301 citations · 2.1k across the 77 of their papers we have counts for
44 papers · 1 filter
Skewness as a test of dark energy perturbations
Raquel Emy Fazolo, Luca Amendola, Hermano Velten
We investigate the role played by dark energy perturbations in the skewness of large-scale matter distribution. We consider a two-fluid universe composed by matter and dark e…
Early-time thermalization of cosmic components? A hint for solving cosmic tensions
Hermano Velten, Ingrid Costa, Winfried Zimdahl
We study an expanding two-fluid model of non-relativistic dark matter and radiation which are allowed to interact during a certain time span and to establish an approximate thermal…
Skewness of matter distribution in clustering dark energy cosmologies
Hermano Velten, Raquel Emy Fazolo
We calculate the skewness (the third moment ) of matter distribution in dynamical dark energy cosmologies. We pay particular attention to the impact of dark energy perturbatio…
Is the Hubble diagram of quasars in tension with concordance cosmology?
Hermano Velten, Syrios Gomes
Recently Risaliti \& Lusso [Nature Astron. 3 (2019) 3 272] reported new measurements of the expansion rate of the Universe by constructing the Hubble diagram of 1598 quasars in the…
On (non-)dynamical dark energy
Winfried Zimdahl, Júlio Fabris, Hermano Velten +1
The current Universe is composed by a mixture of relativistic species, baryonic matter, dark matter and dark energy which evolve in a non-trivial way at perturbative level. An adva…
Modified Gravity Away from a CDM Background
Guilherme Brando, Felipe T. Falciano, Eric V. Linder +1
Within the effective field theory approach to cosmic acceleration, the background expansion can be specified separately from the gravitational modifications. We explore the impact…
Matter Growth in Imperfect Fluid Cosmology
Winfried Zimdahl, Hermano Velten, William C. Algoner
Extensions of Einstein's General Relativity (GR) can formally be given a GR structure in which additional geometric degrees of freedom are mapped on an effective energy-momentum te…
Modified gravity versus shear viscosity: imprints on the scalar matter perturbations
C. M. S. Barbosa, H. Velten, J. C. Fabris +1
Cosmological scalar perturbation theory studied in the Newtonian gauge depends on two potentials and . In General Relativity (GR) they must coincide () in the absence o…
Degeneracy between nonadiabatic dark energy models and CDM: ISW effect and the cross correlation of CMB with galaxy clustering data
Hermano Velten, Raquel Emy Fazolo, Rodrigo von Marttens +1
As recently pointed out in Ref. [Phys.\ Rev.\ D {\bf 96}, 8, 083502 (2017)] the evolution of the linear matter perturbations in nonadiabatic dynamical dark energy models is almost…
{\it Gauging} the cosmic acceleration with recent type Ia supernovae data sets
Hermano Velten, Syrios Gomes, Vinicius C. Busti
We revisit a model-independent estimator for cosmic acceleration based on type Ia supernovae distance measurements. This approach does not rely on any specific theory for gravity,…
Revealing the non-adiabatic nature of dark energy perturbations from galaxy clustering data
Hermano Velten, Raquel Fazolo
We study structure formation using relativistic cosmological linear perturbation theory in the presence of intrinsic and relative (with respect to matter) non-adiabatic dark energy…
Matter growth in extended CDM cosmology
W. Zimdahl, H. E. S. Velten, W. C. Algoner
On the basis of a previously established scalar-tensor extension of the CDM model we develop an effective fluid approach for the matter growth function. This extended CDM (he…
Flavour composition and entropy increase of cosmological neutrinos after decoherence
Daniel Boriero, Dominik J. Schwarz, Hermano Velten
We propose that gravitational interactions of cosmic neutrinos with the statistically homogeneous and isotropic fluctuations of space-time leads to decoherence. This working hypoth…
Assessing the impact of bulk and shear viscosities on large scale structure formation
C. M. S. Barbosa, H. Velten, J. C. Fabris +1
It is analyzed the effects of both bulk and shear viscosities on the perturbations, relevant for structure formation in late time cosmology. It is shown that shear viscosity can be…
A free parametrized TOV: Modified Gravity from Newtonian to Relativistic Stars
Hermano Velten, Adriano M. Oliveira, Aneta Wojnar
We test a free {\it ad hoc} parametrization of the Tolman-Oppenheimer-Volkoff (TOV) equation. We do not have in mind any specific extended theory of gravity (ETG) but each new para…
Viscous Cosmology
C. M. S. Barbosa, J. C. Fabris, O. F. Piattella +2
We discuss the possibility to implement a viscous cosmological model, attributing to the dark matter component a behaviour described by bulk viscosity. Since bulk viscosity implies…
Degeneracy between warm and coupled cold dark matter: A clarifying note
Hermano Velten, Humberto A. Borges, Thiago R. P. Caramês
Wei et al [PRD 88, 043510 (2013)] have proposed the existence of a cosmological degeneracy between warm dark matter (WDM), modified gravity and coupled cold dark matter (CDM) cosmo…
Large scale structure and ISW effect in decaying vacuum cosmology
H. Velten, H. A. Borges, S. Carneiro +2
The concordance particle creation model - a class of CDM cosmologies - is studied using large scale structure (LSS) formation, with particular attention to the integrated Sac…
Non-linear clustering during the BEC dark matter phase transition
Rodolfo C. de Freitas, Hermano Velten
Spherical collapse of the Bose-Einstein Condensate (BEC) dark matter model is studied in the Thomas Fermi approximation. The evolution of the overdensity of the collapsed region an…
Structure formation in a CDM universe
Hermano Velten, Thiago R. P. Caramês, Júlio C. Fabris +2
The possibility of dark matter being a dissipative component represents an option for the standard view where cold dark matter (CDM) particles behave on large scales as an ideal fl…
Aspects of the cosmological "coincidence problem"
H. E. S. Velten, R. F. vom Marttens, W. Zimdahl
The observational fact that the present values of the densities of dark energy and dark matter are of the same order of magnitude, , seems to i…
Non-linear dark matter collapse under diffusion
Hermano E. S. Velten, Thiago R. P. Caramês
Diffusion is one of the physical processes allowed for describing the large scale dark matter dynamics. At the same time, it can be seen as a possible mechanism behind the interact…
Exploring non-linear cosmological matter diffusion coefficients
Hermano Velten, Simone Calogero
Since microscopic velocity diffusion can be incorporated into general relativity in a consistent way, we study cosmological background solutions when the diffusion phenomena takes…
Spherical collapse for unified dark matter models
Thiago R. P. Caramês, Júlio C. Fabris, Hermano E. S. Velten
We study the non-linear spherical "top hat" collapse for Chaplygin and viscous unified cosmologies. The term unified refers to models where dark energy and dark matter are replaced…