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In astronomy, dark matter is a hypothetical form of matter that appears not to interact with light or the electromagnetic field. Dark matter is implied by gravitational effects which cannot be explained by general relativity unless more matter is present than can be seen. Such effects occur in the context of formation and evolution of galaxies, gravitational lensing, the observable universe's current structure, mass position in galactic collisions, the motion of galaxies within galaxy clusters, and cosmic microwave background anisotropies.
In particle physics, proton decay is a hypothetical form of particle decay in which the proton decays into lighter subatomic particles, such as a neutral pion and a positron. The proton decay hypothesis was first formulated by Andrei Sakharov in 1967. Despite significant experimental effort, proton decay has never been observed. If it does decay via a positron, the proton's half-life is constrained to be at least 1.67×1034 years.
Weakly interacting massive particles (WIMPs) are hypothetical particles that are one of the proposed candidates for dark matter.
In cosmology and physics, cold dark matter (CDM) is a hypothetical type of dark matter. According to the current standard model of cosmology, Lambda-CDM model, approximately 27% of the universe is dark matter and 68% is dark energy, with only a small fraction being the ordinary baryonic matter that composes stars, planets, and living organisms. Cold refers to the fact that the dark matter moves slowly compared to the speed of light, giving it a vanishing equation of state. Dark indicates that it interacts very weakly with ordinary matter and electromagnetic radiation. Proposed candidates for CDM include weakly interacting massive particles, primordial black holes, and axions.
Supersymmetry is a theoretical framework in physics that suggests the existence of a symmetry between particles with integer spin (bosons) and particles with half-integer spin (fermions). It proposes that for every known particle, there exists a partner particle with different spin properties. There have been multiple experiments on supersymmetry that have failed to provide evidence that it exists in nature. If evidence is found, supersymmetry could help explain certain phenomena, such as the nature of dark matter and the hierarchy problem in particle physics.
In supersymmetry, the neutralino is a hypothetical particle. In the Minimal Supersymmetric Standard Model (MSSM), a popular model of realization of supersymmetry at a low energy, there are four neutralinos that are fermions and are electrically neutral, the lightest of which is stable in an R-parity conserved scenario of MSSM. They are typically labeled
N͂0
1,
N͂0
2,
N͂0
3 and
N͂0
4 although sometimes is also used when is used to refer to charginos.
An axion is a hypothetical elementary particle originally postulated by the Peccei–Quinn theory in 1977 to resolve the strong CP problem in quantum chromodynamics (QCD). If axions exist and have low mass within a specific range, they are of interest as a possible component of cold dark matter.
R-parity is a concept in particle physics. In the Minimal Supersymmetric Standard Model, baryon number and lepton number are no longer conserved by all of the renormalizable couplings in the theory. Since baryon number and lepton number conservation have been tested very precisely, these couplings need to be very small in order not to be in conflict with experimental data. R-parity is a symmetry acting on the Minimal Supersymmetric Standard Model (MSSM) fields that forbids these couplings and can be defined as
The Minimal Supersymmetric Standard Model (MSSM) is an extension to the Standard Model that realizes supersymmetry. MSSM is the minimal supersymmetrical model as it considers only "the [minimum] number of new particle states and new interactions consistent with "Reality". Supersymmetry pairs bosons with fermions, so every Standard Model particle has a superpartner yet undiscovered. If discovered, such superparticles could be candidates for dark matter, and could provide evidence for grand unification or the viability of string theory. The failure to find evidence for MSSM using the Large Hadron Collider has strengthened an inclination to abandon it.
In supersymmetry theories of particle physics, a gaugino is the hypothetical fermionic supersymmetric field quantum (superpartner) of a gauge field, as predicted by gauge theory combined with supersymmetry. All gauginos have a spin of 1/2, except for the gravitino, which has a spin of 3/2.
The DAMA/NaI experiment investigated the presence of dark matter particles in the galactic halo by exploiting the model-independent annual modulation signature. Based on the Earth's orbit around the Sun and the solar system's speed with respect to the center of the galaxy, the Earth should be exposed to a higher flux of dark matter particles around June 1, when its orbital speed is added to the one of the solar system with respect to the galaxy and to a smaller one around December 2, when the two velocities are subtracted. The annual modulation signature is distinctive since the effect induced by dark matter particles must simultaneously satisfy many requirements.
Pran Nath is a theoretical physicist working at Northeastern University, with research focus in elementary particle physics. He holds a Matthews Distinguished University Professor chair.
In particle physics, the lightest supersymmetric particle (LSP) is the generic name given to the lightest of the additional hypothetical particles found in supersymmetric models. In models with R-parity conservation, the LSP is stable; in other words, it cannot decay into any Standard Model particle, since all SM particles have the opposite R-parity. There is extensive observational evidence for an additional component of the matter density in the universe, which goes under the name dark matter. The LSP of supersymmetric models is a dark matter candidate and is a weakly interacting massive particle (WIMP).
