We propose a new seesaw mechanism for neutrino masses within a class of supersymmetric SO(10) mod... more We propose a new seesaw mechanism for neutrino masses within a class of supersymmetric SO(10) models with broken D parity. It is shown that in such scenarios the B-L scale can be as low as TeV without generating inconsistencies with gauge coupling unification nor with the required magnitude of the light neutrino masses. This leads to a possibly light new neutral gauge boson as well as relatively light quasi-Dirac heavy leptons. These particles could be at the TeV scale and mediate lepton flavor and CP violating processes at appreciable levels.
We re-analyse the non-standard interaction (NSI) solutions to the solar neutrino problem in the l... more We re-analyse the non-standard interaction (NSI) solutions to the solar neutrino problem in the light of the latest solar as well as atmospheric neutrino data. The latter require oscillations (OSC), while the former do not. Within such a threeneutrino framework the solar and atmospheric neutrino sectors are connected not only by the neutrino mixing angle ϑ 13 constrained by reactor and atmospheric data, but also by the flavour-changing (FC) and non-universal (NU) parameters accounting for the solar data. Since the NSI solution is energy-independent the spectrum is undistorted, so that the global analysis observables are the solar neutrino rates in all experiments as well as the Super-Kamiokande day-night measurements. We find that the NSI description of solar data is slightly better than that of the OSC solution and that the allowed NSI regions are determined mainly by the rate analysis. By using a few simplified ansätze for the NSI interactions we explicitly demonstrate that the NSI values indicated by the solar data analysis are fully acceptable also for the atmospheric data. In the appendix we present an updated analysis combining the latest data from all solar neutrino experiments with the first results from KamLAND. We show that, although NSI still gives an excellent description of the solar data, the inclusion of KamLAND excludes at more than 3σ the NSI hypothesis as a solution to the solar neutrino problem.
We reanalyze the contributions to neutrinoless double beta (ββ 0ν) decay from supersymmetry with ... more We reanalyze the contributions to neutrinoless double beta (ββ 0ν) decay from supersymmetry with explicit breaking of R-parity. Although we keep both bilinear and trilinear terms, our emphasis is put on bilinear R-parity breaking terms, because these mimic more closely the models where the breaking of R-parity is spontaneous. Comparing the relevant Feynman diagrams we conclude that the usual mass mechanism of double beta decay is the dominant one. From the non-observation of ββ 0ν decay we set limits on the bilinear R-parity breaking parameters of typically a (few) 100 keV. Despite such stringent bounds, we stress that the magnitude of R-parity violating phenomena that can be expected at accelerator experiments can be very large, since they involve mainly the third generation, while ββ 0ν decay constrains only the first generation couplings.
We consider active-sterile neutrino conversions in the early universe hot plasma in the presence ... more We consider active-sterile neutrino conversions in the early universe hot plasma in the presence of a random magnetic field generated at the electroweak phase transition. Within a random field domain the magnetization asymmetty of the lepton antilepton plasma produced by a uniform constant magnetic field is huge in contrast to their small density asymmetry, leading to a drastic change in the active-sterile conversion rates. Assuming that the random field provides the seed for the galactic field one can estimate the restrictions from primottlial nucleosynthesis. Requiring that the extra sterile neutrino does not enter in equilibrium with the active ones before nucleosynthesis we find limits of the oscillation parameters which are stronger than in the isotropic case.
We extend the minimal supersymmetric standard model with bilinear R-parity violation to include a... more We extend the minimal supersymmetric standard model with bilinear R-parity violation to include a pair of Higgs triplet superfields. The neutral components of the Higgs triplets develop small vacuum expectation values (VEVs) quadratic in the bilinear R-parity breaking parameters. In this scheme the atmospheric neutrino mass scale arises from bilinear R-parity breaking while for reasonable values of parameters the solar neutrino mass scale is generated from the small Higgs triplet VEVs. We calculate neutrino masses and mixing angles in this model and show how the model can be tested at future colliders. The branching ratios of the doubly charged triplet decays are related to the solar neutrino angle via a simple formula.
