Although the existence of neutrinos has been hypothesised in the 1930's and their detection occured in the 1950's, they enclose still a number of mysteries and remain an open threshold for new physics.

One of the most beautiful issues in particle physics in the late 20th and early 21th century was the solar neutrino puzzle, whereby much fewer than expected neutrinos were observed to be coming from the sun. Initially thought to be an innacuracy both insolr models predictions and solar neutrino experiments, independent experiments have shown that the solar neutrino deficit was in fact a consequence of the intrinsic neutrino properties, namely that neutrinos have mass and they change their identity on their way from the Sun to the Earth, in other words, they oscillate. This was a major step forward in particle physics, since the standard model of particle physics predicted massless neutrinos, unable to oscillate.

Neutrino oscillations may not however be the only source of the solar neutrino deficit, In fact a vast energy region of the solar neutrino spectrum still remains unobserved, despite the enormous experimental efforts undertaken. Moreover there are known to exist inconsistencies between the predictions from the oscillation theory and the observations. We have proposed several independent models that overcome this difficulty: two of them involve the oscillation of the known neutrinos into a new kind, the so called sterile neutrino. This may occur either as a consequence of a magnetic moment interaction with the solar magnetic field, or a mixing with the sterile neutrino itself that promotes oscillations in much the same way that the known 'active' neutrinos oscillate among themselves. The other proposal we presented to understand the above mentioned inconsistencies is the non-standard neutrino oscillations that, interestingly enough open the possibility for neutrino decay in dense matter.

Publications (João Pulido)
. Determination of the ?23 octant in LBNO
C.R. Das (Jyvaskyla U. & Lisbon, CFTP & Lisbon, IST & Ahmedabad, Phys. Res. Lab), Jukka Maalampi (Jyvaskyla U.), João Pulido (Lisbon,
CFTP & Lisbon, IST), Sampsa Vihonen (Jyvaskyla U.). Nov 11, 2014. 12 pp.
Published in JHEP 1502 (2015) 048
DOI: 10.1007/JHEP02(2015)048
e-Print: arXiv:1411.2829 [hep-ph] | PDF

Sterile neutrinos in the 3+s scenario and solar data
Joao Pulido (Lisbon, CFTP), C.R. Das (Lisbon, CFTP & Jyvaskyla U.). Oct 1, 2013. 7 pp.
Published in PoS EPS-HEP2013 (2013) 527
Conference: C13-07-18 Proceedings
e-Print: arXiv:1310.0426 [hep-ph] | PDF

Long baseline neutrino experiments, mass hierarchy and delta(CP)
C.R. Das, Joao Pulido (Lisbon, CFTP). Feb 2013. 26 pp.
e-Print: arXiv:1302.0779 [hep-ph] | PDF

Solar neutrinos with non-standard interactions
Joao Pulido, C.R. Das (Lisbon, CFTP & Lisbon, IST). 2012.
Published in Nucl.Phys.Proc.Suppl. 229-232 (2012) 563

Possible trace of neutrino nonstandard interactions in the supernova
C.R. Das, Joao Pulido (Lisbon, CENTRA). Nov 2011. 4 pp.
Published in J.Phys.Conf.Ser. 375 (2012) 042040
DOI: 10.1088/1742-6596/375/1/042040
Conference: C11-09-05 Proceedings
e-Print: arXiv:1111.6939 [hep-ph] | PDF

Neutrino nonstandard interactions in the supernova
C.R. Das, Joao Pulido (Lisbon, IST). Jun 2011. 15 pp.
Published in Phys.Rev. D84 (2011) 105040
DOI: 10.1103/PhysRevD.84.105040
e-Print: arXiv:1106.4268 [hep-ph] | PDF

NSI can improve LMA predictions: neutrino decay in solar matter?
Joao Pulido, C.R. Das (Lisbon, CFTP). Dec 2010. 3 pp.
Published in Nucl.Phys.Proc.Suppl. 217 (2011) 350-352
DOI: 10.1016/j.nuclphysbps.2011.04.136
Conference: C10-09-04 Proceedings
e-Print: arXiv:1012.3842 [hep-ph] | PDF

Improving LMA predictions with non-standard interactions: Neutrino decay in solar matter?
C.R. Das, Joao Pulido (Lisbon, CFTP & Lisbon, IST). Jul 2010. 22 pp.
Published in Phys.Rev. D83 (2011) 053009
DOI: 10.1103/PhysRevD.83.053009
e-Print: arXiv:1007.2167 [hep-ph] | PDF

Improving LMA predictions with non standard interactions
C.R. Das, Joao Pulido (Lisbon, CFTP & Lisbon, IST). Mar 2010. 17 pp.
e-Print: arXiv:1003.5904 [hep-ph] | PDF

Remaining inconsistencies with solar neutrinos: Can spin flavour precession provide a clue?
Joao Pulido, C.R. Das (Lisbon, CFTP), Marco Picariello (INFN, Lecce & Salento U.). Oct 2009. 3 pp.
Published in J.Phys.Conf.Ser. 203 (2010) 012086
DOI: 10.1088/1742-6596/203/1/012086

Neutrino Dipole Moments and Solar Experiments
M. Picariello, B.C. Chauhan, C.R. Das (Salento U. & Lisbon, CFTP), J.J. Fernandez-Melgarejo (Murcia U.), D. Montanino, J. Pulido, E.
Torrente-Lujan (Salento U. & Lisbon, CFTP). Jul 2009. 6 pp.
Conference: C09-03-07, p.551-556 Proceedings
e-Print: arXiv:0907.0637 [hep-ph] | PDF

Light sterile neutrinos, spin flavour precession and the solar neutrino experiments
C.R. Das, Joao Pulido (Lisbon, CFTP & Lisbon, IST), Marco Picariello (INFN, Lecce & Salento U.). Feb 2009. 22 pp.
Published in Phys.Rev. D79 (2009) 073010
DOI: 10.1103/PhysRevD.79.073010
e-Print: arXiv:0902.1310 [hep-ph] | PDF

Probing neutrino magnetic moment and unparticle interactions with Borexino
Daniele Montanino, Marco Picariello (Salento U. & INFN, Lecce), Joao Pulido (Lisbon, IST). Jan 2008. 15 pp.
Published in Phys.Rev. D77 (2008) 093011
DOI: 10.1103/PhysRevD.77.093011
e-Print: arXiv:0801.2643 [hep-ph] | PDF

Resonance spin flavor precession of solar neutrinos after SNO NC data
Bhag C. Chauhan, Joao Pulido (CFIF, Lisbon & Lisbon, IST). Jun 2002. 15 pp.
Published in Phys.Rev. D66 (2002) 053006
DOI: 10.1103/PhysRevD.66.053006
e-Print: hep-ph/0206193 | PDF

SNO and the neutrino magnetic moment solution of the solar neutrino problem
Evgeny K. Akhmedov, Joao Pulido (Lisbon, IST). May 2000. 12 pp.
Published in Phys.Lett. B485 (2000) 178-186
DOI: 10.1016/S0370-2693(00)00695-X
e-Print: hep-ph/0005173 | PDF