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1、130ò16ÏpUÔnØÔnVol.30,No.62006c6HIGHENERGYPHYSICSANDNUCLEARPHYSICSJun.,2006Scalar-FieldModelforDarkEnergywithaFixedBackgroundVectorField*1)LIYan-Heng(InstituteofHighEnergyPhysics,ChineseAcademyofSciences,Beijing100049,China)(GraduateUniversityofChineseAcademyofSciences,Beijing1
2、00049,China)AbstractWeproposeadarkenergymodelwithsingledynamicalscalarfieldandfixedbackgroundvectorfield,inwhichtheparameterwcancross−1duringtheevolutionoftheuniverse.Itisfoundthatincertaincaseswcancross−1andtransitionfromdeceleratingtoacceleratingoccuratz≈0.2andz≈1.7respectively,
3、whichisconsistentwiththeobservations.Keywordsscalarfield,darkenergy,vectorfield,equationofstate[8]1Introductionparameterwforthegeneralk-essencemodelsalsofailstocrossw=−1.[1—3]TherecentobservationssuggestthattheUni-verseconsistsofdarkenergy(73%),darkmatter2Theevolutionequationofun
4、iverse(23%)andbaryonmatter(4%).Whatthedarkene-innewmodelrgybecomesoneoftheessentialquestionsintheo-reticalphysicsandcosmology.AlthoughthesimplestRecentlysomedynamicaldarkenergymodelsformofdarkenergy—thecosmologicalconstant—withthepropertyofwcrossing−1havebeen[4][9—14]fitstheobse
5、rvationquitewell,whichhastheef-proposed.Inthepresentletter,weshallfurtherfectiveequationofstatep=−ρ,orw=−1,therestudythescalar-fieldmodelfordarkenergywitha[5][14]isevidencetoshowthatdarkenergymightevolvefixedbackgroundvectorfield.Inthismodelthefromω>−1inthepasttoω<−1today.Itseemsd
6、arkenergyiseffectivelydescribedbyadynamicalthatthedynamicsmodelwithavaryingwisprefe-scalarfieldcoupledtoafixedbackgroundvectorfieldrableratherthanthesimpleconstant.withaconstantnormandconstantzeroth-componentVariousmodelshavebeenproposedinordertoinacomovingsystem,whichdescribessome
7、unknowndescribetheevolvingdarkenergy.Mostofthemareeffectsoftheuniverse.Namely,thedarkenergyischaracterizedbyascalarfield,whichgrewinpartoutsupposedtobegovernedbytheLagrangian,oftheinflationscenarioinpartfromideasfrompar-1effµνµνLφ=gφ,µφ,ν−gφ,µAν−V(φ).(1)ticlephysics.Unfortunately,m
8、ostofthesedynamical2darkenergymodelscannotexplainthefa