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- I am an astrophysicists with interest in cosmology. My research topics include theoretical cosmology, cosmic microwa... moreI am an astrophysicists with interest in cosmology. My research topics include theoretical cosmology, cosmic microwave background, large-scale structure, galaxy clusters, statistical applications and data analysis. I am interested in the study of large-scale structure of the Universe and in the analysis of galaxy surveys.I am involved with several projects: Sloan Digital Sky survey III, DESI, Euclid, COrE.edit
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We investigate the accuracy of Eulerian perturbation theory for describing the matter and galaxy power spectra in real and redshift space in light of future observational probes for precision cosmology. Comparing the analytical results... more
We investigate the accuracy of Eulerian perturbation theory for describing the matter and galaxy power spectra in real and redshift space in light of future observational probes for precision cosmology. Comparing the analytical results with a large suite of N-body simulations (160 independent boxes of 13.8 (Gpc/h)^3 volume each, which are publicly available), we find that re-summing terms in the standard perturbative approach predicts the real-space matter power spectrum with an accuracy of < 2% for k < 0.20 h/Mpc at redshifts z < 1.5. This is obtained following the widespread technique of writing the resummed propagator in terms of 1-loop contributions. We show that the accuracy of this scheme increases by considering higher-order terms in the resummed propagator. By combining resummed perturbation theories with several models for the mappings from real to redshift space discussed in the literature, the multipoles of the dark-matter power spectrum can be described with sub-percent deviations from N-body results for k < 0.15h/Mpc at z < 1. As a consequence, the logarithmic growth rate, f, can be recovered with sub-percent accuracy on these scales. Extending the models to massive dark-matter haloes in redshift space, our results describe the monopole term from N-body data within 2% accuracy for scales k < 0.15 h/Mpc at z < 0.5; here f can be recovered within < 5% when the halo bias is known. We conclude that these techniques are suitable to extract cosmological information from future galaxy surveys.
We examine whether future, nearly all-sky galaxy redshift surveys, in combination with CMB priors, will be able to detect the signature of the cosmic neutrino background and determine the absolute neutrino mass scale. We also consider... more
We examine whether future, nearly all-sky galaxy redshift surveys, in combination with CMB priors, will be able to detect the signature of the cosmic neutrino background and determine the absolute neutrino mass scale. We also consider what constraints can be imposed on the effective number of neutrino species. In particular we consider two spectroscopic strategies in the near-IR, the so-called ``slitless'' and ``multi-slit'' approaches, whose examples are given by future space-based galaxy surveys, as EUCLID for the slitless case, or SPACE, JEDI, and possibly WFIRST in the future, for the multi-slit case. We find that, in combination with Planck, these galaxy probes will be able to detect at better than 3-sigma level and measure the mass of cosmic neutrinos: a) in a cosmology-independent way, if the sum of neutrino masses is above 0.1 eV; b) assuming spatial flatness and that dark energy is a cosmological constant, otherwise. We find that the sensitivity of such surveys is well suited to span the entire range of neutrino masses allowed by neutrino oscillation experiments, and to yield a clear detection of non-zero neutrino mass. The detection of the cosmic relic neutrino background with cosmological experiments will be a spectacular confirmation of our model for the early Universe and a window into one of the oldest relic components of our Universe.
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Measurements of Baryonic Acoustic Oscillations in galaxy surveys have been recognized as a powerful tool for constraining dark energy. However, this method relies on the knowledge of the size of the acoustic horizon at recombination... more
Measurements of Baryonic Acoustic Oscillations in galaxy surveys have been recognized as a powerful tool for constraining dark energy. However, this method relies on the knowledge of the size of the acoustic horizon at recombination derived from Cosmic Microwave Background Anisotropy measurements. This estimate is typically derived assuming a standard recombination scheme; additional radiation sources can delay recombination altering the cosmic ionization history and the cosmological inferences drawn from CMB and BAO data. In this paper we quantify the effect of delayed recombination on the determination of dark energy parameters from future BAO surveys such as BOSS and WFMOS. We find the impact to be small but still not negligible. In particular, if recombination is non-standard (to a level still allowed by CMB data), but this is ignored, future surveys may incorrectly suggest the presence of a redshift dependent dark energy component. On the other hand, in the case of delayed recombination, adding to the analysis one extra parameter describing deviations from standard recombination, does not significantly degrade the error-bars on dark energy parameters and yields unbiased estimates.
