Working group report: Neutrino and astroparticle physics

This is the report of neutrino and astroparticle physics working group at WHEPP-8. We present the discussions carried out during the workshop on selected topics in the above fields and also indicate progress made subsequently. The neutrino physics subgroup studied the possibilities of constraining neutrino masses, mixing and CPT violation in lepton sector from future experiments. Neutrino mass models in the context of Abelian horizontal symmetries, warped extra dimensions and in the presence of triplet Higgs were studied. Effect of threshold corrections on radiative magnification of mixing angles was investigated. The astroparticle physics subgroup focused on how various particle physics inputs affect the CMBR fluctuation spectrum, and on brane cosmology. This report also contains an introduction on how to use the publicly available code CMBFAST to calculate the CMBR fluctuations.     

Neutrino mass and mixing in the 3-3-1 model and S 3 flavor symmetry with minimal Higgs content

A new S ₃ flavor model based on the SU(3) _C ? SU(3) _L ? U(1) _X gauge symmetry responsible for fermion masses and mixings different from our previous work [14, 17] is constructed. The new feature is a two-dimensional representation of a Higgs anti-sextet under S ₃, which is responsible for neutrino masses and mixings. The neutrinos acquire small masses from only an anti-sextet of SU(3), which is in a doublet under S ₃. If the difference of components of the anti-sextet is regarded as a small perturbation, S ₃ is equivalently broken into identity, the corresponding neutrino mass mixing matrix acquires the most general form, and the model can fit the latest data on neutrino oscillations. This way of symmetry breaking helps us reduce a content in the Higgs sector, to only one anti-sextet instead of two as in our previous work [14]. Our results show that the neutrino masses are naturally small and a small deviation from the tri-bimaximal neutrino mixing form can be realized. The Higgs potential of the model as well as the minimization conditions and gauge boson masses and mixings are also considered.     

Resurrection of grand unified theory baryogenesis

A "new" scenario is proposed for baryogenesis. We show that the delayed decay of colored Higgs particles in grand unified theories may generate an excess baryon number of the empirically desired amount, if the mass of the heaviest neutrino is in the range 0.02 eV相似文献   

θ_(13) and the Higgs Mass from High Scale Supersymmetry

In the framework in which supersymmetry is used for understanding fermion masses rather than stabilizing the electroweak scale, we elaborate on the phenomenological analysis for the neutrino physics. A relatively large sinθ13 0.13 is naturally obtained. The model further predicts vanishingly small CP violation in neutrino oscillations. While the high scale supersymmetry generically results in a Higgs mass of about 141 GeV, our model reduces this mass to 126 GeV via introducing SU(2)L triplet fields which make the electroweak vacuum metastable (with a safe lifetime) and also contribute to neutrino masses.     

Inverse seesaw in NMSSM and 126 GeV Higgs boson

We consider extensions of the next-to-minimal supersymmetric model (NMSSM) in which the observed neutrino masses are generated through a TeV scale inverse seesaw mechanism. The new particles associated with this mechanism can have sizable couplings to the Higgs field which can yield a large contribution to the mass of the lightest CP-even Higgs boson. With this new contribution, a 126 GeV Higgs is possible along with order of 200 GeV masses for the stop quarks for a broad range of tan β. The Higgs production and decay in the diphoton channel can be enhanced due to this new contribution. It is also possible to solve the little hierarchy problem in this model without invoking a maximal value for the NMSSM trilinear coupling and without severe restrictions on the value of tan β.     

Explicit SO(10) supersymmetric grand unified model for the higgs and yukawa sectors

A complete set of fermion and Higgs superfields is introduced with well-defined SO(10) properties and U(1)xZ2xZ2 family charges from which the Higgs and Yukawa superpotentials are constructed. The structures derived for the four Dirac fermion and right-handed Majorana neutrino mass matrices coincide with those previously obtained from an effective operator approach. Ten mass matrix input parameters accurately yield the twenty masses and mixings of the quarks and leptons with the bimaximal atmospheric and solar neutrino vacuum solutions favored in this simplest version.     

Neutrino masses and lepton-flavor-violating τ decays in the supersymmetric left-right model

In the supersymmetric left-right model,the light neutrino masses are given by the Type-II seesaw mechanism.A duality property of this mechanism indicates that there exist eight possible Higgs triplet Yukawa couplings which result in the same neutrino ma6s matrix.In this paper,we work out the one-loop renormalization group equations for the effective neutrino mass matrix in the supersymmetric left-right model.The stability of the Type-II seesaw scenario is briefly discussed.We also study the lepton-flavor-violating processes (τ→μγ and τ→eγ)by using the reconstructed Higgs triplet Yukawa couplings.     

