Parametrizing growth in dark energy and modified gravity models

It is well-known that an extremely accurate parametrization of the growth function of matter density perturbations in $\Lambda$CDM cosmology, with errors below $0.25 \%$, is given by $f(a)=\Omega_{m}^{\gamma} \,(a)$ with $\gamma \simeq 0.55$. In this work, we show that a simple modification of this expression also provides a good description of growth in modified gravity theories. We consider the model-independent approach to modified gravity in terms of an effective Newton constant written as $\mu(a,k)=G_{eff}/G$ and show that $f(a)=\beta(a)\Omega_{m}^{\gamma} \,(a)$ provides fits to the numerical solutions with similar accuracy to that of $\Lambda$CDM. In the time-independent case with $\mu=\mu(k)$, simple analytic expressions for $\beta(\mu)$ and $\gamma(\mu)$ are presented. In the time-dependent (but scale-independent) case $\mu=\mu(a)$, we show that $\beta(a)$ has the same time dependence as $\mu(a)$. As an example, explicit formalae are provided in the DGP model. In the general case, for theories with $\mu(a,k)$, we obtain a perturbative expansion for $\beta(\mu)$ around the General Relativity case $\mu=1$ which, for $f(R)$ theories, reaches an accuracy below $1 \%$. Finally, as an example we apply the obtained fitting functions in order to forecast the precision with which future galaxy surveys will be able to measure the $\mu$ parameter.Comment: 12 pages, 12 figures. New section on applications to forecasts for galaxy surveys and new references included. Matches version published in PR

Parametrizaciones de modelos cosmológicos alternativos y cotas para futuros mapas de galaxias

Tesis inédita de la Universidad Complutense de Madrid, Facultad de Ciencias Físicas, Departamento de Física Teórica, leída el 28/04/2021The next generation of galaxy surveys will shed new light on our understanding of the Universe on large scales. Thanks to the large number of galaxies and the accuracy of these galaxy maps, the cosmological parameters will be measured at the 1% level and below. This makes it necessary to develop forecast analysis to explore what are the parameters that galaxy surveys will constrain with better accuracy, and also the best configurations of these surveys to exploit the maximum potential of the observables. From the theoretical point of view, there are many different models that have been proposed in recent years to describe the yet unknown dark sector of cosmology. Regarding models for the late-time accelerated expansion of the Universe, they can be classified in twotypes: dark energy models and modified gravity models. The former considers a modification in the matter-energy term, this modification extends the constant dark energy term of CDM model into a dynamical dark energy. Instead, modified gravity models consider a modification in the gravity term that generates accelerated expansion...La próxima generación de mapas de galaxias arrojará luz en nuestra comprensión del Universo a gran escala. Gracias al gran número de galaxias y a la precisión de éstos mapas, se podrán medir los parámetros cosmológicos con precisión del 1% y menor. Es por ello que es necesario el desarrollo de estimaciones de las futuras medidas para explorar qué parámetros se podrán medir con mayor precisión, así como encontrar las mejores configuraciones de los mapas de galaxias para explotar el máximo potencial de los observables. Desde el punto de vista teórico, hay una gran cantidad de modelos que se han propuesto recientemente para describir el aún desconocido sector oscuro de la cosmología. En cuanto a los modelos que describen la actual expansión acelerada del Universo, se pueden clasificar principalmente en dos tipos: modelos de energía oscura y modelos de gravedad modificada. El primer tipo considera una modificación en el término de materia y energía, ésta modificación generaliza la constante cosmológica del modelo de CDM en una energía oscura dinámica. Por otro lado, los modelos de gravedad modificada generalizan el término de gravedad de la Relatividad General estándar para poder generar una expansión acelerada. En el contexto de mapas de galaxias y modelos cosmológicos del sector oscuro y gravedad modificada, la presente tesis tiene como objetivo estudiar parametrizaciones independientes del modelo para modelos de gravedad modificada. Además, realizaremos un análisis de Fisher con el fin de estimar la sensibilidad de futuros mapas de galaxias a la hora de detectar tales desviaciones...Fac. de Ciencias FísicasTRUEunpu

The Fisher gAlaxy suRvey cOde (FARO\texttt{FARO})