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We critically investigate current statistical tests applied to high redshift clusters of galaxies in order to test the standard cosmological model and describe their range of validity. We carefully compare a sample of high-redshift,... more
We critically investigate current statistical tests applied to high redshift clusters of galaxies in order to test the standard cosmological model and describe their range of validity. We carefully compare a sample of high-redshift, massive, galaxy clusters with realistic Poisson sample simulations of the theoretical mass function, which include the effect of Eddington bias. We compare the observations and simulations using the following statistical tests: the distributions of ensemble and individual existence probabilities (in the >M,>z sense), the redshift distributions, and the 2d Kolmogorov-Smirnov test. Using seemingly rare clusters from Hoyle et al. (2011), and Jee et al. (2011) and assuming the same survey geometry as in Jee et al. (2011, which is less conservative than Hoyle et al. 2011), we find that the (>M,>z) existence probabilities of all clusters are fully consistent with LCDM. However assuming the same survey geometry, we use the 2d K-S test probability to show that the observed clusters are not consistent with being the least probable clusters from simulations at >95% confidence, and are also not consistent with being a random selection of clusters, which may be caused by the non-trivial selection function and survey geometry. Tension can be removed if we examine only a X-ray selected sub sample, with simulations performed assuming a modified survey geometry.
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We compute the cosmic microwave background bispectrum arising from the cross-correlation of primordial, lensing, and Rees-Sciama signals. The amplitude of the bispectrum signal is sensitive to the matter density parameter Ω0 and the... more
We compute the cosmic microwave background bispectrum arising from the cross-correlation of primordial, lensing, and Rees-Sciama signals. The amplitude of the bispectrum signal is sensitive to the matter density parameter Ω0 and the equation of state of the dark energy, which we parametrize by wQ. We conclude that the data set of the Atacama Cosmology Telescope, combined with MAP 2-year data, or the Planck data set alone will allow us to break the degeneracy between Ω0 and wQ that arises from the analysis of the CMB power spectrum. In particular a joint measurement of Ω0 and wQ with 10% and 30% error on the two parameters, respectively, at the 90% confidence level can realistically be achieved.
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We detect a correlation between the ages of the oldest galaxies and their redshift. This opens up the possibility of measuring w(z) by computing the relative ages of the oldest galaxies in the universe as a function of redshift, dz/dt. We... more
We detect a correlation between the ages of the oldest galaxies and their redshift. This opens up the possibility of measuring w(z) by computing the relative ages of the oldest galaxies in the universe as a function of redshift, dz/dt. We show that this is a realistic possibility by computing dz/dt at z~0 from SDSS galaxies and obtain an independent estimate for the Hubble constant, H_0 = 69 \pm 12 km s-1 Mpc-1. The small number of galaxies considered at z>0.2 does not yield, currently, a precise determination of w(z), but shows that the age--redshift relation is consistent with a Standard LCDM universe with $w=-1$.
