The Acoustic Peak in the Lyman Alpha Forest

We present the first simulation of the signature of baryonic acoustic oscillations (BAO) in Lyman alpha forest data containing 180,000 mock quasar sight-lines. We use eight large dark-matter only simulations onto which we paint the Lyman alpha field using the fluctuating Gunn-Peterson approximation. We argue that this approach should be sufficient for the mean signature on the scales of interest. Our results indicate that Lyman alpha flux provides a good tracer of the underlying dark matter field on large scales and that redshift space distortions are well described by a simple linear theory prescription. We compare Fourier and configuration space approaches to describing the signal and argue that configuration space statistics provide useful data compression. We also investigate the effect of a fluctuating photo-ionizing background using a simplified model and find that such fluctuations do add smooth power on large scales. The acoustic peak position is, however, unaffected for small amplitude fluctuations (<10%). Larger amplitude fluctuations make the recovery of the BAO signal more difficult and may degrade the achievable significance of the measurement.Comment: 10 pages, 8 figures; v2: minor revision matching version accepted by JCAP (new references, better figures, clarifications

Cosmological parameters from large scale structure - geometric versus shape information

The matter power spectrum as derived from large scale structure (LSS) surveys contains two important and distinct pieces of information: an overall smooth shape and the imprint of baryon acoustic oscillations (BAO). We investigate the separate impact of these two types of information on cosmological parameter estimation, and show that for the simplest cosmological models, the broad-band shape information currently contained in the SDSS DR7 halo power spectrum (HPS) is by far superseded by geometric information derived from the baryonic features. An immediate corollary is that contrary to popular beliefs, the upper limit on the neutrino mass m_\nu presently derived from LSS combined with cosmic microwave background (CMB) data does not in fact arise from the possible small-scale power suppression due to neutrino free-streaming, if we limit the model framework to minimal LambdaCDM+m_\nu. However, in more complicated models, such as those extended with extra light degrees of freedom and a dark energy equation of state parameter w differing from -1, shape information becomes crucial for the resolution of parameter degeneracies. This conclusion will remain true even when data from the Planck surveyor become available. In the course of our analysis, we introduce a new dewiggling procedure that allows us to extend consistently the use of the SDSS HPS to models with an arbitrary sound horizon at decoupling. All the cases considered here are compatible with the conservative 95%-bounds \sum m_\nu < 1.16 eV, N_eff = 4.8 \pm 2.0.Comment: 18 pages, 4 figures; v2: references added, matches published versio

Redshifting Rings of Power

The cosmic microwave background (CMB) has provided a precise template for features in the linear power spectrum: the matter-radiation turnover, sound horizon drop, and acoustic oscillations. In a two dimensional power spectrum in redshift and angular space, the features appear as distorted rings, and yield simultaneous, purely geometric, measures of the Hubble parameter H(z) and angular diameter distance D_A(z) via an absolute version of the Alcock-Paczynski test. Employing a simple Fisher matrix tool, we explore how future surveys can exploit these rings of power for dark energy studies. High-z CMB determinations of H and D_A are best complemented at moderate to low redshift (z < 0.5) with a population of objects that are at least as abundant as clusters of galaxies. We find that a sample similar to that of the ongoing SDSS Luminous Red Galaxy (LRG) survey can achieve statistical errors at the ~5% level for D_A(z) and H(z) in several redshift bins. This, in turn, implies errors of sigma(w)=0.03-0.05 for a constant dark energy equation of state in a flat universe. Deep galaxy cluster surveys such as the planned South Pole Telescope (SPT) survey, can extend this test out to z~1 or as far as redshift followup is available. We find that the expected constraints are at the sigma(w)=0.04-0.08 level, comparable to galaxies and complementary in redshift coverage.Comment: 8 pages, 5 figures submitted to PR

Towards an Optimal Reconstruction of Baryon Oscillations

The Baryon Acoustic Oscillations (BAO) in the large-scale structure of the universe leave a distinct peak in the two-point correlation function of the matter distribution. That acoustic peak is smeared and shifted by bulk flows and non-linear evolution. However, it has been shown that it is still possible to sharpen the peak and remove its shift by undoing the effects of the bulk flows. We propose an improvement to the standard acoustic peak reconstruction. Contrary to the standard approach, the new scheme has no free parameters, treats the large-scale modes consistently, and uses optimal filters to extract the BAO information. At redshift of zero, the reconstructed linear matter power spectrum leads to a markedly improved sharpening of the reconstructed acoustic peak compared to standard reconstruction.Comment: 20 pages, 5 figures; footnote adde

Non-linear matter power spectrum from Time Renormalisation Group: efficient computation and comparison with one-loop

We address the issue of computing the non-linear matter power spectrum on mildly non-linear scales with efficient semi-analytic methods. We implemented M. Pietroni's Time Renormalization Group (TRG) method and its Dynamical 1-Loop (D1L) limit in a numerical module for the new Boltzmann code CLASS. Our publicly released module is valid for LCDM models, and optimized in such a way to run in less than a minute for D1L, or in one hour (divided by number of nodes) for TRG. A careful comparison of the D1L, TRG and Standard 1-Loop approaches reveals that results depend crucially on the assumed initial bispectrum at high redshift. When starting from a common assumption, the three methods give roughly the same results, showing that the partial resumation of diagrams beyond one loop in the TRG method improves one-loop results by a negligible amount. A comparison with highly accurate simulations by M. Sato & T. Matsubara shows that all three methods tend to over-predict non-linear corrections by the same amount on small wavelengths. Percent precision is achieved until k~0.2 h/Mpc for z>2, or until k~0.14 h/Mpc at z=1.Comment: 24 pages, 7 figures, revised title and conclusions, version accepted in JCAP, code available at http://class-code.ne

