Graviton spectrum in simplified Dark Matter models with graviton mediators in the de Sitter space

This is the second in a series of papers investigating the formulation of the simplified Dark Matter models with graviton mediators in cosmological backgrounds. We address here the crucial problem of the fundamental observable of interest, namely the graviton spectrum in a FRW cosmological background with an arbitrary Dark Matter background component. We calculate the correction to the free graviton two-point function up to the second order in the coupling constant between the Dark Matter and the graviton in the simplified Dark Matter model with graviton mediators approach in the de Sitter space. Our result is model independent in the sense that it does not depend on the particular form of the Dark Matter fields. Also, due to the universality of the interaction between the Dark Matter and the graviton, the result obtained here apply to the interaction between the baryonic matter and the gravitons. As an application, we discuss in detail the massive scalar Dark Matter model and calculate the first order correction to the two-point function due to two Dark Matter modes in the adiabatic regime.Comment: Typos corrected. A new section on the scalar Dark Matter model adde

Note on Four Dp-Branes at Angles

In this note we analyse the dynamical potential of a system of four $Dp$-branes at arbitrary angles. The equilibrium configurations for various values of the relative angles and distances among branes are discussed. The known configurations of parallel branes and brane-antibranes are obtained at extrema of the dynamical potential.Comment: misprints corrected, a new paragraph added, 11 pages LATe

BRST cohomology in Beltrami parametrization

We study the BRST cohomology within a local conformal Lagrangian field theory model built on a two dimensional Riemann surface with no boundary. We deal with the case of the complex structure parametrized by Beltrami differential and the scalar matter fields. The computation of {\em all} elements of the BRST cohomology is given.Comment: 25 pages, LATE

Thermodynamic analysis of Spark Ignition engines using the Entropy Generation Minimisation method

The recent improvement on Spark Ignition Engines has been the result of improved engine thermodynamic cycles, made possible by advances in technologies such as Variable Valve Timing (VVT) and Variable Compression Ratio (VCR). To evaluate the potential of these techniques a thermodynamic analysis is made. Numerical models were implemented in Matlab Simulink using the laws of thermodynamics and include heat transfer, combustion, real working fluid characteristics and intake and exhaust events. The second law analysis allowed the identification of inefficiency sources and directions for improvement. A SI engine was analysed and its processes were evaluated by the amount of entropy generated