ABSTRACT
Unimodular gravity is an alternative theory of gravity to general relativity. The gravitational field equations are given by the trace-free version of Einstein’s field equations. Due to the ...structure of the theory, unimodular gravity admits a diffusion term that characterizes a possible non-conservation of the canonical energy–momentum tensor locally. Employing this feature of unimodular gravity, in this work, we explicitly show how to construct an inflationary phase that can be contrasted with current observations. In particular, we focus on three different inflationary scenarios of physical interest. An important element in these scenarios is that the accelerated expansion is driven by the diffusion term exclusively, i.e. there is no inflaton. Furthermore, the primordial spectrum during inflation is generated by considering inhomogeneous perturbations associated to standard hydrodynamical matter (modelled as a single ultra-relativistic fluid). For each of the scenarios, we obtain the prediction for the primordial spectrum and contrast it with recent observational bounds using Planck 2018 + Bicep2/KECK Array data.
The physical mechanism responsible for the emergence of primordial cosmic seeds from a perfect isotropic and homogeneous Universe has not been fully addressed in standard cosmic inflation. To handle ...this shortcoming, D. Sudarsky et al have developed a proposal: the self-induced collapse hypothesis. In this scheme, the objective collapse of the inflaton’s wave function generates the inhomogeneity and anisotropy at all scales. In this paper we analyze the viability of a set of inflationary potentials in both the context of the collapse proposal and within the standard inflationary framework. For this, we perform a statistical analysis using recent CMB and BAO data to obtain the prediction for the scalar spectral index ns in the context of a particular collapse model: the Wigner scheme. The predicted ns and the tensor-to-scalar ratio r in terms of the slow roll parameters is different between the collapse scheme and the standard inflationary model. For each potential considered we compare the prediction of ns and r with the limits established by observational data in both pictures. The result of our analysis shows in most cases a difference in the inflationary potentials allowed by the observational limits in both frameworks. In particular, in the standard approach the more concave a potential is, the more is favored by the data. On the other hand, in the Wigner scheme, the data favors equally all type of concave potentials, including those at the border between convex and concave families.
Emergent universe revisited through the CSL theory Bengochea, Gabriel R.; Piccirilli, María Pía; León, Gabriel
The European physical journal. C, Particles and fields,
12/2021, Letnik:
81, Številka:
12
Journal Article
Recenzirano
Odprti dostop
In this work we analyze how the spectrum of primordial scalar perturbations is modified, within the emergent universe scenario, when a particular version of the Continuous Spontaneous Localization ...(CSL) model is incorporated as the generating mechanism of initial perturbations, providing also an explanation to the quantum-to-classical transition of such perturbations. On the other hand, a phase of super-inflation, prior to slow-roll inflation, is a characteristic feature of the emergent universe hypothesis. In recent works, it was shown that the super-inflation phase could generically induce a suppression of the temperature anisotropies of the CMB at large angular scales. We study here under what conditions the CSL maintains or modifies these characteristics of the emergent universe and their compatibility with the CMB observations.
Inflation, a period of exponential expansion in the early Universe, is considered an important part of the standard ΛCDM cosmological model, and plays a crucial role in explaining a wide range of ...current observations. The standard inflationary model predicts a primordial spectrum of fluctuations that is nearly scale-independent, fitting remarkably well the latest observational data. Nevertheless, there is an ongoing discussion surrounding the transition from an initial homogeneous and isotropic quantum state, characterizing the matter fields during inflation, to a classical inhomogeneous/anisotropic one, which gives rise to large-scale structure in the Universe. To tackle this issue, in the present work we explore an inflationary scenario where quantum “collapse” (or reduction) occurs naturally during the evolution of the system; this model is inspired in the so called Continuous Spontaneous Localization (CSL) model. Our present work builds upon previous results by considering the primordial power spectrum up to the second order in the Hubble Flow Functions, where we perform an estimation of the model free parameters. By validating the predictions of the model against observational data, we investigate whether this second-order calculation can explain the slight departure from the power law observed in the scalar spectral running index. We hope this research contributes to the understanding of the quantum-to-classical transition and its implications for cosmology.
The precise physical mechanism describing the emergence of the seeds of cosmic structure from a perfect isotropic and homogeneous universe has not been fully explained by the standard version of ...inflationary models. To handle this shortcoming, D. Sudarsky and collaborators have developed a proposal:
the self-induced collapse hypothesis.
In this scheme, the objective collapse of the inflaton wave function is responsible for the emergence of inhomogeneity and anisotropy at all scales. In previous papers, the proposal was developed with an almost exact de Sitter space-time approximation for the background that led to a perfect scale-invariant power spectrum. In the present article, we consider a full quasi-de Sitter expansion and calculate the primordial power spectrum for three different choices of the self-induced collapse. The consideration of a quasi-de Sitter background allows us to distinguish departures from an exact scale-invariant power spectrum that are due to the inclusion of the collapse hypothesis. These deviations are also different from the prediction of standard inflationary models with a running spectral index. A comparison with the primordial power spectrum and the CMB temperature fluctuation spectrum preferred by the latest observational data is also discussed. From the analysis performed in this work, it follows that most of the collapse schemes analyzed in this paper are viable candidates to explain the present observations of the CMB fluctuation spectrum.
Retroclival epidural hematomas (REDHs) are rare and almost exclusively found in the pediatric age group. Frequently, the etiology is related to accidental trauma, though other mechanisms have been ...observed, including coagulopathy, non-accidental trauma, and pituitary apoplexy. A 76-year-old man was admitted to our emergency department after a loss of consciousness. He presented with a Glasgow Coma Scale of 13(E3V4M6). He complained of headache accompanied by nausea and vomiting. A computer tomography (CT) revealed a hemorrhage along the clivus and dens. Magnetic resonance imaging (MRI) demonstrated the retroclival hematoma in epidural space. At discharge headache resolved without medical or operative intervention. REDHs are likely underdiagnosed in adults and magnetic resonance imaging is superior for identifying these lesions. Atlanto-occipital dislocation should be considered in all cases of REDH. Most cases exhibit a benign clinical course with conservative management, surgical management is dictated based on the presence of hydrocephalus, brainstem compression, and occipitocervical instability.
Abstract Background Congenital cytomegalovirus (CMV) infection is a major cause of central nervous system damage leading to sensorineural hearing loss, mental retardation and cerebral palsy. ...Objectives Identify the type of organ involvement and understand the histopathogenesis of damage in foetuses of women with a CMV-highly positive amniotic fluid. Study design 34 foetuses with congenital CMV infection documented by prenatal diagnosis were studied. Three foetuses died in utero . The remaining pregnancies were electively terminated at 20–21 weeks gestation. Results Foetal organs positive for CMV antigens were: placenta (100%), pancreas (100%), lung (87%), kidney (87%), liver (71%), brain (55%) and heart (44%). Inflammatory infiltrate was almost always present in CMV-infected foetal organs and the severity of the inflammatory response was correlated with the organ damage. Brain damage with necrosis was observed in 33% (9/27) and a mild telencephalic leukoencephalopathy in 22% (6/27) of foetuses studied. Conclusions Focal necrosis was observed very frequently in organs such as pancreases, livers, hearts and kidneys. However the damage in these organs is likely to be resolved by parenchymal regeneration. Brain damage, which seems to be the results of a combined effect of viral infection, inflammatory infiltration and hypoxia due to severe placentitis, is less likely to be resolved because of the low regeneration ability of this organ.
PDF
