Cosmological phase transition: Difference between revisions

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

A '''cosmological phase transition''' is an overall change in the [[state of matter]] 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=631–635 |doi=10.1103/PhysRevLett.44.631|bibcode=1980PhRvL..44..631G |osti=1447535 }}</ref><ref name="witten-1984">{{Cite journal |last=Witten |first=Edward |date=1984-07-15 |title=Cosmic separation of phases |url=https://link.aps.org/doi/10.1103/PhysRevD.30.272 |journal=Physical Review D |language=en |volume=30 |issue=2 |pages=272–285 |bibcode=1981NuPhB.177..477W |doi=10.1103/PhysRevD.30.272 |issn=0556-2821|url-access=subscription }}</ref>

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 [[cosmic microwave background|opaque to light]].<ref>{{cite journal |last1=Kibble |first1=T. W. B. |title=Some implications of a Cosmological Phase Transition |journal=Phys. Rep. |date=1980 |volume=67 |issue=1 |pages=183–199 |doi=10.1016/0370-1573(80)90091-5|bibcode=1980PhR....67..183K }}</ref>

== Character ==

The [[Standard modelModel]] of particle physics, parameterized by values measured in laboratories, can be used to predict the nature of cosmic phase transitions.<ref name=Manzudar-2019>{{Cite journal |last=Mazumdar |first=Anupam |last2=White |first2=Graham |date=2019-06-25 |title=Review of cosmic phase transitions: their significance and experimental signatures |journal=Reports on Progress in Physics |volume=82 |issue=7 |pages=076901 |doi=10.1088/1361-6633/ab1f55 |issn=0034-4885|arxiv=1811.01948 }}</ref> A system in the ground state at a high temperature changes as the temperature drops due to expansion of the universe. A new ground state may become favorable and a transition between the states is a phase transition.<ref name=Manzudar-2019/>{{rp|9}}

A phase transition can be related to a difference in symmetry between the two states. For example liquid is isotropic but solid water, [[ice]], has directions with different properties. The two states have different energy: ice has less energy than liquid water.

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Second order transitions are continuous rather than abrupt and are less likely to leave observable imprints cosmic structures.<ref name=Manzudar-2019/>

==Within the standardStandard modelModel==

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>

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===Electroweak phase transition===

The electroweak phase transition marks the moment when the [[Higgs mechanism]] breaks the <math>SU(2)\otimes U(1)</math> symmetry of the Standard model.<ref name=Peacock-1998/>{{rp|305}}

Lattice studies of the electroweak model have found the transition to be a smooth crossover, taking place at a temperature of {{nobr| 159.5 ± 1.5 [[GeV]].}}<ref name=donofrio-rummukainen>

{{cite journal

|last1 = d'Onofrio |first1 = Michela