arXiv subjects

A. de la Macorra

Publications and source records attributed to A. de la Macorra.

At least 253 records · Page 14Linked to original sources

arXiv2022

A data compression and optimal galaxy weights scheme for Dark Energy Spectroscopic Instrument and weak lensing datasets

Combining different observational probes, such as galaxy clustering and weak lensing, is a promising technique for unveiling the physics of the Universe with upcoming dark energy experiments. The galaxy redshift sample from the Dark Energy Spectroscopic Instrument (DESI) will have a significant overlap with major ongoing imaging surveys specifically designed for weak lensing measurements: the Kilo-Degree Survey (KiDS), the Dark Energy Survey (DES) and the Hyper Suprime-Cam (HSC) survey. In this work we analyse simulated redshift and lensing catalogues to establish a new strategy for combining high-quality cosmological imaging and spectroscopic data, in view of the first-year data assembly analysis of DESI. In a test case fitting for a reduced parameter set, we employ an optimal data compression scheme able to identify those aspects of the data that are most sensitive to the cosmological information, and amplify them with respect to other aspects of the data. We find this optimal compression approach is able to preserve all the information related to the growth of structure; we also extend this scheme to derive weights to be applied to individual galaxies, and show that these produce near-optimal results.

astro-ph.CO↗

arXiv2022

Overview of the Instrumentation for the Dark Energy Spectroscopic Instrument

The Dark Energy Spectroscopic Instrument (DESI) has embarked on an ambitious five-year survey to explore the nature of dark energy with spectroscopy of 40 million galaxies and quasars. DESI will determine precise redshifts and employ the Baryon Acoustic Oscillation method to measure distances from the nearby universe to z > 3.5, as well as measure the growth of structure and probe potential modifications to general relativity. In this paper we describe the significant instrumentation we developed for the DESI survey. The new instrumentation includes a wide-field, 3.2-deg diameter prime-focus corrector that focuses the light onto 5020 robotic fiber positioners on the 0.812 m diameter, aspheric focal surface. The positioners and their fibers are divided among ten wedge-shaped petals. Each petal is connected to one of ten spectrographs via a contiguous, high-efficiency, nearly 50 m fiber cable bundle. The ten spectrographs each use a pair of dichroics to split the light into three channels that together record the light from 360 - 980 nm with a resolution of 2000 to 5000. We describe the science requirements, technical requirements on the instrumentation, and management of the project. DESI was installed at the 4-m Mayall telescope at Kitt Peak, and we also describe the facility upgrades to prepare for DESI and the installation and functional verification process. DESI has achieved all of its performance goals, and the DESI survey began in May 2021. Some performance highlights include RMS positioner accuracy better than 0.1", SNR per \sqrtÅ > 0.5 for a z > 2 quasar with flux 0.28e-17 erg/s/cm^2/A at 380 nm in 4000s, and median SNR = 7 of the [OII] doublet at 8e-17 erg/s/cm^2 in a 1000s exposure for emission line galaxies at z = 1.4 - 1.6. We conclude with highlights from the on-sky validation and commissioning of the instrument, key successes, and lessons learned. (abridged)

astro-ph.IM↗

arXiv2019

Non-linear Structure Formation for Dark Energy Models with a Steep Equation of State

We study the nonlinear regime of large scale structure formation considering a dynamical dark energy (DE) component determined by a Steep Equation of State parametrization (SEoS) $w(z)=w_0+w_i\frac{(z/z_T)^q}{1+(z/z_T)^q}$. In order to perform the model exploration at low computational cost, we modified the public code L-PICOLA. We incorporate the DE model by means of the first and second-order matter perturbations in the Lagrangian frame and the expansion parameter. We analyze deviations of SEoS models with respect to $Λ$CDM in the non-linear matter power spectrum ($P_k$), the halo mass function (HMF), and the two-point correlation function (2PCF). On quantifying the nature of steep (SEoS-I) and smooth transitions in DE field (CPL-lim), no signature of steep transition is observed, rather found the overall impact of DE behaviors in $P_k$ at level of $\sim 2-3\%$ and $\sim 3-4\%$ differences w.r.t $Λ$CDM at $z=0$ respectively. HMF shows the possibility to distinguish between the models at the high mass ends. The best-fitted model assuming only background and linear perturbations dubbed as SEoS-II largely deviates from $Λ$CDM and current observations on studying the nonlinear growth. This large deviation in SEoS-II also quantified the combined effect of the dynamical DE and the larger amount of matter contained, $Ω_{m0}$ and $H_{0}$ accordingly. 2PCF results are relatively robust with $\sim 1-2 \%$ deviation for SEoS-I and CPL-lim and a significant deviation for SEoS-II throughout $r$ from $Λ$CDM. Finally, we conclude that the search for viable DE models (like the SEoS) must include non-linear growth constraints.

