Mass Term Research Articles

The self-interacting Dirac fields in FLRW spacetime

We prove the existence of global in time solution with the small initial data for the semilinear equation of the spin-\(\frac{1}{2}\) particles in the Friedmann–Lemaître–Robertson–Walker spacetime. Moreover, we also prove that if the initial function satisfies the Lochak–Majorana condition, then the global solution exists for arbitrary large initial value. The solution scatters to free solution for large time. The mass term is assumed to be complex-valued. The conditions on the imaginary part of mass are discussed by proving nonexistence of the global solutions if certain relation between scale function and the mass are fulfilled.

Fundamental scalar field with zero dimension from anomaly cancellations

In this article a novel mechanism for dynamical electroweak symmetry breaking and the ensuing appearance of fermion mass terms in the action is proposed. The action contains massless fermions of the standard model coupled to gravity through a new type of nonminimal coupling to the vielbein field. The corresponding coupling constants in our approach become zero-dimension scalar fields. Such scalar fields provide the cancellation of the Weyl anomaly [Latham Boyle and Neil Turok, arXiv:2110.06258].

Strongly correlated crystalline higher-order topological phases in two-dimensional systems: A coupled-wire study

Coupled-wire constructions have been widely applied to quantum Hall systems and symmetry-protected topological (SPT) phases. In this Letter, we use the coupled one-dimensional nonchiral Luttinger liquids with domain-wall structured mass terms as quantum wires to construct the crystalline higher-order topological superconductors (HOTSC) in two-dimensional interacting fermionic systems by two representative examples: $D_4$-symmetric class-D HOTSC and $C_4$-symmetric class-BD\1 HOTSC, with Majorana corner modes on the edge. Furthermore, based on the coupled-wire constructions, the quantum phase transition between different phases of 2D HOTSC by tuning the inter-wire couplings is investigated in a straightforward way.

Symmetric Mass Generation

The most well-known mechanism for fermions to acquire a mass is the Nambu–Goldstone–Anderson–Higgs mechanism, i.e., after a spontaneous symmetry breaking, a bosonic field that couples to the fermion mass term condenses, which grants a mass gap for the fermionic excitation. In the last few years, it was gradually understood that there is a new mechanism of mass generation for fermions without involving any symmetry breaking within an anomaly-free symmetry group, also applicable to chiral fermions with anomaly-free chiral symmetries. This new mechanism is generally referred to as the symmetric mass generation (SMG). It is realized that the SMG has deep connections with interacting topological insulator/superconductors, symmetry-protected topological states, perturbative local and non-perturbative global anomaly cancellations, and deconfined quantum criticality. It has strong implications for the lattice regularization of chiral gauge theories. This article defines the SMG, summarizes the current numerical results, introduces an unifying theoretical framework (including the parton-Higgs and the s-confinement mechanisms, as well as the symmetry-extension construction), and presents an overview of various features and applications of SMG.

W boson mass anomaly and grand unification

It is known that the recently reported shift of the W boson mass can be easily explained by an SU(2)L triplet Higgs boson with a zero hypercharge if it obtains a vacuum expectation value (VEV) of O(1) GeV. Surprisingly, the addition of a TeV scale complex triplet Higgs boson to the standard model (SM) leads to a precise unification of the gauge couplings at around 1014 GeV. We consider that it is a consequence of SU(5) grand unification and show a possible potential for the Higgs fields yielding a weak scale complex SU(2) triplet scalar boson. Although it seems the proton decay constraint would doom such a low-scale unification, we show that the constraint can be avoided by introducing vector-like fermions which mix with the SM fermions through mass terms involving the VEV of GUT breaking Higgs field. Importantly, the simplest viable model only requires the addition of one pair of vector-like fermions transforming 10 and 10‾.

