Dark-matter bound states

Transcription

1 Dark-matter bound states Kallia Petraki Université Pierre et Marie Curie, LPTHE, Paris Recontres du Vietnam, Quy Nhon 27 July 2017

2 Long-range interactions mediated by massless or light particles Bound states 2

3 Long-range interactions Motivation Self-interacting DM DM explanations of astrophysical anomalies, e.g. galactic positrons, IceCube neutrinos Little hierarchy problem, e.g. twin Higgs models Sectors with stable particles in String Theory Hidden sector DM 3

4 Long-range interactions Motivation Self-interacting DM DM explanations of astrophysical anomalies, e.g. galactic positrons, IceCube neutrinos Little hierarchy problem, e.g. twin Higgs models Sectors with stable particles in String Theory WIMP DM with mdm > few TeV! Particular scenarios of sub-tev WIMPs Hidden sector DM [Hisano et al. 2002] Minimal DM [Cirelli+] LHC implications for SUSY Direct/Indirect detection constraints Coannihilating with charged/coloured particles, e.g. degenerate neutralino-stop scenarios in the MSSM [Laura Covi s talk] 4

5 Bound states Varieties A. Confining theories Hadronic-like bound states ( non-perturbative non-perturbative bound states ). Cosmologically, they definitely form. May leave a remnant weakly coupled long(-ish) range interaction. B. Weakly coupled theories Perturbative non-perturbative bound states, e.g. atoms. Formation efficiency depends on the details: (i) bound-state formation cross-section, and (ii) thermodynamic environment (early universe, DM halos, interior of stars) 5

6 Bound states Phenomenological implications Asymmetric DM Stable bound states Kinetic decoupling of DM from radiation, in the early universe DM self-scattering in halos: Screening [KP, Pearce, Kusenko (2014)] Indirect detection signals: Radiative level transitions [Pearce, Kusenko (2013); Cline+ (2014); Detmold+ (2014); Pearce, KP, Kusenko (2015)] Direct detection signals: Screening, inelastic scattering Symmetric / Self-conjugate DM Unstable bound states Formation + Decay = Extra annihilation channel Relic abundance [von Harling, KP (2014); Ellis+ (2015); Liew, Luo (2016), El Hedri+ (2017)] Indirect detection [Pospelov+ (2008); March-Russel+ (2009); An+ (2016); Cirelli, Panci, KP, Sala, Taoso, (2016)] Collider signatures [Shepherd, Tait, Zaharijas 2009, Pospelov+ 2015] 6

7 Bound states Phenomenological implications Asymmetric DM Stable bound states Kinetic decoupling of DM from radiation, in the early universe DM self-scattering in halos: Screening [KP, Pearce, Kusenko (2014)] Indirect detection signals: Radiative level transitions [Pearce, Kusenko (2013); Cline+ (2014); Detmold+ (2014); Pearce, KP, Kusenko (2015)] Direct detection signals: Screening, inelastic scattering Symmetric / Self-conjugate DM Unstable bound states Formation + Decay = Extra annihilation channel Relic abundance [von Harling, KP (2014); Ellis+ (2015); Liew, Luo (2016), El Hedri+ (2017)] Indirect detection [Pospelov+ (2008); March-Russel+ (2009); An+ (2016); Cirelli, Panci, KP, Sala, Taoso, (2016)] 7

8 Bound states Phenomenological implications Asymmetric DM Stable bound states Kinetic decoupling of DM from radiation, in the early universe DM self-scattering in halos: Screening [KP, Pearce, Kusenko (2014)] Indirect detection signals: Radiative level transitions [Pearce, Kusenko (2013); Cline+ (2014); Detmold+ (2014); Pearce, KP, Kusenko (2015)] Direct detection signals: Screening, inelastic scattering Symmetric / Self-conjugate DM Unstable bound states Formation + Decay = Extra annihilation channel Relic abundance [von Harling, KP (2014); Ellis+ (2015); Liew, Luo (2016), El Hedri+ (2017)] Indirect detection [Pospelov+ (2008); March-Russel+ (2009); An+ (2016); Cirelli, Panci, KP, Sala, Taoso, (2016)] 8

9 Outline Effect of bound states on relic density: dark U(1) sector & MSSM Unitarity limit on thermal-relic DM Indirect detection signals from dark U(1) sector 9

