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Carlo Giunti

Publications and source records attributed to Carlo Giunti.

At least 37 records · Page 2Linked to original sources
arXiv2018

Mixed states for mixing neutrinos

Here we discuss the description of flavor neutrinos produced or detected in processes which involve more than one neutrino. We show that in these cases flavor neutrinos cannot be separately described by pure states, but require a density matrix description. We consider explicitly the examples of $ν_{e}$ and $\barν_μ$ production in $μ^{+}$ decay and $ν_μ$ detection through scattering on electrons. We show that the density matrix which describes a flavor neutrino can be approximated with a density matrix of a pure state only when the differences of the neutrino masses are neglected in the interaction process. In this approximation, the pure states are the standard flavor states and one recovers the standard expression for the neutrino oscillation probability. We discuss also the effects of mixing of the three standard light neutrinos with heavy neutrinos which can be either decoupled because their masses are much larger than the maximum neutrino energy in the neutrino production process or because they are produced and detected incoherently. Finally, we discuss the more complicated case of neutrino-electron elastic scattering, in which the initial and final neutrinos do not have determined flavors, but there is a flavor dependence due to the different contributions of charged-current and neutral-current interactions.

hep-ph↗
arXiv2017

Improved Determination of the $^{235}\text{U}$ and $^{239}\text{Pu}$ Reactor Antineutrino Cross Sections per Fission

We present the results of a combined fit of the reactor antineutrino rates and the Daya Bay measurement of $σ_{f,235}$ and $σ_{f,239}$. The combined fit leads to a better determination of the two cross sections per fission: $σ_{f,235} = 6.29 \pm 0.08$ and $σ_{f,239} = 4.24 \pm 0.21 $ in units of $10^{-43} \, \text{cm}^2 / \text{fission}$, with respective uncertainties of about $1.2\%$ and $4.9\%$. Since the respective deviations from the theoretical cross sections per fission are $2.5σ$ and $0.7σ$, we conclude that, if the reactor antineutrino anomaly is not due to active-sterile neutrino oscillations, it is likely that it can be solved with a revaluation of the $^{235}\text{U}$ reactor antineutrino flux. However, the $^{238}\text{U}$, $^{239}\text{Pu}$, and $^{241}\text{Pu}$ fluxes, which have larger uncertainties, could also be significantly different from the theoretical predictions.

hep-ph↗
arXiv2017

Joint short- and long-baseline constraints on light sterile neutrinos

Recent studies have evidenced that long-baseline (LBL) experiments are sensitive to the extra CP-phases involved with light sterile neutrinos, whose existence is suggested by several anomalous short-baseline (SBL) results. We show that, within the 3+1 scheme, the combination of the existing SBL data with the LBL results coming from the two currently running experiments NO$ν$A and T2K, enables us to simultaneously constrain two active-sterile mixing angles $θ_{14}$ and $θ_{24}$ and two CP-phases $δ_{13} \equiv δ$ and $δ_{14}$, albeit the information on the second CP-phase is still weak at the moment. The two mixing angles are basically determined by the SBL data, while the two CP-phases are constrained by the LBL experiments, once the information coming from the SBL setups is taken into account. We also assess the robustness/fragility of the estimates of the standard 3-flavor parameters in the more general 3+1 scheme. To this regard we find that: i) the indication of CP-violation found in the 3-flavor analyses persists also in the 3+1 scheme, with $δ_{13} \equiv δ$ having still its best fit value around $-π/2$; ii) the 3-flavor weak hint in favor of the normal hierarchy becomes even less significant when sterile neutrinos come into play; iii) the weak indication of non-maximal $θ_{23}$ (driven by NO$ν$A disappearance data) persists in the 3+1 scheme, where maximal mixing is disfavored at almost the 90\% C.L. in both normal and inverted mass hierarchy; iv) the preference in favor of one of the two octants of $θ_{23}$ found in the 3-flavor framework (higher octant for inverted mass hierarchy) is completely washed out in the 3+1 scheme.

hep-ph↗
arXiv2017

Precise Determination of the U-235 Reactor Antineutrino Cross Section per Fission

We consider the possibility that the reactor antineutrino anomaly is due to a miscalculation of one or more of the $^{235}\text{U}$, $^{238}\text{U}$, $^{239}\text{Pu}$, and $^{241}\text{Pu}$ reactor antineutrino fluxes. From the fit of the data we obtain the precise determination $σ_{f,235} = ( 6.33 \pm 0.08 ) \times 10^{-43} \, \text{cm}^2 / \text{fission}$ of the $^{235}\text{U}$ cross section per fission, which is more precise than the calculated value and differs from it by $2.2σ$. The cross sections per fission of the other fluxes have large uncertainties and in practice their values are undetermined by the fit. We conclude that it is very likely that at least the calculation of the $^{235}\text{U}$ flux must be revised.

hep-ph↗
arXiv2016

Precise Determination of the U-235 Reactor Antineutrino Cross Section per Fission

