Cosmological phase transition: Difference between revisions

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{{Short description|A phase transition for the whole universe}}

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.<ref>{{cite journal |last1=Guth |first1=Alan H. |last2=Tye |first2=S.H. H. |title=Phase Transitions and Magnetic Monopole Production in the Very Early Universe |journal=Phys. Rev. Lett. |date=1980 |volume=44 |issue=10 |pages=631631–635 |doi=10.1103/PhysRevLett.44.631|bibcode=1980PhRvL..44..631G |osti=1447535 }}</ref><ref name="witten-1984">{{cite journal |last1=Witten |first1=Edward |title=Cosmic Separation of Phases |journal=Phys. Rev. D |date=1984 |volume=30 |pages=272–285 |doi=10.1016/0550-3213(81)90182-6}}</ref>

Any cosmological phase transitions which took place in the early universe may have left signals which are observable today. For example, a [[Phase Transition#Classifications|first-order phase transition]] would lead to the production of a [[gravitational wave background|stochastic background of gravitational waves]].<ref name="witten-1984" /><ref name="hogan-gws">{{cite journal |last1=Hogan |first1=C. J. |title=Gravitational radiation from cosmological phase transitions |journal=Mon. Not. Roy. Astron. Soc. |date=1986 |volume=218 |issue=4 |pages=629-636629–636 |doi=10.1093/mnras/218.4.629 |url=https://adsabs.harvard.edu/pdf/1986MNRAS.218..629H |access-date=9 August 2023|doi-access=free }}</ref> Experiments such as [[NANOGrav]] and [[Laser Interferometer Space Antenna|LISA]] may be sensitive to this signal.<ref name="nanograv">{{cite journal |last1=NANOGrav |title=The NANOGrav 15 yr Data Set: Search for Signals of New Physics |journal=Astrophys. J. Lett. |date=2023 |volume=951 |issue=1 |pages=L11 |doi=10.3847/2041-8213/acdc91|arxiv=2306.16219 |bibcode=2023ApJ...951L..11A |doi-access=free }}</ref><ref name="lisa-pt">{{cite journal |last1=LISA Cosmology Working Group |title=Science with the space-based interferometer eLISA. II: Gravitational waves from cosmological phase transitions |journal=JCAP |date=2016 |volume=04 |issue=4 |pages=001 |doi=10.1088/1475-7516/2016/04/001|arxiv=1512.06239 |bibcode=2016JCAP...04..001C |s2cid=53333014 }}</ref>

==Examples==

The [[Standard Model]] of particle physics contains three [[fundamental force]]s, 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.<ref name="georgi-glashow">{{cite journal |last1=Georgi |first1=H. |last2=Glashow |first2=S. L. |title=Unity of All Elementary Forces |journal=Phys. Rev. Lett. |date=1974 |volume=32 |pages=438–441 |doi=10.1103/PhysRevLett.32.438}}</ref><ref name="weinberg-gauge">{{cite journal |last1=Weinberg |first1=Steven |title=Gauge and Global Symmetries at High Temperature |journal=Phys. Rev. D |date=1974 |volume=9 |issue=12 |pages=3357–3378|doi=10.1103/PhysRevD.9.3357 |bibcode=1974PhRvD...9.3357W }}</ref>

===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.<ref name="aoki-qcd">{{cite journal |last1=Aoki |first1=Y. |last2=Endrodi |first2=G. |last3=Fodor |first3=Z. |last4=Katz |first4=S. D. |last5=Szabo |first5=K. K. |title=The order of the quantum chromodynamics transition predicted by the standard model of particle physics |journal=Nature |date=2006 |volume=443 |issue=7112 |pages=675–678 |doi=10.1038/nature05120|pmid=17035999 |arxiv=hep-lat/0611014 |bibcode=2006Natur.443..675A }}</ref>

===Electroweak phase transition===

The electroweak phase transition marks the moment when the [[Higgs mechanism]] first activated, ending the [[electroweak epoch]].<ref name ="guth-weinberg-higgs">{{cite journal |last1=Guth |first1=Alan H. |last2=Weinberg |first2=Eric J. |title=A Cosmological Lower Bound on the Higgs Boson Mass |journal=Phys. Rev. Lett. |date=1980 |volume=45 |issue=14 |pages=11311131–1134 |doi=10.1103/PhysRevLett.45.1131|bibcode=1980PhRvL..45.1131G }}</ref><ref name="witten-higgs">{{cite journal |last1=Witten |first1=Edward |title=Cosmological Consequences of a Light Higgs Boson |journal=Nucl. Phys. B |date=1981 |volume=177 |issue=3 |pages=477–488|doi=10.1016/0550-3213(81)90182-6|bibcode=1981NuPhB.177..477W }}</ref> 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]].<ref name="donofrio-rummukainen">

{{cite journal

|author1 = D'Onofrio, Michela