New Higgs Signatures in Supersymmetry with Spontraneously Broken R Parity"
Higgs production from $Z$ decay in supersymmetry with spontaneous broken R parity proceeds mostly by the Bjorken process as in the standard model. However, the corresponding production rates can be weaker than in the standard model (SM), especially in the low mass region. This will substantially weaken the Higgs boson mass limits derived from LEP1. More strikingly, the main Higgs decay channel is "invisible", over most of the mass range accessible to LEP1, leading to events with large missing energy carried by majorons. This possibility should be taken into account in the planning of Higgs boson search strategies not only at LEP but also at high energy supercolliders.
Neutrino Physics at the Turn of the Millenium
Recent solar & atmospheric nu-data strongly indicate need for physics beyond the Standard Model. I review the ways of reconciling them in terms of 3-nu oscillations. Though not implied by data, bi-maximal nu-mixing models emerge as a possibility. SUSY with broken R-parity provides an attractive way to incorporate it, opening the possibility of testing nu-anomalies at high- energy colliders such as the LHC or at the upcoming long-baseline or nu- factory experiments. Reconciling, in addition, the LSND hint requires a fourth, light sterile neutrino, nus. The simplest are the most symmetric scenarios, in which 2 of the 4 neutrinos are maximally-mixed and lie at the LSND scale, while the oth…
Active-active and active-sterile neutrino oscillation solutions to the atmospheric neutrino anomaly
We perform a fit to the full data set corresponding to 33.3 kt-yr of data of the Super-Kamiokande experiment as well as to all other experiments in order to compare the two most likely solutions to the atmospheric neutrino anomaly in terms of oscillations in the $\nu_\mu \to \nu_\tau$ and $\nu_\mu \to \nu_s$ channels. Using state-of-the-art atmospheric neutrino fluxes we have determined the allowed regions of oscillation parameters for both channels. We find that the $\Delta m^2$ values for the active-sterile oscillations (both for positive and negative $\Delta m^2$) are higher than for the $\nu_\mu \to \nu_\tau$ case, and that the increased Super-Kamiokande sample slightly favours $\nu_\mu…
Standard and non-standard neutrino properties
I review the interpretation of solar and atmospheric neutrino data in terms neutrino oscillations and describe some ways to account for the required neutrino masses and mixing angles from first principles, both within top-down and bottom-up approaches. I also discuss non-oscillation phenomena such as nu-less double beta which may probe the absolute scale of neutrino mass, and also reveal its Majorana nature. I note that leptonic CP violation induced by ``Majorana'' phases drop from oscillations but play a role in the leptogenesis scenario for the baryon asymmetry of the Universe. Direct tests of leptonic CP violation in oscillation experiments, such as neutrino factories, will be a tough ch…
Solar neutrino oscillation parameters and the broken R parity majoron
Matter-enhanced neutrino-oscillation parameters can be probed in a variety of conventional experiments in supergravity models where the small neutrino mass arises from spontaneous R-parity violation. A combined analysis of astrophysical and laboratory limits tends to exclude regions of oscillation parameters where the high-energy neutrinos are adiabatically converted. This suggests the possibility of a large reduction in the pp and /sup 7/Be neutrino flux even for a mildly reduced /sup 8/B neutrino flux, thus stressing the importance of gallium experiments.
Neutrino masses: evidences and implications
I give an overview of the evidences for neutrino masses and mixing, the associated neutrino mass generation schemes, as well as the resulting implications in particle physics experiments and cosmology.
Bilinear R-parity violating SUSY: Neutrinoless double beta decay in the light of solar and atmospheric neutrino data
Neutrinoless double beta ($\znbb$) decay is considered within bilinear R-parity breaking supersymmetry, including the full one-loop corrections to the neutrino-neutralino mass matrix. Expected rates for $\znbb$ decay in this model are discussed in light of recent atmospheric and solar neutrino data. We conclude that (a) tree-level calculations for $\znbb$ decay within the bilinear model are not reliable in the range of parameters preferred by current solar and atmospheric neutrino problems. And (b) if the solar and atmospheric neutrino problems are to be solved within bilinear R-parity violating SUSY the expected rates for $\znbb$ decay are very low; the effective Majorana neutrino mass at …
Radiative neutrino mass in 331 scheme
We propose a new radiative mechanism for neutrino mass generation based on the 3-3-1 electroweak gauge group. Lepton number is a symmetry of the Yukawa sector but spontaneously broken in the gauge sector. As a result light Majorana masses arise from neutral gauge boson exchange at the one-loop level. In addition to the isosinglet neutrinos which may be produced at the LHC through the extended gauge boson "portals", the model contains new isosinglet quarks which can also lie at the TeV scale and provide a plethora of collider phenomena.
Accidental stability of dark matter
We propose that dark matter is stable as a consequence of an accidental Z(2) that results from a flavour symmetry group which is the double-cover group of the symmetry group of one of the regular geometric solids. Although model-dependent, the phenomenology resembles that of a generic >inert Higgs> dark matter scheme.
Neutrinos and physics beyond the standard model
A brief sketch is made of the present observational status of neutrino physics, with emphasis on the hints that follow from solar and atmospheric neutrino observations, as well as cosmological data on the amplitude of primordial density fluctuations. I also briefly review the ways to account for the observed anomalies and some of their implications.
Model independent Higgs boson mass limits at LEP
We derive model-independent constraints on Higgs mass and couplings from associated signals for higher masses, accessible at LEP2. This work is motivated by the fact that, in many extensions of the standard model, the Higgs boson can have substantial "invisible" decay modes, for example, into light or massless weakly interacting Goldstone bosons associated to the spontaneous violation of lepton number below the weak scale.
Unifying left–right symmetry and 331 electroweak theories
We propose a realistic theory based on the $\mathrm{SU(3)_c \otimes SU(3)_L \otimes SU(3)_R \otimes U(1)_{X}}$ gauge group which requires the number of families to match the number of colors. In the simplest realization neutrino masses arise from the canonical seesaw mechanism and their smallness correlates with the observed V-A nature of the weak force. Depending on the symmetry breaking path to the Standard Model one recovers either a left-right symmetric theory or one based on the $\mathrm{SU(3)_c \otimes SU(3)_L \otimes U(1)}$ symmetry as the "next" step towards new physics.
Updated CMB and x- and gamma-ray constraints on Majoron dark matter
The Majoron provides an attractive dark matter candidate, directly associated with the mechanism responsible for spontaneous neutrino mass generation within the standard model SU(3)(c) circle times SU(2)(L) circle times U(1)(Y) framework. Here we update the cosmological and astrophysical constraints on Majoron dark matter coming from the cosmic microwave background and a variety of x- and gamma-ray observations.
Supernova bounds on resonant active-sterile neutrino conversions
We discuss the effects of resonant $\nu_e \to \nu_s$ and $\bar{\nu}_e \to \bar{\nu}_s$ ($\nu_s$ is a sterile neutrino) conversions in the dense medium of a supernova. In particular, we assume the sterile neutrino $\nu_s$ to be in the hot dark matter few eV mass range. The implications of such a scenario for the supernova shock re-heating, the detected $\bar\nu_e$ signal from SN1987A and for the r-process nucleosynthesis hypothesis are analysed in some detail. The resulting constraints on mixing and mass difference for the $\nu_e-\nu_s$ system are derived. There is also an allowed region in the neutrino parameter space for which the r-process nucleosynthesis can be enhanced.