Digital Object Identifier (DOI) 10.1140/epjc/s2005-02460-1 Eur. Phys. J. C 46, 43–60 (2006) ... T... more Digital Object Identifier (DOI) 10.1140/epjc/s2005-02460-1 Eur. Phys. J. C 46, 43–60 (2006) ... T HE E UROPEAN P HYSICAL J OURNAL C ... Supersymmetry parameter analysis: SPA convention and project ... JA Aguilar-Saavedra 1 , A. Ali 2 , BC Allanach 3 , R. Arnowitt 4 , ...
We have reconsidered the atmospheric neutrino anomaly in light of the laetst data from Super-Kami... more We have reconsidered the atmospheric neutrino anomaly in light of the laetst data from Super-Kamiokande contained events and from Super-Kamiokande and MACRO up-going muons. We have reanalysed the proposed solution to the atmospheric neutrino anomaly in terms of non-standard neutrino-matter interactions (NSI) as well as the standard nu_mu -> nu_tau oscillations (OSC). Our statistical analysis shows that a pure NSI mechanism is now ruled out at 99%, while the standard nu_mu -> nu_tau OSC mechanism provides a quite remarkably good description of the anomaly. We therefore study an extended mechanism of neutrino propagation which combines both oscillation and non-standard neutrino-matter interactions, in order to derive limits on flavour-changing (FC) and non-universal (NU) neutrino interactions. We obtain that the off-diagonal flavour-changing neutrino parameter epsilon and the diagonal non-universality neutrino parameter epsilon' are confined to -0.03 < epsilon < 0.02 and |epsilon'| < 0.05 at 99.73% CL. These limits are model independent and they are obtained from pure neutrino-physics processes. The stability of the neutrino oscillation solution to the atmospheric neutrino anomaly against the presence of non-standard neutrino interactions establishes the robustness of the near-maximal atmospheric mixing and massive-neutrino hypothesis. The best agreement with the data is obtained for Delta_m^2 = 2.3*10^{-3} eV^2, sin^2(2*theta) = 1, epsilon = 6.7*10^{-3} and epsilon' = 1.1*10^{-3}, although the chi^2 function is quite flat in the epsilon and epsilon' directions for epsilon, epsilon' -> 0.
We study a left-right symmetric model which contains only elementary gauge boson and fermion fiel... more We study a left-right symmetric model which contains only elementary gauge boson and fermion fields and no scalars. The phenomenologically required symmetry breaking emerges dynamically leading to a composite Higgs sector with a renormalizable effective Lagrangian. We discuss the pattern of symmetry breaking and phenomenological consequences of this scenario. It is shown that a viable top quark mass can be achieved for the ratio of the VEV's of the bidoublet tanβ≡κ/κ'~=1.3-4. For a theoretically plausible choice of the parameters the right-handed scale can be as low as ~20 TeV; in this case one expects several intermediate and low-scale scalars in addition to the standard model Higgs boson. These may lead to observable lepton flavor violation effects including μ-->eγ decay with the rate close to its present experimental upper bound.
We review the present status of global analyses of neutrino oscillations, taking into account the... more We review the present status of global analyses of neutrino oscillations, taking into account the most recent neutrino data including the latest KamLAND and K2K updates presented at Neutrino2004, as well as state-of-the-art solar and atmospheric neutrino flux calculations. We give the two-neutrino solar + KamLAND results, and the two-neutrino atmospheric + K2K oscillation regions, discussing in each case the robustness of the oscillation interpretation against departures from the Standard Solar Model and the possible existence of non-standard neutrino physics. Furthermore, we give the best fit values and allowed ranges of the three-flavour oscillation parameters from the current worlds' global neutrino data sample and discuss in detail the status of the small parameters α ≡ ∆m 2 sol /∆m 2 atm as well as sin 2 θ 13 , which characterize the strength of CP violating effects in neutrino oscillations. We also update the degree of rejection of four-neutrino interpretations of the LSND evidence in view of the most recent developments.
We determine the restrictions imposed by primordial nucleosynthesis upon a heavy tau neutrino, in... more We determine the restrictions imposed by primordial nucleosynthesis upon a heavy tau neutrino, in the presence of ντ annihilations into majorons, as expected in a wide class of particle physics models of neutrino mass. We determine the equivalent number of light neutrino species Neq as a function of mντ and the ντ-ντ-majoron coupling g. We show that for theoretically plausible g values >~ 10-4 present nucleosynthesis observations can not rule out ντ masses in the MeV range. Moreover, these models give Neq <= 3 in the ντ mass region 1-10 MeV, for very reasonable values of g >= 3 × 10-4. The evasion of the cosmological limits brings new interest to the improvement of the present laboratory limit on the ντ mass which can be achieved at a tau-charm factory.
