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Register a new userEmergent gravity from direct-action EM in a toy universe of electrons and positrons
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M. Ibison
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We sketch the derivation of a Newtonian gravity-like force emerging from a direct-action variant of classical electromagnetism. The binding energy is a consequence of maximal phase correlation of the sources mediated by approximately monochromatic direct-action fields. The resulting force then has the character of a strong version of the van der Waals force, whose superior strength can be attributed to relatively coherent primary fields (compared with the totally incoherent effects of the ZPF). The model also predicts the existence of a background having some of the character of dark energy.
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An obstacle to the development of direct action version of electromagnetism was that in the end it failed to fulfill its initial promise of avoiding the problem of infinite Coulomb self-energy in the Maxwell theory of the classical point charge. This paper suggests a small but significant modification of the traditional direct action theory which overcomes that obstacle. Self-action is retained but the associated energy is rendered finite and equal to zero in the special case of null motion.
We construct an idealized universe for didactic purposes. This universe is assumed to consist of absolute Euclidean space and to be filled with a classical medium which allows for sound waves. A known solution to the wave equation describing the dynamics of the medium is a standing spherical wave. Although this is a problem of classical mechanics, we demonstrate that the Lorentz transformation is required to generate a moving solution from the stationary one. Both solutions are here collectively referred to as spherons. These spherons exhibit properties which have analogues in the physical description of matter with rest mass, among them de Broglie like phase waves and at the same time relativistic effects such as contraction and a speed limit. This leads to a theory of special relativity by assuming the point of view of an observer made of such spheronic matter. The argument made here may thus be useful as a visualisation or didactic approach to the real universe, in which matter has wave-like properties and obeys the laws of special relativity.
Teleparallel gravity is a modified theory of gravity for which the Ricci scalar $R$ of the underlying geometry in the action is replaced by an arbitrary functional form of torsion scalar $T$. In doing so, cosmology in $% f(T)$ gravity becomes greatly simplified owing to the fact that $T$ contains only the first derivatives of the vierbeins. The article exploits this appealing nature of $f(T)$ gravity and present cosmological scenarios from hybrid and logarithmic teleparallel gravity models of the form $% f=e^{mT}T^n $ and $f=Dlog(bT)$ respectively, where $m$, $n$, $D$ and $b$ are free parameters constrained to suffice the late time acceleration. We employ a well motivated parametrization of the deceleration parameter having just one degree of freedom constrained with a $chi^{2}$ test from 57 data points of Hubble data set in the redshift range $0.07<z<2.36$, to obtain the expressions of pressure, density and EoS parameter for both the teleparallel gravity models and study their temporal evolution. We find the deceleration parameter to experience a signature flipping for the $chi^{2}$ value of the free parameter at $z_{tr}simeq0.6$ which is consistent with latest Planck measurements. Next, we present few geometric diagnostics of this parametrization to understand the nature of dark energy and its deviation from the $Lambda$CDM cosmology. Finally, we study the energy conditions to check the consistency of the parameter spaces for both the teleparallel gravity models. We find the SEC to violate for both the models which is an essential recipe to obtain an accelerating universe.
High energy cosmic ray electrons plus positrons (CREs), which lose energy quickly during their propagation, provide an ideal probe of Galactic high-energy processes and may enable the observation of phenomena such as dark-matter particle annihilation or decay. The CRE spectrum has been directly measured up to $sim 2$ TeV in previous balloon- or space-borne experiments, and indirectly up to $sim 5$ TeV by ground-based Cherenkov $gamma$-ray telescope arrays. Evidence for a spectral break in the TeV energy range has been provided by indirect measurements of H.E.S.S., although the results were qualified by sizeable systematic uncertainties. Here we report a direct measurement of CREs in the energy range $25~{rm GeV}-4.6~{rm TeV}$ by the DArk Matter Particle Explorer (DAMPE) with unprecedentedly high energy resolution and low background. The majority of the spectrum can be properly fitted by a smoothly broken power-law model rather than a single power-law model. The direct detection of a spectral break at $E sim0.9$ TeV confirms the evidence found by H.E.S.S., clarifies the behavior of the CRE spectrum at energies above 1 TeV and sheds light on the physical origin of the sub-TeV CREs.
The $f(R,T)$ theory of gravitation is an extended theory of gravitation in which the gravitational action contains both the Ricci scalar $R$ and the trace of energy momentum tensor $T$ and hence the cosmological models based on $f(R,T)$ gravity are eligible to describing late time acceleration of present universe. In this paper, we investigate an accelerating model of flat universe with linearly varying deceleration parameter (LVDP). We apply the linearly time varying law for deceleration parameters that generates a model of transitioning universe from early decelerating phase to current accelerating phase. We carry out the state-finder and Om(z) analysis, and obtain that LVDP model have consistency with astrophysical observations. We also discuss profoundly the violation of energy-momentum conservation law in $f(R,T)$ gravity and dynamical behavior of the model.
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