Neutrino masses and mixings from supersymmetry with bilinear R-parity violation: A theory for solar and atmospheric neutrino oscillations
The simplest unified extension of the MSSM with bi-linear R--Parity violation naturally predicts a hierarchical neutrino mass spectrum, in which one neutrino acquires mass by mixing with neutralinos, while the other two get mass radiatively. We have performed a full one-loop calculation of the neutralino-neutrino mass matrix in the bi-linear \rp MSSM, taking special care to achieve a manifestly gauge invariant calculation. Moreover we have performed the renormalization of the heaviest neutrino, needed in order to get meaningful results. The atmospheric mass scale and maximal mixing angle arise from tree-level physics, while solar neutrino scale and oscillations follow from calculable one-lo…
Signatures of Spontaneous Breaking of R-Parity in Gluino Cascade Decays at LHC
We study the pattern of gluino cascade decays in a class of supersymmetric models where R-parity is spontaneously broken. We give a detailed discussion of the R-parity violating decays of the lightest neutralino, the second lightest neutralino and the lightest chargino. The multi-lepton and same-sign dilepton signal rates expected in these models are compared with those predicted in the Minimal Supersymmetric Standard Model. We show that these rates can be substantially enhanced in broken R-parity models.
Status of four-neutrino mass schemes: a global and unified approach to current neutrino oscillation data
We present a unified global analysis of neutrino oscillation data within the framework of the four-neutrino mass schemes (3+1) and (2+2). We include all data from solar and atmospheric neutrino experiments, as well as information from short-baseline experiments including LSND. If we combine only solar and atmospheric neutrino data, (3+1) schemes are clearly preferred, whereas short-baseline data in combination with atmospheric data prefers (2+2) models. When combining all data in a global analysis the (3+1) mass scheme gives a slightly better fit than the (2+2) case, though all four-neutrino schemes are presently acceptable. The LSND result disfavors the three-active neutrino scenario with …
R-parity violating signals for chargino production at LEP II
We study chargino pair production at LEP II in supersymmetric models with spontaneously broken R-parity. We perform signal and background analyses, showing that a large region of the parameter space of these models can be probed through chargino searches at LEP II. In particular, we determine the attainable limits on the chargino mass as a function of the magnitude of the effective bilinear R-parity violation parameter $\epsilon$, demonstrating that LEP II is able to unravel the existence of charginos with masses almost up to its kinematical limit even in the case of R-parity violation. This requires the study of several final state topologies since the usual MSSM chargino signature is reco…
Global three-neutrino oscillation analysis of neutrino data
A global analysis of the solar, atmospheric and reactor neutrino data is presented in terms of three-neutrino oscillations. We include the most recent solar neutrino rates of Homestake, SAGE, GALLEX and GNO, as well as the recent 1117 day Super-Kamiokande data sample, including the recoil electron energy spectrum both for day and night periods and we treat in a unified way the full parameter space for oscillations, correctly accounting for the transition from the matter enhanced (MSW) to the vacuum oscillations regime. Likewise, we include in our description conversions with $\theta_{12} > \pi/4$. For the atmospheric data we perform our analysis of the contained events and the upward-going …
Physics at new accelerators: Looking beyond the Standard Model
Abstract Neutrino masses can have important implications in nuclear and particle physics, astrophysics and cosmology. Apart from the effects related to solar neutrinos, neutrino oscillations, dark matter, beta and double beta decays, massive neutrinos can also produce signals in the new accelerators. Here I focus on μ and τ number violating processes, very promising for muon and tau factories, as well as on the signatures associated with spontaneously broken R parity supersymmetry and neutral heavy leptons. These include the possibility of high rates for single chargino and neutralino production at LEP, LHC/SSC, as well as new signatures involving invisibly decaying Higgs bosons.
Neutrino mass and invisible Higgs decays at the LHC
The discovery of the Higgs boson suggests that also neutrinos get their mass from spontaneous symmetry breaking. In the simplest ungauged lepton number scheme, the Standard Model (SM) Higgs has now two other partners: a massive CP-even, as well as the massless Nambu-Goldstone boson, called majoron. For weak-scale breaking of lepton number the invisible decays of the CP- even Higgs bosons to the majoron lead to potentially copious sources of events with large missing energy. Using LHC results we study how the constraints on invisible decays of the Higgs boson restrict the relevant parameters, substantially extending those previously derived from LEP and shedding light on spontaneous lepton n…
Reconciling Cold Dark Matter with COBE/IRAS Plus Solar and Atmospheric Neutrino Data
We present a model where an unstable MeV Majorana tau \neu can naturally reconcile the cold dark matter model (CDM) with cosmological observations of large and small scale density fluctuations and, simultaneously, with data on solar and atmospheric neutrinos. The solar \neu deficit is explained through long wavelength, so-called {\sl just-so} oscillations involving conversions of \ne into both \nm and a sterile species \ns, while atmospheric \neu data are explained through \nm to \ne conversions. Future long baseline \neu oscillation experiments, as well as some reactor experiments will test this hypothesis. The model is based on the spontaneous violation of a global lepton number symmetry …
Atmospheric neutrino observations and flavor changing interactions
Flavor changing (FC) neutrino-matter interactions can account for the zenith-angle dependent deficit of atmospheric neutrinos observed in the SuperKamiokande experiment, without directly invoking neither neutrino mass, nor mixing. We find that FC $\nu_\mu$-matter interactions provide a good fit to the observed zenith angle distributions, comparable in quality to the neutrino oscillation hypothesis. The required FC interactions arise naturally in many attractive extensions of the Standard Model.
Confusing nonzero theta(13) with nonstandard interactions in the solar neutrino sector
Solar and KamLAND data are in slight tension when interpreted in the standard two-flavor oscillations framework and this may be alleviated allowing for a non-zero value of the mixing angle theta_13. Here we show that, likewise, non-standard flavor-changing interactions (FCI), possibly intervening in the propagation of solar neutrinos, are equally able to alleviate this tension and therefore constitute a potential source of confusion in the determination of theta_13. By performing a full three-flavor analysis of solar and KamLAND data in presence of FCI we provide a quantitative description of the degeneracy existing between theta_13 and the vectorial coupling eps_e\tau^dV characterizing the…
Seesaw Majoron Model of Neutrino Mass and Novel Signals in Higgs Boson Production at LEP
We perform a careful study of the neutral scalar sector of a model which includes a singlet, a doublet, and a triplet scalar field under $SU(2)$. This model is motivated by neutrino physics, since it is simply the most general version of the seesaw model of neutrino mass generation through spontaneous violation of lepton number. The neutral Higgs sector contains three CP-even and one massive CP-odd Higgs boson $A$, in addition to the massless CP-odd majoron $J$. The weakly interacting majoron remains massless if the breaking of lepton number symmetry is purely spontaneous. We show that the massive CP-odd Higgs boson may invisibly decay to three majorons, as well as to a CP-even Higgs $H$ bo…
A simple analytic three-flavour description of the day night effect in the solar neutrino flux
In the 3-flavour framework we derive a simple approximate analytic expression for the day-night difference of the flux of solar $\nu_e$ at terrestrial detectors which is valid for an arbitrary Earth density profile. Our formula has the accuracy of a few per cent and reproduces all the known analytic expressions for the Earth matter effects on the solar neutrino oscillations obtained under simplifying assumptions about the Earth's density profile (matter of constant density, 3 layers of constant densities, and adiabatic approximation). It can also be used for studying the Earth matter effects on the oscillations of supernova neutrinos. We also discuss the possibility of probing the leptonic …
Neutral heavy lepton signatures at the Z0 peak
Abstract Gauge singlet Neutral Heavy Leptons (NHL) arise in many extensions of the standard electroweak theory such as superstring inspired models and their existence may be related to the observed smallness of the neutrino masses. Existing limits on such particles are still fairly poor. A brief discussion is given of the signatures arising from their production through Z 0 → N + ν or Z 0 → N + ν and their subsequent decays within different models. Taking into account the expected luminosities and typical detector efficiencies of the different LEP/SLC experiments one concludes that these may either discover isosinglets or else substantially improve and extend present limits on their mass an…
Top-quark phenomenology in models with bilinearly and spontaneously broken R-parity
We study unconventional decays of the top-quark in the framework of SUSY models with spontaneously broken R-parity. In particular we discuss an effective theory which consists of the MSSM plus bilinearly broken R-parity. We demonstrate that the decay modes t -> stau + b and t -> tau + sbottom can have large branching ratios even in scenarios where the tau-neutrino mass is very small. We show that existing Tevatron data already probe the theoretical parameters, with promising prospects for further improvement at the Run 2 of the Tevatron.
