Scalar field phase dynamics in preheating

We study the model of a massive inflaton field $\phi$ coupled to another scalar filed $\chi$ with interaction term $g^2\phi^2\chi^2$ for the first stage of preheating. We obtain the the behavior of the phase in terms of the iteration of a simple family of circle maps. When expansion of the universe is taken into account the qualitative behavior of the phase and growth number evolution is reminiscent of the behavior found in the case without expansion.Comment: 4 pages, 4 figures, LaTeX; submitted to the Proceedings of Eleventh Marcel Grossmann Meetin

Dynamical study of the empty Bianchi type I model in generalised scalar-tensor theory

A dynamical study of the generalised scalar-tensor theory in the empty Bianchi type I model is made. We use a method from which we derive the sign of the first and second derivatives of the metric functions and examine three different theories that can all tend towards relativistic behaviours at late time. We determine conditions so that the dynamic be in expansion and decelerated at late time.Comment: 18 pages, 3 figures, to appear in General Relativity and Gravitatio

An anti-Schwarzshild solution: wormholes and scalar-tensor solutions

We investigate a static solution with an hyperbolic nature, characterised by a pseudo-spherical foliation of space. This space-time metric can be perceived as an anti-Schwarzschild solution, and exhibits repulsive features. It belongs to the class of static vacuum solutions termed "a degenerate static solution of class A". In the present work we review its fundamental features, discuss the existence of generalised wormholes, and derive its extension to scalar-tensor gravity theories in general.Comment: 3 pages, contribution to the proceedings of the Spanish Relativity Meeting-ERE200

Self-interacting scalar field cosmologies: unified exact solutions and symmetries

We investigate a mechanism that generates the exact solutions of scalar field cosmologies in a unified way. The procedure investigated here permits to recover allmost all known solutions, and allows one to derive new solutions as well. In particular, we derive and discuss one novel solution defined in terms of the Lambert function. The solutions are organized in a classification which depends on the choice of a generating function which we have denoted by $x(\phi)$ that reflects the underlying thermodynamics of the model. We also analyse and discuss the existence of form invariances and dualities between solutions. A general way of defining the latter in an appropriate fashion for scalar fields is put forward.Comment: 6 figures, 30 page

One Aneurysm and Two Pseudoaneurysms, Same Patient

Ventricular pseudoaneurysms are rare pathological entities that mainly arise in the context of myocardial infarction or post-cardiac surgery. The clinical presentation is usually non-specific, and at times patients are asymptomatic. Mortality is high even with timely surgical intervention.The authors present a case of postoperative recurrence of a left ventricular pseudoaneurysm superimposed on an ischaemic true aneurysm.info:eu-repo/semantics/publishedVersio

Isolated anaemia as a manifestation of Rh isoimmunisation

Rh isoimmunisation leads to haemolytic anaemia and hyperbilirubinaemia in the first h of life. Isolated early onset neonatal anaemia has rarely been reported. The authors describe the case of a term infant, born to an 'A' negative, second gravida mother. On the second day of life, pallor was noticed. His haemoglobin (Hb) was 6.8 g/dl, he had reticulocytosis and a positive direct antiglobulin test. However, he did not have a high total serum bilirubin (TSB) (87.2 μmol/l). He was transfused with red blood cells and kept under phototherapy for 3 days. Three weeks later, he received another transfusion for severe anaemia (Hb 6 5 g/dl). During this period, he was never jaundiced and the maximum level of TSB was 122 μmol/l. On follow-up, his Hb stabilised and he had no further problems. This report highlights the possibility of early onset anaemia without jaundice as the sole manifestation of Rh isoimmunisation

Brane Isotropisation in Extra-Dimensional Tolman-Bondi Universe

We consider the dynamics of a 3-brane embedded in an extra-dimensional Tolman-Bondi Universe where the origin of space plays a special role. The embedding is chosen such that the induced matter distribution on the brane respects the spherical symmetry of matter in the extra dimensional space. The mirage cosmology on the probe brane is studied, resulting in an inhomogeneous and anisotropic four dimensional cosmology where the origin of space is also special. We then focus on the spatial geometry around the origin and show that the induced geometry, which is initially inhomogeneous and anisotropic, converges to an isotropic and homogeneous Friedmann-Lemaitre 4d space-time. For instance, when a 3-brane is embedded in a 5d matter dominated model, the 4d dynamics around the origin converge to a Friedmann-Lemaitre Universe in a radiation dominated epoch. We analyse this isotropisation process and show that it is a late time attractor.Comment: 16 pages, 8 figures, one reference adde

Plane-symmetric inhomogeneous Brans-Dicke cosmology with an equation of state p=γρp=\gamma \rho

We present a new exact solution in Brans-Dicke theory. The solution describes inhomogeneous plane-symmetric perfect fluid cosmological model with an equation of state $p=\gamma \rho$. Some main properties of the solution are discussed.Comment: 6 pages, Late

What if Newton's Gravitational Constant was negative?

In this work, we seek a cosmological mechanism that may define the sign of the effective gravitational coupling constant, {\em G}. To this end, we consider general scalar-tensor gravity theories as they provide the field theory natural framework for the variation of the gravitational coupling. We find that models with a quadratic potential naturally stabilize the value of {\em G} into the positive branch of the evolution and further, that de Sitter inflation and a relaxation to General Relativity is easily attained.Comment: 16 pages, 16 figure

Reheating induced by competing decay modes

We address the problem of studying the decay of the inflaton field $\phi$ to another scalar field $\chi$ through parametric resonance in the case of a coupling that involves several decay modes. This amounts to the presence of extra harmonic terms in the perturbation of the $\chi$ field dynamics. For the case of two frequencies we compute the geometry of the resonance regions, which is significantly altered due to the presence of non-cuspidal resonance regions associated to higher harmonics and to the emergence of instability `pockets'. We discuss the effect of this change in the efficiency of the energy transfer process for the simplest case of a coupling given by a combination of the two interaction terms of homogeneous degree usually considered in the literature. We find that the presence of higher harmonics has limited cosmological implications.Comment: 14 pages, 4 figures Added references. Corrected typo