arXiv subjects

Joao Pulido

Publications and source records attributed to Joao Pulido.

At least 19 recordsLinked to original sources

arXiv2018

Optimizing the $θ_{23}$ octant search in long baseline neutrino experiments

We study the possibility of determining the octant of the neutrino mixing angle $θ_{23}$, that is, whether $θ_{23}> 45^\circ$ or $θ_{23}<45^\circ$, in long baseline neutrino experiments. Here we numerically derived the sensitivity limits within which these experiments can determine, by measuring the probability of the $ν_μ\to ν_{e}$ transitions, the octant of $θ_{23}$ with a $5σ$ certainty. The interference of the CP violation angle $δ$ with these limits, as well as the effects of the baseline length and the run-time ratio of neutrino and antineutrino modes of the beam have been analyzed.

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arXiv2018

Effects of BSMs on $θ_{23}$ determination

We investigate the prospects for determining the octant of $θ_{23}$ in the future long baseline oscillation experiments. We present our results as contour plots on the ($θ_{23}-45^\circ$, $δ$)--plane, where $δ$ is the CP phase, showing the true values of $θ_{23}$ for which the octant can be experimentally determined at 3$\,σ$, 2$\,σ$ and 1$\,σ$ confidence level, in particular, the impact of the non-unitarity of neutrino mixing.

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arXiv2015

Determination of the $θ_{23}$ octant in LBNO

According to the recent results of the neutrino oscillation experiment MINOS, the neutrino mixing angle $θ_{23}$ may not be maximal ($45^{\circ}$). Two nearly degenerate solutions are possible, one in the lower octant (LO) where $θ_{23}<45^{\circ}$, and one in the higher octant (HO) where $θ_{23}>45^{\circ}$. Long baseline experiments measuring the $ν_μ\rightarrowν_{e}$ are capable of resolving this degeneracy. In this work we study the potential of the planned European LBNO experiment to distinguish between the LO and HO solutions.

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arXiv2013

Sterile neutrinos in the 3+s scenario and solar data

The flatness of the SuperKamiokande neutrino electron scattering spectrum and the apparent downturn of the charged current spectrum in the SNO data which the Large Mixing Angle solution (LMA) to the solar neutrino problem fails to predict are analysed in the context of an extension to the standard electroweak model with light sterile neutrinos. It is found that a sterile neutrino which is quasi degenerate with the active ones with $Δm^2_{41}=10^{-5}eV^2$ and mixing $sinθ_{14}=0.04$ provides a suitable improvement to the LMA data fits.

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arXiv2013

Possible trace of neutrino nonstandard interactions in the supernova

Neutrino non-standard interactions (NSI), previously introduced for the sun, are studied in the supernova context. For normal hierarchy the probability for electron neutrinos and antineutrinos at low energy ($E\lesssim 0.8-0.9 MeV$) is substantially increased with respect to the non-NSI case and joins its value for inverse hierarchy which is constant with energy. Also for inverse hierarchy the NSI and non-NSI probabilities are the same for each neutrino and antineutrino species. These are the possible visible effects of NSI in the supernova. The decay into antineutrinos, which has been previously shown to be implied by dense matter, cannot be seen experimentally, owing to the smallness of the antineutrino production probability.

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arXiv2013

Long baseline neutrino experiments, mass hierarchy and delta(CP)

