Selected Topics in Numerical Methods for Cosmology

The large amount of cosmological data already available (and in the near future) makes necessary the development of efficient numerical codes. Many software products have been implemented to perform cosmological analyses considering one or few probes. The need of multi-task software is rapidly increasing, in order to combine numerous cosmological probes along with their specificity (e.g., astrophysical descriptions and systematic errors). In this work we mention some of these libraries, bringing out some challenges they will face in the few-percent error era (on the cosmological parameters). We review some concepts of the standard cosmological model, and examine some specific topics on their implementation, bringing, for example, the discussion on how some quantities are numerically defined in different codes. We also consider implementation differences between public codes, mentioning their advantages/disadvantages.Comment: 23 pages, 3 figures. Contribution to the 3rd Jos\'e Pl\'inio Baptista School on Cosmology held in 2016 in Pedra Azul, Esp\'irito Santo, Brazil. Submitted to Univers

New formalism to define vacuum states for scalar fields in curved space-times

The problem of finding a vacuum definition for a single quantum field in curved space-times is discussed under a new geometrical perspective. The phase space dynamics of the quantum field modes are mapped to curves in a 2-dimensional hyperbolic metric space, in which distances between neighbor points are shown to be proportional to the Bogoliubov coefficients associated with their corresponding mode solutions in phase space. The vacuum state for each mode is then defined as the unique trajectory from which all mapped phase space solutions move within thin annular regions around it. This property implies the stability of the vacuum state: solutions evolved from a point in this trajectory stay close to it as both evolve, and the particle creation is therefore minimized. The new approach is applied to the well-known cases of the time-independent dynamics, where the solutions draw circles around this curve, and when the adiabatic approximation is valid. The analysis is then extended to time-dependent cases in which the adiabatic approximation is not applicable, in the super-Hubble or low-frequency regimes. It is shown that stability trajectories can also be found in these situations, and stable quantum vacua can be obtained. This new formalism is applied to two situations: de Sitter space, where the Bunch-Davies vacuum is obtained in a completely different manner through an analysis in the super-Hubble regime, and in the context of cosmological bouncing models, in which the contracting phase is dominated by a cosmological constant in the asymptotic past. A new vacuum state for cosmological perturbations is proposed in this situation.Comment: 31 pages, 6 figure

Molecular analysis of pathogens in cerebrospinal fluid by the polymerase chain reaction in HIV-infected patients

Introdução: A reação em cadeia da polimerase (PCR) foi teste de grande impacto no diagnóstico das meningites e encefalites linfocíticas durante a última década. Esse método foi extensivamente usado no diagnóstico das infecções do sistema nervoso central (SNC), devido a sua habilidade em detectar amostras mínimas de DNA-alvo no líquido cefalorraquiano. Objetivo: O objetivo deste estudo foi identificar a prevalência dos patógenos oportunistas responsáveis por causar problemas neurológicos em pacientes infectados com o vírus da imunodeficiência humana (HIV) e avaliar sua associação com os achados clínicos, laboratoriais e da tomografia computadorizada cerebral (TCC). Pacientes e métodos: Um estudo transversal foi realizado em 203 amostras de líquido cefalorraquiano (LCR) de pacientes do sul do Brasil infectados com HIV e com aparente encefalite e meningite linfocíticas. As amostras foram analisadas para os seguintes agentes pelo método da reação em cadeia da polimerase “nested” ou dupla (N-PCR): citomegalovírus, vírus do Epstein-Barr, vírus do herpes simplex tipos 1 e 2, vírus da varicella zoster, vírus do herpes humano tipo 6, vírus JC, Toxoplasma gondii e micobactérias. Resultado: Pelo menos um patógeno foi encontrado em 77 (38%) dos indivíduos. O Epstein-Barr foi o mais prevalente, com 40 casos (19,7%), seguido pelo citomegalovívus, com 12 casos (15%) e pelo vírus JC, em 9 casos (4,4%). Um N-PCR positivo mostrou associação com aumento de proteínas e de celularidade (P=0,001), meningismo (P=0,017) e tomografia computadorizada anormal (P=0,006). Conclusão: O painel de PCR empregado foi efetivo na identificação de infecções neurológicas severas em pacientes HIV positivos.Introduction: Polymerase chain reaction (PCR) has had great impact on the diagnosis of lymphocytic meningitis and encephalitis over the last decade. It has been extensively used in the diagnosis of central nervous system (CNS) infections for its ability to detect small amounts of target DNA in the cerebrospinal fluid (CSF). Objective: The aim of this study was to identify the prevalence of opportunistic pathogens responsible for neurological disorders in patients infected with human immunodeficiency virus (HIV) and to evaluate its association with clinical, laboratory and cerebral computed tomography (CCT) findings. Patients and methods: A cross-sectional study was performed on 203 cerebrospinal fluids (CSF) from HIV-infected patients from Southern Brazil, with apparent lymphocytic meningitis and encephalitis. CSF samples were analyzed with probes for cytomegalovirus, Epstein-Barr virus, herpes simplex virus types 1 and 2, varicella zoster virus, human herpes virus type 6, JC virus, Toxoplasma gondii and mycobacterium in nested polymerase chain reaction (N-PCR). Results: At least one pathogen was found in 77 (38.0%) individuals. Epstein-Barr virus was the most prevalent with 40 cases (19.7%), followed by cytomegalovirus with 12 cases (5.9%) and JC virus with 9 cases (4.4%). Positive NPCR showed association with high spinal fluid protein and cell count (P=0.001), meningism (P=0.017) and abnormal CCT (P=0.006). Conclusion: The PCR panel used was effective in screening several neurological infections in HIV positive patients

Impact of COVID-19 on cardiovascular testing in the United States versus the rest of the world

