arXiv subjects

M. Maris

Publications and source records attributed to M. Maris.

82 records · Page 5Linked to original sources

arXiv2001

Power spectrum of the polarized diffuse Galactic radio emission

We have analyzed the available polarization surveys of the Galactic emission to estimate to what extent it may be a serious hindrance to forthcoming experiments aimed at detecting the polarized component of Cosmic Microwave Background (CMB) anisotropies. Regions were identified for which independent data consistently indicate that depolarization must be small. The power spectrum of the polarized emission, in terms of antenna temperature, was found to be described by $C_{\ell}\simeq (1.2\pm 0.8)\cdot 10^{-9}\cdot (\ell / 450)^{-1.8\pm 0.3}\cdot (ν/ 2.4{\rm GHz})^{-5.8}$ K$^{2}$, from arcminute to degree scales. Data on larger angular scales ($\ell\le 100$) indicate a steeper slope $\sim \ell^{-3}$. We conclude that polarized Galactic emission is unlikely to be a serious limitation to CMB polarization measurements at the highest frequencies of the MAP and {\sc Planck}/LFI instruments, at least for $\ell\ge 50$ and standard cosmological models. The weak correlation between polarization and total power and the low polarization degree of radio emission close to the Galactic plane, found also in low-depolarization regions, is interpreted as due to large contributions to the observed intensity from unpolarized sources, primarily strong HII regions, concentrated on the Galactic plane. Thus estimates of the power spectrum of total intensity at low Galactic latitudes are not representative of the spatial distribution of Galactic emission far from the plane. Both total power and polarized emissions show highly significant deviations from a Gaussian distribution.

astro-ph↗

arXiv2000

Neural networks and separation of Cosmic Microwave Background and astrophysical signals in sky maps

The Independent Component Analysis (ICA) algorithm is implemented as a neural network for separating signals of different origin in astrophysical sky maps. Due to its self-organizing capability, it works without prior assumptions on the signals, neither on their frequency scaling, nor on the signal maps themselves; instead, it learns directly from the input data how to separate the physical components, making use of their statistical independence. To test the capabilities of this approach, we apply the ICA algorithm on sky patches, taken from simulations and observations, at the microwave frequencies, that are going to be deeply explored in a few years on the whole sky, by the Microwave Anisotropy Probe (MAP) and by the {\sc Planck} Surveyor Satellite. The maps are at the frequencies of the Low Frequency Instrument (LFI) aboard the {\sc Planck} satellite (30, 44, 70 and 100 GHz), and contain simulated astrophysical radio sources, Cosmic Microwave Background (CMB) radiation, and Galactic diffuse emissions from thermal dust and synchrotron. We show that the ICA algorithm is able to recover each signal, with precision going from 10% for the Galactic components to percent for CMB; radio sources are almost completely recovered down to a flux limit corresponding to $0.7σ_{CMB}$, where $σ_{CMB}$ is the rms level of CMB fluctuations. The signal recovering possesses equal quality on all the scales larger then the pixel size. In addition, we show that the frequency scalings of the input signals can be partially inferred from the ICA outputs, at the percent precision for the dominant components, radio sources and CMB.

astro-ph↗

arXiv2000

The Super - Kamiokande Day - Night Effect Data and the MSW Solutions of the Solar Neutrino Problem

The current Super-Kamiokande data on the D-N asymmetry between the the day event rate and the {\it Night} and {\it Core} event rates, produced by solar neutrinos which respectively cross the Earth along any trajectory and cross the Earth core before reaching the detector, imply rather stringent constraints on the MSW small mixing angle (SMA) $ν_e \to ν_{μ(τ)}$ solution of the solar neutrino problem. A simplified analysis shows, in particular, that a substantial subregion of the SMA solution region is disfavored by these data. The {\it Core} D-N asymmetry data alone allow to rule out at 99.7% C.L. a part of this subregion. The constraints on the MSW large mixing angle and LOW $ν_e \to ν_{μ(τ)}$ solutions as well as on the MSW $ν_e \to ν_{s}$ solution, following from the data on the {\it Night} and {\it Core} D-N asymmetries are also discussed.

hep-ph↗

arXiv2000

Data Streams from the Low Frequency Instrument On-Board the Planck Satellite: Statistical Analysis and Compression Efficiency

The expected data rate produced by the Low Frequency Instrument (LFI) planned to fly on the ESA Planck mission in 2007, is over a factor 8 larger than the bandwidth allowed by the spacecraft transmission system to download the LFI data. We discuss the application of lossless compression to Planck/LFI data streams in order to reduce the overall data flow. We perform both theoretical analysis and experimental tests using realistically simulated data streams in order to fix the statistical properties of the signal and the maximal compression rate allowed by several lossless compression algorithms. We studied the influence of signal composition and of acquisition parameters on the compression rate Cr and develop a semiempirical formalism to account for it. The best performing compressor tested up to now is the arithmetic compression of order 1, designed for optimizing the compression of white noise like signals, which allows an overall compression rate = 2.65 +/- 0.02. We find that such result is not improved by other lossless compressors, being the signal almost white noise dominated. Lossless compression algorithms alone will not solve the bandwidth problem but needs to be combined with other techniques.

