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 $U(1)$ symmetry, as in, e.g. , Majoron models. In such scenarios, neutrinos still decouple at $T\simeq 1$ 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 $\gamma_{\nu \nu}^4$, parameterizing the neutrino collision rate due to (pseudo)scalar interactions. We consider both a minimal extension of the standard $\Lambda$CDM model, and scenarios with extra relativistic species or non-vanishing tensors. We find a typical constraint $\gamma_{\nu \nu}^4 < 0.9\times 10^{-27}$ (95% C.L.), implying an upper limit on the redshift $z_{rec}$ of neutrino recoupling $< 8500$. In the framework of Majoron models, the upper limit on $\gamma_{\nu \nu}$ roughly translates on a constraint $g < 8.2\times 10^{-7}$ on the Majoron-neutrino coupling constant $g$. In general, the data show a weak ($\sim 1\sigma$) but intriguing preference for non-zero values of $\gamma_{\nu \nu}^4$, with best fits in the range $\gamma_{\nu \nu}^4 = (0.15 - 0.35)\times 10^{-27}$, 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 $\Lambda$CDM +$\gamma_{\nu \nu}$ and including the Planck 2013, ACT and SPT data, we report $\gamma_{\nu \nu}^4=( 0.45^{+0.15}_{-0.38} )\times10^{-27}$ ($200 < z_{rec} < 5700$) 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 (NS$\nu$I) 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 NS$\nu$I inducing $\nu-\nu$ scattering, under the assumption that the mediator $\phi$ of the secret interaction is very light. We find that the effective coupling constant of the interaction, $g_\mathrm{eff}^4 \equiv \langle \sigma v\rangle T_\nu^2$, is constrained at $< 2.35\times10^{-27}$ (95\% credible interval), which stregthens to $g_\mathrm{eff}^4 < 1.64\times10^{-27}$ when Planck non-baseline small-scale polarization is considered. Our findings imply that after decoupling at $T\simeq 1$ MeV, cosmic neutrinos are free streaming at redshifts $z>3800$, or $z>2300$ 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 $H_0$ and the amplitude of matter fluctuations $\sigma_8$ are not significantly reduced. Our results are independent on the underlying particle physics model as long as $\phi$ is very light. Considering a model with Majorana neutrinos and a pseudoscalar mediator we find that the coupling constant $g$ of the secret interaction is constrained at $\lesssim 7\times 10^{-7}$. 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 $v_\sigma$ as $\gtrsim (1.4\times 10^{6})m_\nu$.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 Λ\mathbf{\Lambda}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 $\ell$ alignments and assuming $\Lambda$CDM, we confirm that the quadrupole/octupole and the dipole/quadrupole/octupole alignments are anomalous with a significance up to $99.9\%$ 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 $\Lambda$CDM. We conclude that the dipolar model does not provide a better fit to the data than the $\Lambda$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 $l,m,\sigma$ 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 $h+k+l=$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 $5-10\%$. 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