Showing papers by "Olga Mena published in 2015"

Spectral analysis of the high-energy IceCube neutrinos

Abstract: A full energy and flavor-dependent analysis of the three-year high-energy IceCube neutrino events is presented. By means of multidimensional fits, we derive the current preferred values of the high-energy neutrino flavor ratios, the normalization and spectral index of the astrophysical fluxes, and the expected atmospheric background events, including a prompt component. A crucial assumption resides on the choice of the energy interval used for the analyses, which significantly biases the results. When restricting ourselves to the $\ensuremath{\sim}30\text{ }\text{ }\mathrm{TeV}--3\text{ }\text{ }\mathrm{PeV}$ energy range, which contains all the observed IceCube events, we find that the inclusion of the spectral information improves the fit to the canonical flavor composition at Earth, $(1\ensuremath{\mathbin:}1\ensuremath{\mathbin:}1{)}_{\ensuremath{\bigoplus}}$, with respect to a single-energy bin analysis. Increasing both the minimum and the maximum deposited energies has dramatic effects on the reconstructed flavor ratios as well as on the spectral index. Imposing a higher threshold of 60 TeV yields a slightly harder spectrum by allowing a larger muon neutrino component, since above this energy most atmospheric tracklike events are effectively removed. Extending the high-energy cutoff to fully cover the Glashow resonance region leads to a softer spectrum and a preference for tau neutrino dominance, as none of the expected electron (anti)neutrino induced showers have been observed so far. The lack of showers at energies above 2 PeV may point to a broken power-law neutrino spectrum. Future data may confirm or falsify whether the recently discovered high-energy neutrino fluxes and the long-standing detected cosmic rays have a common origin.

Revisiting cosmological bounds on sterile neutrinos

Abstract: We employ state-of-the art cosmological observables including supernova surveys and BAO information to provide constraints on the mass and mixing angle of a non-resonantly produced sterile neutrino species, showing that cosmology can effectively rule out sterile neutrinos which decay between BBN and the present day. The decoupling of an additional heavy neutrino species can modify the time dependence of the Universe's expansion between BBN and recombination and, in extreme cases, lead to an additional matter-dominated period; while this could naively lead to a younger Universe with a larger Hubble parameter, it could later be compensated by the extra radiation expected in the form of neutrinos from sterile decay. However, recombination-era observables including the Cosmic Microwave Background (CMB), the shift parameter RCMB and the sound horizon rs from Baryon Acoustic Oscillations (BAO) severely constrain this scenario. We self-consistently include the full time-evolution of the coupled sterile neutrino and standard model sectors in an MCMC, showing that if decay occurs after BBN, the sterile neutrino is essentially bounded by the constraint sin2???0.026?(ms/eV)?2.

Do current data prefer a nonminimally coupled inflaton

Abstract: We examine the impact of a nonminimal coupling of the inflaton to the Ricci scalar, $\frac{1}{2}\ensuremath{\xi}R{\ensuremath{\phi}}^{2}$, on the inflationary predictions. Such a nonminimal coupling is expected to be present in the inflaton Lagrangian on fairly general grounds. As a case study, we focus on the simplest inflationary model governed by the potential $V\ensuremath{\propto}{\ensuremath{\phi}}^{2}$, using the latest combined 2015 analysis of Planck and the $\mathrm{BICEP}2/Keck$ Array. We find that the presence of a coupling $\ensuremath{\xi}$ is favored at a significance of 99% C.L., assuming that nature has chosen the potential $V\ensuremath{\propto}{\ensuremath{\phi}}^{2}$ to generate the primordial perturbations and a number of $e$-foldings $N=60$. Within the context of the same scenario, we find that the value of $\ensuremath{\xi}$ is different from zero at the $2\ensuremath{\sigma}$ level. When considering the cross-correlation polarization spectra from the $\mathrm{BICEP}2/Keck$ Array and Planck, a value of $r=0.03{8}_{\ensuremath{-}0.030}^{+0.039}$ is predicted in this particular nonminimally coupled scenario. Future cosmological observations may therefore test these values of $r$ and verify or falsify the nonminimally coupled model explored here.

Exploring dark matter microphysics with galaxy surveys

Abstract: We use present cosmological observations and forecasts of future experiments to illustrate the power of large-scale structure (LSS) surveys in probing dark matter (DM) microphysics and unveiling potential deviations from the standard ΛCDM scenario. To quantify this statement, we focus on an extension of ΛCDM with DM-neutrino scattering, which leaves a distinctive imprint on the angular and matter power spectra. After finding that future CMB experiments (such as COrE+) will not significantly improve the constraints set by the Planck satellite, we show that the next generation of galaxy clustering surveys (such as DESI) could play a leading role in constraining alternative cosmologies and even have the potential to make a discovery. Typically we find that DESI would be an order of magnitude more sensitive to DM interactions than Planck, thus probing effects that until now have only been accessible via N-body simulations.

Exploring dark matter microphysics with galaxy surveys

Abstract: We use present cosmological observations and forecasts of future experiments to illustrate the power of large-scale structure (LSS) surveys in probing dark matter (DM) microphysics and unveiling potential deviations from the standard $\Lambda$CDM scenario. To quantify this statement, we focus on an extension of $\Lambda$CDM with DM-neutrino scattering, which leaves a distinctive imprint on the angular and matter power spectra. After finding that future CMB experiments (such as COrE+) will not significantly improve the constraints set by the Planck satellite, we show that the next generation of galaxy clustering surveys (such as DESI) could play a leading role in constraining alternative cosmologies and even have the potential to make a discovery. Typically we find that DESI would be an order of magnitude more sensitive to DM interactions than Planck, thus probing effects that until now have only been accessible via $N$-body simulations.

