Neutral Current Research Articles

Novel flavour-changing neutral currents in the top quark sector

We demonstrate that flavour-changing neutral currents in the top sector, mediated by leptophilic scalars at the electroweak scale, can easily arise in scenarios of new physics, and in particular in composite Higgs models. We moreover show that such interactions are poorly constrained by current experiments, while they can be searched for at the LHC in rare top decays and, more generally, in the channels $pp\to tS(S)+j$, with $S\to\ell^+\ell^-$. We provide dedicated analyses in this respect, obtaining that cut-off scales as large as $\Lambda\sim$ 90 TeV can be probed with an integrated luminosity of $\mathcal{L} = 150$ fb$^{-1}$.

Probing new physics in semileptonic Σb and Ωb decays

Recently, several hints of lepton non-universality have been observed in the semileptonic B meson decays in terms of both in the neutral current ($b\to s l \bar{l}$) and charged current ($b\to c l \bar{\nu_{l}}$) transitions. Motivated by these inspiring results, we perform the analysis of the baryon decays ${\Sigma_b}\to \Sigma_c l \bar{\nu_{l}}$ and $\Omega_b\to \Omega_c l \bar{\nu_{l}} (l=e,\mu,\tau)$ which are mediated by $ b \to c l \bar{\nu_{l}}$ transitions at the quark level, to scrutinize the nature of new physics (NP) in the model independent method. We first use the experimental measurements of $\mathcal{B}( B\to D^{(*)} l\bar{\nu_{l}})$, ${\rm R}_{D^{(*)}}$ and ${\rm R}_{J/\psi}$ to constrain the NP coupling parameters in a variety of scenarios. Using the constrained NP coupling parameters, we report numerical results on various observables related to the processes ${\Sigma_b}\to \Sigma_c l \bar{\nu_{l}}$ and $\Omega_b\to \Omega_c l \bar{\nu_{l}}$, such as the branching ratios, the ratio of branching fractions, the lepton side forward-backward asymmetries, the hadron and lepton longitudinal polarization asymmetries and the convexity parameter. We also provide the $q^2$ dependency of these observables and we hope that the corresponding numerical results in this work will be testified by future experiments.

Modeling and Analysis of Transformer DC Bias Current Caused by Metro Stray Current

The metro stray current leaked during the subway operation causes the nearby earth surface potential to change, so that the various neutral‐grounded transformers to be at different earth surface potentials, resulting transformer DC bias. In order to analyze the influence of metro stray current on transformer DC bias, the polarization potential monitoring data in metro traction power supply system and neutral point current of nearby transformer were compared, and the positive correlation characteristics between the two were pointed out. By studying the stray current leakage reason in the metro traction power supply system and the circulation path causing transformer DC bias, the mechanism of the transformer DC bias under the subway operating environment was revealed. Based on the discrete model of the stray current distribution, considering the mechanism of stray current on DC bias, the equivalent resistance model of the transformer DC bias caused by metro stray current was built with double‐end power supply environment. Then the calculation formula of transformer neutral point current changing with subway operating conditions was derived, the numerical calculation of DC bias current of transformer caused by metro stray current was realized. The validity of the proposed model was verified by current distribution, electromagnetic field, grounding and soil structure analysis, the simulation results showed that the proposed model can calculate the stray current distribution and the nearby transformer DC bias current with high accuracy, which provided a quantitative analysis method for studying the correlation between metro stray current and transformer DC bias phenomenon. © 2020 Institute of Electrical Engineers of Japan. Published by Wiley Periodicals LLC.

Distributed Power Quality Conditioning System for Three-Phase Four-Wire Low Voltage Networks

This paper presents distributed power quality conditioning system to compensate current and voltage distortions in three-phase four-wire networks caused by unbalanced non-linear single-phase loads. The proposed conditioning system consists of several hybrid filter units installed in various nodes for compensation of excessive neutral currents and voltage distortions in a selected area of the distribution network. The system is open and it can be easily modified by installation of new filter units. A novel hybrid filter design procedure based on filter frequency characteristics optimization in the parameters of passive and active parts is presented. A digital system of control signal computation for active filters based on the use of modern methods of spectral analysis is considered. The proposed digital control system enables selective compensation of fundamental and harmonic components. The mathematical model of the proposed power quality conditioning system is developed in the MatLab software. The simulated results show that the presented conditioning system reduces the level of neutral conductor currents and the voltage unbalance as well ensures harmonic compensation in three-phase four-wire networks.