Resonant conversion of massless neutrinos in supernovae
It has been noted for a long time that, in some circumstances, {\sl massless} neutrinos may be {\sl mixed} in the leptonic charged current. Conventional neutrino oscillation searches in vacuum are insensitive to this mixing. We discuss the effects of resonant massless-neutrino conversions in the dense medium of a supernova. In particular, we show how the detected $\bar\nu_e$ energy spectra from SN1987a and the supernova $r$-process nucleosynthesis may be used to provide very stringent constraints on the mixing of {\sl massless} neutrinos.
Lepton flavour violation in a left-right symmetric model
We consider in this paper a Left-Right symmetric gauge model in which a global lepton-number-like symmetry is introduced and broken spontaneously at a scale that could be as low as 10^4 GeV or so. The corresponding physical Nambu-Goldstone boson, which we call majoron and denote J, can have tree-level flavour-violating couplings to the charged fermions, leading to sizeable majoron-emitting lepton-flavour-violating weak decays. We consider explicitly a leptonic variant of the model and show that the branching ratios for \mu -> e+J, \tau -> e + J and \tau -> \mu + J decays can be large enough to fall within the sensitivities of future \mu and \tau factories. On the other hand the left-right g…
Reconciling neutrino anomalies in a simple four-neutrino scheme with R-parity violation
We propose a simple extension of the MSSM based on extra compact dimensions which includes an $SU(2) \otimes U(1)$ singlet superfield. The fermion present in this superfield is the sterile neutrino, which combines with one linear combination of $\nu_e-\nu_{\mu}-\nu_{\tau}$ to form a Dirac pair whose mass accounts for the LSND anomaly. Its small mass can be ascribed to a volume suppression factor associated with extra compact dimensions. On the other hand the sterile neutrino scalar partner can trigger the spontaneous violation of R-parity, thereby inducing the necessary mass splittings to fit also the solar and atmospheric neutrino data. Thus the model can explain all neutrino oscillation d…
Supernova Bounds on Supersymmetric $R$-parity Violating Interactions
We re-examine resonant massless-neutrino conversions in a dense medium induced by flavour changing neutral current (FCNC) interactions. We show how the observed $\bar\nu_e$ energy spectra from SN1987a and the supernova $r$-process nucleosynthesis provide constraints on supersymmetric models with $R$ parity violation, which are much more stringent than those obtained from the laboratory. We also suggest that resonant massless-neutrino conversions may play a positive role in supernova shock reheating. Finally, we examine the constraints on explicit $R$-parity-violating FCNCs in the presence of non-zero neutrino masses in the eV range, as indicated by present hot dark matter observations.
Seasonal dependence in the solar neutrino flux
MSW solutions of the solar neutrino problem predict a seasonal dependence of the zenith angle distribution of the event rates, due to the non-zero latitude at the Super-Kamiokande site. We calculate this seasonal dependence and compare it with the expectations in the no-oscillation case as well as just-so scenario, in the light of the latest Super-Kamiokande 708-day data. The seasonal dependence can be sizeable in the large mixing angle MSW solution and would be correlated with the day-night effect. This may be used to discriminate between MSW and just-so scenarios and should be taken into account in refined fits of the data.
Can OPERA help in constraining neutrino non-standard interactions?
We study how much the unique ability of the OPERA experiment to directly detect \nu_\tau can help in probing new, non-standard contact interactions of the third family of neutrinos. We perform a combined analysis of future, high-statistics MINOS and OPERA data. For the case of non-standard interactions in \nu_\mu to \nu_e transitions we also include the impact of possible DoubleCHOOZ data. In all cases we find that the \nu_\tau sample of OPERA is too small to be statistically significant, even if one doubles the nominal exposure of OPERA to 4.5E20 pot. OPERA's real benefit for this measurement lies in its very high neutrino energy and hence very different L/E compared to MINOS.
Predicting charged lepton flavor violation from 3-3-1 gauge symmetry
7 pages.- 2 figures.- v2: discussion extended
Charged Higgs mass bounds from b → sγ in a bilinear R-parity violating model
The experimental measurement of $B(b \to s\gamma)$ imposes important constraints on the charged Higgs boson mass in the MSSM. If squarks are in the few TeV range, the charged Higgs boson mass in the MSSM must satisfy $m_{H^{\pm}} \gsim 440$ GeV. For lighter squarks, then light charged Higgs bosons can be reconciled with $B(b \to s\gamma)$ only if there is also a light chargino. In the MSSM if we impose $m_{\chi^{\pm}_1}>90$ GeV then we need $m_{H^{\pm}} \gsim 110$ GeV. We show that by adding bilinear R--Parity violation (BRpV) in the tau sector, these bounds are relaxed. The bound on $m_{H^{\pm}}$ in the MSSM--BRpV model is $\gsim 340$ GeV for the the heavy squark case and $m_{H^{\pm}} \gsi…
Constraints on additionalZ′gauge bosons from a precise measurement of theZmass
We analyze the constraints on the mass and mixing of superstring-inspired E{sub 6} {ital Z}{prime} neutral gauge boson that follow from the recent precise {ital Z} mass measurements and show that they depend very sensitively on the assumed value of the {ital W} mass and also, to a lesser extent, on the top-quark mass.
Charge Breaking Minima in the Broken R-parity Minimal Supersymmetric Standard Model
We reconsider the possible presence of charge and colour breaking minima in the scalar potential of the minimal supersymmetric standard model (MSSM) and its minimal generalization with R-parity explicitly broken by bilinear terms (RMSSM). First we generalize some results previously derived for the MSSM case. Next we investigate how robust is the MSSM against its RMSSM extension. We examine the constraints on the RMSSM parameter space that follow from the required absence of charge breaking minima in the scalar potential. We point out the possibility of generating non--zero vacuum expectation values for the charged Higgs field which is not present in the MSSM. However, given the smallness of…
Neutrino physics overview
Seesaw-type and low-scale models of neutrino masses are reviewed, along with the corresponding structure of the lepton mixing matrix. The status of neutrino oscillation parameters as of June 2006 is given, including recent fluxes, as well as latest SNO, K2K and MINOS results. Some prospects for the next generation of experiments are given. This writeup updates the material presented in my lectures at the Corfu Summer Institute on Elementary Particle Physics in September 2005.