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We generalize to non-flat geometries the formalism of Simon et al (2005 Phys. Rev. D 71 123001 [astro-ph/0412269]) to reconstruct the dark energy potential. This formalism makes use of quantities similar to the horizon-flow parameters in... more
We generalize to non-flat geometries the formalism of Simon et al (2005 Phys. Rev. D 71 123001 [astro-ph/0412269]) to reconstruct the dark energy potential. This formalism makes use of quantities similar to the horizon-flow parameters in inflation, can, in principle, be made non-parametric and is general enough to be applied outside the simple, single-scalar-field quintessence. Since currently available and forthcoming data do not allow a non-parametric and exact reconstruction of the potential, we consider a general parametric description in terms of Chebyshev polynomials. We then consider present and future measurements of H(z), baryon acoustic oscillation (BAO) surveys and supernovae type 1A surveys, and investigate their constraints on the dark energy potential. We find that relaxing the flatness assumption increases the errors in the reconstructed dark energy evolution but does not open up significant degeneracies, provided that a modest prior is imposed on the geometry. Direct measurements of H(z), such as those provided by BAO surveys, are crucially important for constraining the evolution of the dark energy potential and the dark energy equation of state, especially for non-trivial deviations from the standard ΛCDM (CDM: cold dark matter) model.
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The latest cosmological data seem to indicate a significant deviation from scale invariance of the primordial power spectrum when parameterized either by a power law or by a spectral index with non-zero 'running'. This deviation, by... more
The latest cosmological data seem to indicate a significant deviation from scale invariance of the primordial power spectrum when parameterized either by a power law or by a spectral index with non-zero 'running'. This deviation, by itself, serves as a powerful tool for discriminating among theories for the origin of cosmological structures such as inflationary models. Here, we use a minimally parametric smoothing spline technique to reconstruct the shape of the primordial power spectrum. This technique is well suited to searching for smooth features in the primordial power spectrum such as deviations from scale invariance or a running spectral index, although it would recover sharp features of high statistical significance. We use the WMAP three-year results in combination with data from a suite of higher resolution cosmic microwave background experiments (including the latest ACBAR 2008 release), as well as large-scale structure data from SDSS and 2dFGRS. We employ cross-validation to assess, using the data themselves, the optimal amount of smoothness in the primordial power spectrum consistent with the data. This minimally parametric reconstruction supports the evidence for a power law primordial power spectrum with a red tilt, but not for deviations from a power law power spectrum. Smooth variations in the primordial power spectrum are not significantly degenerate with the other cosmological parameters.
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Current results from the Lyman alpha forest assume that the primordial power spectrum of density perturbations follows a simple power-law form. We present the first analysis of Lyman alpha data to study the effect of relaxing this strong... more
Current results from the Lyman alpha forest assume that the primordial power spectrum of density perturbations follows a simple power-law form. We present the first analysis of Lyman alpha data to study the effect of relaxing this strong assumption on primordial and astrophysical constraints. We perform a large suite of numerical simulations, using them to calibrate a minimally parametric framework for describing the power spectrum. Combined with cross-validation, a statistical technique which prevents overfitting of the data, this framework allows us to reconstruct the power spectrum shape without strong prior assumptions. We find no evidence for deviation from scale-invariance; our analysis also shows that current Lyman alpha data do not have sufficient statistical power to robustly probe the shape of the power spectrum at these scales. In contrast, the ongoing Baryon Oscillation Sky Survey will be able to do so with high precision. Furthermore, this near-future data will be able to break degeneracies between the power spectrum shape and astrophysical parameters.
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We analyze substructure of dark matter halos using high resolution LCDM cosmological simulations at unprecedented resolution. Two of our simulated halos have almost 107 particles within the virial radius and a spatial resolution of 0.001... more
We analyze substructure of dark matter halos using high resolution LCDM cosmological simulations at unprecedented resolution. Two of our simulated halos have almost 107 particles within the virial radius and a spatial resolution of 0.001 Rvir. Our halo sample includes a dozen clusters, two groups, and one Milky Way. In general, density profiles of dark matter halos are steeper than the Navarro, Frenk, & White (NFW) profile, with a scatter that ranges rougly from the NFW value of -1 to the Moore et al. value of -1.5. We show that the inner part of the density profile of each individual halo is rather stable over time and that its slope has been set at high redshift. This work has been supported by a NASA Graduate Student Research Program Fellowship.