Impact of Nonlinear Lighting Loads on the Neutral Conductor Current of Low Voltage Residential Grids

In the last decade, mainly due to political incentives towards energy efficiency, the share of lamps with power electronic interfaces, like Compact Fluorescent Lamps (CFL) and Light Emitting Diode (LED) lamps, has significantly increased in the residential sector. Their massive use might have a substantial impact on harmonic currents and, consequently, on the current flowing in the neutral conductor. This paper analyzes the impact of modern energy-efficient lighting technologies on the neutral conductor current by using a synthetic Low Voltage residential grid. Different load scenarios reflecting the transition from incandescent lamps, via CFL, to LED lamps are compared concerning the neutral conductor current at different points in the network. The inherent randomness related to the use of lighting devices by each residential customer is considered employing a Monte Carlo simulation. Obtained results show that the use of CFL has a greater impact on the neutral conductor current of Low Voltage (LV) residential grids and that, with increasing use of LED lamps, a decreasing impact can be expected in the future.

Charged Higgs boson production via cb -fusion at the Large Hadron Collider

We analyse the production of a light charged Higgs boson at the Large Hadron Collider (LHC) via the quark-fusion mechanism $c \bar{b} \to H^- $ considering the decay channel $H^- \to \tau \bar \nu_\tau$ in the final state. We study this process in the framework of the 2-Higgs Doublet Model Type III (2HDM-III) which assumes a four-zero texture in the Yukawa matrices and a general Higgs potential, wherein the two Higgs doublets coupling to both up and down fermions do generate Flavour Changing Neutral Currents (FCNCs) yet the latter can be controlled by the texture when flavour physics constraints are considered. We consider the parameter space of the model where this signal is enhanced and in agreement with both theoretical constraints and experimental data. In particular, we exploit the setup with lepton-specific-like Yukawa couplings and assess the LHC sensitivity to such $H^\pm$ signals against the dominant {irreducible and} reducible backgrounds. We show that in our model BR$(H^\pm \to cb) \sim 0.1- 0.2$ and BR$(H^\pm \to \tau \nu) \sim 0.7-0.9$ so that, under these conditions, the prospects for $H^\pm$ detection in the 2HDM-III in the aforementioned production and decay channels are excellent assuming standard collider energy and luminosity conditions.

HV Transformer Protection and Stabilization under Geomagnetically Induced Currents

This paper presents the results of research related to the issues arising from DC excitation of power transformers due to geomagnetically induced currents (GIC). First, the GIC phenomena and their influence on power system operation are discussed. Then, a recorded case of tripping of the transformer differential protection due to geomagnetic disturbances (GD), as well as simulation signals from a developed model of a transformer subjected to a GD are analyzed. Next, two algorithms for GIC detection utilizing the rate of change of transformer differential currents and the DC component in the neutral current are proposed, thoroughly tested, and recommended.

Multiobjective Optimization Technique for Mitigating Unbalance and Improving Voltage Considering Higher Penetration of Electric Vehicles and Distributed Generation

The increasing penetration of distributed generations (DGs) and electric vehicles (EVs) offers not only several opportunities but also introduces many challenges for the distribution system operators (DSOs) regarding power quality. This article investigates the network performances due to uncoordinated DG and EV distribution. It also considers power quality-related performances such as the neutral current, energy loss, voltage imbalance, and bus voltage as a multiobjective optimization problem. The differential evolution optimization algorithm is employed to solve the multiobjective optimization problem to coordinate EV and DG in a distribution grid. This article proposed a method to coordinate EV and DG distribution. The proposed method allows DSOs to jointly optimize the phase sequence and optimal dispatch of DGs to improve the network's performance. If the network requires further improvement, the EV charging or discharging rate is coordinated for a particular location. The efficacy of the proposed method is tested in an Australian low-voltage distribution grid considering the amount of imbalance due to higher penetration of DG and EV. It is observed that the proposed method reduces voltage unbalance factor by up to 98.24%, neutral current up to 94%, and energy loss by 59.45%, and improve bus voltage by 10.42%.