Weak Interactions and Solar Neutrinos: Testing the Oscillation Hypothesis
Various proposals for understanding the reduced solar neutrino flux in terms of non-standard neutrino propagation properties are briefly reviewed in the context of weak interaction theory. Emphasis is given to neutrino oscillation models which may be tested experimentally, despite the small mass parameter involved. Spontaneous lepton number (and R parity) breaking in supergravity — the supersymmetric doublet Majoron model — solves the solar neutrino problem through matter-enhanced neutrino oscillations. The spectrum of supersymmetric particles is restricted in a way that will be probed by high energy collider experiments. In addition, low energy processes associated with the existence of th…
A flavour physics scenario for the 750 GeV diphoton anomaly
A simple variant of a realistic flavor symmetry scheme for fermion masses and mixings provides a possible interpretation of the diphoton anomaly as an electroweak singlet ``flavon.'' The existence of TeV scale vectorlike T-quarks required to provide adequate values for Cabibbo-Kobayashi-Maskawa (CKM) parameters can also naturally account for the diphoton anomaly. Correlations between ${V}_{ub}$ and ${V}_{cb}$ with the vectorlike T-quark mass can be predicted. Should the diphoton anomaly survive in a future run, our proposed interpretation can also be tested in upcoming B and LHC studies.
Small neutrino masses and gauge coupling unification
The physics responsible for gauge coupling unification may also induce small neutrino masses. We propose a novel gauge mediated radiative seesaw mechanism for calculable neutrino masses. These arise from quantum corrections mediated by new $SU(3)_c \times SU(2)_L \times U(1)_X$ (3-3-1) gauge bosons and the physics driving gauge coupling unification. Gauge couplings unify for a 3-3-1 scale in the TeV range, making the model directly testable at the LHC.
Fermion masses, leptogenesis, and supersymmetric SO(10) unification
Current neutrino oscillation data indicate the existence of two large lepton mixing angles, while Kobayashi-Maskawa matrix elements are all small. Here we show how supersymmetric SO(10) with extra chiral singlets can easily reconcile large lepton mixing angles with small quark mixing angles within the framework of the successful Fritzsch ansatz. Moreover we show how this is fully consistent with the thermal leptogenesis scenario, avoiding the so-called gravitino problem. A sizeable asymmetry can be generated at relatively low scales. We present our results in terms of the leptonic CP violation parameter that characterizes neutrino oscillations.
Three-flavour neutrino oscillation update
We review the present status of three-flavour neutrino oscillations, taking into account the latest available neutrino oscillation data presented at the Neutrino 2008 Conference. This includes the data released this summer by the MINOS collaboration, the data of the neutral current counter phase of the SNO solar neutrino experiment, as well as the latest KamLAND and Borexino data. We give the updated determinations of the leading 'solar' and 'atmospheric' oscillation parameters. We find from global data that the mixing angle $\theta_{13}$ is consistent with zero within $0.9\sigma$ and we derive an upper bound of $\sin^2\theta_{13} < 0.035 (0.056)$ at 90% CL (3$\sigma$).
Neutrino electron scattering and left-right symmetry: future tests
Low-energy high-resolution neutrino-electron scattering experiments may play an important role in testing the gauge structure of the electroweak interaction. We propose the use of radioactive neutrino sources (e.g. $^{51}$Cr) in underground experiments such as BOREXINO and HELLAZ as a probe of the weak neutral current structure. As an illustration, we display the sensitivity of these detectors in testing the possible existence of right-handed weak neutral currents.
Neutrino oscillations refitted
Here we update our previous global fit of neutrino oscillations by including the recent results which have appeared since the Neutrino-2012 conference. These include the measurements of reactor anti-neutrino disappearance reported by Daya Bay and RENO, together with latest T2K and MINOS data including both disappearance and appearance channels. We also include the revised results from the third solar phase of Super-Kamiokande, SK-III, as well as new solar results from the fourth phase of Super-Kamiokande, SK-IV. We find that the preferred global determination of the atmospheric angle $\theta_{23}$ is consistent with maximal mixing. We also determine the impact of the new data upon all the o…
Matter Effects in Neutrino Propagation
After briefly reviewing the Mikheyev-Smirnov-Wolfenstein effect, I present a particle physics model where the required small neutrino mass arises from spontaneous R parity violation in supergravity theories. It is related to measurable processes associated with the existence of the Majoron and of supersymmetric (SUSY) particles. Astrophysical and laboratory limits tend to exclude regions of oscillation parameters where the high energy neutrinos are adiabatically converted. This suggests the possibility of a large reduction in the pp and 7 Be neutrino flux even for a mildly reduced 8 B neutrino flux, thus stressing the importance of the gallium experiments. Finally I consider other types of …
Dynamical left-right symmetry breaking.
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 VEVs of the bi--doublet $\tan\beta\equiv\kappa/\kappa'$ =~ 1.3--4. For a theoretically plausible choice of the parameters the right--handed scale can be as low as $\sim 20 TeV$; in this case one expects several intermediate and low--scale scalars in addition…
Neutrino conversions in a polarized medium
Electron polarization induced by magnetic fields can modify the potentials relevant for describing neutrino conversions in media with magnetic fields. The magnitudes of polarization potentials are determined for different conditions. We show that variations of the electron polarization along the neutrino trajectory can induce resonant conversions in the active-sterile neutrino system, but cannot lead to level crossing in the active-active neutrino system. For neutrino flavour conversions the polarisation leads only to a shift of the standard MSW resonance. For polarizations $\lambda \lsim 0.04$ the direct modifications of the potential (density) due to the magnetic field pressure are smalle…
Consistency of the triplet seesaw model revisited
14 pages.- 5 figures
Physics of Massive Neutrinos
I summarize the present status of global analyses of neutrino oscillations, including the most recent KamLAND and K2K data, as well as the latest solar and atmospheric neutrino fluxes. I give the allowed ranges of the three--flavour oscillation parameters from the current worlds' global neutrino data sample, their best fit values and discuss the small parameters DeltaM_solar/DeltaM_atm and sin^2 theta_13, which characterize the strength of CP violation in neutrino oscillations. I briefly discuss neutrinoless double beta decay and the LSND neutrino oscillation hint, as well as the robustness of the neutrino oscillation results in the presence of non-standard physics.
Neutrino mass and new light gauge boson in superstring models
Abstract 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.
Geotomography with solar and supernova neutrinos
We show how by studying the Earth matter effect on oscillations of solar and supernova neutrinos inside the Earth one can in principle reconstruct the electron number density profile of the Earth. A direct inversion of the oscillation problem is possible due to the existence of a very simple analytic formula for the Earth matter effect on oscillations of solar and supernova neutrinos. From the point of view of the Earth tomography, these oscillations have a number of advantages over the oscillations of the accelerator or atmospheric neutrinos, which stem from the fact that solar and supernova neutrinos are coming to the Earth as mass eigenstates rather than flavour eigenstates. In particula…
X-ray photons from late-decaying majoron dark matter
An attractive way to generate neutrino masses as required to account for current neutrino oscillation data involves the spontaneous breaking of lepton number. The resulting majoron may pick up a mass due to gravity. If its mass lies in the kilovolt scale, the majoron can play the role of late-decaying Dark Matter (LDDM), decaying mainly to neutrinos. In general the majoron has also a sub-dominant decay to two photons leading to a mono-energetic emission line which can be used as a test of the LDDM scenario. We compare expected photon emission rates with observations in order to obtain model independent restrictions on the relevant parameters. We also illustrate the resulting sensitivities w…
Neutrino electron scattering and electroweak gauge structure: Future tests
Low-energy high-resolution neutrino-electron scattering experiments may play an important role in testing the gauge structure of the electroweak interaction. We propose the use of radioactive neutrino sources (e.g. $^{51}$Cr) in underground experiments such as BOREXINO, HELLAZ and LAMA. As an illustration, we display the sensitivity of these detectors in testing the possible existence of extra neutral gauge bosons, both in the framework of E_6 models and of models with left-right symmetry.
