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We introduce a new supersymmetric extension of the standard model in which the gauge sector contains complete N = 2 supersymmetry multiplets. Supersymmetry breaking from the D-term vev of a hidden sector U (1) gauge field leads to Dirac soft supersymmetry breaking gaugino masses, and a new type of soft scalar trilinear couplings. The resulting squark and slepton masses are finite, calculable, positive and flavor universal. The Higgs soft mass squared is negative. The phenomenology of these theories differs significantly from the MSSM. We discuss a variety of possible origins for the soft operators and new fields, including models in both four and higher dimensions.

We show that mass varying neutrinos (MaVaNs) can behave as a negative pressure fluid which could be the origin of the cosmic acceleration. We derive a model independent relation between the neutrino mass and the equation of state parameter of the neutrino dark energy, which is applicable for general theories of mass varying particles. The neutrino mass depends on the local neutrino density and the observed neutrino mass can exceed the cosmological bound on a constant neutrino mass. We discuss microscopic realizations of the MaVaN acceleration scenario, which involve a sterile neutrino. We consider naturalness constraints for mass varying particles, and find that both eV cutoffs and eV mass particles are needed to avoid fine-tuning. These considerations give a (current) mass of order an eV for the sterile neutrino in microscopic realizations, which could be detectable at MiniBooNE. Because the sterile neutrino was much heavier at earlier times, constraints from big bang nucleosynthesis on additional states are not problematic. We consider regions of high neutrino density and find that the most likely place today to find neutrino masses which are significantly different from the neutrino masses in our solar system is in a supernova. The possibility of different neutrino mass in different regions of the galaxy and the local group could be significant for Z-burst models of ultra-high energy cosmic rays. We also consider the cosmology of and the constraints on the "acceleron", the scalar field which is responsible for the varying neutrino mass, and briefly discuss neutrino density dependent variations in other constants, such as the fine structure constant.

In light of recent positive results from the DAMA experiment, as well as new null results from CDMS Soudan, Edelweiss, ZEPLIN-I and CRESST, we reexamine the framework of inelastic dark matter with a standard halo. In this framework, which was originally introduced to reconcile tensions between CDMS and DAMA, dark matter particles can scatter off of nuclei only by making a transition to a nearly degenerate state that is roughly 100 keV heavier. We find that recent data significantly constrains the parameter space of the framework, but that there are still regions consistent with all experimental results. Due to the enhanced annual modulation and dramatically different energy dependence in this scenario, we emphasize the need for greater information on the dates of data taking, and on the energy distribution of signal and background. We also study the specific case of "mixed sneutrino" dark matter, and isolate regions of parameter space which are cosmologically interesting for that particular model. A significant improvement in limits by heavy target experiments such as ZEPLIN or CRESST should be able to confirm or exclude the inelastic dark matter scenario in the near future. Within the mixed sneutrino model, an elastic scattering signature should be seen at upcoming germanium experiments, including future results from CDMS Soudan.

We propose a dark matter candidate with an ''excited state'' 1-2 MeV above the ground state, which may be collisionally excited and deexcites by e e ÿ pair emission. By converting its kinetic energy into pairs, such a particle could produce a substantial fraction of the 511 keV line observed by the International Gamma-Ray Astrophysics Laboratory/SPI in the inner Milky Way. Only a small fraction of the dark matter candidates have sufficient energy to excite, and that fraction drops sharply with galactocentric radius, naturally yielding a radial cutoff, as observed. Even if the scattering probability in the inner kpc is 1% per Hubble time, enough power is available to produce the 3 10 42 pairs per second observed in the galactic bulge. We specify the parameters of a pseudo-Dirac fermion designed to explain the positron signal, and find that it annihilates chiefly to e e ÿ and freezes out with the correct relic density. We discuss possible observational consequences of this model.

We show that cold dark matter particles interacting through a Yukawa potential could naturally explain the recently observed cores in dwarf galaxies without affecting the dynamics of objects with a much larger velocity dispersion, such as clusters of galaxies. The velocity dependence of the associated cross-section as well as the possible exothermic nature of the interaction alleviates earlier concerns about strongly interacting dark matter. Dark matter evaporation in low-mass objects might explain the observed deficit of satellite galaxies in the Milky Way halo and have important implications for the first galaxies and reionization. PACS numbers: 95.35+d, Introduction. The collisionless cold dark matter (CDM) model has been highly successful in accounting for the gravitational growth of density perturbations from their small observed amplitude at early cosmic times (as imprinted on the cosmic microwave background anisotropies [1]) to the present-day structure of the Universe on large scales. However, it is far from clear that the predictions of this model are valid on small scales.New data on low mass galaxies indicate that their dark matter distribution has a core [2], in contrast to the cusped profile expected from collisionless CDM simulations [3]. The mean value of the inner logarithmic slope of the mass density profile in seven dwarf galaxies within the THINGS survey is observed to be −0.29±0.07[4], much shallower than the expected slope of ∼ −1 from pure CDM simulations. Moreover, the dynamics of dwarf spheroidal galaxies, such as Fornax [5], Ursa-Minor [6], and Sculptor [7], whose luminosities and dynamical masses are smaller by 2-3 orders of magnitude than the THINGS galaxies, indicates a characteristic core density of ∼ 0.1 ± 0.05M pc −3 = (7 ± 4) × 10 −24 g cm −3 . Since these dwarf spheroidals are dominated by dark matter throughout, it is challenging to explain their inferred cores by the gravitational interaction of the dark matter with the baryons [8]. Although it is conceivable that powerful gas outflows from an early baryon-dominated nucleus would reduce the central dark matter density in luminous galaxies [9,10], the formation of a massive baryonic nucleus would initially compress the CDM [11] and exacerbate the discrepancy that needs to be resolved [8], and also potentially violate the observed low luminosities from dwarf galaxies at higher redshifts [12,13]. High-redshift observations of dwarf galaxies must find evidence for the required strong feedback phase, or else an alternative process is at play. Some recent simulations that include feedback do not observe the appearance of cores within the lowest luminosity galaxies [14].To alleviate early signs of the above discrepancy, Spergel & Steinhardt [15] adopted the Strongly-

We propose a new solution to the supersymmetric flavor problem without flavor-blind mediation. Our proposal is to enforce a continuous or a suitably large discrete R-symmetry on weak scale supersymmetry, so that Majorana gaugino masses, trilinear A terms, and the term are forbidden. We find that replacing the minimal supersymmetric standard model with an R-symmetric supersymmetric model allows order one flavor-violating soft masses, even for squarks of order a few hundred GeV. The minimal R-symmetric supersymmetric model contains Dirac gaugino masses and R-symmetric Higgsino masses with no leftright mixing in the squark or slepton sector. Dirac gaugino masses of order a few TeV with vanishing A terms solve most flavor problems, while the R-symmetric Higgs sector becomes important at large tan.K can be accommodated if CP is preserved in the SUSY breaking sector, or if there is a moderate flavor degeneracy, which can arise naturally. 0 =, as well as neutron and electron electric dipole moments, are easily within experimental bounds. The most striking phenomenological distinction of this model is the order one flavor violation in the squark and slepton sector, while the Dirac gaugino masses tend to be significantly heavier than the corresponding squark and slepton masses.

What is the form of the neutrino mass matrix which governs the oscillations of the atmospheric and solar neutrinos? Features of the data have led to a dominant viewpoint where the mass matrix has an ordered, regulated pattern, perhaps dictated by a flavor symmetry. We challenge this viewpoint, and demonstrate that the data are well accounted for by a neutrino mass matrix which appears to have random entries.