Indirect Detection of WIMPs Joakim Edsj Stockholm University - PowerPoint PPT Presentation

Indirect Detection of WIMPs Joakim Edsjö Stockholm University Sweden edsjo@physto.se ν 2004 Paris, June 19, 2004

Outline • WIMP candidates – will focus on the neutralino in the MSSM • Ways to search indirectly for WIMPs • Direct detection versus neutrino telescopes • Recent developments in Earth rates (gravitational diffusion revisited) • Comparison of future searches

Many groups work on this, e.g. • Ellis, Falk, Olive, Santoso, Spanos et al. • Bottino, Donato, Fornengo, Scopel et al. • Baer, Belyaev, Krupovnickas, O’Farrill, Tata et al. • Silk, Bertone, Hooper, et al. • Nezri, Orloff, et al. • Roszkowski, Nihei, Ruiz de Austri, et al. • Bergström, Baltz, Edsjö, Gondolo, Ullio, Schelke et al. • …

The neutralino as a WIMP Will focus on the neutralino in the MSSM as a dark matter WIMP candidate. The neutralino: W 3 + N 13 ˜ 1 = N 11 ˜ B + N 12 ˜ 1 + N 14 ˜ χ 0 H 0 H 0 ˜ 2 The neutralino can be the lightest supersymmetric particle (LSP). If R-partity is conserved, it is stable. The gaugino fraction Z g = | N 11 | 2 + | N 12 | 2

Calculational flowchart 1. Select model parameters 2. Calculate masses etc 3. Check accelerator constraints 4. Calculate the relic density Ω χ h 2 5. Check if the relic density is cosmologically OK 6. Calculate fluxes, rates, etc Calculation done with DarkSUSY 4.1 available on The relic density www.physto.se/~edsjo/darksusy Ω χ h 2 = 0 . 103 +0 . 020 astro-ph/0406204 − 0 . 022 from WMAP+SDSS M.Tegmark et al., astro-ph/0310723

The parameter space m χ − Z g 10 5 J. Edsjö, 2004 Z g / (1-Z g ) Gaugino 10 4 Ω χ h 2 > 0 . 2 10 3 10 2 LEP 10 1 Mixed -1 Ω χ h 2 < 0 . 05 10 -2 10 -3 10 -4 10 In this and the -5 coming plots, 10 0.05 ! ! h 2 ! 0.08 -6 sfermion 10 0.08 ! ! h 2 ! 0.12 coannihilations -7 0.12 ! ! h 2 ! 0.2 10 Low sampling are not included Higgsino -8 10 in the relic 2 3 4 10 10 10 10 density Neutralino Mass (GeV) calculation (yet).

WIMP search strategies Use CDMS @ Soudan to • Direct detection constrain our models • Indirect detection: Focus on – neutrinos from the Earth/Sun these – antiprotons from the galactic halo Use – antideuterons from the galactic halo these to – positrons from the galactic halo constrain – gamma rays from the galactic halo our – gamma rays from external galaxies/halos models – synchrotron radiation from the galactic (future) center / galaxy clusters ... –

Annihilation in the halo Neutral annihilation products χχ → γγ , Z γ , ν χχ → γ , ν • Gamma rays can be searched for with Air Cherenkov Telescopes (ACTs) or GLAST. • Signal depends strongly on the halo profile, � ρ 2 dl Φ ∝ line of sight

Annihilation in the halo Charged annihilation products p, ¯ D, e + χχ → ¯ Diffusion zone • Diffusion of charged particles. Diffusion model with parameters fixed from studies of conventional cosmic rays (especially unstable isotopes). • Current detectors are e.g. HEAT, Caprice and BESS. Future detectors are e.g. AMS, Pamela and GAPS.

Direct detection current limits -3 J. Edsjö, 2004 10 Cross section, ! SI (pb) Excluded, CDMS Soudan, May 2004 -4 10 • CDMS @ Soudan, -5 10 astro-ph/0405033 -6 10 • Direct detection -7 10 experiments have -8 10 really started to -9 10 explore the MSSM -10 parameter space! 10 Gaugino-like -11 Mixed 10 Higgsino-like -12 10 2 3 4 10 10 10 10 Neutralino Mass (GeV)

Neutralino Capture velocity distribution χ ρ χ Sun ν interactions Earth ν µ σ ann σ scatt Γ capture µ Γ ann Detector Freese ‘86 Silk, Olive and Srednicki ‘85 Krauss, Srednicki & Wilczek ‘86 Gaisser, Steigman & Tilav ‘86 Gaisser, Steigman & Tilav ‘86

Neutrino Telescopes Capture Capture in Sun • Mostly on Hydrogen • Both spin-independent and spin-dependent scattering Capture in Earth • Mostly on Iron • Essentially only spin- independent scattering • Resonant scattering when mass matches element in Earth • Capture from WIMPs bound in the solar system Figure from Jungman, Kamionkowski and Griest

Review of capture rate calculations • 1985: Press & Spergel, ApJ 296 (1985) 679: Capture in the Sun • 1987: Gould, ApJ 321 (1987) 571: Refined Press & Spergel’ s calculation for the Earth. • 1988: Gould, ApJ 328 (1988) 919: Pointed out that the Earth cannot capture efficiently from the halo since the Earth is deep within the potential well of the Sun (vesc ≈ 42 km/s) • 1991: Gould, ApJ 368 (1991) 610: WIMPs will diffuse around in the solar system due to gravitational scattering off the planets. Net result is that the velocity distribution at Earth is approximately as if the Earth was in free space, i.e. the 1987 expressions are still valid.

