Cosmological phase transition

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 transition may have left signals which are observable today, even if it took place in the first moments after the Big Bang, when the universe was opaque to light.[3]

Cosmological first-order phase transitions

Phase transitions can be categorised by their order. Transitions which are first order proceed via bubble nucleation and release latent heat as the bubbles expand.

As the universe cooled after the hot Big Bang, such a phase transition would have released huge amounts of energy, both as heat and as the kinetic energy of growing bubbles. In a strongly first-order phase transition, the bubble walls may even grow at near the speed of light.[4] This, in turn, would lead to the production of a stochastic background of gravitational waves.[2][5] Experiments such as NANOGrav and LISA may be sensitive to this signal.[6][7]

Shown below are two snapshots from simulations of the evolution of a first-order cosmological phase transition.[8] Bubbles first nucleate, then expand and collide, eventually converting the universe from one phase to another.

  • Earlier stages: the first bubbles nucleate and expand.
    Earlier stages: the first bubbles nucleate and expand.
  • Later stages: overlapping bubble collisions.
    Later stages: overlapping bubble collisions.

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.[9][10]

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 would have taken place at a temperature of approximately 155 MeV, and would have been a smooth crossover transition.[11]

This conclusion assumes the simplest scenario at the time of the transition, and first- or second-order transitions are possible in the presence of a quark, baryon or neutrino chemical potential, or strong magnetic fields.[12][13][14] The different possible phase transition types are summarised by the strong force phase diagram.

Electroweak phase transition

The electroweak phase transition marks the moment when the Higgs mechanism first activated, ending the electroweak epoch.[15][16] 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.[17]

Just as for the strong force, the conclusion that the transition is a crossover assumes the minimal scenario, and is modified by the presence of additional fields or particles. Particle physics models which account for dark matter or which lead to successful baryogenesis may predict a strongly first-order electroweak phase transition.[18]

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.[9][10] Cosmological phase transitions may also have taken place in a dark or hidden sector, amongst particles and fields that are only very weakly coupled to visible matter. [19]

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 (10): 631–635. Bibcode:1980PhRvL..44..631G. doi:10.1103/PhysRevLett.44.631. OSTI 1447535.
  2. Witten, Edward (1984). "Cosmic Separation of Phases". Phys. Rev. D. 30: 272–285. doi:10.1016/0550-3213(81)90182-6.
  3. Kibble, T. W. B. (1980). "Some implications of a Cosmological Phase Transition". Phys. Rept. 67 (1): 183–199. Bibcode:1980PhR....67..183K. doi:10.1016/0370-1573(80)90091-5.
  4. Moore, Guy D.; Prokopec, Tomislav (1995). "Bubble wall velocity in a first order electroweak phase transition". Phys. Rev. Lett. 75 (5): 777–780. arXiv:hep-ph/9503296. Bibcode:1995PhRvL..75..777M. doi:10.1103/PhysRevLett.75.777. PMID 10060116. S2CID 17239930.
  5. Hogan, C. J. (1986). "Gravitational radiation from cosmological phase transitions". Mon. Not. R. Astron. Soc. 218 (4): 629–636. doi:10.1093/mnras/218.4.629. Retrieved 9 August 2023.
  6. NANOGrav (2023). "The NANOGrav 15 yr Data Set: Search for Signals of New Physics". Astrophys. J. Lett. 951 (1): L11. arXiv:2306.16219. Bibcode:2023ApJ...951L..11A. doi:10.3847/2041-8213/acdc91.
  7. LISA Cosmology Working Group (2016). "Science with the space-based interferometer eLISA. II: Gravitational waves from cosmological phase transitions". JCAP. 04 (4): 001. arXiv:1512.06239. Bibcode:2016JCAP...04..001C. doi:10.1088/1475-7516/2016/04/001. S2CID 53333014.
  8. Weir, David (2018). "Gravitational waves from a first order electroweak phase transition: a brief review". Phil. Trans. Roy. Soc. Lond. A. 376: 20170126. doi:10.1098/rsta.2017.0126.
  9. Georgi, H.; Glashow, S. L. (1974). "Unity of All Elementary Forces". Phys. Rev. Lett. 32: 438–441. doi:10.1103/PhysRevLett.32.438.
  10. Weinberg, Steven (1974). "Gauge and Global Symmetries at High Temperature". Phys. Rev. D. 9 (12): 3357–3378. Bibcode:1974PhRvD...9.3357W. doi:10.1103/PhysRevD.9.3357.
  11. 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 (7112): 675–678. arXiv:hep-lat/0611014. Bibcode:2006Natur.443..675A. doi:10.1038/nature05120. PMID 17035999.
  12. Boeckel, Tillman; Schettler, Simon; Schaffner-Bielich, Jurgen (2011). "The Cosmological QCD Phase Transition Revisited". Prog. Part. Nucl. Phys. 66: 266–270. arXiv:1012.3342. doi:10.1016/j.ppnp.2011.01.017.
  13. Schwarz, Dominik J.; Stuke, Maik (2009). "Lepton asymmetry and the cosmic QCD transition". JCAP. 11: 025. arXiv:0906.3434. doi:10.1088/1475-7516/2009/11/025.
  14. Cao, Gaoging (2023). "First-order QCD transition in a primordial magnetic field". Phys. Rev. D. 107: 014021. arXiv:2210.09794. doi:10.1103/PhysRevD.107.014021.
  15. Guth, Alan H.; Weinberg, Eric J. (1980). "A Cosmological Lower Bound on the Higgs Boson Mass". Phys. Rev. Lett. 45 (14): 1131–1134. Bibcode:1980PhRvL..45.1131G. doi:10.1103/PhysRevLett.45.1131.
  16. Witten, Edward (1981). "Cosmological Consequences of a Light Higgs Boson". Nucl. Phys. B. 177 (3): 477–488. Bibcode:1981NuPhB.177..477W. doi:10.1016/0550-3213(81)90182-6.
  17. 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.
  18. Cline, James; Kainulainen, Kimmo (2013). "Electroweak baryogenesis and dark matter from a singlet Higgs". JCAP. 01: 012. arXiv:1210.4196. doi:10.1088/1475-7516/2013/01/012.
  19. Schwaller, Pedro (2015). "Gravitational waves from a dark phase transition". Phys. Rev. Lett. 115: 181101. doi:10.1103/PhysRevLett.115.181101.
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