International Journal of Theoretical Physics最新文献

Trapped-ion systems are a leading platform for quantum computing. The Mølmer-Sørensen (MS) gate is a widely used method for implementing controlled interactions in multipartite systems. However, due to unavoidable interactions with the environment, quantum states undergo non-unitary evolution, leading to significant deviations from ideal dynamics. Common techniques such as Quantum Process Tomography (QPT) and Bell State Tomography (BST) are typically employed to evaluate MS gate performance and to characterize noise in the system. In this work, we propose leveraging the geometric phase (GP) as a tool for performance assessment and noise identification in the MS gate. Our findings indicate that the GP is particularly sensitive to environmental noise occurring around twice the clock pulse time. Given that GP measurements do not require full-state tomography, this approach offers a practical and experimentally feasible method to detect entanglement and classify the nature of noise affecting the system.

We present an exact interior solution to Einstein’s field equations describing a static, spherically symmetric compact object with isotropic pressure. While inspired by gravastar models, our configuration does not attain the ultracompactness (M/R sim 0.5) typically required for black hole mimickers [1, 2]. Instead, we interpret it as a gravastar-inspired model for neutron star–scale objects. The solution is regular, stable, and consistent with neutron star observables within classical general relativity. Unlike earlier models relying on thin shells or exotic matter, our approach employs a single monotonic gravitational potential and provides exact, closed-form expressions for pressure, density, mass, and redshift. Although smooth interior solutions exist in the literature, our model is a rare case where such profiles are derived analytically from the isotropic Einstein equations, yielding a continuous solution that satisfies all energy and stability conditions and remains dynamically stable only within specific parameter ranges, as confirmed by eigenvalue analysis, without invoking anisotropy, numerical integration, or exotic components. The model satisfies the Buchdahl compactness limit, energy conditions, and causality. Dynamical stability is further examined by solving the Sturm–Liouville eigenvalue problem, confirming stability in some parameter regimes while identifying instabilities in others. Our results align closely with neutron star observables such as mass, radius, and surface redshift. Comparison with NICER data for PSR J0030+0451 and PSR J0740+6620 shows observational consistency. Phase diagrams, redshift surfaces, and mass–radius curves reveal smooth transitions between stable and unstable regimes. Overall, this study demonstrates that exact isotropic gravastar interiors can reproduce neutron star observables while satisfying all theoretical requirements.

This report proposes the novel relation between gravity and the weak force, namely the graviweak correspondence. We construct a geometrical Yang-Mills theory that includes gravity, called the Yang-Mills-Utiyama theory. The theory treats the space-time symmetry of the local Lorentz group in the same manner as the internal gauge symmetry. We extend the theory into a more expansive space, including Euclidean and Lorentzian metrics at its boundaries. This extension suggests a relation between space-time and internal symmetry. The perspective provided by the extended theory suggests the novel relation between gravity and the weak force, leading us to the graviweak correspondence.

In this study, we examine large-amplitude ion-acoustic (IA) solitary waves (SWs) in unmagnetized, collisionless plasma. This plasma consists of inertial fluid ions, while non-Maxwellian positrons and electrons are noninertial. In our model, both positrons and electrons follow a (kappa)-deformed Kaniadakis distribution. To analyze these large-amplitude IASWs, we reduce the fundamental equations to a single energy-balance-like equation using the Sagdeev pseudopotential (SP) approach. We also numerically discuss the conditions required for the existence of IASWs. Furthermore, we identify the regions where IASWs can occur based on key plasma parameters such as positron concentration, Mach number, temperature ratio, and the deformed parameter. We also examine how these parameters affect the Sagdeev potential and the soliton profile. This research is especially relevant to ongoing studies of generalized entropies in plasma physics.

This work analyzes the magnetic properties of a ferromagnetic B(_{36}) borophene-like monolayer, described by the spin-3/2 Blume-Capel model in the presence of a two-dimensional crystal field. The method is based on the mean-field approximation using the Gibbs-Bogoliubov inequality. We study the effect of temperature (T) and both longitudinal (D) and transverse ((Gamma)) crystal fields on the magnetization and the phase diagrams in the ((Gamma), T) and (D, T) planes. The results reveal first- and second-order phase transitions, along with critical, bicritical, and multicritical points, as well as highly degenerate states at (T = 0).

The Riga plate is a significant tool in the development of the engineering world driven by technical innovation. In this study, the same plate is considered, which is infinite and accelerating with some velocity. A convective flow of Casson fluid will then be generated due to the motion of the plate. The constant proportional Caputo (CPC) operator uses Fick’s and Fourier’s laws to obtain the governing equations. The Laplace method is applied to the resultant fractional PDEs to transform them into ODEs and then solved to get analytical and semi-analytical solutions. With the help of Zakian’s numerical method, the Laplace transform is inverted only for the case of velocity, while precise solutions for concentration and temperature are formed. Variations of parameters like Casson parameter, mass Grashof number, Prandtl number, modified Hartmann number Ha, Grashof number, fractional parameters, magnetic parameter M, and Schmidt number are taken and sketched graphs to discuss the flow behavior. It is noted that thermal, concentration, and momentum profiles derived with the CPC derivative are deteriorating as compared to the classical Caputo operator. Furthermore, the presence of the Riga plate increases the dynamic character of the fractional Casson fluid.

