2,449 research outputs found
Cosmological constraints on neutrino self-interactions with a light mediator
If active neutrinos undergo non-standard (`secret') interactions (NSI)
the cosmological evolution of the neutrino fluid might be altered, leaving an
imprint in cosmological observables. We use the latest publicly available CMB
data from Planck to constrain NSI inducing scattering, under the
assumption that the mediator of the secret interaction is very light. We
find that the effective coupling constant of the interaction, , is constrained at (95\% credible interval), which stregthens to
when Planck non-baseline small-scale
polarization is considered. Our findings imply that after decoupling at
MeV, cosmic neutrinos are free streaming at redshifts , or
if small-scale polarization is included. These bounds are only
marginally improved when data from geometrical expansion probes are included in
the analysis to complement Planck. We also find that the tensions between CMB
and low-redshift measurements of the expansion rate and the amplitude of
matter fluctuations are not significantly reduced. Our results are
independent on the underlying particle physics model as long as is very
light. Considering a model with Majorana neutrinos and a pseudoscalar mediator
we find that the coupling constant of the secret interaction is constrained
at . By further assuming that the pseudoscalar
interaction comes from a dynamical realization of the see-saw mechanism, as in
Majoron models, we can bound the scale of lepton number breaking as
.Comment: V2. Replaced to match version accepted for publication in PRD. Added
more detailed discussion about parameter degeneracies. 14 pages, 6 figures, 3
table
On the possible role of massive neutrinos in cosmological structure formation
In addition to the problem of galaxy formation, one of the greatest open
questions of cosmology is represented by the existence of an asymmetry between
matter and antimatter in the baryonic component of the Universe. We believe
that a net lepton number for the three neutrino species can be used to
understand this asymmetry. This also implies an asymmetry in the
matter-antimatter component of the leptons. The existence of a nonnull lepton
number for the neutrinos can easily explain a cosmological abundance of
neutrinos consistent with the one needed to explain both the rotation curves of
galaxies and the flatness of the Universe. Some propedeutic results are
presented in order to attack this problem.Comment: RevTeX4, 25 pages, 5 figures, to appear in the "Proceedings of the
Xth Brazilian School of Cosmology and Gravitation", M. Novello, editor, AIP,
in pres
Detection and measurement of planetary systems with GAIA
We use detailed numerical simulations and the Andromedae,
planetary system as a template to evaluate the capability of the ESA
Cornerstone Mission GAIA in detecting and measuring multiple planets around
solar-type stars in the neighborhood of the Solar System. For the outer two
planets of the Andromedae, system, GAIA high-precision global
astrometric measurements would provide estimates of the full set of orbital
elements and masses accurate to better than 1--10%, and would be capable of
addressing the coplanarity issue by determining the true geometry of the system
with uncertainties of order of a few degrees. Finally, we discuss the
generalization to a variety of configurations of potential planetary systems in
the solar neighborhood for which GAIA could provide accurate measurements of
unique value for the science of extra-solar planets.Comment: 4 pages, 2 pictures, accepted for publication in A&A Letter
Decaying warm dark matter and neutrino masses
Neutrino masses may arise from spontaneous breaking of ungauged lepton
number. Due to quantum gravity effects the associated Goldstone boson - the
majoron - will pick up a mass. We determine the lifetime and mass required by
cosmic microwave background observations so that the massive majoron provides
the observed dark matter of the Universe. The majoron DDM scenario fits nicely
in models where neutrino masses arise a la seesaw, and may lead to other
possible cosmological implications.Comment: 4 pages, 3 figures. Replaced to match published version. Minor
changes made to address referees' comments. References adde
Gaia: The Astrometry Revolution
The power of micro-arcsecond (as) astrometry is about to be unleashed.
ESA's Gaia mission, now headed towards the end of the first year of routine
science operations, will soon fulfil its promise for revolutionary science in
countless aspects of Galactic astronomy and astrophysics. The potential of Gaia
position measurements for important contributions to the astrophysics of
planetary systems is huge. We focus here on the expectations for detection and
improved characterization of 'young' planetary systems in the neighborhood of
the Sun using a combination of Gaia as astrometry and direct imaging
techniques.Comment: 6 pages, 3 figures, to appear in the Proceedings of IAU Symposium 314
'Young Stars & Planets Near the Sun', held on May 11-15 2015 in Atlanta (GA),
USA (J. H. Kastner, B. Stelzer, & S. A. Metchev, eds.
The observed chemical structure of L1544
Prior to star formation, pre-stellar cores accumulate matter towards the
centre. As a consequence, their central density increases while the temperature
decreases. Understanding the evolution of the chemistry and physics in this
early phase is crucial to study the processes governing the formation of a
star. We aim at studying the chemical differentiation of a prototypical
pre-stellar core, L1544, by detailed molecular maps. In contrast with single
pointing observations, we performed a deep study on the dependencies of
chemistry on physical and external conditions. We present the emission maps of
39 different molecular transitions belonging to 22 different molecules in the
central 6.25 arcmin of L1544. We classified our sample in five families,
depending on the location of their emission peaks within the core. Furthermore,
to systematically study the correlations among different molecules, we have
performed the principal component analysis (PCA) on the integrated emission
maps. The PCA allows us to reduce the amount of variables in our dataset.
Finally, we compare the maps of the first three principal components with the
H column density map, and the T map of the core. The results of
our qualitative analysis is the classification of the molecules in our dataset
in the following groups: (i) the -CH family (carbon chain
molecules), (ii) the dust peak family (nitrogen-bearing species), (iii) the
methanol peak family (oxygen-bearing molecules), (iv) the HNCO peak family
(HNCO, propyne and its deuterated isotopologues). Only HCO and
CS do not belong to any of the above mentioned groups. The principal
component maps allow us to confirm the (anti-)correlations among different
families that were described in a first qualitative analysis, but also points
out the correlation that could not be inferred before.Comment: 29 pages, 19 figures, 2 appendices, accepted for publication in A&A,
arXiv abstract has been slightly modifie
Testing Planet Formation Models with Gaia as Astrometry
In this paper, we first summarize the results of a large-scale double-blind
tests campaign carried out for the realistic estimation of the Gaia potential
in detecting and measuring planetary systems. Then, we put the identified
capabilities in context by highlighting the unique contribution that the Gaia
exoplanet discoveries will be able to bring to the science of extrasolar
planets during the next decade.Comment: 4 pages, 1 figure. To appear in the proceedings of "IAU Symposium 248
- A Giant Step: from Milli- to Micro-arcsecond Astrometry", held in Shanghai,
China, 15-19 Oct. 200
- …