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Helium Photodisintegration and Nucleosynthesis View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by CERN Document Server FERMILAB-Pub-95/051-A HELIUM PHOTODISINTEGRATION AND NUCLEOSYNTHESIS: IMPLICATIONS FOR TOPOLOGICAL DEFECTS, HIGH ENERGY COSMIC RAYS, AND MASSIVE BLACK HOLES 1;2 1;4 1;2;3 5 G. Sigl , K. Jedamzik ,D.N.Schramm and V. S. Berezinsky 1 Department of Astronomy & Astrophysics EnricoFermi Institute, The University of Chicago, Chicago, IL 60637-1433 2 NASA/Fermilab Astrophysics Center Fermi National Accelerator Laboratory, Batavia, IL 60510-0500 3 Department of Physics, EnricoFermi Institute The University of Chicago, Chicago, IL 60637-1433 4 University of California, Lawrence Livermore National Laboratory Livermore, CA 94550 5 INFN Laboratori Nazionali del Gran Sasso, 67010 Assergi (AQ), Italy processed by the SLAC/DESY Libraries on 27 Mar 1995. 〉 ABSTRACT 3 2 4 We consider the pro duction of He and Hby He photo disintegration initiated by non- PostScript thermal energy releases during early cosmic ep o chs. We nd that this pro cess cannot b e 2 3 the predominant source of primordial H since it would result in anomalously high He/D ratios in con ict with standard chemical evolution assumptions. We apply this fact to constrain top ological defect mo dels of highest energy cosmic ray (HECR) pro duction. Such mo dels have b een prop osed as p ossible sources of ultrahigh energy particles and -rays with 20 4 energies ab ove10 eV. The constraints on these mo dels derived from He-photodisintegra- tion are compared to corresp onding limits from sp ectral distortions of the cosmic microwave background radiation (CMBR) and from the observed di use -ray background. It is shown that for reasonable primary particle injection sp ectra sup erconducting cosmic strings, unlike ordinary strings or annihilating monop oles, cannot pro duce the HECR ux at the present 4 epoch without violating at least the He-photodisintegration b ound. The constraint from the ASTRO-PH-9503094 di use -ray background rules out the dominant pro duction of HECR by the decay of Grand Uni cation particles in mo dels with cosmological evolution assuming standard fragmentation functions. Constraints on massive black hole induced photodisintegration are also discussed. 1 Intro duction In this pap er we consider various constraints inferred from the p ossible photodisintegra- 4 tion of He in the early universe. Following Prothero e, Stanev, and Berezinsky [1] we note that the photodisintegration of this isotop e can b e employed to place stringent limits on early cosmic energy injections asso ciated with, for example, decaying particles [2, 3], evap orating black holes [4], or annihilating top ological defects [5, 6 , 7, 8, 9, 10 ]. Our fo cus here will 4 b e particularly on constraining the latter scenario. It has also b een suggested that He- photodisintegration in the early universe could b e a pro duction mechanism for the observed 3 light-element abundances of deuterium and He [11]. In this work we will study the feasibility 3 2 of such a scenario and show that the ( He/ H) ratio p oses a problem to it. We will show 3 2 2 3 that photodisintegration yields ( He= H) >> 1 and since H is destroyed and He increases 3 2 with evolution, measures of ( He/ H) place severe constraints on photo disintegration. Nonthermal energy releases at high redshifts may leavevarious observable signatures. The cosmic microwave background radiation (hereafter, CMBR) has b een measured to have a blackb o dy sp ectrum to very high accuracy [12 ]. Any injection of energy b etween redshifts 3 6 of z ' 10 and z ' 3 10 may pro duce observable sp ectral distortions of the blackbody spec- trum [13]. Here the lower redshift represents the approximate ep o ch of decoupling (assuming no re-ionization), whereas the higher redshift represents the ep o ch at which double-Compton scattering is still ecient enough to completely thermalize signi cant energy releases [14 ]. The di use -ray background observed at the present epoch can also b e used to constrain < 300 1000 pair pro duction by -rays early cosmic energy injections [15]. For redshifts z 4 on protons and He is rare so that the universe b ecomes transparentto -rays with energies b elow E . Here the energy E is max max 2 1 m T e E ' ' 17GeV ; (1) max 15T 1eV where T is the CMBR temp erature and m is the electron mass. E is related to the e max + threshold energy for e e -pair creation by high-energy -rays scattering o CMBR-photons. Any radiation with energies ab ove this threshold is e ectively instantaneously \recycled" by + e ) and inverse Compton scattering of the created electrons pair pro duction ( ! e CM BR and p ositrons (e ! e ). These pro cesses yield a degraded -ray sp ectrum with generic CM BR 1:5 energy dep endence / E considerably b elow E b efore steep ening and nally cutting o max at E [3]. Signi cant energy releases in form of high-energy -rays and charged particles max at ep o chs with redshifts b elow z ' 300 1000 may therefore pro duce a presentday -ray background and are sub ject to constraint. 