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We use ΛCDM numerical simulations to model the density profiles and substructure populations in a set of sixteen dark matter halos with resolutions of up to seven million particles within the virial radius. These simulations allow us to... more
We use ΛCDM numerical simulations to model the density profiles and substructure populations in a set of sixteen dark matter halos with resolutions of up to seven million particles within the virial radius. These simulations allow us to follow robustly the formation and evolution of the central cusp over a large mass range of 1011 to 1014 Msun down to approximately 0.5% of the virial radius, and from redshift 5 to the present. The cusp of the density profile is set at redshifts of two or greater and remains remarkably stable to the present time, when considered in non-comoving coordinates.
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... University of Arizona) Jonathan Bagger (Johns Hopkins University) Karl Glazebrook (Swinburne University of Technology) Catherine Heymans (University of ... It dramatically showed that galaxieslie on the surfaces of bubble-like... more
... University of Arizona) Jonathan Bagger (Johns Hopkins University) Karl Glazebrook (Swinburne University of Technology) Catherine Heymans (University of ... It dramatically showed that galaxieslie on the surfaces of bubble-like structures, with superclusters of galaxies at their ...
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We develop a formalism to characterize the redshift evolution of the dark energy potential. Our formalism makes use of quantities similar to the Horizon-flow parameters in inflation and is general enough that can deal with multiscalar... more
We develop a formalism to characterize the redshift evolution of the dark energy potential. Our formalism makes use of quantities similar to the Horizon-flow parameters in inflation and is general enough that can deal with multiscalar quintessence scenarios, exotic matter components, and higher order curvature corrections to General Relativity. We show how the shape of the dark energy potential can be recovered non parametrically using this formalism and we present approximations analogous to the ones relevant to slow-roll inflation. Since presently available data do not allow a non-parametric and exact reconstruction of the potential, we consider a general parametric description. This reconstruction can also be used in other approaches followed in the literature (e.g., the reconstruction of the redshift evolution of the dark energy equation of state w(z)). Using observations of passively evolving galaxies and supernova data we derive constraints on the dark energy potential shape in the redshift range 0.1 < z < 1.8. Our findings show that at the 1sigma level the potential is consistent with being constant, although at the same level of confidence variations cannot be excluded with current data. We forecast constraints achievable with future data from the Atacama Cosmology Telescope.
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We show how to place constraints on cluster physics by stacking the weak lensing signals from multiple clusters found through the Sunyaev-Zeldovich (SZ) effect. For a survey that covers about 200 sq. deg. both in SZ and weak lensing... more
We show how to place constraints on cluster physics by stacking the weak lensing signals from multiple clusters found through the Sunyaev-Zeldovich (SZ) effect. For a survey that covers about 200 sq. deg. both in SZ and weak lensing observations, the slope and amplitude of the mass vs. SZ luminosity relation can be measured with few percent error for clusters at z~0.5. This can be used to constrain cluster physics, such as the nature of feedback. For example, we can distinguish a pre-heated model from a model with a decreased accretion rate at more than 5sigma. The power to discriminate among different non-gravitational processes in the ICM becomes even stronger if we use the central Compton parameter y_0, which could allow one to distinguish between models with pre-heating, SN feedback and AGN feedback, for example, at more than 5sigma. Measurement of these scaling relations as a function of redshift makes it possible to directly observe e.g., the evolution of the hot gas in clusters. With this approach the mass-L_SZ relation can be calibrated and its uncertainties can be quantified, leading to a more robust determination of cosmological parameters from clusters surveys. The mass-L_SZ relation calibrated in this way from a small area of the sky can be used to determine masses of SZ clusters from very large SZ-only surveys and is nicely complementary to other techniques proposed in the literature.
