Dark Matter Particle Candidates Paolo Gondolo University of Utah Evidence for cold dark matter 0.04175±0.00004 pJ/m3 photons 37.6±0.2 pJ/m3 ordinary matter 1 to 4 pJ/m3 neutrinos 535±7 pJ/m3 dark energy Cold Dark 201±2 pJ/m3 cold dark matter Matter The observed energy content of the Universe matter p≪ρ radiation p=ρ/3 -12 Planck (2015) 1 pJ = 10 J vacuum p=-ρ TT,TE,EE+lowP+lensing+ext 2 3 ρcrit=1688.29 h pJ/m Is cold dark matter an elementary particle? is the particle of light couples to the plasma disappears too quickly is hot dark matter HiggsH boson No known particle can be nonbaryonic cold dark matter! What particle model for cold dark matter? • It should have the cosmic cold dark matter density • It should be stable or very long-lived (≳1024 yr) • It should be compatible with collider, astrophysics, etc. bounds • Ideally, it would be possible to detect it in outer space and produce it in the laboratory • For the believer, it would explain claims of dark matter detection (annual modulation, positrons, X-ray line, γ-ray excess, etc.) Particle dark matter • SM neutrinos (hot) • lightest supersymmetric particle (cold) thermal relics • lightest Kaluza-Klein particle (cold) • sterile neutrinos, gravitinos (warm) • Bose-Einstein condensates, (cold) axions, axion clusters non-thermal relics • solitons (Q-balls, B-balls, ...) (cold) • supermassive wimpzillas (cold) Mass range Interaction strength range 10-22 eV (10-59kg) B.E.C.s Only gravitational: wimpzillas -8 +22 10 M⦿ (10 kg) axion clusters Strongly interacting: B-balls Particle dark matter Hot dark matter - relativistic at kinetic decoupling (last scattering, start of free streaming) - big structures form first, then fragment light neutrinos Cold dark matter - non-relativistic at kinetic decoupling - small structures form first, then merge neutralinos, axions, WIMPZILLAs, solitons Warm dark matter - semi-relativistic at kinetic decoupling - smallest structures are erased sterile neutrinos, gravitinos Particle dark matter Thermal relics - in thermal equilibrium with the plasma in the early universe - produced in collision of plasma particles - insensitive to initial conditions neutralinos, other WIMPs, .... Non-thermal relics - not in thermal equilibrium with the plasma in the early universe - produced in decays of heavier particles or extended structures - have a memory of initial conditions axions, WIMPZILLAs, solitons, .... Particle dark matter - in plasma reactions DM production collider searches - from decays of decoupled species cosmic density - emitted from extended objects DM-DM annihilation - self-conjugate DM indirect detection χ+χ̅ →anything - asymmetric DM cosmic density hot/cold/warm DM—SM scattering - elastic/inelastic scattering halo (sub)structure χ+SM→χ′+SM - short-/long-range interactions direct detection DM—DM scattering - collisionless dark halo structure χ+χ→χ+χ - self-interacting - stable DM decay - long-lived indirect detection χ→anything - ensemble of short-lived particles Particle dark matter Some factors affecting the particle dark matter cosmic density — Production mechanism: • produced in reactions of plasma (thermal) particles - reaching reaction equilibrium WIMP freeze-out, … - not reaching reaction equilibrium FIMP freeze-in, … - coannihilating with similar mass particles neutralinos, … • produced in decays of non-thermal particles gravitinos, … • emitted from extended objects axions, … — Dark matter-antimatter asymmetry: • self-conjugate Majorana fermions, neutralinos, axions, gravitinos, … • not self-conjugate Dirac fermions, asymmetric dark matter, … — Hubble expansion rate before nucleosynthesis: • standard vs nonstandard cosmology low temperature reheating, kination, … The magnificent WIMP (Weakly Interacting Massive Particle) 0.04175±0.00004 pJ/m3 photons • One naturally obtains the 37.6±0.2 pJ/m3 ordinary matter right cosmic density of 1 to 4 pJ/m3 neutrinos WIMPs 201±2 535±7 pJ/m3 pJ/m3 dark energy cold dark Thermal production in matter hot primordial plasma. • One can experimentally test the WIMP hypothesis The same physical processes that produce the right density of WIMPs make their detection possible Cosmic density Indirect detection Annihilation Direct detection χ f The power of the WIMP Scattering (—) (—) χ f Large scale structure Production Colliders Cosmic density Børge Kile Gjelsten, University of Oslo 44 IDM, Aug 2008 Neutrinos Cosmic density of massive neutrinos Active neutrinos ~ few GeV preferred cosmological mass Excluded as cold dark matter (1991) Lee & Weinberg 1977 Direct Searches LEP bound Z ⌫⌫¯ ! Sterile neutrino dark matter Standard model + right-handed neutrinos Active and sterile neutrinos oscillate into each other. case 1 case 2 -4 -4 10 