astro-ph.CO↗

arXiv2018

Testing the nature of Dark Energy with Precision Cosmological constraints

We present a Dark Energy (DE) model with a sound derivation as a natural extension of the Standard Model of particle physics with no free parameters and an excellent fit with current cosmological data improving by 21% the $Λ$CDM fit of the Baryon Acoustic Oscillations (BAO) measurements, specially designed to determine the dynamics of DE. DE corresponds to the lightest bound state scalar particle $ϕ$ with a potential $V=Λ_c^{4+2/3}ϕ^{-2/3}$ dynamically formed at the condensation energy scale $Λ_c$ and scale factor $a_c$. The value of $Λ_c$, the exponent $n=2/3$, and the initial conditions of $ϕ$ are all derived quantities. We obtain an exact constraint $a_cΛ_c/\textrm{eV}=1.0939\times 10^{-4}$ and a theoretical prediction $Λ_c=34 ^{+16}_{-11} \textrm{ eV}$, consistent with the best fit $Λ_c=44.08\pm 0.27 \textrm{ eV}$. We test our model constraint on $a_cΛ_c$ by allowing $a_c$ and $Λ_c$ to vary independently and remarkably our prediction has a relative difference of only 0.2% with the best fit value. Unlike a cosmological constant $Λ$, our DE model predicts the amount of DE and leaves detectable cosmological imprints at different times and scales at a background and perturbation level.

astro-ph.CO↗

arXiv2016

The SDSS-IV extended Baryon Oscillation Spectroscopic Survey: selecting emission line galaxies using the Fisher discriminant

We present a new selection technique of producing spectroscopic target catalogues for massive spectroscopic surveys for cosmology. This work was conducted in the context of the extended Baryon Oscillation Spectroscopic Survey (eBOSS), which will use ~200 000 emission line galaxies (ELGs) at 0.6<zspec<1.0 to obtain a precise baryon acoustic oscillation measurement. Our proposed selection technique is based on optical and near-infrared broad-band filter photometry. We used a training sample to define a quantity, the Fisher discriminant (linear combination of colours), which correlates best with the desired properties of the target: redshift and [OII] flux. The proposed selections are simply done by applying a cut on magnitudes and this Fisher discriminant. We used public data and dedicated SDSS spectroscopy to quantify the redshift distribution and [OII] flux of our ELG target selections. We demonstrate that two of our selections fulfil the initial eBOSS/ELG redshift requirements: for a target density of 180 deg^2, ~70% of the selected objects have 0.6<zspec<1.0 and only ~1% of those galaxies in the range 0.6<zspec<1.0 are expected to have a catastrophic zspec estimate. Additionally, the stacked spectra and stacked deep images for those two selections show characteristic features of star-forming galaxies. The proposed approach using the Fisher discriminant could, however, be used to efficiently select other galaxy populations, based on multi-band photometry, providing that spectroscopic information is available. This technique could thus be useful for other future massive spectroscopic surveys such as PFS, DESI, and 4MOST.

astro-ph.GA↗

arXiv2013

Spectroscopic Needs for Imaging Dark Energy Experiments: Photometric Redshift Training and Calibration

Large sets of objects with spectroscopic redshift measurements will be needed for imaging dark energy experiments to achieve their full potential, serving two goals:_training_, i.e., the use of objects with known redshift to develop and optimize photometric redshift algorithms; and_calibration_, i.e., the characterization of moments of redshift (or photo-z error) distributions. Better training makes cosmological constraints from a given experiment stronger, while highly-accurate calibration is needed for photo-z systematics not to dominate errors. In this white paper, we investigate the required scope of spectroscopic datasets which can serve both these purposes for ongoing and next-generation dark energy experiments, as well as the time required to obtain such data with instruments available in the next decade. Large time allocations on kilo-object spectrographs will be necessary, ideally augmented by infrared spectroscopy from space. Alternatively, precision calibrations could be obtained by measuring cross-correlation statistics using samples of bright objects from a large baryon acoustic oscillation experiment such as DESI. We also summarize the additional work on photometric redshift methods needed to prepare for ongoing and future dark energy experiments.