The axino is a hypothetical elementary particle predicted by some theories of particle physics. Peccei–Quinn theory attempts to explain the observed phenomenon known as the strong CP problem by introducing a hypothetical real scalar particle called the axion. Adding supersymmetry to the model predicts the existence of a fermionic superpartner for the axion, the axino, and a bosonic superpartner, the saxion. They are all bundled up in a chiral superfield.
In theoretical physics, unparticle physics is a speculative theory that conjectures a form of matter that cannot be explained in terms of particles using the Standard Model of particle physics, because its components are scale invariant.
Light dark matter, in astronomy and cosmology, are dark matter weakly interacting massive particles (WIMPS) candidates with masses less than 1 GeV. These particles are heavier than warm dark matter and hot dark matter, but are lighter than the traditional forms of cold dark matter, such as Massive Compact Halo Objects (MACHOs). The Lee-Weinberg bound limits the mass of the favored dark matter candidate, WIMPs, that interact via the weak interaction to GeV. This bound arises as follows. The lower the mass of WIMPs is, the lower the annihilation cross section, which is of the order , where m is the WIMP mass and M the mass of the Z-boson. This means that low mass WIMPs, which would be abundantly produced in the early universe, freeze out much earlier and thus at a higher temperature, than higher mass WIMPs. This leads to a higher relic WIMP density. If the mass is lower than GeV the WIMP relic density would overclose the universe.
In astrophysics and cosmology scalar field dark matter is a classical, minimally coupled, scalar field postulated to account for the inferred dark matter.
In theoretical physics, a mass generation mechanism is a theory that describes the origin of mass from the most fundamental laws of physics. Physicists have proposed a number of models that advocate different views of the origin of mass. The problem is complicated because the primary role of mass is to mediate gravitational interaction between bodies, and no theory of gravitational interaction reconciles with the currently popular Standard Model of particle physics.
Fuzzy cold dark matter is a hypothetical form of cold dark matter proposed to solve the cuspy halo problem. It would consist of extremely light scalar particles with masses on the order of eV; so a Compton wavelength on the order of 1 light year. Fuzzy cold dark matter halos in dwarf galaxies would manifest wave behavior on astrophysical scales, and the cusps would be avoided through the Heisenberg uncertainty principle. The wave behavior leads to interference patterns, spherical soliton cores in dark matter halo centers, and cylindrical soliton-like cores in dark matter cosmic web filaments.
Céline Bœhm is a professor of Particle Physics at the University of Sydney. She works on astroparticle physics and dark matter.
References
- ↑ Jia, Lian-Bao; Li, Xue-Qian (13 February 2014). "Study of a WIMP dark matter model with the updated results of CDMS II". Physical Review D . 89 (3): 035006. arXiv: 1309.6029 . Bibcode:2014PhRvD..89c5006J. doi:10.1103/PhysRevD.89.035006. ISSN 1550-7998. S2CID 118570160.
- 1 2 3 Xiao-Gang, He (June 2009). "Darkon dark matter, unparticle effects and collider physics". Chinese Physics C . 33 (6): 451–455. doi:10.1088/1674-1137/33/6/010. ISSN 1674-1137. S2CID 250794700 . Retrieved 7 January 2023.
- ↑ Cai, Yi; He, Xiao-Gang; Ren, Bo (28 April 2011). "Low Mass Dark Matter and Invisible Higgs Width In Darkon Models". Physical Review D. 83 (8): 083524. arXiv: 1102.1522 . Bibcode:2011PhRvD..83h3524C. doi:10.1103/PhysRevD.83.083524. S2CID 119204162.
- ↑ Stichel, P. C.; Zakrzewski, Wojtek J. (1 September 2012). "Darkon fluid — a model for the dark sector of the universe?". International Journal of Geometric Methods in Modern Physics . 09 (6): 1261014. arXiv: 1202.4895 . doi:10.1142/S0219887812610142. ISSN 0219-8878. S2CID 119210010 . Retrieved 7 January 2023.
- ↑ He, Xiao-Gang; Li, Tong; Li, Xue-Qian; Tandean, Jusak; Tsai, Ho-Chin (January 2011). "Constraints On Scalar Dark Matter From Direct Experimental Searches". International Journal of Modern Physics: Conference Series . 01: 257–265. arXiv: 0811.0658 . Bibcode:2011IJMPS...1..257H. doi:10.1142/S2010194511000377 . Retrieved 7 January 2023.
- ↑ Cheung, Kingman; Tsai, Yue-Lin S.; Tseng, Po-Yan; Yuan, Tzu-Chiang; Zee, A. (1 January 2014). "Global Constraints of the Simplest Darkon Model". Nuclear Physics B - Proceedings Supplements. 246–247: 116–126. Bibcode:2014NuPhS.246..116C. doi:10.1016/j.nuclphysbps.2013.10.074. ISSN 0920-5632 . Retrieved 7 January 2023.
