Neutrino Bounds on Dark Matter

Neutrino Bounds on Dark Matter

Available online at www.sciencedirect.com Nuclear Physics B (Proc. Suppl.) 237–238 (2013) 242–245 www.elsevier.com/locate/npbps Neutrino Bounds on D...

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Available online at www.sciencedirect.com

Nuclear Physics B (Proc. Suppl.) 237–238 (2013) 242–245 www.elsevier.com/locate/npbps

Neutrino Bounds on Dark Matter Alejandro Ibarra Physik-Department T30d, Technische Universit¨at M¨unchen, James-Franck-Straße, 85748 Garching, Germany.

Abstract We review in this talk the limits on the dark matter properties which stem from indirect dark matter searches with neutrinos. Concretely we review the limits on the dark matter self-annihilation cross section, the scattering cross section with protons and the lifetime. Keywords: dark matter:annihilation, dark matter:lifetime, neutrino:flux

1. Introduction Despite the many evidences for the existence of dark matter in galaxies and in the Universe at large (see [1] for a review), practically nothing is known about the dark matter properties from the particle physics point of view, such as the spin, the mass, the self-annihilation cross section, the interaction cross section with nucleons or the lifetime. In this talk we will review the constraints on the dark matter properties that follow from dark matter searches using neutrinos as messengers, concretely the limits on the annihilation cross section, the scattering cross section with protons and the lifetime. 2. Limits on the annihilation cross section The neutrino flux from dark matter annihilations in the Milky Way in the direction determined by the galactic latitude b and the galactic longitude l reads: 1   σann v f dNνf  4π f 2m2DM dEν  ∞ ρ2halo [r(s, l, b)]ds . ×

dJhalo (l, b) = dEν

(1)

0

In this equation, the dependence on the particle physics model is encoded in the term in the bracket, mDM being the dark matter mass, dNνf /dEν the energy spectrum 0920-5632/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.nuclphysbps.2013.04.098

of neutrinos produced in the annihilation of dark matter particles in the channel “ f ” and σann v f the velocity weighted annihilation cross section in that channel. On the other hand, the dependence on the dark matter halo profile is encoded in the line of sight integral of the dark matter density distribution ρ(r), which is determined from N-body simulations. Here we will adopt, for definiteness, the Navarro-Frenk-White (NFW) density profile [2]: ρDM (r) =

ρ0 , (r/rs )[1 + (r/rs )]2

(2)

with scale radius r s = 24 kpc and ρ0 chosen to reproduce the local dark matter density ρ(r = R ) = 0.39 GeV/cm3 [3] with R = 8.5 kpc. Lastly, the parameter s is related to the Galactic coordinates, l and b, and to the distance of the Sun to the Milky Way center by  (3) r(s, l, b) = s2 + R2 − 2sR cos b cos l . The IceCube collaboration has conducted in [4] a search for muon neutrinos from dark matter annihilations in the Milky Way Center region using data collected in 367 days of live-time with the 40-string configuration (a similar search in the galactic halo using 276 days of data from the IceCube 22-string was reported in [5]). The limits on the annihilation cross section in ¯ W + W − , μ+ μ− and νν can the channels DM DM → bb,

A. Ibarra / Nuclear Physics B (Proc. Suppl.) 237–238 (2013) 242–245

10−17

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Figure 1: Upper limits at the 90% C.L. on the cross section of the self¯ W + W − , μ+ μ− and νν (taken annihilation processes DM DM → bb, from [4]).

be found in Fig.1. The limits are still a few orders of magnitude away from the annihilation cross section expected for a thermal relic σv = 3 × 10−26 cm3 s−1 . However, indirect dark matter searches with neutrinos can be relevant in scenarios with large boost factors, such as those invoked to explain in terms of dark matter annihilations the excess in the positron fraction reported by the PAMELA collaboration [6] and the excess in the total electron+positron flux reported by the Fermi-LAT collaboration [7]. In fact, the IceCube limits start to be in tension with this interpretation for the annihilation channel DM DM → τ+ τ− [4]. 3. Limits on the scattering cross section

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used to constrain the dark matter scattering cross section with protons. A search for an excess in the muon neutrino flux has been conducted by the IceCube collaboration in [10] combining data collected with AMANDA-II and with the 40-string configuration of IceCube, allowing to set limits for dark matter masses in the range 50 GeV5000 GeV. A similar search has been conducted by the Super-Kamiokande collaboration in [11]. The results of these analyses are show in Fig.3 for the spin-dependent dark matter-proton cross section as a function of the dark matter mass for annihilations into bb¯ and W + W − , compared to the limits from the direct search experiments KIMS and COUPP. It is remarkable that indirect search experiments provide limits on the spin dependent dark matter-proton cross section which are stronger than those from direct detection experiments. 4. Limits on the dark matter lifetime The astrophysical and cosmological evidences for dark matter require this particle to be very long lived, although not necessarily stable. Searches of neutrinos originated in the decay of dark matter particles allow to set limits on the dark matter lifetime, which can then be translated into limits on the parameters of the model and which can be used to better understand the mechanism that underlies the longevity of the dark matter particle, in analogy to the searches for proton decay, which allow to establish the conservation of baryon number up to very high energy scales. The flux of neutrinos produced in the decay of dark matter particles in the Milky Way halo reads: 1   Γ f dNνf  dJhalo (l, b) = dEν 4π f mDM dEν  ∞ ρhalo [r(s, l, b)]ds , (4) × 0

