Tijana Prodanović University of Novi Sad, Serbia Brian D. Fields University of Illinois at Urbana-Champaign Double Trouble: The Lithium Problems June 13 th, 2007 KICP, University of Chicago

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Outline The Lithium-7 Problem  WMAP prediction > observation  Gets worse! Structure-formation cosmic-rays A Lithium-6  GCR nucleosynthesis  Cosmic-Ray prediction < observation  New problem! Gamma-Ray Problem: “GeV excess”  TeV excess?

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Lithium Observations Lithium observed in halo stars Plateau & plateau? Asplund et al. (2006) Expected but inconsistent Unexpected 7 Li plateau 6 Li plateau

University of ChicagoJune, 13 th 2007 Tijana Prodanovic The Lithium Problem 7 Li made predominantly in the Big Bang Nucleosynthesis (Cyburt, Fields, Schramm) Low-metallicity halo stars: 7 Li plateau (Spite & Spite 1982) → indicate primordial lithium But WMAP (2003) result: primordial Li~ 2-3 times higher than observed in halo-stars The lithium problem Any pre-Galactic sources of Li would contribute to halo-stars and make problem even worse! And then there were cosmological cosmic rays… Cyburt 2005 (private communication) 4 He D 3 He 7 Li

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Structure Formation Cosmic Rays Structure formation shocks - cosmological shocks that arise from baryonic infall and merger events during the growth of large-scale structures (Miniati 2000; Pavlidou & Fields 2006) Diffusive shock acceleration mechanism structure formation/cosmological cosmic rays X-ray observations of galaxy clusters: non-thermal excess (see eg. Fusco-Femiano et al. 2004) A large reservoir of energy and non- thermal pressure Miniati et al. 2000

University of ChicagoJune, 13 th 2007 Tijana Prodanovic How To Find Them? Implications still emerging CRs make gamma-rays  Will contribute to extragalactic gamma-ray background (Loeb & Waxman 2000) CRs make LiBeB (Fields, Olive, Ramaty, Vangioni-Flam)  But structure formation CRs are mostly protons and α-particles → only LiBeB  Will contribute to halo star Li abundance “Li problem” even worse! “Li problem” even worse! (Suzuki & Inoue 2002) How much worse can it get?

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Hadronic Cosmic-Ray Interaction Observables  Gamma-rays  Lithium, Beryllium & Boron

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Li-g-ray Connection Any cosmic-ray source produces both gamma- rays and lithium Connected essentially with ratio of reaction rates (Fields and Prodanović 2005)  Li abundance: local CR fluence  Diffuse extragalactic : CR fluence across Universe Given one, constrain other

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Extragalactic Gamma-Ray Background Still emission at the Galactic poles Subtract the Galaxy EGRB is the leftover (Strong 2004, Sreekumar 1998) Guaranteed components (Pavlidou & Fields 2002)  Normal galaxies  Blazars (Stecker & Salamon 1996)  Any other cosmic-ray source

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Gamma-Ray Spectrum  “Pionic” gamma-rays  Distinctive spectrum – pion “bump”; peaks at m π /2 (Stecker 1971; Dermer 1986)  But no strong evidence for pion “bump” either in the EGRB or in the MW diffuse gamma-ray spectrum  Can use the shape of the spectrum (Pfrommer & Enßlin 2003) to find max “pionic” fraction (Prodanović & Fields 2004)

University of ChicagoJune, 13 th 2007 Tijana Prodanovic SFCR“pionic” g-rays from EGRB Structure Formation Cosmic Rays – assume all come from strong shocks with spectrum (about the same source spectrum as for Galactic CRs, but does not suffer propagation effects) Assume all pionic g-rays are from SFCRs and all come from single redshift (unlike for Galactic CRs, history not known in this case) Max “pionic” fraction z=0 z=10 Prodanović and Fields(2004a)

University of ChicagoJune, 13 th 2007 Tijana Prodanovic SFCRs and Lithium Use Li-gamma-ray connection From observed EGRB estimate maximal pionic contribution, assign it to structure formation CRs → estimate Li SFCR production (depending on the assumed redshift ) Structure formation CRs can be potentially significant source of pre-Galactic Lithium! Need constrain structure formation CRs!

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Searching for SFCRs in High Velocity Clouds  Clouds of gas falling onto our Galaxy (Wakker & van Woerden 1997)  Some high-velocity clouds show evidence for little or no dust  Origins:  Galactic fountain model (Shapiro & Field 1976)  Extragalactic  Magellanic Stream-type objects or  gas left over from formation of the Galaxy (Oort, Blitz, Braun)  Some high-velocity clouds have metallicity 10% of solar low-metallicity, HVCs with little dust are promising sites for testing pre-Galactic Li and SFCRs (Prodanović and Fields 2004b)

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Outline The Lithium-7 Problem  WMAP prediction > observation  Gets worse! Structure-formation cosmic-rays A Lithium-6  GCR nucleosynthesis  Cosmic-Ray prediction < observation  New problem! Gamma-Ray Problem: “GeV excess”  TeV excess?

