Search results for "Superstring theory"
showing 10 items of 19 documents
Lepton physics versus neutrino mass
1990
Abstract The relationship between the strength of lepton flavour violating processes and the magnitude of the neutrino mass is rather model dependent. I review this question within different neutrino mixing models including superstring inspired models. Processes such as μ → e + γ , μ → 3 e , μ - e conversion in nuclei, etc. as well as lepton flavour violating Z ° decays can occur even if the physical neutrinos are strictly massless. As a result, the corresponding rates are unconstrained by bounds on the neutrino mass that follow from laboratory, astrophysics and cosmology and can therefore be large. Leptonic CP violation may also occur even when the physical neutrinos are strictly massless.
Twistor string as tensionless superstring
2007
6 pages.-- PACS nrs.: 11.30.Pb, 11.25.-w, 11.10.Kk, 12.60.Jv.-- ISI Article Identifier: 000247103400009.-- ArXiv pre-print available at: http://arxiv.org/abs/hep-th/0702133
D=4 supergravity dynamically coupled to superstring in a superfield Lagrangian approach
2003
We elaborate a full superfield description of the interacting system of dynamical D=4, N=1 supergravity and dynamical superstring. As far as minimal formulation of the simple supergravity is used, such a system should contain as well the tensor (real linear) multiplet which describes the dilaton and the two-superform gauge field whose pull-back provides the Wess-Zumino term for the superstring. The superfield action is given by the sum of the Wess-Zumino action for D=4, N=1 superfield supergravity, the superfield action for the tensor multiplet in curved superspace and the Green-Schwarz superstring action. The latter includes the coupling to the tensor multiplet both in the Nambu-Goto and i…
On the Super Higgs Effect in Extended Supergravity
2002
We consider the reduction of supersymmetry in N-extended four dimensional supergravity via the super Higgs mechanism in theories without cosmological constant. We provide an analysis largely based on the properties of long and short multiplets of Poincare' supersymmetry. Examples of the super Higgs phenomenon are realized in spontaneously broken N=8 supergravity through the Scherk-Schwarz mechanism and in superstring compactification in presence of brane fluxes. In many models the massive vectors count the difference in number of the translation isometries of the scalar sigma-model geometries in the broken and unbroken phase.
Production mechanisms and signatures of isosinglet neutral heavy leptons in Z0 decays
1990
Abstract Neutral Heavy Leptons (NHLs) arise in many extensions of the standard electroweak theory such as superstring inspired models. The possibility of gauge singlets NHLs is especially attractive because it gives an explanation for the observed smallness of the neutrino mass. Existing limits on the possible existence of such particles are still fairly poor. We have investigated isosinglet NHL production and decays within different models. The dominant production cross section is single production (i.e. Z 0 → N + ν or Z 0 → N + ν ) as a result of mixing with the standard doublet neutrinos. Subsequent NHL decays lead to striking signatures. Taking into account the expected luminosities and…
Supersymmetry currents and WZ-like terms in (supersymmetry)2 models
1990
Abstract Using the superfield formulation of the N = 1 spinning superparticle model as an example, the superfield currents associated with the target space supersymmetry are given, and the component expression of the corresponding superalgebra is found to describe a graded “doubling” of the Poincare superalgebra. Further, it is shown how the torsion-like term in the spinning super-particle model can be obtained from the form associated with the Green-Schwarz WZ term for the superstring, and a possible way of introducing extended spinning supersymmetric objects is discussed.
Lorentz harmonics and superfield action. D=10, N=1 superstring
2000
We propose a new version of the superfield action for a closed D=10, N=1 superstring where the Lorentz harmonics are used as auxiliary superfields. The incorporation of Lorentz harmonics into the superfield action makes possible to obtain superfield constraints of the induced worldsheet supergravity as equations of motion. Moreover, it becomes evident that a so-called 'Wess-Zumino part' of the superfield action is basically a Lagrangian form of the generalized action principle. We propose to use the second Noether theorem to handle the essential terms in the transformation lows of hidden gauge symmetries, which remove dynamical degrees of freedom from the Lagrange multiplier superfield.
Gauged extended supergravity without cosmological constant: No-scale structure and supersymmetry breaking
2002
We consider the interplay of duality symmetries and gauged isometries of supergravity models giving N-extended, spontaneously broken supergravity with a no-scale structure. Some examples, motivated by superstring and M-theory compactifications are described.
Neutral heavy lepton signatures at the Z0 peak
1990
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…
Flavour-violating charged lepton decays in seesaw-type models
1994
Analytic expressions of lepton-flavour- and lepton-number-violating decays of charged leptons are derived in the context of general $SU(2)_L\otimes U(1)_Y$ seesaw scenarios that are motivated by grand unified theories (GUT's) or superstring models, in which left-handed and/or right-handed neutral singlets are present. Possible constraints imposed by cosmology and low-energy data are briefly discussed. The violation of the decoupling theorem in flavour-dependent graphs due to the presence of heavy neutral leptons of Dirac or Majorana nature is emphasized. Numerical estimates reveal that the decays $\tau^-\to e^-e^-e^+$ or $\tau^-\to e^-\mu^-\mu^+$ can be as large as $\sim 10^{-6}$, which may…