Dark Matter Electron Anisotropy: A universal upper limit

Transcription

1 Seminari teorici del venerdì Enrico Borriello Università degli Studi di Napoli Federico II & INFN Sezione di Napoli Dark Matter Electron Anisotropy: A universal upper limit Based on Borriello, Maccione, and Cuoco arxiv:

2 Outline... Part 1: Dark Matter The content of the Universe Candidates Detection techniques Part 4: Astrophysical implications Two possibilities AP dominated anisotropy scenario Excluding the DM interpretation of a forthcoming anisotropy detection Part 2: DM Galactic Substructures N-body simulations Detectability at γ-rays energies Detectability at radio wavelenghts Angular power spectrum of γ-rays Part 3: DM electron anisotropy Definition of dipole anisotropy Fermi LAT upper limit Limit cases Clumpiness and anisotropy Universality of the DM electron anisotropy upper limit

3 Part 1: Dark Matter

4 Dark Matter Larson et al. arxiv: The content of the Universe Baryonic matter Atoms, ordinary matter Dark matter No interaction with light Only gravitational effect dark energy 72.8 % baryonic matter 4.5 % dark matter 22.7 % 4.5 % 22.7 %. Dark energy 72.8 % Anti-gravity accelerated expansion of he Universe

5 Dark Matter Feng arxiv: Candidates WIMPs SuperWIMPs Light gravitino Hidden DM Sterile neutinos Axions Motivation Gauge hierar. prob. Gauge hierar. prob. Gauge hierar. & NP flavor prob. Gauge hierar. & NP flavor prob. Neutino masses Strong CP Naturally correct Ω Yes Yes No Possible No No Production mechanism Freeze out Decay Thermal Various Various Various Mass range GeV TeV GeV TeV ev kev GeV TeV kev µev mev Temperature Cold Cold/Warm Cold/Warm Cold/Warm Warm Cold Dir. detection Ind. detection CMB & BBN Colliders Collisional

6 Dark Matter Detection techniques Direct detection Phenomenon: Interaction of the DM with the visible matter Experiments: Underground laboratories Phys. observable: Energy recoil of a nucleus Inirect detection Phenomenon: DM annihilation or decay Experiments: Space telescopes Phys. observable: Cosmic ray spectrum Colliders Phenomenon: Production of DM Experiments: Particle accelerators Phys. observable: Missing transverse momentum

7 Dark Matter Detection techniques: Indirect detection χ+χ q+q π +... νµ + µ π γ+γ p +... νµ+νe + e Dark matter search in all-sky surveys Planck... W ++ W...

8 Dark Matter Detection techniques: Indirect detection χ+χ q+q π +... νµ + µ π γ+γ p +... νµ+νe + e Dark matter search in all-sky surveys Fermi LAT... W ++ W...

9 Dark Matter Ackermann et al. ArXiv: Detection techniques: Indirect detection χ+χ q+q π +... νµ + µ π γ+γ p +... νµ+νe + e Dark matter search in (particle) cosmic rays Fermi LAT... W ++ W... χ+χ µ+ + µ ν µ +ν e + e ν µ +ν e + e +

10 Dark Matter Adriani et al. ArXiv: Detection techniques: Indirect detection χ+χ q+q π +... νµ + µ π γ+γ p +... νµ+νe + e Dark matter search in (particle) cosmic rays Pamela... W ++ W... χ+χ µ+ + µ ν µ +ν e + e ν µ +ν e + e +

11 Dark Matter Adriani et al. ArXiv: Detection techniques: Indirect detection χ+χ q+q π +... νµ + µ π γ+γ p +... νµ+νe + e Dark matter search in (particle) cosmic rays Pamela... W ++ W... χ+χ µ+ + µ ν µ +ν e + e ν µ +ν e + e +

12 Part 2: DM galactic substructures

13 DM galactic substructures N-body simulations Diemand et al. arxiv: Springer at al. arxiv: Numerical simulations: smooth and homogeneous Universe before a redshift of z = 100. Then, the tiny fluctuations of the matter distribution began to collapse because of gravity. The first objects to form are Earth-mass dark-matter subhaloes. 40 kpc3 Stable against gravitational disruption: over 1017 clumps survive. Mass distribution: m kpc3

14 DM galactic substructures N-body simulations Diemand et al. arxiv: Springer at al. arxiv: The highest mass objects: 1010 M (10% of the mass of the Milky Way)Equipartition in mass among the smooth halo and the subhaloes distri_ bution is found if the results are extra_ polated till Earth mass substructures. Current numerical resolution: resolution M Via Lactea II 40 kpc3 104 M Aquarius 800 kpc3

