Papers by Alejandro Felipe Avilés
arXiv (Cornell University), Jun 9, 2023
The Dark Energy Spectroscopic Instrument (DESI) completed its five-month Survey Validation in May... more The Dark Energy Spectroscopic Instrument (DESI) completed its five-month Survey Validation in May 2021. Spectra of stellar and extragalactic targets from Survey Validation constitute the first major data sample from the DESI survey. This paper describes the public release of those spectra, the catalogs of derived properties, and the intermediate data products. In total, the public release includes good-quality spectral information from 466,447 objects targeted as part of the Milky Way Survey, 428,758 as part of the Bright Galaxy Survey, 227,318 as part of the Luminous Red Galaxy sample, 437,664 as part of the Emission Line Galaxy sample, and 76,079 as part of the Quasar sample. In addition, the release includes spectral information from 137,148 objects that expand the scope beyond the primary samples as part of a series of secondary programs. Here, we describe the spectral data, data quality, data products, Large-Scale Structure science catalogs, access to the data, and references that provide relevant background to using these spectra.
arXiv (Cornell University), Jun 9, 2023
The Dark Energy Spectroscopic Instrument (DESI) was designed to conduct a survey covering 14,000 ... more The Dark Energy Spectroscopic Instrument (DESI) was designed to conduct a survey covering 14,000 deg 2 over five years to constrain the cosmic expansion history through precise measurements of Baryon Acoustic Oscillations (BAO). The scientific program for DESI was evaluated during a five month Survey Validation (SV) campaign before beginning full operations. This program produced deep spectra of tens of thousands of objects from each of the stellar (MWS), bright galaxy (BGS), luminous red galaxy (LRG), emission line galaxy (ELG), and quasar target classes. These SV spectra were used to optimize redshift distributions, characterize exposure times, determine calibration procedures, and assess observational overheads for the five-year program. In this paper, we present the final target selection algorithms, redshift distributions, and projected cosmology constraints resulting from those studies. We also present a 'One-Percent survey' conducted at the conclusion of Survey Validation covering 140 deg 2 using the final target selection algorithms with exposures of a depth typical of the main survey. The Survey Validation indicates that DESI will be able to complete the full 14,000 deg 2 program with spectroscopically-confirmed targets from the MWS, BGS, LRG, ELG, and quasar programs with total sample sizes of 7.2, 13.8, 7.46, 15.7, and 2.87 million, respectively. These samples will allow exploration of the Milky Way halo, clustering on all scales, and BAO measurements with a statistical precision of 0.28% over the redshift interval z < 1.1, 0.39% over the redshift interval 1.1 < z < 1.9, and 0.46% over the redshift interval 1.9 < z < 3.5.
arXiv (Cornell University), Jul 6, 2023
Upcoming imaging surveys will allow for high signal-to-noise measurements of galaxy clustering at... more Upcoming imaging surveys will allow for high signal-to-noise measurements of galaxy clustering at small scales. In this work, we present the results of the Rubin Observatory Legacy Survey of Space and Time (LSST) bias challenge, the goal of which is to compare the performance of different nonlinear galaxy bias models in the context of LSST Year 10 (Y10) data. Specifically, we compare two perturbative approaches, Lagrangian perturbation theory (LPT) and Eulerian perturbation theory (EPT) to two variants of Hybrid Effective Field Theory (HEFT), with our fiducial implementation of these models including terms up to second order in the bias expansion as well as nonlocal bias and deviations from Poissonian stochasticity. We consider a variety of different simulated galaxy samples and test the performance of the bias models in a tomographic joint analysis of LSST-Y10-like galaxy clustering, galaxy-galaxy-lensing and cosmic shear. We find both HEFT methods as well as LPT and EPT combined with non-perturbative predictions for the matter power spectrum to yield unbiased constraints on cosmological parameters up to at least a maximal scale of k max = 0.4 Mpc -1 for all samples considered, even in the presence of assembly bias. While we find that we can reduce the complexity of the bias model for HEFT without compromising fit accuracy, this is not generally the case for the perturbative models. We find significant detections of non-Poissonian stochasticity in all cases considered, and our analysis shows evidence that small-scale galaxy clustering predominantly improves constraints on galaxy bias rather than cosmological parameters. These results therefore suggest that the systematic uncertainties associated with current nonlinear bias models are likely to be subdominant compared to other sources of error for tomographic analyses of upcoming photometric surveys, which bodes well for future galaxy clustering analyses using these high signal-to-noise data. F Three-dimensional power spectrum analysis 39 G Consistency of results for different data sets 40
arXiv (Cornell University), Sep 18, 2014
Evaluation of Brittle Layers Obtained by Boriding on AISI H13 Steels
Advanced Materials Research, Mar 1, 2009
The fracture toughness of AISI H13 borided steel and the strength adhesion of the coated system w... more The fracture toughness of AISI H13 borided steel and the strength adhesion of the coated system were estimated in the present work. The formation of the layers was carried out by the powder pack boriding process at 1273 K with 8 h of treatment. The fracture toughness (KC) of the layer is estimated at 25 and 45 m from the surface using four different Vickers indentation loads. The KC values were estimated by the extension of Palmqvist cracks parallel and perpendicular to the surface obtained at the indentation corners. The adherence of the layer/substrate was evaluated in qualitative form through the Rockwell-C indentation technique. The results obtained by both techniques, show, in first instance, that the fracture toughness of the boride layer can be expressed in the form (KC) (π/2) &gt; (KC) &gt; (KC) (0). Also, high delamination is obtained around the Rockwell-C indentation prints that denote poor adhesion in the coating-substrate interface.
