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M. Maltoni

Publications and source records attributed to M. Maltoni.

54 records · Page 3Linked to original sources
arXiv2002

Status of four-neutrino mass schemes: a global and unified approach to current neutrino oscillation data

We present a unified global analysis of neutrino oscillation data within the framework of the four-neutrino mass schemes (3+1) and (2+2). We include all data from solar and atmospheric neutrino experiments, as well as information from short-baseline experiments including LSND. If we combine only solar and atmospheric neutrino data, (3+1) schemes are clearly preferred, whereas short-baseline data in combination with atmospheric data prefers (2+2) models. When combining all data in a global analysis the (3+1) mass scheme gives a slightly better fit than the (2+2) case, though all four-neutrino schemes are presently acceptable. The LSND result disfavors the three-active neutrino scenario with only $Δm^2_{sol}$ and $Δm^2_{atm}$ at 99.9% CL with respect to the four-neutrino best fit model. We perform a detailed analysis of the goodness of fit to identify which sub-set of the data is in disagreement with the best fit solution in a given mass scheme.

hep-ph↗
arXiv2001

Cornering (3+1) sterile neutrino schemes

Using the most recent atmospheric neutrino data, as well as short-baseline, long-baseline and tritium $β$-decay data we show that the joint interpretation of the LSND, solar and atmospheric neutrino anomalies in (3+1) sterile neutrino schemes is severely disfavored, in contrast to the theoretically favored (2+2) schemes.

hep-ph↗
arXiv2001

Update on Solar and Atmospheric Four-Neutrino Oscillations

In this talk we present the update (including the recent SNO results) of our analysis of the neutrino oscillation solutions of the solar and atmospheric neutrino problems in the framework of four-neutrino mixing where a sterile neutrino is added to the three standard ones and the mass spectra present two separated doublets. Such scenarios allow for simultaneous transitions of solar $ν_e$, as well as atmospheric $ν_μ$, into a combination of active and sterile neutrinos. We evaluate the allowed active-sterile admixture in both solar and atmospheric oscillations from the combined analysis. Our results show that, although the Super-Kamiokande data disfavour both the pure $ν_μ\toν_s$ atmospheric channel and, in combination with SNO, the pure $ν_e\toν_s$ solar channel, the result from the combined analysis still favours close-to-pure active and sterile oscillations and disfavours oscillations into a near-maximal active-sterile admixture.

hep-ph↗
arXiv2001

Solar and Atmospheric Four-Neutrino Oscillations

We present an analysis of the neutrino oscillation solutions of the solar and atmospheric neutrino problems in the framework of four-neutrino mixing where a sterile neutrino is added to the three standard ones and the mass spectra presents two separated doublets. Such scenarios allow for simultaneous transitions of solar $ν_e$, as well as atmospheric $ν_μ$, into active and sterile neutrinos controlled by the additional mixing angles $\vartheta_{23}$ and $\vartheta_{24}$, and they contain as limiting cases the pure solar $ν_e$-active and $ν_e$-sterile neutrino oscillations, and the pure atmospheric $ν_μ\toν_s$ and $ν_μ\toν_τ$ oscillations, respectively. We evaluate the allowed active-sterile admixture in both solar and atmospheric oscillations from the combined analysis. Our results show that, although the Super-Kamiokande data disfavour both the pure $ν_μ\toν_s$ atmospheric channel and the pure $ν_e\toν_s$ solar channel, the result from the combined analysis still favours close-to-pure active and sterile oscillations and disfavours oscillations into a near-maximal active-sterile admixture.

hep-ph↗
arXiv2000

Analysis of the atmospheric neutrino data in terms of 3-neutrino oscillations

A global analysis of atmospheric and reactor neutrino data is presented in terms of three-neutrino oscillations. We consider in our analysis both contained events and upward-going neutrino-induced muon events, including the previous data samples of Frejus, IMB, Nusex, and Kamioka experiments as well as the full 71 kton-yr (1144 days) Super-Kamiokande data set, the recent 5.1 kton-yr contained events of Soudan-2 and the results on upgoing muons from the MACRO detector. After presenting the results for the analysis of atmospheric data alone, we add to our data sample the reactor bound of the CHOOZ experiment, showing and important complementarity between the atmospheric and reactor limits which results in a stronger constraint on the allowed value of theta_13.

