Search

In the Randall-Sundrum model, a bulk neutrino field in five-dimensional spacetime can give rise to tiny Dirac masses for neutrinos. In such a scenario, we have computed the contribution of the bulk neutrino field to the anomalous magnetic moment (g -- 2)μ of the muon. We have computed this contribution in the't Hooft-Feynman gauge and have found that the contribution has the right sign to fit the current discrepancy between the experiment and the standard model value of (g -- 2)μ. We have also studied possible constraints on the model parameters by including contributions to (g -- 2)μ from other sources such as bulk gravitons. [ABSTRACT FROM AUTHOR]

In R-parity violating supersymmetric models both leptogenesis and the correct neutrino masses are hard to achieve together. The presence of certain soft nonholomorphic R-parity violating terms helps to resolve this problem. We consider a scenario where the lightest and the second-lightest neutralino are nearly degenerate in mass and enough CP-asymmetry can be produced through resonant leptogenesis. In this model, the lighter chargino and the lightest neutralino are highly degenerate. We have relatively lighter gauginos which can be produced at the LHC (with √s = 14 TeV) leading to heavily ionizing charged tracks. At the same time this model can also generate the correct neutrino mass scale. Thus our scenario is phenomenologically rich and testable at colliders. [ABSTRACT FROM AUTHOR]

We propose that the γ+E signal at the Belle-II detector will be a smoking gun for supersymmetry (SUSY) in the presence of a gauged U(1)Lμ-Lτ symmetry. A striking consequence of breaking the enhanced symmetry appearing in the limit of degenerate (s)leptons is the nondecoupling of the radiative contribution of heavy charged sleptons to the γ-Z′ kinetic mixing. The signal process, e+e-→γZ′→γ+E, is an outcome of this ubiquitous feature. We take into account the severe constraints on gauged U(1)Lμ-Lτ models by several low-energy observables and show that any significant excess in all but the highest photon energy bin would be an undeniable signature of such heavy scalar fields in SUSY coupling to Z′. The number of signal events depends crucially on the logarithm of the ratio of stau to smuon mass in the presence of SUSY. In addition, the number is also inversely proportional to the e+-e- collision energy, making a low-energy, high-luminosity collider like Belle-II an ideal testing ground for this channel. This process can probe large swathes of the slepton mass ratio vs the additional gauge coupling (gX) parameter space. More importantly, it can explore the narrow slice of MZ′-gX parameter space still allowed in gauged U(1)Lμ-Lτ models for superheavy sparticles. [ABSTRACT FROM AUTHOR]

We study the stability constraints on the parameter space of a triplet extension of the Minimal Supersymmetric Standard Model (MSSM). Existence of unbounded-from-below directions in the potential can spoil successful electroweak (EW) symmetry breaking by making the corresponding minimum unstable, and hence the model should be free from those directions. Avoiding those directions restricts the parameter space of the model. We derive four stability constraints, of which only three are independent from each other. After scanning the parameter space of the model for phenomenologically viable data points, we impose the stability constraints and find that only about a quarter of the data points features a stable EW minimum. At those data points featuring stability, p and the up Higgs soft mass turn out to be smaller than about a TeV in absolute value, which makes the mass of the lightest chargino and neutralino smaller than about 700 GeV. Two relevant phenomenological consequences of lifting the unbounded-frombelow directions are that the lightest Higgs boson decay rate to diphoton predicted by the triplet extension of MSSM generally features larger deviations from MSSM, and fine-tuning is actually higher than what each of the two would be without imposing stability constraints. [ABSTRACT FROM AUTHOR]

We consider the minimal seesaw model in which two gauge singlet right-handed neutrinos with opposite lepton numbers are added to the Standard Model. In this model, the smallness of the neutrino mass is explained by the tiny lepton number violating coupling between one of the singlets with the standard left-handed neutrinos. This allows one to have the right-handed neutrino mass at the TeV scale as well as appreciable mixing between the light and heavy states. This model is fully reconstructible in terms of the neutrino oscillation parameters apart from the overall coupling strengths. We show that the overall coupling strength y„ for the Dirac-type coupling between the left-handed neutrino and one of the singlets can be restricted by consideration of the (meta)stability bounds on the electroweak vacuum. In this scenario the lepton flavor violating decays of charged leptons can be appreciable, which can put further constraint on yv for right-handed neutrinos at TeV scale. We discuss the combined constraints on yv for this scenario from the process μ eγ and from the consideration of vacuum (meta)stability constraints on the Higgs self-coupling. We also briefly discuss the implications for neutrinoless double beta decay and possible signatures of the model that can be expected at colliders. [ABSTRACT FROM AUTHOR]

