DARK MATTER – HOW CAN WE SEE IT AND UNDERSTAND IT? Gordy Kane Mitchell Symposium College Station May 2007

OUTLINE OF TALK Long introduction What does detection of dark matter at LHC, in direct and indirect experiments, IMPLY The relic density of dark matter cannot be measured – it must be calculated -- Obstacles to calculation: # particle physics # cosmological history – non-thermal equilbrium Example – HEAT + AMS, wino LSP Conclusions

 Astronomy and cosmology have measured how much dark matter there is, but not what it is  Learning what the dark matter is has to come from “laboratory” experiments, from particle physics  For cosmologists having more than one component of dark matter is often said to be unnecessary, or “ugly”  For particle theorists the default is that several kinds of particles will behave as dark matter, and all of them occur in essentially all theories – the question is how much of each, and it can naturally occur that each gives a significant amount  The dark matter cannot come from the Standard Model of particle physics, with matter made of quarks and leptons interacting via the weak, electromagnetic, strong and gravitational forces, and mass originating via interactions with a Higgs sector

Dark matter candidates with independent motivation: The lightest superpartner (LSP), normally stable – most naturally a “neutralino”, i.e. superpartner of photon, Z, Higgs boson, perhaps a superposition – photino, zino, higgsino, wino, bino -- if supersymmetry is relevant to completing and understanding the SM, LSPs will be produced at LHC -- importance as DM with needed properties recognized in 1982 Axions – no LHC connection Neutrinos -- ∑ I  1 eV   h 2  they do exist, with some mass

This talk: Generically “Weakly Interacting Massive Particles”, “WIMPs” LSPs a special case – well motivated

Supersymmetry remains the default to extend the SM and strengthen its foundations – very good motivation Part of attractive top-down picture – deeper, simpler theory at ~ unification scale – few parameters there Stabilizes hierarchy – assume (or derive from theory) superpartners (and µ) have TeV masses to get weak scale Then derive gauge coupling unification, electroweak symmetry breaking (Higgs mechanism) Can have dark matter candidate particle, can explain matter asymmetry, can calculate electroweak mixing angle Consistent with all data, predicts no physics beyond-the-SM at LEP, m h <200 GeV All simultaneously, not introduced for any of these

Data will come from several kinds of experiments/facilities: [see talk of Nicolao Fornengo here…]  LHC – produce superpartners, all decay to lightest one, which interacts weakly (like a neutrino) and escapes the detector – since WIMPs must annihilate significantly to not overclose the universe, and annihilation and scattering rates related, production at colliders likely  “Direct detection” – nucleus in a detector scatters off a WIMP, recoils, deposits energy  WIMPs lose energy in scattering, concentrate in center of sun or earth, annihilate, energetic ’s from annihilation products produce a muon, detected in an underground detector  WIMPs in galaxy annihilate into discrete or continuum photons, detected in EGRET or GLAST  WIMPs in galaxy annihilate into positrons or antiprotons, detected in HEAT, AMS, PAMELA ILC – but here concentrate on next few years…

We are studying DM just when experiments might detect signals! XYPQ-mn on line now at interesting levels, with upgrades to levels that will cover most of the probable regions – multiple techniques so can confirm any signal, and study it in several ways – sensitive to cm 2 soon, upgraded one to two orders of magnitude after that – and LHC Suppose some indeed do! – wonderful! After the champagne … have we found the dark matter of the universe? … how do we know? Examine some models with LHC signals, and LSPs that do give some relic density Detection at LHC depends mainly on gluino mass – gluino produced by QCD coupling to gluons Detection in direct experiments depends mainly on LSP mass and its weak force couplings Gluino mass and LSP mass in general independent

gluino chargino LSP relic density dark matter type (GeV) (  h 2  0.12)  higgsino    bino,.5 higgsino    bino,.075 wino Examples easily observable at LHC, but with small relic density! Bourjaily and GK, hep-ph/

We have to calculate the relic density! CANNOT measure it! Calculation depends on cosmological history, and on how LSPs annihilate -- Big Bang, lots of particles and superpartners, thermal equilibrium, after a while have stable particles including LSPs, some LSPs annihilate until freeze out, e.g.

But – can have non-thermal contributions String theories always have gravitinos and moduli (describe the small dimensions) – also produced, often decay after LSP thermal freezeout (before BBN), produce more LSPs, perhaps many more, and more entropy -- Moroi, Randall “Affleck-Dine” mechanism, inflaton or scalar fields radiate superpartners as settle to minimum of potential, increase relic density Cosmic string decay Such non-thermal contributions the default in string theories (i.e. in complete theories)  LSP h 2  [H freezeout /s ] M LSP  if σ large, increase H -- e.g. quintessance with rapidly varying kinetic term – see Chung, Everett, Matchev arXiv: for example tied to inflation – Lahanas, Mavromatos, Nanopoulos hep-ph/ for dilaton-like dilution  if thermal relic density too large, increase entropy A THERMAL CALCULATION COULD GIVE THE WMAP ANSWER BUT THE ACTUAL RELIC DENSITY COULD BE SMALLER IF EXTRA ENTROPY PRESENT BUT NOT INCLUDED