Ant lion algorithm for optimized controller gains for power quality enrichment of off-grid wind power harnessing units

The proposed system uses an algorithm that works on the admittance of the system, for estimating the reference values of generated currents for an off-grid wind power harnessing unit (WPHU). The controller controls the voltage and maintains the frequency within the limits while working with both linear and nonlinear loads for varying wind speeds. The admittance algorithm is simple and easy to implement and works very efficiently to generate the triggering signals for the controller of the WPHU. The wind power harnessing unit comprising of a squirrel cage induction generator, a star-delta transformer, a battery storage system and the control unit are modeled using Matlab/Simulink R2019. An isolated transformer with a star-delta configuration connects the load and the generator circuit with the controller to reduce the dc bus voltage and mitigate current in the neutral line. The response of the system during the dynamic loading depends on the best possible compensator proportional-integral (PI) gains. The antlion optimization algorithm is compared with particle swarm optimization and grey wolf optimization and is found to have the advantages of good convergence, high efficiency and fast calculating speed. It is therefore used to extract the optimal values of frequency and voltage PI gains. The simulation results of the control algorithm for the WPHU are validated in a real-time environment in a dSpace1104 laboratory set up. This algorithm is proven to have a quick response, maintain the required frequency, suppress the current harmonics, regulate voltage, help in balancing the load and compensating for the neutral current.

A Comprehensive AC Current Ripple Analysis and Performance Enhancement via Discontinuous PWM in Three-Phase Four-Leg Grid-Connected Inverters

A complete analysis of the ac output current ripple in four-leg voltage source inverters considering multiple modulation schemes is provided. In detail, current ripple envelopes and peak-to-peak profiles have been determined in the whole fundamental period and a comprehensive method providing the current ripple rms has been achieved, all of them as a function of the modulation index. These characteristics have been determined for both phase and neutral currents, considering the most popular common-mode injection schemes. Particular attention has been paid to the performance of discontinuous pulse width modulation (DPWM) methods, including DPWMMAX and DPWMMIN, and their four most popular combinations DPWM0, DPWM1, DPWM2, and DPWM3. Furthermore, a comparison with a few continuous techniques (sinusoidal, centered pulse width modulations, and third harmonic injection) has been provided as well. Moreover, the average switching frequency and switching losses are analyzed, determining which PWM technique ensures minimum output current ripple within the linear modulation range at different assumptions. Numerical simulations and laboratory tests have been conducted to extensively verify all the analytical claims for all the considered PWM injections.

PMU-Based System State Estimation for Multigrounded Distribution Systems

Linear network modeling and phasor measurement units (PMUs) simplify the traditional system state estimation (SSE) problem. The existing multiphase SSE-PMU-based models are linear including earthing resistances as a fixed and invariable parameter. However, earthing resistances strongly depend on moisture and temperature changes over time. Thus, under unbalanced operation time-varying Neutral-Earth Voltages (NEV) could be higher than admisible touch and step voltages in urban areas. Earthing resistances can be now monitored using specialized meters and therefore duly incorporated as measured and state variables in a multigrounded SSE problem. Thus, the SSE problem becomes non-linear and the standard linear solution approach is no longer suitable. This fact has been overlooked in the literature. To fulfill the research gap, a new multi-grounded SSE-PMU-based formulation is presented. As a key contribution, the normal-equation structure used in linear SSE approaches was extended to a non-linear one in order to allow the estimation of grounding resistances, neutral-to-earth voltages, and neutral currents. The proposal was applied in a 2-bus example for illustration purposes and successfully applied and compared with existing methods under large-scale conditions.

First simulation study of trackless events in the INO-ICAL detector to probe the sensitivity to atmospheric neutrino oscillation parameters

The proposed India-based Neutrino Observatory will host a 50 kton magnetized iron calorimeter (ICAL) with resistive plate chambers as its active detector element. Its primary focus is to study charged-current interactions of atmospheric muon neutrinos via the reconstruction of muons in the detector. We present the first study of the energy and direction reconstruction of the final state lepton and hadrons produced in charged current interactions of atmospheric electron neutrinos at ICAL and the sensitivity of these events to neutrino oscillation parameters $\theta_{23}$ and $\Delta m_{32}^2$. However, the signatures of these events are similar to those from neutral-current interactions and charged-current muon neutrino events in which the muon track is not reconstructed. On including the entire set of events that do not produce a muon track, we find that reasonably good sensitivity to $\theta_{23}$ is obtained, with a relative $1\sigma$ precision of 15% on the mixing parameter $\sin^2\theta_{23}$, which decreases to 21%, when systematic uncertainties are considered.