Effects of the scale-dependent vacuum expectation values in the renormalisation group analysis of neutrino masses

The contribution of scale-dependent vacuum expectation values (VEVs) of Higgs scalars, which gives significant effects in the evolution of the fundamental fermion masses in the minimal supersymmetric standard model (MSSM), is now considered in the derivation of the analytic one-loop expression for the evolution of the left-handed Majorana neutrino masses with energies. The inclusion of such an effect of the running VEV increases the stability of the neutrino masses under quantum corrections even for the low values of at the scale GeV, and leads to a mild decrease of the neutrino masses with higher energies. Such a trend is common with that of other fundamental fermion masses. Received: 18 September 2000 / Published online: 23 February 2001     

Probing neutrino and Higgs sectors in $$\text{ SU(2) }_1 \times \text{ SU(2) }_2 \times \text{ U(1) }_Y $$ model with lepton-flavor non-universality

The neutrino and Higgs sectors in the \(\text{ SU(2) }_1 \times \text{ SU(2) }_2 \times \text{ U(1) }_Y \) model with lepton-flavor non-universality are discussed. We show that active neutrinos can get Majorana masses from radiative corrections, after adding only new singly charged Higgs bosons. The mechanism for the generation of neutrino masses is the same as in the Zee models. This also gives a hint to solving the dark matter problem based on similar ways discussed recently in many radiative neutrino mass models with dark matter. Except the active neutrinos, the appearance of singly charged Higgs bosons and dark matter does not affect significantly the physical spectrum of all particles in the original model. We indicate this point by investigating the Higgs sector in both cases before and after singly charged scalars are added into it. Many interesting properties of physical Higgs bosons, which were not shown previously, are explored. In particular, the mass matrices of charged and CP-odd Higgs fields are proportional to the coefficient of triple Higgs coupling \(\mu \). The mass eigenstates and eigenvalues in the CP-even Higgs sector are also presented. All couplings of the SM-like Higgs boson to normal fermions and gauge bosons are different from the SM predictions by a factor \(c_h\), which must satisfy the recent global fit of experimental data, namely \(0.995<|c_h|<1\). We have analyzed a more general diagonalization of gauge boson mass matrices, then we show that the ratio of the tangents of the W–\(W'\) and Z–\(Z'\) mixing angles is exactly the cosine of the Weinberg angle, implying that number of parameters is reduced by 1. Signals of new physics from decays of new heavy fermions and Higgs bosons at LHC and constraints of their masses are also discussed.     

Discriminating neutrino mass models using type-II see-saw formula

An attempt has been made to discriminate theoretically the three possible patterns of neutrino mass models,viz., degenerate, inverted hierarchical and normal hierachical models, within the framework of Type-II see-saw formula. From detailed numerical analysis we are able to arrive at a conclusion that the inverted hierarchical model with the same CP phase (referred to as Type [IIA]), appears to be most favourable to survive in nature (and hence most stable), with the normal hierarchical model (Type [III]) and inverted hierarchical model with opposite CP phase (Type [IIB]), follow next. The degenerate models (Types [IA,IB,IC]) are found to be most unstable. The neutrino mass matrices which are obtained using the usual canonical see-saw formula (Type I), and which also give almost good predictions of neutrino masses and mixings consistent with the latest neutrino oscillation data, are re-examined in the presence of the left-handed Higgs triplet within the framework of non-canonical see-saw formula (Type II). We then estimate a parameter (the so-called discriminator) which may represent the minimum degree of suppression of the extra term arising from the presence of left-handed Higgs triplet, so as to restore the good predictions on neutrino masses and mixings already acquired in Type-I see-saw model. The neutrino mass model is said to be favourable and hence stable when its canonical see-saw term dominates over the non-canonical (perturbative) term, and this condition is used here as a criterion for discriminating neutrino mass models.     

Higgs-mediated tau-->3micro in the supersymmetric seesaw model

Recent observations of neutrino oscillations imply nonzero neutrino masses and lepton flavor violation (LFV), most economically explained by the seesaw mechanism. Within the context of supersymmetry, LFV among the neutrinos can be communicated to the sleptons and from there to the charged leptons. We show that LFV can appear in the couplings of the neutral Higgs bosons, an effect that is strongly enhanced at large tan(beta. We calculate the branching fraction for tau-->3micro and micro-->3e mediated by Higgs and find they can be as large as 10(-7) and 5x10(-14), respectively. These modes, along with tau-->mugamma and mu-->egamma, can provide key insights into the neutrino mass matrix.     

