Constant Couplings Research Articles

Pseudo-Nambu-Goldstone boson production from inflaton coupling during reheating

The existence of pseudo-Nambu-Goldstone boson (pNGB) fields is a common feature in many models beyond the Standard Model, characterized by their exclusive derivative couplings. This paper investigates a scenario where a pNGB is coupled to the inflaton field during the reheating phase of the early universe. We calculate the perturbative decay rate of a coherently oscillating inflaton into pNGBs on a general basis, considering both constant and field-dependent couplings with monomial potentials at the minimum. As a concrete application, we explore the production of axions when the radial mode of the Peccei-Quinn (PQ) scalar serves as the inflaton, particularly in the presence of a large gravitational non-minimal coupling. Our findings suggest that the presence of pNGBs during reheating can lead to significant non-thermal relics, offering new constraints on inflationary reheating models and providing potential observational signatures in the form of dark radiation.

Masses of magnetized pseudoscalar and vector mesons in an extended NJL model: The role of axial vector mesons

We study the mass spectrum of light pseudoscalar and vector mesons in the presence of an external uniform magnetic field B→, considering the effects of the mixing with the axial-vector meson sector. The analysis is performed within a two-flavor NJL-like model which includes isoscalar and isovector couplings together with a flavor mixing ’t Hooft-like term. The effect of the magnetic field on charged particles is taken into account by retaining the Schwinger phases carried by quark propagators, and expanding the corresponding meson fields in proper Ritus-like bases. The spin-isospin and spin-flavor decomposition of meson mass states is also analyzed. For neutral pion masses it is shown that the mixing with axial vector mesons improves previous theoretical results, leading to a monotonic decreasing behavior with B that is in good qualitative agreement with lattice QCD (LQCD) calculations, both for the case of constant or B-dependent couplings. Regarding charged pions, it is seen that the mixing softens the enhancement of their mass with B. As a consequence, the energy becomes lower than the one corresponding to a pointlike pion, improving the agreement with LQCD results. The agreement is also improved for the magnetic behavior of the lowest ρ+ energy state, which does not vanish for the considered range of values of B—a fact that can be relevant in connection with the occurrence of meson condensation for strong magnetic fields. Published by the American Physical Society 2024

An Angle‐Sensitive Microcolumn‐Based Capacitive Shear Force Sensor for Robot Grasping

AbstractShear force sensors play an indispensable role in tactile perception for robot manipulation tasks. However, recent advancements in shear force sensors have been hindered by issues such as direction sensitivity and integration limitations. This paper proposes a microcolumn array dielectric layer produced using photolithography technology that enables tunability of sensor sensitivity and detection range by adjusting the aspect ratio and interval of the microstructures. Meanwhile, the impact of five constant normal force couplings on the sensitivity of shear force perception is investigated. The structure array with a 1:2 aspect ratio and 600 µm interval demonstrates an ultrahigh sensitivity of 6.189 N−1 and outstanding linearity (R2 = 0.9873) within the range up to 0.1 N. The sensor exhibits low hysteresis and robust stability over 3000 cycles. Additionally, it exhibits remarkable anisotropic direction sensitivity, enabling accurate positioning within a quarter‐circle angle. An intentionally designed orthogonal array is employed to extend the shear angle range up to 360°. Owing to the high performance of the sensor, it is further integrated onto a gripper to facilitate the grasping operation and effectively capture delicate movements. The experimental outcomes highlight that the designed sensor holds promise for applications in robotic applications and electronic skin domains.

Radicalization phenomena: Phase transitions, extinction processes and control of violent activities

In this work, we study a simple mathematical model to analyze the emergence and control of radicalization phenomena. The population consists of core and sensitive subpopulations, and their ways of life may be at least partially incompatible. In such a case, if a conflict exists, core agents act as inflexible individuals about the issue. On the other hand, the sensitive agents choose between two options: live peacefully with core population, or oppose it. This kind of modeling was recently considered by Galam and Javarone (2016) with constant pairwise couplings. Here, we consider the more general case with time-dependent transition rates, with the aim of study the impact of such time dependence on the critical behavior of the model. The analytical and numerical results show that the nonequilibrium active-absorbing phase transition can be suppressed in some cases, with the destruction of the absorbing phase where the radical agents disappear of the population in the stationary states.