We investigate the possibilities offered by the long baseline experiments T2K, No$ν$a, LBNE and LAGUNA for the evaluation of the neutrino mass hierarchy and CP violating phase $δ_{CP}$. We consider a neutrino and antineutrino energy in the interval [0.5,12] GeV. It is found that the clearest possible distinction between the two hierarchy signatures is provided by LAGUNA for an (anti)neutrino energy $E_{(\barν)ν}\simeq 0.5$ GeV in the $(\barν_μ \rightarrow \barν_μ) ν_μ\rightarrow ν_μ$ disappearance channel. For LBNE at $E_{\barν}\simeq 1$ GeV the $\barν_μ\rightarrow \barν_μ$ channel may also provide a distinction, although not so clear, and for No$ν$a this may be even less clear. These results are essentially the same for the $θ_{23}$ first and second octant solutions. As for $δ_{CP}$ determination, LAGUNA also offers the best chances at $E_{\barν}\simeq 0.5$ GeV in the $\barν_μ\rightarrow \barν_{e}$ channel with $θ_{23}$ in either octant. Regarding nonstandard interactions, the best possibility for their investigation resides in No$ν$a whose source-far detector distance can become a magic baseline if the hierarchy is normal for channels $ν_μ\rightarrow ν_μ$, $\barν_μ\rightarrow \barν_{e}$, $\barν_μ\rightarrow \barν_μ$ with energy (8.9-9.1) GeV, (11.6-12) GeV, (8.8-12) GeV. If the hierarchy is inverse, magic baselines for No$ν$a occur for $ν_μ\rightarrow ν_{e}$, $ν_μ\rightarrow ν_μ$, and $\barν_μ\rightarrow \barν_μ$ with energy (11.8-12) GeV, (8.9-12.3) GeV, (8.8-8.9) GeV. For LAGUNA a magic baseline appears for the $\barν_μ\rightarrow \barν_μ$ channel only at (4.7-5.0) GeV in inverse hierarchy. We have also investigated a possible complementarity between T2K and No$ν$a.

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arXiv2011

Neutrino nonstandard interactions in the supernova

Neutrino nonstandard interactions (NSI) were investigated earlier in the solar case and were shown to reduce the tensions between the data and the large mixing angle solution predictions. We extend the previous framework to the supernova and evaluate the appearance probabilities for neutrinos and antineutrinos as a function of their energy after leaving the collapsing star with and without NSI. For normal hierarchy the probability for electron neutrinos and antineutrinos at low energy ($E\lesssim 0.8-0.9 MeV$) is substantially increased with respect to the non-NSI case and joins its value for inverse hierarchy which is constant with energy. Also for inverse hierarchy the NSI and non-NSI probabilities are the same for each neutrino and antineutrino species. Although detection in such a low energy range remains at present an experimental challenge, it will become a visible trace of NSI with normal hierarchy if they exist. On the other hand the neutrino decay probability into an antineutrino and a majoron, an effect previously shown to be induced by dense matter, is, as in the case of the sun, too small to be observed as a direct consequence of NSI.

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arXiv2011

Improving LMA predictions with non-standard interactions: neutrino decay in solar matter?

It has been known for some time that the well established LMA solution to the observed solar neutrino deficit fails to predict a flat energy spectrum for SuperKamiokande as opposed to what the data indicates. It also leads to a Chlorine rate which appears to be too high as compared to the data. We investigate the possible solution to these inconsistencies with non standard neutrino interactions, assuming that they come as extra contributions to the $ν_αν_β$ and $ν_αe$ vertices that affect both the propagation of neutrinos in the sun and their detection. We find that, among the many possibilities for non standard couplings, only the diagonal imaginary ones lead to a solution to the tension between the LMA predictions and the data, implying neutrino instability in the solar matter. Unitarity requirements further restrict the solution and a neutrino decay into an antineutrino and a majoron within the sun is the one favoured. Antineutrino probability is however too small to open the possibility of experimentally observing antineutrinos from the sun due to NSI.

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arXiv2011

NSI can improve LMA predictions: neutrino decay in solar matter?

We investigate the prospects for non-standard interactions (NSI) in solar neutrino propagation and detection and find that these may solve the tension between the observed flatness of the SuperKamiokande electron spectrum and its LMA prediction which has a clear negative slope. Also the Cl rate prediction from NSI comes within 1$σ$ of its experimental value instead of the LMA one which lies more than 2$σ$ above. A remarkable consequence of NSI for solar neutrinos is the possibility of neutrino decay into majorons and antineutrinos whose appearance probability is calculated but found to be rather small.

