Dan Hooper Particle Astrophysics Center Fermi National Accelerator Laboratory dhooper@fnal

1. MeV Dark Matter With Couplings To Neutrinos Dan Hooper Particle Astrophysics Center Fermi National Accelerator Laboratory dhooper@fnal.gov 2007 Pheno Symposium University of Wisconsin, Madison

2. 511 keV Emission from the Galactic Bulge • INTEGRAL/SPI has observed bright 511 keV emission from the bulge (1.3 x 1043 positrons injected per second) • Gaussian, spherically symmetric morphology (FWHM of 8˚) • The source of these positrons remains unknown Dan Hooper - MeV Dark Matter With Couplings to Neutrinos

3. 511 keV Emission from the Galactic Bulge • Type Ia supernovae are unable to generate the observed injection rate (too few escape) • Hypernovae (type Ic SNe) or Gamma Ray Bursts could potentially generate enough positrons if high estimates for rates are considered • Even if the injection rate is sufficient, a mechanism is required to transport from disk to bulge - appears difficult Dan Hooper - MeV Dark Matter With Couplings To Neutrinos

4. 511 keV Emission and MeV Dark Matter • The INTEGRAL morphology matches well that which would be generated through the annihilation (or decay) of dark matter • 1-10 MeV dark matter particles annihilating to e+e- could simultaneously generate the measured dark matter relic abundance, and the observed 511 keV emission Boehm, Hooper, Silk, Casse, Paul, PRL, astro-ph/0309686 Dan Hooper - MeV Dark Matter With Couplings To Neutrinos

5. 511 keV Emission and MeV Dark Matter • The INTEGRAL morphology matches well that which would be generated through the annihilation (or decay) of dark matter • 1-10 MeV dark matter particles annihilating to e+e- could simultaneously generate the measured dark matter relic abundance, and the observed 511 keV emission Boehm, Hooper, Silk, Casse, Paul, PRL, astro-ph/0309686 The Mega-tron Dan Hooper - MeV Dark Matter With Couplings To Neutrinos

6. 511 keV Emission and MeV Dark Matter • A simple scalar dark matter particle (), annihilating via the s-channel exchange of a new gauge boson (U) • Light mediator, lack of Z-coupling avoids stringent LEP (and other) constraints e-   e+ Boehm, Hooper, Silk, Casse, Paul, PRL, astro-ph/0309686; Boehm and Fayet, Nucl. Phys. B, hep-ph/0305261 Dan Hooper - MeV Dark Matter With Couplings To Neutrinos

7. Coupling to Neutrinos? • The U-neutrino-neutrino coupling is not determined by astrophysical or other considerations in this scenario • Neutrino-electron scattering experiments place the most stringent constraints • If the U coupling to neutrinos is comparable to its coupling to electrons, dark matter-neutrino scattering can be significant   Hooper, M. Kaplinghat, K. Zurek, L. Strigari, astro-ph/0704.2558 Dan Hooper - MeV Dark Matter With Couplings To Neutrinos

8. Kinetic Decoupling • Neutrino-dark matter elastic scattering keeps the dark matter in kinetic equlibrium well after the number density freezes out • Setting equal to H, yields:   2 Hooper, M. Kaplinghat, K. Zurek, L. Strigari, astro-ph/0704.2558 Dan Hooper - MeV Dark Matter With Couplings To Neutrinos

9. Kinetic Decoupling • The kinetic decoupling temperature can be used to estimate the cutoff in the scale scale power spectrum • Which in our MeV-dark matter scenario yields:   Hooper, M. Kaplinghat, K. Zurek, L. Strigari, astro-ph/0704.2558 Dan Hooper - MeV Dark Matter With Couplings To Neutrinos