Isocurvature modes and Baryon Acoustic Oscillations

The measurement of Baryonic Acoustic Oscillations from galaxy surveys is well known to be a robust and powerful tool to constrain dark energy. This method relies on the knowledge of the size of the acoustic horizon at radiation drag derived from Cosmic Microwave Background Anisotropy measurements. In this paper we quantify the effect of non-standard initial conditions in the form of an isocurvature component on the determination of dark energy parameters from future BAO surveys. In particular, if there is an isocurvature component (at a level still allowed by present data) but it is ignored in the CMB analysis, the sound horizon and cosmological parameters determination is biased, and, as a consequence, future surveys may incorrectly suggest deviations from a cosmological constant. In order to recover an unbiased determination of the sound horizon and dark energy parameters, a component of isocurvature perturbations must be included in the model when analyzing CMB data. Fortunately, doing so does not increase parameter errors significantly.Comment: 23 pages, 3 figure

A dynamical dark energy model with a given luminosity distance

It is assumed that the current cosmic acceleration is driven by a scalar field, the Lagrangian of which is a function of the kinetic term only, and that the luminosity distance is a given function of the red-shift. Upon comparison with Baryon Acoustic Oscillations (BAOs) and Cosmic Microwave Background (CMB) data the parameters of the models are determined, and then the time evolution of the scalar field is determined by the dynamics using the cosmological equations. We find that the solution is very different than the corresponding solution when the non-relativistic matter is ignored, and that the universe enters the acceleration era at larger red-shift compared to the standard $\Lambda CDM$ model.Comment: 4 pages, 3 figures, accepted for publication in GER

Next-to-leading resummation of cosmological perturbations via the Lagrangian picture: 2-loop correction in real and redshift spaces

We present an improved prediction of the nonlinear perturbation theory (PT) via the Lagrangian picture, which was originally proposed by Matsubara (2008). Based on the relations between the power spectrum in standard PT and that in Lagrangian PT, we derive analytic expressions for the power spectrum in Lagrangian PT up to 2-loop order in both real and redshift spaces. Comparing the improved prediction of Lagrangian PT with $N$-body simulations in real space, we find that the 2-loop corrections can extend the valid range of wave numbers where we can predict the power spectrum within 1% accuracy by a factor of 1.0 ($z=0.5$), 1.3 (1), 1.6 (2) and 1.8 (3) vied with 1-loop Lagrangian PT results. On the other hand, in all redshift ranges, the higher-order corrections are shown to be less significant on the two-point correlation functions around the baryon acoustic peak, because the 1-loop Lagrangian PT is already accurate enough to explain the nonlinearity on those scales in $N$-body simulations.Comment: 18pages, 4 figure

Cosmological constraints on unparticle dark matter

In unparticle dark matter (unmatter) models the equation of state of the unmatter is given by $p=\rho/(2d_U+1)$, where $d_U$ is the scaling factor. Unmatter with such equations of state would have a significant impact on the expansion history of the universe. Using type Ia supernovae (SNIa), the baryon acoustic oscillation (BAO) measurements and the shift parameter of the cosmic microwave background (CMB) to place constraints on such unmatter models we find that if only the SNIa data is used the constraints are weak. However, with the BAO and CMB shift parameter data added strong constraints can be obtained. For the $\Lambda$UDM model, in which unmatter is the sole dark matter, we find that $d_U > 60$ at 95% C.L. For comparison, in most unparticle physics models it is assumed $d_U<2$. For the $\Lambda$CUDM model, in which unmatter co-exists with cold dark matter, we found that the unmatter can at most make up a few percent of the total cosmic density if $d_U<10$, thus it can not be the major component of dark matter.Comment: Replaced with revised version. BAO data is added to make a tighter constraint. Version accepted for publication on Euro.Phys.J.

Large-scale periodicity in the distribution of QSO absorption-line systems

The spatial-temporal distribution of absorption-line systems (ALSs) observed in QSO spectra within the cosmological redshift interval z = 0.0--4.3 is investigated on the base of our updated catalog of absorption systems. We consider so called metallic systems including basically lines of heavy elements. The sample of the data displays regular variations (with amplitudes ~ 15 -- 20%) in the z-distribution of ALSs as well as in the eta-distribution, where eta is a dimensionless line-of-sight comoving distance, relatively to smoother dependences. The eta-distribution reveals the periodicity with period Delta eta = 0.036 +/- 0.002, which corresponds to a spatial characteristic scale (108 +/- 6) h(-1) Mpc or (alternatively) a temporal interval (350 +/- 20) h(-1) Myr for the LambdaCDM cosmological model. We discuss a possibility of a spatial interpretation of the results treating the pattern obtained as a trace of an order imprinted on the galaxy clustering in the early Universe.Comment: AASTeX, 13 pages, with 9 figures, Accepted for publication in Astrophysics & Space Scienc