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arXiv2010

Improving LMA predictions with non standard interactions

It has been known for some time that the well established LMA solution to the observed solar neutrino deficit fails to predict a flat energy spectrum for SuperKamiokande as opposed to what the data indicates. It also leads to a Chlorine rate which appears to be too high as compared to the data. We investigate the possible solution to these inconsistencies with non standard neutrino interactions, assuming that they come as extra contributions to the $ν_αν_β$ and $ν_αe$ vertices that affect both the propagation of neutrinos through solar matter and their detection. We find that, among the many possibilities for non standard couplings, only one of them leads to a flat SuperKamiokande spectral rate in better agreement with the data and predicts a Chlorine rate within 1$σ$ of the observed one, while keeping all other predictions accurate.

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arXiv2009

Remaining inconsistencies with solar neutrinos: can spin flavour precession provide a clue?

A few inconsistencies remain after it has been ascertained that LMA is the dominant solution to the solar neutrino problem: why is the SuperKamiokande spectrum flat and why is the Chlorine rate prediction over two standard deviations above the data. There also remains the ananswered and important question of whether the active neutrino flux is constant or time varying. We propose a scenario involving spin flavour precession to sterile neutrinos with three active flavours that predicts a flat SuperK spectrum and a Chlorine rate prediction more consistent with data. We also argue that running the Borexino experiment during the next few years may provide a very important clue as to the possible variability of the solar neutrino flux.

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arXiv2009

Light sterile neutrinos, spin flavour precession and the solar neutrino experiments

We generalize to three active flavours a previous two flavour model for the resonant spin flavour conversion of solar neutrinos to sterile ones, a mechanism which is added to the well known LMA one. The transition magnetic moments from the muon and tau neutrinos to the sterile play the dominant role in fixing the amount of active flavour suppression. We also show, through numerical integration of the evolution equations, that the data from all solar neutrino experiments except Borexino exhibit a clear preference for a sizable magnetic field either in the convection zone or in the core and radiation zone. This is possibly related to the fact that the data from the first set are average ones taken during a period of mostly intense solar activity, whereas in contrast Borexino data were taken during a period of quiet sun. We argue that the solar neutrino experiments are capable of tracing the possible modulation of the solar magnetic field. Those monitoring the high energy neutrinos, namely the $^8 B$ flux, appear to be sensitive to a field modulation either in the convection zone or in the core and radiation zone. Those monitoring the low energy fluxes will be sensitive to the second type of solar field profiles only. In this way Borexino alone may play an essential role, since it examines both energy sectors, although experimental redundance from other experiments will be most important.

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arXiv2007

Predictions from non trivial Quark-Lepton complementarity

The complementarity between the quark and lepton mixing matrices is shown to provide robust predictions. We obtain these predictions by first showing that the matrix V_M, product of the quark (CKM) and lepton (PMNS) mixing matrices, may have a zero (1,3) entry which is favored by experimental data. We obtain that any theoretical model with a vanishing (1,3) entry of V_M that is in agreement with quark data, solar, and atmospheric mixing angle leads to $θ_{13}^{PMNS}=(9{^{+1}_{-2}})^\circ$. This value is consistent with the present 90% CL experimental upper limit. We also investigate the prediction on the lepton phases. We show that the actual evidence, under the only assumption that the correlation matrix V_M product of CKM and PMNS has a zero in the entry (1,3), gives us a prediction for the three CP-violating invariants J, S_1, and S_2. A better determination of the lepton mixing angles will give stronger prediction for the CP-violating invariants in the lepton sector. These will be tested in the next generation experiments. Finally we compute the effect of non diagonal neutrino mass in "l_i -> l_j gamma" in SUSY theories with non trivial Quark-Lepton complementarity and a flavor symmetry. The Quark-Lepton complementarity and the flavor symmetry strongly constrain the theory and we obtain a clear prediction for the contribution to "mu -> e gamma" and the "tau" decays "tau -> e gamma" and "tau -> mu gamma". If the Dirac neutrino Yukawa couplings are degenerate but the low energy neutrino masses are not degenerate, then the lepton decays are related among them by the V_M entries. On the other hand, if the Dirac neutrino Yukawa couplings are hierarchical or the low energy neutrino masses are degenerate, then the prediction for the lepton decays comes from the CKM hierarchy.