Dark matter particles, if they are weakly interacting, are captured in the Sun via their multiple scatterings with the protons at a rate which is proportional to the interaction cross section dark matter-proton [8]. The number of dark matter particles in the interior of the Sun, however, does not increase indefinitely due to annihilations and evaporations, which decrease this number. Therefore, after a sufficiently long time the number of dark matter particles remains constant. Concretely, and neglecting evaporation, this occurs when the annihilation rate ΓA and the capture rate Cc are in the relation ΓA  C2c [9]. Therefore, the search for a neutrino flux originated in dark matter annihilations in the Sun can be

where now Γ f is the decay width of the channel “ f ”. Limits on the dark matter lifetime have been derived in [12] from the non-observation at SuperKamiokande of an excess in the neutrino flux with respect to the expected background of atmospheric neutrinos (calculated by Honda et al. [13]). The limits are shown in Fig.4, left plot, for various decay channels. Furthermore, this reference presented prospects for the sensitivity of IceCube after one year of data taking to the dark matter lifetime, which are shown in Fig.4, right plot. The mass of the dark matter particle is bounded from above by mDM  100 TeV from the unitarity of the S -matrix if the dark matter particle is a thermal relic.

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Figure 2: Upper limits at the 90% C.L. on the spin-dependent dark matter-proton cross section from neutrino searches produced in the annihilations DM DM → bb¯ and W + W − in the Sun (taken from [10]).

However, in a class of models the dark matter particle was never in thermal equilibrium and hence the dark matter mass is completely unconstrained. In [14] it was presented the limits on the lifetime of dark matter particles from the searches for a high energy neutrino flux in AMANDA, IceCube, Auger and ANITA. The limits are shown in Fig.4 for the decay channel DM → ν¯ν and are O(1026 − 1028 ) s for masses between 10 TeV and the Grand Unification scale. 5. Conclusions Indirect dark matter searches with neutrinos have entered a golden era thanks to a new generation of neutrino detectors with very large effective volumes which allow to compensate the tiny neutrino interaction rate, thus allowing to set fairly stringent limits on the neutrino flux from exotic sources. In this talk we have reviewed the limits on the dark matter properties which can be set from present measurements in neutrino detectors, concretely the dark matter self-annihilation cross section, the interaction cross section with protons and the lifetime. References [1] G. Bertone, D. Hooper and J. Silk, Phys. Rept. 405 (2005) 279. [2] J. F. Navarro, C. S. Frenk and S. D. M. White, Astrophys. J. 490 (1997) 493. [3] R. Catena and P. Ullio, JCAP 1008 (2010) 004.

[4] R. Abbasi et al. [IceCube Collaboration], arXiv:1210.3557 [hep-ex]. [5] R. Abbasi et al. [IceCube Collaboration], Phys. Rev. D 84 (2011) 022004. [6] O. Adriani et al. [PAMELA Collaboration], Nature 458 (2009) [7] A. A. Abdo et al. [Fermi LAT Collaboration], Phys. Rev. Lett. 102 (2009) 181101. [8] W. H. Press and D. N. Spergel, Astrophys. J. 296 (1985) 679. [9] K. Griest and D. Seckel, Nucl. Phys. B 283 (1987) 681 [Erratum-ibid. B 296 (1988) 1034]. [10] R. Abbasi et al. [IceCube Collaboration], Phys. Rev. D 85 (2012) 042002. [11] T. Tanaka et al. [Super-Kamiokande Collaboration], Astrophys. J. 742 (2011) 78. [12] L. Covi, M. Grefe, A. Ibarra and D. Tran, JCAP 1004 (2010) 017. [13] M. Honda, T. Kajita, K. Kasahara, S. Midorikawa and T. Sanuki, Phys. Rev. D 75 (2007) 043006. [14] A. Esmaili, A. Ibarra and O. L. G. Peres, JCAP 1211 (2012) 034.

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DM → νν DM → Zν DM → eeν DM → μμν (ττν) DM → μμ (ττ) DM → ZZ (WW) DM → We DM → Wμ (Wτ)

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Figure 3: Lower limits at the 90% C.L. on the dark matter lifetime for various dark matter decay channels from the non-observation of an excess in the Super-Kamiokande data, left plot, and the prospects for the limits after one year of data at IceCube, right plot (taken from [12]).

Figure 4: Lower limits at the 90% C.L. on the dark matter lifetime derived using data from Super-Kamiokande, AMANDA, IceCube-22, IceCube40, Auger and ANITA assuming the two body decay DM → ν¯ν (taken from [14]).