Asymmetric WIMP DM. Luca Vecchi. Aspen (CO) 2/2011. in collaboration with Michael Graesser and Ian Shoemaker (LANL)

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1 Asymmetric WIMP DM Luca Vecchi in collaboration with Michael Graesser and Ian Shoemaker (LANL) Aspen (CO) 2/2011

2 Outline 1 Motivations 2 The relic abundance of asymmetric species 3 Asymmetric WIMP Dark Matter How asymmetric can WIMPs be? The parameter space Indirect signals 4 Conclusions

3 Motivations Motivations 1) DM might be stable due to a global symmetry that distinguishes between particles and anti-particles ex: U(1) 2) If 1), then (primordial) particle/anti-particle asymmetries are generic if Baryogenesis occured the 3 Sakharov conditions were satisfied 3) If 2), then the DM η might be related to the baryon asymmetry η B Typically, some heavy states (Afflek-Dine, Q-balls, RH neutrinos) decay at a temperature T into DM and baryons (and/or leptons): ift > T D one expects η O(1)η B ift < T D one can also have η O(1)η B What is the effect of a primordial asymmetry η on the DM physics? Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

4 Working assumptions Motivations Let us assume that below some temperature T D the DM has a particle/anti-particle asymmetry η (Y ± = n ± /s): η = Y + Y [Here η can be (much) bigger or (much) smaller than η B ] Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

5 Motivations Two extreme regimes: 1) Thermal (WIMP) DM if the dynamics is weak In this case Y Y + η and Ω DM 2Y ± η [this is what is typically assumed for WIMPs] 2) Asymmetric DM (ADM) regime if the dynamics is strong 1 In this case Y Y + η and the abundance is set by Ω DM Y + η [this is what happens to baryons] 1 see for example D. E. Kaplan et al. 09 Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

6 Motivations To have a better understanding of this physics (what does strong or weak dynamics mean?) we need to solve the Boltzmann equations (x = m/t ) 2 : dy ± dx = λ g 1/2 x n 2 Y + Y Y + eqyeq with Y + (x i ) Y (x i )=η and σ ann v σ 0 (T /m) n λ = π 45 1/2 MPl mσ 0 [focus on weakly coupled theories with T f m/20 and use the non-relativistic distributions] 2 For previous works: Scherrer and Turner 85; Griest and Seckel 87 Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

7 The relic abundance of asymmetric species Fractional asymmetry It is convenient to change variables (Y +, Y ) (η, r) with r(x) = Y Y + η = Y + Y The fractional asymmetry r(x) fully determines the relative abudances Y + = η 1 1 r Y = η r 1 r measures the amount of symmetry ( symmetric component ) [r =0/1 meansasymmetric/symmetricirrespectiveofη] controls the indirect signals Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

8 The relic abundance of asymmetric species The Boltzmann equations reduce to: dr dx dη dx = ληg 1/2 1 r 2 x n 2 r r eq 1 r eq = 0 The solution r(x) is found in the standard way: for small x (10 < x < x f )wehaver r eq at freeze-out x = x f the two terms (LHS and RHS) become comparable for x > x f the evolution is controlled by the first term on the RHS Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

9 The relic abundance of asymmetric species To a very high accuracy, the present fractional asymmetry reads r = r eq (x f ) e λη Φ with Φ= dx x n 2 g 1/2 x f For (σ 0 ; η) within several orders of magnitude from (σ 0,WIMP ; η B ) one finds: r eq (x f ) 1 x f x f (η = 0) Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

10 The relic abundance of asymmetric species Accuracy of the analytic solution rx x Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

11 Asymmetric WIMP Dark Matter Asymmetric DM: relic abundance Finally, a DM candidate with a primordial asymmetry satisfies with m m p η η B = 1 r 1+r r = e λη Φ ΩDM Ω B Notice that r depends exponentially on σ 0 mη Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

12 Asymmetric WIMP Dark Matter WIMP DM For (strongly) symmetric DM r 1 the relic abundance is attained by tuning the cross section: [nice consistency check for r ] σ 0,WIMP = 1 Ω B η B m p Ω DM M Pl Φ π Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

13 (strongly) ADM Asymmetric WIMP Dark Matter For (strongly) asymmetric DM r 0 the relic abundance is attained by tuning the mass: m ADM Ω DM Ω B η B η m p Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

14 Asymmetric WIMP Dark Matter How asymmetric can WIMPs be? How strong ADM scenarios need to be? r Σ 0 Σ 0,WIMP Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

15 Asymmetric WIMP Dark Matter The parameter space Asymmetric WIMP DM More generally: For Asymmetric WIMP DM the allowed parameter space is defined by 0 < r < 1 i) an upper bound on the DM mass: m m ADM 5 η B η m p ii) a lower bound on the cross section: σannv σannv WIMP Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

16 Asymmetric WIMP Dark Matter The parameter space Σ0 GeV Ε m GeV η = η B Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

17 Asymmetric WIMP Dark Matter Indirect signals Indirect signals for Asymmetric WIMPs AsyWIMP WIMP r σ ann v 2 2 r 1 [ 0.5 when r 0.1] σ ann v WIMP 1+r Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

18 Conclusions Discussion 1) A typical (perturbative) UV completion of the SM is likely to predict a WIMP DM candidate ( WIMP miracle ) 2) If DM = DM aprimordialdmasymmetryisverylikely Hence... Asymmetric WIMP DM is rather generic Luca Vecchi (LANL) Asymmetric WIMP DM February / 19

19 Conclusions Conclusions In Asymmetric WIMP models DM and baryons (asymmetries) might have a common origin (η η B ): whether or not the DM is asymmetric today depends on the dynamics (via r ) Given η = 0,theallowedparameterspaceis m 5 η B η m p σ ann v σ ann v WIMP Asymmetric WIMP scenarios can have m m p if r 1 One can have r 1alreadywithσannv (2 3)σannv WIMP Indirect signals are not significantly suppressed 0.5 onlyforr 0.1 Luca Vecchi (LANL) Asymmetric WIMP DM February / 19