University of ChicagoJune, 13 th 2007 Tijana Prodanovic How Well Do We Understand 6 Li? 7 Li origin: cosmic rays + BBN But 6 Li only made by cosmic rays via fusion and spallation reactions. Standard assumption: 6 Li Solar made by Galactic CRs But recent observations indicate a 6 Li Solar plateau? Also recent theories: 6 Li from dark matter decay Use Li—gamma-ray connection to test the standard picture of 6 Li GCR nucleosynthesis. Asplund et al.(2006)

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Galactic CRs and 6 Li Use Li-gamma connection to check if things add up Initial estimate  Simple CR and pionic gamma-ray spectrum (analytic)  6 Li Solar demands 3x larger EGRB than observed! In full detail, numerically  GCR spectrum Solve propagation equation for Leaky Box model  Gamma-ray spectrum Numerically calculate from Dermer (1986) model

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Galactic CRs and 6 Li : Results 6 Li production channels included  fusion  spallation (take average CNO abundance ½ Solar )  2-step reactions, eg. Pionic gamma-ray fraction estimate (normalized to the MW)  pionic (normal galaxies) is ~30% of the total EGRB Account for astration  some gas was processed in stars – some Li was destroyed  estimate astration from Deuterium: ~ 25% of gas was processed Result: 6 Li GCR ≈ Li tot Result: 6 Li GCR ≈ Li tot Gamma rays allow for only ~50% of 6 Li to be produced by GCRs! Gamma rays allow for only ~50% of 6 Li to be produced by GCRs! Prodanović & Fields (2006)

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Implications Only ~ 50% of solar 6 Li can be explained by GCRs without overproducing gamma-rays Need new important 6 Li source  Recent observations in halo stars: 6 Li plateau? But at 10% level of solar (Asplund et al. 2006)  Milky Way GCR flux higher than the cosmic mean?  MW CR flux--star formation rate ratio not the cosmic mean?  Low-energy CR component? Energetics and LiBeB ratio constraints Realistic estimate of pionic gamma-ray spectrum required normalization to Milky Way…

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Outline The Lithium-7 Problem  WMAP prediction > observation  Gets worse! Structure-formation cosmic-rays A Lithium-6  GCR nucleosynthesis  Cosmic-Ray prediction < observation  New problem! Gamma-Ray Problem: “GeV excess”  TeV excess?

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Galactic “Pionic” Gamma Rays EGRET: GeV range Find max “pionic” flux so that “pion bump” stays below observed Galactic spectrum Galactic CRs: Max “pionic” fraction But notice the residual! GeV Excess Prodanović and Fields (2004a) Brems/IC Strong et al. (2004)

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Pionic Gamma-Rays: New Approach Though inverse Compton component at low end, cutoff at ~ TeV Recently suggested DM annihilation signal would cut off ~ 100 GeV TeV regime pionic gamma’s should dominate Thus “pionic wing” should resurface! Use GeV and TeV diffuse Galactic gamma-ray observations is sinc

University of ChicagoJune, 13 th 2007 Tijana Prodanovic TeV Diffuse Galactic Gamma-Ray Measurement  Milagro Water Cherenkov Detector  Pionic gamma’s dominate?  Unconventional spectral index  Milagro: pionic dominates indeed  Observed spectral index  Milagro: pionic only ~20% !  “ TeV excess”?  Another component? Dark matter? Point sources? Prodanović, Fields & Beacom (2006) Milagro Water Cherenkov Detector

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Point sources in Milagro Region We have identified 10 EGRET sources in Milagro region Combined extrapolated flux of these 10 sources is at least an order of magnitude higher than Milagro point at TeV energies 4 of those sources observed in TeV show significant departure from extrapolation Indicates a break in point source (mostly SNRs) spectra! Implications for GCR acceleration: max acceleration energy Need more data! Prodanović, Fields & Beacon (2006)

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Outline The Lithium-7 Problem  WMAP prediction > observation  Gets worse! Structure-formation cosmic-rays A Lithium-6  GCR nucleosynthesis  Cosmic-Ray prediction < observation  New problem! Gamma-Ray Problem: “GeV excess”  TeV excess?

University of ChicagoJune, 13 th 2007 Tijana Prodanovic New Data on the Way! GLAST:  A view into “unopened window” (up to 300 GeV)  Better extragalactic background determination  Pion feature? Cherenkov experiments: TeV window  H.E.S.S. Southern hemisphere Observing since 2004  VERITAS Northern hemisphere upcoming

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Summary SFCRs may be important source of pre-Galactic 7 Li  Make primordial Li problem even worse  HVCs can provide an independent test of the primordial Li and potential exposure to SFCRs GCR nucleosynthesis can account for only ~50% of total 6 Li produced  New Li problem?  More indication for a new important Li source  MW not a typical star-forming galaxy? Must determine Galactic pionic gamma-ray component  Use TeV and GeV gamma-ray observations is sinc  Potential TeV Excess  Break in point source (mostly SNRs) spectra

University of ChicagoJune, 13 th 2007 Tijana Prodanovic Thank You!