121 research outputs found
Constraints on secret neutrino interactions after Planck
(Abridged) Neutrino interactions beyond the standard model may affect the
cosmological evolution and can be constrained through observations. We consider
the possibility that neutrinos possess secret scalar or pseudoscalar
interactions mediated by the Nambu-Goldstone boson of a still unknown
spontaneously broken global symmetry, as in, e.g. , Majoron models. In
such scenarios, neutrinos still decouple at MeV, but become tightly
coupled again ('recouple') at later stages of the cosmological evolution. We
use available observations of CMB anisotropies, including Planck 2013 and the
joint BICEP2/Planck 2015 data, to derive constraints on the quantity
, parameterizing the neutrino collision rate due to
(pseudo)scalar interactions. We consider both a minimal extension of the
standard CDM model, and scenarios with extra relativistic species or
non-vanishing tensors. We find a typical constraint (95% C.L.), implying an upper limit on the redshift
of neutrino recoupling . In the framework of Majoron models,
the upper limit on roughly translates on a constraint on the Majoron-neutrino coupling constant . In general,
the data show a weak () but intriguing preference for non-zero
values of , with best fits in the range , depending on the particular dataset. This is
more evident when either observations from ACT and SPT are included, or the
possibility of non-vanishing tensor modes is considered. In particular, for the
minimal model CDM + and including the Planck 2013,
ACT and SPT data, we report () at 68% confidence level.Comment: 19 pages, 7 figures, 3 tables. Replaced to match version accepted for
pubblication in JCA
The generation: present and future constraints on neutrino masses from cosmology and laboratory experiments
We perform a joint analysis of current data from cosmology and laboratory
experiments to constrain the neutrino mass parameters in the framework of
bayesian statistics, also accounting for uncertainties in nuclear modeling,
relevant for neutrinoless double decay () searches. We find
that a combination of current oscillation, cosmological and data
constrains () at 95\% C.L. for normal (inverted)
hierarchy. This result is in practice dominated by the cosmological and
oscillation data, so it is not affected by uncertainties related to the
interpretation of data, like nuclear modeling, or the exact
particle physics mechanism underlying the process. We then perform forecasts
for forthcoming and next-generation experiments, and find that in the case of
normal hierarchy, given a total mass of eV, and assuming a
factor-of-two uncertainty in the modeling of the relevant nuclear matrix
elements, it will be possible to measure the total mass itself, the effective
Majorana mass and the effective electron mass with an accuracy (at 95\% C.L.)
of , , respectively, as well as to be
sensitive to one of the Majorana phases. This assumes that neutrinos are
Majorana particles and that the mass mechanism gives the dominant contribution
to decay. We argue that more precise nuclear modeling will be
crucial to improve these sensitivities.Comment: v2: 6 pages, 3 figures, 1 table; added definition of parameter
minimal value from oscillation measurements; corrected confidence interval,
that in v1 were reported at 90% C.L. and misidentified as 95% C.L.; accepted
for publicatio
Signatures of the neutrino thermal history in the spectrum of primordial gravitational waves
In this paper we study the effect of the anisotropic stress generated by
neutrinos on the propagation of primordial cosmological gravitational waves.
