String-net liquid: Difference between revisions

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{{Beyond the Standard Model|cTopic=[[Quantum gravity]]}}

{{Mergeto|String-net|date=November 2008}}

{{Expert-subject|Physics|date=November 2008}}

In [[condensed matter physics]], a '''string-net''' is an extended object whose collective behavior has been proposed as a physical explanation for [[topological order]] by [[Michael A. Levin]] and [[Xiao-Gang Wen]]. A particular string-net model may involve only closed loops; or networks of oriented, labeled strings obeying branching rules given by some [[gauge group]]; or still more general networks. <ref>{{cite journal |author=Levin, Michael A. and Xiao-Gang Wen |title=String-net condensation: A physical mechanism for topological phases |journal=Physical Review B: Condensed Matter and Materials Physics |volume=71 |issue=045110 |pages=21 |date=12 January 2005|arxiv=cond-mat/0404617 |doi=10.1103/PhysRevB.71.045110 |bibcode=2005PhRvB..71d5110L }}</ref>

'''String-net liquid''' is the phrase used for a hypothetical [[state of matter]] in which the atoms do not line up in opposing "spins", but in a more erratic order, as if they had partial spins or charges. [[Herbertsmithite]], a crystalline material occurring in nature, may have such qualities. It was Discovered by Xiao-Gang at the Massachusetts Institute of Technology. First thought of in 1983.

Their model purports to show the derivation of photons, electrons, and U(1) gauge charge, small (relative to the [[planck mass]]) but nonzero masses, and suggestions that the [[leptons]], [[quarks]], [[gluons]], and [[graviton]], can be modelled in the same way. However, their model does not account for the [[chiral]] coupling between the [[fermions]] and the SU(2) [[gauge bosons]] in the [[standard model]].

==See also==

*[[string-net]]

For strings labeled by the positive integers, string-nets are the [[spin networks]] studied in [[loop quantum gravity]]. This has led to the proposal by Levin and Wen,<ref>Photons and electrons as emergent phenomena Michael Levin, Xiao-Gang Wen http://arxiv.org/abs/cond-mat/0407140 page 8 "loop quantum gravity appears to be a string net condensation..."</ref> and Smolin, Markopoulou and Konopka<ref>{{cite arxiv |eprint=hep-th/0611197|quote=we argue, but do not prove, that loop quantum gravity's spin networks can reproduce Levin and Wen's string net condensation in quantum gravity... |author1=Tomasz Konopka |author2=Fotini Markopoulou |author3=Lee Smolin |title=Quantum Graphity |class=hep-th |year=2006}}</ref> that loop quantum gravity's spin networks can give rise to the [[standard model]] of [[particle physics]] through this mechanism, along with [[fermi statistics]] and [[gauge interactions]]. To date, a rigorous derivation from LQG's spin networks to Levin and Wen's spin lattice has yet to be done, but the project to do so is called "[[quantum graphity]]", and in a more recent paper, Tomasz Konopka, [[Fotini Markopoulou]], [[Simone Severini]] argued that there are some similarities to spin networks (but not necessarily an exact equivalence) that gives rise to U(1) gauge charge and electrons in the string net mechanism.<ref>Quantum Graphity: a model of emergent locality http://arxiv.org/abs/0801.0861 page #19 "the excitation of the ground state...is expected to give rise to U(1) gauge charge, ...main difference between this model and the original model of Levin and Wen is that in the present case the background is dynamical, and has hexagonal rather than square plaquettes</ref>

==References==

{{reflist}}

http://www.newscientist.com/article/mg19325954.200?DCMP=Matt_Sparkes&nsref=fourth-state

[[Herbertsmithite]] may be the only known example of String-net matter.<ref>[http://www.eurekalert.org/pub_releases/2007-03/ns-hrf031407.php www.EurekAlert.org - ''Have researchers found a new state of matter?'']</ref><ref>[http://www.newscientist.com/article.ns?id=mg19325954.200 www.newscientist.com - ''The universe is a string-net liquid'']</ref>

==External links==

* [http://www.newscientist.com/article.ns?id=mg19325954.200&feedId=online-news_rss20 The universe is a string-net liquid] - "New Scientist" (15 March 2007).

==References==

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{{Reflist|2}}

{{State of matter}}

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[[Category:Quantum phases]]

[[Category:Condensed matter physics]]

[[Category:Chemical engineering]]

[[Category:Phases of matter| ]]

[[Category:Quantum phases]]

{{State of matter}}

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