We investigate which among the reactor antineutrino fluxes from the decays of the fission products of $^{235}\text{U}$, $^{238}\text{U}$, $^{239}\text{Pu}$, and $^{241}\text{Pu}$ may be responsible for the reactor antineutrino anomaly if the anomaly is due to a miscalculation of the antineutrino fluxes. We find that it is very likely that at least the calculation of the $^{235}\text{U}$ flux must be revised. From the fit of the data we obtain the precise determination $σ_{f,235} = ( 6.33 \pm 0.08 ) \times 10^{-43} \, \text{cm}^2 / \text{fission}$ of the $^{235}\text{U}$ cross section per fission, which is more precise than the calculated value and differs from it by $2.2σ$. The cross sections per fission of the other fluxes have large uncertainties and in practice their values are undetermined by the fit.

hep-ph↗
arXiv2016

Pseudoscalar - sterile neutrino interactions: reconciling the cosmos with neutrino oscillations

The Short BaseLine (SBL) neutrino oscillation anomalies hint at the presence of a sterile neutrino with a mass of around 1 eV. However, such a neutrino is incompatible with cosmological data, in particular observations of the Cosmic Microwave Background (CMB) anisotropies. However, this conclusion can change by invoking new physics. One possibility is to introduce a secret interaction in the sterile neutrino sector mediated by a light pseudoscalar. In this pseudoscalar model, CMB data prefer a sterile neutrino mass that is fully compatible with the mass ranges suggested by SBL anomalies. In addition, this model predicts a value of the Hubble parameter which is completely consistent with local measurements.

astro-ph.CO↗
arXiv2016

Light Sterile Neutrinos: Status and Perspectives

The indications in favor of the existence of light sterile neutrinos at the eV scale found in short-baseline neutrino oscillation experiments is reviewed. The future perspectives of short-baseline neutrino oscillation experiments and the connections with beta-decay measurements of the neutrino masses and with neutrinoless double-beta decay experiments are discussed.

hep-ph↗
arXiv2015

Electromagnetic neutrinos in laboratory experiments and astrophysics

An overview of neutrino electromagnetic properties, which open a door to the new physics beyond the Standard Model, is given. The effects of neutrino electromagnetic interactions both in terrestrial experiments and in astrophysical environments are discussed. The experimental bounds on neutrino electromagnetic characteristics are summarized. Future astrophysical probes of electromagnetic neutrinos are outlined.

hep-ph↗
arXiv2015

Neutrino electromagnetic interactions: a window to new physics

We review the theory and phenomenology of neutrino electromagnetic interactions, which give us powerful tools to probe the physics beyond the Standard Model. After a derivation of the general structure of the electromagnetic interactions of Dirac and Majorana neutrinos in the one-photon approximation, we discuss the effects of neutrino electromagnetic interactions in terrestrial experiments and in astrophysical environments. We present the experimental bounds on neutrino electromagnetic properties and we confront them with the predictions of theories beyond the Standard Model.

hep-ph↗
arXiv2014

Light sterile neutrinos after BICEP-2

The recent discovery of B-modes in the polarization pattern of the Cosmic Microwave Background by the BICEP2 experiment has important implications for neutrino physics. We revisit cosmological bounds on light sterile neutrinos and show that they are compatible with all current cosmological data provided that the mass is relatively low. Using CMB data, including BICEP-2, we find an upper bound of $m_s < 0.85$ eV ($2σ$ Confidence Level). This bound is strengthened to 0.48 eV when HST measurements of $H_0$ are included. However, the inclusion of SZ cluster data from the Planck mission and weak gravitational measurements from the CFHTLenS project favours a non-zero sterile neutrino mass of $0.44^{+0.11}_{-0.16}$ eV. Short baseline neutrino oscillations, on the other hand, indicate a new mass state around 1.2 eV. This mass is highly incompatible with cosmological data if the sterile neutrino is fully thermalised ($Δχ^2>10$). However, if the sterile neutrino only partly thermalises it can be compatible with all current data, both cosmological and terrestrial.

astro-ph.CO↗
arXiv2013

Sterile Neutrinos: Cosmology vs Short-BaseLine Experiments

Cosmology and short baseline neutrino oscillation data both hint at the existence of light sterile neutrinos with masses in the 1 eV range. Here we perform a detailed analysis of the sterile neutrino scenario using both cosmological and SBL data. We have additionally considered the possibility that the extra neutrino degrees of freedom are not fully thermalised in the early universe. Even when analyzing only cosmological data we find a preference for the existence of massive sterile neutrinos in both (3+1) and (3+2) scenarios, and with the inclusion of SBL data the evidence is formally at the 3.3sigma level in the case of a (3+1) model. Interestingly, cosmological and SBL data both point to the same mass scale of approximately 1 eV. In the (3+1) framework WMAP9+SPT provide a value of the sterile mass eigenstate m_4 = (1.72 \pm 0.65) eV: this result is strenghtened by adding the prior from SBL posterior to m_4 = (1.27 \pm 0.12) eV (m_4 = (1.23 \pm 0.13) eV when SDSS is also considered in the cosmological analysis). In the (3+2) scheme, two additional, non--fully thermalized, neutrinos are compatible with the whole set of cosmological and SBL data, leading to mass values of m_4 = (0.95 \pm 0.30) eV and m_5 = (1.59 \pm 0.49) eV. The inclusion of Planck data does not change our considerations about the mass scale; concerning the extra neutrino degrees of freedom, invoking a partial thermalisation the 3+1 model is still consistent with the latest data.

