arXiv subjects

Michele Maltoni

Publications and source records attributed to Michele Maltoni.

At least 55 records · Page 3Linked to original sources

arXiv2011

Robust Cosmological Bounds on Neutrinos and their Combination with Oscillation Results

We perform a global analysis of cosmological observables in generalized cosmologies which depart from $Λ$CDM models by allowing non-vanishing curvature $Ω_k\neq 0$, dark energy with equation of state with $ω\neq -1$, the presence of additional relativistic degrees of freedom $ΔN_{\rm rel}$, and neutrino masses $Ω_ν\neq 0$. By combining the data from cosmic microwave background (CMB) experiments (in particular the latest results from WMAP-7), the present day Hubble constant (H0) measurement, the high-redshift Type-I supernovae (SN) results and the information from large scale structure (LSS) surveys, we determine the parameters in the 10-dimensional parameter space for such models. We present the results from the analysis when the full shape information from the LSS matter power spectrum (LSSPS) is included versus when only the corresponding distance measurement from the baryon acoustic oscillations (BAO) is accounted for. We compare the bounds on the neutrino mass scale in these generalized scenarios with those obtained for the 6+1 parameter analysis in $Λ{\rm CDM}+m_ν$ models and we also study the dependence of those on the set of observables included in the analysis. Finally we combine these results with the information on neutrino mass differences and mixing from the global analysis of neutrino oscillation experiments and derive the presently allowed ranges for the two laboratory probes of the absolute scale of neutrino mass: the effective electron neutrino mass in single beta decay and the effective Majorana neutrino mass in neutrinoless $ββ$ decay.

hep-ph↗

arXiv2011

Testing matter effects in propagation of atmospheric and long-baseline neutrinos

We quantify our current knowledge of the size and flavor structure of the matter effects in the evolution of atmospheric and long-baseline neutrinos based solely on the analysis of the corresponding neutrino data. To this aim we generalize the matter potential of the Standard Model by rescaling its strength, rotating it away from the e-e sector, and rephasing it with respect to the vacuum term. This phenomenological parametrization can be easily translated in terms of non-standard neutrino interactions in matter. We show that in the most general case, the strength of the potential cannot be determined solely by atmospheric and long-baseline data. However its flavor composition is very much constrained and the present determination of the neutrino masses and mixing is robust under its presence. We also present an update of the constraints arising from this analysis in the particular case in which no potential is present in the e-mu and e-tau sectors. Finally we quantify to what degree in this scenario it is possible to alleviate the tension between the oscillation results for neutrinos and antineutrinos in the MINOS experiment and show the relevance of the high energy part of the spectrum measured at MINOS.

hep-ph↗

arXiv2011

Are there sterile neutrinos at the eV scale?

New predictions for the anti-neutrino flux emitted by nuclear reactors suggest that reactor experiments may have measured a deficit in the anti-neutrino flux, which can be interpreted in terms of oscillations between the known active neutrinos and new sterile states. Motivated by this observation, we perform a re-analysis of global short-baseline neutrino oscillation data in a framework with one or two sterile neutrinos. While one sterile neutrino is still not sufficient to reconcile the signals suggested by reactor experiments and by the LSND and MiniBooNE experiments with null results from other searches, we find that, with the new reactor flux prediction, the global fit improves considerably when the existence of two sterile neutrinos is assumed.

hep-ph↗

arXiv2010

Summary report of MINSIS workshop in Madrid

Recent developments on tau detection technologies and the construction of high intensity neutrino beams open the possibility of a high precision search for non-standard μ - τ flavour transition with neutrinos at short distances. The MINSIS - Main Injector Non-Standard Interaction Search- is a proposal under discussion to realize such precision measurement. This document contains the proceedings of the workshop which took place on 10-11 December 2009 in Madrid to discuss both the physics reach as well as the experimental requirements for this proposal.

hep-ph↗

arXiv2008

Three-flavour neutrino oscillation update and comments on possible hints for a non-zero theta_{13}