Physical review, Feb 5, 2013
We address the issue of constraining the class of f (R) able to reproduce the observed cosmologic... more We address the issue of constraining the class of f (R) able to reproduce the observed cosmological acceleration, by using the so called cosmography of the universe. We consider a model independent procedure to build up a f (z)-series in terms of the measurable cosmographic coefficients; we therefore derive cosmological late time bounds on f (z) and its derivatives up to the fourth order, by fitting the luminosity distance directly in terms of such coefficients. We perform a Monte Carlo analysis, by using three different statistical sets of cosmographic coefficients, in which the only assumptions are the validity of the cosmological principle and that the class of f (R) reduces to ΛCDM when z ≪ 1. We use the updated union 2.1 for supernovae Ia, the constrain on the H0 value imposed by the measurements of the Hubble space telescope and the Hubble dataset, with measures of H at different z. We find a statistical good agreement of the f (R) class under exam, with the cosmological data; we thus propose a candidate of f (R), which is able to pass our cosmological test, reproducing the late time acceleration in agreement with observations.
arXiv (Cornell University), Jun 29, 2016
With the use of simulated supernova catalogs, we show that the statefinder parameters turn out to... more With the use of simulated supernova catalogs, we show that the statefinder parameters turn out to be poorly and biased estimated by standard cosmography. To this end, we compute their standard deviations and several bias statistics on cosmologies near the concordance model, demonstrating that these are very large, making standard cosmography unsuitable for future and wider compilations of data. To overcome this issue, we propose a new method that consists in introducing the series of the Hubble function into the luminosity distance, instead of considering the usual direct Taylor expansions of the luminosity distance. Moreover, in order to speed up the numerical computations, we estimate the coefficients of our expansions in a hierarchical manner, in which the order of the expansion depends on the redshift of every single piece of data. In addition, we propose two hybrids methods that incorporates standard cosmography at low redshifts. The methods presented here perform better than the standard approach of cosmography both in the errors and bias of the estimated statefinders. We further propose a one-parameter diagnostic to reject non-viable methods in cosmography.
Numerical Simulation of Water Flow in a Venturi Tube Using the Smoothed Particle Hydrodynamics Method
Environmental science and engineering, 2015
A numerical simulation of water flow through a Venturi tube was made with the DualSPHysics code, ... more A numerical simulation of water flow through a Venturi tube was made with the DualSPHysics code, which uses the Smoothed Particle Hydrodynamics (SPH) method. The dimensions of the simulated system are equal to the laboratory experimental setup. The experimental data were measured in the laboratory using a rotameter and a mercury manometer. The experimental and numerical results show a similar behavior. Discharge coefficient values are obtained from the numerical results.
On the galaxy 3-point correlation function in Modified Gravity
Nucleation and Atmospheric Aerosols, 2011
We propose an effective model, geometric, to describe the dynamics of extended objects with maxim... more We propose an effective model, geometric, to describe the dynamics of extended objects with maximal acceleration, which evolve in a Minkowski spacetime. The effective model involves the extrinsic curvature of the trajectory generated by the object during its evolution. The Lagrangian describing this theory is of second order in derivatives and thus the equations of motion are of fourth order in the coordinates. We show that in the case of codimension one, the equations of motion resembles a Klein-Gordon type equation. For illustration, we study the dynamics of a (3+1) spherical surface, having an accelerated expansion where there is a noticeable maximal acceleration.
Nucleation and Atmospheric Aerosols, 2013
Dark matter and dark energy are essential in the description of the late Universe, since at least... more Dark matter and dark energy are essential in the description of the late Universe, since at least the epoch of equality. On the other hand, the inflation is also necessary and demands a "dark" component, usually associated to a scalar field that dominated the dynamics and kinematics in the very early Universe. Yet, these three dark components of standard model of cosmology are independent from each other, although there are alternative models that pursue to achieve a triple unification, or at least a double. In the present work we present an update of two models that we have considered in recent years. The first is the dark fluid model in which dark matter and dark energy are the same thing, achieving a double unification with specific properties that exactly emulate the standard model of cosmology, given the dark degeneracy that exists in the ΛCDM model. The second model is given by a single F(X) scalar field Lagrangian, with which one is able to model the whole cosmological dynamics, from inflation to today, representing a triple unification model. We highlight the main properties of these models, as well as we test them against known cosmological probes.