We predict an unconventional background free signal of the Higgs boson in R-parity violating nonminimal supersymmetric models at the Large Hadron Collider (LHC). The signal comprises a dilepton plus four hadronic jets and two large displaced vertices. The displaced leptons and jets are coming from the decay of the lightest supersymmetric particle (LSP), which is predominantly a gauge-singlet neutrino. A pair of such LSPs can couple to a Higgs boson, created via gluon fusion. We have analyzed two cases-one corresponding to the tree-level Higgs boson mass and another with the one-loop corrected mass of the Higgs boson. A reliable Higgs mass reconstruction using this signal can lead to discovery at the LHC with center-of-mass energy √s = 14 TeV and 5 fb-1 of integrated luminosity (L). Even at √s = 7 TeV and L = 5 fb-1i, a reasonable number of events are expected. Besides, mass reconstruction of a gauge-singlet LSP can provide an estimate of the seesaw scale. [ABSTRACT FROM AUTHOR]

Recently the CDF Collaboration reported a statistically significant excess in the distribution of the dijet invariant mass between 120-160 GeV in Wjj event sample in 4.3 fb-1 of data and later confirmed with 7.3 fb-1 of data, which has generated considerable interest. We offer a possible explanation of this observation in the general framework of minimal supersymmetric standard model with R-parity violation through resonance production of ṽτ decaying into the LSP τ̃1 and W boson. We also give the predictions of this scenario for the LHC operating at 7 TeV center of mass energy. [ABSTRACT FROM AUTHOR]

We study a distinct supersymmetric signal of multiphotons in association with jets and missing transverse energy. At least one of these photons has the origin in displaced vertex, and thus it is delayed and nonpointing. We consider a supersymmetric scenario in which the gravitino is the lightest supersymmetric particle (LSP) (with a mass ∼1 keV) and the lightest neutralino is the next-to-lightest supersymmetric particle (NLSP). The NLSP decays dominantly into a photon and a gravitino within the detector with a decay length ranging from ctx∼50-100??cm. In addition, we assume that the second-lightest neutralino and the lightest neutralino are nearly degenerate and this leads to a prompt radiative decay of the next-to-lightest neutralino into a photon and a lightest neutralino with a large branching ratio. Such degenerate neutralinos can be realized in various representations of the SU(5), SO(10) and E(6) GUT group. The nonpointing photons can be reconstructed at the electromagnetic calorimeter of the ATLAS detector, which have been designed with good timing and directional resolution. We find that with a center-of-mass energy Ecm=14??TeV at an integrated luminosity of 100??fb-1 one may see evidence of hundreds of triphoton events at the LHC, in addition to several thousands diphoton events. We also predict the event rates even at the early phase of LHC run. [ABSTRACT FROM AUTHOR]

The minimal gauged U(1)Lμ-Lτ model has long been known to be able to explain the tension between the theoretical and experimental values of the muon magnetic moment. It has been explored and tested extensively, pushing the viable parameter space into a very tight corner. Further, embedding the U(1)Lμ-Lτ model in a supersymmetric (SUSY) framework has been shown to relax some of these constraints and has recently been shown to explain the electron anomalous magnetic moment as well. In this model, the logarithm of the mass ratio of third to second generation (s)leptons control the non-negligible kinetic mixing and may crucially alter many of the constraints. We confront both the non-SUSY and SUSY versions of this class of models with the CsI(2017), the recently released CENNS10 data from the liquid Argon detector, as well as the updated CsI(2020) data of the COHERENT experiment. We use the recoil energy and timing binned data from CsI(2017) and the energy, time, and pulse shape discriminator binned data from CENNS10 to find estimates for the model parameters in a likelihood maximization test. We also show updated exclusions using all of the above data from the COHERENT Collaboration, as well as projected exclusions from the ongoing Coherent CAPTAIN-Mills experiment. The (g-2)μ favored values of the U(1)Lμ-Lτ gauge coupling that are still unconstrained overlap with the estimates from COHERENT data within 1σ. The combined COHERENT data is found to prefer the presence of the U(1)Lμ-Lτ gauge boson over the Standard Model at ∼1.4σ. The global minima of a chi-square deviation function using CsI(2020) as well as CENNS10 total counts has significant overlap with the (g-2)μ favored parameter space in the context of the SUSY and non-SUSY Lμ-Lτ models with a mediator mass in the 20-100 MeV range. [ABSTRACT FROM AUTHOR]