Primordial Nucleosynthesis, Majorons and Heavy Tau Neutrinos
We determine the restrictions imposed by primordial nucleosynthesis upon a heavy tau neutrino, in the presence of nu-tau 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 $N_{eq}$ as a function of nu-tau mass and the nu-tau-Majoron coupling $g$. We show that for theoretically plausible $g$ values $\gsim 10^{-4}$ present nucleosynthesis observations can not rule out nu-tau masses in the MeV range. Moreover, these models give $N_{eq} \leq 3$ in the nu-tau mass region 1-10 MeV, for very reasonable values of $g \geq 3 \times 10^{-4}$. The evasion of the cosmological limits brings new…
Left-right symmetry breaking in NJL approach
We study left-right symmetric models which contain only fermion and gauge boson fields and no elementary scalars. The Higgs bosons are generated dynamically through a set of gauge- and parity-invariant 4-fermion operators. It is shown that in a model with a composite bi-doublet and two triplet scalars there is no parity breaking at low energies, whereas in the model with two doublets instead of two triplets parity is broken automatically regardless of the choice of the parameters of the model. For phenomenologically allowed values of the right-handed scale a tumbling symmetry breaking mechanism is realized in which parity breaking at a high scale $\mu_R$ propagates down and eventually cause…
Cornering the revamped BMV model with neutrino oscillation data
Using the latest global determination of neutrino oscillation parameters from~\cite{deSalas:2017kay} we examine the status of the simplest revamped version of the BMV (Babu-Ma-Valle) model, proposed in~\cite{Morisi:2013qna}. The model predicts a striking correlation between the "poorly determined" atmospheric angle $\theta_{23}$ and CP phase $\delta_{CP}$, leading to either maximal CP violation or none, depending on the preferred $\theta_{23}$ octants. We determine the allowed BMV parameter regions and compare with the general three-neutrino oscillation scenario. We show that in the BMV model the higher octant is possible only at $99\%$ C.L., a stronger rejection than found in the general c…
Probing atmospheric mixing and leptonic CP violation in current and future long baseline oscillation experiments
We perform realistic simulations of the current and future long baseline experiments such as T2K, NO$\nu$A, DUNE and T2HK in order to determine their ultimate potential in probing neutrino oscillation parameters. We quantify the potential of these experiments to underpin the octant of the atmospheric angle $\theta_{23}$ as well as the value and sign of the CP phase $\delta_{CP}$.
Neutrino properties
A brief sketch is made of the present observational status of neutrino properties, with emphasis on the hints from solar and atmospheric neutrinos, as well as cosmological data on the amplitude of primordial density fluctuations. Implications of neutrino mass in particle accelerators, astrophysics and cosmology are discussed.
Neutrino magnetic moments and low-energy solar neutrino-electron scattering experiments
The scattering of solar neutrinos on electrons is sensitive to the neutrino magnetic moments through an interference of electromagnetic and weak amplitudes in the cross section. We show that future low-energy solar neutrino experiments with good angular resolution can be sensitive to the resulting azimuthal asymmetries in event number and should provide useful information on non-standard neutrino properties such as magnetic moments. We compare asymmetries expected at HELLAZ (mainly pp neutrinos) with those at the Kamiokande and Super-Kamiokande experiments (Boron neutrinos), both for the case of Dirac and Majorana neutrinos and discuss the advantages of low energies. Potentially interesting…
Supernova Bounds on Majoron-emitting decays of light neutrinos
Neutrino masses arising from the spontaneous violation of ungauged lepton-number are accompanied by a physical Goldstone boson, generically called Majoron. In the high-density supernova medium the effects of Majoron-emitting neutrino decays are important even if they are suppressed in vacuo by small neutrino masses and/or small off-diagonal couplings. We reconsider the influence of these decays on the neutrino signal of supernovae in the light of recent Super-Kamiokande data on solar and atmospheric neutrinos. We find that majoron-neutrino coupling constants in the range $3\times 10^{-7}\lsim g\lsim 2\times 10^{-5}$ or $g \gsim 3 \times 10^{-4}$ are excluded by the observation of SN1987A. T…
Probing neutrino mass with multilepton production at the Tevatron in the simplest R-parity violation model
We analyze the production of multileptons in the simplest supergravity model with bilinear violation of R parity at the Fermilab Tevatron. Despite the small R-parity violating couplings needed to generate the neutrino masses indicated by current atmospheric neutrino data, the lightest supersymmetric particle is unstable and can decay inside the detector. This leads to a phenomenology quite distinct from that of the R-parity conserving scenario. We quantify by how much the supersymmetric multilepton signals differ from the R-parity conserving expectations, displaying our results in the $m_0 \otimes m_{1/2}$ plane. We show that the presence of bilinear R-parity violating interactions enhances…
Bilinear R-parity violation and small neutrino masses: A self-consistent framework
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 of approximately $(\theta^2)^\delta$ eV where $\theta\approx 0.22$ is the U(1)_H breaking parameter and $\delta$ is an integer number that depends on the horizontal charges of the leptons. For $\delta=1$ a unique self-consistent model arises in which i) all the superpotential trilinear R-parity violating couplings are forbidden by holomorphy; ii) the tree level neutrino mass falls in the range suggested by the atmospheric neutrino problem; iii) radiative contributions to neutrino masses are strongly suppre…
A Supersymmetric Solution to the Solar and Atmospheric Neutrino Problems
The simplest unified extension of the Minimal Supersymmetric Standard Model with bi-linear R--Parity violation provides a predictive scheme for neutrino masses which can account for the observed atmospheric and solar neutrino anomalies in terms of bi-maximal neutrino mixing. The maximality of the atmospheric mixing angle arises dynamically, by minimizing the scalar potential, while the solar neutrino problem can be accounted for either by large or by small mixing oscillations. One neutrino picks up mass by mixing with neutralinos, while the degeneracy and masslessness of the other two is lifted only by loop corrections. Despite the smallness of neutrino masses R-parity violation is observab…
Production and decays of supersymmetric Higgs bosons in spontaneously brokenRparity
We study the mass spectra, production and decay properties of the lightest supersymmetric CP-even and CP-odd Higgs bosons in models with spontaneously broken R-parity (SBRP). We compare the resulting mass spectra with expectations of the Minimal Supersymmetric Standard Model (MSSM), stressing that the model obeys the upper bound on the lightest CP-even Higgs boson mass. We discuss how the presence of the additional scalar singlet states affects the Higgs production cross sections, both for the Bjorken process and the "associated production". The main phenomenological novelty with respect to the MSSM comes from the fact that the spontaneous breaking of lepton number leads to the existence of…
Neutrino Mass and Missing Momentum Higgs Boson Signals
In the simplest scheme for neutrino masses invoking a triplet of Higgs scalars there are two CP-even neutral Higgs bosons $H_i$ (i=1,2) and one massive pseudoscalar $A$. For some choices of parameters, the lightest $H_1$ may be lighter than the Standard Model Higgs boson. If the smallness of neutrino mass is due to the small value of the triplet expectation value, as expected in a seesaw scheme, the Higgs bosons may decay dominantly to the invisible neutrino channel. We derive limits on Higgs masses and couplings that follow from LEP I precision measurements of the invisible Z width.