Journal of Molecular Modeling, Dec 15, 2017
Energy profiles for the lowest lying triplet and singlet electronic pathways that link the reacta... more Energy profiles for the lowest lying triplet and singlet electronic pathways that link the reactants Zr + CH 3 CH 3 with the products observed under matrix-isolation conditions were obtained from DFT and CASSCF-MRMP2 calculations. The insertion of the metal into the C-H bond of the organic molecule to yield the oxidative addition product is not favorable for any of the investigated channels. However, the inserted structure H-Zr-CH 2 CH 3 can be obtained from two sequential reactions involving the radical species ZrH and CH 2 CH 3 . According to this scheme, a first reaction produces the radical fragments from the ground state of the reactants. Then, the radicals can recombine themselves in a second reaction to form the inserted species H-Zr-CH 2 CH 3 . As the triplet and singlet radical asymptotes ZrH + CH 2 CH 3 that vary only in spin of the non-metallic fragment are degenerate, the rebounding of the radicals can occur through both multiplicity channels. It is shown that the low spin channel leads to the most stable structures of the dihydride ZrH 2 -(CH 2 ) 2 and the vinyl metal trihydride complexes ZrH 3 -CH=CH 2 experimentally determined for this reaction under matrix-isolation conditions. The description attained for this interaction does not invoke interactions between the triplet and singlet electronic states emerging from the reactants, as proposed by other authors.
Constraints from Cosmography in Various Parametrizations
Journal of Cosmology and Astroparticle Physics, Jan 2, 2020
We develop perturbation theory approaches to model the marked correlation function constructed to... more We develop perturbation theory approaches to model the marked correlation function constructed to up-weight low density regions of the Universe, which might help distinguish modified gravity models from the standard cosmology model based on general relativity. Working within Convolution Lagrangian Perturbation Theory, we obtain that weighted correlation functions are expressible as double convolution integrals that we approximate using a combination of Eulerian and Lagrangian schemes. We find that different approaches agree within 1% on quasi non-linear scales. Compared with N-body simulations, the perturbation theory is found to provide accurate predictions for the marked correlation function of dark matter fields, dark matter halos as well as Halo Occupation Distribution galaxies down to 30 Mpc/h. These analytic approaches help to understand the degeneracy between the mark and the galaxy bias and find a way to maximize the differences among various cosmological models.
Journal of Cosmology and Astroparticle Physics, Jan 28, 2020
We extend the scale-dependent Gaussian Streaming Model (GSM) to produce analytical predictions fo... more We extend the scale-dependent Gaussian Streaming Model (GSM) to produce analytical predictions for the anisotropic redshift-space correlation function for biased tracers in modified gravity models. Employing the Convolution Lagrangian Perturbation Theory (CLPT) re-summation scheme, with a local Lagrangian bias schema provided by the peak-background split formalism, we predict the necessary ingredients that enter the GSM, the real-space halo pairwise velocity and the pairwise velocity dispersion. We further consider effective field theory contributions to the pairwise velocity dispersion in order to model correctly its large scale behavior. We apply our method on two widely-considered modified gravity models, the chameleon-screened f (R) Hu-Sawicki model and the nDGP Vainshtein model and compare our predictions against state-of-the-art N-body simulations for these models. We demonstrate that the GSM approach to predict the monopole and the quadrupole of the redshift-space correlation function for halos, gives very good agreement with the simulation data, for a wide range of screening mechanisms, levels of screening and halo masses at z = 0.5 and z = 1. Our work shows the applicability of the GSM, for cosmologies beyond GR, demonstrating that it can serve as a powerful predictive tool for the next stage of cosmological surveys like DESI, Euclid, LSST and WFIRST.
Physical review, Dec 14, 2012
We use cosmography to present constraints on the kinematics of the Universe, without postulating ... more We use cosmography to present constraints on the kinematics of the Universe, without postulating any underlying theoretical model. To this end, we use a Monte Carlo Markov Chain analysis to perform comparisons to the supernova Ia Union 2 compilation, combined with the Hubble Space Telescope measurements of the Hubble constant, and the Hubble parameter datasets. We introduce a sixth order cosmographic parameter and show that it does not enlarge considerably the posterior distribution when comparing to the fifth order results. We also propose a way to construct viable parameter variables to be used as alternatives of the redshift z. These can overcome both the problems of divergence and lack of accuracy associated with the use of z. Moreover, we show that it is possible to improve the numerical fits by re-parameterizing the cosmological distances. In addition, we constrain the equation of state of the Universe as a whole by the use of cosmography. Thus, we derive expressions which can be directly used to fit the equation of state and the pressure derivatives up to fourth order. To this end, it is necessary to depart from a pure cosmographic analysis and to assume the Friedmann equations as valid. All our results are consistent with the ΛCDM model, although alternative fluid models, withnearly constant pressure and no cosmological constant, match the results accurately as well.
