25 research outputs found
Signature of gravity via Lema\^itre-Tolman-Bondi inhomogeneous perturbations
We analyze inhomogeneous cosmological models in the local Universe, based on
the Lema\^itre-Tolman-Bondi (LTB) metric and developed using linear
perturbation theory on a homogeneous and isotropic Universe background.
Focusing on the different evolution of spherical symmetric inhomogeneities, we
want to compare the LTB model, in which the cosmological constant
is included in the LTB formalism, with inhomogeneous cosmological
models based on modified gravity theories viewed in the Jordan frame. In
particular, we adopt the Hu-Sawicki model in the Jordan frame to
describe the cosmic accelerated phase for the background Universe. The key
difference between the LTB model and the gravity in an
inhomogeneous cosmology is outlined by the 0-1 component of the gravitational
field equations, since it intrinsically links the metric tensor components to
the non-minimally coupled scalar field, present in the Jordan frame. We solve
the system of field equations for both cosmological models adopting the method
of separation of variables: we can integrate analytically the radial profiles
of local perturbations, while their time evolution requires a numerical
approach. The main result of the analysis concerns the different radial
profiles of local inhomogeneities in the two cosmological scenarios: the radial
perturbations follow a power-law in the LTB model, while Yukawa-like
contributions appear in the theory. Interestingly, this latter peculiar
behavior of radial profiles is not affected by the choice of the
functional form. The numerical solution of time-dependent perturbations
exhibits a non-diverging profile. This work suggests that investigations about
local inhomogeneities in the late Universe may allow us to discriminate if the
present cosmic acceleration is caused by a cosmological constant term or a
modified gravity effect.Comment: 21 pages, 5 figures, submitted to Physical Review D. [v2]:
Introduction, Sects. VI and VII are modified; updated reference
gravity in the Jordan Frame as a Paradigm for the Hubble Tension
We analyze the gravity in the so-called Jordan frame, as implemented
to the isotropic Universe dynamics. The goal of the present study is to show
that, according to recent data analyses of the supernovae Ia Pantheon sample,
it is possible to account for an effective redshift-dependence of the Hubble
constant via the dynamics of a non-minimally coupled scalar field, emerging in
the gravity. We face the question both from an analytical and purely
numerical point of view, following the same technical paradigm. We arrive to
establish that the expected decay of the Hubble constant with the redshift
is ensured by a form of the scalar field potential, which remains essentially
constant for , independently if this request is made a priori, as
in the analytical approach, or obtained a posteriori, when the numerical
procedure is addressed. Thus, we demonstrate that an dark energy model
is able to account for an apparent variation of the Hubble constant due to the
rescaling of the Einstein constant by the scalar mode.Comment: 6 pages, 3 figures, accepted for publication in MNRAS Letter
On the Hubble constant tension in the SNe Ia Pantheon sample
The Hubble constant () tension between Type Ia Supernovae (SNe Ia) and
Planck measurements ranges from 4 to 6 . To investigate this tension,
we estimate in the CDM and CDM models by dividing
the Pantheon sample, the largest compilation of SNe Ia, into 3, 4, 20 and 40
bins. We fit the extracted values with a function mimicking the
redshift evolution: , where
indicates an evolutionary parameter and at . We set the
absolute magnitude of SNe Ia so that , and we fix fiducial values for
and .
We find that evolves with redshift, showing a slowly decreasing trend,
with coefficients consistent with zero only from 1.2 to 2.0 .
