The Dark Matter Puzzle and a Supersymmetric Solution Andrew Box UH Physics
Outline What is the Dark Matter (DM) problem? How can we solve it? What is Supersymmetry (SUSY)? One possible SUSY solution How we detect DM will be the next talk... Many figures taken from SLAC Summer School Lectures 2004 www-conf.slac.stanford.edu/ssi/2004/
What makes up Hubble Constant 70 km/s / Mpc (h~0 the Universe? ucture Formation washed ut by relativistic particles MAP significantly lowers limit) CDM C About 95% is unknown BBN Only 0.5% emits visible light Neutrinos cannot be all the DM SuperK! " ~0.1 ev! µ ~0.01-0.001 ev Observation
How do we know Dark Matter is out there? Rotation Curves Spiral Galaxies Bulk of luminous matter Doppler shifts of 21-cm H emission line Can see gravitational influence of dark halo v ~ const data bulge, disk & halo v ~ r 1/2 bulge & disk bulge disk Velocities of Galaxies in Galactic Clusters halo Velocities too high to be produced by gravitational attraction of luminous matter alone...
How do we know Dark Matter is out there? II X-ray Measurements Can calculate the mass of the cluster from the temperature of intra-cluster gas. matter density 0.3 Strong Lensing Kochanski, Dell Antonio, Tyson Mass distribution from Hubble image shows DM as a hump Rick Gaitskell, Brown University
Types of DM Speed at Early Times Relativistic Non-Relativistic Hot Cold Hot Dark Matter washes out large scale structure
What do we need to make Dark Matter? We know the density of DM. Can we get limits on its mass and interactions? Dark Matter must be: Optically Dark from Radio to Gamma Weak EM interactions OR heavy Collision-less Small self-interaction strength
What do we need to make Dark Matter? II Dark Matter must be: Cold Constrains the mass of thermal relics to be > kev Fluid - to avoid excessive heating Particles must be 1 10 5 M Dust-like no pressure support Only constrains mass to > 1 10 23 ev
Possible Choices Thermal Relics SUSY candidates Sterile/ Right-handed Neutrinos Non-thermal Relics Axions Primordial Black Holes
Why Neutrinos are disfavoured Neutrinos are there and are also dark BUT not enough and not cold A kev sterile ν could work A TeV right-handed ν is acceptable with some assumptions
What about Non-Thermal Relics? Axions arise when trying to solve the strong CP problem. They would have a mass mev It can be difficult to explain the formation of Non-Thermal Relics...
What is Supersymmetry? Supersymmetry became popular when people realised it could explain apparent fine-tuning of scalars in the Standard Model (SM) SUSY links bosons and fermions Since SUSY is not seen in nature, we double the number of particles. Each known particle has a SUSY partner.
BONUS!
BONUS! People hoping for unification of the forces in the SM were disappointed. In SUSY it seems as though we could get it for free! 70 70 60 60 50 40 50 40! "!!! "! "! "! #! "! 30! "! 30 20 10! "!!! "! "! "! # 20 10 0 1 10 2 10 4 10 6 10 8 10 10 10 12 10 14 10 16 10 18 Energy (GeV) 0 1 10 2 10 4 10 6 10 8 10 10 10 12 10 14 10 16 10 18 Energy (GeV)
The MSSM and msugra There are a huge number of free parameters in The Minimal Supersymmetric Model (MSSM). The minimal Supergravity Model (msugra) restricts things by assuming unification of masses at a Grand Unified (GUT) scale The fundamental parameters reduce to: m 0 ; m 1/2 ; A 0 ; tanβ ; sign(µ) ; m t
Does SUSY have a good DM candidate? R-parity superpartners interact in pairs. The lightest SUSY particle is stable. Neutralino favoured candidate Gravitino Axino
How do we make SUSY predictions? Use msugra to predict sparticle masses Z 1 Insist on being LSP constrains parameter space by 1/2 Regions where the density of the LSP is acceptable are very limited
Allowed msugra parameter space 1600 msugra with tan! = 30, A 0 = 0,! " 0!" "h 2 # 0.129!" LEP2 excluded 1400 1200 m 1/2 (GeV) 1000 800 LHC 600 LC 1000 400 200 LC 500 Tevatron 0 1000 2000 3000 4000 5000 6000 7000 8000 m 0 (GeV)
Allowed msugra parameter space msugra with tan! = 30, A 0 = 0,! " 0 The region where DM and msugra 1600!" "h 2 # 0.129!" LEP2 excluded 1400 coincide is very small and on the edges of 1200 the SM allowed region LHC 1000 m 1/2 (GeV) Do we have 800 too much choice in the LC 1000 parameter 600 space? 400 LC 500 Is msugra being Tevatron restricted too much? 200 0 1000 2000 3000 4000 5000 6000 7000 8000 There are many more m 0 (GeV) unanswered questions...
Conclusions We know Dark Matter is out there We know that we don t know what it is There are many suggestions SUSY is a strong contender Minimal SUSY models are becoming squeezed out Is SUSY too much of a fiddle?