Electron scattering of inhomogeneous gap in graphene quantum dots

We study the scattering of Dirac electrons in circular graphene quantum dots with two different gaps subject to an electrostatic potential. The obtained solutions of the energy spectrum are used to determine the scattering coefficients at the interface of the two regions. Using the asymptotic solutions at large arguments, we explicitly determine the radial component of the reflected current density and the scattering efficiency. It is found that the presence of a mass term outside, in addition to another one inside the quantum dot, strongly affects the scattering of electrons. In particular, a non-null square modulus of the scattering coefficient is found at zero energy.

Reconciling LSND and Super-Kamiokande data through the dynamical Lorentz symmetry breaking in a four-Majorana fermion model

We propose a model of Majorana fermions with quartic self-couplings. These Majorana fermions acquire masses via a type II seesaw mechanism in which the physical eigenstates are identified as a light Majorana fermion and another heavy Majorana fermion. On a physical basis, the quartic self-couplings involve axial currents of these Majorana fermions, and also the interaction of the axial current for the light particle with the heavy particle one. We introduce two auxiliaries gauge fields in this model, and we study the stability conditions of the correspondent effective potential of the model. The ground state of the effective potential introduces two 4-vectors as scales of vacuum expected values, and consequently, the dynamical Lorentz symmetry breaking (DLSB) emerges in the model. We use the expansion of the effective action to calculate the effective Lagrangian up to second order in the auxiliary fields as fluctuations around the ground state. This mechanism generates dynamics for the auxiliary gauge fields, mixed mass terms, longitudinal propagation, and Chern-Simons term through radiative corrections. After the diagonalization, the two gauge fields gain masses through an analogous type II seesaw mechanism in which a gauge boson has a light mass, and the other one acquires a heavy mass. In this scenario of Lorentz symmetry breaking, we obtain the correspondent dispersion relations for the Majorana fermions and the gauge boson fields. Posteriorly, we analyze the neutrino's oscillations in the presence of a DLSB parameter, in the transition $\nu_{e} \rightarrow \nu_{\mu}$. We discuss the parameter space of this transition and show that the DLSB can conciliate the LSND and super-Kamiokande results.

Open charm mesons and charmonia in magnetized strange hadronic matter * *A.J.C.S acknowledges the support towards this work from the Department of Science and Technology, Government of India, via an INSPIRE fellowship (INSPIRE Code IF170745). AM acknowledges financial support from Department of Science and Technology (DST), Government of India (CRG/2018/002226)

We investigate the in-medium masses of open charm mesons (D( , ), ( , ), ( , )) and charmonium states ( , , , , ) in strongly magnetized isospin asymmetric strange hadronic matter using a chiral effective model. In the presence of a magnetic field, the number and scalar densities of charged baryons have contributions from Landau energy levels. The mass modifications of open charm mesons result from their interactions with nucleons, hyperons, and the scalar fields (the non-strange field σ, strange field ζ, and isovector field δ) in the presence of a magnetic field. The mass modifications of the charmonium states result from the modification of gluon condensates in a medium simulated by the variation in the dilaton field (χ) in the chiral effective model. The effects of finite quark masses are also incorporated in the trace of the energy-momentum tensor in quantum chromodynamics to investigate the mass shifts of charmonium states. The in-medium masses of open charm mesons and charmonia are observed to decrease with an increase in baryon density. The charged , , , and mesons have additional positive mass shifts due to Landau quantization in the presence of a magnetic field. The effects of the strangeness fraction are observed to be more dominant for mesons compared with D mesons. The mass shifts of charmonia are observed to be larger in hyperonic media compared with nuclear media when the effect of the finite quark mass term is neglected. These medium mass modifications can have observable consequences on the production of the open charm mesons and charmonia in high-energy asymmetric heavy-ion collision experiments.

