14700928
Vacuum oscillation solution to the solar neutrino problem in standard and nonstandard pictures.
The neutrino long wavelength (just-so) oscillation is reexamined as a solution to the solar neutrino problem. We consider the just-so scenario in various cases: in the framework of the solar models with a relaxed prediction of the boron neutrino flux, as well as in the presence of the nonstandard weak range interactions between neutrino and matter constituents. We show that the fit of the experimental data in the just-so scenario is not very good for any reasonable value of the {sup 8}B neutrino flux, but it substantially improves if the nonstandard {tau}-neutrino--electron interaction is included. These new interactions could also remove the conflict of the just-so picture with the shape of the SN 1987A neutrino spectrum. Special attention is devoted to the potential of the future real-time solar neutrino detectors such as Super-Kamiokande, SNO, and BOREXINO, which could provide the model-independent tests for the just-so scenario. In particular, these imply a specific deformation of the original solar neutrino energy spectra and time variation of the intermediate energy monochromatic neutrino ({sup 7}Be and pep) signals.
17698502
Neutrino magnetic moment and solar neutrino experiments
Abstract We have studied the effect of a non-vanishing neutrino magnetic moment ( μ ν ) on the ν x (x = e , μ , π ) elastic scattering off electrons for the Super-Kamiokande detector. The bounds on the μ ν we have obtained are comparable to that extracted from laboratory experiments. Furthermore, we outline the potential of the Borexino experiment which may be sensitive to neutrino magnetic moments ⪅ 10 −10 μ B . In our analysis we have considered both cases of Majorana and Dirac neutrinos.
14098722
Predictive Grand Unified Textures for Quark and Neutrino Masses and Mixings
Abstract We propose new textures for the fermion Yukawa matrices which are generalizations of the so-called Stech ansatz. We discuss how these textures can be realized in supersymmetric grand unified models with horizontal symmetry SU(3) H among the fermion generations. In this framework the mass and mixing hierarchy of fermions (including neutrinos) can emerge in a natural way. We emphasize the central role played by the SU(3) H adjoint Higgs field which reduces SU(3) H to U(2) H at the GUT scale. A complete SO(10)×SU(3) H model is presented in which the desired Yukawa textures can be obtained by symmetry reasons. The phenomenological implications of these textures are thoroughly investigated. Among various realistic possibilities for the Clebsch factors between the quark and lepton entries, we find three different solutions which provide excellent fits of the quark masses and CKM mixing angles. Interestingly, all these solutions predict the correct amount of CP violation via the CKM mechanism, and, in addition, lead to an appealing pattern of the neutrino masses and mixing angles. In particular, they all predict nearly maximal 23 mixing and small 12 mixing in the lepton sector, respectively, in the range needed for the explanation of the atmospheric and solar neutrino anomaly.
17937629
Limits on the non-standard interactions of neutrinos from e+e− colliders
Abstract We provide an effective Lagrangian analysis of contact non-standard interactions of neutrinos with electrons, which can be effectively mediated by extra particles, and examine the associated experimental limits. At present, such interactions are strongly constrained only for ν μ : the bounds are loose for ν e and absent for ν τ . We emphasize the unique role played by the reaction e + e − →ν ν γ in providing direct constraints on such non-standard interactions.
14842705
'Just so' oscillation: As just as MSW?
Abstract The long wavelength (just-so) neutrino oscillation is reconsidered as a solution to the solar neutrino problem, in the context of various solar models with different original fluxes of relevant components (boron, beryllium neutrinos etc.). In the light of the presently updated results of the four solar neutrino experiments, the data fit in this scenario substantially improves and becomes almost as good as in the MSW scenario. Surprising result of our analysis is that the best data fit is achieved when the oscillation occurs only between the two neutrino states: switching on the oscillation into third neutrino increases the χX 2 value. Namely, by considering the vacuum oscillation scenario in the three-neutrino system (4 parameters), we find out that the minimum of χX 2 is always achieved in the two parameter subspace in which actually only two neutrino states oscillate. The possible implications of this observation for the neutrino mass matrix textures are also discussed.
7635713
Phenomenology of the triplet seesaw mechanism with gauge and Yukawa mediation of SUSY breaking
Abstract We thoroughly discuss a new supersymmetric grand unified scenario of the triplet seesaw mechanism where the exchange of heavy SU ( 2 ) W triplet states generates both neutrino masses and soft supersymmetry breaking terms. This framework, recently proposed by us in a previous work, is highly predictive since it contains only three free parameters connecting low-energy neutrino parameters, lepton and quark flavour violation, sparticle and Higgs boson spectra and electroweak symmetry breakdown. These three parameters are the triplet mass M T , the effective supersymmetry breaking scale B T and a coupling constant λ . We perform a complete analysis of the parameter space taking into account the present experimental constraints and considering different types of neutrino spectrum. A special emphasis is given to the particular features of the sparticle and Higgs spectra and to the model independent predictions obtained for the processes μ → e X , μ → e conversion in nuclei, τ → e Y and τ → μ Y ( X = γ , e e , Y = γ , e e , μ μ ). In the appendices, we present some technical aspects relevant for our analysis.
7861050
Topological susceptibility and string tension in the lattice CPN-1 models.
