Mia Schelke, Ph.D. Student

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Supersymmetric Dark Matter coannihilations

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

Cosmo 03
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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 workmSUGRA
• Results of relic density calculations including
  all coannihilations
• J. Edsjö, M. Schelke, P. Ullio P. Gondolo
• JCAP 0304 (2003) 001 (hep-ph/0301106)

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Broken N1 SUSY with conserved R-parity
Minimal N1 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.

• Multiplicatively conserved
• even nb of susys in vertex
• The lightest susy particle (LSP) is stable

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LSP Neutralino WIMP

• The lightest supersymmetric particle (LSP)
• will often be a neutralino c0
• But lightest might mean O(100 GeV)
• a weakly interacting massive particle (WIMP)
• a natural cold dark matter candidate

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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 gt the
effective neutralino annihilation rate (H gt s v
n) The comoving c0 relic density will stay
constant ever after. NOTElarge s small n
Solve Boltzmann eq. for nc0 with
I.e. a coupled system of annihilations/interaction
s But all leftover susy particles decay into
c0 So dont solve for n1,n2,., but for ?ni nc0
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Coannihilation mass splitting

• So seff is large when sij and are
  large.
• mltltT
  Boltzmann suppression
• small mass splittings
• effective coannihilations
• lowering (in general) nc0 (i.e. WCDM)

Freeze out
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Effective coannihilations -- small
masssplittings-- another illustration p.1/3

• Thermal averaging of all s v
• Boltzmann suppression of high velocities (fixed
  T)

Effective distribution function
LSP-LSP CM frame
Effective s v
JCAP 0304 (2003) 001
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Effective coannihilations -- small
masssplittings-- another illustration p.2/3
Coannihilation processes in individual CM frames
(m1ltm2ltm3.)
etc
p11
p12
p22
Translatation to neutralino annihilations CM
frame
p22
p11
p12
p11
Initial states look like final state thresholds
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Effective coannihilations -- small
masssplittings-- another illustration p.3/3

• Thermal averaging of the effective s v
• Boltmann suppression of heavy initial states

Fig JCAP 0304 (2003) 001
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Our work in mSUGRA

• J. Edsjö, M. Schelke, P. Ullio P. Gondolo
• JCAP 0304 (2003) 001 (hep-ph/0301106)
• We include all coannihilations and use the
  DarkSUSY package
• Gondolo, Edsjö, Ullio, Bergström, Schelke and
  Baltz http//www.physto.se/edsjo/darksusy/
• 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).

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Minimal supergravity

• N1 local susy with gravity mediated breakdown of
  susy
• Effective modelN1 global susy (MSSM) plus
• soft susy breaking terms
• The five free mSUGRA parameters
• m1/2GUT unification value of soft susy breaking
  fermionic mass parameters
• m0 GUT unification value of soft susy breaking
  bosonic mass parameters
• A0 GUT unification value of soft susy breaking
  trilinear scalar coupling parameters
• tan b v2/v1 ratio of the Higgs fields vevs
• sign(m) m is the Higgs superfield parameter

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All coannihilations are included
The DarkSUSY code includes all channels of all 2
-gt 2 tree-level coannihilation processes (Except
initial state gluinos)
To gain computational speed Only include initial
state sparticles with mlt1.5m(c0) (better than 1
accuracy)
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The stau coannihilation region
Neutralino relic density isolevel curves.
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The stau coannihilation region
Effective coannihilations -- small mass splittings
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The stau coannihilation region
Increasing the upper bound on the neutralino mass.
--- Wh2 without coannih.
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The stau coannihilation region
Increasing the upper bound on the neutralino mass.
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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
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Stop coannihilation region
Coannihilations decrease the lower bound on the
neutralino mass in this region
JCAP 0304 (2003) 001
stau coannihilation region
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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 c0 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 c0 are highly correlated
• Efficient coannihilations are found for small
  mass splittings