LMC 10 LMC MW 6 MW 6 M31 10 n / s M31 -6 10 n / s -6 ν ν e Sterile neutrinos can be warm 10 e MW 10 MW 0.0 SPI 0.0 SPI dark matter (mass > 0.3 keV) -8 -8 10 DM density 10 θ θ Dodelson, Widrow 1994; Shi, Fuller 2 2 2 -10 2 -10 1999; Laine, Shaposhnikov 2008 10 2 10 2 sin Lyman-α sin 4 4 (SDDS) 25 16 12 25 16 12 8 8 -12 70 -12 70 10 250 10 250 700 700 2500 2500 -14 -14 10 10 -16 -16 νMSM 10 0 1 2 10 0 1 2 10 10 10 10 10 10 Laine, Shaposhnikov 2008 M1 / keV M1 / keV Figure 4: The central region of Fig. 3, M1 =0.3 ...100.0keV,comparedwithregionsexcluded by various X-ray constraints [22, 25, 30, 31], coming from XMM-Newton observations of the Large Magellanic Cloud (LMC), the Milky Way (MW), and the Andromedagalaxy(M31).SPImarksthe constraints from 5 years of observations of the Milky Way galactic center by the SPI spectrometer on board the Integral observatory. dark matter simulations, which have not been carried out withactualnon-equilibriumspec- tra so far. Nevertheless, adopting a simple recipe for estimating the non-equilibrium effects (cf. Eq. (5.1)), the results of refs. [34, 35] can be re-interpreted as the constraints M1 > 11.6 ∼ keV and M1 > 8 keV, respectively (95% CL), at vanishing asymmetry [12]. Very recently limits stronger∼ by a factor 2–3 have been reported [36]. We return to how the constraints change in the case of a non-zero lepton asymmetry in Sec. 5. We note, however, that the most conservative bound, the so-called Tremaine-Gunn bound[52,53],ismuchweakerand reads M1 > 0.3keV[54],whichwehavechosenasthelowerendofthehorizontal axes in Figs. 4, 6. ∼ In Fig. 5 we show examples of the spectra, for a relatively small mass M1 =3keV(like in Fig. 1), at which point the significant changes caused by theasymmetrycanbeclearly identified. The general pattern to be observed in Fig. 5 is thatforasmallasymmetry,the distribution function is boosted only at very small momenta.Quantitiesliketheaverage momentum q then decrease, as can be seen in Fig. 6. For large asymmetry, the resonance ⟨ ⟩s affects all q;thetotalabundanceisstronglyenhancedwithrespecttothecasewithouta resonance, but the shape of the distribution function is lessdistortedthanatsmallasymmetry, so that the average momentum q returns back towards the value in the non-resonant case. ⟨ ⟩s Therefore, for any given mass, we can observe a minimal value of q s in Fig. 6, q s > 0.3 q a. ⟨ ⟩ ⟨ ⟩ ∼ ⟨ ⟩ This minimal value is remarkably independent of M1,butthevalueofasymmetryatwhich 15 Sterile neutrino dark matter Radiative decay of sterile neutrinos An unidentified 3.5-keV X-ray line has been reported in galaxy ⌫s ⌫a Eγ = ms/2 ! clusters and the Andromeda galaxy. 2 -11 mν = 7.1 keV sin (2θ) = 7×10 Bulbul et al 2014; Boyarski et al 2014; case 1 case 2 Iakubovskyi et al 2015 -4 -4 10 LMC 10 LMC ) -1 MW 6 MW 0.8 XMM-MOS 6 M31 10 n / s M31 keV 3.57 ± 0.02 (0.03) -6 -6 ν -1 10 n / s Full Sample ν e 0.7 6 Ms 10 e MW 10 MW 0.0 SPI 0.0 SPI 0.6 stacked clusters Flux (cnts s 0.02 -8 -8 0.01 10 DM density 10 0 θ θ 2 2 2 2 Residuals -0.01 -10 -10 2 2 -0.02 10 10 sin Lyman-α sin ) 4 2 315 4 310 (SDDS) 25 16 12 25 16 12 8 8 70 70 305 -12 -12 10 250 10 250 300 700 700 Eff. Area (cm 2500 2500 3 3.2 3.4 3.6 3.8 4 Energy (keV) -14 -14 10 10 Fuller, Lowenstein,Jeltema, -16 -16 νMSM 10 0 1 2 10 0 1 2 Kusenko, Abazajian, Smith 10 10 10 10 10 10 (Thursday) Laine, Shaposhnikov 2008 M1 / keV M1 / keV Figure 4: The central region of Fig. 3, M1 =0.3 ...100.0keV,comparedwithregionsexcluded by various X-ray constraints [22, 25, 30, 31], coming from XMM-Newton observations of the Large Magellanic Cloud (LMC), the Milky Way (MW), and the Andromedagalaxy(M31).SPImarksthe constraints from 5 years of observations of the Milky Way galactic center by the SPI spectrometer on board the Integral observatory. dark matter simulations, which have not been carried out withactualnon-equilibriumspec- tra so far. Nevertheless, adopting a simple recipe for estimating the non-equilibrium effects (cf. Eq. (5.1)), the results of refs. [34, 35] can be re-interpreted as the constraints M1 > 11.6 ∼ keV and M1 > 8 keV, respectively (95% CL), at vanishing asymmetry [12]. Very recently limits stronger∼ by a factor 2–3 have been reported [36]. We return to how the constraints change in the case of a non-zero lepton asymmetry in Sec. 5. We note, however, that the most conservative bound, the so-called Tremaine-Gunn bound[52,53],ismuchweakerand reads M1 > 0.3keV[54],whichwehavechosenasthelowerendofthehorizontal axes in Figs. 4, 6. ∼ In Fig. 5 we show examples of the spectra, for a relatively small mass M1 =3keV(like in Fig. 1), at which point the significant changes caused by theasymmetrycanbeclearly identified. The general pattern to be observed in Fig.