Dark Matter

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Dark matter is a hypothetical form of matter thought to account for approximately 85% of the matter in the universe.[1] Dark matter is called "dark" because it does not appear to interact with the electromagnetic field, which means it does not absorb, reflect, or emit electromagnetic radiation and is, therefore, difficult to detect. Various astrophysical observations – including gravitational effects which cannot be explained by currently accepted theories of gravity unless more matter is present than can be seen – imply dark matter's presence. For this reason, most experts think that dark matter is abundant in the universe and has had a strong influence on its structure and evolution.[2]

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The primary evidence for dark matter comes from calculations showing that many galaxies would behave quite differently if they did not contain a large amount of unseen matter. Some galaxies would not have formed at all and others would not move as they currently do.[3] Other lines of evidence include observations in gravitational lensing[4] and the cosmic microwave background, along with astronomical observations of the observable universe's current structure, the formation and evolution of galaxies, mass location during galactic collisions,[5] and the motion of galaxies within galaxy clusters. In the standard Lambda-CDM model of cosmology, the total mass-energy content of the universe contains 5% ordinary matter, 26.8% dark matter, and 68.2% of a form of energy known as dark energy.[6][7][8][9] Thus, dark matter constitutes 85%[a] of the total mass, while dark energy and dark matter constitute 95% of the total mass-energy content.[10][11][12][13]

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Because no one has directly observed dark matter yet – assuming it exists – it must barely interact with ordinary baryonic matter and radiation except through gravity. Dark matter is thought to be non-baryonic; it may be composed of some as-yet-undiscovered subatomic particles.[b] The primary candidate for dark matter is some new kind of elementary particle that has not yet been discovered, particularly weakly interacting massive particles (WIMPs).[14] Other possibilities include black holes such as primordial black holes. Many experiments to detect and study dark matter particles directly are being actively undertaken, but none have yet succeeded.[15] Dark matter is classified as "cold", "warm", or "hot" according to its velocity (more precisely, its free streaming length). Current models favor a cold dark matter scenario, in which structures emerge by the gradual accumulation of particles.

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Although the scientific community generally accepts dark matter's existence,[16] some astrophysicists, intrigued by specific observations that are not well-explained by ordinary dark matter, argue for various modifications of the standard laws of general relativity. These include modified Newtonian dynamics, tensor–vector–scalar gravity, or entropic gravity. These models attempt to account for all observations without invoking supplemental non-baryonic matter.

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Dark Photons

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A recent analysis [15] undertaken by an international team of physicists has put forward an intriguing hypothesis regarding the enigmatic dark photons. These hypothetical particles are believed to be carriers of forces associated with dark matter, and the analysis, led by Nicholas Hunt-Smith and his team at the University of Adelaide in Australia, has the potential to shed light on the elusive nature of dark matter. Despite its dominance, accounting for approximately 85% of the universe's mass according to established cosmological models, dark matter remains an enigma due to its peculiar property of not interacting with electromagnetic radiation, neither absorbing, reflecting, nor emitting it. As a result, laboratory detection efforts have thus far proven futile.

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Anthony Thomas, a physicist at the University of Adelaide and a co-author of the analysis, emphasizes the challenge of this quest: "No particle beyond the Standard Model, which comprehensively describes all the matter we are acquainted with, has ever been observed." He underscores the likelihood that dark matter consists of particles lying beyond the standard model, further emphasizing the mysteries surrounding this cosmic enigma.

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Dark matter, despite its elusive nature, is the prevailing explanation for various cosmic phenomena, such as the faster-than-expected rotation of galaxies concerning their visible matter content. However, the mechanism by which dark matter interacts with the universe remains unclear. One possible avenue of exploration is the existence of dark photons, which could be part of an additional dark sector where dark matter resides. These dark photons might weakly interact with the ordinary sector through the mixing of a gauge boson, the dark photon, with standard neutral gauge bosons, such as photons, W, and Z bosons.

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In their most recent study, the team led by Adelaide, in collaboration with researchers from the Jefferson Lab in Virginia, conducted a global quantum chromodynamics (QCD) analysis of high-energy scattering data using the Jefferson Lab Angular Momentum (JAM) framework. The results indicate a preference for a model incorporating dark photons when explaining the outcomes of deep inelastic scattering (DIS) experiments over the conventional Standard Model hypothesis, with a significance of 6.5σ.

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Deep inelastic scattering (DIS) occurs when high-energy probes, like electrons, muons, or neutrinos, collide with protons with such significant energy and momentum transfer that they essentially break the proton into fragments. This analysis involves calculating parton distribution functions (PDFs), which provide information about the probability of finding specific types of quarks within the original proton.

The study has garnered attention for its "provocative" nature, as it explores fitting proton and neutron scattering data with a beyond the Standard Model (BSM) scenario, such as the dark photon hypothesis, alongside the PDFs. This approach, which has been gaining interest in recent years, is seen as a promising avenue for further investigation.

