We study the Standard Model effective field theory ($ν$SMEFT) extended with operators involving right-handed neutrinos, focussing on the regime where the right-handed neutrinos decay promptly on collider scales to a photon and a Standard Model neutrino. This scenario arises naturally for right-handed neutrinos with masses of the order $m_N \sim 0.1 \dots 10\, \text{GeV}$. We limit the relevant dimension-six operator coefficients using LEP and LHC searches with photons and missing energy in the final state as well as pion and tau decays. While bounds on new physics contributions are generally in the TeV scale for order one operator coefficients, some coefficients, however, remain very poorly constrained or even entirely evade bounds from current data. Consequently, we identify such weakly constrained scenarios and propose new searches for rare top and tau decays involving photons to probe potential new physics in the $ν$SMEFT parameter space. Our analysis highlights the importance of performing dedicated searches for new rare tau and top decays.
We propose a low energy extension of the Standard Model consisting of an additional gauged $U(1)_{B-L}$ plus three right-handed neutrinos. The lightest right-handed neutrinos have TeV scale masses and may be produced at colliders via their couplings to the $Z_{B-L}$ gauge boson whose mass and gauge coupling is constrained by the out-of-equilibrium condition leading to upper bounds on the right-handed neutrino and $Z_{B-L}$ production cross-sections at colliders. We propose a brane-world scenario which motivates such TeV mass right-handed neutrinos. Our analysis opens up the possibility that th…
For the D=5 Majorana neutrino mass operator to have a see-saw ultraviolet completion that is viable up to the Planck scale, the see-saw scale is bounded above due to triviality limits on the see-saw couplings. For supersymmetric see-saw models, with realistic neutrino mass textures, we compare constraints on the see-saw scale from triviality bounds, with those arising from experimental limits on induced charged-lepton flavour violation, for both the CMSSM and for models with split supersymmetry.
For the D=5 Majorana neutrino mass operator to have a see-saw ultraviolet completion that is viable up to the Planck scale, the see-saw scale is bounded above due to triviality limits on the see-saw couplings. For supersymmetric see-saw models, with realistic neutrino mass textures, we compare constraints on the see-saw scale from triviality bounds, with those arising from experimental limits on induced charged-lepton flavour violation, for both the CMSSM and for models with split supersymmetry.
We show that the see-saw neutrino mass mechanism can coexist naturally with an extended gauge symmetry (i.e. without any gauge heirarchy problem) provided that the gauge symmetry contains gauged lepton number differences. The simplest such `natural' see-saw models are constructed and their implications for neutrino anomalies discussed.
We study the see-saw enhancement mechanism in presence of the right-handed phases of the Dirac neutrino mass matrix and the Majorana mass matrix. The enhancement condition given by Smirnov is modified. We point out that the see-saw enhancement could be obtained due to the right-handed phases even if the Majorana matrix is proportional to the unit matrix. We show a realistic Dirac mass matrix which causes the see-saw enhancement.
We consider a TeV scale see-saw mechanism leading to light scalar resonances in models with otherwise intrinsically heavy scalars. The mechanism can provide a 125 GeV technicolor Higgs in e.g. two-scale TC models
While the triplet-like Higgses up to a few hundred GeV masses are already excluded for a vast region of the model parameter space from the LHC searches, strikingly, there is a region of this parameter space that is beyond the reach of the existing LHC searches, and doubly/singly-charged and neutral Higgses as light as 200 GeV or even lighter are still allowed by the LHC data. We study several search strategies targeting different parts of this LHC elusive parameter space at two configurations of $e^-e^+$ colliders -- 500 GeV and 1 TeV centre of mass energies. We find that a vast region of this…
The See-Saw mechanism provides a nice way to explain why neutrino masses are so much lighter than their charged lepton partners. It also provides a nice way to explain baryon asymmetry in our universe via the leptogenesis mechanism. In this talk we review leptogenesis and LHC physics in a See-Saw model proposed in 1989, now termed the Type III See-Saw model. In this model, $SU(2)_L$ triplet leptons are introduced with the neutral particles of the triplets playing the role of See-Saw. The triplet leptons have charged partners with standard model gauge interactions resulting in many new features…
A new lefthanded see-saw mechanism is constructed, implying both the smallness of active-neutrino masses and decoupling of heavy passive neutrinos, similarly to the situation in the case of conventional see-saw. But now, in place of the conventional righthanded neutrinos, the lefthanded sterile neutrinos play the role of heavy passive neutrinos, the righthanded neutrinos and righthanded sterile neutrinos being absent. In this case, the neutrino mass term is necessarily of pure Majorana type.
