1. Lisa Randall Harvard University @lirarandall

2.  It has gravitational interactions—of matter!  Gravitational lensing  Rotation curves in galaxies  Detailed measurements of energy abundances—total and normal matter  It has no other discernible interactions  It’s not dark—it’s effectively transparent!  Hopes to see it based on it being a little opaque…

3.  Clearly we don’t yet know  For a long time WIMP “miracle” has been the reigning paradigm  Now in position to test it fairly well  So far no sign…  We need to consider all possibilities  Does it interact as we might hope?

4.  Searches based on somewhat optimistic assumptions  Namely dark matter does interact with our matter at some level  In principle could be purely gravity coupling  We see that already!  But does it have other interactions?  Talk today: reasons to think it might  And alternatives to standard WIMP paradigm  Asymmetric dark matter/Xogenesis  Partially interacting dark matter

5.  Existence of dark matter not necessarily so mysterious  Why should everything be like our matter?  What is mysterious is that energy stored in dark matter and ordinary matter so similar  But how to find what it is?  Look under the lamppost  Find theoretical, experimental clues  What are the right lampposts?

6.  Look for low probability dark matter interactions with large detectors  Look for small nuclear recoil  Good way to look for a well- motivated class of candidates (WIMPs)  We haven’t seen it yet  Waiting for more sensitive searches

7.  LHC: Look for evidence of a stable particle with weak scale mass  Remarkably, has the right energy density to constitute dark matter  Such a particle likely in ANY weak scale model that supplements Higgs theory  WIMP not necessarily supersymmetric!  Any stable weak scale particle can be a candidate  We haven’t yet seen beyond Higgs  Waiting for higher energies, more intensity  Don’t yet know if this lamppost in the right region

8.  Indirect Searches  Rather than directly interact with nuclei,  Dark matter particle hits another dark matter particle and annihilates  Hope is  This happens often enough  Annihilation produces Standard Model particles  The kind we can detect  Not dark!  Focus on any signal that is distinguishable from astrophysical background

9.  Focus on what is less likely to occur in ordinary astrophysical settings  Antiparticles  AMS: antideuteron  Gamma ray signals  Particularly gamma ray lines  Continuum from stars  Lines direct consequence of annihilation  Observations have seen a lot!  Need to determine  What really is not background  What models of dark matter can produce such signals

10.  Exciting thing about Indirect Detection  Is the many signals  Has precipitated better understanding of astrophysics  And of range of dark matter models  I’ll talk about one motivated by Fermi satellite “signal” soon  Again, general lessons whether or not signal survives  Important to understand range of reasonable models  Part of art is deciding what is reasonable  Interesting  Has consequences

11.  Direct dark matter detection  Look for feeble interactions  LHC searches  Look for missing energy indicating noninteracting weak-mass particle produced  Neither has seen anything yet  But both are increasing sensitivity  Dark matter “vats” becoming bigger  LHC exploring higher energy and higher intensity (sensitive to lower probability)  Both are important

12.  Most-researched candidates are WIMPS  WIMPS have weak-scale mass  That is mass such that it can be produced at LHC  Doesn’t have to have anything to do with supersymmetry  Any weak mass stable particle could yield correct abundance  And if connected to weak scale have reason to believe will be produced  WIMP—coincidence that weak mass particle has measured abundance?

13.  Similarity of amount of energy in dark matter and ordinary matter  Maybe matter and dark matter are produced in similar ways?  Excess “matter” over “antimatter”

14.  Key observation:   X ~6  B  Why should dark matter and ordinary matter energy densities be at all comparable?  Could just be independently generated—baryogenesis somehow and weak miracle  On other hand, maybe clue their origin is in fact related

15. Asymmetric Dark Matter  Create dark matter first  Then transfer asymmetry from dark matter to matter  Can be weak scale  Can be light  Baryon number and Dark matter number could be connected in early universe  Produce both at the same time

16.  Explain connection dark matter and ordinary matter energy densities  Dark matter energy similar in spirit to that of baryons  Asymmetry in dark matter density; not thermal  Need interactions between baryons and dark matter to explain the similar relative size  Chemical potentials related  Number densities are too nB~nX;  Nonrelativistic solution allows more general possibilities  Xogenesis  And DM created first

