Dirac-Brueckner-Hartree-Fock calculations for isospin asymme

We present Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter which are based on improved approximations schemes. The potential matrix elements have been adapted for isospin asymmetric nuclear matter in order to account for the

Dirac-Brueckner-Hartree-Fockcalculationsforisospinasymmetric

nuclearmatterbasedonimprovedapproximationschemes.

E.N.E.vanDalen,C.Fuchs,andAmandFaessler

Institutfu¨rTheoretischePhysik,Universita¨tTu¨bingen,

AufderMorgenstelle14,D-72076Tu¨bingen,Germany

arXiv:nucl-th/0612066v1 14 Dec 2006AbstractWepresentDirac-Brueckner-Hartree-Fockcalculationsforisospinasymmetricnuclearmatterwhicharebasedonimprovedapproximationsschemes.Thepotentialmatrixelementshavebeenadaptedforisospinasymmetricnuclearmatterinordertoaccountfortheproton-neutronmasssplittinginamoreconsistentway.Theprotonpropertiesareparticularlysensitivetothisadaptionanditsconsequences,whereastheneutronpropertiesremainsalmostuna ectedinneutronrichmatter.AlthoughatpresentfullBruecknercalculationsarestilltoocomplextoapplyto nitenu-clei,theserelativisticBruecknerresultscanbeusedasaguidancetoconstructadensitydependentrelativisticmean eldtheory,whichcanbeappliedto nitenuclei.ItisfoundthatanaccuratereproductionoftheDirac-Brueckner-Hartree-Fockequationofstaterequiresarenormalizationofthesecouplingfunctions.PACSnumbers:21.65.+f,21.60.-n,21.30.-x,21.30.FeKeywords:Nuclearequationofstate,isospindependence,relativisticBruecknerapproach,densitydependentrelativisticmean eldtheory

We present Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter which are based on improved approximations schemes. The potential matrix elements have been adapted for isospin asymmetric nuclear matter in order to account for the

I.INTRODUCTION

Theinvestigationofasymmetricmatterisofimportanceforastrophysicalandnuclearstructurestudies.Inthe eldofastrophysicsthisinvestigationisimportantforthephysicsofsupernovaexplosions[1]andofneutronstars[2],e.g.thechemicalcompositionandcoolingmechanismofprotoneutronstars[3,4],mass-radiuscorrelations[5,6],andsomeothertopics.Inthe eldofnuclearstructuretheinvestigationofisospinasymmetricmatterisofinterestinstudyofneutron-richnuclei[7].Thisisovectordependenceofthenuclearforcecanbeinvestigatedintheheavyionexperiments[8].However,thedataforneutron-richnucleiwereratherscarceinthepast.Thissituationischangingwiththeforthcomingnewgenerationofradioactivebeamfacilities,e.g.thefutureGSIfacilityFAIRinGermany,theRareIsotopeAcceleratorplannedintheUnitedStatesofAmericaorSPIRAL2atGANIL/France,whichwillproducelargeamountsofnewdata.

Modelswhichmakepredictionsonthenuclearequationofstate(EoS)canroughlybedividedintothreeclasses:Phenomenologicaldensityfunctionals,e ective eldtheory(EFT)approaches,andabinitioapproaches.Phenomenologicaldensityfunctionalsarebasedone ectivedensitydependentinteractionssuchasGognyorSkyrmeforces[9]orrelativisticmean eld(RMF)models[10]withusuallymorethansixandlessthan15parameters.Thee ective eldtheoryapproachesleadtoamoresystematicexpansionoftheEoSinpowersofdensity,respectivelytheFermimomentumkF.TheadvantageofEFTisthesmallnumberoffreeparametersandacorrespondinglyhigherpredictivepower.Abinitioapproachesarebasedonhighprecisionfreespacenucleon-nucleoninteractionsandthenuclearmany-bodyproblemistreatedmicroscopically.PredictionsforthenuclearEoSareessentiallyparameterfree.Examplesarevariationalcalculations[11],Brueckner-Hartree-Fock(BHF)[6,12]orrelativisticDirac-Brueckner-Hartree-Fock(DBHF)[13,14,15,16,17,18,19,20]calculationsandGreensfunctionsMonte-Carloapproaches[21].

Many-bodycalculations,ontheotherhand,havetorelyonthesummationofrelevantdi-agramclassesandarestilltooinvolvedforsystematicapplicationsto nitenuclei.However,theseresultscanbeusedasaguidancefortheconstructionofa”semi”-phenomenologicaldensityfunctional.Examplesaree.g.Gognyforces[22]derivedfromG-matricesordensitydependentrelativisticmean eld(DDRMF)theory[23,24],whichcanbebasedonDBHFresults.

We present Dirac-Brueckner-Hartree-Fock calculations for isospin asymmetric nuclear matter which are based on improved approximations schemes. The potential matrix elements have been adapted for isospin asymmetric nuclear matter in order to account for the

Thetheoreticalpredictionsfortheisospindependenceofnuclearinteractionsarestilldiverse.RMFtheorycannotdescribethecomplexnonlinearbehavioroftheDBHFandBHFbindingenergyatdensitiesnearρ=0.Furthermore,thesymmetryenergyinrela-tivisticDBHFcalculationsisfoundtobesigni cantlysti erthaninnon-relativisticBHFapproaches[25],inparticularathighdensities.TheBHFcalculations[26]predictaproton-

neutronmasssplittingofm NR,n>mNR,pinneutrondominatednuclearmatter.Incon-

trast,RMFtheorywiththescalarisovectorδ-mesonincludedpredicttheoppositebehavior,

m D,n<mD,p[8,27].ThevariousSkyrmeforcesgiveoppositepredictionsfortheneutron-protonmasssplitting.Relativisticabinitiocalculationsbasedonrealisticnucleon-nucleoninteractions,asforinstancetheDBHFapproach,arethepropertooltoanswertheseques-tions.

InthisworkwedescribeasymmetricnuclearmatterintheframeworkoftherelativisticDBHFapproachbasedonprojectiontechniquesusingtheBonnpotentialandtheirbareNNmatrixelementsV[28].Furthermore,theoptimalrepresentationschemefortheT-matrix,thesubtractedTmatrixrepresentation,isapplied.Thisschemehaspreviouslybeenappliedtoasymmetricnuclearmatterinrefs.[18,19,20].However,inthepresentworkwegobeyondtheapproachusedin[18,19,20]inthesensethatweimproveatacoupleofapproximations.Tobemoreprecise,theBonnpotentialhasnowbeenadaptedforasymmetricnuclearmatter.

InthesolutionofBethe-Salpeter(BS)equationweabandontheapproximationofanaveragednpmassinthenpchannelanddistinguishexplicitlybetweenthedi erentisospindependentmatrixelements.Asaconsequences,thepotentialandT-matrixareevaluatedintermsofsixindependenthelicityorcovariantamplitudesinsteadof ve[15],whicharesu cientinthecaseofanaverag …… 此处隐藏：20018字，全部文档内容请下载后查看。喜欢就下载吧 ……