Earth Capture Why are low velocities needed? • Capture can only occur when a WIMP scatters off a nucleus to a velocity less than the escape velocity 3 Capture on Fe most 10 important. Cutoff velocity ucut (km/s) For a given lowest 2 10 velocity of the velocity distribution, we can forbidden only capture WIMPs up to a maximal mass. 1 10 allowed 0 10 1 2 3 4 5 10 10 10 10 10 Wimp mass (GeV )

Diffusion effects of the planets • Gravitational scattering off one planet causes diffusion along spheres of constant velocity with respect to that planet. • When seen from another planet’ s frame, the velocity can have changed. The net effect is 25 u ♀ = 16 Speed at the Earth (km/s) that Venus and u ♀ = 14 20 Jupiter diffuse to u ♀ = 12 u ♀ = 10 velocities down to u ♀ = 9 15 u ♀ = 8 2.5 km/s u ♀ = 7 u ♀ = 6 10 u ♀ = 5 The velocity u ♀ = 4 5 distribution at u ♀ = 3 Earth is ‘as in 0 25 20 15 10 5 0 5 10 15 20 free space’ Speed at the Earth (km/s) A. Gould, ApJ 368 (1991) 610, J. Lundberg & J. Edsjö, PRD69 (2004) 123505.

Possible problems: solar capture • 1994: Farinella et al, Nature 371 (1994) 314: Simulations of asteroids thrown out of the asteroid belt showed that they were typically forced into the Sun in less than 2·106 years. • 2001: Gould and Alam, ApJ 549 (2001) 72: If Farinella’ s results hold for general WIMP orbits, the bound WIMPs in the solar system could be depleted. • 2004: J. Lundberg and J. Edsjö, PRD69 (2004) 123505: Numerical simulation of WIMP orbits to find out if this is the case.

Velocity distribution at Earth ! ' #! P hase space densit y: FM x / ρ x [ sm − 1 ] • Without solar capture, ! ( #! Gould’ s results of ‘capture as in free space’ ! * #! are confirmed. ! ) • Including solar #! capture, we G aussian get a ! #! #! W it hout solar depl. significant suppression at B est est im at e low velocities, R aw num erical ! ## #! not as bad as C onservat ive initially U lt ra conservat ive ! #$ thought, but #! ! " #! #" $! $" %! %" &! &" "! "" '! '" (! still significant W I M P velocit y u at t he E art h (km / s)

Earth capture rates !' !" Gaussian Best estimate Conservative !& !" Ultra conservative !( !" Capture rate [s − 1 ] !# !" Up to almost an order of !" !" magnitude suppression at higher masses! ' !" σ scatt = 10 − 42 cm 2 & !" !" !"" #"" $"" %"" !""" %""" WIMP mass (GeV)

Earth annihilation rates J. Lundberg and J. Edsjö, 2003 Suppression of annihilation rate Γ A = 1 2 C tanh 2 t 0.05 # " h 2 # 0.2 1 τ max # sup min # Annihilation and sup capture is not in equilibrium in the Earth -1 10 ⇩ The annihilation ! ! old " 10 km -2 yr -1 rates are ! ! old # 10 km -2 yr -1 suppressed by up to almost two -2 10 orders of 2 3 4 10 10 10 10 magnitude! Neutralino Mass (GeV)

Neutrino-induced muon fluxes from the Earth Usual Gaussian New estimate including approximation solar capture 10 6 10 6 J. Lundberg and J. Edsjö, 2004 J. Lundberg and J. Edsjö, 2004 Muon flux from the Earth (km -2 yr -1 ) Muon flux from the Earth (km -2 yr -1 ) AMANDA 2004 AMANDA 2004 lim lim ! SI ! ! SI ! SI ! ! SI BAKSAN 1997 BAKSAN 1997 MACRO 2002 MACRO 2002 lim lim lim lim ! ! SI ! 0.1 ! SI ! ! SI ! 0.1 ! SI ! SI ! SI 10 5 10 5 SUPER-K 2004 SUPER-K 2004 lim lim 0.1 ! SI ! ! SI 0.1 ! SI ! ! SI IceCube Best-Case IceCube Best-Case lim lim = CDMS 2004 = CDMS 2004 ! SI ! SI E th E th " = 1 GeV " = 1 GeV 10 4 10 4 New solar system diffusion 10 3 10 3 10 2 10 2 0.05 # " # h 2 # 0.2 0.05 # " # h 2 # 0.2 10 10 1 1 2 3 4 2 3 4 10 10 10 10 10 10 10 10 Neutralino Mass (GeV) Neutralino Mass (GeV) Maxwell-Boltzmann velocity distribution assumed.

Neutrino-induced muon fluxes from the Sun 10 6 J. Edsjö, 2004 Muon flux from the Sun (km -2 yr -1 ) BAKSAN 1997 lim ! SI ! ! SI MACRO 2002 SUPER-K 2004 lim lim ! SI ! ! SI ! 0.1 ! SI 10 5 IceCube Best-Case lim 0.1 ! SI ! ! SI Antares, 3 yrs • Compared to E th " = 1 GeV lim = CDMS 2004 ! SI 10 4 the Earth, much better 10 3 complementarity due to spin- dependent 10 2 0.05 # " # h 2 # 0.2 capture in the Sun. 10 AMANDA-II, 2001 1 2 3 4 10 10 10 10 Neutralino Mass (GeV)

A note about velocity distributions Remember the different velocity dependencies! Capture sensitive to the Direct detection sensitive low-velocity region to the high-velocity region f(v) v