Although the coefficients are compatible with 0 in 3 , this
however may affect cosmological results. We measure locally a variation of
in 3 and 4
bins. Extrapolating to , the redshift of the last scattering
surface, we obtain values of compatible in 1 with Planck
measurements independently of cosmological models and number of bins we
investigated. Thus, we have reduced the tension from to for
the CDM and CDM models, respectively. If the decreasing
trend of is real, it could be due to astrophysical selection effects
or to modified gravity.Comment: 20 pages, 6 figures, 1 table; Accepted, to be published in Ap
The “Diabetes Comorbidome”: A Different Way for Health Professionals to Approach the Comorbidity Burden of Diabetes
(1) Background: The disease burden related to diabetes is increasing greatly, particularly in older subjects. A more comprehensive approach towards the assessment and management of diabetes’ comorbidities is necessary. The aim of this study was to implement our previous data identifying and representing the prevalence of the comorbidities, their association with mortality, and the strength of their relationship in hospitalized elderly patients with diabetes, developing, at the same time, a new graphic representation model of the comorbidome called “Diabetes Comorbidome”. (2) Methods: Data were collected from the RePoSi register. Comorbidities, socio-demographic data, severity and comorbidity indexes (Cumulative Illness rating Scale CIRS-SI and CIRS-CI), and functional status (Barthel Index), were recorded. Mortality rates were assessed in hospital and 3 and 12 months after discharge. (3) Results: Of the 4714 hospitalized elderly patients, 1378 had diabetes. The comorbidities distribution showed that arterial hypertension (57.1%), ischemic heart disease (31.4%), chronic renal failure (28.8%), atrial fibrillation (25.6%), and COPD (22.7%), were the more frequent in subjects with diabetes. The graphic comorbidome showed that the strongest predictors of death at in hospital and at the 3-month follow-up were dementia and cancer. At the 1-year follow-up, cancer was the first comorbidity independently associated with mortality. (4) Conclusions: The “Diabetes Comorbidome” represents the perfect instrument for determining the prevalence of comorbidities and the strength of their relationship with risk of death, as well as the need for an effective treatment for improving clinical outcomes
Antidiabetic Drug Prescription Pattern in Hospitalized Older Patients with Diabetes
Objective: To describe the prescription pattern of antidiabetic and cardiovascular drugs in a cohort of hospitalized older patients with diabetes. Methods: Patients with diabetes aged 65 years or older hospitalized in internal medicine and/or geriatric wards throughout Italy and enrolled in the REPOSI (REgistro POliterapuie SIMI—Società Italiana di Medicina Interna) registry from 2010 to 2019 and discharged alive were included. Results: Among 1703 patients with diabetes, 1433 (84.2%) were on treatment with at least one antidiabetic drug at hospital admission, mainly prescribed as monotherapy with insulin (28.3%) or metformin (19.2%). The proportion of treated patients decreased at discharge (N = 1309, 76.9%), with a significant reduction over time. Among those prescribed, the proportion of those with insulin alone increased over time (p = 0.0066), while the proportion of those prescribed sulfonylureas decreased (p < 0.0001). Among patients receiving antidiabetic therapy at discharge, 1063 (81.2%) were also prescribed cardiovascular drugs, mainly with an antihypertensive drug alone or in combination (N = 777, 73.1%). Conclusion: The management of older patients with diabetes in a hospital setting is often sub-optimal, as shown by the increasing trend in insulin at discharge, even if an overall improvement has been highlighted by the prevalent decrease in sulfonylureas prescription
Clinical features and outcomes of elderly hospitalised patients with chronic obstructive pulmonary disease, heart failure or both
Background and objective: Chronic obstructive pulmonary disease (COPD) and heart failure (HF) mutually increase the risk of being present in the same patient, especially if older. Whether or not this coexistence may be associated with a worse prognosis is debated. Therefore, employing data derived from the REPOSI register, we evaluated the clinical features and outcomes in a population of elderly patients admitted to internal medicine wards and having COPD, HF or COPD + HF.
Methods: We measured socio-demographic and anthropometric characteristics, severity and prevalence of comorbidities, clinical and laboratory features during hospitalization, mood disorders, functional independence, drug prescriptions and discharge destination. The primary study outcome was the risk of death.
Results: We considered 2,343 elderly hospitalized patients (median age 81 years), of whom 1,154 (49%) had COPD, 813 (35%) HF, and 376 (16%) COPD + HF. Patients with COPD + HF had different characteristics than those with COPD or HF, such as a higher prevalence of previous hospitalizations, comorbidities (especially chronic kidney disease), higher respiratory rate at admission and number of prescribed drugs. Patients with COPD + HF (hazard ratio HR 1.74, 95% confidence intervals CI 1.16-2.61) and patients with dementia (HR 1.75, 95% CI 1.06-2.90) had a higher risk of death at one year. The Kaplan-Meier curves showed a higher mortality risk in the group of patients with COPD + HF for all causes (p = 0.010), respiratory causes (p = 0.006), cardiovascular causes (p = 0.046) and respiratory plus cardiovascular causes (p = 0.009).