15 DM galactic substructures Detectability at γ-rays energies DM particle: Neutralino DM mass: 40 GeV Annihilation rate: cm3 s-1 Energy treshold: 3 GeV Annihilation channel: χ + χ b quarks π0 γ + γ Pieri et al. arxiv:arxiv: Full sky map of the number of photons produced by DM annihilation Observable clumps: Via Lactea II 9.2 ± 2.6 at 3 σ

16 DM galactic substructures Detectability at radio wavelenghts clump # distance kpc scale rad. kpc density par. GeV c-2cm-3 GMF µg flux GeV cm-2s-1hz Clumps from 107 to 1010 Msun Borriello et al. arxiv:arxiv: At ν 23 GHz (1st WMAP band) the flux is ) order GeV cm-2s-1hz-1 (100 GeV χ 1 e± diffuse in a 1 kpc radius sphere: Ω 0.1 sr (d 5 kpc) Flux/Ω GeV cm-2s-1hz-1sr-1 Experiment Sensitivity GeV cm-2 s-1 Hz-1 sr-1 WMAP ALMA 10 19

17 DM galactic substructures Angular power spectrum of γ-rays Fluctuation of the radiation intensity coming from the angular region Ω: I = I I = lm a lm Y lm I Clumps from 107 to 1010 Msun Siegal-Gaskins arxiv: Angular power spectrum of δi (Ω ): C l = a lm 2 = m alm 2 2 l 1 Clumps from 10 to 1010 Msun

18 DM galactic substructures Angular power spectrum of γ-ray emission Fluctuation of the radiation intensity coming from the angular region Ω: I = I I = lm a lm Y lm I Siegal-Gaskins arxiv: Angular power spectrum of δi (Ω ): C l = a lm 2 = m alm 2 2 l 1 DM particle: Neutralino (MSSM) DM mass: 85 GeV Annihilation rate: cm3 s-1 Energy treshold: 10 GeV Annihilation channel: χ + χ quarks π0 γ + γ

19 Intelude: Why electron anisotropy could be better? A lot of uncertainty affects every attempt to detect the DM Its nature (mass, rate of annihilation or decay, etc.) Spiked or cored galactic mass density profile? Smooth or clumpy distribution etc... DM electron intrinsic anisotropy will be defined in terms of a ratio in which the two term vary in a coherent way with respect to integrated unknowns. Any multiplicative factors is simplified. Electrons and positrons can travel only few kpc. kpc Almost no difference among spiked and cored profiles

20 Part 3: Electron anisotropy

21 Electron anisotropy e.g. Berezinskii et al., North Holland, 1990 Definition of dipole anisotropy I = cosmic rays intensity (# of particles/sr/cm2/s) I E d Total flux: E = I max Diffusion in the turbulent GMF almost isotropic flux Residual degree of anisotropy: anisotropy I max I min = I max I min Dipole anisotropy: Total flux: = 4 I 0 = nv Flux from z : z = I E =I 0 E I 1 E cos 4 I 3 1 Anisotropy: I1 = I0 I min

22 Electron anisotropy e.g. Berezinskii et al., North Holland, 1990 Definition of dipole anisotropy I = cosmic rays intensity (# of particles/sr/cm2/s) Total flux: E = I E d z = D zz Diffusion in the turbulent GMF almost isotropic flux Residual degree of anisotropy: anisotropy I max I min = I max I min Dipole anisotropy: Total flux: n z In general: 3 D = v If the propagation is isotropic: isotropic I E =I 0 E I 1 E cos = 4 I 0 = nv 4 I Flux from z : z = 3 1 In a diffusive approach: approach 3 D E = v Anisotropy: I1 = I0

23 Electron anisotropy Fermi LAT upper limit Fermi LAT Collaboration, arxiv: Fermi LAT Upper limits on the integrated dipole anisotropy versus the minimum energy for different confidence levels. 1σ 3σ

24 Electron anisotropy Limit cases Total flux = Astrophysical flux + Dark Matter flux Intrinsic degree of anisotropy: / / 3 D AS DM DM AS = AS DM v AS DM 1/ AS 1/ DM 3 D i i = v i DM S = DM / DM, 0 energy is fixed AP AP energy is fixed DM S S

