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Статті в журналах з теми "Cosmological constant,galactic rotation curves":
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Kulchoakrungsun, Ekapob, Adrian Lam, and David A. Lowe. "Effect of the cosmological constant on halo size." Modern Physics Letters A 33, no. 10n11 (April 10, 2018): 1850059. http://dx.doi.org/10.1142/s0217732318500591.
In this work, we consider the effect of the cosmological constant on galactic halo size. As a model, we study the general relativistic derivation of orbits in the Schwarzschild–de Sitter metric. We find that there exists a length scale [Formula: see text] corresponding to a maximum size of a circular orbit of a test mass in a gravitationally bound system, which is the geometric mean of the cosmological horizon size squared and the Schwarzschild radius. This agrees well with the size of a galactic halo when the effects of dark matter are included. The size of larger structures such as galactic clusters and superclusters are also well-approximated by this scale. This model provides a simplified approach to computing the size of such structures without the usual detailed dynamical models. Some of the more detailed approaches that appear in the literature are reviewed, and we find the length scales agree to within a factor of order one. Finally, we note the length scale associated with the effects of MOND or Verlinde’s emergent gravity, which offer explanations of the flattening of galaxy rotation curves without invoking dark matter, may be expressed as the geometric mean of the cosmological horizon size and the Schwarzschild radius, which is typically 100 times smaller than [Formula: see text].
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Oakley, William S. "Calculating the MOND constant and addressing flat galactic orbital star rotation velocity curves." International Journal of Scientific Reports 1, no. 7 (November 29, 2015): 283. http://dx.doi.org/10.18203/issn.2454-2156.intjscirep20151255.
<p class="abstract"><span lang="EN-US">A particle based explanation for the MOND constant, a<sub>o</sub>, is proposed. For stars orbiting in the outer region of galaxies Newton’s inverse square law fails at the same classical angular acceleration v<sup>2</sup>/R, (= a<sub>o</sub>), regardless of the mass of the galaxy or star, the star orbital velocity v, or the orbit radius R. Gravitational orbital dynamics, where orbital matter propagates un-accelerated in curved space-time as described by General Relativity, applies equally to systems of vastly different masses, i.e. at cosmological and elementary particle scales, with gravity simply an observer domain manifestation of the force localizing electromagnetic energy to form particles. Comparison of astronomical data and particle concepts, with scale adjustments, enables an expression for a<sub>o</sub> to be derived and a numerical value obtained within the uncertainty bounds of empirical data. Newton’s law fails and stellar orbital velocities become independent of the orbit radius at the same gravitational field strength as at the proton radius. A quantum loop based cause of orbital velocity curve flattening is proposed.</span></p>
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Edmonds, Douglas, Duncan Farrah, Chiu Man Ho, Djordje Minic, Y. Jack Ng, and Tatsu Takeuchi. "Testing Modified Dark Matter with galaxy clusters: Does dark matter know about the cosmological constant?" International Journal of Modern Physics A 32, no. 18 (June 28, 2017): 1750108. http://dx.doi.org/10.1142/s0217751x17501081.
We discuss the possibility that the cold dark matter mass profiles contain information on the cosmological constant [Formula: see text], and that such information constrains the nature of cold dark matter (CDM). We call this approach Modified Dark Matter (MDM). In particular, we examine the ability of MDM to explain the observed mass profiles of 13 galaxy clusters. Using general arguments from gravitational thermodynamics, we provide a theoretical justification for our MDM mass profile. In order to properly fit the shape of the mass profiles in galaxy clusters, we find it necessary to generalize the MDM mass profile from the one we used previously to fit galactic rotation curves. We successfully compare it to the NFW mass profiles both on cluster and galactic scales, though differences in form appear with the change in scales. Our results suggest that indeed the CDM mass profiles contain information about the cosmological constant in a nontrivial way.
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Pérez-Cuéllar, G., and M. Sabido. "On planetary orbits in entropic gravity." Modern Physics Letters A 36, no. 08 (February 3, 2021): 2150050. http://dx.doi.org/10.1142/s0217732321500504.
Starting with an entropy that includes volumetric, area and length terms as well as logarithmic contributions, we derive the corresponding modified Newtonian gravity and derive the expression for planetary orbits. We calculate the shift of the perihelion of Mercury to find bounds to the parameters associated to the modified Newtonian gravity. We compare the parameter associated to the volumetric contribution in the entropy-area relationship with the value derived for galactic rotation curves and the value obtained from the cosmological constant.