A formal proof is given that in a see-saw type neutrino mass matrix with only two neutrino mass scales ($m_D \ll m_R$) and the maximal rank of $m_{R(D)}$, we can not get a fourth light sterile neutrino.
We review the present electroweak precision data constraints on the mediators of the three types of see-saw mechanisms. Except in the see-saw mechanism of type I, with the heavy neutrino singlets being mainly produced through their mixing with the Standard Model leptons, LHC will be able to discover or put limits on new scalar (see-saw of type II) and lepton (see-saw of type III) triplets near the TeV. If discovered, it may be possible in the simplest models to measure the light neutrino mass and mixing properties that neutrino oscillation experiments are insensitive to.
On the basis of see-saw mechanism, possible generation structure is investigated. Assuming that right-handed neutrinos are realistic particles below GUTs mass, it is shown that there is a choice of new scheme of generation,where the combination of leptons and quarks is different from the ordinary one. Our scheme predict a new proton decay mode.
We show how the renormalizable see-saw mechanism in the context of supersymmetry and spontaneously broken B-L symmetry implies exact R-parity at all energies. We argue that supersymmetry plays an important role in providing a "canonical" form for the see-saw, in particular in grand unified theories that solve the doublet-triplet splitting problem via the Dimopoulos-Wilczek mechanism.
We apply the see-saw mechanism and an SO(10) model to neutrino masses and mixing in order to estimate the heavy Majorana masses. We discuss shortly the decay modes of heavy Majorana neutrinos and calculate their contribution to the lepton number violating processes μ\to eγ, τ\toμγand τ\to eγ.
We consider the neutrino mixing angles in an SO(10) GUT with the usual Higgs structure in which neutrino masses are explained by the type-I see-saw mechanism. The Dirac-neutrino Yukawa matrix then has a structure similar to that of the $u$-quark. We determine the light neutrino mass matrix through type-I see-saw mechanism using the experimentally consistent $u$-quark Yukawa matrix. We find that large neutrino mixing-angles emerge naturally in this model.
We study the approximate flavour symmetries imposed on the lepton sector assuming see-saw mechanism as the neutrino mass structure. We apply the symmetry to various neutrino phenomenologies and obtain constraints on neutrino masses and mixings.
We give a new mechanism for generating very small, and almost degenerate, neutrino masses, without resorting to the see-saw mechanism or unnatural small Yukawa couplings. It requires the existence of at least 4 families with an almost democratic structure for the Yukawa couplings. It is also proven that this structure can account for large lepton mixings of the three light leptons.
We consider the corrections that arise at one loop when integrating out heavy fields in supersymmetric models. We show that, in type-I see-saw models, complex A and B terms of the heavy right-handed neutrino give radiative contributions to the neutron EDM, as well as new dominant contributions to the electron EDM. Type-II and type-III see-saw also predict a pure gauge correction that makes complex the masses of the weak gauginos. All the see-saw models can predict observable EDM for the electron and for the neutron in a peculiar ratio.
If the sterile neutrino mass matrix in an otherwise conventional see-saw model has a rank less than the number of flavors, it is possible to produce pseudo-Dirac neutrinos. For the rank 1 case, 3+2 scenarios devolve naturally, as we show by example. Additionally, we find that the lower rank see-saw suppresses some mass differences, so that small mass differences do not require that the individual masses of each neutrino must also be small.
We study the second and third generation masses in the context of the minimal renormalizable SO(10) theory. We show that if the see-saw takes the non-canonical (type II) form, large atmospheric neutrino mixing angle requires b-tau unification.
Several aspects of next-to-leading (NLO) order corrections to see-saw formulas are discussed and phenomenologically relevant situations are identified. We generalize the formalism to calculate the NLO terms developed for the type I see-saw to variants like the inverse, double or linear see-saw, i.e., to cases in which more than two mass scales are present. In the standard type I case with very heavy fermion singlets the sub-leading terms are negligible. However, effects in the percent regime are possible when sub-matrices of the complete neutral fermion mass matrix obey a moderate hierarchy, e…
It has been shown that only certain neutrino mass matrices with texture zeros are compatible with existing data. We discuss the stability of phenomenological consequences of texture zeros under radiative corrections in the type-I see-saw scenario. We show that under certain conditions additional patterns are allowed due to these effects.