Minimal supergravity with R-parity breaking
We show that the minimal R-parity breaking model characterized by an effective bilinear violation of R-parity in the superpotential is consistent with minimal N=1 supergravity unification with radiative breaking of the electroweak symmetry and universal scalar and gaugino masses. This one-parameter extension of the MSSM-SUGRA model provides therefore the simplest reference model for the breaking of R-parity and constitutes a consistent truncation of the complete dynamical models with spontaneous R-parity breaking proposed previously. We comment on the lowest-lying CP-even Higgs boson mass and discuss its minimal N=1 supergravity limit, determine the ranges of $\tan\beta$ and bottom quark Yu…
Novel Scalar Boson Decays in SUSY with Broken R-Parity
R parity violation can induce mixing of the supersymmetric Higgs bosons with the sneutrinos at the tree level. We study the effect of this mixing on the decays of Higgs scalars as well as sneutrinos in an effective model where the violation of R parity is included in the minimal supersymmetric model through bilinear lepton number violating superpotential terms. We show that a small violation of R parity can lead to a sizeable branching ratio for the supersymmetric Higgs boson decay mode $H \to \chi \ell$ (where $\chi$ denotes an electroweak gaugino and $\ell$ is either a tau neutrino or a tau lepton). Relevant constraints on R parity violation as well as those coming from SUSY particle sear…
Isosinglet-neutral heavy-lepton production in Z-decays and neutrino mass
Abstract The possible existence of NHLs is often related to neutrino mass. As a result their production cross section may be correspondingly constrained by observational limits on neutrino masses. We analyze the discovery potential of isosinglet NHLs within various models taking also into account cosmological limits on relic neutrino abundances.
SO(10) grand unification model for degenerate neutrino masses
This version corrects the first one in eq.3.4 and table 1 where there was a bar missing in the 126 representation. All other equations and results are unchanged and correct. However, the criticism we had made in the earlier version to the work of Caldwell and Mohapatra was not correct and has been removed from the "note added" where it appeared. Moreover one new reference has been added to ref.13.
Decaying warm dark matter and neutrino masses
Neutrino masses may arise from spontaneous breaking of ungauged lepton number. Due to quantum gravity effects the associated Goldstone boson - the majoron - will pick up a mass. We determine the lifetime and mass required by cosmic microwave background observations so that the massive majoron provides the observed dark matter of the Universe. The majoron DDM scenario fits nicely in models where neutrino masses arise a la seesaw, and may lead to other possible cosmological implications.
Testing for new physics with low-energy anti-neutrino sources: LAMA as a case study
Some electroweak models with extended neutral currents, such as those based on the $E_6$ group, lead to an increase of the $\bar{\nu}-e$ scattering cross section at energies below 100 keV. We propose to search for the heavy Z' boson contribution in an experiment with a high-activity artificial neutrino source and with a large-mass detector. We present the case for the LAMA experiment with a large NaI(Tl) detector located at the Gran Sasso underground laboratory. The neutrino flux is known to within a one percent accuracy, in contrast to the reactor case and one can reach lower neutrino energies. Both features make our proposed experiment more sensitive to extended gauge models, such as the …
SINGLE PHOTON DECAYS OF THE $Z^0$ AND SUSY WITH SPONTANEOUSLY BROKEN R-PARITY
Spontaneous violation of R parity can induce rare single photon decays of the $Z^0$ involving the emission of (nearly) massless pseudoscalar Goldstone bosons, majorons, as well as massive CP even or CP odd spin zero bosons that arise in the electroweak breaking sector of these models. We show that the majoron emitting decays can have a sizeable branching ratio of $10^{-5}$ or so, without conflicting any experimental observation from neutrino physics or particle searches. These decays may lead to interesting structures for the single photon spectrum involving either mono chromatic photons as well as continuous spectra that grow with energy. They would easily account for an excess of single p…
Status of global fits to neutrino oscillations
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, as well as 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' …
Supersymmetric origin of neutrino mass
Supersymmetry with breaking of R-parity provides an attractive way to generate neutrino masses and lepton mixing angles in accordance to present neutrino data. We review the main theoretical features of the bilinear R-parity breaking (BRpV) model, and stress that it is the simplest extension of the minimal supersymmetric standard model (MSSM) which includes lepton number violation. We describe how it leads to a successful phenomenological model with hierarchical neutrino masses. In contrast to seesaw models, the BRpV model can be probed at future collider experiments, like the Large Hadron Collider or the Next Linear Collider, since the decay pattern of the lightest supersymmetric particle …
Borexino as a test of solar matter density fluctuations
This talk summarizes some results of our recent work focusing on the possibility to test solar matter density fluctuations by the future Borexino experiment.
SN 1987A and the status of oscillations solutions to the solar neutrino problem
We study neutrino oscillations and the level-crossing probability ${P}_{\mathrm{LSZ}}$ in power-law potential profiles $A(r)\ensuremath{\propto}{r}^{n}.$ We give local and global adiabaticity conditions valid for all mixing angles $\ensuremath{\vartheta}$ and discuss different representations for ${P}_{\mathrm{LSZ}}.$ For the ${1/r}^{3}$ profile typical of supernova envelopes we compare our analytical to numerical results and to earlier approximations used in the literature. We then perform a combined likelihood analysis of the observed SN 1987A neutrino signal and of the latest solar neutrino data, including the recent SNO CC measurement. We find that, unless all relevant supernova paramet…
Charged Higgs boson and stau phenomenology in the simplest R-parity breaking model
We consider the charged scalar boson phenomenology in the simplest effective low-energy R-parity breaking model characterized by a bilinear violation of R-parity in the superpotential. This induces a mixing between staus and the charged Higgs boson. We show that the charged Higgs boson mass can be lower than expected in the MSSM, even before including radiative corrections. We also study the charged scalar boson decay branching ratios and show that the R-parity violating decay rates can be comparable or even bigger than the R-parity conserving ones. Moreover, if the stau is the LSP it will have only decays into standard model fermions. These features could have important implications for ch…
LEP sensitivities to spontaneous R-parity violating signals
We illustrate the sensitivities of LEP experiments to leptonic signals associated to models where supersymmetry (SUSY) is realized with spontaneous breaking of R-parity. We focus on missing transverse momentum plus acoplanar muon events arising from lightest neutralino single production $\chi \nu$ as well as pair production $\chi \chi$, followed by $\chi$ decays, where $\chi$ denotes the lightest neutralino. We show that the integrated luminosity achieved at LEP already starts probing the basic parameters of the theory. We discuss the significance of these constraints for the simplest spontaneous R-parity breaking models and their relevance for future searches of SUSY particles.
Is charged lepton flavor violation a high energy phenomenon?