The gauged U(1)Lμ-Lτ model can provide for additional contributions to the muon anomalous magnetic moment by means of a loop involving the Z′ gauge boson. However, the parameter space of such models is severely constrained if one combines the latest muon (g-2) data with various neutrino experiments, such as neutrino trident production, ν-e and ν-q elastic scattering, etc. In a supersymmetric U(1)Lμ-Lτ model, a larger region of parameter space opens up, thus enabling one to explore otherwise forbidden regions of parameter space in nonsupersymmetric models involving the new gauge coupling (gX) and the mass of the Z′ gauge boson (MZ′). We show that the minimal model with the minimal supersymmetric Standard Model (MSSM) field content is strongly disfavored from Z-boson decay and neutrino data. We also show that the nonminimal model with two extra singlet superfields can lead to correct neutrino masses and mixing involving both tree-level and one-loop contributions. We find that, in this model, both muon (g-2) and neutrino data may be simultaneously explained in a parameter region consistent with experimental observations. In addition, we observe that the muon (g-2) anomaly can be accommodated even with higher values of electroweak sparticle masses compared to the MSSM. Charged lepton-flavor-violating processes (like μ→eγ, τ→μγ, etc.) may have potentially large branching ratios in this scenario. Depending on the magnitude of the supersymmetry contribution to these processes, they may constrain hitherto unconstrained regions of the MZ-gX′ parameter space. However, we find that these branching fractions never exceed their upper bounds in a region where both muon (g-2) and neutrino oscillation data can be simultaneously accommodated. [ABSTRACT FROM AUTHOR]

We study the possible constraints on nonstandard interaction (NSIs) in a model-independent way by considering the recent results from the T2K and Daya Bay neutrino oscillations experiments. Using the perturbation method we present generic formulas (suitable for T2K baseline and for large θ13 as evident from Daya Bay) for the probability of oscillation for vμ→ ve, taking into account NSIs at the source (∈s), the detector (∈d), and during propagation (∈m) of neutrinos through matter. Two separate cases of perturbation with small (slightly large) NSI [∈mαβ~0.03(0.18)] are discussed in detail. Using various possible presently allowed NSI values we reanalyze numerically the θ13 -- δ allowed region given by recent T2K experimental data. We obtain model-independent constraints on NSIs in the δ -- ∈mαβ plane using the θ13 value as measured by Daya Bay, where δ is the CP violating phase. Depending on δ values, significant constraints on ∈eT and ∈TT, in particular, are possible for both hierarchies of neutrino masses. Corresponding to T2K's 66% confidence level result, the constraints on ∈TT are shown to be independent of any 5 value. [ABSTRACT FROM AUTHOR]

Sneutrino-antisneutrino oscillation can be a very useful probe to look for signatures of lepton number violation (ΔL = 2) at the Tevatron. Here, we discuss a scenario where the total decay width of the sneutrino is very small, producing interesting signals at the Tevatron for a mass splitting Δm as small as 10-14 GeV between the sneutrino mass eigenstates. [ABSTRACT FROM AUTHOR]

We investigate a model with local U(1)B-L and discrete Z2 symmetries where two types of weak isospin singlet neutrinos, vectorlike charged leptons, and exotic scalar fields are introduced. The linear seesaw mechanism is induced at the one-loop level through Yukawa interactions associated with the standard model leptons and exotic fields. We also discuss lepton flavor violation and a muon anomalous dipole magnetic moment induced by the new Yukawa interaction. In addition, our model has dark matter candidate which is the lightest Z2 odd neutral particle. We calculate the relic density and constraints from direct detection. [ABSTRACT FROM AUTHOR]