Lepton number violation in D meson decay

The lepton number violation(LNV) process can be induced by introducing a fourth generation heavy Majorana neutrino,which is coupled to the charged leptons of the Standard Model(SM). There have been many previous studies on the leptonic number violating decay processes with this mechanism. We follow the trend to study the process: D→Kllπ with the same-sign dilepton final states. We restrict ourselves to certain neutrino mass regions,in which the heavy neutrino could be on-shell and the dominant contribution to the branching fraction comes from the resonance enhanced effect. Applying the narrow width approximation(NWA),we found that the upper limit for the branching fractions for D0→ K-l+l+π-are generally at the order of 10-12 to 10-9,if we take the most stringent upper limit bound currently available in the literature for the mixing matrix elements. We also provide the constraints,which is competitive compared to the LNV B decays,on the mixing matrix element |VeN|2 based on the upper limit of D0→ K-e+e+π-estimated from the Monte-Carlo(MC) study at BESⅢ. Although the constraints are worse than the ones from(0νββ) decay in the literature,the future experiment at the charm factory may yield more stringent constraints.     

Search for flavor lepton number violation in slepton decays at LHC

We show that in supersymmetric models with explicit flavor lepton number violation due to soft supersymmetry breaking mass terms there could be detectable flavor lepton number violation in slepton decays. We estimate the potential for discovery of lepton flavor number violation in slepton decays at LHC. Pis’ma Zh. éksp. Teor. Fiz. 65, No. 2, 139–144 (25 January 1997) Published in English in the original Russian journal. Edited by Steve Torstveit.     

Lepton decay channels of egret gluinos at the LHC

Prospects for observing a SUSY-like signal from two gluinos are investigated within a certain region of the mSUGRA parameter space, where the cross section of the two gluino production in pp collisions at the LHC ( = 14 TeV) via gluon-gluon fusion (gg → ) is estimated at a rather high level of 17.3 pb. In this so-called EGRET region, the lightest stable neutralinos can serve as cold dark matter particles and are natural explanations of the excess of diffuse galactic gamma rays observed by the EGRET space apparatus. The -event selection relies on a very clear signature when decay products of each gluino contain one b-anti-b pair, one or two lepton-antilepton pair(s) and a neutralino. Rather high transverse-missing energy, carried away by the two neutralinos, is an essential signature of the events and also allows the relevant Standard Model background to be reduced significantly. In particular, it was found that the clear signatures of the selected processes demonstrate good prospects discovering the EGRET gluinos at the LHC. Furthermore, these signatures allow one to distinguish different mSUGRA parameters m _1/2 inside the EGRET region. The text was submitted by the authors in English.     

Lepton number violation in softly broken supersymmetry (II)

We study the implications of explicit lepton-number violating soft operators in a general low-energy effective theory with softly broken supersymmetry. Nonzero but relatively small VEVs of scalar neutrinos could exist. In the case where the VEVs of scalar neutrinos vanish, appreciable coefficients of the lepton-number violating soft operators are allowed. We also emphasize the role played by the mixing between the superpartners of the left- and right-handed leptons in the lepton family number violating process μ→eγ.     

Higgs induced light leptoquark–diquark mixing and proton decay

A so-called Renormalization Group (RG) analysis is performed in order to shed some light on why the density of prime numbers in decreases like the single power of the inverse neperian logarithm. Received: 14 June 2000 / Published online: 31 August 2000     

Test of lepton flavour violation at the LHC

We study lepton flavour violating decays of neutralinos and sleptons within the minimal supersymmetric standard model, assuming two and three generation mixings in the slepton sector. We take into account the most recent bounds on flavour violating rare lepton decays. Taking the SPS1a’ scenario as an example, we show that some of the lepton flavour violating branching ratios of neutralinos and sleptons can be sizable (∼5–10%). We study the impact of the lepton flavour violating neutralino and slepton decays on the di-lepton mass distributions measured at the LHC. We find that they can result in novel and characteristic edge structures in the distributions. In particular, double-edge structures can appear in the eτ and μτ mass spectra if is the lightest slepton. The appearance of these remarkable structures provides a powerful test of supersymmetric lepton flavour violation at the LHC.     

Lepton flavor violation and seesaw symmetries

When the standard model is extended with right-handed neutrinos the symmetries of the resulting Lagrangian are enlarged with a new global U(1) _R Abelian factor. In the context of minimal seesaw models we analyze the implications of a slightly broken U(1) _R symmetry on charged lepton flavor violating decays. We find, depending on the R-charge assignments, models where charged lepton flavor violating rates can be within measurable ranges. In particular, we show that in the resulting models due to the structure of the light neutrino mass matrix muon flavor violating decays are entirely determined by neutrino data (up to a normalization factor) and can be sizable in a wide right-handed neutrino mass range.     

Lepton and flavor violation in SUSY models

Lepton and flavor violating processes resulting from neutral scalar-lepton mixing are examined in the context of supersymmetric models. Contributions arising at the one-loop level for μ → eγ, μ → 3e, μμ ⇄ ee as well as for neutrinoless ββ-decay are found to be suppressed for a general class of supersymmetry breaking parameters.     