We investigate black hole entropy in a broad class of modified gravity theories defined by generalized Lagrangians of the form (mathcal {L} = alpha R + F(T, Q, R_{mu nu }T^{mu nu }, R_{mu nu }Q^{mu nu }, dots )), where (R), (T), and (Q) represent curvature, torsion, and non-metricity scalars. Using the vielbein formalism, we derive the Wald entropy for various subclasses of these models, extending the classical entropy formula to accommodate non-Riemannian geometry. Our focus is on how the additional geometric degrees of freedom modify the entropy expression. The analysis shows that such corrections arise systematically from the extended structure of the action and preserve diffeomorphism invariance. These results refine the theoretical framework for gravitational thermodynamics in extended geometry settings.

It is a standard practice to derive velocity addition rules for point particles from Galilean and Lorentz transformations in point (classical) mechanics, and to apply such rules to wave velocities for explaining Doppler effect. However, in such standard practice, it is never shown whether the equation for wave propagation actually transforms in a way such that the velocity addition rules get manifested through the equation itself. We address this gap in the literature as follows. We claim that the velocity addition for waves, being the one and only mean to explain the empirically verified Doppler effect, should be considered as an element of physical reality in accord with EPR’s completeness condition of a physical theory. Therefore, the ‘equation for wave propagation’ should manifest such velocity addition so as to be considered as a part of the respective physical theory of waves. We show that such manifestation is possible if and only if wave propagation is modeled with first order partial differential equations. From a historical point of view, this work settles the Doppler-Petzval debate which originated from Petzval’s demand for an explanation of Doppler effect in terms of differential equations. From the foundational perspective, this work sets the stage for a renewed focus on the mathematical modeling of wave phenomena, especially in the context of various Doppler effects.

This study investigates the vibrational resonance and complex dynamics of a nonpolynomial Van der Pol oscillator driven by biharmonic excitation. This specific class of nonpolynomial oscillators models a nonlinear RLC series circuit where inductance and resistance are current-dependent. Using the method of direct separation of fast and slow motions, we analyze how various system parameters including inertial and impure cubic damping nonlinearities, linear damping, and the frequencies of the biharmonic signals influence the system’s behavior. Our analysis reveals the existence of single and double resonances, showing that parameter variations significantly affect the frequency response amplitude and the critical resonance point. The system’s performance, evaluated by its gain factor, identifies the weak signal frequency as a critical control parameter for signal amplification. The analytical solution is validated through excellent agreement with numerical results. A global analysis of the system’s dynamic changes, performed using a 4th-order Runge-Kutta algorithm, reveals complex behaviors such as periodic, quasiperiodic, and chaotic oscillations, including a notable period-one route to chaos. These behaviors are further confirmed by phase portraits and time series. Furthermore, the system’s sensitivity to initial conditions highlights the coexistence of multiple attractors, a phenomenon validated through bifurcation diagrams, Lyapunov exponents, and phase portraits.

The nonlinear cubic Schrödinger equation not only starts from realistically physical phenomena, but can also be widely used to many physically significant areas such as fluid dynamics, condensed matter physics, plasma physics, quantum mechanics, nonlinear optics and superconductivity. As a consequence, it is a very significant and challenging topic to research the explicit and accurate travelling wave solutions to the nonlinear cubic Schrödinger equation. In this work, based on the ideas of the complex tanh-function method and the extended tanh-function method, an extended complex tanh-function approach is presented for constructing the explicit and accurate travelling wave solutions of nonlinear Schrödinger-type equations. Crucial to our technique is to take full advantage of a complex Riccti equation containing a parameter b and to employ its solutions to replace the tanh function in the complex tanh-function method. It is quite interesting that the sign of the parameter b can be applied to exactly judge the numbers and types of traveling wave solutions. We have illustrated its feasibility by application to the nonlinear cubic Schrödinger equation. As a result, some explicit and accurate travelling wave solutions of the nonlinear cubic Schrödinger equation are successfully investigated in a simple manner. Our approach can not only obtain the all solutions given in Ref [21], but also derive solutions that cannot be seen in Ref [21]. In addition, compared with the proposed approaches in the existing references, the approach described herein appears to be less calculative. Our technique may provide a novel way of thinking for solving nonlinear Schrödinger-type equations. We believe that the procedure used herein may also be applied to explore the explicit and accurate travelling wave solutions of other nonlinear Schrödinger-type equations. We try to generalize this approach to search for the explicit and accurate travelling wave solutions of other ordinary coefficient even variable coefficient nonlinear Schrödinger-type equations.