To calculate the relic density must know the number of LSPs, and their mass Battaglia, Hinchliffe, Tovey ph/ , Bourjaily and GK, ph/ How can the mass be measured? Information from direct detection experiments -- see recent summary by Anne Green hep-ph/ LHC kinematics – doable if clear decay chains with endpoints exist – probably doable well enough eventually for any spectrum, ~ 20% or better Maybe lucky and see discrete photon line from LSP annihilation – wino LSP favorable here

Suppose we detect DM candidates at LHC, and also in direct or indirect detection – how can we learn if the candidates are really the same? – crucial in order to be confident have found the dark matter Measure mass and interactions – must be same So – first, measure independently to test whether same -- if consistent, combine information to determine properties

Are relic densities related to LSP masses?Bourjaily, GK ph/

Bourjaily, GK

How much can we learn about the LSP at LHC or Tevatron if there is a superpartner signal? More obstacles…

DEGENERACIES! Generally assumed in past that experimenters would find a set of signals, from which we would learn the superpartner masses But at a hadron collider turns out there are degeneracies [Arkani-Hamed, GK, Thaler, Wang hep-ph/ ] e.g. some flat directions

That degeneracies would occur perhaps not surprising – but assumed by many they would not occur – we have understood, organized them Islands are different in important ways – e.g. some LSPs give very different relic densities from others, some have gaugino mass unification

CATALOG DEGENERACIES: models different if anything not on diagonal have same LHC signatures within errors Different LSP type, mass

Another issue – phases [Brhlik, Chung, GK hep-ph/ ] Contributions to supersymmetry Lagrangian can be complex The phases can be measured – EDMs, time-reversal violating observables at LHC, etc The relation between the relic density and the superpartner masses and cross sections and decays is affected by the phases – for a given set of LHC masses, cross sections, direct detection, positron excess etc the calculated relic density depends significantly on the phases microOMEGAs 2.0 now included phases

Models often have very similar LHC signals but very different DM relic density and DM signals Note model with smaller gaugino fraction has larger relic density

Similar direct and indirect detection rates for two models with different relic densities, similar LHC signals

Note in special cases may be able to get more confidence that LHC observations are providing complete answer e.g. Arnowitt, Aurisano, Dutta, Kamon, Kolev, Simeon, Toback, Wagner point out (hep-ph/ ) that observing a small mass difference between the stau and the neutralino LSP at LHC is both possible experimentally and is what is needed to get the WMAP relic density by co-annihilation

Other collider information may be needed to learn the relic density:

So, many obstacles – careful work and good understanding and care needed – more data, e.g. from ILC, would be helpful, especially sooner No one has studied yet how well the relic density can be calculated in representative models

Consider an amusing example, motivated by data and theory

e + /(e + +e - ) Jan Olzem, arXiv: , Combined data from HEAT, AMS, other sources

Probably a real signal, not systematics Astrophysical backgrounds? [discussed by Nicolao Fornengo] Another flatter component? Another source giving 5-10 GeV positrons? Need higher energy data to see whether there is a decrease PAMELA (this summer)? AMS? Connect to antiprotons?

GK, Liantao Wang, Ting Wang Hep-ph/ e + /(e + +e - ) Interpretation? LSP that annihilates mainly into W can work– wino has large annihilation cross section, rate ok if normalize to local relic density

Wino LSP well motivated theoretically: Generic in “anomaly mediated supersymmetry breaking” Some string theories, e.g. -- compactify M theory on 7D manifold with G2 holonomy, supersymmetry broken by hidden sector gaugino and fermion condensation, all moduli stabilized, successfully generate electroweak scale from Planck scale and solve hierarchy problem, unique de Sitter minimum, gaugino masses suppressed so gluinos  TeV, quaisi-stable chargino, wino LSP with appropriate mass [Archarya, Bobkov, GK, Kumar, Shao, Vaman hep-th/ , ]

Wino LSP annihilates well, how get WMAP relic density? Non-thermal increases – moduli decay, Affleck-Dine, quintessance In G 2 case we can calculate – gravitino mass ~ TeV, moduli masses ≈ 1.96 gravitino mass, ~ 100 moduli giving on average one LSP each so get big non-thermal increase in LSP number – and extra entropy – but coming from an understandable part of the theory with an understandable cosmological history, calculable

Reasonable to expect discovery of WIMP dark matter candidates in next few years! Can only be confident of determining relic density associated with a discovered WIMP in the context of a definite theory – so that measuring a set of parameters determines what is needed to do cosmological and annihilation calculations Collider, direct and indirect detection all likely to be very important – any given data will allow several LSP candidates – hopefully different detections will reduce the degeneracy and provide a consistent candidate – of course need a non-collider experiment to establish WIMP lifetime  universe lifetime Finding WMAP relic density calculated from properties learned in detection experiments in the context of a theory will oConvince us we know and understand the dark matter oTeach us a lot about the history of the universe in the GeV and TeV region – greatly constrain non-thermal mechanisms oTeach us about the underlying theory

Positron energy [GK, Liantao Wang, Ting Wang hep-ph/ ]  These LSPs easily in LHC range, probably in Tevatron’s – recently supported by AMS – Pamela next opportunity, in orbit June 15!  These annihilate well, so thermal density small compared to Ω DM h 2 – good non-thermal mechanisms exist to get observed amount – or maybe small and rest is axions