astro-ph.CO↗
arXiv2013

The strongest bounds on active-sterile neutrino mixing after Planck data

Light sterile neutrinos can be excited by oscillations with active neutrinos in the early universe. Their properties can be constrained by their contribution as extra-radiation, parameterized in terms of the effective number of neutrino species N_ eff, and to the universe energy density today Ω_νh^2. Both these parameters have been measured to quite a good precision by the Planck satellite experiment. We use this result to update the bounds on the parameter space of (3+1) sterile neutrino scenarios, with an active-sterile neutrino mass squared splitting in the range (10^{-5} - 10^2 ) eV^2. We consider both normal and inverted mass orderings for the active and sterile states. For the first time we take into account the possibility of two non-vanishing active-sterile mixing angles. We find that the bounds are more stringent than those obtained in laboratory experiments. This leads to a strong tension with the short-baseline hints of light sterile neutrinos. In order to relieve this disagreement, modifications of the standard cosmological scenario, e.g. large primordial neutrino asymmetries, are required.

astro-ph.CO↗
arXiv2013

Cosmology with sterile neutrino masses from oscillation experiments

There are hints, both from cosmology and from neutrino oscillation experiments, that one or two sterile neutrinos with eV masses are favored. We consider the implications of combining data from short baseline neutrino experiments with cosmological observations. In particular we consider cosmological models where the equation of state of dark energy and the curvature are allowed to vary. We find that the consistency of results from short baseline experiments and cosmology is dependent on the cosmological data sets that are used. When the two are consistent, we find that the inclusion of information from short baseline experiments only mildly affects the preferred values of the cosmological model parameters. A universe with a cosmological constant type dark energy and zero curvature is still fully consistent with the data we use. We also report that a thermalized sterile neutrino in the 10 eV range is fully consistent with a wide range of cosmological data as long as information on the matter power spectrum in not taken into account.

astro-ph.CO↗
arXiv2012

Testing 3+1 and 3+2 neutrino mass models with cosmology and short baseline experiments

Recent results from short--baseline neutrino oscillation experiments and Cosmic Microwave Background anisotropy measurements suggest the presence of additional sterile neutrinos. In this paper we properly combine these data sets to derive bounds on the sterile neutrino masses in the 3+1 and 3+2 frameworks, finding a potentially good agreement between the two datasets. However, when galaxy clustering is included in the analysis a tension between the oscillation and cosmological data is clearly present.

astro-ph.CO↗
arXiv2011

First Double-Chooz Results and the Reactor Antineutrino Anomaly

We investigate the possible effects of short-baseline antinu_e disappearance implied by the reactor antineutrino anomaly on the Double-Chooz determination of theta_{13} through the normalization of the initial antineutrino flux with the Bugey-4 measurement. We show that the effects are negligible and the value of theta_{13} obtained by the Double-Chooz collaboration is accurate only if Delta m^2_{41} is larger than about 3 eV^2. For smaller values of Delta m^2_{41} the short-baseline oscillations are not fully averaged at Bugey-4 and the uncertainties due to the reactor antineutrino anomaly can be of the same order of magnitude of the intrinsic Double-Chooz uncertainties.

hep-ph↗
arXiv2011

Implications of 3+1 Short-Baseline Neutrino Oscillations

We present an upgrade of the 3+1 global fit of short-baseline neutrino oscillation data obtained with the addition of KARMEN and LSND nu_e-Carbon scattering data. We discuss the implications for the measurements of the effective neutrino mass in beta-decay and neutrinoless double-beta-decay experiments. We find respective predicted ranges of about 0.1-0.7 eV and 0.01-0.1 eV.

hep-ph↗
arXiv2011

Status of 3+1 Neutrino Mixing

We present an update of our analysis of short-baseline neutrino oscillation data in the framework of 3+1 neutrino mixing taking into account the recent update of MiniBooNE antineutrino data and the recent results of the MINOS search for nu_mu disappearance into sterile neutrinos (the more complicated 3+2 neutrino mixing is not needed since the CP-violating difference between MiniBooNE neutrino and antineutrino data has diminished). The results of our fits of short-baseline neutrino oscillation data including the MiniBooNE low-energy anomaly (now present both in the neutrino and antineutrino data) leads to a strong tension between appearance and disappearance data. Hence, it seems likely that the low-energy anomaly is not due to nu_mu -> nu_e transitions. Excluding the MiniBooNE low-energy anomaly, appearance and disappearance data are marginally compatible. The global analysis has the best-fit point at Delta m^2_{41} about 5.6 eV^2, which is rather large in comparison with cosmological bounds, but there are three regions within 1 sigma at Delta m^2_{41} about 1.6, 1.2, 0.91 eV^2. We also show that the data on the Gallium neutrino anomaly favor values of Delta m^2_{41} larger than about 1 eV^2.

hep-ph↗