Stability analysis for the background equations for inflation with dissipation and in a viscous radiation bath

The effects of bulk viscosity are examined for inflationary dynamics in which dissipation and thermalization are present. A complete stability analysis is done for the background inflaton evolution equations, which includes both inflaton dissipation and radiation bulk viscous effects. Three representative approaches of bulk viscous irreversible thermodynamics are analyzed: the Eckart noncausal theory, the linear and causal theory of Israel-Stewart and a more recent nonlinear and causal bulk viscous theory. It is found that the causal theories allow for larger bulk viscosities before encountering an instability in comparison to the noncausal Eckart theory. It is also shown that the causal theories tend to suppress the radiation production due to bulk viscous pressure, because of the presence of relaxation effects implicit in these theories. Bulk viscosity coefficients derived from quantum field theory are applied to warm inflation model building and an analysis is made of the effects to the duration of inflation. The treatment of bulk pressure would also be relevant to the reheating phase after inflation in cold inflation dynamics and during the radiation dominated regime, although very little work in both areas has been done, the methodology developed in this paper could be extended to apply to these other problems.Comment: 27 pages, 14 figures, Published version JCA

A note on inflation and transplanckian physics

In this paper we consider the influence of transplanckian physics on the CMBR anisotropies produced by inflation. We consider a simple toy model that allows for analytic calculations and argue on general grounds, based on ambiguities in the choice of vacuum, that effects are expected with a magnitude of the order of $H/\Lambda$, where $H$ is the Hubble constant during inflation and $\Lambda$ the scale for new physics, e.g. the Planck scale.Comment: 12 pages. v2: typos corrected and references added. v3: final version accepted for publication by PRD. Improved discussion of adiabatic vacuu

Trans-Planckian Dark Energy?

It has recently been proposed by Mersini et al. 01, Bastero-Gil and Mersini 02 that the dark energy could be attributed to the cosmological properties of a scalar field with a non-standard dispersion relation that decreases exponentially at wave-numbers larger than Planck scale (k_phys > M_Planck). In this scenario, the energy density stored in the modes of trans-Planckian wave-numbers but sub-Hubble frequencies produced by amplification of the vacuum quantum fluctuations would account naturally for the dark energy. The present article examines this model in detail and shows step by step that it does not work. In particular, we show that this model cannot make definite predictions since there is no well-defined vacuum state in the region of wave-numbers considered, hence the initial data cannot be specified unambiguously. We also show that for most choices of initial data this scenario implies the production of a large amount of energy density (of order M_Planck^4) for modes with momenta of order M_Planck, far in excess of the background energy density. We evaluate the amount of fine-tuning in the initial data necessary to avoid this back-reaction problem and find it is of order H/M_Planck. We also argue that the equation of state of the trans-Planckian modes is not vacuum-like. Therefore this model does not provide a suitable explanation for the dark energy.Comment: RevTeX - 15 pages, 7 figures: final version to appear in PRD, minor changes, 1 figure adde

Tachyon warm inflationary universe model in the weak dissipative regime

Warm inflationary universe model in a tachyon field theory is studied in the weak dissipative regime. We develop our model for an exponential potential and the dissipation parameter $\Gamma=\Gamma_0$=constant. We describe scalar and tensor perturbations for this scenario.Comment: 9 pages, accepted by European Physical Journal

Insuficiencia respiratoria neonatal asociada a mutación en el gen de la proteína C del surfactante

La insuficiencia respiratoria en el recién nacido a término durante las primeras semanas de vida extrauterina es una situación poco frecuente. Entre sus causas se incluyen las enfermedades difusas del intersticio pulmonar, un grupo heterogéneo de enfermedades, la mayoría idiopáticas, caracterizadas por infiltrados difusos, alteraciones funcionales de tipo restrictivo y afectación del intercambio gaseoso. Una forma de enfermedad pulmonar intersticial que puede afectar a lactantes, niños o adultos jóvenes es la que se asocia al déficit congénito de proteínas B o C del surfactante pulmonar. En estos casos los procesos inflamatorios que evolucionan hacia la fibrosis pulmonar están precedidos por la acumulación de material proteináceo en el alvéolo. Se indagó la presencia de mutaciones en los genes de las proteínas B y C del surfactante en una familia española en la cual dos lactantes presentaron insuficiencia respiratoria progresiva desde el nacimiento, con alteraciones radiológicas y anatomopatológicas compatibles con enfermedad del intersticio pulmonar, y el padre refería historia de problemas respiratorios desde la infancia. Se encontró que los dos hermanos de esta familia afectados por la enfermedad presentaban una expresión anómala del precursor de la proteína C del surfactante y concentraciones muy bajas de proteína madura. Se describe además una mutación nueva en el gen que codifica la proteína C del surfactante y que cosegrega con la enfermedad en esta familia