Subscribe to the gold package and get unlimited access to Shamra Academy
Register a new userBrane Gravitational Extension of Diracs Extensible Model of the Electron
149
0
0.0
(
0
)
Ask ChatGPT about the research
No Arabic abstract
A gravitational extension of Diracs Extensible model of the electron is presented. The Dirac bubble, treated as a 3-dim electrically charged brane, is dynamically embedded within a 4-dim $Z_{2}$-symmetric Reissner-Nordstrom bulk. Crucial to our analysis is the gravitational extension of Diracs brane variation prescription; its major effect is to induce a novel geometrically originated contribution to the energy-momentum tensor on the brane. In turn, the effective potential which governs the evolution of the bubble exhibits a global minimum, such that the size of the bubble stays finite (Planck scale) even at the limit where the mass approaches zero. This way, without fine-tuning, one avoids the problem so-called classical radius of the electron.
rate research
Read More
The Standard-Model Extension (SME) provides a comprehensive effective field-theory framework for the study of CPT and Lorentz symmetry. This work reviews the structure and philosophy of the SME and provides some intuitive examples of symmetry violation. The results of recent gravitational tests performed within the SME are summarized including analysis of results from the Laser Interferometer Gravitational-Wave Observatory (LIGO), sensitivities achieved in short-range gravity experiments, constraints from cosmic-ray data, and results achieved by studying planetary ephemerids. Some proposals and ongoing efforts will also be considered including gravimeter tests, tests of the Weak Equivalence Principle, and antimatter experiments. Our review of the above topics is augmented by several original extensions of the relevant work. We present new examples of symmetry violation in the SME and use the cosmic-ray analysis to place first-ever constraints on 81 additional operators.
This paper is dedicated to revisit the modifications caused by branes in the collapse of a stellar structure under the Snyder-Oppenheimer scheme. Due to the homogeneity and isotropy of the model, we choose study the case of a closed geometry described by $k=1$, through the tool of dynamical systems. We revisit the different components of the star and its evolution during the stellar collapse, paying particular attention to the non-local effects and the quadratic terms of the energy momentum tensor that come from branes corrections. In the same vein we realize a phase portrait together with a stability analysis with the aim of obtain information about the attractors or saddle points of the dynamical system under different initial conditions in the density parameters, remarking the parameters that come from branes contributions.
We present an explicit detailed theoretical and observational investigation of an anisotropic massive Brans-Dicke (BD) gravity extension of the standard $Lambda$CDM model, wherein the extension is characterized by two additional degrees of freedom; the BD parameter, $omega$, and the present day density parameter corresponding to the shear scalar, $Omega_{sigma^2,0}$. The BD parameter, determining the deviation from general relativity (GR), by alone characterizes both the dynamics of the effective dark energy (DE) and the redshift dependence of the shear scalar. These two affect each other depending on $omega$, namely, the shear scalar contributes to the dynamics of the effective DE, and its anisotropic stress --which does not exist in scalar field models of DE within GR-- controls the dynamics of the shear scalar deviating from the usual $propto(1+z)^6$ form in GR. We mainly confine the current work to non-negative $omega$ values as it is the right sign --theoretically and observationally-- for investigating the model as a correction to the $Lambda$CDM. By considering the current cosmological observations, we find that $omegagtrsim 250$, $Omega_{sigma^2,0}lesssim 10^{-23}$ and the contribution of the anisotropy of the effective DE to this value is insignificant. We conclude that the simplest anisotropic massive BD gravity extension of the standard $Lambda$CDM model exhibits no significant deviations from it all the way to the Big Bang Nucleosynthesis. We also point out the interesting features of the model in the case of negative $omega$ values; for instance, the constraints on $Omega_{sigma^2,0}$ could be relaxed considerably, the values of $omegasim-1$ (relevant to string theories) predict dramatically different dynamics for the expansion anisotropy.
Big bang of the Friedmann-Robertson-Walker (FRW)-brane universe is studied. In contrast to the spacelike initial singularity of the usual FRW universe, the initial singularity of the FRW-brane universe is point-like from the viewpoint of causality including gravitational waves propagating in the bulk. Existence of null singularities (seam singuralities) is also shown in the flat and open FRW-brane universe models.
The shear dynamics in Bianchi I cosmological model on the brane with a perfect fluid (the equation of state is $p=(gamma-1) mu$) is studied. It is shown that for $1 < gamma < 2$ the shear parameter has maximum at some moment during a transition period from nonstandard to standard cosmology. An exact formula for the matter density $mu$ in the epoch of maximum shear parameter as a function of the equation of state is obtained.
Log in to be able to interact and post comments
comments
Fetching comments
Sign in to be able to follow your search criteria