Conclusion: In this real-life cohort of hospitalized elderly patients, the coexistence of COPD and HF significantly worsened prognosis at one year. This finding may help to better define the care needs of this population
Clinical features and outcomes of elderly hospitalised patients with chronic obstructive pulmonary disease, heart failure or both
Background and objective: Chronic obstructive pulmonary disease (COPD) and heart failure (HF) mutually increase the risk of being present in the same patient, especially if older. Whether or not this coexistence may be associated with a worse prognosis is debated. Therefore, employing data derived from the REPOSI register, we evaluated the clinical features and outcomes in a population of elderly patients admitted to internal medicine wards and having COPD, HF or COPD + HF. Methods: We measured socio-demographic and anthropometric characteristics, severity and prevalence of comorbidities, clinical and laboratory features during hospitalization, mood disorders, functional independence, drug prescriptions and discharge destination. The primary study outcome was the risk of death. Results: We considered 2,343 elderly hospitalized patients (median age 81 years), of whom 1,154 (49%) had COPD, 813 (35%) HF, and 376 (16%) COPD + HF. Patients with COPD + HF had different characteristics than those with COPD or HF, such as a higher prevalence of previous hospitalizations, comorbidities (especially chronic kidney disease), higher respiratory rate at admission and number of prescribed drugs. Patients with COPD + HF (hazard ratio HR 1.74, 95% confidence intervals CI 1.16-2.61) and patients with dementia (HR 1.75, 95% CI 1.06-2.90) had a higher risk of death at one year. The Kaplan-Meier curves showed a higher mortality risk in the group of patients with COPD + HF for all causes (p = 0.010), respiratory causes (p = 0.006), cardiovascular causes (p = 0.046) and respiratory plus cardiovascular causes (p = 0.009). Conclusion: In this real-life cohort of hospitalized elderly patients, the coexistence of COPD and HF significantly worsened prognosis at one year. This finding may help to better define the care needs of this population
Large-scale structure of the Universe in General Relativity and beyond
The large-scale structure of the Universe and the nature of dark energy are beginning to be comprehensively understood, as we have recently entered the era of precision cosmology. The standard LCDM cosmological model, which includes a cosmological constant L and a cold dark matter component, successfully explains the evolution and composition of our Universe. However, recent measurements with tighter constraints on cosmological parameters have revealed several serious anomalies, such as the Hubble constant tension, which could be a signal of a possible theoretical model crisis. Therefore, it is necessary to reassess the fundamental pillars of the LCDM model, i.e., 1) General Relativity is the underlying gravitational theory that governs cosmological dynamics; 2) the Universe is homogeneous and isotropic on scales greater than approximately 100 Mpc (cosmological principle). This thesis aims to discuss the robustness of these two pillars by exploring possible close scenarios with respect to the LCDM model, such as modified gravity theories and inhomogeneous cosmologies. We are interested in addressing the following questions: how can cosmological data enable us to distinguish between the LCDM cosmological model and modified gravity theories? What is the impact of local inhomogeneities on cosmological observables? Firstly, modified gravity theories predict deviations from LCDM, providing alternatives to the cosmological constant to ensure the present cosmic acceleration. Secondly, the large-scale structure of the Universe and local deviations from spatial homogeneity could impact our cosmological measurements. All these alternative proposals allow us to investigate unresolved cosmological issues
Signature of f(R) gravity via Lemaître–Tolman–Bondi inhomogeneous perturbations
Abstract We analyze inhomogeneous cosmological models in the local Universe, described by the Lemaître–Tolman–Bondi (LTB) metric and developed using linear perturbation theory on a homogeneous and isotropic Universe background. Focusing on the different evolution of spherical symmetric inhomogeneities, we compare the Λ LTB model, in which the cosmological constant Λ is included in the LTB formalism, with inhomogeneous cosmological models based on f R modified gravity theories viewed in the Jordan frame. We solve the system of field equations for both inhomogeneous cosmological models adopting the method of separation of variables: we integrate analytically the radial profiles of local perturbations, while their time evolution requires a numerical approach. The main result of the analysis concerns the different radial profiles of local inhomogeneities due to the presence of a non-minimally coupled scalar field in the Jordan frame of f R gravity. While radial perturbations follow a power-law in the Λ LTB model, Yukawa-like contributions appear in the f R theory. Interestingly, this latter peculiar behavior of radial profile is not affected by the choice of the f R functional form. The numerical solution of time-dependent perturbations exhibits a non-diverging profile. This work suggests that investigations about local inhomogeneities in the late Universe may allow us to discriminate if the present cosmic acceleration is caused by a cosmological constant term or a modified gravity effect
On the evolution of inhomogeneous perturbations in the ΛCDM model and f(R) modified gravity theories
We focus on weak inhomogeneous models of the Universe at low redshifts, described by the Lemaitre-Tolman-Bondi (LTB) metric. The principal aim of this work is to compare the evolution of inhomogeneous perturbations in the ΛCDM cosmological model and f(R) modified gravity theories, considering a flat Friedmann-Lemaitre-Robertson-Walker (FLRW) metric for the background. More specifically, we adopt the equivalent scalar-tensor formalism in the Jordan frame, in which the extra degree of freedom of the f(R) function is converted into a non-minimally coupled scalar field. We investigate the evolution of local inhomogeneities in time and space separately, following a linear perturbation approach. Then, we obtain spherically symmetric solutions in both cosmological models. Our results allow us to distinguish between the presence of a cosmological constant and modified gravity scenarios, since a peculiar Yukawa-like solution for radial perturbations occurs in the Jordan frame. Furthermore, the radial profile of perturbations does not depend on a particular choice of the f(R) function, hence our results are valid for any f(R) model