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However, as enthusiastic as researchers are about this work, there remain critical considerations, particularly in terms of uncertainty quantification, which is a vital aspect of interpretation in this field. Addressing questions surrounding how to establish consistent and reproducible uncertainties in complex, multi-parameter models is a crucial frontier in the development of this field. This analysis used a more aggressive definition of uncertainty, which may have influenced the perceived significance of the dark photon signature extracted from DIS data, along with its correlation with the PDFs.

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The study's focus on DIS has prompted some to wonder about the broader implications. For instance, dark photons would also impact the results of electron-positron experiments like BABAR and LEP. The values of the mixing parameter epsilon are not negligible, and any such effects should be discernible. However, a previous analysis of BABAR data did not reveal dark-photon-related effects. Therefore, further exploration and analysis are warranted to explore the full scope of these findings.

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In conclusion, while this analysis provides strong but indirect evidence of the existence of dark photons, it is imperative to seek confirmation through additional analyses and, ideally, through direct experiments or other reactions. The quest for understanding dark matter remains a compelling challenge, and these recent findings offer a promising avenue for further research and exploration. [17]

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Recent Research Papers

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• Dark matter search with CMB: a study of foregrounds.  Zi-Xuan Zhanga, Yi-Ming Wang, Junsong Cang, Zirui Zhang, Yang Liu, Si-Yu Lia Yu Gao and  Hong Li.  (2023)

• Detecting Hidden Photon Dark Matter Using the Direct Excitation of Transmon Qubits.  Shion Chen a.o. Physical Review Letters 131, 211001 (2023)

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References

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 [1]  "NASA Science Universe – Dark Energy, Dark Matter". NASA Science. Retrieved 23 May 2021.

[2]   "Dark Matter". CERN Physics. 20 January 2012.

[3]  Siegfried, T. (5 July 1999). "Hidden space dimensions may permit parallel universes, explain cosmic mysteries". The Dallas Morning News.

[4]  Trimble, V. (1987). "Existence and nature of dark matter in the universe" (PDF). Annual Review of Astronomy and Astrophysics. 25: 425–472. Bibcode:1987ARA&A..25..425T. doi:10.1146/annurev.aa.25.090187.002233. S2CID 123199266. Archived (PDF) from the original on 18 July 2018.

[5]   "A history of dark matter". 2017.

[6]   "Planck Mission Brings Universe into Sharp Focus". NASA Mission Pages. 21 March 2013.

[7]   "Dark Energy, Dark Matter". NASA Science: Astrophysics. 5 June 2015.

[8]   Ade, P. A. R.; Aghanim, N.; Armitage-Caplan, C.; et al. (Planck Collaboration) (22 March 2013). "Planck 2013 results. I. Overview of products and scientific results – Table 9". Astronomy and Astrophysics. 1303: 5062. arXiv:1303.5062. Bibcode:2014A&A...571A...1P. doi:10.1051/0004-6361/201321529. S2CID 218716838.

[9]  Francis, Matthew (22 March 2013). "First Planck results: the Universe is still weird and interesting". Ars Technica.

[10]  "Planck captures portrait of the young Universe, revealing earliest light". University of Cambridge. 21 March 2013. Retrieved 21 March 2013.

[11]  Carroll, Sean (2007). Dark Matter, Dark Energy: The dark side of the universe. The Teaching Company. Guidebook Part 2 p. 46. ... dark matter: An invisible, essentially collisionless component of matter that makes up about 25 percent of the energy density of the universe ... it's a different kind of particle... something not yet observed in the laboratory ...

[12]  Ferris, Timothy (January 2015). "Dark matter". Hidden cosmos. National Geographic Magazine. Retrieved 10 June 2015.

[13]  Jarosik, N.; et al. (2011). "Seven-year Wilson microwave anisotropy probe (WMAP) observations: Sky maps, systematic errors, and basic results". Astrophysical Journal Supplement. 192 (2): 14. arXiv:1001.4744. Bibcode:2011ApJS..192...14J. doi:10.1088/0067-0049/192/2/14. S2CID 46171526.

[14]  Jump up to:a b c d Copi, C.J.; Schramm, D.N.; Turner, M.S. (1995). "Big-Bang Nucleosynthesis and the Baryon Density of the Universe". Science. 267 (5195): 192–199. arXiv:astro-ph/9407006. Bibcode:1995Sci...267..192C. doi:10.1126/science.7809624. PMID 7809624. S2CID 15613185.

[15]  Jump up to:a b c d e f g Bertone, G.; Hooper, D.; Silk, J. (2005). "Particle dark matter: Evidence, candidates and constraints". Physics Reports. 405 (5–6): 279–390. arXiv:hep-ph/0404175. Bibcode:2005PhR...405..279B. doi:10.1016/j.physrep.2004.08.031. S2CID 118979310.

[16]  Global QCD analysis and dark photons.Journal of High Energy Physics. N. T. Hunt-Smith,  W. Melnitchouk, N. Sato, A. W. Thomas, X. G. Wang &  M. J. White on behalf of the Jefferson Lab Angular Momentum (JAM) collaboration

[17]  Physics World.. Particle and interactions. Dark photons could explain high-energy scattering data. Kevin Jackson. 2023