2,448 research outputs found
Distributed multi-generation systems: energy models and analyses
Libro riguardante la caratterizzazione di sistemi per la produzione combinata di energia da sistemi di multi-generazione distribuita (Distributed Multi-Generation, DMG). Il libro tratta componenti, schemi e modelli di sistemi di multi-generazione distribuita, illustra concetti derivanti da proposte originali degli autori in merito all'analisi e alla pianificazione dei sistemi, con i corrispondenti indicatori energetici e ambientali approccio formulati secondo un approccio unificato. Numerosi esempi applicativi inclusi nel libro riguardano in particolare sistemi di cogenerazione e trigenerazion
Statistical Mechanics of an Ideal Gas of Non-Abelian Anyons
We study the thermodynamical properties of an ideal gas of non-Abelian
Chern-Simons particles and we compute the second virial coefficient,
considering the effect of general soft-core boundary conditions for the
two-body wavefunction at zero distance. The behaviour of the second virial
coefficient is studied as a function of the Chern-Simons coupling, the isospin
quantum number and the hard-coreness parameters. Expressions for the main
thermodynamical quantities at the lower order of the virial expansion are also
obtained: we find that at this order the relation between the internal energy
and the pressure is the same found (exactly) for 2D Bose and Fermi ideal gases.
A discussion of the comparison of obtained findings with available results in
literature for systems of hard-core non-Abelian Chern-Simons particles is also
supplied.Comment: Submitted versio
Conformal symmetry and nonlinear extensions of nonlocal gravity
We study two nonlinear extensions of the nonlocal gravity
theory. We extend this theory in two different ways suggested by conformal
symmetry, either replacing with , which is the
operator that enters the action for a conformally-coupled scalar field, or
replacing with the inverse of the Paneitz operator, which is a
four-derivative operator that enters in the effective action induced by the
conformal anomaly. We show that the former modification gives an interesting
and viable cosmological model, with a dark energy equation of state today
, which very closely mimics CDM and evolves
asymptotically into a de Sitter solution. The model based on the Paneitz
operator seems instead excluded by the comparison with observations. We also
review some issues about the causality of nonlocal theories, and we point out
that these nonlocal models can be modified so to nicely interpolate between
Starobinski inflation in the primordial universe and accelerated expansion in
the recent epoch.Comment: 27 pages, 4 figure
Effective Theory of Dark Energy at Redshift Survey Scales
We explore the phenomenological consequences of general late-time
modifications of gravity in the quasi-static approximation, in the case where
cold dark matter is non-minimally coupled to the gravitational sector. Assuming
spectroscopic and photometric surveys with configuration parameters similar to
those of the Euclid mission, we derive constraints on our effective description
from three observables: the galaxy power spectrum in redshift space,
tomographic weak-lensing shear power spectrum and the correlation spectrum
between the integrated Sachs-Wolfe effect and the galaxy distribution. In
particular, with CDM as fiducial model and a specific choice for the
time dependence of our effective functions, we perform a Fisher matrix analysis
and find that the unmarginalized CL errors on the parameters describing
the modifications of gravity are of order --. We
also consider two other fiducial models. A nonminimal coupling of CDM enhances
the effects of modified gravity and reduces the above statistical errors
accordingly. In all cases, we find that the parameters are highly degenerate,
which prevents the inversion of the Fisher matrices. Some of these degeneracies
can be broken by combining all three observational probes.Comment: 41 pages, 5 figures, 2 tables, improved analysis of ISW-galaxy
correlation, matches published version on JCA
Non-local gravity with a Weyl-square term
Recent work has shown that modifications of General Relativity based on the
addition to the action of a non-local term , or on the addition
to the equations of motion of a term involving ,
produce dynamical models of dark energy which are cosmologically viable both at
the background level and at the level of cosmological perturbations. We explore
a more general class of models based on the addition to the action of terms
proportional to and , where is the Weyl
tensor. We find that the term does not give a
viable background evolution. The non-local Weyl-square term, in contrast, does
not contribute to the background evolution but we find that, at the level of
cosmological perturbations, it gives instabilities in the tensor sector. Thus,
only non-local terms which depend just on the Ricci scalar appear to be
cosmologically viable. We discuss how these results can provide a hint for the
mechanism that might generate these effective non-local terms from a
fundamental local theory.Comment: 25 pages, 6 figures. v2: the version to appear in PR
- …