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We report on the finding of a correlation between galaxies' past star formation activity and the degree to which neighbouring galaxies rotation axes are aligned. This is obtained by cross-correlating star formation histories, derived with... more
We report on the finding of a correlation between galaxies' past star formation activity and the degree to which neighbouring galaxies rotation axes are aligned. This is obtained by cross-correlating star formation histories, derived with MOPED, and spin direction (chirality), as determined by the Galaxy Zoo project, for a sample of SDSS galaxies. Our findings suggest that spiral galaxies which formed the majority of their stars early (z > 2) tend to display coherent rotation over scales of ~10 Mpc/h. The correlation is weaker for galaxies with significant recent star formation. We find evidence for this alignment at more than the 5-sigma level, but no correlation with other galaxy stellar properties. This finding can be explained within the context of hierarchical tidal-torque theory if the SDSS galaxies harboring the majority of the old stellar population where formed in the past, in the same filament and at about the same time. Galaxies with significant recent star formation instead are in the field, thus influenced by the general tidal field that will align them in random directions or had a recent merger which would promote star formation, but deviate the spin direction.
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We use a Press-Schechter-like calculation to study how the abundance of voids changes in models with non-Gaussian initial conditions. While a positive skewness increases the cluster abundance, a negative skewness does the same for the... more
We use a Press-Schechter-like calculation to study how the abundance of voids changes in models with non-Gaussian initial conditions. While a positive skewness increases the cluster abundance, a negative skewness does the same for the void abundance. We determine the dependence of the void abundance on the non-Gaussianity parameter fnl for the local-model bispectrum—which approximates the bispectrum in some multi-field inflation models—and for the equilateral bispectrum, which approximates the bispectrum in single-field slow-roll inflation and in string-inspired DBI models of inflation. We show that the void abundance in large-scale-structure surveys currently being considered should probe values as small as fnl lesssim 10 and fnleq lesssim 30, over distance scales ~ 10 Mpc.
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Gamma-ray bursts (GRBs) are copious sources of gamma rays whose interaction with a planetary atmosphere can pose a threat to complex life. Using recent determinations of their rate and probability of causing massive extinction, we explore... more
Gamma-ray bursts (GRBs) are copious sources of gamma rays whose interaction with a planetary atmosphere can pose a threat to complex life. Using recent determinations of their rate and probability of causing massive extinction, we explore what types of universes are most likely to harbor advanced forms of life. We use cosmological N-body simulations to determine at what time and for what value of the cosmological constant (Λ) the chances of life being unaffected by cosmic explosions are maximized. Life survival to GRBs favors Lambda-dominated universes. Within a cold dark matter model with a cosmological constant, the likelihood of life survival to GRBs is governed by the value of Λ and the age of the Universe. We find that we seem to live in a favorable point in this parameter space that minimizes the exposure to cosmic explosions, yet maximizes the number of main sequence (hydrogen-burning) stars around which advanced life forms can exist.
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We examine the cosmological implications of the measurements of the linear growth rate of cosmological structure obtained in a companion paper from the power spectrum and bispectrum monopoles of the Sloan Digital Sky Survey III Baryon... more
We examine the cosmological implications of the measurements of the linear growth rate of cosmological structure obtained in a companion paper from the power spectrum and bispectrum monopoles of the Sloan Digital Sky Survey III Baryon Oscillation Spectroscopic Survey Data, Release 11, CMASS galaxies. This measurement was of $f^{0.43}\sigma_8$, where $\sigma_8$ is the amplitude of dark matter density fluctuations, and $f$ is the linear growth rate, at the effective redshift of the survey, $z_{\rm eff}=0.57$. In conjunction with Cosmic Microwave Background (CMB) data, interesting constraints can be placed on models with non-standard neutrino properties and models where gravity deviates from general relativity on cosmological scales. In particular, the sum of the masses of the three species of the neutrinos is constrained to $m_\nu<0.49\,{\rm eV}$ (at 95\% confidence level) when the $f^{0.43}\sigma_8$ measurement is combined with state-of-the-art CMB measurements. Allowing the effective number of neutrinos to vary as a free parameter does not significantly change these results. When we combine the measurement of $f^{0.43}\sigma_8$ with the complementary measurement of $f\sigma_8$ from the monopole and quadrupole of the two-point correlation function we are able to obtain an independent measurements of $f$ and $\sigma_8$. We obtain $f=0.63\pm0.16$ and $\sigma_8=0.710\pm0.086$ (68\% confidence level). This is the first time when these parameters have been able to be measured independently using the redshift-space power spectrum and bispectrum measurements from galaxy clustering data only.
