Hypothetic Graviton in the Standard Model [2]

 

The gravitational force can be considered to have existed from the very beginning of the universe, as it is one of the fundamental forces of nature. However, it is not until the universe has cooled enough and the densities of matter have become high enough that gravity becomes the dominant force in shaping the structure of the universe.

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During the radiation-dominated era, which lasted from about 10^-43 seconds to about 10^-11 seconds after the Big Bang, the universe was so hot and dense that the radiation was the dominant force, and the gravitational force had little effect on the distribution of matter.

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It is not until the matter-dominated era, which began after the electroweak epoch [T] , that the gravitational force becomes important in shaping the structure of the universe.

 

As the universe expanded and cooled, matter began to clump together under the influence of gravity, leading to the formation of galaxies, stars, and planets. The first structure that we can identify as being formed by the gravitational force is the cosmic microwave background radiation which was formed at about 380,000 years after the Big Bang, so we can say that the first time we can speak about gravitational force in the history of the universe is around that point.

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In-depth reading

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• Graviton Physics. Barry R. Holstein (Department of Physics—LGRT University of Massachusetts Amherst, MA 01003) (2008)

• J.-P. Gazeau, M. Novello. The Nature of Λ and the Mass of the Graviton: a Critical View. International Journal of Modern Physics A, World Scientific Publishing, 2011, 26, pp.3697-3720. ff10.1142/S0217751X11054176ff. ffhal-00105287f

• The standard model coupled to quantum gravitodynamics. Fermin Aldabe. Eur. Phys. J. C (2017) 77:4 DOI 10.1140/epjc/s10052-016-4520-z (2016)

• The Mechanism of Graviton Exchange between Bodies. H. Javadi, F. Forouzbakhsh (2016)

• Mass for the graviton. Matt Visser (Physics Department Washington University Saint Louis Missouri 63130-4899 USA) (1998)

• Graviton production in inflationary cosmology. L.F. Abott  and D.D. Hararri (1985)

• Reporting New Evidence of Gravitons. Paul T. Smith (Centre for Physics Research, VNS, 20 Henley Marine Drive, Rodd Point 2046, Sydney, Australia) (2016)

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Recent Developments

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• Gravitational radiation from binary systems in massive graviton theories. Tanmay Kumar Poddar, Subhendra Mohanty and Soumya Jana (2022)

• Reconstructing the graviton. Alfio Bonanno, Tobias Denz, Jan M. Pawlowski and Manuel Reichert. (2022)

• Generalized symmetries of the graviton. Valentin Benedetti, Horacio Casinia and Javier M. Magán (2022)

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Graviton in the String Theory [2]

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String theory predicts the existence of gravitons and their well-defined interactions. A graviton in perturbative string theory is a closed string in a very particular low-energy vibrational state. The scattering of gravitons in string theory can also be computed from the correlation functions in conformal field theory, as dictated by the AdS/CFT correspondence, or from matrix theory.[citation needed]

A feature of gravitons in string theory is that, as closed strings without endpoints, they would not be bound to branes and could move freely between them. If we live on a brane (as hypothesized by brane theories), this "leakage" of gravitons from the brane into higher-dimensional space could explain why gravitation is such a weak force, and gravitons from other branes adjacent to our own could provide a potential explanation for dark matter. However, if gravitons were to move completely freely between branes, this would dilute gravity too much, causing a violation of Newton's inverse-square law. To combat this, Lisa Randall found that a three-brane (such as ours) would have a gravitational pull of its own, preventing gravitons from drifting freely, possibly resulting in the diluted gravity we observe, while roughly maintaining Newton's inverse square law.  [5]  See brane cosmology.

A theory by Ahmed Farag Ali and Saurya Das adds quantum mechanical corrections (using Bohm trajectories) to general relativistic geodesics. If gravitons are given a small but non-zero mass, it could explain the cosmological constant without need for dark energy and solve the smallness problem.  [6]   The theory received an Honorable Mention in the 2014 Essay Competition of the Gravity Research Foundation for explaining the smallness of cosmological constant.  [7]  Also the theory received an Honorable Mention in the 2015 Essay Competition of the Gravity Research Foundation for naturally explaining the observed large-scale homogeneity and isotropy of the universe due to the proposed quantum corrections.  [8]

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