hep-ph↗
arXiv2000

Global three-neutrino oscillation analysis of neutrino data

A global analysis of the solar, atmospheric and reactor neutrino data is presented in terms of three-neutrino oscillations. We include the most recent solar neutrino rates of Homestake, SAGE, GALLEX and GNO, as well as the recent 1117 day Super-Kamiokande data sample, including the recoil electron energy spectrum both for day and night periods and we treat in a unified way the full parameter space for oscillations, correctly accounting for the transition from the matter enhanced (MSW) to the vacuum oscillations regime. Likewise, we include in our description conversions with $θ_{12} > π/4$. For the atmospheric data we perform our analysis of the contained events and the upward-going $ν$-induced muon fluxes, including the previous data samples of Frejus, IMB, Nusex, and Kamioka experiments as well as the full 71 kton-yr (1144 days) Super-Kamiokande data set, the recent 5.1 kton-yr contained events of Soudan2 and the results on upgoing muons from the MACRO detector. We first present the allowed regions of solar and atmospheric oscillation parameters $θ_{12}$, $Δm^2_{21}$ and $θ_{23}$, $Δm^2_{32}$, respectively, as a function of $θ_{13}$ and determine the constraints from atmospheric and solar data on the mixing angle $θ_{13}$, common to solar and atmospheric analyses. We also obtain the allowed ranges of parameters from the full five-dimensional combined analysis of the solar, atmospheric and reactor data.

hep-ph↗
arXiv2000

Planck LFI: Comparison Between Galaxy Straylight Contamination and other Systematic Effects

The straylight contamination due to the Galactic emission (GSC, Galaxy Straylight Contamination) entering at large angles from the antenna centre direction may be one of the most critical sources of systematic effects in observations of the cosmic microwave background (CMB) anisotropies by future satellite missions like {\sc Planck} and MAP. We describe here different methods to evaluate the impact of this effect and compare it with other systematics of instrumental and astrophysical origin. The contributions within few degrees from the beam centre dominate the GSC near the Galaxy plane. The antenna sidelobes at intermediate and large angles from the beam centre dominate the GSC at medium and high Galactic latitudes. We find a GSC peak at $\sim 15μ$K and a GSC angular power spectrum above that of the white noise for multipoles $\ell \lsim 10$ albeit smaller than that of CMB anisotropies by a factor larger than $\sim 10$. Although the GSC is largest at low Galactic latitudes, the contamination produced by far pattern features at medium and high Galactic latitudes, peaking at $\sim 4μ$K, has to be carefully investigated, because the combination of low amplitude of Galaxy emission in those regions with the extremely good nominal {\sc Planck} sensitivity naturally makes high Galactic latitude areas the targets for unprecedentedly precise estimation of cosmological CMB anisotropy.

astro-ph↗
arXiv2000

Precision measurements, extra generations and heavy neutrino

The existence of extra chiral generations with all fermions heavier than $M_Z$ is strongly disfavored by the precision electroweak data. The exclusion of one additional generation of heavy fermions in SUSY extension of Standard Model is less forbidden if chargino and neutralino have low degenerate masses with $Δm \simeq 1$ GeV. However the data are fitted nicely even by a few extra generations, if one allows neutral leptons to have masses close to 50 GeV. Such heavy neutrino can be searched in the reaction $e^+ e^- \to N\bar{N}γ$ at LEP-200 with total final luminosity of $2600 pb^{-1}$.

hep-ph↗
arXiv2000

On the search for 50 GeV neutrinos

Using the computer code CompHEP we estimate the number of events and the background, at LEP II and TESLA, for the reaction $e^+ e^- \to N\bar{N}γ$, where $N$ is a hypothetical Dirac neutrino with mass of the order of 50 GeV.

hep-ph↗
arXiv2000

Bounds on extra quark-lepton generations from precision measurements

The existence of extra chiral generations is strongly disfavored by the precision electroweak data if all the extra fermions are heavier than m_Z. However fits as good as the SM can be obtained if one allows the new neutral leptons to have masses close to 50 GeV. In the framework of SUSY models precision measurements cannot exclude one additional generation of heavy fermions if chargino and neutralino have masses around 60 GeV with delta_m around 1 GeV.