We present the 2D angular power-spectrum of the Luminous Red Galaxies (LRGs) selected from SDSS III - DR8 data release. It consists of 12,000 sq deg, more than 1.5 million LRGs, making it the largest volume ever used for a galaxy... more
We present the 2D angular power-spectrum of the Luminous Red Galaxies (LRGs) selected from SDSS III - DR8 data release. It consists of 12,000 sq deg, more than 1.5 million LRGs, making it the largest volume ever used for a galaxy clustering measurement. These LRGs have accurate photometric redshifts, enabling us to reconstruct the 3D power-spectrum from their angular power-spectrum. We present initial cosmological constraints from these data.
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Baryon Acoustic Oscillations (BAO) in the radial direction offer a method to directly measure the Universe expansion history, and to set limits to space curvature when combined to the angular BAO signal. In addition to spectroscopic... more
Baryon Acoustic Oscillations (BAO) in the radial direction offer a method to directly measure the Universe expansion history, and to set limits to space curvature when combined to the angular BAO signal. In addition to spectroscopic surveys, radial BAO might be measured from accurate enough photometric redshifts obtained with narrow-band filters. We explore the requirements for a photometric survey using Luminous Red Galaxies (LRG) to competitively measure the radial BAO signal and discuss the possible systematic errors of this approach. If LRG were a highly homogeneous population, we show that the photo-z accuracy would not substantially improve by increasing the number of filters beyond $\sim 10$, except for a small fraction of the sources detected at high signal-to-noise, and broad-band filters would suffice to achieve the target $\sigma_z = 0.003 (1+z)$ for measuring radial BAO. Using the LRG spectra obtained from SDSS, we find that the spectral variability of LRG substantially worsens the achievable photometric redshift errors, and that the optimal system consists of $\sim$ 30 filters of width $\Delta \lambda / \lambda \sim 0.02$. A $S/N > 20$ is generally necessary at the filters on the red side of the $H\alpha$ break to reach the target photometric accuracy. We estimate that a 5-year survey in a dedicated telescope with etendue in excess of 60 ${\rm m}^2 {\rm deg}^2$ would be necessary to obtain a high enough density of galaxies to measure radial BAO with sufficiently low shot noise up to $z= 0.85$. We conclude that spectroscopic surveys have a superior performance than photometric ones for measuring BAO in the radial direction.
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A four-dimensional universe, arising from a flux compactification of Type IIB string theory, contains scalar fields with a potential determined by topological and geometric parameters of the internal -hidden- dimensions. We show that... more
A four-dimensional universe, arising from a flux compactification of Type IIB string theory, contains scalar fields with a potential determined by topological and geometric parameters of the internal -hidden- dimensions. We show that inflation can be realized via rolling towards the large internal volume minima that are generic in these scenarios, and we give explicit formulae relating the microscopic parameters (e.g., the Euler number of the internal space) to the cosmological observables (e.g., the spectral index). We find that the tensor-to-scalar ratio, the running of the spectral index, and the potential energy density at the minimum are related by consistency relations and are exponentially small in the number of e-foldings. Further, requiring that these models arise as low-energy limits of string theory eliminates most of them, even if they are phenomenologically valid. In this context, this approach provides a strategy for systematically falsifying stringy inflation models.