The Fisher gAlaxy suRvey cOde ($\texttt{FARO}$) is a new public Python code that computes the Fisher matrix for galaxy surveys observables. The observables considered are the linear multitracer 3D galaxy power spectrum, the linear convergence power spectrum for weak lensing, and the linear multitracer power spectrum for the correlation between galaxy distribution and convergence. The code allows for tomographic and model-independent analysis in which, for scale-independent growth, the following functions of redshift $A_a (z) \equiv \sigma_{8}(z) \, b_a (z)$, $R(z) \equiv \sigma_{8}(z) \, f(z)$, $L(z) \equiv \Omega_{m} \, \sigma_{8}(z) \, \Sigma (z)$ and $E(z) \equiv H(z)/H_0$, together with the function of scale $\hat{P}(k)$, are taken as free parameters in each redshift and scale bins respectively. In addition, a module for change of variables is provided to project the Fisher matrix on any particular set of parameters required. The code is built to be as fast as possible and user-friendly. As an application example, we forecast the sensitivity of future galaxy surveys like DESI, Euclid, J-PAS and LSST and compare their performance on different redshift and scale ranges.Comment: https://www.ucm.es/iparcos/far

Testing for gravitational preferred directions with galaxy and lensing surveys

We analyze the sensitivity of galaxy and weak-lensing surveys to detect preferred directions in the gravitational interaction. We consider general theories of gravity involving additional vector degrees of freedom with non-vanishing spatial components in the background. We use a model-independent parametrization of the perturbations equations in terms of four effective parameters, namely, the standard effective Newton constant G(eff) and slip parameter gamma for scalar modes and two new parameters mu(Q) and mu(h) for vector and tensor modes respectively, which are required when preferred directions are present. We obtain the expressions for the multipole galaxy power spectrum in redshift space and for the weak-lensing shear, convergence and rotation spectra in the presence of preferred directions. By performing a Fisher matrix forecast analysis, we estimate the sensitivity of a future Euclid-like survey to detect this kind of modification of gravity. We finally compare with the effects induced by violations of statistical isotropy in the primordial power spectrum and identify the observables which could discriminate between them

Modified gravity or imperfect dark matter: a model-independent discrimination

We analyze how to parametrize general modifications of the dark matter perturbations equations in a model-independent way. We prove that a general model with an imperfect and non-conserved dark matter fluid with bulk and shear viscosities and heat flux in a modified gravity scenario can be described with five general functions of time and scale. We focus on the sub-Hubble regime within the quasi-static approximation and calculate the observable power spectra of the galaxy distribution, galaxy velocities and weak lensing and find that these observables are only sensitive to three combinations of the initial five functions. Deviations of these three observable functions with respect to $\mathrm{\Lambda CDM}$ give us different characteristic signals which allow us to determine in which cases it is possible to discriminate a modification of gravity from an imperfect or non-conserved dark matter. Finally, we perform a Fisher forecast analysis for these three parameters and show an example for a particular model with shear viscosity

J-PAS: forecasts on dark energy and modified gravity theories

The next generation of galaxy surveys will allow us to test one of the most fundamental assumptions of the standard cosmology, i.e. that gravity is governed by the general theory of relativity (GR). In this paper, we investigate the ability of the Javalambre Physics of the AcceleratingUniverseAstrophysical Survey (J-PAS) to constrainGR and its extensions. Based on the J-PAS information on clustering and gravitational lensing, we perform a Fisher matrix forecast on the effective Newton constant, mu, and the gravitational slip parameter, eta, whose deviations from unity would indicate a breakdown of GR. Similar analysis is also performed for the DESI and Euclid surveys and compared to J-PAS with two configurations providing different areas, namely an initial expectation with 4000 deg(2) and the future best case scenario with 8500 deg(2). We show that J-PAS will be able to measure the parameters mu and eta at a sensitivity of 2-7 per cent, and will provide the best constraints in the interval z = 0.3-0.6, thanks to the large number of ELGs detectable in that redshift range. We also discuss the constraining power of J-PAS for dark energy models with a time-dependent equation-of-state parameter of the type w(a) = w(0) + w(a)(1 - a), obtaining Delta w(0) = 0.058 and Delta w(a) = 0.24 for the absolute errors of the dark energy parameters