6 For redshifts smaller than z ' 10 stringent constraints on various forms of injected 4 energy can also b e derived from the p ossible photo disintegration of He and the concomitant 3 pro duction of deuterium and He. The injection of high-energy particles and -rays ab ove the energy threshold E will initiate an ep o ch of cascade nucleosynthesis subsequentto max the ep o ch of standard primordial nucleosynthesis at T 100 keV . The abundance yields of 2 3 4 H and He pro duced by He-photodisintegration during cascade nucleosynthesis are quite 1 indep endent from the primary -ray and charged particle energy sp ectra. Deuterium and 3 He abundance yields dep end only on the amount of injected energy and the injection ep o ch. For the detailed calculations leading to these conclusions the reader is referred to the work by Prothero e, Stanev, and Berezinsky [1]. The nucleosynthesis limits on the release of energy into the primordial gas can b e up to a factor of 100 more stringent than equivalent limits on energy releases derived from distortions of the CMBR-blackb o dy sp ectrum. 6 > > For redshifts z 10 , corresp onding to CMBR-temp eratures of T 200 eV, the photo- 4 disintegration of He is inecient. This is b ecause the energy threshold for pair pro duction 4 He 4 < E . The b est nu- falls b elow the energy threshold for He-photodisintegration , E max th cleosynthesis limits on decaying particles and annihilating top ological defects in the cosmic < < temp erature range 1 keV T 10 keV come from the p ossible photodisintegration of deu- terium [3, 16]. These limits are stronger than analogous limits from distortions of the CMBR blackb o dy sp ectrum. In this narrow temp erature range limits on decaying particles and top ological defects may, in fact, b e more stringent due to e ects of injecting antinucleons. Antinucleons may 5 > 10 GeV or when there is a b e pro duced during pair pro duction for -energies E CM BR signi cant hadronic decaychannel for a massive decaying particle or top ological defect. These 4 antinucleons can then annihilate on He thereby pro ducing approximately equal amounts of 2 3 H and He [17]. We will, however, not further pursue this idea here. For temp eratures ab ove T ' 1 keV there are virtually no constraints on decaying parti- cles and top ological defects from distortions of the CMBR blackb o dy sp ectrum. However, stringent limits on decaying particles and top ological defects may obtain from the injection of hadrons (for a review see [3]). An injection of mesons and baryons generally increases the 4 > > 100 keV ) T neutron-to-proton ratio and results in increased He-mass fractions (1 MeV 2 3 > > 10 keV ; [18 ]). It has b een sug- T and/or increased H and He-abundances (100 keV 4 2 3 gested that a combination of He-hadro destruction and H, He-photo destruction induced by a late-decaying particle (T 3 keV )may bring big-bang-pro duced light-element abun- dances close to observationally inferred abundance constraints for a wide range of fractional contributions of baryons to the closure density, [19 ]. b 3 2 The observational signatures of such scenarios are primordial isotop e ratios of ( He/ H)' 6 7 2 3 and Li= Li 1, contrasting the predictions of a standard, or inhomogeneous, big-bang freeze-out from nuclear statistical equilibrium.For a wide range of parameters, such as de- 2 caying particle life times and hadronic branching ratios, these mo dels would overpro duce H 3 and He and therefore the calculations by Dimop oulos et al. [19 ] do also serve as constraints 3 2 on particle parameters and abundances. We note here that the high ( He/ H) ratio mayin fact b e a severe problem for such scenarios. In this pap er we restrict ourselves to constraints derived from the e ects of nonthermal 6 < energy injections at ep o chs with redshifts z 10 . The outline of the pap er is as follows. 2 In Section 2 we brie y review the observationally inferred light-element abundances of H 3 4 and He. We then consider He-photodisintegration scenarios and their compatibility with the observations. In Section 3 we study the e ects of p ossible energy injection by sup er- 2 3 conducting strings, ordinary strings, and magnetic monop oles on the primordial H and He 2 abundances, the distortions of the CMBR-blackbody, and the di use -ray background.
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