The presence of anisotropic stress, like the one generated by free-streaming
neutrinos, partially absorbs the gravitational waves (GWs) propagating across
the Universe. We find that in the standard case of three neutrino families, 22%
of the intensity of the wave is absorbed, in fair agreement with previous
studies. We have also calculated the maximum possible amount of damping,
corresponding to the case of a flat Universe completely dominated by
ultrarelativistic collisionless particles. In this case 43% of the intensity of
the wave is absorbed. Finally, we have taken into account the effect of
collisions, using a simple form for the collision term parameterized by the
mean time between interactions, that allows to go smoothly from the case of a
tigthly-coupled fluid to that of a collisionless gas. The dependence of the
absorption on the neutrino energy density and on the effectiveness of the
interactions opens the interesting possibility of observing spectral features
related to particular events in the thermal history of the Universe, like
neutrino decoupling and electron-positron annihilation, both occurring at T~1
MeV. GWs entering the horizon at that time will have today a frequency \nu\sim
10^{-9} \Hz, a region that is going to be probed by Pulsar Timing Arrays.Comment: V1: 14 pages, 2 figures. To appear in Gen. Rel. Grav. V2: References
Adde
Connecting neutrino physics with dark matter
The origin of neutrino masses and the nature of dark matter are two of the
most pressing open questions of the modern astro-particle physics. We consider
here the possibility that these two problems are related, and review some
theoretical scenarios which offer common solutions. A simple possibility is
that the dark matter particle emerges in minimal realizations of the see-saw
mechanism, like in the majoron and sterile neutrino scenarios. We present the
theoretical motivation for both models and discuss their phenomenology,
confronting the predictions of these scenarios with cosmological and
astrophysical observations. Finally, we discuss the possibility that the
stability of dark matter originates from a flavour symmetry of the leptonic
sector. We review a proposal based on an A_4 flavour symmetry.Comment: 21 pages, 4 figures. Review prepared for the focus issue on "Neutrino
Physics". Matches published versio
Decaying Majoron Dark Matter and Neutrino Masses
We review the recent proposal by Lattanzi & Valle of the majoron as a
suitable warm dark matter candidate. The majoron is the Goldstone boson
associated to the spontaneous breaking of ungauged lepton number, one of the
mechanisms proposed to give rise to neutrino masses. The majoron can acquire a
mass through quantum gravity effects, and can possibly account for the observed
dark matter component of the Universe. We present constraints on the majoron
lifetime, mass and abundance obtained by the analysis of the cosmic microwave
background data. We find that, in the case of thermal production, the limits
for the majoron mass read 0.12 keV<m_J<0.17 keV, and discuss how these limits
are modified in the non-thermal case. The majoron lifetime is constrained to be
larger than 250 Gyrs. We also apply this results to a given seesaw model for
the generation of neutrino masses, and find that this constraints the energy
scale for the lepton number breaking phase transition to be above 10^6 GeV. We
thus find that the majoron decaying dark matter (DDM) scenario fits nicely in
models where neutrino masses arise "a la seesaw" and may lead to other possible
cosmological implications.Comment: 7 pages, 3 figures. Contribution to proceedings of the 4th
Sino-Italian Workshop on Relativistic Astrophysics, Pescara, 20-30 July 200
Features in the primordial spectrum: new constraints from WMAP7+ACT data and prospects for Planck
We update the constraints on possible features in the primordial inflationary
density perturbation spectrum by using the latest data from the WMAP7 and ACT
Cosmic Microwave Background experiments. The inclusion of new data
significantly improves the constraints with respect to older work, especially
to smaller angular scales. While we found no clear statistical evidence in the
data for extensions to the simplest, featureless, inflationary model, models
with a step provide a significantly better fit than standard featureless
power-law spectra. We show that the possibility of a step in the inflationary
potential like the one preferred by current data will soon be tested by the
forthcoming temperature and polarization data from the Planck satellite
mission.Comment: V2: 8 pages, 8 figures. Minor changes. Two figures and references
added. Matches version published in Phys. Rev.
Model independent constraints on mass-varying neutrino scenarios
Models of dark energy in which neutrinos interact with the scalar field
supposed to be responsible for the acceleration of the universe usually imply a
variation of the neutrino masses on cosmological time scales. In this work we
propose a parameterization for the neutrino mass variation that captures the
essentials of those scenarios and allows to constrain them in a model
independent way, that is, without resorting to any particular scalar field
model. Using WMAP 5yr data combined with the matter power spectrum of SDSS and
2dFGRS, the limit on the present value of the neutrino mass is eV at 95% C.L. for the case in which the neutrino
mass was lighter (heavier) in the past, a result competitive with the ones
imposed for standard (i.e., constant mass) neutrinos. Moreover, for the ratio
of the mass variation of the neutrino mass over the current
mass we found that at 95% C.L.
for , totally consistent with no mass
variation. These stringent bounds on the mass variation are not related to the
neutrino free-streaming history which may affect the matter power spectrum on
small scales. On the contrary, they are imposed by the fact that any
significant transfer of energy between the neutrino and dark energy components
would lead to an instability contradicting CMB and large scale structure data
on the largest observable scales.Comment: 13 pages, 7 figures, 2 tables. Some few comments and references
added. To be published in PR
Can the WIMP annihilation boost factor be boosted by the Sommerfeld enhancement?