Assessment of subgrid dispersion models for large-eddy simulations of turbulent jet flows with dilute spray droplets

High-fidelity simulations for polydispersed sprays in the Eulerian–Lagrangian framework need to incorporate subgrid-scale effects in the particle evolution equations. Although the quasi-linear evaporation rate formulation captures evaporating droplet statistics, further improvement is required when subgrid-scale velocity effects become essential. The subgrid dispersion model strongly affects droplets spatial distribution, and subsequently net evaporation rate, depending on how rapidly they are dispersed into the dry air region. The main original contribution of this study is to assess the performances of a number of commonly used dispersion models in a consistent manner, against a reference direct simulation results. The models considered are (i) discrete random walk, (ii) approximate deconvolution method, (iii) stochastic model based on the Langevin equation, and (iv) combined approximate deconvolution method with the Langevin equation. Mass and enthalpy transfer source terms together with droplet diameters and particle distributions were compared against corresponding direct numerical and large-eddy simulations without a model as reference cases. Numerical results at low Stokes and moderate Reynolds numbers indicate that the dispersion model choice does not affect Eulerian field averages or fluctuations. However, proper dispersion models are essential to capture droplet distributions in the far-field region after jet breakup for Stokes number smaller than unity. The unclosed Lagrangian momentum equation without any dispersion model most accurately reproduces direct numerical simulation in the near field.

Robust Quantum Anomalous Hall States in Monolayer and Few-Layer TiTe

Quantum anomalous Hall (QAH) insulators possess exotic properties driven by novel topological physics, but related studies and potential applications have been hindered by the ultralow temperatures required to sustain the operating mechanisms dictated by key material parameters. Here, using first-principles calculations, we predict a robust QAH state in monolayer TiTe that exhibits a high ferromagnetic Curie temperature of 650 K and a sizable band gap of 261 meV. These outstanding benchmark properties stem from the Te atom's large size that favors ferromagnetic kinetic exchange with the neighboring Ti atoms and strong spin-orbit coupling that creates a QAH state by adding a mass term to the Dirac half-semimetal state. Remarkably, the ferromagnetic order remains robust against interlayer stacking via the d-pz/py-pz-d super-super exchange, generating unprecedented QAH states in few-layer configurations with enhanced Curie temperatures and higher Chern numbers. These results signify layered TiTe to be a prime template for exploring novel QAH physics at ambient and higher temperatures.

Witten’s cubic open string field theory on multiple Dp-branes

We study Witten's cubic open string field theory on multiple $Dp$-branes. On multiple $Dp$-branes the string fields carry $U(N)$ group indices. Mapping the string world-sheet onto the upper half complex plane and evaluating the Polyakov string path integral of Witten's cubic open string, we obtain a Fock space representation of one, two and three-string vertex operators. In the low energy region, the system is described by massless gauge fields and massless scalar fields, carrying $U(N)$ group indices. The two-string vertex induces mass terms for the gauge fields and the scalar fields. The cubic interaction reduces correctly to the cubic term of the non-Abelian gauge fields, cubic interaction terms of the gauge fields, and the scalar fields on $(p+1)$ dimensional space. Thus, Witten's string field theory may be a useful tool to study the quantum dynamics of open strings on multiple $Dp$-branes.

Anomalous Response in the Orbital Magnetic Susceptibility of 2D Topological Systems

2D compounds with nonzero Berry curvature are ideal systems to study exotic and technologically favorable thermoelectric and magnetoelectric properties. Within this class of materials, the topological trivial and nontrivial regimes have to present very different behaviors, which are encoded for the orbital susceptibility and magnetization. To try to reveal them, it is found that it was necessary to introduce a k‐dependent mass term in the relativistic formalism of these materials. Thus, while a topologically trivial insulator is predicted to have a very limited response, in the nontrivial regime, a singular contribution to the orbital magnetic susceptibility, which is inversely proportional to the square of the quantum magnetic flux is unveiled. In this scenario, besides determining the measurement conditions a new route for enhancing the intrinsic orbital magnetism of topological materials widening the range of temperatures and magnetic fields without involving tiny bandgaps is found.