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Bahamonde, Sebastian, David Benisty, and Eduardo Guendelman. "Linear Potentials in Galaxy Halos by Asymmetric Wormholes." Universe 4, no. 11 (October 29, 2018): 112. http://dx.doi.org/10.3390/universe4110112.
A spherically symmetric space-time solution for a diffusive two measures theory is studied. An asymmetric wormhole geometry is obtained where the metric coefficients has a linear term for galactic distances and the analysis of Mannheim and collaborators, can then be used to describe the galactic rotation curves. For cosmological distances a de-Sitter space-time is realized. Center of gravity coordinates for the wormhole are introduced which are the most suitable for the collective motion of a wormhole. The wormholes connect universes with different vacuum energy densities which may represent different universes in a “landscape scenario”. The metric coefficients depend on the asymmetric wormhole parameters. The coefficient of the linear potential is proportional to both the mass of the wormhole and the cosmological constant of the observed universe. Similar results are also expected in other theories like k-essence theories, that may support wormholes.
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Zloshchastiev, Konstantin G. "An Alternative to Dark Matter and Dark Energy: Scale-Dependent Gravity in Superfluid Vacuum Theory." Universe 6, no. 10 (October 15, 2020): 180. http://dx.doi.org/10.3390/universe6100180.
We derive an effective gravitational potential, induced by the quantum wavefunction of a physical vacuum of a self-gravitating configuration, while the vacuum itself is viewed as the superfluid described by the logarithmic quantum wave equation. We determine that gravity has a multiple-scale pattern, to such an extent that one can distinguish sub-Newtonian, Newtonian, galactic, extragalactic and cosmological terms. The last of these dominates at the largest length scale of the model, where superfluid vacuum induces an asymptotically Friedmann–Lemaître–Robertson–Walker-type spacetime, which provides an explanation for the accelerating expansion of the Universe. The model describes different types of expansion mechanisms, which could explain the discrepancy between measurements of the Hubble constant using different methods. On a galactic scale, our model explains the non-Keplerian behaviour of galactic rotation curves, and also why their profiles can vary depending on the galaxy. It also makes a number of predictions about the behaviour of gravity at larger galactic and extragalactic scales. We demonstrate how the behaviour of rotation curves varies with distance from a gravitating center, growing from an inner galactic scale towards a metagalactic scale: A squared orbital velocity’s profile crosses over from Keplerian to flat, and then to non-flat. The asymptotic non-flat regime is thus expected to be seen in the outer regions of large spiral galaxies.
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GRUMILLER, D., and F. PREIS. "RINDLER FORCE AT LARGE DISTANCES." International Journal of Modern Physics D 20, no. 14 (December 31, 2011): 2761–66. http://dx.doi.org/10.1142/s0218271811020585.
Given some assumptions, it is possible to derive the most general post-general relativistic theory of gravity for the distant field of a point mass. The force law derived from this theory contains a Rindler term in addition to well-known contributions, a Schwarzschild mass and a cosmological constant. The same force law recently was confronted with solar system precision data. The Rindler force, if present in Nature, has intriguing consequences for gravity at large distances. In particular, the Rindler force is capable of explaining about 10% of the Pioneer anomaly and simultaneously ameliorates the shape of galactic rotation curves.
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Edmonds, Douglas, Duncan Farrah, Djordje Minic, Y. Jack Ng, and Tatsu Takeuchi. "Modified dark matter: Relating dark energy, dark matter and baryonic matter." International Journal of Modern Physics D 27, no. 02 (January 2018): 1830001. http://dx.doi.org/10.1142/s021827181830001x.
Modified dark matter (MDM) is a phenomenological model of dark matter, inspired by gravitational thermodynamics. For an accelerating universe with positive cosmological constant ([Formula: see text]), such phenomenological considerations lead to the emergence of a critical acceleration parameter related to [Formula: see text]. Such a critical acceleration is an effective phenomenological manifestation of MDM, and it is found in correlations between dark matter and baryonic matter in galaxy rotation curves. The resulting MDM mass profiles, which are sensitive to [Formula: see text], are consistent with observational data at both the galactic and cluster scales. In particular, the same critical acceleration appears both in the galactic and cluster data fits based on MDM. Furthermore, using some robust qualitative arguments, MDM appears to work well on cosmological scales, even though quantitative studies are still lacking. Finally, we comment on certain nonlocal aspects of the quanta of modified dark matter, which may lead to novel nonparticle phenomenology and which may explain why, so far, dark matter detection experiments have failed to detect dark matter particles.