We demonstrate that the Sommerfeld correction to CDM annihilations can be
appreciable if even a small component of the dark matter is extremely cold.
Subhalo substructure provides such a possibility given that the smallest clumps
are relatively cold and contain even colder substructure due to incomplete
phase space mixing. Leptonic channels can be enhanced for plausible models and
the solar neighbourhood boost required to account for PAMELA/ATIC data is
plausibly obtained, especially in the case of a few TeV mass neutralino for
which the Sommerfeld-corrected boost is found to be Saturation
of the Sommerfeld effect is shown to occur below thereby
constraining the range of contributing substructures to be above We find that the associated diffuse gamma ray signal from
annihilations would exceed EGRET constraints unless the channels annihilating
to heavy quarks or to gauge bosons are suppressed. The lepton channel gamma
rays are potentially detectable by the FERMI satellite, not from the inner
galaxy where substructures are tidally disrupted, but rather as a
quasi-isotropic background from the outer halo, unless the outer substructures
are much less concentrated than the inner substructures and/or the CDM density
profile out to the virial radius steepens significantly.Comment: 8 pages, 5 figures. References added. Replaced to match published
versio
Breaking Be: a sterile neutrino solution to the cosmological lithium problem
The possibility that the so-called "lithium problem", i.e. the disagreement
between the theoretical abundance predicted for primordial Li assuming
standard nucleosynthesis and the value inferred from astrophysical
measurements, can be solved through a non-thermal BBN mechanism has been
investigated by several authors. In particular, it has been shown that the
decay of a MeV-mass particle, like, e.g., a sterile neutrino, decaying after
BBN not only solves the lithium problem, but also satisfies cosmological and
laboratory bounds, making such a scenario worth to be investigated in further
detail. In this paper, we constrain the parameters of the model with the
combination of current data, including Planck 2015 measurements of temperature
and polarization anisotropies of the CMB, FIRAS limits on spectral distortions,
astrophysical measurements of primordial abundances and laboratory constraints.
We find that a sterile neutrino with mass (at
c.l.), a decay time (at
c.l.) and an initial density (at c.l.) in units of the number density of CMB photons,
perfectly accounts for the difference between predicted and observed Li
primordial abundance. This model also predicts an increase of the effective
number of relativistic degrees of freedom at the time of CMB decoupling at c.l..
The required abundance of sterile neutrinos is incompatible with the standard
thermal history of the Universe, but could be realized in a low reheating
temperature scenario. We provide forecasts for future experiments finding that
the combination of measurements from the COrE+ and PIXIE missions will allow to
significantly reduce the permitted region for the sterile lifetime and density.Comment: 28 pages, 13 figures, 4 tables, matching the published versio
Relic Neutrinos, thermal axions and cosmology in early 2014
We present up to date cosmological bounds on the sum of active neutrino
masses as well as on extended cosmological scenarios with additional thermal
relics, as thermal axions or sterile neutrino species. Our analyses consider
all the current available cosmological data in the beginning of year 2014,
including the very recent and most precise Baryon Acoustic Oscillation (BAO)
measurements from the Baryon Oscillation Spectroscopic Survey. In the minimal
three active neutrino scenario, we find Sum m_nu < 0.22 eV at 95% CL from the
combination of CMB, BAO and Hubble Space Telescope measurements of the Hubble
constant. A non zero value for the sum of the three active neutrino masses of
about 0.3 eV is significantly favoured at more than 3 standard deviations when
adding the constraints on sigma_8 and Omega_m from the Planck Cluster catalog
on galaxy number counts. This preference for non zero thermal relic masses
disappears almost completely in both the thermal axion and massive sterile
neutrino schemes. Extra light species contribute to the effective number of
relativistic degrees of freedom, parameterised via Neff. We found that when the
recent detection of B mode polarization from the BICEP2 experiment is
considered, an analysis of the combined CMB data in the framework of LCDM+r
models gives Neff=4.00pm0.41, suggesting the presence of an extra relativistic
relic at more than 95 % c.l. from CMB-only data.Comment: 19 pages, 10 figure
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