astro-ph.CO↗

arXiv2012

Dark Matter from the Inflaton Field

We present a model where inflation and Dark Matter takes place via a single scalar field phi. Without introducing any new parameters we are able unify inflation and Dark Matter using a scalar field phi that accounts for inflation at an early epoch while it gives a Dark Matter WIMP particle at low energies. After inflation our universe must be reheated and we must have a long period of radiation dominated before the epoch of Dark Matter. Typically the inflaton decays while it oscillates around the minimum of its potential. If the inflaton decay is not complete or sufficient then the remaining energy density of the inflaton after reheating must be fine tuned to give the correct amount of Dark Matter. An essential feature here, is that Dark Matter-Inflaton particle is produced at low energies without fine tuning or new parameters. This process uses the same coupling g as for the inflaton decay. Once the field phi becomes non-relativistic it will decouple as any WIMP particle, since n_phi is exponentially suppressed. The correct amount of Dark Matter determines the cross section and we have a constraint between the coupling $g$ and the mass $m_o$ of phi. The unification scheme we present here has four free parameters, two for the scalar potential V(phi) given by the inflation parameter lambda of the quartic term and the mass m_o. The other two parameters are the coupling $g$ between the inflaton phi and a scalar filed varphi and the coupling h between varphi with standard model particles psi or chi. These four parameters are already present in models of inflation and reheating process, without considering Dark Matter. Therefore, our unification scheme does not increase the number of parameters and it accomplishes the desired unification between the inflaton and Dark Matter for free.

astro-ph.CO↗

arXiv2011

The BigBOSS Experiment

BigBOSS is a Stage IV ground-based dark energy experiment to study baryon acoustic oscillations (BAO) and the growth of structure with a wide-area galaxy and quasar redshift survey over 14,000 square degrees. It has been conditionally accepted by NOAO in response to a call for major new instrumentation and a high-impact science program for the 4-m Mayall telescope at Kitt Peak. The BigBOSS instrument is a robotically-actuated, fiber-fed spectrograph capable of taking 5000 simultaneous spectra over a wavelength range from 340 nm to 1060 nm, with a resolution R = 3000-4800. Using data from imaging surveys that are already underway, spectroscopic targets are selected that trace the underlying dark matter distribution. In particular, targets include luminous red galaxies (LRGs) up to z = 1.0, extending the BOSS LRG survey in both redshift and survey area. To probe the universe out to even higher redshift, BigBOSS will target bright [OII] emission line galaxies (ELGs) up to z = 1.7. In total, 20 million galaxy redshifts are obtained to measure the BAO feature, trace the matter power spectrum at smaller scales, and detect redshift space distortions. BigBOSS will provide additional constraints on early dark energy and on the curvature of the universe by measuring the Ly-alpha forest in the spectra of over 600,000 2.2 < z < 3.5 quasars. BigBOSS galaxy BAO measurements combined with an analysis of the broadband power, including the Ly-alpha forest in BigBOSS quasar spectra, achieves a FOM of 395 with Planck plus Stage III priors. This FOM is based on conservative assumptions for the analysis of broad band power (kmax = 0.15), and could grow to over 600 if current work allows us to push the analysis to higher wave numbers (kmax = 0.3). BigBOSS will also place constraints on theories of modified gravity and inflation, and will measure the sum of neutrino masses to 0.024 eV accuracy.

astro-ph.IM↗

arXiv2009

Inflation-Dark Matter unified through Quantum Generation

We unify inflation and dark matter via a single scalar field phi. One of the main difficulties for this unification is that between inflation and dark matter one needs a successful reheating process and a long lasting period of radiation. Therefore the amount of energy density in the inflaton-dark matter field phi must be fine tune after reheating to give dark matter. Here we show an alternative scheme in which the inflaton decays completely, disappearing entirely from the spectrum. However, at low energies, before matter-radiation equality, the same interaction term that leads to the inflaton decay, regenerates phi. An essential feature is that the transition between the intermediate radiation dominated to the dark matter phase is related to a quantum generation of the scalar field ϕinstead to purely classical dynamics. Thanks to this quantum transition the inflation-dark matter unification can take place naturally without fine tuning. The unification scheme presented here has three parameters, the mass of the dark matter particle m_o, the inflation parameter lambda and the coupling g for the inflaton interaction. Phenomenology fixes the value for lambda and gives a constraint between g and m_o, leaving only the mass of the dark matter particle m_o as a free parameter. These same three parameters lambda, m_o, g are present in models with inflation and a dark matter wimp particle but without unification. Therefore our unification scheme does not increase the number of parameters and it accomplishes the desired unification between inflaton and dark matter for free.