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We critically investigate current statistical tests applied to high redshift clusters of galaxies in order to test the standard cosmological model and describe their range of validity. We carefully compare a sample of high-redshift,... more
We critically investigate current statistical tests applied to high redshift clusters of galaxies in order to test the standard cosmological model and describe their range of validity. We carefully compare a sample of high-redshift, massive, galaxy clusters with realistic Poisson sample simulations of the theoretical mass function, which include the effect of Eddington bias. We compare the observations and simulations using the following statistical tests: the distributions of ensemble and individual existence probabilities (in the > M, > z sense), the redshift distributions, and the 2d Kolmogorov-Smirnov test. Using seemingly rare clusters from Hoyle et al. (2011), and Jee et al. (2011) and assuming the same survey geometry as in Jee et al. (2011, which is less conservative than Hoyle et al. 2011), we find that the ( > M, > z) existence probabilities of all clusters are fully consistent with LambdaCDM. However assuming the same survey geometry, we use the 2d K-S test probability to show that the observed clusters are not consistent with being the least probable clusters from simulations at > 95% confidence, and are also not consistent with being a random selection of clusters, which may be caused by the non-trivial selection function and survey geometry. Tension can be removed if we examine only a X-ray selected sub sample, with simulations performed assuming a modified survey geometry.
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Using the spectroscopic sample of the SDSS DR1 we measure how gas was transformed into stars as a function of time and stellar mass: the baryonic conversion tree (BCT). There is a clear correlation between early star formation activity... more
Using the spectroscopic sample of the SDSS DR1 we measure how gas was transformed into stars as a function of time and stellar mass: the baryonic conversion tree (BCT). There is a clear correlation between early star formation activity and present-day stellar mass: the more massive galaxies have formed about 80% of their stars at $z>1$, while for the less massive ones the value is only about 20%. By comparing the BCT to the dark matter merger tree, we find indications that star formation efficiency at $z>1$ had to be about a factor of two higher than today ($\sim 10%$) in galaxies with present-day stellar mass larger than $2 \times 10^{11}M_\odot$, if this early star formation occurred in the main progenitor. Therefore, the LCDM paradigm can accommodate a large number of red objects. On the other hand, in galaxies with present-day stellar mass less than $10^{11}$ M$_{\odot}$, efficient star formation seems to have been triggered at $z \sim 0.2$. We show that there is a characteristic mass (M$_* \sim 10^{10}$ M$_{\odot}$) for feedback efficiency (or lack of star formation). For galaxies with masses lower than this, feedback (or star formation suppression) is very efficient while for higher masses it is not. The BCT, determined here for the first time, should be an important observable with which to confront theoretical
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Scaling relations among galaxy cluster observables, which will become available in large future samples of galaxy clusters, could be used to constrain not only cluster structure, but also cosmology. We study the utility of this approach,... more
Scaling relations among galaxy cluster observables, which will become available in large future samples of galaxy clusters, could be used to constrain not only cluster structure, but also cosmology. We study the utility of this approach, employing a physically motivated parametric model to describe cluster structure, and applying it to the expected relation between the Sunyaev-Zel'dovich decrement (S_\nu) and the emission-weighted X-ray temperature (T_ew). The slope and normalization of the entropy profile, the concentration of the dark matter potential, the pressure at the virial radius, and the level of non-thermal pressure support, as well as the mass and redshift-dependence of these quantities are described by free parameters. With a suitable choice of fiducial parameter values, the cluster model satisfies several existing observational constraints. We employ a Fisher matrix approach to estimate the joint errors on cosmological and cluster structure parameters from a measurement of S_\nu vs. T_ew in a future survey. We find that different cosmological parameters affect the scaling relation differently: predominantly through the baryon fraction (\Omega_m and \Omega_b), the virial overdensity (w_0 and w_a for low-z clusters) and the angular diameter distance (w_0, w_a for high-z clusters; \Omega_DE and h). We find that the cosmology constraints from the scaling relation are comparable to those expected from the number counts (dN/dz) of the same clusters. The scaling relation approach is relatively insensitive to selection effects and it offers a valuable consistency check; combining the information from the scaling relation and dN/dz is also useful to break parameter degeneracies and help disentangle cluster physics from cosmology.
