Incorporation Of Gravity Research Articles

Naturally-Coupled Dark Sectors

The dark sector, composed of fields that are neutral under the standard model (SM) gauge group, can couple to the SM through the Higgs, hypercharge and neutrino portals, and pull the SM towards its scale by loop corrections. This instability, which is not possible to prevent in the known SM completions, such as supersymmetry, due to the sizable couplings to the SM, calls for alternative mechanisms that can neutralize sensitivities of the SM to the dark sector scale and to the ultraviolet cutoff above it. Here we review such a mechanism in which incorporation of gravity into the SM predicts the existence of a dark sector and allows it to be naturally coupled to the SM. We discuss and illustrate salient processes that can probe the naturally coupled dark sectors.

Effect of gravity on subject-specific human lung deformation

ABSTRACTA biomechanical model of human lung is developed and used to investigate the effect of gravity on lung deformation. The lung is assumed to behave as a poro-elastic medium with spatially dependent elastic property. Finite element analysis is performed on a three-dimensional (3D) lung geometry reconstructed from a four-dimensional Computed Tomography (4DCT) scan dataset of human patient. The spatially dependent Young’s modulus (YM) values are estimated using inverse analysis from a linear elastic deformation model. The predicted deformation of selected landmarks is monitored with and without gravity, and compared with data obtained from 4DCT registration. The results show that gravity indeed significantly affects the magnitude and distribution of lung deformation with the maximum displacement enhanced by 54% in the direction of gravity, for the conditions investigated. In summary, the accuracy of predicted deformation is improved through incorporation of gravity in the biomechanical model of lung.

Simulation of gravity fingering in porous media using a modified invasion percolation model

We introduce a modified invasion percolation (MIP) model for the immiscible displacement of a nonwetting fluid by a wetting fluid within a porous network. The model includes the influence of gravity and is applicable in the quasi-static limit of infinitesimal flow rate where viscous forces are negligible with respect to gravity and capillary forces. The incorporation of gravity alone creates complicated, pore-scale gravity fingers. To properly model wetting fluid invasion where macroscopic gravity fingers form, we incorporate a pore-scale geometric capillary smoothing function we refer to as facilitation.Facilitation models the physics of wetting fluid invasion of pores by modifying the capillary pressure required to fill a pore based on the number of adjacent necks connecting the pore to the invading wetting fluid. The wetting fluid invasion facilitation process creates compact clusters and macroscopic fronts in horizontal simulations and in combination with gravity, creates macroscopic, gravity fingers that are in qualitative agreement with physical experiments. The MIP model yields much different imbibition front structures than standard invasion percolation. For MIP, capillary fingering, capillary facilitation, and gravity fingering compete to determine the wetted network structure as a function of pore-size distribution.

Effect of Thermal Expansion on the Stability of Plane, Freely Propagating Flames, Part II: Incorporation of Gravity and Heat Loss

Abstract The full problem of flame stability, in which fluid mechanics is properly taken into account for all disturbance wavelengths, is examined further. Previously obtained results are extended to include the effects of gravity and non-adiabaticity.

Dynamical implementation of the gravitons as Nambu-Goldstone bosons

General relativity can be considered as a theory with a nonlinear realization of the symmetryGL4,R. In analogy to the Nambu-Jona-Lasinio chiral model, it is shown how the massless gravitons arise in the pair approximation. The ultraviolet divergences of the canonical approaches can be avoided by using fields with anomalous dimensions. Such an approach is suggested by the fact that the tetrads contain also the dilatation Goldstone field which affects the dimensions of the fields involved. The characteristic mass for theGL4,R condensation proves to be the Planck mass, which in turn is also related to the most dangerous consequence of the subcanonical structure, the indefinite metric in state space. The dynamical incorporation of gravity shows a way how to determine, by finite gap equations, the ratios of the characteristic masses for the internal breakdowns (e.g. chirality orSU2) to the Plack mass.