We build on a recent paper by Grinstein, Redi and Villadoro, where a see-saw like mechanism for quark masses was derived in the context of spontaneously broken gauged flavour symmetries. The see-saw mechanism is induced by heavy Dirac fermions which are added to the Standard Model spectrum in order to render the flavour symmetries anomaly-free. In this letter we report on the embedding of these fermions into multiplets of an SU(5) grand unified theory and discuss a number of interesting consequences.
A simple ansatz that is well-motivated by group-theoretical considerations is proposed in the context of the type III neutrino see-saw mechanism. It results in predictions for m_s/m_b and m_b/m_tau that relate these quantities to the masses and mixings of neutrinos.
An alternative to the famous see-saw mechanism is proposed to explain the smallness of the neutrino masses (if present). This model involves a fourth family which mixes very little with the other three. It contains one heavy neutrino (mN > mZ /2) and three very light neutrinos whose masses are radiatively induced. In contrast with the see-saw mechanism, all neutrino masses are Dirac masses. In one particular scenario, the three light neutrinos are almost degenerate in mass and are found to be consistent with fits to the Solar and Atmospheric neutrino deficits. They might even account for the H…
The singular see-saw mechanism is a variation of the see-saw mechanism whereby the right-chiral neutrino Majorana mass matrix is singular. Previous works employing the singular see-saw mechanism have assumed a vanishing left-chiral Majorana mass matrix. We study the neutrino spectrum obtained under a singular see-saw mechanism when the left-chiral neutrinos possess a non-zero Majorana mass matrix. We refer to this as the type-II singular see-saw mechanism. The resulting neutrino spectrum is found to be sensitive to the hierarchy of the Dirac and Majorana mass scales used and we explore the phe…
We introduce the idea of bosonic see-saw mechanism in analogy with the see-saw mechanism. Bosonic see-saw is a new symmetry breaking mechanism and we apply it to explain electroweak symmetry breaking as an inevitable consequence of supersymmetry breaking. The breaking of electroweak symmetry occurs at tree level once supersymmetry is broken. Absence of color/charge breaking in this model is related to doublet-triplet splitting in grand unified theory. An extension of MSSM with a weak triplet shows very interesting results especially when mu =0. It provides the most natural understanding of why…
A new lefthanded see-saw mechanism is constructed, implying both the smallness of active-neutrino masses and decoupling of heavy passive neutrinos, similarly to the situation in the case of conventional see-saw. But now, in place of the conventional righthanded neutrinos, the lefthanded sterile neutrinos play the role of heavy passive neutrinos, the righthanded neutrinos and righthanded sterile neutrinos being absent. Here, the lefthanded sterile neutrinos are different from charge conjugates of conventional righthanded neutrinos because their lepton numbers differ. In this case, the neutrino …
In realistic grand unified models there are typically extra vectorlike matter multiplets at the GUT scale that are needed to explain the family hierarchy. These contain neutrinos that, when integrated out, can modify the usual neutrino see-saw formula. A general analysis is given. It is noted that such modifications can explain why the neutrinos do not exhibit a strong family hierarchy like the other types of fermions.
We study the effective ways for generating the linear see-saw neutrino mass relations and large neutrino mixing angles in two classes of grand unified SO(10) models where the texture of Dirac neutrino mass matrix is related to either the charged lepton mass matrix (case A) or the up-quark mass matrix (case B). We also briefly analyse their stability criteria and they are found to be stable under under radiative corrections at low energies.
We introduce the idea of Form Dominance in the (type I) see-saw mechanism, according to which a particular right-handed neutrino mass eigenstate is associated with a particular physical neutrino mass eigenstate, leading to a form diagonalizable effective neutrino mass matrix. Form Dominance, which allows an arbitrary neutrino mass spectrum, may be regarded as a generalization of Constrained Sequential Dominance which only allows strongly hierarchical neutrino masses. We consider alternative implementations of the see-saw mechanism in minimal A4 see-saw models and show that such models satisfy …
We consider the low energy constraints that can be applied to type I see-saw extensions of the Standard Model in which the right-handed neutrinos are taken at the electroweak scale. In the reported scenarios, the flavour structure of the charged current and neutral current weak interactions of the Standard Model leptons with the heavy right-handed neutrinos is essentially determined by the neutrino oscillation parameters. In this case, correlations among different measurable phenomena in the lepton sector may provide compelling indirect evidence of low energy see-saw mechanism of neutrino mass…
I review the profound connection between the see-saw mechanism for neutrino masses and grand unification. This connection points naturally towards SO(10) grand unified theory. The emphasis here is on the supersymmetric theory, but I also discuss salient features of its split supersymmetry version and ordinary non-supersymmetric SO(10). Particular attention is paid to the crucial issue of the minimal such theory, i.e. the question of the Higgs sector needed to break SO(10) down to the Minimal Supersymmetric Standard Model or the Standard Model. Some essential features of the see-saw mechanism a…
In a wide class of unified models there is an additional (and possibly dominant) term in the neutrino mass formula that under the simplest assumption takes the form M_ν = (M_N + M_N^T)u/M_G, where M_N is the neutrino Dirac mass matrix, and u = O(M_W). This makes possible highly predictive models. A generalization of this form yields realistic neutrino masses and mixings more readily than the usual see-saw formula in some models.