astro-ph↗

arXiv2000

Day - Night Effect Predictions for the SNO Detector

Detailed predictions for the day-night (D-N) asymmetry in the energy-integrated one year signals in the SNO detector in the case of the MSW $ν_e \to ν_{μ(τ)}$ and/or $ν_e \to ν_s$ transition solutions of the solar neutrino problem are presented. The asymmetries in the charged current (CC) and $ν- e^{-}$ elastic scattering (ES) event rates are calculated for both MSW solutions; in the case of the $ν_e \to ν_s$ transition solution the D-N asymmetry in the neutral current (NC) event rate are derived as well. The asymmetries are calculated for three night samples of events which are produced by the solar neutrinos crossing i) the Earth mantle only (Mantle), ii) the Earth core (Core) and iii) the Earth core and/or the mantle (Night). The effects of the uncertainties, e.g., in the values of the cross-sections of the CC and NC neutrino-induced reactions on deuterium on the corresponding D-N asymmetry predictions are analyzed. It is shown, in particular, that that due to the strong enhancement of the transitions of the solar neutrinos crossing the Earth core, at $\sin^22θ_V \leq 0.01$ the corresponding one year average D-N asymmetry in the Core sample of CC events in the case of the $ν_e \to ν_{μ(τ)}$ solution can be larger by a factor of up to $\sim 8$ than the asymmetry in the Night sample. Iso - (D-N) asymmetry contours in the $Δm^2 - \sin^22θ_V$ plane for the SNO detector are derived in the region $\sin^22θ_V \gsim 10^{-4}$ for the Core and Night samples of the CC, ES and NC events.

hep-ph↗

arXiv1999

Enhancing the Seasonal Variation Effect in the Case of the Vacuum Oscillation Solution of the Solar Neutrino Problem

We study in detail the threshold energy dependence of the seasonal variation effect in the energy integrated solar neutrino signal of the Super-Kamiokande detector in the case of the $ν_{e}\leftrightarrow ν_{μ,τ}$ vacuum oscillation (VO) solution of the solar neutrino problem. We show, in particular, that for the values of $Δm^2$ and $\sin^22θ$ from the VO solution region, the predicted time and threshold e^- energy ($T_{e,Th}$) dependence of the event rate factorize to a high degree of accuracy. As a consequence, the VO generated seasonal variation asymmetry is given by the product of an time-independent function of $T_{e,Th}$ and the standard geometrical asymmetry. For any given $Δm^2$ and $\sin^22θ$ from the VO solution region there exists at least one value of $T_{e,Th}$ from the interval (5 - 11) MeV, for which the seasonal variation effect in the solar neutrino sample of events, formed by recoil electrons with kinetic energy $T_{e} \geq T_{e,Th}$, is either maximal or very close to the maximal; it can vary dramatically with $T_{e,Th}$. Measuring the seasonal effect in each one of a large number of samples corresponding to different values of $T_{e,Th}$ from the indicated interval, say, to $T_{e,Th} = 5; 6; 7;...; 11 MeV$, provides a very effective test of the VO solution. Predictions for the magnitude of the seasonal effect in such samples are given for a large set of representative values of $Δm^2$ and $\sin^22θ$ from the VO solution region.

hep-ph↗

arXiv1998

On the Oscillation Length Resonance in the Transitions of Solar and Atmospheric Neutrinos Crossing the Earth Core

Assuming two-neutrino mixing takes place in vacuum, we study in detail the conditions under which the $ν_2 \to ν_{e}$ and $ν_μ \to ν_{e}$ ($ν_e \to ν_{μ(τ)}$) transitions in the Earth are strongly enhanced by the neutrino oscillation length resonance when the neutrinos cross the Earth core. We show, in particular, that the neutrino oscillation length resonance is operative also in the $\barν_μ \to \barν_{s}$ transitions at small mixing angles. The properties of the $ν_2 \to ν_{e}$ and $ν_μ \to ν_{e}$ ($ν_e \to ν_{μ(τ)}$) transition probabilities in the corresponding resonance regions are examined. Some implications of our results for the transitions of solar and atmospheric neutrinos traversing the Earth core, relevant for the interpretation of the results of the solar and atmospheric neutrino experiments, are also discussed.

hep-ph↗

arXiv1998

A Study of the Day - Night Effect for the \SK Detector: III. The Case of Transitions into Sterile Neutrino