We provide a short summary of three-flavour neutrino oscillation parameters as determined from a global fit to 2008 data, and we comment on possible hints in favour of a non-zero value of the mixing angle theta_{13} found in arXiv:0806.2649. We do confirm a hint from solar + KamLAND data at about 1.5 sigma, which can be understood from the recent SNO CC/NC measurment. However, we show that a claimed hint from atmospheric data is much less robust. It depends on details of event rate calculations and treatment of theoretical uncertainties. We could identify two data points showing an 'excess' (at the 1 sigma level) in the SK-I multi-GeV e-like data, which seem to be the origin of the slight preference for theta_{13} > 0. We point out that once SK-I and SK-II data are combined this 'excess' disappears, and irrespective of the details of the analysis, no 'hint' from atmospheric data is obtained for the SK-I and SK-II combined data set. As a result the global fit of all data leads to a best fit value of theta_{13} consistent with zero within less than 1 sigma.

hep-ph↗

arXiv2008

New interactions: past and future experiments

In this talk I will review the present status and future perspectives of some popular extensions of the conventional three-neutrino oscillation scenario, from a purely phenomenological point of view. For concreteness I will focus only on three specific scenarios: non-standard neutrino interactions with matters, models with extra sterile neutrinos, and neutrino decay and decoherence.

hep-ph↗

arXiv2008

Prospects and synergies between future atmospheric and long-baseline experiments

In this talk we will discuss the physics reach of the atmospheric neutrino data collected by a future megaton-class neutrino detector. First we will discuss the potentialities of atmospheric neutrinos on general basis, presenting our results in the form of neutrino oscillograms of the Earth: contour plots in the neutrino energy--nadir angle plane. In this context we will analyze in detail the various signatures related to theta_13, to the neutrino mass hierarchy, to the octant of theta_23 and to the delta_CP phase which appear for different values of the neutrino energy and baseline. Then we will consider concrete experimental setups, showing that synergic effects exist between atmospheric and long-baseline neutrino data: the combination of the two data sets is much more powerful than the simple sum of the sensitivity of each individual data sample.

hep-ph↗

arXiv2008

Testing neutrino flavor mixing plus decay with neutrino telescopes

We discuss the interplay of neutrino oscillation and decay properties at neutrino telescopes. Motivated by recent unparticle scenarios, which open the possibility of new neutrino decay modes over astrophysical distances, we perform a complete classification of possible decay schemes, and we illustrate how different scenarios can be identified. Moreover, we show that the sensitivity of neutrino telescopes to standard neutrino properties, such as the mass hierarchy or delta_CP, is greatly enhanced in specific decay scenarios. In particular we discuss the impact of an astrophysical neutrino detection on terrestrial experiments, such as on the mass hierarchy measurement at NOvA. For example, we find that the scenario where only nu_1 is stable can be uniquely identified against all the other decay schemes, and that in this case CP violation can be established (for large theta_13) by the combination of Double Chooz with the track-to-shower ratio at a neutrino telescope, even if the flavor composition at the source is unknown. Our statements are based on a complete analysis of all the present solar, atmospheric, reactor and accelerator neutrino data, as well as on realistic simulation of future terrestrial neutrino oscillation experiments.

hep-ph↗

arXiv2008

Neutrino oscillograms of the Earth: effects of 1-2 mixing and CP-violation

We develop a comprehensive description of three flavor neutrino oscillations inside the Earth in terms of neutrino oscillograms in the whole range of nadir angles and for energies above 0.1 GeV. The effects of the 1-2 mass splitting and mixing as well the interference of the 1-2 and 1-3 modes of oscillations are quantified. The 1-2 mass splitting and mixing lead to the appearance, apart from the resonance MSW peaks, of the parametric resonance peak for core-crossing trajectories at E_nu ~= 0.2 GeV. We show that the interference effects, in particular CP violation, have a domain structure with borders determined by the solar and atmospheric magic lines and the lines of the interference phase condition. The dependence of the oscillograms on the Dirac CP-violating phase is studied. We show that for sin^2(2 theta13) < 0.1 the strongest dependence of the oscillograms on delta is in the 1-2 and 1-3 resonance regions.

