8 research outputs found
Mass freezing in growing neutrino quintessence
Growing neutrino quintessence solves the coincidence problem for dark energy
by a growing cosmological value of the neutrino mass which emerges from a
cosmon-neutrino interaction stronger than gravity. The cosmon-mediated
attraction between neutrinos induces the formation of large scale neutrino
lumps in a recent cosmological epoch. We argue that the non-linearities in the
cosmon field equations stop the further increase of the neutrino mass within
sufficiently dense and large lumps. As a result, we find the neutrino induced
gravitational potential to be substantially reduced when compared to linear
extrapolations. We furthermore demonstrate that inside a lump the possible time
variation of fundamental constants is much smaller than their cosmological
evolution. This feature may reconcile current geophysical bounds with claimed
cosmological variations of the fine structure constant.Comment: 15 pages, 12 figures. Version published in PR
Accelerating the Universe with Gravitational Waves
Inflation generically produces primordial gravitational waves with a red
spectral tilt. In this paper we calculate the backreaction produced by these
gravitational waves on the expansion of the universe. We find that in radiation
domination the backreaction acts as a relativistic fluid, while in matter
domination a small dark energy emerges with an equation of state w=-8/9.Comment: 18 pages, 4 figures. Replaced with version published by JCAP - some
discussion and references added concerning second-order gravitational waves,
typeset in JHEP styl
Relaxing Neutrino Mass Bounds by a Running Cosmological Constant.
We establish an indirect link between relic neutrinos and the dark energy
sector which originates from the vacuum energy contributions of the neutrino
quantum fields. Via renormalization group effects they induce a running of the
cosmological constant with time which dynamically influences the evolution of
the cosmic neutrino background. We demonstrate that the resulting reduction of
the relic neutrino abundance allows to largely evade current cosmological
neutrino mass bounds and discuss how the scenario might be probed by the help
of future large scale structure surveys and Planck data.Comment: 23 pages, 4 figures. References added, typos corrected. Matches
version accepted by JCA
Neutrino Dark Energy -- Revisiting the Stability Issue.
A coupling between a light scalar field and neutrinos has been widely
discussed as a mechanism for linking (time varying) neutrino masses and the
present energy density and equation of state of dark energy. However, it has
been pointed out that the viability of this scenario in the non-relativistic
neutrino regime is threatened by the strong growth of hydrodynamic
perturbations associated with a negative adiabatic sound speed squared. In this
paper we revisit the stability issue in the framework of linear perturbation
theory in a model independent way. The criterion for the stability of a model
is translated into a constraint on the scalar-neutrino coupling, which depends
on the ratio of the energy densities in neutrinos and cold dark matter. We
illustrate our results by providing meaningful examples both for stable and
unstable models.Comment: 24 pages, 8 figures, stable scenario with negative sound speed
squared included, figures added, references added, conclusions unchanged.
Matches version to be published in JCA
Probing Neutrino Dark Energy with Extremely High-Energy Cosmic Neutrinos.
Recently, a new non-Standard Model neutrino interaction mediated by a light
scalar field was proposed, which renders the big-bang relic neutrinos of the
cosmic neutrino background a natural dark energy candidate, the so-called
Neutrino Dark Energy. As a further consequence of this interaction, the
neutrino masses become functions of the neutrino energy densities and are thus
promoted to dynamical, time/redshift dependent quantities. Such a possible
neutrino mass variation introduces a redshift dependence into the resonance
energies associated with the annihilation of extremely high-energy cosmic
neutrinos on relic anti-neutrinos and vice versa into Z-bosons. In general,
this annihilation process is expected to lead to sizeable absorption dips in
the spectra to be observed on earth by neutrino observatories operating in the
relevant energy region above 10^13 GeV. In our analysis, we contrast the
characteristic absorption features produced by constant and varying neutrino
masses, including all thermal background effects caused by the relic neutrino
motion. We firstly consider neutrinos from astrophysical sources and secondly
neutrinos originating from the decomposition of topological defects using the
appropriate fragmentation functions. On the one hand, independent of the nature
of neutrino masses, our results illustrate the discovery potential for the
cosmic neutrino background by means of relic neutrino absorption spectroscopy.
On the other hand, they allow to estimate the prospects for testing its
possible interpretation as source of Neutrino Dark Energy within the next
decade by the neutrino observatories ANITA and LOFAR.Comment: 38 pages, 19 figure