10. MeV Dark Matter and Small Scale Power • The matter power spectrum in these scenarios resembles somewhat that found for warm dark matter m=1 MeV, Tkd=1 keV, 10 keV Warm DM limit (Ly-) Hooper, M. Kaplinghat, K. Zurek, L. Strigari, astro-ph/0704.2558 Dan Hooper - MeV Dark Matter With Couplings To Neutrinos

11. MeV Dark Matter & Small Scale Structure Excluded by (g-2)e • If we assume a common coupling to electrons and neutrinos, we find that power is cutoff below 104-107 solar masses • For comparison, EW-scale WIMPs feature cutoffs typically around 10-3-10-8 solar masses Excluded by e scattering Relic Density OK Hooper, M. Kaplinghat, K. Zurek, L. Strigari, astro-ph/0704.2558 Dan Hooper - MeV Dark Matter With Couplings To Neutrinos

12. MeV Dark Matter & Small Scale Structure Excluded by (g-2)e • If we assume a common coupling to electrons and neutrinos, we find that power is cutoff below 104-107 solar masses • For comparison, EW-scale WIMPs feature cutoffs typically around 10-3-10-8 solar masses • After all constraints and issues are considered, suppression of structure below 105-107 solar masses is expected Excluded by e scattering Relic Density OK Fine Tuned Hooper, M. Kaplinghat, K. Zurek, L. Strigari, astro-ph/0704.2558 Dan Hooper - MeV Dark Matter With Couplings To Neutrinos

13. Missing Satellites? Excluded by (g-2)e • In the upper range of these estimates, suppression could appear in the number of observed Milky Way Satellites (ie. dwarf galaxies) • Possible solution to the so-called “missing satellites problem” Excluded by e scattering Relic Density OK Fine Tuned Hooper, M. Kaplinghat, K. Zurek, L. Strigari, astro-ph/0704.2558 Dan Hooper - MeV Dark Matter With Couplings To Neutrinos

14. High Energy Neutrino Absorption • New boson leads to resonant neutrino interactions with the cosmic neutrino background at: • For SM Z-boson, this corresponds to E~1021 eV (“Z-burst”) • For mU~MeV, E~ TeV • Energy redshift broadens the very narrow resonance • For couplings larger than ~10-5, efficient absorption occurs over the range: ER/(1+z) < E < ER Hooper, hep-ph/0701194; See also Weiler, Palomerez-Ruis, (in preparation) Dan Hooper - MeV Dark Matter With Couplings To Neutrinos

15. The Neutrinos Are Coming! • To date, no (confirmed) sources of high or ultra-high energy neutrinos have been discovered • This is likely to change soon • Experimental sensitivity is rapidly approaching that needed to detect the first extra-galactic sources of high energy neutrinos IceCube Dan Hooper - MeV Dark Matter With Couplings To Neutrinos

16. Extragalactic Sources of High Energy Neutrinos • Cosmic ray spectrum of protons/nuclei extends to ~1020 eV • pp, p interactions generate neutrinos from cosmic ray sources • The flux of neutrinos produced can be tied to the cosmic ray spectrum • “Waxman-Bahcall” Argument: Fraction of proton energy to pions Accounts for source evolution, etc. (~1) Dan Hooper - MeV Dark Matter With Couplings To Neutrinos

17. High Energy Neutrino Absorption • Observing an absorption feature in the high energy neutrino spectrum will be challenging • Requires good neutrino energy resolution (+shower) • Large volume, high resolution (small PMT spacing) experiment • Realistic goal for future designs (log E)~0.1, E2 dN/dE~ 10-7 GeV/cm2 s (high z), 10 km3 yr exposure Hooper, hep-ph/0701194 Dan Hooper - MeV Dark Matter With Couplings To Neutrinos

18. Conclusions • The predictions for small scale structure can be very different in MeV dark matter scenarios than for ordinary CDM WIMPs • Power below 104-107 solar masses is suppressed • Presents a possible solution to the missing satellites problem • Scenario can be tested by searching for ~TeV absorption lines in the cosmic neutrino spectrum