Discrete R parity (RP) is usually imposed in the minimal supersymmetric standard model (MSSM) as ... more Discrete R parity (RP) is usually imposed in the minimal supersymmetric standard model (MSSM) as an unbroken symmetry. In this paper we study very weak gravitationally induced R-parity breaking, described by nonrenormalizable terms inversely proportional to the Planck mass. The lightest supersymmetric particle, a neutralino, is unstable but its lifetime exceeds the age of the Universe and thus it can serve as a dark matter (DM) particle. The neutralino lifetime is severely constrained from below due to the production of positrons and antiprotons, diffuse gamma radiation, etc. The violation of RP generated gravitationally by dimension-five operators in the MSSM is shown to violate these constraints if they are suppressed only by the Planck scale. A general theoretical analysis of gravitationally induced RP violation is performed and two plausible and astrophysically consistent scenarios for achieving the required suppression are identified and discussed.
The problem of finding a suitable parametrization for a nontrivial lepton mixing matrix is consid... more The problem of finding a suitable parametrization for a nontrivial lepton mixing matrix is considered in the framework of the "sequential" Weinberg-Salam theory. It is noted that in the case of n lepton generations there are in fact n+1 different theories, corresponding to different numbers m of right-handed neutrino fields present in the Lagrangian. These (n,m) models conserve CP for leptonic couplings naturally only for m=0 or 1 when n>=3. These models would seem to be useful as self-consistent approximations for reducing the number of parameters in the experimental analysis of lepton mixing matrices.
It is shown that gauge theories give contributions to neutrinoless double-β decay [(ββ)0ν] which ... more It is shown that gauge theories give contributions to neutrinoless double-β decay [(ββ)0ν] which are not covered by the standard parametrizations. While probably small, their existence raises the question of whether the observation of (ββ)0ν implies the existence of a Majorana mass term for the neutrino. For a "natural" gauge theory we argue that this is indeed the case.
We propose a new seesaw mechanism for neutrino masses within a class of supersymmetric SO(10) mod... more We propose a new seesaw mechanism for neutrino masses within a class of supersymmetric SO(10) models with broken D parity. It is shown that in such scenarios the B-L scale can be as low as TeV without generating inconsistencies with gauge coupling unification nor with the required magnitude of the light neutrino masses. This leads to a possibly light new neutral gauge boson as well as relatively light quasi-Dirac heavy leptons. These particles could be at the TeV scale and mediate lepton flavor and CP violating processes at appreciable levels.
We re-analyse the non-standard interaction (NSI) solutions to the solar neutrino problem in the l... more We re-analyse the non-standard interaction (NSI) solutions to the solar neutrino problem in the light of the latest solar as well as atmospheric neutrino data. The latter require oscillations (OSC), while the former do not. Within such a threeneutrino framework the solar and atmospheric neutrino sectors are connected not only by the neutrino mixing angle ϑ 13 constrained by reactor and atmospheric data, but also by the flavour-changing (FC) and non-universal (NU) parameters accounting for the solar data. Since the NSI solution is energy-independent the spectrum is undistorted, so that the global analysis observables are the solar neutrino rates in all experiments as well as the Super-Kamiokande day-night measurements. We find that the NSI description of solar data is slightly better than that of the OSC solution and that the allowed NSI regions are determined mainly by the rate analysis. By using a few simplified ansätze for the NSI interactions we explicitly demonstrate that the NSI values indicated by the solar data analysis are fully acceptable also for the atmospheric data. In the appendix we present an updated analysis combining the latest data from all solar neutrino experiments with the first results from KamLAND. We show that, although NSI still gives an excellent description of the solar data, the inclusion of KamLAND excludes at more than 3σ the NSI hypothesis as a solution to the solar neutrino problem.
