Earlysupermassiveblack-holeseedsfrom Kaluza–Klein enhancedsmall-scalestructureformation

Theexistenceof supermassiveblackholes(M≳109M⊙)atredshiftsz≳6remainsafundamental challenge forthestandardΛCDMcosmologicalmodel. Amajorbottleneckmaybethescarcityofheavy-seedhosts: inΛCDM,atomic-coolinghalos(M∼107–108M⊙, Tvir ≳104K) capableof hostingdirect-collapseblackholes (DCBHs) areexponentiallyrareatz≳12, limitingboththeabundanceofseedsandthetimeavailableforEddingtonaccretion. Herewe showthat apreviouslyderivedKaluza–Klein (KK)enhancementofthematterpowerspectrum[19]—arisingfromthefreeze-inofKKmodulidarkmatterwithh1,1=40K¨ahlermoduli—raisesthecomovingnumberdensityofatomiccoolinghalosby factorsof 6–53(Sheth–Tormen)at z=10–15,withtheenhancementgrowingto∼260–800at z=18–20. The samemechanismshifts theeffectivecollapseepochto substantiallyearlier times, openinga temporalwindowof∆t≳500Myr forEddingtonaccretion—sufficient togrowaDCBHseedof105M⊙formedatz≃15toMBH∼5×109M⊙byz≃7. Crucially, reconcilingthepredictedhaloreservoirwiththeobservedquasarabundancerequiresaseedefficiencyofonlyfseed∼10−10–10−9,wellbelowtypicalastrophysical suppressionestimates fromLyman–Wernerregulation,metalenrichment, orradiative feedback. Noadditionalparametersare introduced: thepowerspectrumenhancementPKK=(8/3)2PΛCDM,derivedfromtheKKfreeze-inmechanisminPinto[19], isfixedbythesametopological integerh1,1=40thatdeterminesthedarkmatterrelicdensityanddarkenergyequationofstateinthesameframework.Theenhancementisasecondaryconsequenceof theKKfreeze-inmechanismalreadyshowntoexplaintheJWSThigh-redshiftgalaxyexcess, suggestingthatthegalaxyanomalyandtheearlySMBHpopulationaretwoobservational facesofthesameunderlyingcosmologicalphysics.