A Redshift Dependent Color-Luminosity Relation in Type 1a Supernovae

Type 1a supernova magnitudes are used to fit cosmological parameters under the assumption the model will fit the observed redshift dependence. We test this assumption with the Union 2.1 compilation of 580 sources. Several independent tests find the existing model fails to account for a significant correlation of supernova color and redshift. The correlation of magnitude residuals relative to the $\Lambda CDM$ model and $color \times redshift$ has a significance equivalent to 13 standard deviations, as evaluated by randomly shuffling the data. Extending the existing $B-V$ color correction to a relation linear in redshift improves the goodness of fit $\chi^{2}$ by more than 50 units, an equivalent 7-$\sigma$ significance, while adding only one parameter. The $color-redshift$ correlation is quite robust, cannot be attributed to outliers, and passes several tests of consistency. We review previous hints of redshift dependence in color parameters found in bin-by-bin fits interpreted as parameter bias. We show that neither the bias nor the change $\Delta \chi^{2}$ of our study can be explained by those effects. The previously known relation that bluer supernovae have larger absolute luminosity tends to empirically flatten out with increasing redshift. The best-fit cosmological dark energy density parameter is revised from $\Omega_{\Lambda} =0.71 \pm 0.02$ to $\Omega_{\Lambda} = 0.74 \pm 0.02$ assuming a flat universe. One possible physical interpretation is that supernovae or their environments evolve significantly with increasing redshift.Comment: 6 pages, 3 figures. Accepted for publication in MNRAS Letters. Contains few corrections and extra added details to 1303.0580v

Boosted dark matter signals uplifted with self-interaction

We explore detection prospects of a non-standard dark sector in the context of boosted dark matter. We focus on a scenario with two dark matter particles of a large mass difference, where the heavier candidate is secluded and interacts with the standard model particles only at loops, escaping existing direct and indirect detection bounds. Yet its pair annihilation in the galactic center or in the Sun may produce boosted stable particles, which could be detected as visible Cherenkov light in large volume neutrino detectors. In such models with multiple candidates, self-interaction of dark matter particles is naturally utilized in the {\it assisted freeze-out} mechanism and is corroborated by various cosmological studies such as N-body simulations of structure formation, observations of dwarf galaxies, and the small scale problem. We show that self-interaction of the secluded (heavier) dark matter greatly enhances the capture rate in the Sun and results in promising signals at current and future experiments. We perform a detailed analysis of the boosted dark matter events for Super-Kamiokande, Hyper-Kamiokande and PINGU, including notable effects such as evaporation due to self-interaction and energy loss in the Sun.Comment: 24 pages, 8 figures; discussion on the boosted DM flux from the Earth, references added, typos corrected; published in PL

Direct Detection of Dark Matter with MadDM v.2.0

We present MadDM v.2.0, a numerical tool for dark matter physics in a generic model. This version is the next step towards the development of a fully automated framework for dark matter searches at the interface of collider physics, astro-physics and cosmology. It extends the capabilities of v.1.0 to perform calculations relevant to the direct detection of dark matter. These include calculations of spin-independent/spin-dependent nucleon scattering cross sections and nuclear recoil rates (as a function of both energy and angle), as well as a simplified functionality to compare the model points with existing constraints. The functionality of MadDM v.2.0 incorporates a large selection of dark matter detector materials and sizes, and simulates detector effects on the nuclear recoil signals. We validate the code in a wide range of dark matter models by comparing results from MadDM v.2.0 to the existing tools and literature.Comment: 38 pages, 8 figures, 5 tables; v2. Matches the version accepted for publication in Physics of the Dark Universe. We have improved table IV by validating the other sps points of the MSS

Boosted Dark Matter at the Deep Underground Neutrino Experiment

We investigate the detection prospects of a non-standard dark sector in the context of boosted dark matter. We consider a scenario where two stable particles have a large mass difference and the heavier particle accounts for most of dark matter in our current universe. The heavier candidate is assumed to have no interaction with the standard model particles at tree-level, hence evading existing constraints. Although subdominant, the lighter dark matter particles are efficiently produced via pair-annihilation of the heavier ones in the center of the Galaxy or the Sun. The large Lorentz boost enables detection of the non-minimal dark sector in large volume terrestrial experiments via exchange of a light dark photon with electrons or nuclei. Various experiments designed for neutrino physics and proton decay are examined in detail, including Super-K and Hyper-K. In this study, we focus on the sensitivity of the far detector at the Deep Underground Neutrino Experiment for boosted dark matter produced in the center of the Sun, and compare our findings with recent results for boosted dark matter produced in the galactic center.Comment: 11 Pages, 5 Figure