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Cosmological phase transition

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A cosmological phase transition is a physical process, whereby the overall state of matter changes together across the whole universe. The success of the Big Bang model led researchers to conjecture possible cosmological phase transitions taking place in the very early universe, at a time when it was much hotter and denser than today.[1][2]

Any cosmological phase transitions which took place in the early universe may have left signals which are observable today. For example, a first-order phase transition would lead to the production of a stochastic background of gravitational waves.[2][3] Experiments such as NANOGrav and LISA may be sensitive to this signal.[4][5]

Examples

The Standard Model of particle physics contains three fundamental forces, the electromagnetic force, the weak force and the strong force. Shortly after the Big Bang, the extremely high temperatures may have modified the character of these forces. While these three forces act differently today, it has been conjectured that they may have been unified in the high temperatures of the early universe.[6][7]

Strong force phase transition

Today the strong force binds together quarks into protons and neutrons, in a phenomenon known as color confinement. However, at sufficiently high temperatures, protons and neutrons disassociate into free quarks. The strong force phase transition marks the end of the quark epoch. Studies of this transition based on lattice QCD have demonstrated that it took place at a temperature of approximately 155 MeV, and is a smooth crossover transition.[8]

Electroweak phase transition

The electroweak phase transition marks the moment when the Higgs mechanism first activated, ending the electroweak epoch.[9][10] Just as for the strong force, lattice studies of the electroweak model have found the transition to be a smooth crossover, taking place at 159.5±1.5 GeV.[11]

Phase transitions beyond the Standard Model

If the three forces of the Standard Model are unified in a Grand Unified Theory, then there would have been a cosmological phase transition at even higher temperatures, corresponding to the moment when the forces first separated out.[6][7]

See also

References

  1. ^ Guth, Alan H.; Tye, S.H. H. (1980). "Phase Transitions and Magnetic Monopole Production in the Very Early Universe". Phys. Rev. Lett. 44: 631. doi:10.1103/PhysRevLett.44.631.
  2. ^ a b Witten, Edward (1984). "Cosmic Separation of Phases". Phys. Rev. D. 30: 272–285. doi:10.1016/0550-3213(81)90182-6.
  3. ^ Hogan, C. J. (1986). "Gravitational radiation from cosmological phase transitions". Mon. Not. Roy. Astron. Soc. 218: 629–636. doi:10.1093/mnras/218.4.629. Retrieved 9 August 2023.
  4. ^ NANOGrav (2023). "The NANOGrav 15 yr Data Set: Search for Signals of New Physics". Astrophys. J. Lettl. 951 (1): L11. doi:10.3847/2041-8213/acdc91.
  5. ^ LISA Cosmology Working Group (2016). "Science with the space-based interferometer eLISA. II: Gravitational waves from cosmological phase transitions". JCAP. 04: 001. doi:10.1088/1475-7516/2016/04/001.
  6. ^ a b Georgi, H.; Glashow, S. L. (1974). "Unity of All Elementary Forces". Phys. Rev. Lett. 32: 438–441. doi:10.1103/PhysRevLett.32.438.
  7. ^ a b Weinberg, Steven (1974). "Gauge and Global Symmetries at High Temperature". Phys. Rev. D. 9: 3357–3378.
  8. ^ Aoki, Y.; Endrodi, G.; Fodor, Z.; Katz, S. D.; Szabo, K. K. (2006). "The order of the quantum chromodynamics transition predicted by the standard model of particle physics". Nature. 443: 675–678. arXiv:hep-lat/0611014. doi:10.1038/nature05120.
  9. ^ Guth, Alan H.; Weinberg, Eric J. (1980). "A Cosmological Lower Bound on the Higgs Boson Mass". Phys. Rev. Lett. 45: 1131. doi:10.1103/PhysRevLett.45.1131.
  10. ^ Witten, Edward (1981). "Cosmological Consequences of a Light Higgs Boson". Nucl. Phys. B. 177: 477–488. doi:10.1016/0550-3213(81)90182-6.
  11. ^ D'Onofrio, Michela; Rummukainen, Kari (2016). "Standard model cross-over on the lattice". Phys. Rev. D. 93 (2): 025003. arXiv:1508.07161. Bibcode:2016PhRvD..93b5003D. doi:10.1103/PhysRevD.93.025003. hdl:10138/159845. S2CID 119261776.
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