25 Electron anisotropy Borriello et al. arxiv:arxiv: Clumpiness and anisotropy The ideal case: The real case: Several MC simulation of the distribution of substructure. We are dealing with 1017 substructures! Flux from each substructure. Sum over the distribution. Mean over the realizations. We start evaluating the mean values analytically. We discover that the smooth halo and the small clumps do not contribute to the anisotropy o 10 M mean flux, zero anisotropy 10 o 1010 M 100 MC realizations high mass 3 D E DM DM = smooth low mass high mass v DM DM DM

26 Electron anisotropy Universality of the DM electron anisotropy upper limit 3 D E DM DM = v DM profile: NFW propagation: KRA Mass: From 100 to 3500 GeV δap δdm Borriello et al. arxiv:arxiv: Annihilation models: quark pairs muon pairs tau particle pairs DM mass density profile: NFW (spiked) Burkert (cored) Propagation model: Kraichnan Kolmogorov 100 MC realization of the distribution of the clumps with m M for each model Annihilation rate: Independent (by def.) Local DM density: Independent (by def.)

27 Electron anisotropy Universality of the DM electron anisotropy upper limit 3 D E DM DM = v DM profile: NFW propagation: KOL Mass: From 100 to 3500 GeV δap δdm Borriello et al. arxiv:arxiv: Annihilation models: quark pairs muon pairs tau particle pairs DM mass density profile: NFW (spiked) Burkert (cored) Propagation model: Kraichnan Kolmogorov 100 MC realization of the distribution of the clumps with m M for each model Annihilation rate: Independent (by def.) Local DM density: Independent (by def.)

28 Electron anisotropy Universality of the DM electron anisotropy upper limit 3 D E DM DM = v DM profile: BUR propagation: KRA Mass: From 100 to 3500 GeV δap δdm Borriello et al. arxiv:arxiv: Annihilation models: quark pairs muon pairs tau particle pairs DM mass density profile: NFW (spiked) Burkert (cored) Propagation model: Kraichnan Kolmogorov 100 MC realization of the distribution of the clumps with m M for each model Annihilation rate: Independent (by def.) Local DM density: Independent (by def.)

29 Electron anisotropy Universality of the DM electron anisotropy upper limit 3 D E DM DM = v DM profile: BUR propagation: KOL Mass: From 100 to 3500 GeV δap δdm Annihilation models: quark pairs muon pairs tau particle pairs DM mass density profile: NFW (spiked) Burkert (cored) Propagation model: Kraichnan Kolmogorov 100 MC realization of the distribution of the clumps with m M for each model Annihilation rate: Independent (by def.) Local DM density: Independent (by def.)

30 Part 4: Astrophisical implications

31 Astrophysical implications Excluding the DM interpretation of a forthcoming anisotropy detection UL 2 AP e.g. energy = 500 GeV 2nd possibility e.g. energy = 500 GeV 1 ~10 1 ~ 10 2 AP 2nd possibility ~ UL DM 1 AP fixed 1st possibility ~10 2 DM 3 AP ~10 S 1 1 ~ 10 fixed 1st possibility ~ ~10 S

32 Astrophysical implications AP anisotropy dominated scenario Di Bernardo et al. ArXiv: AP DM Nearby pulsars (within 2 kpc, KRA diffusion setup) contribution is able to explain the excess seen by Fermi LAT with respect to a standard electron and positron astrophysical background. The same model is able to perfectly reproduce the positron fraction observed by Pamela. The associ_ ated electron anisotropy would be on the verge of being dete_ cted by Fermi LAT.

33 Astrophysical implications Excluding the DM interpretation of a forthcoming anisotropy detection UL 2 AP e.g. energy = 500 GeV 2nd possibility e.g. energy = 500 GeV 1 ~10 1 ~ 10 2 AP 2nd possibility 1 ~ 10 detection! ~ UL DM 1 AP fixed 1st possibility ~10 2 DM 3 AP ~10 S 1 fixed 1st possibility ~ ~10 S

34 Astrophysical implications Excluding the DM interpretation of a forthcoming anisotropy detection Conclusions: Dipole anisotropy can exceed the DM intrinsic upper limit only thanks to the contribution of non standard astrophy_ sical sources. sources If a detection will be made by Fermi LAT in the next ten years, then this argument could be used as a criterion to deduce the presence of exotic astrophysical sources. The possibility that such a high degree of anisotropy could be entirely due to a near DM clump is ruled out. out 2 AP e.g. energy = 500 GeV 2nd possibility 1 ~ 10 detection! ~ UL DM 1 AP fixed 1st possibility ~ ~10 S