870 research outputs found
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
-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
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