Bouncing cosmologies in massive gravity on de Sitter

In the framework of massive gravity with a de Sitter reference metric, we study homogeneous and isotropic solutions with positive spatial curvature. Remarkably, we find that bounces can occur when cosmological matter satisfies the strong energy condition, in contrast to what happens in classical general relativity. This is due to the presence in the Friedmann equations of additional terms, which depend on the scale factor and its derivatives and can be interpreted as an effective fluid. We present a detailed study of the system using a phase space analysis. After having identified the fixed points of the system and investigated their stability properties, we discuss the cosmological evolution in the global physical phase space. We find that bouncing solutionsComment: 14 pages, 8 figure

Multi-disformal invariance of nonlinear primordial perturbations

We study disformal transformations of the metric in the cosmological context. We first consider the disformal transformation generated by a scalar field $\phi$ and show that the curvature and tensor perturbations on the uniform $\phi$ slicing, on which the scalar field is homogeneous, are non-linearly invariant under the disformal transformation. Then we discuss the transformation properties of the evolution equations for the curvature and tensor perturbations at full non-linear order in the context of spatial gradient expansion as well as at linear order. In particular, we show that the transformation can be described in two typically different ways: one that clearly shows the physical invariance and the other that shows an apparent change of the causal structure. Finally we consider a new type of disformal transformation in which a multi-component scalar field comes into play, which we call a "multi-disformal transformation". We show that the curvature and tensor perturbations are invariant at linear order, and also at non-linear order provided that the system has reached the adiabatic limit.Comment: 8 page

Cosmological disformal invariance

The invariance of physical observables under disformal transformations is considered. It is known that conformal transformations leave physical observables invariant. However, whether it is true for disformal transformations is still an open question. In this paper, it is shown that a pure disformal transformation without any conformal factor is equivalent to rescaling the time coordinate. Since this rescaling applies equally to all the physical quantities, physics must be invariant under a disformal transformation, that is, neither causal structure, propagation speed nor any other property of the fields are affected by a disformal transformation itself. This fact is presented at the action level for gravitational and matter fields and it is illustrated with some examples of observable quantities. We also find the physical invariance for cosmological perturbations at linear and high orders in perturbation, extending previous studies. Finally, a comparison with Horndeski and beyond Horndeski theories under a disformal transformation is made.Comment: 23 pages + Appendix, updated versio

Preeclampsia and diuresis criteria: our experience at the University of Iowa Hospitals and Clinics

Preeclampsia is a multisystem disorder that complicates approximately 5-8% of pregnancies. It is known that the clinical manifestations of preeclampsia are a result of widespread vasoconstriction. It is therefore thought that the onset of diuresis may signal a reversal of this vasoconstriction, and thus resolution of the disease. This retrospective cohort study was conducted at the University of Iowa Hospitals and Clinics (UIHC) to validate our diuresis criteria and determine if there was a trend for diuresis that was dependent on the type of preeclampsia. This study suggests that the diuresis curves for those women with mild preeclampsia and severe preeclampsia do not vary significantly after the first 5 hours We were able to separate the women with severe preeclampsia into two groups, one of which would have met our diuresis criteria prior to 24 hours and the other of which would not have met diuresis criteria at 24 hours post-delivery