Stability properties for two coupled reaction-diffusion equations

This paper studies the stability of the interconnection of two reaction-diffusion equations. We focus on the case where the input and output operators of the interconnection are bounded. Using the spectral decomposition of both equations, we propose a sufficient condition to estimate the exponential stability decay rate of the closed-loop system. This stability test is proposed as constraints of a semidefinite programming. An extension of this condition is also outlined in the form of a Hurwitz criterion. The proposed stability analysis conditions are illustrated with an example of two reaction-diffusion equations with constant couplings terms.

Searching for dilaton fields in the Lyman- α forest

Dilatons (and moduli) couple to the masses and coupling constants of ordinary matter, and these quantities are fixed by the local value of the dilaton field. If, in addition, the dilaton with mass ${m}_{\ensuremath{\phi}}$ contributes to the cosmic dark matter density, then such quantities oscillate in time at the dilaton Compton frequency. We show how these oscillations lead to broadening and shifting of the Voigt profile of the Lyman-$\ensuremath{\alpha}$ forest in a manner that is correlated with the local dark matter density. We further show how tomographic methods allow the effect to be reconstructed by observing the Lyman-$\ensuremath{\alpha}$ forest spectrum of distant quasars. We then simulate a large number of quasar lines of sight using the lognormal density field, and forecast the ability of future astronomical surveys to measure this effect. We find that in the ultra low mass range ${10}^{\ensuremath{-}32}\text{ }\text{ }\mathrm{eV}\ensuremath{\le}{m}_{\ensuremath{\phi}}\ensuremath{\le}{10}^{\ensuremath{-}28}\text{ }\mathrm{eV}$ upcoming observations can improve over existing limits to the dilaton electron mass and fine structure constant couplings set by fifth force searches by up to five orders of magnitude. Our projected limits apply assuming that the ultralight dilaton makes up a few percent of the dark matter density, consistent with upper limits set by the cosmic microwave background anisotropies.

Observational constraints on varying fundamental constants in a minimal CPC model

ABSTRACT A minimal model based on the Co-varying Physical Couplings (CPC) framework for gravity is proposed. The CPC framework is based on the assumptions of a metric-compatible four-dimensional Riemannian manifold, where a covariantly conserved stress-energy tensor acts as source of the field equations, which are formally the same as Einstein field equations, but where the couplings {G, c, Λ} are allowed to vary simultaneously. The minimal CPC model takes Λ as a genuine constant while c and G vary in an entangled way that is consistent with Bianchi identity and the aforementioned assumptions. The model is constrained using the most recent galaxy cluster gas mass fraction observational data. Our result indicates that the functions c(z) and G (z) = G0 (c/c0)4 are compatible with constant couplings for the two different parametrizations of c = c(z) adopted here.

The temperature-variable electron-phonon coupling and its role in the inelastic thermal spike in 3C-SiC

In Two Temperature Model calculations of the inelastic thermal spike produced by swift ions, the electron–phonon coupling factor is often treated as a constant. However, recent first principles calculations in 3C-SiC have shown that this factor is strongly dependent on the electron temperature. The evolution of the electron and phonon temperatures were calculated using both an electron-temperature-variable electron–phonon coupling as well as constant couplings. Temperatures were compared for different stopping powers and at different radii from the ion path. While the use of constant couplings appears to be justified for certain combinations of radius and stopping power, the high energy densities at the center of ion paths formed by swift heavy ions are capable of greatly enhancing the coupling, sometimes by several orders of magnitude. This work emphasizes the importance of the temperature parameterization of the electron–phonon coupling in Two Temperature Model calculations.

Inverse Nonlinear Eigenvalue Problem Framework for the Synthesis of Coupled-Resonator Filters With Nonresonant Nodes and Arbitrary Frequency-Variant Reactive Couplings

A novel, general circuit-level description of coupled-resonator microwave filters is introduced in this article. Unlike well-established coupling-matrix models based on frequency-invariant couplings or linear frequency-variant couplings (LFVCs), a model with arbitrary reactive frequency-variant coupling (AFVC) networks is proposed. The engineered formulation is more general than prior-art ones—with the only restriction that the coupling network is a reactive-type two-port circuit—and can be treated as an extension of previous synthesis models since constant or linear couplings are special cases of arbitrary frequency dependence. The suggested model is fully general, which allows for AFVCs with highly nonlinear (even singular) characteristics, loaded or unloaded nonresonating nodes (NRNs), frequency-dependent source–load coupling, multiple frequency-variant cross couplings, and/or multiple dispersive couplings for connecting the source and load to the filter network. The model is accompanied by a powerful synthesis technique that is based on the zeros and poles of the admittance or scattering parameters and the eigenvalues of properly defined eigenproblems. In the most general case, the zeros and poles of the admittance or scattering parameters are related to solutions of nonlinear eigenvalue problems. The synthesis is defined as an inverse nonlinear eigenvalue problem (INEVP) where the matrix is constructed from three sets of eigenvalues. This is accomplished by optimization using an iterative nonlinear least-squares solver with excellent convergence property. Finally, the third- and fifth-order examples of bandpass filter topologies involving AFVCs are shown, and the experimental validation of the proposed theory is presented through the manufacturing and characterization of a microstrip filter prototype with transmission zeros (TZs).