Objectives: This study sought to quantify and compare the decline in volumes of cardiovascular procedures between the United States and non-US institutions during the early phase of the coronavirus disease-2019 (COVID-19) pandemic. Background: The COVID-19 pandemic has disrupted the care of many non-COVID-19 illnesses. Reductions in diagnostic cardiovascular testing around the world have led to concerns over the implications of reduced testing for cardiovascular disease (CVD) morbidity and mortality. Methods: Data were submitted to the INCAPS-COVID (International Atomic Energy Agency Non-Invasive Cardiology Protocols Study of COVID-19), a multinational registry comprising 909 institutions in 108 countries (including 155 facilities in 40 U.S. states), assessing the impact of the COVID-19 pandemic on volumes of diagnostic cardiovascular procedures. Data were obtained for April 2020 and compared with volumes of baseline procedures from March 2019. We compared laboratory characteristics, practices, and procedure volumes between U.S. and non-U.S. facilities and between U.S. geographic regions and identified factors associated with volume reduction in the United States. Results: Reductions in the volumes of procedures in the United States were similar to those in non-U.S. facilities (68% vs. 63%, respectively; p = 0.237), although U.S. facilities reported greater reductions in invasive coronary angiography (69% vs. 53%, respectively; p < 0.001). Significantly more U.S. facilities reported increased use of telehealth and patient screening measures than non-U.S. facilities, such as temperature checks, symptom screenings, and COVID-19 testing. Reductions in volumes of procedures differed between U.S. regions, with larger declines observed in the Northeast (76%) and Midwest (74%) than in the South (62%) and West (44%). Prevalence of COVID-19, staff redeployments, outpatient centers, and urban centers were associated with greater reductions in volume in U.S. facilities in a multivariable analysis. Conclusions: We observed marked reductions in U.S. cardiovascular testing in the early phase of the pandemic and significant variability between U.S. regions. The association between reductions of volumes and COVID-19 prevalence in the United States highlighted the need for proactive efforts to maintain access to cardiovascular testing in areas most affected by outbreaks of COVID-19 infection

Cosmological Synergies Enabled by Joint Analysis of Multi-probe data from WFIRST, Euclid, and LSST

WFIRST, Euclid, and LSST are all missions designed to perform dedicated cosmology surveys that offer unprecedented statistical constraining power and control of systematic uncertainties. There is a growing realization that these missions will be significantly more powerful when the data are processed and analyzed in unison

Cluster abundance cosmology: Towards including Super-Sample Covariance in the unbinned likelihood

International audienceThe measure of the abundance of galaxy clusters in the Universe is a sensitive probe of cosmology, sensitive to both the expansion history and the growth of structure. Density fluctuations across the finite survey volume induce noise to this measure, often referred to as Super-Sample Covariance (SSC). In the past for unbinned cluster analysis such noise has not been included in the cluster likelihood. In this paper, we present a derivation of the unbinned likelihood accounting for Super-Sample Covariance by using a Gauss-Poisson Compound (GPC) likelihood. We show that deriving the unbinned likelihood with SSC from the expansion of the GPC formalism to the second order in density perturbation is not sufficient, preventing us from using analytical methods already explored in the literature. In order to solve this issue, we still used the GPC model to derive an alternative "hybrid" likelihood, by using standard redshift bins. Using simulated dark matter halo catalog obtained by the PINOCCHIO algorithm, we found that the hybrid likelihood, accounting for both Poisson noise and SSC, increases the dispersion of the parameter posteriors by 25 per cent using 2,500 clusters, compared to the standard Poisson likelihood

Cluster abundance cosmology: Towards including Super-Sample Covariance in the unbinned likelihood

International audienceThe measure of the abundance of galaxy clusters in the Universe is a sensitive probe of cosmology, sensitive to both the expansion history and the growth of structure. Density fluctuations across the finite survey volume induce noise to this measure, often referred to as Super-Sample Covariance (SSC). In the past for unbinned cluster analysis such noise has not been included in the cluster likelihood. In this paper, we present a derivation of the unbinned likelihood accounting for Super-Sample Covariance by using a Gauss-Poisson Compound (GPC) likelihood. We show that deriving the unbinned likelihood with SSC from the expansion of the GPC formalism to the second order in density perturbation is not sufficient, preventing us from using analytical methods already explored in the literature. In order to solve this issue, we still used the GPC model to derive an alternative "hybrid" likelihood, by using standard redshift bins. Using simulated dark matter halo catalog obtained by the PINOCCHIO algorithm, we found that the hybrid likelihood, accounting for both Poisson noise and SSC, increases the dispersion of the parameter posteriors by 25 per cent using 2,500 clusters, compared to the standard Poisson likelihood

Cluster abundance cosmology: Towards including Super-Sample Covariance in the unbinned likelihood

International audienceThe measure of the abundance of galaxy clusters in the Universe is a sensitive probe of cosmology, sensitive to both the expansion history and the growth of structure. Density fluctuations across the finite survey volume induce noise to this measure, often referred to as Super-Sample Covariance (SSC). In the past for unbinned cluster analysis such noise has not been included in the cluster likelihood. In this paper, we present a derivation of the unbinned likelihood accounting for Super-Sample Covariance by using a Gauss-Poisson Compound (GPC) likelihood. We show that deriving the unbinned likelihood with SSC from the expansion of the GPC formalism to the second order in density perturbation is not sufficient, preventing us from using analytical methods already explored in the literature. In order to solve this issue, we still used the GPC model to derive an alternative "hybrid" likelihood, by using standard redshift bins. Using simulated dark matter halo catalog obtained by the PINOCCHIO algorithm, we found that the hybrid likelihood, accounting for both Poisson noise and SSC, increases the dispersion of the parameter posteriors by 25 per cent using 2,500 clusters, compared to the standard Poisson likelihood