astro-ph.CO↗

arXiv2009

Quantum Generation of Dark Energy

We present a type of dark energy models where the particles of dark energy phi are dynamically produced via a quantum transition at very low energies. The scale where the transition takes places depends on the strength g of the interaction between phi and a relativistic field varphi. We show that a g \simeq 10^{-12} gives a generation scale E_gen simeq eV with a cross section sigma simeq 1 pb close to the WIMPs cross section sigma_w simeq pb at decoupling. The number density n_phi of the ϕparticles are a source term in the eq. of motion of phi and it generates the scalar potential v(phi) responsible for the late time acceleration of our universe. Since the appearance of phi may be at very low scales, close to present time, the cosmological coincidence problem can be explained simply due to the size of the coupling constant. We unify dark energy with inflation in terms of a single scalar field phi, and we use the same potential v for inflation and dark energy. However, after inflation phi decays completely and reheats the universe at a scale E_RH propto h^2 m_Pl, where h is the coupling between the SM particles and varphi. The field phi disappears from the spectrum during, from reheating until its re-generation, and therefore it does not interfere with the standard decelerating radiation/matter cosmological model allowing for a successful unification scheme. The same interaction term that gives rise to the inflaton decay accounts for the late time re-generation of phi. We present a simple model where the strength of the g and h couplings are set by the inflation scale E_I with g=h^2 propto E_I/m_Pl giving a reheating scale E_RH propto E_I=100TeV and phi-generation scale E_gen propto E_I^2/m_pl=eV << E_RH.

astro-ph.CO↗

arXiv2009

Accelerating Cosmological Models for an Interacting Tachyon

We study the cosmological evolution of a tachyon scalar field T with a Dirac- Born- Infeld type lagrangian and potential V (T) coupled to a canonically normalized scalar field with an arbitrary but factorizeable interaction potential B (T,phi) in the presence of a barotropic fluid. We will assume that the force between the barotropic fluid and the scalar field is only gravitational and we show that all models dependence is given in terms of three parameters: L1= -V_T/V, L2= -B_T/B and L3= -B_phi/B which are field and time dependent. We give the general solution to the cosmological equations of motion and determine in which cases we can have an accelerating universe giving rise to dark energy.

hep-ph↗

arXiv2008

Inflation-Dark Energy unified through Quantum Regeneration

We study a scalar phi field that unifies inflation and dark energy with a long period of a hot decelerating universe in between these two stages of inflation. A key feature is that the transition between the intermediate decelerated phase to the dark energy phase is related to a quantum regeneration of the scalar field phi instead to purely classical dynamics. The interaction V_int(phi,varphi) between phi and a second scalar field varphi allows not only for phi to decay at a high energy E_I, even though phi does not oscillate around the minimum of its potential, but it also regenerates phi at an energy E_{BD} \simeq E_I^2 close to present time. It predicts extra relativistic energy and an interacting dark energy which may account for a w<-1. In the model presented here we have E_I \simeq 100 TeV and E_{BD} \simeq 1 eV. The low value of the back decay energy E_{BD} gives an explanation of the coincidence problem.

astro-ph↗

arXiv2008

Cosmology of the very early universe

We study cosmological solutions for the very early universe beginning at the Planck scale for a universe containing radiation, curvature and, as a simplification of a possible scalar field potential, a cosmological constant term. The solutions are the natural counterpart of the well known results for a post-inflationary universe of non-relativistic matter, curvature and a cosmological constant. Contrary to the common belief that inflation arises independently of the initial curvature we show that in the positive curvature case the universe collapses again into a Big Crunch without allowing the cosmological term to dominate and to produce inflation. There is a critical value for the cosmological constant which divide the regions where inflation is allowed from those where inflation cannot occur. One can also have loitering solutions where the scale factor remains almost constant growing to produce inflation (or decreasing to a Big Crunch) after a time which depends on the amount of energy above (or below) the critical energy. At the critical energy the solution approaches asymptotically a particular value for the scale factor (Einstein's static pre-inflationary universe). The cases where the cosmological term vanishes or becomes negative are also studied providing a complete discussion of Friedmann models.

