5,439 research outputs found
Large-scale magnetic fields from inflation in teleparallel gravity
Generation of large-scale magnetic fields in inflationary cosmology is
studied in teleparallelism, where instead of the scalar curvature in general
relativity, the torsion scalar describes the gravity theory. In particular, we
investigate a coupling of the electromagnetic field to the torsion scalar
during inflation, which leads to the breaking of conformal invariance of the
electromagnetic field. We demonstrate that for a power-law type coupling, the
current magnetic field strength of G on 1 Mpc scale can be
generated, if the backreaction effects and strong coupling problem are not
taken into consideration.Comment: 4 pages, no figure, to be published in the Proceedings of the "12th
Asia Pacific Physics Conference.
Inverse-Chirp Imprint of Gravitational Wave Signals in Scalar Tensor Theory
The scalar tensor theory contains a coupling function connecting the
quantities in the Jordan and Einstein frames, which is constrained to guarantee
a transformation rule between frames. We simulate the supernovae core collapse
with different choices of coupling functions defined over the viable region of
the parameter space and find that a generic inverse-chirp feature of the
gravitational waves in the scalar tensor scenario.Comment: 13 pages, 4 figures, revised version accepted by EPJ
Unified lattice Boltzmann method with improved schemes for multiphase flow simulation: Application to droplet dynamics under realistic conditions
As a powerful mesoscale approach, the lattice Boltzmann method (LBM) has been widely used for the numerical study of complex multiphase flows. Recently, Luo et al. [Philos. Trans. R. Soc. A: Math. Phys. Eng. Sci. 379, 20200397 (2021)] proposed a unified lattice Boltzmann method (ULBM) to integrate the widely used lattice Boltzmann collision operators into a unified framework. In this study, we incorporate additional features into this ULBM in order to simulate multiphase flow under realistic conditions. A nonorthogonal moment set [Fei et al., Phys. Rev. E 97, 053309 (2018)] and the entropic-multi-relaxation-time (KBC) lattice Boltzmann model are used to construct the collision operator. An extended combined pseudopotential model is proposed to realize multiphase flow simulation at high-density ratio with tunable surface tension over a wide range. The numerical results indicate that the improved ULBM can significantly decrease the spurious velocities and adjust the surface tension without appreciably changing the density ratio. The ULBM is validated through reproducing various droplet dynamics experiments, such as binary droplet collision and droplet impingement on superhydrophobic surfaces. Finally, the extended ULBM is applied to complex droplet dynamics, including droplet pancake bouncing and droplet splashing. The maximum Weber number and Reynolds number in the simulation reach 800 and 7200, respectively, at a density ratio of 1000. The study demonstrates the generality and versatility of ULBM for incorporating schemes to tackle challenging multiphase problems
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