hep-ph↗

arXiv2008

Status of Oscillation plus Decay of Atmospheric and Long-Baseline Neutrinos

We study the interplay of neutrino oscillation and invisible decay in atmospheric and long-baseline neutrinos experiments. We perform a global analysis of the full atmospheric data from Super-Kamiokande together with long-baseline K2K and MINOS in these scenarios. We find that the admixture of nu_mu -> nu_tau oscillations with parameters Delta_m32^2 = 2.6e-3 eV^2 and theta_23 ~ 34 degrees plus decay of the heavy neutrino, nu_3, with lifetime of the order tau_3/m_3 ~ 2.6e-12 s/eV provides a reasonable fit to atmospheric neutrinos, although this solution becomes more disfavored (dropping to the 99% CL) once long-baseline data are included. Other than this local minimum, the analysis shows no evidence in favor of a non-vanishing neutrino decay width and an lower bound on the decay lifetime tau_3/m_3 > 9.3e-11 s/eV is set at 99% CL. In the framework of Majoron models, this constraint can be translated into a bound on the Majoron coupling to nu_3 and an unmixed very light sterile state, |g_s3| < 8.6e-3 (2.2 eV/m_3).

hep-ph↗

arXiv2008

Radiography of the Earth's Core and Mantle with Atmospheric Neutrinos

A measurement of the absorption of neutrinos with energies in excess of 10 TeV when traversing the Earth is capable of revealing its density distribution. Unfortunately, the existence of beams with sufficient luminosity for the task has been ruled out by the AMANDA South Pole neutrino telescope. In this letter we point out that, with the advent of second-generation kilometer-scale neutrino detectors, the idea of studying the internal structure of the Earth may be revived using atmospheric neutrinos instead.

hep-ph↗

arXiv2007

Sterile neutrinos after the first MiniBooNE results

In view of the recent results from the MiniBooNE experiment we revisit the global neutrino oscillation fit to short-baseline neutrino data by adding one, two or three sterile neutrinos with eV-scale masses to the three Standard Model neutrinos. We find that four-neutrino oscillations of the (3+1) type, which have been only marginally allowed before the recent MiniBooNE results, become even more disfavored with the new data. In the framework of so-called (3+2) five-neutrino mass schemes the MiniBooNE results can be nicely reconciled with the LSND appearance evidence thanks to the possibility of CP violation available in such oscillation schemes; however, the tension between appearance and disappearance experiments represents a serious problem in (3+2) schemes, so that these models are ultimately not viable. This tension remains also when a third sterile neutrino is added, and we do not find a significant improvement of the global fit in a (3+3) scheme.

hep-ph↗

arXiv2007

Phenomenology with Massive Neutrinos

The current status and some perspectives of the phenomenology of massive neutrinos is reviewed. We start with the phenomenology of neutrino oscillations in vacuum and in matter. We summarize the results of neutrino experiments using solar, atmospheric, reactor and accelerator neutrino beams. We update the leptonic parameters derived from the three-neutrino oscillation interpretation of this data. We describe the method and present results on our understanding of the solar and atmospheric neutrino fluxes by direct extraction from the corresponding neutrino event rates. We present some tests of different forms of new physics which induce new sources of leptonic flavor transitions in vacuum and in matter which can be performed with the present neutrino data. The aim and potential of future neutrino experiments and facilities to further advance in these fronts is also briefly summarized. Last, the implications of the LSND observations are discussed, and the status of extended models which could accommodate all flavor-mixing signals is presented in the light of the recent results from MiniBooNE.

