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Constraining Neutrinos and Dark Energy with Galaxy Clustering in the Dark Energy Survey

We determine the forecast errors on the absolute neutrino mass scale and the equation of state of dark energy by combining synthetic data from the Dark Energy Survey (DES) and the Cosmic Microwave Background (CMB) Planck surveyor. We use angular clustering of galaxies for DES in 7 redshift shells up to $z\sim 1.7$ including cross-correlations between different redshift shells. We study models with massless and massive neutrinos and three different dark energy models: $Λ$CDM ($w=-1$), wCDM (constant $w$), and waCDM (evolving equation of state parameter $w(a)=w_0 + w_{a}(1-a)$). We include the impact of uncertainties in modeling galaxy bias using a constant and a redshift-evolving bias model. For the $Λ$CDM model we obtain an upper limit for the sum of neutrino masses from DES+Planck of $Σm_ν< 0.08$ eV (95\% C.L.) for a fiducial mass of $Σm_ν= 0.047$ eV, with a 1$σ$ error of 0.02 eV, assuming perfect knowledge of galaxy bias. For the wCDM model the limit is $Σm_ν< 0.10 $ eV. For a wCDM model where galaxy bias evolves with redshift, the upper limit on the sum of neutrino masses increases to 0.19 eV. DES will be able to place competitive upper limits on the sum of neutrino masses of 0.1-0.2 eV and could therefore strongly constrain the inverted mass hierarchy of neutrinos. In a wCDM model the 1$σ$ error on constant $w$ is $Δw= 0.03$ from DES galaxy clustering and Planck. Allowing $Σm_ν$ as a free parameter increases the error on $w$ by a factor of 2, with $Δw=0.06$. In a waCDM model, in which the dark energy equation of state varies with time, the errors are $Δw_0 = 0.2$ and $Δw_a = 0.42$. Including neutrinos and redshift dependent galaxy bias increases the errors to $Δw_0 = 0.35$ and $Δw_a = 0.89$.