Reassessment of steady-state operation in ITER with NBI and EC heating and current drive

One of the three goals of the ITER project is to demonstrate fusion gain Q ≥ 5 in steady-state operation (SSO). A reassessment of the necessary conditions for Q ≥ 5 SSO in ITER has been carried out for steady-state scenarios assuming no internal transport barrier in the core plasma and with the sole use of neutral beam injection (NBI) and electron cyclotron heating and current drive (EC H&CD) as heating and current drive sources in these scenarios. The parametric operational space for SSO in ITER has been reassessed utilizing an inverse evaluation approach that takes into account the baseline design of the NBI and EC H&CD systems with PNBI = 33 MW, PEC = 20 MW and their possible upgrade capabilities included in their design, PNBI ≤ 49.5 MW, and PEC ≤ 30 MW. The optimal operational points from this evaluation approach have been chosen for detailed 1.5-D transport modelling by ASTRA and followed-up by magnetohydrodynamic (MHD) stability analysis to demonstrate the conditions in which the Q = 5 SS goal can be achieved in ITER where the plasma current is fully accounted for by the driven current by NBI and EC H&CD and the self-driven bootstrap current. The ideal MHD stability of plasma configurations with self-consistently simulated plasma profiles and equilibrium for the chosen OPs has been analysed by the KINX code. Using this analysis, the possibility to control the MHD stability of these steady-state plasmas by tailoring the current profile with the flexibility provided by design of the systems for electron cyclotron current drive and neutral beam current drive in ITER has been demonstrated. Issues related to the realization of such scenarios from the point of view of plasma physics, experimental demonstration and design limits of the ITER systems and components is discussed.

Probing top quark FCNC couplings in the triple-top signal at the high energy LHC and future circular collider

Our main aim in this paper is to present detailed studies to probe the top quark flavor changing neutral current (FCNC) interactions at tqg, tqγ, tqH and tqZ(σμν,γμ) vertices in the triple-top signal pp→tt¯t(t¯tt¯) at the high energy proposal of Large Hadron Collider (HE-LHC) and future circular hadron-hadron collider (FCC-hh). To this end, we investigate the production of three top quarks which arises from the FCNC couplings taken into account the fast simulation at s=27 TeV of HE-LHC and 100 TeV of FCC-hh considering the integrated luminosities of 10, 15 and 20 ab−1. All the relevant backgrounds are considered in a cut based analysis to obtain the limits on the anomalous couplings and the corresponding branching ratios. The obtained exclusion limits on the coupling strengths and the branching ratios are summarized and compared in detail with the results in the literature, namely the most recent direct LHC experimental limits and HL-LHC projections as well. We show that, for the higher energy phase of LHC, a dedicated search for the top quark FCNC couplings can achieve much better sensitivities to the triple-top signal than other top quark production scenarios. We found that the limits for the branching ratios of tqg and tqH transitions could reach an impressive sensitivity and the obtained 95% CL limits are at least three orders of magnitude better than the current LHC experimental results as well as the existing projections of HL-LHC.

Neutral-Point Voltage-Balancing Strategies of NPC-Inverter Fed Dual Three-Phase AC Motors

In this article, the mechanism of neutral-point potential oscillations of neutral-point-clamped (NPC) three-level inverter fed dual three-phase ac motors is described. In a dual three-phase ac motor drive system, the three-level NPC inverter can be controlled as one six-phase system or two separate conventional three-phase systems. Therefore, this article extends the traditional control strategy, which injects the uniform zero-sequence voltage into the three-phase system to the six-phase system. The relationship of the uniform zero-sequence voltage and the neutral current is analyzed in detail. Meanwhile, the neutral-point potential-balancing strategy adopting dual zero-sequence voltages is presented in this article. The simulation and experiment verify that the proposed strategy adopting dual zero-sequence voltages has better control of the neutral point potential than the strategy adopting uniform zero-sequence voltage.