hep-ph↗

arXiv2007

Sterile neutrino oscillations after first MiniBooNE results

In view of the recent results from the MiniBooNE experiment we revisit the global neutrino oscillation fit to short-baseline neutrino data by adding one or two sterile neutrinos with eV-scale masses to the three Standard Model neutrinos, and for the first time we consider also the global fit with three sterile neutrinos. Four-neutrino oscillations of the (3+1) type have been only marginally allowed before the recent MiniBooNE results, and become even more disfavored with the new data (at the level of $4σ$). In the framework of so-called (3+2) five-neutrino mass schemes we find severe tension between appearance and disappearance experiments at the level of more than $3σ$, and hence no satistfactory fit to the global data is possible in (3+2) schemes. This tension remains also when a third sterile neutrino is added, and the quality of the global fit does not improve significantly in a (3+3) scheme. It should be noted, however, that in models with more than one sterile neutrino the MiniBooNE results are in perfect agreement with the LSND appearance evidence, thanks to the possibility of CP violation available in such oscillation schemes. Furthermore, if disappearance data are not taken into account (3+2) oscillations provide an excellent fit to the full MiniBooNE spectrum including the event excess at low energies.

hep-ph↗

arXiv2007

Potentialities of atmospheric neutrinos

In this talk we will discuss the physics reach of the atmospheric neutrino data collected by a future megaton-class neutrino detector. After a general discussion of the potentialities of atmospheric neutrinos on general basis, we will consider concrete experimental setups and show that synergic effects exist between atmospheric and long-baseline neutrino data. Finally, we will show that present Super-Kamiokande data already have the capability to allow for a direct and unbiased measurement of the energy spectrum of the atmospheric neutrino fluxes.

hep-ph↗

arXiv2007

1-3 leptonic mixing and the neutrino oscillograms of the Earth

We develop a detailed and comprehensive description of neutrino oscillations driven by the 1-3 mixing in the matter of the Earth. The description is valid for the realistic (PREM) Earth density profile in the whole range of nadir angles and for neutrino energies above 1 GeV. It can be applied to oscillations of atmospheric and accelerator neutrinos. The results are presented in the form of neutrino oscillograms of the Earth, i.e. the contours of equal oscillation probabilities in the neutrino energy--nadir angle plane. A detailed physics interpretation of the oscillograms, which includes the MSW peaks, parametric ridges, local maxima, zeros and saddle points, is given in terms of the amplitude and phase conditions. Precise analytic formulas for the probabilities are obtained. We study the dependence of the oscillation pattern on theta_13 and find, in particular, that the transition probability P > 1/2 appears for sin^2(2theta_13) as small as 0.009. We consider the dependence of the oscillation pattern on the matter density profile and comment on the possibility of the oscillation tomography of the Earth.

hep-ph↗

arXiv2006

Determination of the atmospheric neutrino fluxes from experimental data

The precise knowledge of the atmospheric neutrino fluxes is a key ingredient in the interpretation of the results from any atmospheric neutrino experiment. In the standard atmospheric neutrino data analysis, these fluxes are theoretical inputs obtained from sophisticated numerical calculations. In this contribution we present an alternative approach to the determination of the atmospheric neutrino fluxes based on the direct extraction from the experimental data on neutrino event rates.

astro-ph↗

arXiv2005

Atmospheric neutrinos as probes of neutrino-matter interactions

Neutrino oscillation experiments provide a unique tool for probing neutrino-matter interactions, especially those involving the tau neutrino. We describe the sensitivity of the present atmospheric neutrino data to these interactions in the framework of a three-flavor analysis. Compared to the two-flavor nu_mu-nu_tau analyses, we find qualitatively new features, in particular, that large non-standard interactions, comparable in strength to those in the Standard Model, can be consistent with the data. The existence of such interactions could imply a smaller value of the neutrino mixing angle and larger value of the mass-squared splitting than in the case of standard interactions only. This and other effects of non-standard interactions may be tested in the next several years by MINOS, KamLAND and solar neutrino experiments.

hep-ph↗