Identification of Couplings in Adaptive Dynamical Networks of Time-Delayed Feedback Oscillators

An approach to solve the inverse problem of the reconstruction of the network of time-delay oscillators from their time series is proposed and studied in the case of the nonstationary connectivity matrix. Adaptive couplings have not been considered yet for this particular reconstruction problem. The problem of coupling identification is reduced to linear optimization of a specially constructed target function. This function is introduced taking into account the continuity of the nonlinear functions of oscillators and does not exploit the mean squared difference between the model and observed time series. The proposed approach allows us to minimize the number of estimated parameters and gives asymptotically unbiased estimates for a large class of nonlinear functions. The approach efficiency is demonstrated for the network composed of time-delayed feedback oscillators with a random architecture of constant and adaptive couplings in the absence of a priori knowledge about the connectivity structure and its evolution. The proposed technique extends the application area of the considered class of methods.

Amino Acid-Based Synthesis and Glycosidase Inhibition of Cyclopropane-Containing Iminosugars.

Synthesis of four iminosugars fused to a cyclopropane ring is described using l-serine as the chiral pool. The key steps are large-scale preparation of an α,β-unsaturated piperidinone followed by completely stereoselective sulfur ylide cyclopropanation. Stereochemistry of compounds has been studied by nuclear Overhauser effect spectroscopy (NOESY) experiments and 1H homonuclear decoupling to measure constant couplings. The activity of these compounds against different glycosidases has been evaluated. Although inhibition activity was low (compound 8a presents a (Ki) of 1.18 mM against β-galactosidase from Escherichia coli), interestingly, we found that compounds 8a and 8b increase the activity of neuraminidase from Vibrio cholerae up to 100%.

Gödel-type solutions in cubic Galileon gravity

We address the homogeneous in space and time (ST-homogeneous) G\"{o}del-type metrics within the cubic galileon theory, a particular class of generalized galileon theories. We check the consistency of such spacetimes for a physically well-motivated matter content, namely, a perfect fluid and an electromagnetic field. In this scenario, we find that the admissible solutions impose constraints on the constant couplings ($c_{i}$'s) of the cubic galileon theory to ensure the consistency. Also, we show the existence of a vacuum completely causal solution.

Sample shape and boundary dependence of measured transverse thermal properties

Despite increased interest in thermal Hall measurements for the analysis of insulating quantum materials, there remains large uncertainty in such measurements due to contact misalignment. In this paper, we propose that sample geometry and uncertain boundary conditions provide an additional source of uncertainty in the measurement of Dxy or κxy. By running simple simulations in an open source finite-element solver, we demonstrate that measured Dxy can be changed by a non-negligible fraction in samples with similar width and length. This geometric corrective factor depends on the distinction between a uniform heat flow and constant temperature boundary couplings to a bath. Sample geometry and boundary conditions can be accounted for through simulation or by using rectangular samples to make thermal Hall measurements more reliable and reproducible. Finally, we detail a contactless optical method for measuring Dxy based on an existing photothermal microscope technique. This method is insensitive to the longitudinal diffusivity pollution caused by contact misalignment.

Optical Phase Transitions in Photonic Networks: a Spin-System Formulation

We investigate the collective dynamics of nonlinearly interacting modes in multimode photonic settings with long-range couplings. To this end, we have established a connection with the theory of spin networks. The emerging "photonic spins" are complex, soft (their size is not fixed) and their dynamics has two constants of motion. Our analysis shed light on the nature of the thermal equilibrium states and reveals the existence of optical phase-transitions which resemble a paramagnetic to a ferromagnetic and to a spin-glass phase transitions occurring in spin networks. We show that, for fixed average optical power, these transitions are driven by the type (constant or random couplings) of the network connectivity and by the total energy of the optical signal.

