Cosmological neutrino mass detection: The best probe of neutrino lifetime

Future cosmological data may be sensitive to the effects of a finite sum of neutrino masses even as small as ~0.06 eV, the lower limit guaranteed by neutrino oscillation experiments. We show that a cosmological detection of neutrino mass at that level would improve by many orders of magnitude the existing limits on neutrino lifetime, and as a consequence on neutrino secret interactions with (quasi-)massless particles as in majoron models. On the other hand, neutrino decay may provide a way-out to explain a discrepancy <~ 0.1 eV between cosmic neutrino bounds and Lab data.Comment: 5 pages, 1 eps figure; clarifications and references added, improved discussion, conclusions unchanged. Matches version published in PR

Non-linear cosmic ray Galactic transport in the light of AMS-02 and Voyager data

Context: Features in the spectra of primary cosmic rays (CRs) provide invaluable information on the propagation of these particles in the Galaxy. In the rigidity region around a few hundred GV, such features have been measured in the proton and helium spectra by the PAMELA experiment and later confirmed with a higher significance by AMS-02. We investigate the implications of these datasets for the scenario in which CRs propagate under the action of self-generated waves. Aims: We show that the recent data on the spectrum of protons and helium nuclei as collected with AMS-02 and Voyager are in very good agreement with the predictions of a model in which the transport of Galactic CRs is regulated by self-generated waves. We also study the implications of the scenario for the boron-to-carbon ratio: although a good overall agreement is found, at high energy we find marginal support for a (quasi) energy independent contribution to the grammage, that we argue may come from the sources themselves Results: A break in the spectra of all nuclei is found at rigidity of a few hundred GV, as a result of a transition from self-generated waves to pre-existing waves with a Kolmogorov power spectrum. Neither the slope of the diffusion coefficient, nor its normalisation are free parameters. Moreover, at rigidities below a few GV, CRs are predicted to be advected with the self-generated waves at the local Alfv\'en speed. This effect, predicted in our previous work, provides an excellent fit to the Voyager data on the proton and helium spectra at low energies, providing additional support to the model.Comment: Submitted to A&A Research Note, 5 pages, 4 Figures. arXiv admin note: text overlap with arXiv:1306.201

The Nuclear Reactions in Standard BBN

Nowadays, the Cosmic Microwave Background (CMB) anisotropies studies accurately determine the baryon fraction omega_b, showing an overall and striking agreement with previous determinations of omega_b obtained from Big Bang Nucleosynthesis (BBN). However, a deeper comparison of BBN predictions with the determinations of the primordial light nuclides abundances shows slight tensions, motivating an effort to further improve the accuracy of theoretical predictions, as well as to better evaluate systematics in both observations and nuclear reactions measurements. We present some results of an important step towards an increasing precision of BBN predictions, namely an updated and critical review of the nuclear network, and a new protocol to perform the nuclear data regression.Comment: 4 pp.,4figs. Few typos corrected and updated refs. to match the version appearing in the proceedings of Conference ``Nuclei in the Cosmos VIII'', Vancouver, BC, Canada, 19-23 Jul 2004, published in Nucl. Phys.

Non-universal BBN bounds on electromagnetically decaying particles

In Poulin and Serpico [Phys. Rev. Lett. 114, 091101 (2015)] we have recently argued that when the energy of a photon injected in the primordial plasma falls below the pair-production threshold, the universality of the non-thermal photon spectrum from the standard theory of electromagnetic cascades onto a photon background breaks down. We showed that this could reopen or widen the parameter space for an exotic solution to the 'lithium problem'. Here we discuss another application, namely the impact that this has on non-thermal big bang nucleosynthesis constraints from 4He, 3He and 2H, using the parametric example of monochromatic photon injection of different energies. Typically, we find tighter bounds than those existing in the literature, up to more than one order of magnitude. As a consequence of the non-universality of the spectrum, the energy-dependence of the photodissociation cross-sections is important. We also compare the constraints obtained with current level and future reach of cosmic microwave background spectral distortion bounds.Comment: 8 pages, 7 figures. v2: minor typographical corrections, extended comments and reference

Are IceCube neutrinos unveiling PeV-scale decaying dark matter?