Seesaw mechanism in the R-parity-violating supersymmetric standard model with the gauged flavor U(1)X symmetry

Abstract We study the seesaw mechanism in the supersymmetric standard model (SSM) with the ${\mathbb {Z}}_3$ symmetry called matter triality (M3). The Abelian discrete symmetry prohibits the baryon number violation operators at the (non-)renormalizable level, which ensures proton longevity. The cubic coupling by right-handed neutrinos generates the Majorana mass term after the right-handed sneutrinos develop into the vacuum expectation values. Due to the R-parity violation, the active neutrino masses can be generated not only from the mixings with the right-handed neutrinos but also from those with the minimal SSM neutralinos. We propose a model where M3 is embedded in the gauged flavor symmetry. The flavor charges are constrained by the anomaly cancellation conditions and the requirements to realize the fermion masses and mixing angles in the quark and lepton sectors. We analyze the assignments of the flavor charge, and show that the sterile neutrino mass is allowed to be below the soft supersymmetry-breaking scale, which is constrained by the half-lifetime of the neutrinoless double beta decay.

Custodial symmetry, the Georgi-Machacek model, and other scalar extensions

In an SU(2) gauge theory, if the gauge bosons turn out to be degenerate after spontaneous symmetry breaking, obviously these mass terms are invariant under a global SU(2) symmetry that is unbroken. The pure gauge terms are also invariant under this symmetry. This symmetry is called the custodial symmetry (CS). In $\mathrm{SU}(2)\ifmmode\times\else\texttimes\fi{}\mathrm{U}(1)$ gauge theories, CS implies a mass relation between the $W$ and the $Z$ bosons. The Standard Model, as well as various extensions of it in the scalar sector, possesses such a symmetry. In this paper, we critically examine the notion of CS and show that there may be three different classes of CS, depending on the gauge couplings and self-couplings of the scalars. Among old models that preserve CS, we discuss the two-Higgs-doublet model and the one-doublet plus two-triplet model by Georgi and Machacek. We show that for two-triplet extensions, the Georgi-Machacek model is not the most general possibility with CS. Rather, we find, as the most general extension, a new model with more parameters and hence a richer phenomenology. Some of the consequences of this new model have also been discussed.

Thermoelectric transport in two-terminal topological nodal-line semimetals nanowires

Recently discovered topological nodal-line semimetals (TNLSMs) have received considerable research interest due to their rich physical properties and potential applications. TNLSMs have the particular band structure to lead to many novel properties. Here we theoretically study the thermoelectric transport of a two-terminal pristine TNLSM nanowires and TNLSMs p–n–p junctions. The Seebeck coefficients S c and the thermoelectrical figure of merit ZT are calculated based on the Landauer-Büttiker formula combined with the nonequilibrium Green’s function method. In pristine TNLSM nanowires, we discuss the effect of the magnetic fields φ, the disorder D, the on-site energy µ z , and the mass term m on the thermoelectric coefficient and find that the transport gap can lead to a large S c and ZT. When transmission coefficient jumps from one integer plateau to another, S c and ZT show a series of peaks. The peaks of S c and ZT are determined by the jump of the transmission coefficient plateau and are not associated with the plateau itself. For TNLSMs p–n–p junctions, S c and ZT strongly depend on the parameter ξ of potential well. We can get a large ZT by adjusting the parameter ξ and magnetic field φ. In TNLSMs p–n–p junctions, ZT has the large value and is easily regulated. This setup has promising application prospects as a thermoelectric device.

Dynamical quantum phase transitions in a noisy lattice gauge theory

Lattice gauge theories form an intriguing class of theories highly relevant to both high-energy particle physics and low-energy condensed matter physics with the rapid development of engineered quantum devices providing new tools to study, e.g., dynamics of such theories. The massive Schwinger model is known to exhibit intricate properties of more complicated theories and has recently been shown to undergo dynamical quantum phase transitions out of equilibrium. With current technology, noise is inevitable and potentially fatal for a successful quantum simulation. This paper studies the dynamics subject to noise of a $(1+1)\mathrm{D}\phantom{\rule{4pt}{0ex}}\mathrm{U}(1)$ quantum link model following a quench of the sign of the mass term. We find that not only is the system capable of handling noise at rates realistic in NISQ-era devices, promising the possibility to study the target dynamics with current technology, but the effect of noise can be understood in terms of simple models. Specifically the gauge-breaking nature of bit flip channels results in exponential dampening of state amplitudes, and thus observables, which does not affect the structures of interest. This is especially important as it demonstrates that the gauge theory can be successfully studied with devices that only exhibit approximate gauge invariance.

