The Astrophysical Journal / 24/2/2010

Dark Fluid: A Unified Framework for Modified Newtonian Dynamics,
Dark Matter, and Dark Energy
HongSheng Zhao and Baojiu Li
2010 ApJ 712 130-141
Abstract: http://www.iop.org/EJ/abstract/-alert=41052/0004-637X/712/1/130
Full text PDF: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/130/apj_712_1_130.pdf
Full text HTML: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/130/apj_712_1_130.html

Empirical theories of dark matter (DM) like modified Newtonian
dynamics (MOND) gravity and of dark energy (DE) like f(R) gravity
were motivated by astronomical data. But could these theories be
branches rooted from a more general and hence generic framework?
Here we propose a very generic Lagrangian of such a framework based
on simple dimensional analysis and covariant symmetry requirements,
and explore various outcomes in a top-down fashion. The desired
effects of quintessence plus cold DM particle fields or MOND-like
scalar field(s) are shown to be largely achievable by one vector
field only. Our framework preserves the covariant formulation of
general relativity, but allows the expanding physical metric to be
bent by a single new species of dark fluid flowing in spacetime. Its
non-uniform stress tensor and current vector are simple functions of
a vector field with variable norm, not coupled with the baryonic
fluid and the four-vector potential of the photon fluid. The dark
fluid framework generically branches into a continuous spectrum of
theories with DE and DM effects, including the f(R) gravity,
tensor-vector-scalar-like theories, Einstein-Aether, and nL theories
as limiting cases. When the vector field degenerates into a pure
scalar field, we obtain the physics for quintessence. Choices of
parameters can be made to pass Big Bang nucleosynthesis,
parameterized post-Newtonian, and causality constraints. In this
broad setting we emphasize the non-constant dynamical field behind
the cosmological constant effect, and highlight plausible
corrections beyond the classical MOND predictions.

Observations of Milky Way Dwarf Spheroidal Galaxies with the Fermi-Large Area Telescope Detector and Constraints on Dark Matter Models A. A. Abdo, M. Ackermann, M. Ajello, W. B. Atwood, L. Baldini, J. Ballet, G. Barbiellini, D. Bastieri, K. Bechtol, R. Bellazzini, B. Berenji, E. D. Bloom, E. Bonamente, A. W. Borgland, J. Bregeon, A. Brez, M. Brigida, P. Bruel, T. H. Burnett, S. Buson, G. A. Caliandro, R. A. Cameron, P. A. Caraveo, J. M. Casandjian, C. Cecchi, A. Chekhtman, C. C. Cheung, J. Chiang, S. Ciprini, R. Claus, J. Cohen-Tanugi, J. Conrad, A. de Angelis, F. de Palma, S. W. Digel, E. do Couto e Silva, P. S. Drell, A. Drlica-Wagner, R. Dubois, D. Dumora, C. Farnier, C. Favuzzi, S. J. Fegan, W. B. Focke, P. Fortin, M. Frailis, Y. Fukazawa, P. Fusco, F. Gargano, N. Gehrels, S. Germani, B. Giebels, N. Giglietto, F. Giordano, T. Glanzman, G. Godfrey, I. A. Grenier, J. E. Grove, L. Guillemot, S. Guiriec, M. Gustafsson, A. K. Harding, E. Hays, D. Horan, R. E. Hughes, M. S. Jackson, T. E. Jeltema, G. Johannesson, A. S. Johnson, R. P. Johnson, W. N. Johnson, T. Kamae, H. Katagiri, J. Kataoka, M. Kerr, J. Knodlseder, M. Kuss, J. Lande, L. Latronico, M. Lemoine-Goumard, F. Longo, F. Loparco, B. Lott, M. N. Lovellette, P. Lubrano, G. M. Madejski, A. Makeev, M. N. Mazziotta, J. E. McEnery, C. Meurer, P. F. Michelson, W. Mitthumsiri, T. Mizuno, A. A. Moiseev, C. Monte, M. E. Monzani, E. Moretti, A. Morselli, I. V. Moskalenko, S. Murgia, P. L. Nolan, J. P. Norris, E. Nuss, T. Ohsugi, N. Omodei, E. Orlando, J. F. Ormes, D. Paneque, J. H. Panetta, D. Parent, V. Pelassa, M. Pepe, M. Pesce-Rollins, F. Piron, T. A. Porter, S. Profumo, S. Raino, R. Rando, M. Razzano, A. Reimer, O. Reimer, T. Reposeur, S. Ritz, A. Y. Rodriguez, M. Roth, H. F.-W. Sadrozinski, A. Sander, P. M. Saz Parkinson, J. D. Scargle, T. L. Schalk, A. Sellerholm, C. Sgro, E. J. Siskind, D. A. Smith, P. D. Smith, G. Spandre, P. Spinelli, M. S. Strickman, D. J. Suson, H. Takahashi, T. Takahashi, T. Tanaka, J. B. Thayer, J. G. Thayer, D. J. Thompson, L. Tibaldo, D. F. Torres, A. Tramacere, Y. Uchiyama, T. L. Usher, V. Vasileiou, N. Vilchez, V. Vitale, A. P. Waite, P. Wang, B. L. Winer, K. S. Wood, T. Ylinen, M. Ziegler, James S. Bullock, Manoj Kaplinghat, and Gregory D. Martinez 2010 ApJ 712 147-158 Abstract: http://www.iop.org/EJ/abstract/-alert=41052/0004-637X/712/1/147 Full text PDF: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/147/apj_712_1_147.pdf Full text HTML: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/147/apj_712_1_147.html
We report on the observations of 14 dwarf spheroidal galaxies (dSphs) with the Fermi Gamma-Ray Space Telescope taken during the first 11 months of survey mode operations. The Fermi telescope, which is conducting an all-sky g-ray survey in the 20 MeV to >300 GeV energy range, provides a new opportunity to test particle dark matter models through the expected g-ray emission produced by pair annihilation of weakly interacting massive particles (WIMPs). Local Group dSphs, the largest galactic substructures predicted by the cold dark matter scenario, are attractive targets for such indirect searches for dark matter because they are nearby and among the most extreme dark matter dominated environments. No significant g-ray emission was detected above 100 MeV from the candidate dwarf galaxies. We determine upper limits to the g-ray flux assuming both power-law spectra and representative spectra from WIMP annihilation. The resulting integral flux above 100 MeV is constrained to be at a level below around 10-9 photons cm-2 s-1. Using recent stellar kinematic data, the g-ray flux limits are combined with improved determinations of the dark matter density profile in eight of the 14 candidate dwarfs to place limits on the pair-annihilation cross section of WIMPs in several widely studied extensions of the standard model, including its supersymmetric extension and other models that received recent attention. With the present data, we are able to rule out large parts of the parameter space where the thermal relic density is below the observed cosmological dark matter density and WIMPs (neutralinos here) are dominantly produced non-thermally, e.g., in models where supersymmetry breaking occurs via anomaly mediation. The g-ray limits presented here also constrain some WIMP models proposed to explain the Fermi and PAMELA e + e - data, including low-mass wino-like neutralinos and models with TeV masses pair annihilating into muon-antimuon pairs.

