Spontaneous R-parity Breaking Research Articles

ON THE ORIGIN OF R-PARITY VIOLATION IN SUPERSYMMETRY

The fate of R-parity in supersymmetric theories is discussed in detail. We make a strong case for R-parity violation showing that the simplest theories based on the local B - L symmetry predict the spontaneous breaking of R-parity at the SUSY scale. The possible implications for the searches at the Large Hadron Collider are discussed.

The minimal theory for R-parity violation at the LHC

We investigate the simplest gauge theory for spontaneous R-parity breaking and its testability at the LHC. This theory based on a local B-L gauge symmetry can be considered as the simplest framework for understanding the origin of the R-parity violating interactions, giving rise to potential lepton number violating signals and suppressed baryon number violating operators. The full spectrum of the theory and the constraints coming from neutrino masses are analyzed in great detail. We discuss the proton decay issue and the possible dark matter candidates. In order to assess the testability of the theory we study the properties of the new gauge boson, the neutralino decays and the main production channels for the charged sleptons at the LHC. We find that the channels with four charged leptons, three of them with the same sign, and four jets give us the most striking signals for the testability of lepton number violation at the LHC.

Three layers of neutrinos

In this Letter we point out that in a class of models for spontaneous R-parity breaking based on gauged B−L, the spectrum for neutrinos is quite peculiar. We find that those models generally predict three layers of neutrinos: one heavy sterile neutrino, two massive active neutrinos, and three nearly massless (one active and two sterile) neutrinos.

Spontaneous R-parity violation and the origin of neutrino mass

We study the phenomenology of supersymmetric models that explain neutrino masses through the spontaneous breaking of R-parity, finding strong correlations between the decays of the lightest neutralino and the neutrino mixing angles. In addition, the existence of a Goldstone boson, usually called Majoron (J), completely modifies the phenomenology with respect to the standard picture, inducing large invisible branching ratios and charged lepton decays, like μ → eJ, interesting signals that can be used to constrain the model.

Majoron emission in muon and tau decays revisited

In models where the breaking of lepton number is spontaneous a massless Goldstone boson, the Majoron ($J$), appears. We calculate the theoretically allowed range for the branching ratios of Majoron emitting charged lepton decays, such as Br($\mu \to e J$) and Br($\mu \to e J \gamma$), in a supersymmetric model with spontaneous breaking of R-parity. Br($\mu\to eJ$) is maximal in the same region of parameter space for which the lightest neutralino decays mainly invisibly. A measurement of Br($\mu\to eJ$) thus potentially provides information on R-parity violation complementary to accelerator searches. We also briefly discuss existing bounds and prospects for future improvements on the Majoron coupling to charged leptons.

Spontaneous R-parity breaking and left–right symmetry

We propose a simple renormalizable left–right theory where R-parity is spontaneously broken and neutrino masses are generated through the Type I seesaw mechanism and R-parity violation. In this theory R-parity and the gauge symmetry are broken by the sneutrino vacuum expectation values and there is no Majoron problem. The SU(2)R and R-parity violation scales are determined by the SUSY breaking scale making the model very predictive. We discuss the spectrum and possible tests of the theory through the neutralinos, charginos, Z′ and WR± decays at the Large Hadron Collider.

Search for R-parity violation at LEP

We discuss the present status of the searches for R-parity violation at LEP. The following topics are considered: pair-production of supersymmetric particles via λ, λ′ or λ″ couplings, sneutrino single production and spontaneous R-parity breaking. No evidence of signal is found in the total data sample at centre-of-mass energies up to √ s = 208 GeV, with an integrated luminosity of 700 pb −1 per experiment. Limits are set on the production cross sections, on the MSSM parameters and on the masses of the supersymmetric particles.

SpontaneousR-parity violation bounds

We investigate bounds from tree-level and one-loop processes in generic supersymmetric models with spontaneous R-parity breaking in the superpotential. We analyse the bounds from a general point of view. The bounds are applicable both for all models with spontaneous R-parity violation and for explicit bilinear R-parity violation based on general lepton-chargino and neutrino-neutralino mixings. We find constraints from semileptonic B, D and K decays, leptonic decays of the mu and tau, electric dipole moments, as well as bounds for the anomalous magnetic moment of the muon.