CKM pattern from localized generations in extra dimension

We revisit the issue of the quark masses and mixing angles in the framework of large extra dimension. We consider three identical standard model families resulting from higher-dimensional fields localized on different branes embedded in a large extra dimension. Furthermore we use a decaying profile in the bulk different form previous works. With the Higgs field also localized on a different brane, the hierarchy of masses between the families results from their different positions in the extra space. When the left-handed doublet and the right-handed singlets are localized with different couplings on the branes, we found a set of brane locations in one extra dimension which leads to the correct quark masses and mixing angles with the sufficient strength of CP-violation. We see that the decaying profile of the Higgs field plays a crucial role for producing the hierarchies in a rather natural way.     

Neutrino masses and oscillations in SU(5)

The masslessness of neutrinos and B - L conservation are not fundamental in SU(5), but “accidental” reflexions of the choice of a simple Higgs system. We argue that a low energy effective two-fermion interaction with two 5's of Higgs field can violate B - L at a very low level and generate neutrino masses of order 10⁻⁵ eV. These may cause oscillations detectable in solar neutrino experiments.     

Radiative seesaw mechanism and degenerate neutrinos

The radiative seesaw mechanism of Witten generates the right-handed neutrino masses in SO(10) with the spinorial 16(H) Higgs field. We study here analytically the 2nd and 3rd generations for the minimal Yukawa structure containing and Higgs representations. In the approximation of small 2nd generation masses and gauge loop domination we find the following results: (1) beta-tau unification, (2) natural coexistence between large theta(l) and small theta(q), and (3) degenerate neutrinos.     

Probing the Majorana nature of TeV-scale radiative seesaw models at collider experiments

A general feature of TeV-scale radiative seesaw models, in which tiny neutrino masses are generated via loop corrections, is an extended scalar (Higgs) sector. Another feature is the Majorana nature; e.g., introducing right-handed neutrinos with TeV-scale Majorana masses under the discrete symmetry, or otherwise introducing some lepton number violating interactions in the scalar sector. We study phenomenological aspects of these models at collider experiments. We find that, while properties of the extended Higgs sector of these models can be explored to some extent, the Majorana nature of the models can also be tested directly at the International Linear Collider via the electron–positron and electron–electron collision experiments.     

TeV-scale seesaw from a multi-Higgs model

We suggest new simple model of generating tiny neutrino masses through a TeV-scale seesaw mechanism without requiring tiny Yukawa couplings. This model is a simple extension of the standard model by introducing extra one Higgs singlet, and one Higgs doublet with a tiny vacuum expectation value. Experimental constraints, electroweak precision data and no large flavor changing neutral currents, are satisfied since the extra doublet only has a Yukawa interaction with lepton doublets and right-handed neutrinos, and their masses are heavy of order a TeV-scale. Since active light neutrinos are Majorana particles, this model predicts a neutrinoless double beta decay.     

Majorana neutrinos from inverse seesaw in warped extra dimension

We propose the inverse seesaw mechanism as a way to understand small Majorana masses for neutrinos in warped extra dimension models with seesaw scale in the TeV range. The ultra-small lepton number violation needed in implementing inverse seesaw mechanism in 4D models is explained in this model as a consequence of lepton number breaking occurring on the Planck brane. We construct realistic models based on this idea that fit observed neutrino oscillation data for both normal and inverted mass patterns. We compute the corrections to light neutrino masses from the Kaluza-Klein modes and show that they are small in the parameter range of interest. Another feature of the model is that the absence of global parity anomaly implies the existence of at least one light sterile neutrino with sterile and active neutrino mixing in the range suggested by the LSND and MiniBooNE observations.     

Neutrino mass and new light gauge boson in superstring models

The proposal that the neutrino owes the smallness of its mass to the spontaneous breaking of R parity in superstring models with an additional gauge boson coupled to the right-handed neutrino is analysed. The right-handed neutrino can not in general decouple from the low-energy theory in models with supersymmetry at the TeV scale and which possess the light Higgs doublets necessary for generating fermion masses. Experimental limits on neutrino mass then imply an upper limit on the new gauge boson mass m_Zr ⪅ 220 GeV.     

Gauge and Yukawa mediated supersymmetry breaking in the triplet seesaw scenario

We propose a novel supersymmetric unified scenario of the triplet seesaw mechanism where the exchange of the heavy triplets generates both neutrino masses and soft supersymmetry breaking terms. Our framework is very predictive since it relates neutrino mass parameters, lepton-flavor-violation in the slepton sector, sparticle and Higgs spectra, and electroweak symmetry breakdown. The phenomenological viability and experimental signatures in lepton flavor-violating processes are discussed.