Type I Planet Migration in Nearly Laminar Disks: Long-Term Behavior C. Yu, H. Li, S. Li, S. H. Lubow, and D. N. C. Lin 2010 ApJ 712 198-208 Abstract: http://www.iop.org/EJ/abstract/-alert=41052/0004-637X/712/1/198 Full text PDF: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/198/apj_712_1_198.pdf Full text HTML: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/198/apj_712_1_198.html
We carry out two-dimensional high-resolution numerical simulations of type I planet migration with different disk viscosities. We find that the planet migration is strongly dependent on disk viscosities. Two kinds of density wave damping mechanisms are discussed. Accordingly, the angular momentum transport can be either viscosity dominated or shock dominated, depending on the disk viscosities. The long-term migration behavior is different as well. Influences of the Rossby vortex instability on planet migration are also discussed. In addition, we investigate very weak shock generation in inviscid disks by small mass planets and compare the results with prior analytic results.

The Rise and Fall of Type Ia Supernova Light Curves in the SDSS-II Supernova Survey Brian T. Hayden, Peter M. Garnavich, Richard Kessler, Joshua A. Frieman, Saurabh W. Jha, Bruce Bassett, David Cinabro, Benjamin Dilday, Daniel Kasen, John Marriner, Robert C. Nichol, Adam G. Riess, Masao Sako, Donald P. Schneider, Mathew Smith, and Jesper Sollerman 2010 ApJ 712 350-366 Abstract: http://www.iop.org/EJ/abstract/-alert=41052/0004-637X/712/1/350 Full text PDF: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/350/apj_712_1_350.pdf Full text HTML: http://www.iop.org/EJ/article/-alert=41052/0004-637X/712/1/350/apj_712_1_350.html
We analyze the rise and fall times of Type Ia supernova (SN Ia) light curves discovered by the Sloan Digital Sky Survey-II (SDSS-II) Supernova Survey. From a set of 391 light curves k-corrected to the rest-frame B and V bands, we find a smaller dispersion in the rising portion of the light curve compared to the decline. This is in qualitative agreement with computer models which predict that variations in radioactive nickel yield have less impact on the rise than on the spread of the decline rates. The differences we find in the rise and fall properties suggest that a single "stretch" correction to the light curve phase does not properly model the range of SN Ia light curve shapes. We select a subset of 105 light curves well observed in both rise and fall portions of the light curves and develop a "2-stretch" fit algorithm which estimates the rise and fall times independently. We find the average time from explosion to B-band peak brightness is 17.38 +- 0.17 days, but with a spread of rise times which range from 13 days to 23 days. Our average rise time is shorter than the 19.5 days found in previous studies; this reflects both the different light curve template used and the application of the 2-stretch algorithm. The SDSS-II supernova set and the local SNe Ia with well-observed early light curves show no significant differences in their average rise-time properties. We find that slow-declining events tend to have fast rise times, but that the distribution of rise minus fall time is broad and single peaked. This distribution is in contrast to the bimodality in this parameter that was first suggested by Strovink from an analysis of a small set of local SNe Ia. We divide the SDSS-II sample in half based on the rise minus fall value, tr - tf [?] 2 days and tr - tf > 2 days, to search for differences in their host galaxy properties and Hubble residuals; we find no difference in host galaxy properties or Hubble residuals in our sample.