1,721,349 research outputs found
Theoretical models on the structure of the neutrino mixing matrix
Full text linkWe briefly review symmetry approaches to the flavour problem in the lepton sector, focusing on the structure of the neutrino mixing matrix. We first discuss traditional (linearly realised) non-Abelian discrete flavour symmetries and then modular flavour symmetries. The importance of future neutrino oscillation experiments for testing and narrowing down the broad classes of flavour models based on these symmetries is emphasised
Heavy Neutral Leptons in the NRSMEFT and the High-Luminosity LHC
No full textWe study heavy neutral leptons (HNLs) in the NRSMEFT, the effective field theory of the Standard Model extended with gauge singlet right-handed fermions. Four-fermion operators which contain two HNLs and two quarks can lead to a sizeable enhancement of the HNL pair-production cross section, compared to the minimal case where HNLs are produced only via their mixing with the active neutrinos. We calculate the expected sensitivities for the ATLAS detector and the future far-detector experiments at the high-luminosity LHC: AL3X, ANUBIS, CODEX-b, FASER, MATHUSLA and MoEDAL-MAPP. We find that new physics scales up to 22 TeV and active-heavy mixing squared as small as 10^{-24} could be probed by some of these experiments. Next, we consider four-fermion operators with a single HNL. Such operators might dominate both HNL production and decay, and we find that new physics scales in excess of 20 TeV could be tested at ATLAS
Assessing the viability of A4, S4, and A5 flavor symmetries for description of neutrino mixing
Full text linkWe consider the A4, S4, and A5 discrete lepton flavor symmetries in the case of 3-neutrino mixing, broken down to nontrivial residual symmetries in the charged lepton and neutrino sectors in such a way that at least one of them is a Z2. Such symmetry breaking patterns lead to predictions for some of the three neutrino mixing angles and/or the leptonic Dirac CP violation phase δ of the neutrino mixing matrix. We assess the viability of these predictions by performing a statistical analysis which uses as an input the latest global data on the neutrino mixing parameters. We find 14 phenomenologically viable cases providing distinct predictions for some of the mixing angles and/or the Dirac phase δ. Employing the current best fit values of the three neutrino mixing angles, we perform a statistical analysis of these cases taking into account the prospective uncertainties in the determination of the mixing angles, planned to be achieved in currently running (Daya Bay) and the next generation (JUNO, T2HK, DUNE) of neutrino oscillation experiments. We find that only six cases would be compatible with these prospective data. We show that this number is likely to be further reduced by a precision measurement of δ
One-loop running of dimension-six Higgs-neutrino operators and implications of a large neutrino dipole moment
Full text linkWe compute the one-loop running of the dimension-six CP-even Higgs operators in the Standard Model effective field theory involving the right-handed component of the would-be Dirac neutrinos. Then, on the basis of naturalness arguments, for some operators we obtain bounds that surpass direct constraints by orders of magnitude. We also discuss the implications of a large Dirac neutrino magnetic dipole moment. In particular, we demonstrate that a neutrino magnetic moment explaining the recent XENON1T excess induces Higgs and Z invisible decays with branching ratios in the range [10(-18), 10(-12)]. These numbers are unfortunately beyond the reach of current and near future facilities
Predictions for the Dirac CP violation phase in the neutrino mixing matrix
No full textUsing the fact that the neutrino mixing matrix
, where and
result from the diagonalisation of the charged lepton
and neutrino mass matrices, we analyse
the predictions based on the sum rules which
the Dirac phase present in
satisfies when has a form dictated
by, or associated with, discrete flavour symmetries and
has a ``minimal'' form (in
terms of angles and phases it contains)
that can provide the requisite
corrections to , so that the
reactor, atmospheric and solar neutrino mixing angles
, and
have values compatible with the current data
Neutrino masses in the Standard Model effective field theory
Full text linkWe compute the leading-logarithmic correction to the neutrino mass matrix in the Standard Model effective field theory (SMEFT) to dimension seven. In the limit of negligible lepton and down-type quark Yukawa couplings, it receives contributions from the Weinberg dimension-five operator as well as from 11 dimension-six and five dimension-seven independent interactions. Two of the main implications we derive from this result are the following. First, we find dimension-seven operators which, despite violating lepton number, do not renormalize neutrino masses at one loop. And second, we demonstrate that the presence of dimension-six operators around the TeV scale can modify the Standard Model prediction by up to O(50%). Our result comprises also one step forward towards the renormalization of the SMEFT to order v(3)/Lambda(3)
The A4, S4 and A5 flavor symmetries in light of data on neutrino mixing
Full text linkWe consider the A4, S4 and A5 discrete lepton flavor symmetries broken down to nontrivial residual symmetries in the charged lepton and neutrino sectors in such a way that at least one of them is a Z2. Such symmetry breaking patterns lead to predictions for some of the three neutrino mixing angles and/or the Dirac CP violation phase δ of the neutrino mixing matrix. First, we perform a statistical analysis of these predictions, which uses as input the latest global data on the neutrino mixing parameters. We find 14 phenomenologically viable cases. Further, we assess the viability of these cases taking into account the prospective uncertainties in the determination of the mixing angles, planned to be achieved in current and future neutrino oscillation experiments. We find that only six cases would be compatible with the assumed prospective data. We show that this number will be further reduced by a precision measurement of δ
Effective field theory for vector-like leptons and its collider signals
Full text linkWe argue that in models with several high scales; e.g. in composite Higgs models or in gauge extensions of the Standard Model (SM), vector-like leptons can be likely produced in a relatively large root s region of the phase space. Likewise, they can easily decay into final states not containing SM gauge bosons. This contrasts with the topology in which these new particles are being searched for at the LHC. Adopting an effective field theory approach, we show that searches for excited leptons must be used instead to test this scenario. We derive bounds on all the relevant interactions of dimension six; the most constrained ones being of about 0.05 TeV-2. We build new observables to improve current analyses and study the impact on all single-field UV completions of the SM extended with a vector-like lepton that can be captured by the effective field theory at tree level, in the current and in the high-luminosity phase of the LHC. (C) 2020 The Author(s). Published by Elsevier B.V
CPV predictions from flavour symmetries
Full text linkIn the reference 3-neutrino mixing scheme leptonic CP violation can be caused by the Dirac, δ, and/or Majorana, α21 and α31, CP-violating phases present in the unitary neutrino mixing matrix U. Using the fact that U=U†eUν, Ue and Uν being unitary matrices diagonalising the charged lepton and neutrino mass matrices, respectively, we consider in a systematic way forms of Ue and Uν allowing us to derive sum rules for cosδ, α21 and α31, i.e., to express them in terms of the measured neutrino mixing angles present in U and the angles (and phases in the case of sum rules for α21 and α31) contained in Uν, whose values are fixed by a discrete flavour symmetry (a generalised CP symmetry). We consider several concrete forms of Uν, including the bimaximal, tri-bimaximal and golden ratio mixing forms. For each of these forms and forms of Ue allowing to reproduce the measured values of the neutrino mixing angles, we obtain numerical predictions for δ, α21 and α31. Using the obtained values of the CP-violating phases, we present predictions for the effective Majorana mass in neutrinoless double beta decay
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