hep-ph↗
arXiv2000

Precision measurements of IVB parameters and bounds on new physics

The main purpose of this thesis is to discuss the impact of electroweak precision measurements on the present knowledge of particle physics, both in the framework of the Standard Model and of its most straightforward extensions. In Chapter 1 we give a general overview of the electroweak sector of the SM and of SUSY phenomenology. In Chapter 2 we deal with different definitions of the electroweak mixing angle, with particular attention to the relation between the phenomenological angle $θ$ and the MS parameter $\hatθ$. In Chapter 3 we use results found in the previous chapter to discuss in detail how both the decoupling and the non-decoupling approach to the running of coupling constants in the MS scheme produce the same numerical value of $m_{GUT}$, despite of the different initial conditions. In Chapter 4 we derive simple analytical formulas for the contribution of a chargino almost degenerate with the lightest neutralino to electroweak observables, showing that in the case of wino domination the study of oblique corrections allows a concrete improvement of experimental bounds on chargino mass. Finally, in Chapter 5 we consider the possibility of extra fermion generations, proving that they are strongly disfavoured by the present experimental data if all particles are heavier that Z-boson, while for the specific case of the extra neutrino around 50 GeV in mass (still allowed by experimental data) the quality of the fit is not worse than the SM.

hep-ph↗
arXiv1999

Extra quark-lepton generations and precision measurements

The existence of extra chiral generations with all fermions heavier than M_Z is strongly disfavoured by the precision electroweak data. However the data are fitted nicely even by a few extra generations, if one allows neutral leptons to have masses close to 50 GeV. The data allow inclusion of one additional generation of heavy fermions in SUSY extension of Standard Model if chargino and neutralino have masses close to 60 GeV with Δm =~ 1 GeV.

hep-ph↗
arXiv1999

A preliminary study on destriping techniques of PLANCK/LFI measurements versus observational strategy

We present here the basic issues of our simulations of PLANCK/LFI observations focussing on the study of the stripes generated by the 1/f noise, including realistic estimates of the 1/f knee frequency, based on the Seiffert et al. (1997) study of the properties of the PLANCK/LFI radiometers. The destriping method presented in the report on the PLANCK PHASE A study has been implemented to be applied to different scanning strategies with the freedom of choosing more or less stringent crossing conditions. Numerical methods for saving the amount of required RAM in the solution of the destriping linear system are presented. We provide preliminary results of the efficiency of this destriping technique for different scanning strategies. We focus here on methodological aspects and remind the reader to the Maino et al. (1999) paper (astro-ph/9906010) for further analyses and a more complete discussion.

astro-ph↗
arXiv1999

The Planck-LFI instrument: analysis of the 1/f noise and implications for the scanning strategy

We study the impact of the 1/f noise on the PLANCK Low Frequency Instrument (LFI) osbervations (Mandolesi et al 1998) and describe a simple method for removing striping effects from the maps for a number of different scanning stategies. A configuration with an angle between telescope optical axis and spin-axis just less than 90 degrees (namely 85 degress) shows good destriping efficiency for all receivers in the focal plane, with residual noise degradation < 1-2 %. In this configuration, the full sky coverage can be achieved for each channel separately with a 5 degrees spin-axis precession to maintain a constant solar aspect angle.

astro-ph↗
arXiv1999

On the numerical closeness of the effective phenomenological electroweak mixing angle $θ$ and the $\MS$ parameter $\hatθ$

It happens that $s^2$ and $\hat s^2$ are equal with 0.1% accuracy, though they are split by radiative corrections and a natural estimate for their difference is 1%. This degeneracy occurs only for $m_t$ value close to $170\GeV$, so no deep physical reason can be attributed to it. However, another puzzle of the Standard Model, the degeneracy of $s_\Eff^2$ and $s^2$, is not independent of the previous one since a good physical reason exists for $s_\Eff^2$ and $\hat s^2$ degeneracy. We present explicit formulas which relate these three angles.

hep-ph↗