gr-qc↗

arXiv2007

Interacting Tachyon: generic cosmological evolution for a tachyon and a scalar field

We study the cosmological evolution of a tachyon scalar field T with a Dirac-Born-Infeld type lagrangian and potential V(T) coupled to a canonically normalized scalar field ϕwith an arbitrary interaction term B(T,ϕ) in the presence of a barotropic fluid $\rb$, which can be matter or radiation. The force between the barotropic fluid and the scalar fields is only gravitational. We show that the dynamics is completely determine by only three parameters L1 = - V_T/ V^{3/2}, L2= - B_T /B^{3/2} and L3 =-B_ϕ/B. We determine analytically theconditions for $\lm_i$ under which the energy density of T, ϕand $\rb$ have the same redshift. We study the behavior of T and ϕin the asymptotic limits for L_i and we show the numerical solution for different interesting cases. The effective equation of state for the tachyon field changes due to the interaction with the scalar field and we show that it is possible for a tachyon field to redshift as matter in the absence of an interaction term B and as radiation when B is turned on. This result solves then the tachyonic matter problem.

hep-th↗

arXiv2007

Interacting dark energy: generic cosmological evolution for two scalar fields

We study the cosmological evolution of two coupled scalar fields with an arbitrary interaction term V_T(ϕ,\vp) in the presence of a barotropic fluid, which can be matter or radiation. The force between the barotropic fluid and the scalar fields is only gravitational. We show that the dynamics is completely determine by only three parameters L_i i=1,2,3. We determine all critical points and study their stability. We find six different attractor solutions depending on the values of L_i and we calculate the relevant cosmological parameters. We discuss the possibility of having one of the scalar fields as of dark energy while the other could be a scalar field redshifting as matter.

astro-ph↗

arXiv2007

Interacting Dark Energy: Decay into Fermions

A dark energy component is responsible for the present stage of acceleration of our universe. If no fine tuning is assumed on the dark energy potential then it will end up dominating the universe at late times and the universe will not stop this stage of acceleration. On the other hand, the equation of state of dark energy seems to be smaller than -1 as suggested by the cosmological data. We take this as an indication that dark energy does indeed interact with another fluid (we consider fermion fields) and we determine the interaction through the cosmological data and extrapolate it into the future. We study the conditions under which a dark energy can dilute faster or decay into the fermion fields. We show that it is possible to live now in an accelerating epoch dominated by the dark energy and without introducing any fine tuning parameters the dark energy can either dilute faster or decaying into fermions in the future. The acceleration of the universe will then cease.

astro-ph↗

arXiv2007

The Fate of the Universe: Dark Energy Dilution?

We study the possibility that dark energy decays in the future and the universe stops accelerating. The fact thatthe cosmological observations prefer an equation of state of dark energy smaller than -1 can be a signal that dark energy will decay in the future. This conclusion is based in interpreting a w<-1 as a signal of dark energy interaction with another fluid. We determine the interaction through the cosmological data and extrapolate it into the future. The resulting energy density for dark energy becomes rho=a^{-3(1+w)}e^{-β(a-1)}, i.e. it has an exponential suppression for a >> a_o=1. In this scenario the universe ends up dominated by this other fluid, which could be matter, and the universe stops accelerating at some time in the near future.

astro-ph↗

arXiv2006

The Mass, Normalization and Late Time behavior of the Tachyon Field

We study the dynamics of the tachyon field $T$. We derive the mass of the tachyon as the pole of the propagator which does not coincide with the standard mass given in the literature in terms of the second derivative of $V(T)$ or $Log[V(T)]$. We determine the transformation of the tachyon in order to have a canonical scalar field $ϕ$. This transformation reduces to the one obtained for small $\dot T$ but it is also valid for large values of $\dot T$. This is specially interesting for the study of dark energy where $\dot T\simeq 1$. We also show that the normalized tachyon field $ϕ$ is constrained to the interval $T_2\leq T \leq T_1$ where $T_1,T_2$ are zeros of the original potential $V(T)$. This results shows that the field $ϕ$ does not know of the unboundedness of $V(T)$, as suggested for bosonic open string tachyons. Finally we study the late time behavior of tachyon field using the L'Hôpital rule.

hep-th↗