Patrick McDonald

Cosmological parameters from combining the Lyman-α forest with CMB, galaxy clustering and SN constraints

We combine the Ly-? forest power spectrum (LYA) from the Sloan Digital Sky Survey (SDSS) and high resolution spectra with cosmic microwave background (CMB) including three-year WMAP, and supernovae (SN) and galaxy clustering constraints to derive new constraints on cosmological parameters. The existing LYA power spectrum analysis is supplemented by constraints on the mean flux decrement derived using a principle component analysis for quasar continua, which improves the LYA constraints on the linear power. We find some tension between the WMAP3 and LYA power spectrum amplitudes, at the ~2? level, which is partially alleviated by the inclusion of other observations: we find ?8 = 0.85 ? 0.02 compared to ?8 = 0.80 ? 0.03 without LYA. For the slope, we find ns = 0.965 ? 0.012. We find no evidence for the running of the spectral index in the combined analysis, dn/dlnk = ?(1.5 ? 1.2) ? 10?2, in agreement with inflation. The limits on the sum of neutrino masses are significantly improved: at 95% ( 1.3 (95% c.l.). Assuming a thermalized fourth neutrino, we find ms<0.26?eV at 95% c.l. and such a neutrino cannot be an explanation for the LSND results. In the limits of massless neutrinos, we obtain the effective number of neutrinos N?eff = 5.3?0.6+0.4?1.7+2.1?2.5+3.8 and N?eff = 3.04 is allowed only at 2.4 sigma. The constraint on the dark energy equation of state is w = ?1.04 ? 0.06. The constraint on curvature is ?k = ?0.003 ? 0.006. Cosmic strings limits are G?<2.3 ? 10?7 at 95% c.l. and correlated isocurvature models are also tightly constrained.

Can sterile neutrinos be the dark matter

We use the Ly-alpha forest power spectrum measured by the Sloan Digital Sky Survey and high-resolution spectroscopy observations in combination with cosmic microwave background and galaxy clustering constraints to place limits on a sterile neutrino as a dark matter candidate in the warm dark matter scenario. Such a neutrino would be created in the early Universe through mixing with an active neutrino and would suppress structure on scales smaller than its free-streaming scale. We ran a series of high-resolution hydrodynamic simulations with varying neutrino masses to describe the effect of a sterile neutrino on the Ly-alpha forest power spectrum. We find that the mass limit is m(s) >13 keV at 95% C.L. (9 keV at 99.9%), which is above the upper limit allowed by x-ray constraints, excluding this candidate from being all of the dark matter in this model.

How to evade the sample variance limit on measurements of redshift-space distortions

We show how to use multiple tracers of large-scale density with different biases to measure the redshift-space distortion parameter beta=f/b=(dlnD/dlna)/b (where D is the growth rate and a the expansion factor), to a much better precision than one could achieve with a single tracer, to an arbitrary precision in the low noise limit. In combination with the power spectrum of the tracers this allows a much more precise measurement of the bias-free velocity divergence power spectrum, f^2 P_m - in fact, in the low noise limit f^2 P_m can be measured as well as would be possible if velocity divergence was observed directly, with rms improvement factor ~[5.2(beta^2+2 beta+2)/beta^2]^0.5 (e.g., ~10 times better than a single tracer for beta=0.4). This would allow a high precision determination of f D as a function of redshift with an error as low as 0.1%. We find up to two orders of magnitude improvement in Figure of Merit for the Dark Energy equation of state relative to Stage II, a factor of several better than other proposed Stage IV Dark Energy surveys. The ratio b_2/b_1 will be determined with an even greater precision than beta, producing, when measured as a function of scale, an exquisitely sensitive probe of the onset of non-linear bias. We also extend in more detail previous work on the use of the same technique to measure non-Gaussianity. Currently planned redshift surveys are typically designed with signal to noise of unity on scales of interest, and are not optimized for this technique. Our results suggest that this strategy may need to be revisited as there are large gains to be achieved from surveys with higher number densities of galaxies.

Dark matter clustering: a simple renormalization group approach

I compute a renormalization group (RG) improvement to the standard beyond-linear-order Eulerian perturbation theory (PT) calculation of the power spectrum of large-scale density fluctuations in the Universe. At

The effect of the intergalactic environment on the observability of Lyα emitters during reionization

z=0

Dependence of the non-linear mass power spectrum on the equation of state of dark energy

, for a power spectrum matching current observations, lowest order RGPT appears to be as accurate as one can test using existing numerical simulation-calibrated fitting formulas out to at least

Middle Cranial Fossa Arachnoid Cysts That Come and Go

k\ensuremath{\simeq}0.3h\text{ }\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}

Antiepileptic efficacy of topiramate: assessment in two in vitro seizure models.

; although inaccuracy is guaranteed at some level by approximations in the calculation (which can be improved in the future). In contrast, standard PT breaks down virtually as soon as beyond-linear corrections become non-negligible, on scales even larger than

Primary intracranial fibrosarcoma with intratumoral hemorrhage: Neuropathological diagnosis with review of the literature

k=0.1h\text{ }\text{ }{\mathrm{Mpc}}^{\ensuremath{-}1}

Reionization: characteristic scales, topology and observability

. This extension in range of validity could substantially enhance the usefulness of PT for interpreting baryonic acoustic oscillation surveys aimed at probing dark energy, for example. I show that the predicted power spectrum converges at high