SuperWIMPs are produced in late decays with large velocity (v ~ 0.1c – c) – are warm dark matter. Structure Formation Cembranos, Feng, Rajaraman, Takayama (2005)

8 Oct 07Feng 36 Big Bang Nucleosynthesis Late decays may modify light element abundances Fields, Sarkar, PDG (2002) Feng, Rajaraman, Takayama (2003) Some SUSY parameter space excluded, much ok, and possibly even preferred (explains 7 Li underabundance)

8 Oct 07Feng 37 Late decays may also distort the CMB spectrum For 10 5 s <  < 10 7 s, get “  distortions”:  =0: Planckian spectrum  0: Bose-Einstein spectrum Hu, Silk (1993) Current bound: |  | < 9 x Future (DIMES): |  | ~ 2 x Cosmic Microwave Background Feng, Rajaraman, Takayama (2003)

8 Oct 07Feng 38 IDENTIFYING SUPERWIMPS Slepton trap Reservoir If superWIMPs produced in decays l ̃ → G̃ l Colliders will produce many 100 GeV, charged particles that live ~ a month. These can be trapped, moved to a quiet environment for observation. LHC, ILC can trap as many as ~10,000/yr in 10 kton trap. Hamaguchi, Kuno, Nakaya, Nojiri (2004) Feng, Smith (2004)

8 Oct 07Feng 39 What We Would Learn We are sensitive to gravity in a particle physics experiment! Measurement of   m G̃   G̃. SuperWIMP contribution to dark matter  F. Supersymmetry breaking scale  BBN, CMB, structure formation in the lab Measurement of  and E l  m G̃ and M *  Measurement of G Newton on fundamental particle scale  Gravitino hascorrect spin, couplings to be graviton partner: quantitative confirmation of supergravity

8 Oct 07Feng 40 CONCLUSIONS Dark Matter: rich interplay between cosmology and particle physics Extraordinary progress, but many open questions Both cosmology and particle physics  new particles at 100 GeV: bright prospects

8 Oct 07Feng 41 “One day, all of these will be dark matter papers”

8 Oct 07Feng 42

8 Oct 07Feng 43 Direct Detection: Future Current Sensitivity Near Future Future Theoretical Predictions Baer, Balazs, Belyaev, O’Farrill (2003)

8 Oct 07Feng 44 Entropy Production BBN and CMB constrain  B at different times. Late decays produce entropy and modify  B. Some SUSY parameter space excluded, much ok, and some even preferred (explains 7 Li underabundance)  S/S Feng, Rajaraman, Takayama (2003)

8 Oct 07Feng 45 Large Hadron Collider M 1/2 = 600 GeV m l̃ = 219 GeV L = 100 fb -1 /yr Optimal 10 kton trap has 4  coverage, 1 m thick 10 to 10 4 sleptons trapped / year (~1%) Feng, Smith (2004)