Nonexistence result for the generalized Tricomi equation with the scale-invariant damping, mass term and time derivative nonlinearity

In this article, we consider the damped wave equation in the scale-invariant case with time-dependent speed of propagation, mass term and time derivative nonlinearity. More precisely, we study the blow-up of the solutions to the following equation: ( E ) u t t − t 2 m Δ u + μ t u t + ν 2 t 2 u = | u t | p , in R N × [ 1 , ∞ ) , that we associate with small initial data. Assuming some assumptions on the mass and damping coefficients, ν and μ > 0, respectively, we prove that blow-up region and the lifespan bound of the solution of ( E ) remain the same as the ones obtained for the case without mass, i.e. ( E ) with ν = 0 which constitutes itself a shift of the dimension N by μ 1 + m compared to the problem without damping and mass. Finally, we think that the new bound for p is a serious candidate to the critical exponent which characterizes the threshold between the blow-up and the global existence regions.

Modular symmetry anomaly and nonperturbative neutrino mass terms in magnetized orbifold models

We study the modular symmetry anomaly in magnetized orbifold models. The non-perturbative effects such as D-brane instanton effects can break tree-level symmetry. We study which part of the modular symmetry is broken explicitly by Majorana mass terms with three generations of neutrinos. The modular weight of neutrino mass terms does not match with other coupling terms in tree-level Lagrangian. In addition, the $Z_N$ symmetry of the modular flavor symmetry is broken and a certain normal subgroup of the modular flavor symmetry remains in neutrino mass terms.

Dark matter in the CP-violating NMSSM

In the Next-to-Minimal Supersymmetric Standard Model there is a strong correlation between the mass terms corresponding to the singlet Higgs and the singlino interaction states, both of which are proportional to the parameter kappa . If this parameter is complex, explicit CP-violation occurs in the Higgs as well as the neutralino sectors of the model at the tree level, unlike in the minimal scenario. A small magnitude of kappa typically yields a {{mathcal {O}}}(10) GeV lightest neutralino with a dominant singlino component. In such a scenario, the phase of kappa , beside modifying the properties of the five Higgs bosons, can also have a crucial impact on the phenomenology of the neutralino dark matter. In this study we perform a first investigation of this impact on the relic abundance of the dark matter solutions with sub-100 GeV masses, obtained for parameter space configurations of the model that are consistent with a variety of current experimental data.

Contributions of oceanic and continental AAM to interannual variation in ΔLOD with the detection of 2020–2021 La Nina event

As a strong climate element on interannual scales, the El Nino-Southern Oscillation (ENSO) is a major component of global weather and climate change, and it is also closely related to the interannual atmospheric angular momentum (AAM) and length-of-day changes (ΔLOD). Here, we reprocess and compare the interannual variations of AAM, ΔLOD with ENSO indices, with AAM mass and motion terms calculated over land separately from those over the ocean. Three oscillatory components (at ~ 6, ~ 7, ~ 8 years), due to angular momentum changes in Earth's interior, are removed to obtain the interannual ΔLOD solely related to climatic variations. Our results show that the AAM motion term over the ocean contributes the most to interannual ΔLOD, and that the oceanic AAM has larger variability than that over land, especially during the periods of strong ENSO events. After subtracting contributions associated with interior processes, the interannual ΔLOD anomalies corresponding to extreme ENSO events (1982–1983 ~ 0.43, 1997–1998 ~ 0.36, 2015–2016 ~ 0.42 ms) are about half as strong as those found in previous studies (~ 0.91, ~ 0.76, ~ 0.81 ms). Furthermore, we detect an intermediate La Nina event that occurred from August 2020 to May 2021, forcing the interannual ΔLOD to a minimum value of approximately -0.21 ms.