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We show that cosmological observables can constrain the topology of the compact additional dimensions predicted by string theory. To do this, we develop a general strategy for relating cosmological observables to the microscopic... more
We show that cosmological observables can constrain the topology of the compact additional dimensions predicted by string theory. To do this, we develop a general strategy for relating cosmological observables to the microscopic parameters of the potentials and field-dependent kinetic terms of the multiple scalar fields that arise in the low-energy limit of string theory. We apply this formalism to the Large Volume Scenarios in Type IIB flux compactifications where analytical calculations are possible. Our methods generalize to other settings.
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To date, 14 high-redshift (z>1.0) galaxy clusters with mass measurements have been observed, spectroscopically confirmed and are reported in the literature. These objects should be exceedingly rare in the standard LCDM model. We... more
To date, 14 high-redshift (z>1.0) galaxy clusters with mass measurements have been observed, spectroscopically confirmed and are reported in the literature. These objects should be exceedingly rare in the standard LCDM model. We conservatively approximate the selection functions of these clusters' parent surveys, and quantify the tension between the abundances of massive clusters as predicted by the standard LCDM model and the observed ones. We alleviate the tension considering non-Gaussian primordial perturbations of the local type, characterized by the parameter fnl and derive constraints on fnl arising from the mere existence of these clusters. At the 95% confidence level, fnl>467 with cosmological parameters fixed to their most likely WMAP5 values, or fnl > 123 (at 95% confidence) if we marginalize over WMAP5 parameters priors. In combination with fnl constraints from Cosmic Microwave Background and halo bias, this determination implies a scale-dependence of fnl at approx. 3 sigma. Given the assumptions made in the analysis, we expect any future improvements to the modeling of the non-Gaussian mass function, survey volumes, or selection functions to increase the significance of fnl>0 found here. In order to reconcile these massive, high-z clusters with an fnl=0, their masses would need to be systematically lowered by 1.5 sigma or the sigma8 parameter should be approx. 3 sigma higher than CMB (and large-scale structure) constraints. The existence of these objects is a puzzle: it either represents a challenge to the LCDM paradigme or it is an indication that the mass estimates of clusters is dramatically more uncertain than we think.
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ABSTRACT
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We summarize existing constraints on the epoch of reionization and discuss the observational probes that are sensitive to the process. We focus on the role large scale polarization can play. Polarization probes the integrated optical... more
We summarize existing constraints on the epoch of reionization and discuss the observational probes that are sensitive to the process. We focus on the role large scale polarization can play. Polarization probes the integrated optical depth across the entire epoch of reionization. Future missions such as Planck and CMBPol will greatly enhance our knowledge of the reionization history, allowing us
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ABSTRACT In the past few years there have been new developments in the effort of constraining neutrino properties with cosmology. The Cosmic Microwave Background has been measured with renewed and improved precision and large-scale... more
ABSTRACT In the past few years there have been new developments in the effort of constraining neutrino properties with cosmology. The Cosmic Microwave Background has been measured with renewed and improved precision and large-scale structure surveys have mapped cosmological structures in the Universe over unprecedentedly large volumes. Future, massive large-scale structure surveys have been presented and approved. On the theory side, a significant effort has been devoted to achieve better modelling of small scale clustering and of cosmological non-linearities. As a result it has become clear that forthcoming cosmological data have, in principle, enough statistical power to detect the effect of non-zero neutrino mass (even at the lower mass scale limit imposed by oscillations) and to constrain the absolute neutrino mass scale. I will present some recent work on constraints on neutrino properties from cosmology, concentrating in particular on the work done by my group and my collaborators.