J-PAS: forecasts for dark matter-dark energy elastic couplings

© 2021 IOP Publishing Artículo firmado por más de 10 autores We thank Wilmar Cardona for useful discussions on the fit to different datasets. JBJ, DB, DF and FATP acknowledge support from the Atraccion del Talento Cientifico en Salamanca programme, from project PGC2018-096038-B-I00 by Spanish Ministerio de Ciencia, Innovacion y Universidades and Ayudas del Programa XIII by USAL. DF acknowledges support from the programme Ayudas para Financiar la Contratacion Predoctoral de Personal Investigador (ORDEN EDU/601/2020) funded by Junta de Castilla y Leon and European Social Fund. This work has been supported by the MINECO (Spain) projects FIS201678859-P and PID2019-107394GB-I00 (AEI/FEDER, UE). LRA acknowledges financial support from CNPq (306696/2018-5) and FAPESP (2015/17199-0). JA is supported by CNPq (Grants No. 310790/2014-0 and 400471/2014-0) and FAPERJ (Grant No. 233906). SB acknowledges PGC2018-097585-B-C22, MINECO/FEDER, UE of the Spanish Ministerio de Economia, Industriay Competitividad. CEFCA researchers acknowledge support from the project PGC2018-097585-B-C21. SC is supported by CNPq (Grants No. 307467/2017-1 and420641/2018-1). R.A.D. acknowledges support from the Conselho Nacional de Desenvolvimento Cientifico e Tecnologico -CNPq through BPgrant 308105/2018-4, and the Financiadora de Estudos e Projetos -FINEP grants REF. 1217/13 -01.13.0279.00 and REF 0859/10-01.10.0663.00 and also FAPERJ PRONEX grant E-26/110.566/2010 for hardware funding support for the J-PAS project through the National Observatory of Braziland Centro Brasileiro de Pesquisas Fisicas. VM thanks CNPq (Brazil) and FAPES (Brazil) for partial financial support. This project has received funding from the European Union's Horizon 2020 research and innovation programme under the Marie Sklodowska-Curie grant agreement No 888258. CMdO acknowledges support from Brazilian agencies CNPq (grant 312333/2014-5) and FAPESP (grant 2009/54202-8. IAA researchers acknowledge financial support from the State Agency for Research of the Spanish MCIU through the "Center of Excellence Severo Ochoa" award to the Instituto de Astrofisica de Andalucia (SEV-2017-0709). LSJ acknowledges support from Brazilian agencies CNPq (grant 304819/2017-4) and FAPESP (grant 2012/00800-4).; This paper has gone through internal review by the J-PAS collaboration. Based on observations made with the JST/T250 telescope and JPCam at the Observatorio Astrofisico de Javalambre (OAJ), in Teruel, owned, managed, and operated by the Centro de Estudios de Fisica del Cosmos de Aragon (CEFCA). We acknowledge the OAJ Data Processing and Archiving Unit (UPAD) for reducing and calibrating the OAJ data used in this work. Funding for the J-PAS Project has been provided by the Governments of Spain and Aragon through the Fondo de Inversion de Teruel, European FEDER funding and the Spanish Ministry of Science, Innovation and Universities, and by the Brazilian agencies FINEP, FAPESP, FAPERJ and by the National Observatory of Brazil. Additional funding was also provided by the Tartu Observatory and by the J-PAS Chinese Astronomical Consortium.We consider a cosmological model where dark matter and dark energy feature a coupling that only affects their momentum transfer in the corresponding Euler equations. We perform a fit to cosmological observables and confirm previous findings within these scenarios that favour the presence of a coupling at more than 3a. This improvement is mainly driven by cluster counts from Planck Sunyaev-Zeldovich data that we include as a certain prior. We subsequently perform a forecast for future J-PAS data and find that clustering measurements will permit to clearly discern the presence of an interaction within a few percent level with the uncoupled case at more than 10o(-) when the complete survey, covering 8500 sq. deg., is considered. We found that the inclusion of weak lensing measurements will not help to further constrain the coupling parameter. For completeness, we compare to forecasts for DESI and Euclid, which provide similar discriminating power.Depto. de Física TeóricaFac. de Ciencias FísicasTRUEUnión Europea. H2020Ministerio de Economía y Competitividad (MINECO)/ FEDERMinisterio de Economía y Competitividad (MINECO)Ministerio de Ciencia e Innovación (MICINN)Centros de Excelencia Severo Ochoa (MICINN)pu

Parametrizing modified gravities with vector degrees of freedom: anisotropic growth and lensing

We consider the problem of parametrizing modified gravity theories that include an additional vector field in the sub-Hubble regime within the quasi-static approximation. We start from the most general set of second order equations for metric and vector field perturbations and allow for both temporal and spatial components of the background vector field. We find that in the case in which dark matter obeys standard conservation equations, eight parameters are needed to fully characterize the theory. If dark matter vorticity can be neglected, the number of independent parameters is reduced to four. In addition to the usual scale and redshift dependence, the effective parameters have an additional angular dependence induced by the preferred direction set by the background vector. In the considered sub-Hubble regime, we show that this angular dependence appears only through even multipoles and generates anisotropies in the growth function which translate into anisotropies in the galaxy and lensing convergence power spectra. The angular dependence generated by the preferred direction is different from that induced by redshift space distortions and could be disentangled in the data collected by future galaxy surveys