We reanalyze the contributions to neutrinoless double beta (ββ 0ν) decay from supersymmetry with ... more We reanalyze the contributions to neutrinoless double beta (ββ 0ν) decay from supersymmetry with explicit breaking of R-parity. Although we keep both bilinear and trilinear terms, our emphasis is put on bilinear R-parity breaking terms, because these mimic more closely the models where the breaking of R-parity is spontaneous. Comparing the relevant Feynman diagrams we conclude that the usual mass mechanism of double beta decay is the dominant one. From the non-observation of ββ 0ν decay we set limits on the bilinear R-parity breaking parameters of typically a (few) 100 keV. Despite such stringent bounds, we stress that the magnitude of R-parity violating phenomena that can be expected at accelerator experiments can be very large, since they involve mainly the third generation, while ββ 0ν decay constrains only the first generation couplings.
We consider active-sterile neutrino conversions in the early universe hot plasma in the presence ... more We consider active-sterile neutrino conversions in the early universe hot plasma in the presence of a random magnetic field generated at the electroweak phase transition. Within a random field domain the magnetization asymmetty of the lepton antilepton plasma produced by a uniform constant magnetic field is huge in contrast to their small density asymmetry, leading to a drastic change in the active-sterile conversion rates. Assuming that the random field provides the seed for the galactic field one can estimate the restrictions from primottlial nucleosynthesis. Requiring that the extra sterile neutrino does not enter in equilibrium with the active ones before nucleosynthesis we find limits of the oscillation parameters which are stronger than in the isotropic case.
We extend the minimal supersymmetric standard model with bilinear R-parity violation to include a... more We extend the minimal supersymmetric standard model with bilinear R-parity violation to include a pair of Higgs triplet superfields. The neutral components of the Higgs triplets develop small vacuum expectation values (VEVs) quadratic in the bilinear R-parity breaking parameters. In this scheme the atmospheric neutrino mass scale arises from bilinear R-parity breaking while for reasonable values of parameters the solar neutrino mass scale is generated from the small Higgs triplet VEVs. We calculate neutrino masses and mixing angles in this model and show how the model can be tested at future colliders. The branching ratios of the doubly charged triplet decays are related to the solar neutrino angle via a simple formula.
Digital Object Identifier (DOI) 10.1140/epjc/s2005-02460-1 Eur. Phys. J. C 46, 43–60 (2006) ... T... more Digital Object Identifier (DOI) 10.1140/epjc/s2005-02460-1 Eur. Phys. J. C 46, 43–60 (2006) ... T HE E UROPEAN P HYSICAL J OURNAL C ... Supersymmetry parameter analysis: SPA convention and project ... JA Aguilar-Saavedra 1 , A. Ali 2 , BC Allanach 3 , R. Arnowitt 4 , ...
We have reconsidered the atmospheric neutrino anomaly in light of the laetst data from Super-Kami... more We have reconsidered the atmospheric neutrino anomaly in light of the laetst data from Super-Kamiokande contained events and from Super-Kamiokande and MACRO up-going muons. We have reanalysed the proposed solution to the atmospheric neutrino anomaly in terms of non-standard neutrino-matter interactions (NSI) as well as the standard nu_mu -> nu_tau oscillations (OSC). Our statistical analysis shows that a pure NSI mechanism is now ruled out at 99%, while the standard nu_mu -> nu_tau OSC mechanism provides a quite remarkably good description of the anomaly. We therefore study an extended mechanism of neutrino propagation which combines both oscillation and non-standard neutrino-matter interactions, in order to derive limits on flavour-changing (FC) and non-universal (NU) neutrino interactions. We obtain that the off-diagonal flavour-changing neutrino parameter epsilon and the diagonal non-universality neutrino parameter epsilon' are confined to -0.03 < epsilon < 0.02 and |epsilon'| < 0.05 at 99.73% CL. These limits are model independent and they are obtained from pure neutrino-physics processes. The stability of the neutrino oscillation solution to the atmospheric neutrino anomaly against the presence of non-standard neutrino interactions establishes the robustness of the near-maximal atmospheric mixing and massive-neutrino hypothesis. The best agreement with the data is obtained for Delta_m^2 = 2.3*10^{-3} eV^2, sin^2(2*theta) = 1, epsilon = 6.7*10^{-3} and epsilon' = 1.1*10^{-3}, although the chi^2 function is quite flat in the epsilon and epsilon' directions for epsilon, epsilon' -> 0.