Signals of spontaneous R parity breaking at LEP and at a linear collider

We study the production of neutralinos and charginos at LEP and at a linear collider in the case of spontaneously broken R-parity. We first investigate the constraints on the single neutralino and chargino production from the LEP 1 experiments, and then we consider the production at LEP 2 and at a linear collider. We concentrate on the supersymmetric $SU(2)_L \times SU(2)_R \times U(1)_{B-L}$ model, where the spontaneous R-parity breaking is inevitable and is associated with the breaking of the LR-symmetry.

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 tanβ and bottom quark Yukawa couplings allowed in the model, as well as the relation between the tau neutrino mass and the bilinear R-parity violating parameter.

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.

Signals of spontaneous R parity breaking at LEP and at a linear collider

We study the production of neutralinos and charginos at LEP and at a linear collider in the case of spontaneously broken R-parity. We first investigate the constraints on the single neutralino and chargino production from the LEP 1 experiments, and then we consider the production at LEP 2 and at a linear collider. We concentrate on the supersymmetric $SU(2)_L \times SU(2)_R \times U(1)_{B-L}$ model, where the spontaneous R-parity breaking is inevitable and is associated with the breaking of the LR-symmetry.

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 ( P ̷ T+μ +μ −) arising from lightest neutralino single production χν as well as pair production χχ, followed by χ decays, where χ 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.

Spontaneous R-parity breaking in a supersymmetric majoron model

Spontaneous R-parity breaking is investigated in a supersymmetric majoron model, where the superfields of antineutrinos and an L = 2 singlet are added to the minimal supersymmetric standard model. The analysis is made by considering the effects of renormalization group evolution of the coupling parameters. It is found that for a certain region of the initial parameters at some unification scale, e.g. ∼ 1016 GeV, the desired values of the coupling parameters are reproduced at the electroweak scale ∼ 100 GeV to cause spontaneous R-parity breaking. The masses and decays of the light neutrinos are also examined briefly.

The supersymmetric singlet majoron

We study the supersymmetrized version of the singlet majoron model and, performing an analysis of the renormalization-group improved potential, we find that a spontaneous breaking of R-parity can be achieved for a wide range of the parameters. Studying the finite-temperature effective potential, we show that the phase transition leading to R-parity breaking can be of the first order and can occur at temperatures below the weak scale, thus avoidimg any constraint coming from the requirement of the preservation of the baryon asymmetry in the early universe.

Can solar neutrino oscillation parameters be probed at accelerators?

If supersymmetry is realized with spontaneous breaking of R-parity, there will be many phenomenological consequences. Here we show that the masses and mixing angles of the neutrinos lie in the correct range for the MSW explanation of the solar neutrino problem. At the same time the rates for the processes Z 0 → τ + chargino, τ → μ + Majoron and μ → ϵ + Majoron can be close to the present bounds.

How can R parity be broken?

The most popular model of spontaneous R-parity breaking is analyzed. It is shown that the extremum of the potential found in the model is, in fact, an unstable saddle point, while in the true minimum R parity is not broken. Other existing models involving R-parity breaking are briefly discussed and it is pointed out that none of them can describe successfully the existing experimental data.

Supersymmetry with spontaneous R-parity breaking in Z 0 decays: The case of an additional Z

Single production of SUSY particles in the decays of the Z 0 may proceed with large rates in models with spontaneously broken R-parity. We focus on the case where there is a lepton number symmetry as part of the gauge group. In the simplest of such models there is a single additional neutral gauge boson and the strength of R p -violating interactions is related with that of the new gauge force. We study the phenomenological implications of the model for Z 0 decays, including the study of the rates for single chargino production in Z 0 decays, i.e. Z 0→ ξ ± τ ±, as well as for the so-called Zen events, and find that they may be measurable at LEP. The first process, characteristics of spontaneously broken R-parity models, may proceed with a branching ratio as large as few × 10 −5 and should lead to a very clear signature. Zen events have a different origin than in the minimal SUSY standard model (MSSM). Their rates may also be enhanced with respect to MSSM. Our estimates of these rates take into account all of the relevant observational constraints, such as those that follow from neutrinophyics, from precise Z 0 property measurements, as well as SUSY particle searches at LEP.

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.

Low energy supergravity: R-parity breaking and the top quark mass

We study the process of spontaneous R-parity breaking in minimal low energy supergravity models. We show that it is very hard to obtain models with heavy top quarks if one wants to preserve the radiative breaking of SU(2) L⊗U(1) Y without breaking R-parity.