We review the low energy constraints on type I see-saw extensions of the Standard Model in which the scale of new physics, associated to lepton number violation, can be probed at current collider searches. In such scenarios, the flavour structure of the charged current and neutral current weak interactions of the Standard Model leptons with the heavy right-handed neutrinos, which provide the contribution of new physics, is essentially determined by the neutrino oscillation parameters. Correlations among different low energy observables in the lepton sector emerge, which may provide a striking …
In the Type I see-saw model, the naturalness requirement that corrections to the electroweak $μ$ parameter not exceed 1 TeV results in a rough bound on the lightest right-handed neutrino mass, $M_{N_1}\lesssim 3\times 10^7$ GeV. In this letter we derive generic bounds applicable in any three-flavour Type I see-saw model. We find $M_{N_1}\lesssim 4\times 10^7$ GeV and $M_{N_2}\lesssim 7\times 10^7$ GeV. In the limit of one massless neutrino, there is no naturalness bound on $M_{N_3}$ in the Poincare protected decoupling limit. Our results confirm that no Type I see-saw model can explain the obs…
A possible interplay of both terms in the type II see-saw formula is illustrated by presenting a novel way to generate deviations from exact bimaximal neutrino mixing. In type II see-saw mechanism with dominance of the non-canonical SU(2)_L triplet term, the conventional see-saw term can give a small contribution to the neutrino mass matrix. If the triplet term corresponds to the bimaximal mixing scheme in the normal hierarchy, the small contribution of the conventional see-saw term naturally generates non-maximal solar neutrino mixing. Atmospheric neutrino mixing is also reduced from maximal,…
The lepton flavour violating (LFV) $τ$ decays $τ\to (e,μ)γ$ and $τ\to 3μ$ are investigated in the frameworks of the TeV scale type I see-saw and Higgs Triplet (or type II see-saw) models. Predictions for the rates of these processes are obtained. The implications of the existing stringent experimental upper bounds on the $μ\to e + γ$ and $μ\to 3e$ decay branching ratios for the predictions of the $τ\to (e,μ)γ$ and $τ\to 3μ$ decay rates are studied in detail. The possibilities to observe the indicated LFV $τ$ decays in present and future experiments are analysed.
I introduce and sketch the main features of those see-saw models where a large atmospheric mixing can be achieved starting from nearly diagonal matrices for charged leptons, Dirac neutrinos and Majorana right-handed neutrinos. It turns out that these models can be realized in Grand Unified Theories and they are well compatible with the related phenomenology of fermion masses and mixings.
We systematically analyze quantum corrections in see-saw scenarios, including effects from above the see-saw scales. We derive approximate renormalization group equations for neutrino masses, lepton mixings and CP phases, yielding an analytic understanding and a simple estimate of the size of the effects. Even for hierarchical masses, they often exceed the precision of future experiments. Furthermore, we provide a software package allowing for a convenient numerical renormalization group analysis, with heavy singlets being integrated out successively at their mass thresholds. We also discuss a…
The compatibility of the Frobenius group T13 with the canonical see-saw mechanism of neutrino mixing is examined. The Standard Model is extended in a minimalist way, by introducing a family symmetry and three right-handed neutrinos. To fit experiments and place constraints on the possibilities, tribimaximal mixing is used as a guideline. The application of both a family symmetry group and the canonical see-saw mechanism naturally generates small neutrino masses. The various possibilities from combining these two models are listed. Enough constraints are produced to narrow down the parameters o…
The see-saw mechanism of neutrino mass generation may enhance lepton mixing up to maximal even if the Dirac mass matrices of leptons have structure similar to that in the quark sector. Two sets of conditions for such an enhancement are found. The first one includes the see-saw generation of heavy Majorana masses for right-handed neutrinos and a universality of Yukawa couplings which can follow from the unification of neutrinos with new superheavy neutral leptons. The second set is related to lepton number symmetry of the Yukawa interactions in the Dirac basis of neutrinos. Models which realize…
In order to explain the recently reported result on the double beta decay $(0νββ)$ experiment, together with the earlier established data on LMA MSW solar and atmospheric neutrino oscillations, we generate the textures of the nearly degenerate as well as the inverted hierarchical models of the left-handed Majorana neutrino mass matrices within the framework of the see-saw mechanism in a model independent way. The leptonic mixings are generated from the texture of the right- handed Majorana mass matrices while keeping the Dirac neutrino mass matrices in diagonal forms.