17.  ADM compelling  But origin of operators that mix two sectors?  Higher-dimensional operators can violate both L (or B) and DM numbers  Don’t necessarily expect L, X conservation in early universe

18.  Are B and X conserved?  Maybe not in early universe  Transfer and then restore  Two Higgses, Modulus decay, higher-dimensional operators w/Cui, Shuve

19.  WIMPy baryogenesis  Creates dark matter density inversely proportional to annihilation cross section  As conventional  Baryon density proportional to dark matter density AT WASHOUT FREEZEOUT

21.  Lots of attention devoted to dark matter  Both theory and detection  Sometimes signals are unexpected  They might be wrong  They might lead to interesting unexplored options  Surprisingly, unexplored option:  Interacting dark matter  But rather than assume all dark matter  Assume it’s only a fraction (maybe like baryons?)  w/fan,katz,reece

22.  Almost all constraints on interacting dark matter assume it is the dominant component  If it’s only a fraction, we’ll see most bounds generally don’t apply  structure  Galaxy or cluster interactions  But if a fraction, you’d expect even smaller signals!  However, not necessarily true…

23. Neal Weiner’s talk

24.  Finkbeiner, Sug

25.  Suppose you want to explain Fermi signal with dark matter  If you also assume relic thermal abundance want annihilation into something to be about an order of magnitude bigger  However can’t annihilate into charged particles since the signal would already rule it out  One option is to annihilate to photons through a loop of charged particle that is kinematically inaccessible

26.  Clearly an enormous boost factor is needed  Of order 100-1000 for reasonable parameters  Too high to assume clumping  But what if dark matter actually had structure?  Like baryons for example!  So we consider interacting dark matter  Dissipative dark matter in particular  Idea is to have more collapsed component of dark matter  Even if only a fraction of dark matter, will be most important for signals

27.  Consider possibility that due to interactions, portion of dark matter (like baryons) collapses into a disk  Involves  Dark force (we take U(1) D )  Additional light particles in dark sector  Necessary for cooling in time  Even if new component a fraction of dark matter, if it collapsed to baryonic disk (eg) enhancement factors ~100—10,000

28.  Can have dark atoms  Dark disk  Could be much denser and possibly titled with respect to plane of our galaxy  Very significant implications  Even though subdominant component  Velocity distributions in or near galactic plane constrain fraction to be comparable or less to that of baryons  But because it is in disk and dense signals can be rich

29.  Reasonable to assume disk height between  m P /m X ---1 times baryonic disk height  Can be very narrow disk  For 100 GeV particle, can get boost factor of 10,000!

30.  Photons from plane of galaxy!  Not only center but unassociated sources throughout plane would be expected  Seems rather specific to this type of model  Component of dark matter sitting in small disk in plane of galaxy  Furthermore will affect structure formation

32.  New species (Planck can detect)  Possibly small scale structure  Velocity distributions, lensing (look for structure)  Acoustic Oscillations  Indirect detection  Direct detection (at very low threshold)  Many ways to search and constrain

33.  Whether or not 130 GeV signal survives,  Very interesting new possibility for dark matter  That one might expect to see signals from  Since in some sense only minor modification (just a fraction of dark matter)  hard to know whether or not it’s likely  But presumably would affect structure  Just like baryons do  Research area  Rich arena: lots of questions to answer

34.  Clearly dark matter experiments telling us something  If we find evidence soon could be great vindication of WIMP scenario  If we don’t we’ll still want to know what it means  Perhaps we have been too focused on conventional WIMPs?  Other coincidences worth exploring and explaining  ADM  Xogenesis (weak scale)  Emergent  WIMP annihilation connected to leptogenesis  Usually tradeoff between genericness of model and parameter space  Admittedly much more challenging for experiment  But nature ultimately decides…

35.  Interesting to explore slightly more complex dark matter sectors  Even if not dominant component, new species can have significant observable signals to distinguish it  I know what everyone wants to know is when we will see dark matter  Answer could be sooner--or later-- than we think!