Lepton flavour violating heavy Higgs decays within the and their detection at the LHC

Within the νMSSM, a Minimal Supersymmetric neutrino See-saw Model, Lepton Flavour Violating Higgs couplings are strongly enhanced at large tanβ (30), which can lead to BR(H⁰/A⁰→τμ)O(10⁻⁴), for M_H⁰/A⁰160 GeV. Enhancements on the production of Higgs bosons, through the gluon fusion mechanism, gg→H⁰/A⁰, and the associated production channel , whose rates grow with tanβ, as well as the mass degeneracy that occurs between the H⁰ and A⁰ states in this regime, also contribute to further the possibilities to detect a heavy Higgs signal into τμ pairs. We show that the separation of τμ Higgs events from the background at the upcoming CERN Large Hadron Collider could be done for Higgs masses up to about 600 GeV for 300 fb⁻¹ of luminosity, for large tanβ values. However, even with as little as 10 fb⁻¹ one can probe H⁰/A⁰ masses up to 400 GeV or so, if tanβ=60. Altogether, these processes then provide a new Higgs discovery mode as well as an independent test of flavour physics.     

Lepton flavour violation in the constrained MSSM with constrained sequential dominance

We consider charged lepton flavour violation (LFV) in the constrained minimal supersymmetric Standard Model, extended to include the see-saw mechanism with constrained sequential dominance (CSD), where CSD provides a natural see-saw explanation of tri-bimaximal neutrino mixing. When charged lepton corrections to tri-bimaximal neutrino mixing are included, we discover characteristic correlations among the LFV branching ratios, depending on the mass ordering of the right-handed neutrinos, with a pronounced dependence on the leptonic mixing angle θ₁₃${\theta }_{13}$ (and in some cases also on the Dirac CP phase δ).     

Measurement of CP violation in stop cascade decays at the LHC

We study the potential observation at the LHC of CP-violating effects in stop production and subsequent cascade decays, , , , within the Minimal Supersymmetric Standard Model. We study T-odd asymmetries based on triple products between the different decay products. There may be a large CP asymmetry at the parton level, but there is a significant dilution at the hadronic level after integrating over the parton distribution functions. Consequently, even for scenarios where large CP intrinsic asymmetries are expected, the measurable asymmetry is rather small. High luminosity and precise measurements of masses, branching ratios and CP asymmetries may enable measurements of the CP-violating parameters in cascade decays at the LHC.     

A search for leptoquark bosons and lepton flavor violation in e^+ p collisions at HERA

A search for new bosons possessing couplings to lepton-quark pairs is performed in the H1 experiment at HERA using 1994 to 1997 data corresponding to an integrated luminosity of pb. First generation leptoquarks (LQs) are searched in very high neutral (NC) and charged (CC) current data samples. The measurements are compared to Standard Model (SM) expectations from deep-inelastic scattering (DIS). A deviation in the spectrum previously observed in the 1994 to 1996 dataset at GeV remains, though with less significance. This deviation corresponded to a clustering in the invariant mass spectrum at GeV which is not observed with the 1997 dataset alone. The NC DIS data is used to constrain the Yukawa couplings of first generation scalar and vector LQs in the Buchmüller–Rückl–Wyler effective model. Scalar LQs are excluded for masses up to 275 GeV for a coupling of electromagnetic strength, . A sensitivity to coupling values is established for masses up to 400 GeV for any LQ type. The NC and CC DIS data are combined to constrain for arbitrary branching ratios of the LQ into eq in a generic model. For a decay branching ratio into pairs as small as 10%, LQ masses up to 260 GeV are ruled out for . LQs possessing couplings to mixed fermion generations, which could lead to signals of lepton flavor violation (LFV), are searched in events with a high transverse momentum or . No or event candidate is found that is compatible with LQ kinematics. Constraints are set on the Yukawa coupling involving the and lepton in a yet unexplored mass range. Received: 2 July 1999 / Published online: 28 September 1999     

Electroweak baryon number violation at finite temperature

We consider baryon and lepton number violating processes in the electroweak theory induced by gauge and Higgs fields passing the sphaleron solution at finite temperature. We show that for temperatures larger than 19 GeV the anomalous baryon and lepton number violating processes are suppressed by the Boltzmann factor exp (?βE _sp), whereE _sp is the sphaleron energy, rather than by the instanton tunneling factor exp (?8π²/g ²). We caculate the rate of baryon and lepton number violating processes at finite temperature and determine the freezing temperature of the anomalous processes in the early universe as a function of the Higgs mass. We compare the freezing temperature with the critical temperature of the electroweak phase transition infered from the one-loop finite-temperature effective potential. We obtain a critical Higgs mass of the order of 100 GeV, slightly depending on the top mass and the magnitude of the pre-exponential factor in the rate of theB non-conservation, above which the anomalous processes are certainly in equilibrium after the electroweak phase transition. Assuming that the temperature-dependence of the sphaleron energy is given by that found from the one-loop finitetemperature effective potential, this critical Higgs mass is lowered to a value of the order of 50 GeV.     

Parity violation in high energy Lepton pair production and QCD

We use the quark-parton model with perturbative QCD corrections in the Weinberg-Salam theory to calculate a parity-violating asymmetry in inclusive lepton pair production. We estimate the asymmetry proportional to the triple correlation $\text{〈}\text{P·l}{}^{\mathrm{+}}\text{×}\text{l}{}^{\mathrm{?}}\text{〉}$ of the lepton momenta $\text{l}{}^{\mathrm{+}}\text{and}\text{l}{}^{\mathrm{?}}$ and the incident hadron momentum $\text{P}$. We find that a nonzero asymmetry requires inclusion of nonperturbative effects.