Recent observations by IceCube, notably two PeV cascades accompanied by events at energies ~ (30-400) TeV, are clearly in excess over atmospheric background fluxes and beg for an astroparticle physics explanation. Although some models of astrophysical accelerators can account for the observations within current statistics, intriguing features in the energy and possibly angular distributions of the events make worth exploring alternatives. Here, we entertain the possibility of interpreting the data with a few PeV mass scale decaying Dark Matter, with lifetime of the order of 10^27 s. We discuss generic signatures of this scenario, including its unique energy spectrum distortion with respect to the benchmark $E_\nu^{-2}$ expectation for astrophysical sources, as well as peculiar anisotropies. A direct comparison with the data show a good match with the above-mentioned features. We further discuss possible future checks of this scenario.Comment: 7 pages, 3 figures; v2: discussion improved, reference added, matches the version published in JCA

Gamma-ray bounds from EAS detectors and heavy decaying dark matter constraints

The very high energy Galactic $\gamma$-ray sky is partially opaque in the ($0.1-10$) PeV energy range. In the light of the recently detected high energy neutrino flux by IceCube, a comparable very high energy $\gamma$-ray flux is expected in any scenario with a sizable Galactic contribution to the neutrino flux. Here we elaborate on the peculiar energy and anisotropy features imposed upon these very high energy $\gamma$-rays by the absorption on the cosmic microwave background photons and Galactic interstellar light. As a notable application of our considerations, we study the prospects of probing the PeV-scale decaying DM scenario, proposed as a possible source of IceCube neutrinos, by extensive air shower (EAS) cosmic ray experiments. In particular, we show that anisotropy measurements at EAS experiments are already sensitive to $\tau_{\rm DM}\sim {\cal O}(10^{27})$~s and future measurements, using better gamma/hadron separation, can improve the limit significantly.Comment: 23 pages, 9 figures; v2: the discussion of anisotropy in section 4 improved, matches the version published at JCA

A robust upper limit on N_eff from BBN, circa 2011

We derive here a robust bound on the effective number of neutrinos from constraints on primordial nucleosynthesis yields of deuterium and helium. In particular, our results are based on very weak assumptions on the astrophysical determination of the helium abundance, namely that the minimum effect of stellar processing is to keep constant (rather than increase, as expected) the helium content of a low-metallicity gas. Using the results of a recent analysis of extragalactic HII regions as upper limit, we find that Delta Neff<= 1 at 95 % C.L., quite independently of measurements on the baryon density from cosmic microwave background anisotropy data and of the neutron lifetime input. In our approach, we also find that primordial nucleosynthesis alone has no significant preference for an effective number of neutrinos larger than the standard value. The ~2 sigma hint sometimes reported in the literature is thus driven by CMB data alone and/or is the result of a questionable regression protocol to infer a measurement of primordial helium abundance.Comment: 5 pages, 1 table, 1 figure. Minor improvements and extensions in the analysis, clarifications and reference added, conclusions slightly strengthened. Matches version published in Phys. Lett.

"Discrepant hardenings" in cosmic ray spectra: a first estimate of the effects on secondary antiproton and diffuse gamma-ray yields

Recent data from CREAM seem to confirm early suggestions that primary cosmic ray (CR) spectra at few TeV/nucleon are harder than in the 10-100 GeV range. Also, helium and heavier nuclei spectra appear systematically harder than the proton fluxes at corresponding energies. We note here that if the measurements reflect intrinsic features in the interstellar fluxes (as opposed to local effects) appreciable modifications are expected in the sub-TeV range for the secondary yields, such as antiprotons and diffuse gamma-rays. Presently, the ignorance on the origin of the features represents a systematic error in the extraction of astrophysical parameters as well as for background estimates for indirect dark matter searches. We find that the spectral modifications are appreciable above 100 GeV, and can be responsible for ~30% effects for antiprotons at energies close to 1 TeV or for gamma's at energies close to 300 GeV, compared to currently considered predictions based on simple extrapolation of input fluxes from low energy data. Alternatively, if the feature originates from local sources, uncorrelated spectral changes might show up in antiproton and high-energy gamma-rays, with the latter ones likely dependent from the line-of-sight.Comment: 6 pages, 3 figures. Clarifications and references added, conclusions unchanged. Matches published versio

A loophole to the universal photon spectrum in electromagnetic cascades: application to the "cosmological lithium problem"

The standard theory of electromagnetic cascades onto a photon background predicts a quasi-universal shape for the resulting non-thermal photon spectrum. This has been applied to very disparate fields, including non-thermal big bang nucleosynthesis (BBN). However, once the energy of the injected photons falls below the pair-production threshold the spectral shape is very different, a fact that has been overlooked in past literature. This loophole may have important phenomenological consequences, since it generically alters the BBN bounds on non-thermal relics: for instance it allows to re-open the possibility of purely electromagnetic solutions to the so-called "cosmological lithium problem", which were thought to be excluded by other cosmological constraints. We show this with a proof-of-principle example and a simple particle physics model, compared with previous literature.Comment: 5 pages, 2 figures, typos corrected; matches version published in PRL. (Version 1 of this article was submitted to arxiv on Jan. 8th, kept on hold by arxiv moderators due to unspecified classification doubts for almost one month.