Cold freeze out of superheavy nonthermal dark matter

Cold freeze out of superheavy nonthermal dark matter | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Cold freeze out of superheavy nonthermal dark matter Zhijie Xu This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-7512279/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract We present a unified framework, the "X miracle", in which dark matter consists of superheavy, nonthermal X particles whose relic abundance is determined not by the conventional weak-scale, semi-relativistic ("hot") freeze-out of WIMPs, but by annihilation or decay occurring within the smallest and earliest gravitationally bound objects. Unlike thermal WIMPs, which decouple at velocities of order 0.3$c$ with relic abundance $\rho_{\infty}$ set by weak-scale interactions, X particles are produced nonthermally with an initial overabundance $\rho_{ini}\gg \rho_{\infty}$. They become nonrelativistic extremely early, redshift to ultra-cold velocities, allowing collapse into compact bound structures characterized by a novel quantum-gravitational scale, $r_X=4\hbar^2/Gm_X^3=10^{-13}m\gg \hbar/m_Xc$, much larger than the Compton wavelength. The framework predicts a particle mass of $10^{12}$GeV and an enhanced cross section of $10^{-21}$m$^3$/s. Overlapping particle wavefunctions in these compact structures drive annihilation or decay into additional radiation, leading to a "cold" freeze-out that converts most of $\rho_{ini}$ into radiation while leaving a relic density $\rho_{\infty}$. Solutions to the Boltzmann equation indicate that an extreme depletion, with only one particle in a billion surviving, yields an additional radiation contribution $\Delta N_{eff}\approx$0.4, which could help alleviate the Hubble tension. For particles of $10^{12}$GeV, the scenario predicts an energy production rate density of $10^{45}$erg Mpc$^{-3}$Yr$^{-1}$ and particle lifetime $10^{16}$years (or coupling $\alpha_X=0.09$), consistent with current UHECR bounds. Early collapse at $10^{-6}$s may release binding energy as high-frequency (100kHz) gravitational waves or ultralight GUT-scale axions. Superheavy sterile neutrinos provide a natural particle physics realization, linking dark matter to neutrino mass and baryogenesis. If gravitational production dominates, this framework favors high-scale inflation and efficient reheating. The "X miracle" thus demonstrates that dark matter need not be weak-scale: gravitational dynamics can control freeze-out and evolution, producing multi-messenger observational signatures in UHECRs, axions, gravitational waves, and small-scale structures. Physical sciences/Astronomy and planetary science Physical sciences/Physics dark matter dark radiation axion gravitational wave UHECR Simulation Hubble tension Full Text Additional Declarations No competing interests reported. Cite Share Download PDF Status: Posted Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-7512279","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":509616865,"identity":"635131e0-12fb-49c8-ac99-a335ba462e1b","order_by":0,"name":"Zhijie Xu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA1UlEQVRIiWNgGAWjYDACCcYGgwQQg70BSBSQpIXnAJAwIEoLnJFApBb52c0NBQ8qGBI33Hx77HGBAYNdP1gvHsA45yDQYWcYjA1u56UbzzBgSJ45g4AWZonEBoPENgY5g9s5ZtI8QC0GZw7g18IG1vKPgcfg5hkitfCAtTQAbbnBA9ZiZ3C8Ab8WCZCWhGMSxpJn8tKAWiQSJNsJaJGfkf7M8EeNTWLf8bPHpHkqbOz5mfHrAHvHABI7PGBbEwnYAQbMDyA0WAuDPRE6RsEoGAWjYIQBAMmqO1qPbptLAAAAAElFTkSuQmCC","orcid":"","institution":"Pacific Northwest National Laboratory","correspondingAuthor":true,"prefix":"","firstName":"Zhijie","middleName":"","lastName":"Xu","suffix":""}],"badges":[],"createdAt":"2025-09-02 01:53:09","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-7512279/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-7512279/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":90566749,"identity":"71b98d3a-c0ce-4568-ad4f-d9e66e683f59","added_by":"auto","created_at":"2025-09-04 07:34:35","extension":"pdf","order_by":1,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":6108291,"visible":true,"origin":"","legend":"","description":"","filename":"PapersSR.pdf","url":"https://assets-eu.researchsquare.com/files/rs-7512279/v1_covered_b66573fe-0f48-4d7f-a85d-238631fb83d2.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Cold freeze out of superheavy nonthermal dark matter","fulltext":[],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":false,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":true,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":true,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":true,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"dark matter, dark radiation, axion, gravitational wave, UHECR, Simulation, Hubble tension","lastPublishedDoi":"10.21203/rs.3.rs-7512279/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-7512279/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"We present a unified framework, the \"X miracle\", in which dark matter consists of superheavy, nonthermal X particles whose relic abundance is determined not by the conventional weak-scale, semi-relativistic (\"hot\") freeze-out of WIMPs, but by annihilation or decay occurring within the smallest and earliest gravitationally bound objects. Unlike thermal WIMPs, which decouple at velocities of order 0.3$c$ with relic abundance $\\rho_{\\infty}$ set by weak-scale interactions, X particles are produced nonthermally with an initial overabundance $\\rho_{ini}\\gg \\rho_{\\infty}$. They become nonrelativistic extremely early, redshift to ultra-cold velocities, allowing collapse into compact bound structures characterized by a novel quantum-gravitational scale, $r_X=4\\hbar^2/Gm_X^3=10^{-13}m\\gg \\hbar/m_Xc$, much larger than the Compton wavelength. The framework predicts a particle mass of $10^{12}$GeV and an enhanced cross section of $10^{-21}$m$^3$/s. Overlapping particle wavefunctions in these compact structures drive annihilation or decay into additional radiation, leading to a \"cold\" freeze-out that converts most of $\\rho_{ini}$ into radiation while leaving a relic density $\\rho_{\\infty}$. Solutions to the Boltzmann equation indicate that an extreme depletion, with only one particle in a billion surviving, yields an additional radiation contribution $\\Delta N_{eff}\\approx$0.4, which could help alleviate the Hubble tension. For particles of $10^{12}$GeV, the scenario predicts an energy production rate density of $10^{45}$erg Mpc$^{-3}$Yr$^{-1}$ and particle lifetime $10^{16}$years (or coupling $\\alpha_X=0.09$), consistent with current UHECR bounds. Early collapse at $10^{-6}$s may release binding energy as high-frequency (100kHz) gravitational waves or ultralight GUT-scale axions. Superheavy sterile neutrinos provide a natural particle physics realization, linking dark matter to neutrino mass and baryogenesis. If gravitational production dominates, this framework favors high-scale inflation and efficient reheating. The \"X miracle\" thus demonstrates that dark matter need not be weak-scale: gravitational dynamics can control freeze-out and evolution, producing multi-messenger observational signatures in UHECRs, axions, gravitational waves, and small-scale structures.","manuscriptTitle":"Cold freeze out of superheavy nonthermal dark matter","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-09-04 07:26:12","doi":"10.21203/rs.3.rs-7512279/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"ada40368-64ac-451d-8533-e060cf01f824","owner":[],"postedDate":"September 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":54126836,"name":"Physical sciences/Astronomy and planetary science"},{"id":54126837,"name":"Physical sciences/Physics"}],"tags":[],"updatedAt":"2025-09-04T07:26:12+00:00","versionOfRecord":[],"versionCreatedAt":"2025-09-04 07:26:12","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-7512279","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-7512279","identity":"rs-7512279","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}