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arXiv2007

Two Gallium data sets, spin flavour precession and KamLAND

We reexamine the possibility of a time modulation of the low energy solar neutrino flux which is suggested by the average decrease of the Ga data in line with our previous arguments. We perform two separate fits to the solar neutrino data, one corresponding to 'high' and the other to 'low' Ga data, associated with low and high solar activity respectively. We therefore consider an alternative to the conventional solar+KamLAND fitting, which allows one to explore the much wider range of the $θ_{12}$ angle permitted by the KamLAND fitting alone. We find a solution with parameters $Δm^2_{21}=8.2\times 10^{-5} eV^2, tan^{2}θ=0.31$ in which the 'high' and the 'low' Ga rates lie far apart and are close to their central values and is of comparable quality to the global best fit, where these rates lie much closer to each other. This is an indication that the best fit in which all solar and KamLAND data are used is not a good measure of the separation of the two Ga data sets, as the information from the low energy neutrino modulation is dissimulated in the wealth of data. Furthermore for the parameter set proposed one obtains an equally good fit to the KamLAND energy spectrum and an even better fit than the 'conventional' LMA one for the reactor antineutrino survival probability as measured by KamLAND.

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arXiv2007

Quark-lepton complementarity, neutrino and standard model data predict $(θ_{13}^{PMNS}=9^{+1}_{-2})^\circ$

The complementarity between the quark and lepton mixing matrices is shown to provide a robust prediction for the neutrino mixing angle $θ_{13}^{PMNS}$. We obtain this prediction by first showing that the matrix $V_M$, product of the CKM and PMNS mixing matrices, may have a zero (1,3) entry which is favored by experimental data. Hence models with bimaximal or tribimaximal forms of the correlation matrix $V_M$ are quite possible. Any theoretical model with a vanishing (1,3) entry of $V_M$ that is in agreement with quark data, solar, and atmospheric mixing angle leads to $θ_{13}^{PMNS}=(9{^{+1}_{-2}})^\circ$. This value is consistent with the present 90% CL experimental upper limit.

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arXiv2006

Gallium data variability and KamLAND

We present an alternative fit to the conventional solar+KamLAND one which takes into account the possible time dependence of the Ga data and relies on the partial conversion of active $\to$ sterile neutrinos via the magnetic moment/solar field interaction. We evaluate the prediction for the solar neutrino rates obtaining a fit of similar quality as the LMA one. We also evaluate the KamLAND antineutrino survival probability as a function of reactor distance and find a better agreement with data as compared to LMA.

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arXiv2005

Solar Neutrinos: Spin Flavour Precession and LMA

The time dependence that appears to be hinted by the data from the first 13 years of the solar neutrino Gallium experiments is viewed as resulting from a partial conversion of active neutrinos to light sterile ones through the resonant interaction between the magnetic moment of the neutrino and a varying solar field. A summary of the model and its predictions are presented for the forthcoming experiments Borexino and LENS.

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arXiv2005

Neutrino Mass Matrices with Vanishing Determinant and $θ_{13}$

We investigate the prospects for scenarios with vanishing determinant neutrino mass matrices and vanishing $θ_{13}$ mixing angle. Normal and inverse mass hierarchies are considered separately. For normal hierarchy it is found that neutrinoless double beta decay cannot be observed by any of the present or next generation experiments. For inverse hierarchy the neutrinoless double beta decay is, on the contrary, accessible to experiments. We also analyse for both hierarchies the case for texture zeros and equalities between mass matrix elements. No texture zeros are found to be possible nor any such equalities, apart from the obvious ones.

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