Searches for rare processes such as mu --> e gamma put stringent limits on lepton flavour violation expected in many Beyond the Standard Model physics scenarios. This usually precludes the observation of flavour violation at high energy colliders such as the LHC. We here discuss a scenario where right-handed neutrinos are produced via a Z' portal but which can only decay via small flavour violating couplings. Consequently, the process rate is unsuppressed by the small couplings and can be visible despite unobservably small mu --> e gamma rates.
Searching for Invisibly Decaying Higgs Bosons at LEP II
We study the potential of LEP II to unravel the existence of invisibly decaying Higgs bosons, predicted in a wide class of models. We perform a model independent analysis, focusing our attention to the final state topologies exhibiting $b \bar{b}$ or $\ell^+ \ell^-$ ($\ell=\mu$ or $e$) pairs and missing energy. We carefully evaluate the signals and backgrounds, choosing appropriate cuts to enhance the discovery limits. Our results demonstrate that LEP II is capable of discovering such a Higgs boson for a wide range of masses and couplings.
Parameter Degeneracy in Flavor-Dependent Reconstruction of Supernova Neutrino Fluxes
We reexamine the possibility of reconstructing the initial fluxes of supernova neutrinos emitted in a future core-collapse galactic supernova explosion and detected in a Megaton-sized water Cherenkov detector. A novel key element in our method is the inclusion, in addition to the total and the average energies of each neutrino species, of a "pinching" parameter characterizing the width of the distribution as a fit parameter. We uncover in this case a continuous degeneracy in the reconstructed parameters of supernova neutrino fluxes at the neutrinosphere. We analyze in detail the features of this degeneracy and show how it occurs irrespective of the parametrization used for the distribution …
Supersymmetric Unification with Radiative Breaking of R-parity
We show how R-parity can break spontaneously as a result of radiative corrections in unified N=1 supergravity models. We illustrate this with a concrete rank-four unified model, where the spontaneous breaking of R-parity is accompanied by the existence of a physical majoron. We determine the resulting supersymmetric particle mass spectrum and show that R-parity-breaking signals may be detectable at LEP200.
Global status of neutrino oscillation parameters after Neutrino-2012
Here we update the global fit of neutrino oscillations in arXiv:1103.0734 and arXiv:1108.1376 including the recent measurements of reactor antineutrino disappearance reported by the Double Chooz, Daya Bay and RENO experiments, together with latest MINOS and T2K appearance and disappearance results, as presented at the Neutrino-2012 conference. We find that the preferred global fit value of $\theta_{13}$ is quite large: $\sin^2\theta_{13} \simeq 0.025$ for normal and inverted neutrino mass ordering, with $\theta_{13} = 0$ now excluded at more than 10$\sigma$. The impact of the new $\theta_{13}$ measurements over the other neutrino oscillation parameters is discussed as well as the role of th…
Light sterile neutrino from extra dimensions and four-neutrino solutions to neutrino anomalies
We propose a four-neutrino model which can reconcile the existing data coming from underground experiments in terms of neutrino oscillations, together with the hint from the LSND experiment and a possible neutrino contribution to the hot dark matter of the Universe. It applies the idea that extra compact dimensions, probed only by gravity and possibly gauge-singlet fields, can lower the fundamental scales such as the Planck, string or unification scales. Our fourth light neutrino $\nu_s$ ($s$ for sterile) is identified with the zero mode of the Kaluza-Klein states. To first approximation \nu_sterile combines with the nu_mu in order to form a Dirac neutrino with mass in the eV range leaving …
Low-energy anti-neutrinos from the sun
We consider the sensitivity of future neutrino experiments in the low energy region, such as BOREXINO or HELLAZ, to a solar electron antineutrino signal. We show that, if neutrino conversions within the Sun result in partial polarization of initial solar neutrino fluxes, then a new opportunity arises to observe the electron antineutrinos and thus to probe the Majorana nature of the neutrinos. This is achieved by comparing the slopes of the energy dependence of the differential neutrino electron scattering cross section for different neutrino conversion scenarios. We also show how the \nu_e -> \bar{\nu}_e conversions may take place for low energy solar neutrinos while being unobservable at t…
Inflation and majoron dark matter in the neutrino seesaw mechanism
We propose that inflation and dark matter have a common origin, connected to the neutrino mass generation scheme. As a model we consider spontaneous breaking of global lepton number within the seesaw mechanism. We show that it provides an acceptable inflationary scenario consistent with the recent cosmic microwave background B-mode observation by the BICEP2 experiment. The scheme may also account for the baryon asymmetry of the Universe through leptogenesis for reasonable parameter choices.
Large lepton mixing and supernova 1987A
We reconsider the impact of $\bar\nu_e \leftrightarrow \bar\nu_{\mu,\tau}$ neutrino oscillations on the observed $\bar\nu_e$ signal of supernova SN 1987A. Performing a maximum-likelihood analysis using as fit parameters the released binding energy $\Eb$ and the average neutrino energy $\Ee$, we find as previous analyses that $\bar\nu_e \leftrightarrow \bar\nu_{\mu,\tau}$ oscillations with large mixing angles have lower best-fit values for $\Ee$ than small-mixing angle (SMA) oscillations. Moreover, the inferred value of $\Ee$ is already in the SMA case lower than those found in simulations. This apparent conflict has been interpreted as evidence against the large mixing oscillation solutions…
Vacuum stability with spontaneous violation of lepton number
The vacuum of the Standard Model is known to be unstable for the measured values of the top and Higgs masses. Here we show how vacuum stability can be achieved naturally if lepton number is violated spontaneously at the TeV scale. More precise Higgs measurements in the next LHC run should provide a crucial test of our symmetry breaking scenario. In addition, these schemes typically lead to enhanced rates for processes involving lepton flavour violation .
Concluding talk at NOW 2006
This writeup summarizes the status of neutrino oscillations, including recent fluxes and experimental data, as of summer 2006. A discussion is given on the current status of absolute scale of neutrino mass from tritium, neutrinoless double beta decay and cosmological observations, as well as the prospects for the next generation of experiments, including lepton flavor violation searches, and their theoretical significance.
Supersymmetric majoron signatures and solar neutrino oscillations
Spontaneous R-parity breaking in supergravity solves the solar neutrino problem through matter-enhanced neutrino oscillations. The model may be tested in collider experiments and through ``dynamical'' effects associated with the existence of a weakly interacting majoron. Apart from astrophysical effects, majoron emission can produce observable changes in \ensuremath{\mu} and \ensuremath{\tau} decay spectra for parameter values that substantially reduce the solar neutrino flux. A signature of the model is the possible observation of the decay \ensuremath{\mu}\ensuremath{\rightarrow}e+majoron.
Leptonic CP violation with massless neutrinos
Abstract Leptonic CP violation may arise in the SU(2) ⊗ U(1) theory even if the neutrinos are strictly massless and, as a result, it is potentially large. Theoretical scenarios include isosinglet neutral heavy leptons which are present in many extensions of the standard electroweak theory such as superstring inspired models. We discuss in detail the nature of this CP violation and show that it can occur in a two-generation model. Possible effects are briefly discussed.
Status and implications of neutrino masses: a brief panorama
15 pages.- 10 figures
An extended flipped SU(5) GUT model and the fermion mass hierarchy
We present a viable flipped version of the SO(10) model consistent with the phenomenological requirements of having a non-trivial quark mixing matrix, natural doublet-triplet splitting, and a single pair of light electroweak Higgs doublet scalar bosons. In the presence of suitable non-renormalizable superpotential terms the model can reproduce the hierarchy observed in quark masses and mixings as well as an acceptable neutrino mass generated via the seesaw mechanism needed to explain dark matter and solar neutrino data.