Using the results of a high precision calculation of the solar neutrino survival probability for Earth crossing neutrinos in the case of MSW $ν_e --> ν_s$ transition solution of the solar neutrino problem, we derive predictions for the one-year averaged day-night (D-N) asymmetries in the deformed recoil-$e^-$ spectrum and in the energy-integrated event rate due to the solar neutrinos, to be measured with the Super - Kamiokande detector. The asymmetries are calculated for three event samples, produced by solar $ν_e$ crossing the Earth mantle only, the core, and the mantle only + the core (the full night sample). The effects of the uncertainties in the value of the bulk matter density and in the chemical composition of the Earth core on the predictions for the D-N asymmetries are investigated. The dependence of the D - N effect related observables on the threshold recoil - e- kinetic energy, TeTh, is studied. It is shown, in particular, that for $\sin^2 2θ_V \leq 0.030$ the one year average D-N - asymmetry in the sample of events due to the core-crossing neutrinos is larger than the asymmetry in the full night sample typically by a factor $\sim (2 - 4)$. We find, however, that at small mixing angles $\sin^2 2 θ_V \ltap 0.014$, the D-N asymmetry in the case of solar $ν_e --> ν_s$ transitions is considerably smaller than if the transitions were into an active neutrino, $ν_e --> ν_{μ(τ)}$. In particular, a precision better than 1% in the measurement of any of the three one year averaged D-N asymmetries considered by us would be required to test the small mixing angle nonadiabatic $ν_e --> ν_s$ solution at $\sin^2 2θ_V ~\ltap ~0.01$.

hep-ph↗

arXiv1997

A Study of the Day - Night Effect for the Super-Kamiokande Detector: II. Electron Spectrum Deformations and Day - Night Asymmetries

Using the results of a high precision calculation of the solar neutrino survival probability for Earth crossing neutrinos in the case of MSW $ν_e \to ν_{μ(τ)}$ transition solution of the solar neutrino problem, performed in an earlier study, we derive predictions for the one-year averaged day-night (D-N) asymmetry in the deformations of the $e^-$ - spectrum to be measured with the Super - Kamiokande detector, and for the D-N asymmetry in the energy- integrated one year signal in this detector. The asymmetries are calculated for solar $ν_e$ crossing the Earth mantle only, the core and the (mantle + core) for a large representative set of values of the MSW transition parameters $Δm^2$ and $\sin^2 2θ_v$ from the ``conservative'' MSW solution region obtained by taking into account possible uncertainties in the values of the $^8$B and $^7$Be neutrino fluxes. The effect of the uncertainties in the value of the bulk matter density and in the chemical composition of the core, on the D-N asymmetry predictions is discussed. It is shown, in particular, that for $\sin^2 2θ_v \leq 0.013$ the one year average D-N asymmetry for neutrinos crossing the Earth core can be larger than the asymmetry for (only mantle crossing + core crossing) neutrinos by a factor of up to six. Iso - (D-N) asymmetry contours in the $Δm^2 - \sin^2 2θ_v$ plane for the Super - Kamiokande detector are derived in the region $\sin^2 2θ_v \gsim 10^{-4}$ for only mantle crossing, core crossing and (only mantle crossing + core crossing) neutrinos. Our results indicate that the Super - Kamiokande experiment might be able to test the $\sin^2 2θ_v \le 0.01$ region of the MSW solution of the solar neutrino problem by performing selective D-N asymmetry measurements.

hep-ph↗

arXiv1997

A Study of the Day - Night Effect for the Super - Kamiokande Detector: I. Time Averaged Solar Neutrino Survival Probability

This is the first of two articles aimed at providing comprehensive predictions for the day-night (D-N) effect for the Super-Kamiokande detector in the case of the MSW $ν_e \to \numt$ transition solution of the solar neutrino problem. The one-year averaged probability of survival of the solar $\nue$ crossing the Earth mantle, the core, the inner 2/3 of the core, and the (core + mantle) is calculated with high precision (better than 1%) using the elliptical orbit approximation (EOA) to describe the Earth motion around the Sun. Results for the survival probability in the indicated cases are obtained for a large set of values of the MSW transition parameters $Δm^2$ and $sin^22θ_{V}$ from the ``conservative'' regions of the MSW solution, derived by taking into account possible relatively large uncertainties in the values of the $^{8}$B and $^{7}$Be neutrino fluxes. Our results show that the one-year averaged D-N asymmetry in the $ν_e$ survival probability for neutrinos crossing the Earth core can be, in the case of $sin^22 θ_{V} \leq 0.13$, larger than the asymmetry in the probability for (only mantle crossing + core crossing) neutrinos by a factor of up to six. The enhancement is larger in the case of neutrinos crossing the inner 2/3 of the core. This indicates that the Super-Kamiokande experiment might be able to test the $sin^22θ_{V} \leq 0.01$ region of the MSW solution of the solar neutrino problem by performing selective D-N asymmetry measurements.

hep-ph↗