10 1. Relic density 10

11 Inelastic processes: Direct annihilation vs bound-state formation Dirac fermions (X, X) of mass m, coupled to a (massless) vector boson VD, with dark fine-structure constant αd. Toy model: Dark QED Very important parameter: ζ = αd / vrel Annihilation X + X V D + V D σ ann v rel = σ 0 S ann ( ζ ) σ 0 = π α 2D / m2 S ann ( ζ ) = 2π ζ 1 e 2 π ζ S ann ( ζ 1 ) 1 S ann ( ζ 1 ) 2 π ζ 11

12 Inelastic processes: Direct annihilation vs bound-state formation Toy model: Dark QED Dirac fermions (X, X) of mass m, coupled to a (massless) vector boson VD, with dark fine-structure constant αd. Very important parameter: ζ = αd / vrel Bound state formation αnd decay X + X ( X X ) bound + V D ( X X ) bound 2 V D οr 3 V D E > 2mX E < 2mX σ BSF v rel = σ 0 S BSF ( ζ ) σ 0 = π α 2D / m2 S BSF ( ζ ) = von Harling, KP, arxiv: KP, Postma, Wiechers, arxiv: [ 2 3e 9 4 ζ arccot ( ζ ) ζ 4 ( 1 + ζ2) 2 ] 2πζ 2 π ζ 1 e 29 ζ 4 S BSF ( ζ 1 ) S BSF ( ζ 1 ) 2 π ζ 3.13 S ann 4 3e 12

13 Inelastic processes: Direct annihilation vs bound-state formation von Harling, KP, arxiv: KP, Postma, Wiechers, arxiv: S st d n bou f ate ni n a or n o i t ma on i t hila Vector mediator ζ = αd /vrel BSF dominates over annihilation everywhere the Sommerfeld effect is important (ζ > 1)! 13

14 Relic density Dark U(1) model von Harling and KP, arxiv: αd unitarity m [GeV] 14

15 Relic density Dark U(1) model von Harling and KP, arxiv: Effect larger than the experimental uncertainty of 1% Effect larger than the experimental sensitivity ΩSE ann / ΩDM 4 at 140 TeV ΩSE ann / ΩDM 2 at 15 TeV 15

16 Relic density Dark U(1) model von Harling and KP, arxiv: Effect larger than the experimental uncertainty of 1% Effect larger than the experimental sensitivity ΩSE ann / ΩDM 4 s, e i r o t he at 140 TeV x e l mp etween states o c b re o y nd a u m l ct. o p e r f b In f e f t e o n the i d decay r/weaker an t r onge n o i s at ionis sult in a re n a c ΩSE ann / ΩDM 2 at 15 TeV 16

17 Relic density Sub-TeV WIMPs in the MSSM Weak interactions manifest as contact type no Sommerfeld effect for DM particles, no bound states In some MSSM scenarios, NLSP LSP very mass degenerate NLSP LSP co-annihilations [Laura Covi s talk] DM density determined by effective Boltzmann equation for Y = YLSP + YNLSP σeff = (YLSP2 σlsp + YNLSP2 σnlsp + YLSPYNLSP σnlsp LSP) / Y2 If NLSP is coloured and/or charged (e.g. stop), Various (QCD) corrections to tree-level annihilation 17

18 αs corrections to stop annihilation [Klasen+ ( )] QCD loop corrections Gluon emission Sommerfeld effect broadly, the most important 18

19 αs corrections to stop annihilation [Klasen+ ( )] QCD loop corrections Strong coupling (αs ~ 0.1), massless mediators BSF important! Stop-onium formation Gluon emission Sommerfeld effect broadly, the most important 19

20 Relic density MSSM-inspired toy models Liew and Luo, arxiv: ; see also El Hedri+, arxiv: DM co-annihilating with scalar colour-triplet DM co-annihilating with fermionic colour-octet SE annihilation + bound states SE annihilation Perturbative annihilation 20

21 Relic density MSSM with near degenerate LSP-NLSP (stop/sbottom) Keung, Low, Zhang, arxiv: ; see also Ellis, Luo, Olive, arxiv: Bino-Stop coannihilation Bino-Sbottom coannihilation 21

22 2. Unitarity limit on the mass of thermal-relic DM 22

23 Partial-wave unitarity limit ( J) (J) σ inel v rel σ uni v rel = (2 J +1) 4 π 2 M DM v rel Saturation of interaction probability at large couplings. 23

24 Partial-wave unitarity limit ( J) (J) σ inel v rel σ uni v rel = (2 J +1) 4 π 2 M DM v rel Implies upper limit on mass of thermal-relic DM cm / s Saturation of interaction probability at large couplings. Griest, Kamionkowski (1990) v rel 0.3 [ freeze out ] 2 M DM v rel M DM 83 TeV (s-wave annihilation, non-self-conjugate DM) 24

