物理最新文献

We investigate the properties of compact objects in the f(Q, T) theory, where (mathcal {Q}) is the non-metricity scalar and ({ mathcal {T}}) is the trace of the energy–momentum tensor. We derive an interior analytical solution for anisotropic perfect-fluid spheres in hydrostatic equilibrium using the linear form of (f(mathcal {Q}, { mathcal {T}})=mathcal {Q}+psi { mathcal {T}}), where (psi ) represents a dimensional parameter. Based on the observational constraints related to the mass and radius of the pulsar SAX J1748.9-2021, (psi ) is set to a maximum negative value of (psi _1=psi / kappa ^2=-0.04), where (kappa ^2) is the gravitational coupling constant. The solution results in a stable compact object, which does not violate the speed of sound condition (c_s^2le frac{c^2}{3}). The effective equation of state is similar to the quark matter equation of state, and involves the presence of an effective bag constant. When (psi ) is negative, the star has a slightly larger size as compared to GR stars with the same mass. The difference in the predicted star size between the theory with a negative (psi ) and GR for the same mass is attributed to an additional force appearing in the hydrodynamic equilibrium equation. The maximum compactness allowed by the strong energy condition for (f(mathcal {Q}, { mathcal {T}})) theory and for GR is (C = 0.514) and 0.419, respectively, with the (f(mathcal {Q}, { mathcal {T}})) prediction about (10%) higher than the GR one. Assuming a surface density at saturation nuclear density of (rho _{text {nuc}} = 4times 10^{14}~hbox {g}/hbox {cm}^3), the maximum mass of the star is (4.66 M_odot ), with a radius of 14.9 km.

We study the prospect of heavy singlet neutrinos as a dark matter (DM) candidate within a neutrinophilic U(1) model, where the Standard Model (SM) is extended with a U(1) gauge symmetry, and neutrino mass and oscillation parameters are explained through an inverse see-saw mechanism. The lightest of the heavy neutrinos plays the role of the DM, while the newly introduced scalars and the extra gauge boson (Z') act as mediators between the dark sector and the SM sector. We show the range of model parameters where this DM candidate can be accommodated in the Weakly Interacting Massive Particle (WIMP) or Feebly Interacting Massive Particle (FIMP) scenario. The observed DM relic density (DMRD) is achieved via the new gauge boson and singlet scalar portals in the WIMP scenario, whereas within the FIMP scenario, these two particles assume a distinct yet pivotal role in generating the observed DMRD.

We develop a formalism of poly-vector deformations for Type IIB backgrounds with a block diagonal metric and non-vanishing self-dual 5-form RR field strength. Making use of the embedding of the Type IIB theory into the (textrm{E}_{6(6)}) exceptional field theory we derive explicit transformation rules for four-vector deformations. We prove that the algebraic condition following from the Type IIB realization of exceptional Drinfeld algebras is sufficient for the transformation to generate a solution.

Different laser surface texturing (LST) parameters produce varying effects, prompting the need to rationalize a strategy that optimizes structure for specific functionalities while maintaining manufacturing efficiency. This study applied square groove texturing to 304 stainless steel samples using a combination of scanning paths and Burst-mode to explore strategies that enhance texturing effect. In this paper, the texturing effect is quantified by texturing efficiency and surface quality. The square groove textures were manufactured using four scanning paths under picosecond lasers: 90°, 60°, circular, and horizontal-vertical reciprocating (HVR), along with Burst-mode at various pulses per burst (PPB). Multifactorial experiment systematically analyzed the texturing effect of various combination strategies. Additionally, this study established a geometric simulation model to validate the experimental results’ accuracy. Comparative analysis demonstrated that the simulation model effectively reflects the actual texturing results. The results indicated that this strategy achieves better texturing effect compared to traditional methods. Specifically, with the pulse number fixed at 2, the texturing efficiency of the horizontal-vertical reciprocating (HVR) scanning path is nearly twice that of the 60° scanning path, while also maintaining superior surface quality.

The current work discusses on the effect of sodium (Na) and bismuth (Bi) ion doping at different concentrations in the compositional formula La_0.67Sr_0.33–yNa_y/2Bi_y/2MnO₃ (y = 0, 0.0825, 0.165, 0.2475, 0.33) on structural, magnetic, magnetotransport and thermoelectric studies. X-ray diffraction confirms the R(:stackrel{-}{3})c space group with rhombohedral structure and the field emission scanning electron microscope images confirms a systematic growth of grains with increasing in NaBi concentrations. An enhancement in the ferromagnetic ordering and magnetic transitions above 325 K were observed up to y = 0.165 and they decrease thereafter. A broad maximum along with a double peak behavior were noticed in the temperature dependent resistivity curves and they disappear upon the application of external magnetic fields. The Seebeck coefficient show a change of sign from positive to negative with increasing temperature for lower concentrations of NaBi and they exhibit a negative sign for higher substitutions suggesting the variation in the nature of charge carriers. The small polaron hopping mechanism governs the resistivity and thermopower behavior in the high temperature regions while, electron-electron, electron-magnon, magnon-magnon scattering mechanism contributes in the low temperature region.

We consider a counter-rotating torus orbiting a central Kerr black hole (BH) with dimensionless spin a, and its accretion flow into the BH, in an agglomerate of an outer counter-rotating torus and an inner co-rotating torus. This work focus is the analysis of the inter-disks inversion surfaces. Inversion surfaces are spacetime surfaces, defined by the condition (u^{phi }=0) on the flow torodial velocity, located out of the BH ergoregion, and totally embedding the BH. They emerge as a necessary condition, related to the spacetime frame-dragging, for the counter-rotating flows into the central Kerr BH. In our analysis we study the inversion surfaces of the Kerr spacetimes for the counter-rotating flow from the outer torus, impacting on the inner co-rotating disk. Being totally or partially embedded in (internal to) the inversion surfaces, the inner co-rotating torus (or jet) could be totally or in part “shielded”, respectively, from the impact with flow with (a u^{phi }<0). We prove that, in general, in the spacetimes with (a<0.551) the co-rotating toroids are always external to the accretion flows inversion surfaces. For (0.551<a<0.886), co-rotating toroids could be partially internal (with the disk inner region, including the inner edge) in the flow inversion surface. For BHs with (a>0.886), a co-rotating torus could be entirely embedded in the inversion surface and, for larger spins, it is internal to the inversion surfaces. Tori orbiting in the BH outer ergoregion are a particular case. Further constraints on the BHs spins are discussed in the article.

By introducing ansatz and using a PDF at the (N^3LO) approximation in this paper, we have studied the structure of the nucleons in generalized parton distributions. For this purpose, the form factors and the electric radius of nucleons, as well as the quark’s form factors, are calculated in this paper. These calculations give important new information about the nucleons and the distribution of partons within them. The results are analyzed, and to validate them, the abstract emphasizes the importance of comparing the results with existing research and experimental data. By varying the free appropriate parameters of the new ansatz, the study seeks to optimize the model, ensure its suitability for accurately describing the nucleon’s internal structure, and provide valuable insights about the distribution of partons.