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HENRY-COUANNIER, FREDERIC. "DISCRETE SYMMETRIES AND GENERAL RELATIVITY, THE DARK SIDE OF GRAVITY." International Journal of Modern Physics A 20, no. 11 (April 30, 2005): 2341–45. http://dx.doi.org/10.1142/s0217751x05024602.
The parity and time reversal invariant actions, equations and their conjugated metric solutions are obtained in the context of a general relativistic model modified in order to suitably take into account discrete symmetries. The equations are not covariant however the predictions of the model, in particular its Schwarzschild metric solution in vacuum, only start to differ from those of General Relativity at the Post-Post-Newtonian order. No coordinate singularity (black hole) arises in the privileged coordinate system where the energy of gravity is found to vanish. Vacuum energies have no gravitational effects. A flat universe accelerated expansion phase is obtained without resorting to inflation nor a cosmological constant. The context may be promising to help us elucidate several outstanding enigmas such as the Pioneer anomalous blue-shift, flat galactic rotation curves or the universe voids.
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Stuckey, W. M., Timothy McDevitt, A. K. Sten, and Michael Silberstein. "End of a dark age?" International Journal of Modern Physics D 25, no. 12 (October 2016): 1644004. http://dx.doi.org/10.1142/s0218271816440041.
We argue that dark matter (DM)and dark energy phenomena associated with galactic rotation curves (RC’s), X-ray cluster mass profiles, and type Ia supernova data can be accounted for via small corrections to idealized general relativistic spacetime geometries due to disordered locality. Accordingly, we fit the HI nearby galaxy survey (THINGS) RC data rivaling modified Newtonian dynamics, Roentgen Satellite/Advanced Satellite for Cosmology and Astrophysics (ROSAT/ASCA) X-ray cluster mass profile data rivaling metric-skew-tensor gravity, and SCP Union2.1 SN Ia data rivaling [Formula: see text]CDM without nonbaryonic DM or a cosmological constant. In the case of DM, we geometrically modify proper mass interior to the Schwarzschild solution. In the case of dark energy, we modify proper distance in Einstein–de Sitter cosmology. Therefore, the phenomena of DM and dark energy may be chimeras created by an errant belief that spacetime is a differentiable manifold rather than a disordered graph.
Дисертації з теми "Cosmological constant,galactic rotation curves":
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Magi, Matteo. "The role of the cosmological constant for galactic rotation curves." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2020. http://amslaurea.unibo.it/21179/.
In questa tesi sono state studiate le curve di rotazione delle galassie a spirale all'interno dello schema concettuale dato dal modello Lambda CDM, con l'intento di determinare un eventuale effetto, e la relativa portata, della costante cosmologica.
Lo studio del problema è stato condotto in accordo con la prospettiva geometrica dettata dalla teoria della relatività generale: assumendo una galassia descritta dalle soluzioni delle equazioni di campo, si sono studiate le curve di rotazione analizzando le geodetiche circolari.
Inizialmente si è esaminato un toy model di galassia, ottenuto considerando la totalità della massa concentrata in un singolo punto, studiando così la geometria dello spaziotempo di Schwarzschild-de Sitter. Si è passati poi a un modello più realistico, che tenesse conto del contributo energetico della materia oscura presente nell’alone galattico. Questa richiesta ha portato allo studio della metrica di Lemaître-Tolman.
In entrambi i casi la costante cosmologica ha un effetto sulle curve di rotazione: fissata la distanza dal centro della galassia, la velocità di rotazione di una massa di prova risulta essere minore rispetto al caso in cui \Lambda=0. Considerando distanze sempre maggiori si perde l’esistenza delle geodetiche circolari.
La portata di questo effetto è apprezzabile su scale dell'ordine di centinaia di kiloparsec fino a qualche megaparsec, risultando dunque di difficile osservazione necessitando di galassie isolate ben accessibili sperimentalmente. Qualora l’effetto fosse confermato, tuttavia, questo lavoro permetterebbe una nuova misura indiretta della costante cosmologica.
Частини книг з теми "Cosmological constant,galactic rotation curves":
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Kraniotis, Georgios V., and Steven B. Whitehouse. "Measurement of the Cosmological Constant from Galactic Velocity Rotation Data." In Sources and Detection of Dark Matter and Dark Energy in the Universe, 66–73. Berlin, Heidelberg: Springer Berlin Heidelberg, 2001. http://dx.doi.org/10.1007/978-3-662-04587-9_6.
