Mia Schelke, Ph.D. Student The University of Stockholm, Sweden Cosmo 03

Outline SUSY DM phenomenology highlights What are coannihilations Why can coannihilations control the relic neutralino density When are coannihilations important The SUSY model used in our work:mSUGRA Results of relic density calculations including all coannihilations J. Edsjö, M. Schelke, P. Ullio & P. Gondolo JCAP 0304 (2003) 001 (hep-ph/ )

Broken N=1 SUSY with conserved R-parity Multiplicatively conserved even nb of susy’s in vertex The lightest susy particle (LSP) is stable susy SM yes susy SM no Minimal N=1 Supersymmetric extension of the Standard Model one new particle for each elementary particle Partners are identical except for the spin, and when SUSY is broken also the mass differ. R-parity

LSP = Neutralino = WIMP The lightest supersymmetric particle (LSP) will often be a neutralino   But lightest might mean O(100 GeV) a weakly interacting massive particle (WIMP) a natural cold dark matter candidate

Coannihilations and relic density Coannihilations processes in the early Universe determine the relic density of neutralinos : The neutralinos freeze out of thermal equilibrium approx. when: The Hubble expansion rate > the effective neutralino annihilation rate (H >  v n) # The comoving   relic density will stay constant ever after. NOTE:large  small n Coannihilations* *Griest & Seckel,1991 Binetruy, Girardi & Salati,1984 I.e. a coupled system of annihilations/interactions But all `leftover´ susy particles decay into  0 So don’t solve for n 1,n 2,…., but for ∑n i = n  0 # Solve Boltzmann eq. for n  0 with

Coannihilation & mass splitting So  eff is large when  ij and are large. m<<T; Boltzmann suppression small mass splittings effective coannihilations lowering (in general) n  0 (i.e.  CDM ) Freeze out:

JCAP 0304 (2003) 001 Effective coannihilations -- small masssplittings -- another illustration ; p.1/3 Thermal averaging of all  v Boltzmann suppression of high velocities (fixed T) Effective v Effective distribution function LSP-LSP CM frame

Effective coannihilations -- small masssplittings -- another illustration; p.2/3 p 11 p 12 p 22 p 11 p 12 p 22 p 11 Coannihilation processes in individual CM frames (m 1 <m 2 <m 3 ….): Translatation to neutralino annihilations CM frame: Initial states look like final state thresholds etc

Effective coannihilations -- small masssplittings -- another illustration; p.3/3 Thermal averaging of the effective  v Boltmann suppression of heavy initial states Fig: JCAP 0304 (2003) 001

Our work in mSUGRA J. Edsjö, M. Schelke, P. Ullio & P. Gondolo JCAP 0304 (2003) 001 (hep-ph/ ) We include all coannihilations and use the DarkSUSY package: Gondolo, Edsjö, Ullio, Bergström, Schelke and Baltz DarkSUSY is a public fortran package for accurate calculations of neutralino relic density and detection rates. DarkSUSY solves the Boltzmann equation accurately (including resonances and thresholds).

Minimal supergravity N=1 local susy with gravity mediated breakdown of susy Effective model:N=1 global susy (MSSM) plus soft susy breaking terms The five free mSUGRA parameters: m 1/2 :GUT unification value of soft susy breaking fermionic mass parameters m 0 :GUT unification value of soft susy breaking bosonic mass parameters A 0 :GUT unification value of soft susy breaking trilinear scalar coupling parameters tan  = v 2 /v 1 : ratio of the Higgs fields vev’s sign(  ) :  is the Higgs superfield parameter

All coannihilations are included The DarkSUSY code includes all channels of all 2 -> 2 tree-level coannihilation processes (Except initial state gluinos) To gain computational speed: Only include initial state sparticles with m<1.5m(  ) (better than 1% accuracy) The most effective coannihilations (different regions of the parameterspace): stau ( ): partner of  chargino ( ): partners of charged higgs and gauge bosons stop ( ): partner of top

The stau coannihilation region: JCAP 0304 (2003) 001 Neutralino relic density isolevel curves.

~400~300~200~100~45 JCAP 0304 (2003) 001 The stau coannihilation region: Effective coannihilations -- small mass splittings

~400~300~200~100~45 JCAP 0304 (2003) 001 The stau coannihilation region: Increasing the upper bound on the neutralino mass. --- h 2 without coannih.

JCAP 0304 (2003) 001 neutralino -- stau The stau coannihilation region: Increasing the upper bound on the neutralino mass.

No REWB Chargino coannihilation region (high mass focus point region) Increasing the upper bound on the neutralino mass. Coannihilations in this region had not been discussed in detail before

stau coannihilation region Coannihilations decrease the lower bound on the neutralino mass in this region For m  > m t, a light stop is important even without coann.’s, as it boosts this annih. channel: Stop coannihilation region JCAP 0304 (2003) 001

Conclusions The relic neutralino density can be wrong by as much as 100s or 1000s percent if coannihilations are not included Coannihilations open up new regions of parameter space where the density is otherwise too high In the stau and chargino coannihilation regions the upper mass bound to the   mass is increased, while its lower bound is decreased in the stop coann. region The efficiency of the coannihilation with a certain sparticle and the mass splitting between this sparticle and the   are highly correlated Efficient coannihilations are found for small mass splittings