We study extensions of supersymmetric models without R-parity which include an anomalous U (1) H horizontal symmetry. Bilinear R-parity violating terms induce a neutrino mass at tree level m tree ν ≈ (θ 2 ) δ eV where θ ≃ 0.22 is the U (1) H breaking parameter and δ is an integer number that depends on the horizontal charges of the leptons. For δ = 1 a unique self-consistent model arises in which i) all the superpotential trilinear R-parity violating couplings are forbidden by holomorphy; ii) m tree ν falls in the range suggested by the atmospheric neutrino problem; iii) radiative contributions to neutrino masses are strongly suppressed resulting in ∆m 2 solar ≈ few 10 −8 eV 2 which only allows for the LOW (or quasi-vacuum) solution to the solar neutrino problem; iv) the neutrino mixing angles are not suppressed by powers of θ and can naturally be large.
A non anomalous horizontal U (1)H gauge symmetry can be responsible for the fermion mass hierarchies of the minimal supersymmetric standard model. Imposing the consistency conditions for the absence of gauge anomalies yields the following results: i) unification of leptons and down-type quarks Yukawa couplings is allowed at most for two generations. ii) The µ term is necessarily somewhat below the supersymmetry breaking scale. iii) The determinant of the quark mass matrix vanishes, and there is no strong CP problem. iv) The superpotential has accidental B and L symmetries. The prediction mup = 0 allows for an unambiguous test of the model at low energy.PACS numbers: 11.30. Hv, 12.60.Jv, 12.15.Ff, 11.30.Fs One of the most successful ideas in modern particle physics is that of local gauge symmetries. A huge amount of data is beautifully explained in terms of the standard model (SM) gauge groupIdentifying this symmetry required a lot of experimental and theoretical efforts, since SU (2) L × U (1) Y is hidden and color is confined. Today we understand particle interactions but we do not have any deep clue in understanding other elementary particle properties, like fermion masses and mixing angles. The SM can only accommodate but not explain these data. Another puzzle is why CP is preserved by strong interactions to an accuracy < 10 −9 . One solution is to postulate that one quark is massless, but within the SM there are no good justifications for this. Adding supersymmetry does not provide us with any better understanding of these issues. In contrast, it adds new problems. A bilinear coupling for the down-type and up-type Higgs superfields µφ d φ u is allowed both by supersymmetry and by the gauge symmetry. However, phenomenology requires that µ should be close to the scale where these symmetries are broken. With supersymmetry, several operators that violate baryon (B) and lepton (L) numbers can appear. However, none of the effects expected from these operators has ever been observed. Since a few of them can induce fast proton decay, they must be very suppressed or absent.Relying on the gauge principle, in this paper we attempt to gain insight into these problems. We extend minimally G SM with a non anomalous horizontal Abelian U (1) H factor. An unambiguous prediction of the non anomalous U (1) H is a massless up-quark. This represents the crucial low energy test of our framework. Shall future lattice computations rule out m up = 0 [1], the whole idea will have to be abandoned.To explain the fermion mass pattern we follow the approach originally suggested by Froggatt and Nielsen (FG) [2]. U (1) H forbids most of the fermion Yukawa couplings. The symmetry is spontaneously broken by the vacuum expectation value (VEV) of a SM singlet field S, giving rise to a set of effective operators that couple the SM fermions to the electroweak Higgs field. The hierarchy of fermion masses results from the dimensional hierarchy among the various higher order operators. This idea was recently reconsidered by several groups, bot...
We present a new supersymmetric version of the SU (3) ⊗ U (1) gauge model using a more economic content of particles. The model has a smaller set of free parameters than other possibilities considered before. The MSSM can be seen as an effective theory of this larger symmetry. We find that the upper bound of the ligthest CPeven Higgs boson can be moved up to 140 GeV.
Being strictly forbidden in the standard model, experimental detection of the lepton flavor violating decays B (B) → τ + µ − and b (b) → X τ + µ − would constitute an unmistakable indication of new physics. We study these decays in supersymmetric models without R-parity and without lepton number. In order to derive order of magnitude predictions for the branching ratios, we assume a horizontal U (1) symmetry with horizontal charges chosen to explain the magnitude of fermion masses and quark mixing angles. We find that the branching ratios for decays with a τ µ pair in the final state are not particularly suppressed with respect to the lepton flavor conserving channels. In general in these models. While in some cases the rates for final states τ + τ − can be up to one order of magnitude larger than the lepton flavor violating channel, due to better efficiencies for muon detection and to the absence of standard model contributions, decays into τ µ final states appear to be better suited to reveal this kind of new physics.
We study the scalar potential and the mass spectrum of the supersymmetric extension of a threefamily model based on the local gauge group SU (3)C ⊗ SU (3)L ⊗ U (1)X , with anomalies canceled among the three families in a nontrivial fashion. In this model the slepton multiplets play the role of the Higgs scalars and no Higgsinos are required, with the consequence that the sneutrino, the selectron and six other sleptons play the role of the Goldstone bosons of the theory. By introducing an Abelian anomaly-free discrete symmetry and aligning the vacuum in a convenient way, we get a consistent mass spectrum for the scalars and for the spin 1/2 quarks and charged leptons, where only the top and charm quarks and the tau lepton acquire tree level masses while the remaining ordinary charged fermions acquire radiative hierarchical masses.
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