We study a left-right symmetric model which contains only elementary gauge boson and fermion fiel... more We study a left-right symmetric model which contains only elementary gauge boson and fermion fields and no scalars. The phenomenologically required symmetry breaking emerges dynamically leading to a composite Higgs sector with a renormalizable effective Lagrangian. We discuss the pattern of symmetry breaking and phenomenological consequences of this scenario. It is shown that a viable top quark mass can be achieved for the ratio of the VEV's of the bidoublet tanβ≡κ/κ'~=1.3-4. For a theoretically plausible choice of the parameters the right-handed scale can be as low as ~20 TeV; in this case one expects several intermediate and low-scale scalars in addition to the standard model Higgs boson. These may lead to observable lepton flavor violation effects including μ-->eγ decay with the rate close to its present experimental upper bound.
We review the present status of global analyses of neutrino oscillations, taking into account the... more We review the present status of global analyses of neutrino oscillations, taking into account the most recent neutrino data including the latest KamLAND and K2K updates presented at Neutrino2004, as well as state-of-the-art solar and atmospheric neutrino flux calculations. We give the two-neutrino solar + KamLAND results, and the two-neutrino atmospheric + K2K oscillation regions, discussing in each case the robustness of the oscillation interpretation against departures from the Standard Solar Model and the possible existence of non-standard neutrino physics. Furthermore, we give the best fit values and allowed ranges of the three-flavour oscillation parameters from the current worlds' global neutrino data sample and discuss in detail the status of the small parameters α ≡ ∆m 2 sol /∆m 2 atm as well as sin 2 θ 13 , which characterize the strength of CP violating effects in neutrino oscillations. We also update the degree of rejection of four-neutrino interpretations of the LSND evidence in view of the most recent developments.
We determine the restrictions imposed by primordial nucleosynthesis upon a heavy tau neutrino, in... more We determine the restrictions imposed by primordial nucleosynthesis upon a heavy tau neutrino, in the presence of ντ annihilations into majorons, as expected in a wide class of particle physics models of neutrino mass. We determine the equivalent number of light neutrino species Neq as a function of mντ and the ντ-ντ-majoron coupling g. We show that for theoretically plausible g values >~ 10-4 present nucleosynthesis observations can not rule out ντ masses in the MeV range. Moreover, these models give Neq <= 3 in the ντ mass region 1-10 MeV, for very reasonable values of g >= 3 × 10-4. The evasion of the cosmological limits brings new interest to the improvement of the present laboratory limit on the ντ mass which can be achieved at a tau-charm factory.
Discrete R parity (RP) is usually imposed in the minimal supersymmetric standard model (MSSM) as ... more Discrete R parity (RP) is usually imposed in the minimal supersymmetric standard model (MSSM) as an unbroken symmetry. In this paper we study very weak gravitationally induced R-parity breaking, described by nonrenormalizable terms inversely proportional to the Planck mass. The lightest supersymmetric particle, a neutralino, is unstable but its lifetime exceeds the age of the Universe and thus it can serve as a dark matter (DM) particle. The neutralino lifetime is severely constrained from below due to the production of positrons and antiprotons, diffuse gamma radiation, etc. The violation of RP generated gravitationally by dimension-five operators in the MSSM is shown to violate these constraints if they are suppressed only by the Planck scale. A general theoretical analysis of gravitationally induced RP violation is performed and two plausible and astrophysically consistent scenarios for achieving the required suppression are identified and discussed.
The problem of finding a suitable parametrization for a nontrivial lepton mixing matrix is consid... more The problem of finding a suitable parametrization for a nontrivial lepton mixing matrix is considered in the framework of the "sequential" Weinberg-Salam theory. It is noted that in the case of n lepton generations there are in fact n+1 different theories, corresponding to different numbers m of right-handed neutrino fields present in the Lagrangian. These (n,m) models conserve CP for leptonic couplings naturally only for m=0 or 1 when n>=3. These models would seem to be useful as self-consistent approximations for reducing the number of parameters in the experimental analysis of lepton mixing matrices.
It is shown that gauge theories give contributions to neutrinoless double-β decay [(ββ)0ν] which ... more It is shown that gauge theories give contributions to neutrinoless double-β decay [(ββ)0ν] which are not covered by the standard parametrizations. While probably small, their existence raises the question of whether the observation of (ββ)0ν implies the existence of a Majorana mass term for the neutrino. For a "natural" gauge theory we argue that this is indeed the case.
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Papers by Jose Valle