Primordial power spectrum features and f NL constraints

Abstract: The simplest models of inflation predict small non-Gaussianities and a featureless power spectrum. However, there exist a large number of well-motivated theoretical scenarios in which large non-Gaussianties could be generated. In general, in these scenarios the primordial power spectrum will deviate from its standard power law shape. We study, in a model-independent manner, the constraints from future large-scale structure surveys on the local non-Gaussianity parameter ${f}_{\mathrm{NL}}$ when the standard power law assumption for the primordial power spectrum is relaxed. If the analyses are restricted to the large-scale-dependent bias induced in the linear matter power spectrum by non-Gaussianites, the errors on the ${f}_{\mathrm{NL}}$ parameter could be increased by 60% when exploiting data from the future DESI survey, if dealing with only one possible dark matter tracer. In the same context, a nontrivial bias $|\ensuremath{\delta}{f}_{\mathrm{NL}}|\ensuremath{\sim}2.5$ could be induced if future data are fitted to the wrong primordial power spectrum. Combining all the possible DESI objects slightly ameliorates the problem, as the forecasted errors on ${f}_{\mathrm{NL}}$ would be degraded by 40% when relaxing the assumptions concerning the primordial power spectrum shape. Also, the shift on the non-Gaussianity parameter is reduced in this case, $|\ensuremath{\delta}{f}_{\mathrm{NL}}|\ensuremath{\sim}1.6$. The addition of cosmic microwave background priors ensures robust future ${f}_{\mathrm{NL}}$ bounds, as the forecasted errors obtained including these measurements are almost independent on the primordial power spectrum features, and $|\ensuremath{\delta}{f}_{\mathrm{NL}}|\ensuremath{\sim}0.2$, close to the standard single-field slow-roll paradigm prediction.

Phenomenological approaches of inflation and their equivalence

Abstract: In this work, we analyze two possible alternative and model-independent approaches to describe the inflationary period. The first one assumes a general equation of state during inflation due to Mukhanov, while the second one is based on the slow-roll hierarchy suggested by Hoffman and Turner. We find that, remarkably, the two approaches are equivalent from the observational viewpoint, as they single out the same areas in the parameter space, and agree with the inflationary attractors where successful inflation occurs. Rephrased in terms of the familiar picture of a slowly rolling, canonically normalized scalar field, the resulting inflaton excursions in these two approaches are almost identical. Furthermore, once the Galactic dust polarization data from Planck are included in the numerical fits, inflaton excursions can safely take sub-Planckian values.

Robustness of cosmological axion mass limits

Abstract: We present the cosmological bounds on the thermal axion mass in an extended cosmological scenario in which the primordial power spectrum of scalar perturbations differs from the usual power-law shape predicted by the simplest inflationary models. The power spectrum is instead modeled by means of a ``piecewise cubic Hermite interpolating polynomial'' (pchip). When using cosmic microwave background measurements combined with other cosmological data sets, the thermal axion mass constraints are degraded only slightly. The addition of the measurements of ${\ensuremath{\sigma}}_{8}$ and ${\mathrm{\ensuremath{\Omega}}}_{m}$ from the 2013 Planck cluster catalog on galaxy number counts relaxes the bounds on the thermal axion mass, mildly favoring a $\ensuremath{\sim}1\text{ }\text{ }\mathrm{eV}$ axion mass, regardless of the model adopted for the primordial power spectrum. However, in general, such a preference disappears if the sum of the three active neutrino masses is also considered as a free parameter in our numerical analyses, due to the strong correlation between the masses of these two hot thermal relics.

The present and future of the most favoured inflationary models after $Planck$ 2015

Abstract: The value of the tensor-to-scalar ratio $r$ in the region allowed by the latest $Planck$ 2015 measurements can be associated to a large variety of inflationary models. We discuss here the potential of future Cosmic Microwave Background cosmological observations in disentangling among the possible theoretical scenarios allowed by our analyses of current $Planck$ temperature and polarization data. Rather than focusing only on $r$, we focus as well on the running of the primordial power spectrum, $\alpha_s$ and the running of thereof, $\beta_s$. Our Fisher matrix method benefits from a detailed and realistic appraisal of the expected foregrounds. Future cosmological probes, as the COrE mission, may be able to reach an unprecedented accuracy in the extraction of $\beta_s$ and rule out the most favoured inflationary models.

The Flavour Composition of the High-Energy IceCube Neutrinos

Abstract: We present an in-depth analysis of the flavour and spectral composition of the 36 high-energy neutrino events observed after three years of observation by the IceCube neutrino telescope. While known astrophysical sources of HE neutrinos are expected to produce a nearly $(1:1:1)$ flavour ratio (electron : muon : tau) of neutrinos at earth, we show that the best fits based on the events detected above $E_ u \ge 28$ TeV do not necessarily support this hypothesis. Crucially, the energy range that is considered when analysing the HE neutrino data can have a profound impact on the conclusions. We highlight two intriguing puzzles: an apparent deficit of muon neutrinos, seen via a deficit of track-like events; and an absence of $\bar u_e$'s at high energy, seen as an absence of events near the Glashow resonance. We discuss possible explanations, including the misidentification of tracks as showers, and a broken power law, in analogy to the observed HE cosmic ray spectrum.