We present a minimal model in which the Inverse See Saw is realized dynamically. The two unity lepton number breaking term is induced at two-loop level and is naturally around the keV scale, while right-handed neutrinos are at the TeV scale. An interesting extension of the model is obtained by gauging B-L: in this case anomaly cancellation has as direct consequence the presence of a sterile neutrino at the MeV scale that may be a good Dark Matter candidate. Moreover the new gauge boson Z' and the new neutral scalars may have characteristic signatures at LHC.
We propose an SO(10) grand unified theory which has the simplest Higgs structure discussed so far in the literature. We include only two Higgs scalars, a 210-plet and a 16-plet. In addition to the regular fermions we include one singlet, whose mass term breaks chiral symmetry, so that fermions can get masses. All fermions acquire see-saw masses, since there are no Higgs bi-doublets. Required neutrino masses with large mixing as well as leptogenesis are possible in this model.
We determine the nu_{R} Majorana mass matrix from the experimental data on neutrino oscillations in the framework of a see-saw SO(10) model, where we impose the condition (M^R)_{33} = 0 to avoid too large fine-tunings in the see-saw formula. We find a class of solutions with the two lowest neutrino masses almost degenerate and the scale of the matrix elements of M^R in the range 10^{11} -10^{12} GeV in agreement with Pati-Salam intermediate symmetry. We find also solutions with smaller neutrino masses, for which the scale of M_R depends on the solution to the "solar neutrino problem" and on th…
In some classes of flavour models based on unified theories with a type I see-saw mechanism, the prediction for the mass of the lightest right-handed neutrino is in conflict with the lower bound from the requirement of successful thermal leptogenesis. We investigate how lifting the absolute neutrino mass scale by adding a type II see-saw contribution proportional to the unit matrix can solve this problem. Generically, lifting the neutrino mass scale increases the prediction for the mass of the lightest right-handed neutrino while the decay asymmetry is enhanced and washout effects are reduced,…
If the smallness of the mass of the sterile neutrino is to be explained by the see-saw mechanism, the off-diagonal entries of the mass matrix needs to be protected by some symmetry not far above the electroweak scale. We implement see-saw mechanism in a gauge model based on $SU(2)^q_L \times SU(2)^l_L \times U(1)^q_Y \times U(1)^l_Y$ un-unified gauge group which breaks to $SU(2)_L \times U(1)_Y$ at the TeV region via a two-step symmetry breaking chain. The right handed diagonal block is tied to the highest scale up to which the un-unification symmetry holds. The sterile neutrino emerges from a…
Neutrino oscillations give clear evidence for non-vanishing neutrino masses and lepton-flavor violation (LFV) in the neutrino sector. This provides strong motivation to search for signals of LFV also in the charged lepton sector, and to probe the SUSY see-saw mechanism. We compare the sensitivity of rare radiative decays on the right-handed Majorana mass scale M_R with the reach in slepton-pair production at a future linear collider.
Some years ago it was shown by Ma that in the context of the electroweak standard model there are, at the tree level, only three ways to generate small neutrino masses by the see-saw mechanism via one effective dimension-five operator. Here we extend this approach to 3-3-1 chiral models showing that in this case there are several dimension-five operators and we also consider their tree level realization.
We examine one simple mechanism which leads to approximate maximal $ν_μ- ν_τ$ oscillations in the standard see-saw model. In particular, we show that this scheme could be implemented in the Exact Parity Model (also known as the mirror matter model). Within this framework the solar neutrino problem is solved by maximal $ν_e \to ν'_e$ oscillations (with $ν'_e$ is the essentially sterile mirror partner of $ν_e$) and the LSND evidence for $ν_e \to ν_μ$ oscillations can also be explained.