TeV-scale Majorogenesis

The Majoron, the Nambu-Goldstone boson of lepton number symmetry, is an interesting candidate for dark matter as it deeply connects the dark matter and neutrino physics. In this paper, we consider the Majoron dark matter as pseudo Nambu-Goldstone boson with TeV-scale mass. The heavy Majoron generally has the large decay constant and tiny Yukawa couplings to light right-handed neutrinos which are required by cosmological and astrophysical observations. That makes it difficult to realize the desired amount of the relic abundance of Majoron dark matter. We consider three improved scenarios for the generation of Majoron, dubbed as Majorogenesis, in the early universe and find in all cases the parameter space compatible with the relic abundance and cosmic-ray constraints.

Quantum quench in c = 1 matrix model and emergent space-times

We consider quantum quench in large-N singlet sector quantum mechanics of a single hermitian matrix in the double scaling limit. The time dependent parameter is the self-coupling of the matrix. We find exact classical solutions of the collective field theory of the eigenvalue density with abrupt and smooth quench profiles which asymptote to constant couplings at early and late times, and with the system initially in its ground state. With adiabatic initial conditions we find that adiabaticity is always broken regardless of the quench speed. In a class of quench profiles the saddle point solution for the collective field diverges at a finite time, and a further time evolution becomes ambiguous. However the underlying matrix model expressed in terms of fermions predict a smooth time evolution across this point. By studying fluctuations around the saddle point solution we interpret the emergent space-times. They generically have spacelike boundaries where the couplings of the fluctuations diverge and the semi-classical description fails. Only for very finely tuned quench profiles, the space-time is normal.

Charge transfer characteristics of fullerene-free polymer solar cells via multi-state electronic coupling treatment

Dispersion-corrected optimally tuned long-range corrected functional provides constant electronic couplings for non-fullerene polymer solar cell systems regardless of the number of the excited states included in the calculations.

Mixed H_{infty }/passive exponential function projective synchronization of delayed neural networks with hybrid coupling based on pinning sampled-data control

This paper presents the problem of mixed H_{infty }/passive exponential function projective synchronization of delayed neural networks with constant discrete and distributed delay couplings under pinning sampled-data control scheme. The aim of this work is to focus on designing of pinning sampled-data controller with an explicit expression by which the stable synchronization error system is achieved and a mixed H_{infty }/passive performance level is also reached. Particularly, the control method is designed to determine a set of pinned nodes with fixed coupling matrices and strength values, and to select randomly pinning nodes. To handle the Lyapunov functional, we apply some new techniques and then derive some sufficient conditions for the desired controller existence. Furthermore, numerical examples are given to illustrate the effectiveness of the proposed theoretical results.

Dimensional-Invariance Principles in Coupled Dynamical Systems: A Unified Analysis and Applications

In this paper we study coupled dynamical systems and investigate dimension properties of the subspace spanned by solutions of each individual system. Relevant problems on \textit{collinear dynamical systems} and their variations are discussed recently by Montenbruck et. al. in \cite{collinear2017SCL}, while in this paper we aim to provide a unified analysis to derive the dimensional-invariance principles for networked coupled systems, and to generalize the invariance principles for networked systems with more general forms of coupling terms. To be specific, we consider two types of coupled systems, one with scalar couplings and the other with matrix couplings. Via the \textit{rank-preserving flow theory}, we show that any scalar-coupled dynamical system (with constant, time-varying or state-dependent couplings) possesses the dimensional-invariance principles, in that the dimension of the subspace spanned by the individual systems' solutions remains invariant. For coupled dynamical systems with matrix coefficients/couplings, necessary and sufficient conditions (for constant, time-varying and state-dependent couplings) are given to characterize dimensional-invariance principles. The proofs via a rank-preserving matrix flow theory in this paper simplify the analysis in \cite{collinear2017SCL}, and we also extend the invariance principles to the cases of time-varying couplings and state-dependent couplings. Furthermore, subspace-preserving property and signature-preserving flows are also developed for coupled networked systems with particular coupling terms. These invariance principles provide insightful characterizations to analyze transient behaviors and solution evolutions for a large family of coupled systems, such as multi-agent consensus dynamics, distributed coordination systems, formation control systems, among others.

Controllability and Stabilizability of Networks of Linear Systems

We provide necessary and sufficient conditions for the node systems, the graph adjacency matrix, and the input matrix such that a heterogeneous network of multi-input multi-output linear time-invariant (LTI) node systems with constant linear couplings is controllable or stabilizable through the external input. We also provide specializations of these general conditions for homogeneous networks. Finally, we give a very simple, necessary and sufficient condition under which a homogeneous network of single-input single-output LTI node systems is stable in the absence of the external input.