arXiv (Cornell University), May 30, 2017
We present a formalism to compute Lagrangian displacement fields for a wide range of cosmologies ... more We present a formalism to compute Lagrangian displacement fields for a wide range of cosmologies in the context of perturbation theory up to third order. We emphasize the case of theories with scale dependent gravitational strengths, such as chameleons, but our formalism can be accommodated to other modified gravity theories. In the non-linear regime two qualitative features arise. One, as is well known, is that nonlinearities lead to a screening of the force mediated by the scalar field. The second is a consequence of the transformation of the Klein-Gordon equation from Eulerian to Lagrangian coordinates, producing frame-lagging terms that are important especially at large scales, and if not considered, the theory does not reduce to the ΛCDM model in that limit. We apply our formalism to compute the 1-loop power spectrum and the correlation function in f (R) gravity by using different resummation schemes. We further discuss the IR divergences of these formalisms.
Physical review, Mar 17, 2023
The next generation of galaxy surveys will provide highly accurate measurements of the largescale... more The next generation of galaxy surveys will provide highly accurate measurements of the largescale structure of the Universe, allowing for more stringent tests of gravity on cosmological scales. Higher order statistics are a valuable tool to study the non-Gaussianities in the matter field and to break degeneracies between modified gravity and other physical or nuisance parameters. However, understanding from first principles the behaviour of these correlations is essential to characterise deviations from General Relativity (GR), and the purpose of this work. This work uses contemporary ideas of Standard Perturbation Theory on biased tracers to characterize the three point correlation function (3PCF) at tree level for Modified Gravity models with a scale-dependent gravitational strength, and applies the theory to two specific models (f (R) and DGP) that are representative for Chameleon and Vainshtein screening mechanisms. Additionally, we use a multipole decomposition, which apart from speeding up the algorithm to extract the signal from data, also helps to visualize and characterize GR deviations.
Physical review, Mar 18, 2013
A cosmographic reconstruction of f (T) models is here revised in a model independent way by fixin... more A cosmographic reconstruction of f (T) models is here revised in a model independent way by fixing observational bounds on the most relevant terms of the f (T) Taylor expansion. We relate the f (T) models and their derivatives to the cosmographic parameters and then adopt a Monte Carlo analysis. The experimental bounds are thus independent of the choice of a particular f (T) model. The advantage of such an analysis lies on constraining the dynamics of the universe by reconstructing the form of f (T), without any further assumptions apart from the validity of the cosmological principle and the analyticity of the f (T) function. The main result is to fix model independent cosmographic constraints on the functional form of f (T) which are compatible with the theoretical predictions. Furthermore, we infer a phenomenological expression for f (T), compatible with the current cosmographic bounds and show that small deviations are expected from a constant f (T) term, indicating that the equation of state of dark energy could slightly evolve from the one of the ΛCDM model.
Journal of Cosmology and Astroparticle Physics, Apr 1, 2021
We develop a framework to compute the redshift space power spectrum (PS), with kernels beyond Ein... more We develop a framework to compute the redshift space power spectrum (PS), with kernels beyond Einstein-de Sitter (EdS), that can be applied to a wide variety of generalized cosmologies. We build upon a formalism that was recently employed for standard cosmology in Chen, Vlah & White (2020), and utilize an expansion of the density-weighted velocity moment generating function that explicitly separates the magnitude of the k-modes and their angle to the line-of-sight direction dependencies. We compute the PS for matter and biased tracers to 1-loop Perturbation Theory (PT) and show that the expansion has a correct infrared and ultraviolet behavior, free of unwanted divergences. We also add Effective Field Theory (EFT) counterterms, necessary to account for small-scale contributions to PT, and employ an IR-resummation prescription to properly model the smearing of the BAO due to large scale bulk flows within Standard-PT. To demonstrate the applicability of our formalism, we apply it on the ΛCDM and the Hu-Sawicki f (R) models, and compare our numerical results against the elephant suite of N -body simulations, finding very good agreement up to k = 0.27 Mpc -1 h at z = 0.5 for the first three non-vanishing Legendre multipoles of the PS. To our knowledge, the model presented in this work is the most accurate theoretical EFT-PT for modified gravity to date, being the only one that accounts for beyond linear local biasing in redshift-space. Hence, we argue our RSD modeling is a promising tool to construct theoretical templates in order to test deviations from ΛCDM using real data obtained from the next stage of cosmological surveys such as DESI and LSST.
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Papers by Alejandro Felipe Avilés