25 Partial-wave unitarity limit ( J) (J) σ inel v rel σ uni v rel = (2 J +1) 4 π 2 M DM v rel Implies upper limit on mass of thermal-relic DM. Saturation of interaction probability at large couplings. Griest, Kamionkowski (1990) Parametric dependence of σuni (especially v-dependence) Can be realised only via long-range interactions! von Harling, KP s-wave processes, non-self-conjugate DM: MDM < Muni = 83 TeV 140 TeV Higher partial waves contribute significantly, or even dominate, near Baldes, KP the unitarity limit. In a dark QED-like theory: Annihilation, X + X VD VD : s-wave Capture to the ground state, X + X (X X)bound + VD : p-wave Annihilation and BSF of the same order in αd. At αd > vrel : σbsf / σann 3 (as unitarity predicts!) s+ p M DM M uni 280 TeV 25

26 Partial-wave unitarity limit ( J) (J) σ inel v rel σ uni v rel = (2 J +1) 4 π 2 M DM v rel Implies upper limit on mass of thermal-relic DM. Saturation of interaction probability at large couplings. Griest, Kamionkowski (1990) Parametric dependence of σuni (especially v-dependence) Can be realised only via long-range interactions! von Harling, KP s-wave processes, non-self-conjugate DM: MDM < Muni = 83 TeV 140 TeV Higher partial waves contribute significantly, or even dominate, near Baldes, KP the unitarity limit. In a dark QED-like theory: Annihilation, X + X VD VD : s-wave Capture to the ground state, X + X (X X)bound + VD : p-wave Annihilation and BSF of the same order in αd. At αd > vrel : σbsf / σann 3 (as unitarity predicts!) s+ p M DM M uni 280 TeV 26

27 3. Indirect detection 27

28 Everybody's model for anomalies Dark matter: Fermions X, X, with mass MDM Coupled, dark fine structure constant αd Free parameters: 1)Dark matter mass MDM 2)Dark photon mass mvd Dark Photons VD, with mass mv D Coupling between dark photons & ordinary photons kinetic mixing ε 3)Dark fine structure constant αd 4)Kinetic mixing ε 28

29 Indirect detection of a dark U(1) sector Important processes Cirelli, Panci, KP, Sala, Taoso, arxiv: Annihilation X + X VD + VD Sommerfeld effect: enhancement at low velocities if VD light Bound-state formation X + X (XX)bound + VD Dark positronium bound states: exist if VD light 29

30 Parameter space: MDM, mvd and αd Indirect detection of a dark U(1) sector Cirelli, Panci, KP, Sala, Taoso, arxiv: αd determined from relic density, depends on MDM In the Coulomb regime (vrel MDM/2 > mv ): BSF dominates over annihilation D Outside the Coulomb regime: Resonances, but annihilation mostly dominates over BSF 30

31 Indirect detection of a dark U(1) sector Gamma rays Cirelli, Panci, KP, Sala, Taoso, arxiv: Annihilation only Annihilation and bound-state formation 31

32 Indirect detection of a dark U(1) sector AMS-02 antiprotons Cirelli, Panci, KP, Sala, Taoso, arxiv: Annihilation only Annihilation and bound-state formation 32

33 Indirect detection of a dark U(1) sector CMB Cirelli, Panci, KP, Sala, Taoso, arxiv: ; see also Bringmann+, arxiv: Annihilation only Bound-state formation very suppressed due to very small velocity (p-wave) 33

34 Indirect detection of a dark U(1) sector Cirelli, Panci, KP, Sala, Taoso, arxiv: All indirect probes Dark photon mass range mvd ~ MeV GeV highly constrained by γ-rays & CMB (leptophilic DM, self-interacting DM) mvd GeV constrained by p. Some tension for MDM ~ 40 GeV explanation of galactic center excess. Constraints extend to very low ε. Vanishingly small ε constrained by cosmology (BBN & Ωmatter / Ωradiation) SIDM from U(1) dark sector requires massless dark photon or asymm DM. 34

35 Conclusions Light mediators Radiative processes: Bound-state related processes important, even for weak couplings! Early universe regulates DM manifestations today. For long-range interactions, BSF is a major regulator. Symmetric DM: Reduced relic density/predicted couplings. Asymmetric DM: Screening of (self-)scattering processes. Overall, bound states may enhance signals / provide new signatures. 35