In the lattice CP{sup {ital N}{minus}1} models we study the problems related to the measure of observables closely connected to the dynamically generated gauge field, such as the topological susceptibility and the string tension. We perform numerical simulations at {ital N}=4 and {ital N}=10. In order to test the universality, we adopt two different lattice formulations. Scaling and universality tests lead to the conclusion that at {ital N}=10 the geometrical approach gives a good definition of lattice topological susceptibility. On the other hand, {ital N}=4 proves not to be large enough to suppress the unphysical configurations, called dislocations, contributing to {chi}{sub {ital t}}{sup {ital g}} (at least up to {xi}{congruent}30 in our lattice formulations). We obtain other determinations of {chi}{sub {ital t}} by the field-theoretical method, which relies on a local definition of the lattice topological charge density, and the cooling method. They give quite consistent results, showing scaling and universality. The large-{ital N} expansion predicts an exponential area law behavior for sufficiently large Wilson loops, which implies confinement, due to the dynamical matter fields and absence of the screening phenomenon. We determine the string tension, without finding evidence of screening effects.
15179667
Rigorous treatment of the lattice renormalization problem of fB.
The B-meson decay constant can be measured on the lattice using a 1/m b expansion. To relate the physical quantity to Monte Carlo data one has to know the renormalizaton coefficient Z between the lattice operators and their continuum counterparts. We come back to this computation to resolve discrepancies found in previous calculations. We define and discuss in detail the renormalization procedure that allows the (perturbative) computation of Z. Comparing the one-loop calculations in the effective Lagrangian approach with the direct two-loop calculation of the two-point B-meson correlator in the limit of large b-quark mass, we prove that the two schemes give consistent results to order α s
42450422
Strong-coupling analysis of two-dimensional O(N) sigma models with N >= 3 on square, triangular, and honeycomb lattices.
Recently generated long strong-coupling series for the two-point Green{close_quote}s functions of asymptotically free O({ital N}) lattice {sigma} models are analyzed, focusing on the evaluation of dimensionless renormalization-group-invariant ratios of physical quantities and applying resummation techniques to series in the inverse temperature {beta} and in the energy {ital E}. Square, triangular, and honeycomb lattices are considered, as a test of universality and in order to estimate systematic errors. Large-{ital N} solutions are carefully studied in order to establish benchmarks for series coefficients and resummations. Scaling and universality are verified. All invariant ratios related to the large-distance properties of the two-point functions vary monotonically with {ital N}, departing from their large-{ital N} values only by a few per mille even down to {ital N}=3. {copyright} {ital 1996 The American Physical Society.}
32978298
Strong-coupling analysis of two-dimensional O(N) sigma models with N <~ 2 on square, triangular, and honeycomb lattices.
The critical behavior of two-dimensional (2D) O({ital N}) {sigma} models with {ital N}{le}2 on square, triangular, and honeycomb lattices is investigated by an analysis of the strong-coupling expansion of the two-point fundamental Green{close_quote}s function {ital G}({ital x}), calculated up to 21st order on the square lattice, 15th order on the triangular lattice, and 30th order on the honeycomb lattice. For {ital N}{lt}2 the critical behavior is of power-law type, and the exponents {gamma} and {nu} extracted from our strong-coupling analysis confirm exact results derived assuming universality with solvable solid-on-solid models. At {ital N}=2, i.e., for the 2D {ital XY} model, the results from all lattices considered are consistent with the Kosterlitz-Thouless exponential approach to criticality, characterized by an exponent {sigma}=1/2, and with universality. The value {sigma}=1/2 is confirmed within an uncertainty of few percent. The prediction {eta}=1/4 is also roughly verified. For various values of {ital N}{le}2, we determine some ratios of amplitudes concerning the two-point function {ital G}({ital x}) in the critical limit of the symmetric phase. This analysis shows that the low-momentum behavior of {ital G}({ital x}) in the critical region is essentially Gaussian at all values of {ital N}{le}2. Exact results for the long-distance behavior of {italmore » G}({ital x}) when {ital N}=1 (Ising model in the strong-coupling phase) confirm this statement. {copyright} {ital 1996 The American Physical Society.}« less
32382258
Two-dimensional SU(N) x SU(N) chiral models on the lattice. II. The Green's function.
Analytical and numerical methods are applied to principal chiral models on a twodimensional lattice and their predictions are tested and compared. New techniques for the strong coupling expansion of SU(N) models are developed and applied to the evaluation of the two-point correlation function. The momentum-space lattice propagator is constructed with precision O ( β10 ) and an evaluation of the correlation length is obtained for several different definitions. Three-loop weak coupling contributions to the internal energy and to the lattice β and γ functions are evaluated for all N , and the effect of adopting the “energy” definition of temperature is computed with the same precision. Renormalizationgroup improved predictions for the two-point Green’s function in the weak coupling ( continuum ) regime are obtained and successfully compared with Monte Carlo data. We find that strong coupling is predictive up to a point where asymptotic scaling in the energy scheme is observed. Continuum physics is insensitive to the effects of the large N phase transition occurring in the lattice model. Universality in N is already well established for N ∼ 10 and the large N physics is well described by a “hadronization” picture.