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

The Forward Physics Facility at the High-Luminosity LHC

International audienceHigh energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe Standard Model (SM) processes and search for physics beyond the Standard Model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF's physics potential

The Forward Physics Facility at the High-Luminosity LHC

High energy collisions at the High-Luminosity Large Hadron Collider (LHC) produce a large number of particles along the beam collision axis, outside of the acceptance of existing LHC experiments. The proposed Forward Physics Facility (FPF), to be located several hundred meters from the ATLAS interaction point and shielded by concrete and rock, will host a suite of experiments to probe standard model (SM) processes and search for physics beyond the standard model (BSM). In this report, we review the status of the civil engineering plans and the experiments to explore the diverse physics signals that can be uniquely probed in the forward region. FPF experiments will be sensitive to a broad range of BSM physics through searches for new particle scattering or decay signatures and deviations from SM expectations in high statistics analyses with TeV neutrinos in this low-background environment. High statistics neutrino detection will also provide valuable data for fundamental topics in perturbative and non-perturbative QCD and in weak interactions. Experiments at the FPF will enable synergies between forward particle production at the LHC and astroparticle physics to be exploited. We report here on these physics topics, on infrastructure, detector, and simulation studies, and on future directions to realize the FPF's physics potential