Symmetries and Their Breaking in the Fundamental Laws of Physics

Symmetries in the Physical Laws of Nature lead to observable effects. Beyond the regularities and conserved magnitudes, the last few decades in particle physics have seen the identification of symmetries, and their well-defined breaking, as the guiding principle for the elementary constituents of matter and their interactions. Flavour SU(3) symmetry of hadrons led to the Quark Model and the antisymmetric requirement under exchange of identical fermions led to the colour degree of freedom. Colour became the generating charge for flavour-independent strong interactions of quarks and gluons in the exact colour SU(3) local gauge symmetry. Parity Violation in weak interactions led us to consider the chiral fields of fermions as the objects with definite transformation properties under the weak isospin SU(2) gauge group of the Unifying Electro-Weak SU(2) × U(1) symmetry, which predicted novel weak neutral current interactions. CP-Violation led to three families of quarks opening the field of Flavour Physics. Time-reversal violation has recently been observed with entangled neutral mesons, compatible with CPT-invariance. The cancellation of gauge anomalies, which would invalidate the gauge symmetry of the quantum field theory, led to Quark–Lepton Symmetry. Neutrinos were postulated in order to save the conservation laws of energy and angular momentum in nuclear beta decay. After the ups and downs of their mass, neutrino oscillations were discovered in 1998, opening a new era about their origin of mass, mixing, discrete symmetries and the possibility of global lepton-number violation through Majorana mass terms and Leptogenesis as the source of the matter–antimatter asymmetry in the universe. The experimental discovery of quarks and leptons and the mediators of their interactions, with physical observables in spectacular agreement with this Standard Theory, is the triumph of Symmetries. The gauge symmetry is exact only when the particles are massless. One needs a subtle breaking of the symmetry, providing the origin of mass without affecting the excellent description of the interactions. This is the Brout–Englert–Higgs Mechanism, which produces the Higgs Boson as a remnant, discovered at CERN in 2012. Open present problems are addressed with by searching the New Physics Beyond-the-Standard-Model.

First observation of a tau neutrino charged current interaction with charm production in the OPERA experiment

An event topology with two secondary vertices compatible with the decay of short-lived particles was found in the analysis of neutrino interactions in the OPERA target. The observed topology is compatible with tau neutrino charged current (CC) interactions with charm production and neutrino neutral current (NC) interactions with coverline{c} pair production. However, other processes can mimic this topology. A dedicated analysis was implemented to identify the underlying process. A Monte Carlo simulation was developed and complementary procedures were introduced in the kinematic reconstruction. A multivariate analysis technique was used to achieve an optimal separation of signal from background. Most likely, this event is a nu _{tau } CC interaction with charm production, the tau and charm particle decaying into 1 prong and 2 prongs, respectively. The significance of this observation is evaluated.

Magnetic and Thermal Effects in Neutrino Scattering in Hot and Dense Nuclear Matter

Neutrino scattering on nuclei embedded in the hot and dense matter typical of the core collapse of supernovae, neutron star mergers, and proto-neutron stars, is studied. At finite temperatures, neutrinos experience exo- and endo-energy scattering on nuclei due to the Gamow–Teller component of a neutral current. It is shown that the average transfer of energy due to neutrino–nucleus scattering changes from positive to negative values at neutrino energies around four times higher than the temperature of the matter.

Aligned CP-violating Higgs sector canceling the electric dipole moment

We discuss the effect of CP violation in the aligned scenario of the general two-Higgs-doublet model, in which the Higgs potential and the Yukawa interaction provide additional CP-violating phases. An alignment is imposed to the Yukawa interaction in order to avoid dangerous flavor changing neutral currents. The Higgs potential is also aligned such that the coupling constants of the lightest Higgs boson, which is identified as the discovered Higgs boson with the mass of 125 GeV, are the same as those of the standard model. In general, CP-violating phases originated by the Yukawa interaction and the Higgs potential are strongly constrained by the current data for the electric dipole moment (EDM). It is found that in our scenario contributions from the two sources of CP violation can be destructive and consequently their total contribution can satisfy the EDM results, even when each CP-violating phase is large. Such a large CP-violating phase can be tested at collider experiments by looking at the angular distributions of particles generated by the decays of the additional Higgs bosons.

Linking pseudo-Dirac dark matter to radiative neutrino masses in a singlet-doublet scenario

We examine a simple extension of the standard model with a pair of fermions, one singlet and a doublet, in a common thread linking the dark matter problem with the smallness of neutrino masses associated with several exciting features. In the presence of a small bare Majorana mass term, the singlet fermion brings in a pseudo-Dirac dark matter capable of evading the strong spin-independent direct detection bound by suppressing the dark matter annihilation processes mediated by the neutral current. In consequence, the allowed range of a mixing angle between the doublet and the singlet fermions gets enhanced substantially. The presence of the same mass term in an association with singlet scalars also elevates tiny but nonzero masses radiatively for light Majorana neutrino satisfying observed oscillation data.