Fitting Simpson's neutrino into the standard model
Abstract I show how to accomodate the 17 keV state recently reported by Simpson as one of the neutrinos of the standard model. Experimental constraints can only be satisfied if the μ and τ neutrino combine to a very good approximation to form a Dirac neutrino of 17 keV leaving a light ν e . Neutrino oscillations will provide the most stringent test of the model. The cosmological bounds are also satisfied in a natural way in models with Goldstone bosons. Explicit examples are given in the framework of majoron-type models. Constraints on the lepton symmetry breaking scale which follow from astrophysics, cosmology and laboratory experiments are discussed.
Bounds on sterile neutrino mixing for cosmologically interesting mass range
This talk summarizes our recent work which studied the impact of resonant $\nu_e \to\nu_s$ and $\bar{\nu}_e\to\bar{\nu}_s$ ($\nu_s$ is a sterile neutrino) conversions on supernova physics, under the assumption that the mass of the sterile state is in the few eV -cosmologically significant range.
Constraints on an additional Z′ gauge boson versus the W, the top and the Higgs masses
Abstract We analyse the restrictions on the mass and the mixing of an additional Z′ gauge boson that follow from the recent LEP measurements taking into account standard model (SM) radiative corrections. We find that these restrictions depend sharply on the assumed values for the SM structural parameters, the most important of which are M w and m top . The constraints become stronger for lighter W and heavier top.
Gravitational violation of R parity and its cosmological signatures
The discrete R-parity ($R_P$) usually imposed on the Supersymmetric (SUSY) models is expected to be broken at least gravitationally. If the neutralino is a dark matter particle its decay channels into positrons, antiprotons and neutrinos are severely constrained from astrophysical observations. These constraints are shown to be violated even for Planck-mass-suppressed dimension-five interactions arising from gravitational effects. We perform a general analysis of gravitationally induced $R_P$ violation and identify two plausible and astrophysically consistent scenarios for achieving the required suppression.
New Signatures for a Light Stop at LEP2 in SUSY Models with Spontaneously Broken R-Parity
In a class of supersymmetric models with R-parity breaking the lightest stop can have new decay modes into third generation fermions, $\tilde{t}_1 \rightarrow b + \tau$. We show that this decay may be dominant or at least comparable to the ordinary R-parity conserving mode $\tilde{t}_1 \rightarrow c + \tilde{\chi}_1^0$, where $\tilde{\chi}_1^0$ denotes the lightest neutralino. The new R-parity violating decay mode could provide new signatures for stop production at LEP.
Type-II Supernovae and Neutrino Magnetic Moment
The present solar and atmospheric neutrino data together with the LSND results and the presence of hot dark matter (HDM) suggest the existence of a sterile neutrino at the eV scale. We have reanalysed the effect of resonant {\sl sterile} neutrino conversions induced by neutrino magnetic moments in a type-II supernova. We analyse the implications of $\nu_e-\nu_s$ and $\bar{\nu}_e-\bar{\nu}_s$ ($\nu_s$ denotes sterile neutrino) conversions for the supernova shock re-heating, the detected $\bar\nu_e$ signal from SN1987A and the $r$-process nucleosynthesis hypothesis. Using reasonable magnetic field profiles we determine the sensitivity of these three arguments to the relevant neutrino paramete…
Theory and implications of neutrino mass
Abstract I briefly review the basic theory of neutrino mass from the point of view of modern gauge theories. Some of the implications of neutrino masses for particle physics, nuclear physics, cosmology and astrophysics are discussed.
Neutrinos properties beyond the Standard Model
The present observational status of neutrino physics is sketched, with emphasis on the hints that follow from solar and atmospheric neutrino observations, as well as dark matter. I also briefly review the ways to account for the observed anomalies and some of their implications
Modeling quitessential inflation
We develop general criteria to construct unified frameworks for inflation and quintessence which employ a unique scalar field to drive both. By using such a minimal theoretical framework we avoid having to fine-tune couplings and mass-scales. In particular the initial conditions for quintessence are already fixed at the end of the inflationary epoch. We provide concrete realizations of the method which meet all inflationary and quintessence requirements, such as the COBE normalization and the resulting spectral index n = 0.97, which is in excellent agreement with the latest CMB data.
Two-Body Decays of the Lightest Stop in Supergravity with and without R-Parity
We study the decays of the lightest top squark in supergravity models with and without R-parity. Using the simplest model with an effective explicit bilinear breaking of R-parity and radiative electroweak symmetry breaking we show that, below the threshold for decays into charginos $\tilde t_1\to c\chi^+_1$, the lightest stop decays mainly into third generation fermions, $\tilde t_1\to b\tau$ instead of the R-parity conserving mode $\tilde t_1\to c\chi^0_1$, even for tiny tau--neutrino mass values. Moreover we show that, even above the threshold for decays into charginos, the decay $\tilde t_1\to b\tau$ may be dominant. We study the role played by the universality of the boundary conditions…
Unification of gauge couplings and the tau-neutrino mass in supergravity without R parity
Minimal R-parity violating supergravity predicts a value for $alpha_s(M_Z)$ smaller than in the case with conserved R-parity, and therefore closer to the experimental world average. We show that the R-parity violating effect on the $alpha_s$ prediction comes from the larger two-loop b-quark Yukawa contribution to the renormalization group evolution of the gauge couplings which characterizes R-parity violating supergravity. The effect is correlated to the tau neutrino mass and is sensitive to the initial conditions on the soft supersymmetry breaking parameters at the unification scale. We show how a few percent effect on $alpha_s(M_Z)$ may naturally occur even with tau neutrino masses as sma…
CP violation and neutrino oscillations
We review the basic mechanisms of neutrino mass generation and the corresponding structure of the lepton mixing matrix. We summarize the status of three-neutrino oscillation parameters as determined from current observations, using state-of-the-art solar and atmospheric neutrino fluxes, as well as latest experimental data as of September 2007. We also comment on recent attempts to account for these results and to understand flavour from first principles. We discuss extensively the prospects for probing the strength of CP violation in two near term accelerator neutrino oscillation experiments, T2K and NOvA, as well as possible extensions such as T2KK and a second large off-axis detector near…
Reconstructing Neutrino Properties from Collider Experiments in a Higgs Triplet Neutrino Mass Model
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 neutri…
Symmetrical Parametrizations of the Lepton Mixing Matrix
Advantages of the original symmetrical form of the parametrization of the lepton mixing matrix are discussed. It provides a conceptually more transparent description of neutrino oscillations and lepton number violating processes like neutrinoless double beta decay, clarifying the significance of Dirac and Majorana phases. It is also ideal for parametrizing scenarios with light sterile neutrinos.
Planck-scale effects on WIMP dark matter
There exists a widely known conjecture that gravitational effects violate global symmetries. We study the effect of global-symmetry violating higher-dimension operators induced by Planck-scale physics on the properties of WIMP dark matter. Using an effective description, we show that the lifetime of the WIMP dark matter candidate can satisfy cosmological bounds under reasonable assumptions regarding the strength of the dimension-five operators. On the other hand, the indirect WIMP dark matter detection signal is significantly enhanced due to new decay channels.