6,074 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
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
Constraints on CPT violation from WMAP three year polarization data: a wavelet analysis
We perform a wavelet analysis of the temperature and polarization maps of the
Cosmic Microwave Background (CMB) delivered by the WMAP experiment in search
for a parity violating signal. Such a signal could be seeded by new physics
beyond the standard model, for which the Lorentz and CPT symmetries may not
hold. Under these circumstances, the linear polarization direction of a CMB
photon may get rotated during its cosmological journey, a phenomenon also
called cosmological birefringence. Recently, Feng et al. have analyzed a subset
the WMAP and BOOMERanG 2003 angular power spectra of the CMB, deriving a
constraint that mildly favors a non zero rotation. By using wavelet transforms
we set a tighter limit on the CMB photon rotation angle \Delta\alpha= -2.5 \pm
3.0 (\Delta\alpha= -2.5 \pm 6.0) at the one (two) \sigma level, consistent with
a null detection.Comment: 7 pages, 4 figures, some modifications to match accepted (PRD)
version, results unchange
CMB low multipole alignments in the CDM and Dipolar models
The dipolar model \cite{Gordon:2005ai} has attracted much interest because it
may phenomenologically explain the CMB hemispherical power asymmetry found in
the WMAP and Planck data. Since such a model explicitly breaks isotropy at
large angular scales it is natural to wonder whether it can also explain other
CMB directional anomalies. Focusing on the low alignments and assuming
CDM, we confirm that the quadrupole/octupole and the
dipole/quadrupole/octupole alignments are anomalous with a significance up to
C.L., for both WMAP and Planck data. Moreover, we show for the first
time that such features are anomalous also in the dipolar model, roughly at the
same level as in CDM. We conclude that the dipolar model does not
provide a better fit to the data than the CDM.Comment: 13 pages, 2 figures and 4 table
The implications of resonant x-ray scattering data on the physics of the insulating phase of V_2O_3
We have performed a quantitative analysis of recent resonant x-ray scattering
experiments carried out in the antiferromagnetic phase of V_2O_3 by means of
numerical ab-initio simulations. In order to treat magnetic effects, we have
developed a method based on multiple scattering theory (MST) and a relativistic
extension of the Schr\"{o}dinger Equation, thereby working with the usual non
relativistic set of quantum numbers for angular and spin momenta.
Electric dipole-dipole (E1-E1), dipole-quadrupole (E1-E2) and
quadrupole-quadrupole (E2-E2) transition were considered altogether. We obtain
satisfactory agreement with experiments, both in energy and azimuthal scans.
All the main features of the V K edge Bragg-forbidden reflections with
odd can be interpreted in terms of the antiferromagnetic ordering only,
{\it ie}, they are of magnetic origin. In particular the ab-initio simulation
of the energy scan around the (1,1,1)-monoclinic reflection excludes the
possibility of any symmetry reduction due to a time-reversal breaking induced
by orbital ordering.Comment: 11 pages, 6 figure
A note on the birefringence angle estimation in CMB data analysis
Parity violating physics beyond the standard model of particle physics
induces a rotation of the linear polarization of photons. This effect, also
known as cosmological birefringence (CB), can be tested with the observations
of the cosmic microwave background (CMB) anisotropies which are linearly
polarized at the level of . In particular CB produces non-null CMB
cross correlations between temperature and B mode-polarization, and between E-
and B-mode polarization. Here we study the properties of the so called
D-estimators, often used to constrain such an effect. After deriving the
framework of both frequentist and Bayesian analysis, we discuss the interplay
between birefringence and weak-lensing, which, albeit parity conserving,
modifies pre-existing TB and EB cross correlation.Comment: 12 pages. Accepted for publication in JCA
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