The see-saw mechanism of neutrino mass generation, when incorporated in supersymmetric theories with supergravity mediated supersymmetry breaking, results in low-energy lepton-flavour violation arising from the soft supersymmetry breaking slepton masses. The parameter space of supergravity theories with conserved R-parity is severely constrained by the requirement that the LSP provide cold dark matter with a relic density in the range indicated by the recent WMAP measurements, as well as by laboratory constraints. We calculate the $\meg$ branching ratio for the constrained minimal supersymmetr…
We investigate the see-saw mechanism for generally non-fine-tuned $n \times n$ mass matrices involving both Dirac and Majorana neutrinos. We specifically show that the number of naturally light neutrinos cannot exceed half of the dimension of the considered mass matrix. Furthermore, we determine a criterion for mass matrix textures leading to light Dirac neutrinos with the see-saw mechanism. Especially, we study $4 \times 4$ and $6 \times 6$ mass matrix textures and give some examples in order to highlight these types of textures. Next, we present a model scheme based on non-Abelian and discre…
We present a minimal see-saw model based on an extension of the standard model (SM) which includes an additional U(1), with gauge charge $B - \frac{3}{2} (L_μ+ L_τ)$. Requirement of anomaly cancellation implies the existence of two right-handed singlet neutrinos, carrying this gauge charge, which have normal Dirac couplings to $ν_μ$ and $ν_τ$ but suppressed ones to $ν_e$. Assuming the U(1) symmetry breaking scale to be 10$^{12-16}$~GeV, this model can naturally account for the large (small) mixing solutions to the atmospheric (solar) neutrino oscillations.
We study the see-saw realization of seven textures of the neutrino mass matrix, which were presented by Frampton, Glashow and Marfatia. Two of them B_1 and B_2 are not realized in the see-saw mechanism without fine-tuning of parameters. We present some specific textures of the Dirac neutrino mass matrix and the right-handed Majorana neutrino one. In order to test these textures, we discuss the effect on the branching ratio of mu --> e gamma. We also study the U(1)_X times U(1)_{X'} flavor symmetry, in which U(1)_X is anomalous and U(1)_{X'} is non-anomolous, to reproduce texture zeros. We pres…
We have constructed an explicit see-saw model containing two singlet neutrinos, one carrying a $(B-3L_e)$ gauge charge with an intermediate mass scale of $\sim O(10^{10})$ GeV along with a sterile one near the GUT (grand unification theory) scale of $\sim O(10^{16})$ GeV. With these mass scales and a reasonable range of Yukawa couplings, the model can naturally account for the near-maximal mixing of atmospheric neutrino oscillations and the small mixing matter-enhanced oscillation solution to the solar neutrino deficit.
It is shown that the Majorana nature of the heavy neutrinos $N_j$ having masses in the range of $M_j \sim (100 - 1000)$ GeV and present in the TeV scale type I and inverse see-saw scenarios of neutrino mass generation, is unlikely to be observable in the currently operating and future planned accelerator experiments (including LHC) due to the existence of very strong constraints on the parameters and couplings responsible for the corresponding $|ΔL| = 2$ processes, $L$ being the total lepton charge. If the heavy Majorana neutrinos $N_j$ are observed and they are associated only with the type I…
The scaling hypothesis postulates proportionality of two columns of the Majorana neutrino mass matrix in the flavor basis. This Ansatz was shown to lead to an inverted hierarchy and U_{e3} = 0. We discuss theoretical and phenomenological properties of this hypothesis. We show that (i) the neutrino mass matrix with scaling follows as a consequence of a generalized mu-tau symmetry imposed on the type-I see-saw model; (ii) there exists a unique texture for the Dirac mass matrix m_D which leads to scaling for arbitrary Majorana matrix M_R in the context of the type-I see-saw mechanism; (iii) unlik…
We discuss the prospects for detecting right-handed neutrinos which are introduced in the see-saw mechanism at future colliders. This requires a very accurate cancellation between contributions from different right-handed neutrinos to the light neutrino mass matrix. We search for possible symmetries behind this cancellation and find that they have to include lepton number conservation. Light neutrino masses can be generated as a result of small symmetry-breaking perturbations. The impact of these perturbations on LHC physics is negligible, so that the mechanism of neutrino mass generation and …
