Cosmological lithium problem: Difference between revisions

Revision as of 23:34, 8 May 2020

Revision as of 08:42, 9 May 2020

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[[Image:SolarSystemAbundances.svg|thumb|center|800px|Abundances of the chemical elements in the Solar System. Hydrogen and helium are most common, residuals within the paradigm of the Big Bang.<ref>{{cite book |last1=Stiavelli |first1=M. |year=2009 |title=From First Light to Reionization the End of the Dark Ages |url=https://books.google.com/books?id=iCLNBElRTS4C&pg=PA8 |page=8 |publisher=[[Wiley-VCH]] |___location=Weinheim, Germany |isbn=9783527627370|bibcode=2009fflr.book.....S }}</ref> Li, Be and B are rare because they are poorly synthesized in the Big Bang and also in stars; the main source of these elements is [[cosmic ray spallation]].]]

Older stars seem to have less lithium than they should, and some younger stars have much more.<ref name="MWoo">{{cite web|title=The Cosmic Explosions That Made the Universe|url=http://www.bbc.com/earth/story/20170220-the-cosmic-explosions-that-made-the-universe|last=Woo|first=M.|date=21 Feb 2017|website=earth|publisher=BBC|url-status=live|archiveurl=https://web.archive.org/web/20170221214442/http://www.bbc.com/earth/story/20170220-the-cosmic-explosions-that-made-the-universe|archivedate=21 February 2017|access-date=21 Feb 2017|quote=A mysterious cosmic factory is producing lithium. Scientists are now getting closer at finding out where it comes from|df=dmy-all}}</ref> The lack of lithium in older stars is apparently caused by the "mixing" of lithium into the interior of stars, where it is destroyed,<ref name=cld>{{Cite news |url=http://www.universetoday.com/476/why-old-stars-seem-to-lack-lithium/ |title=Why Old Stars Seem to Lack Lithium |date=16 August 2006 |last=Cain |first=F. |url-status=live |archiveurl=https://web.archive.org/web/20160604044857/http://www.universetoday.com/476/why-old-stars-seem-to-lack-lithium/ |archivedate=4 June 2016 |df=dmy-all }}</ref> while lithium is produced in younger stars. Though it [[lithium burning|transmutes]] into two atoms of [[helium]] due to collision with a [[proton]] at temperatures above 2.4 million degrees Celsius (most stars easily attain this temperature in their interiors), lithium is more abundant than current computations would predict in later-generation stars.<ref name=emsley/><ref name="Cain">{{cite web|url=http://www.universetoday.com/24593/brown-dwarf/|archiveurl=https://web.archive.org/web/20110225032434/http://www.universetoday.com/24593/brown-dwarf/|archivedate=25 February 2011|title=Brown Dwarf |accessdate=17 November 2009 |last=Cain |first=F. |publisher=Universe Today}}</ref>

[[File:Nova Centauri 2013 ESO.jpg|thumb|[[Nova Centauri 2013]] is the first in which evidence of lithium has been found.<ref>{{cite web|title=First Detection of Lithium from an Exploding Star|url=http://www.eso.org/public/news/eso1531/|accessdate=29 July 2015|url-status=dead|archiveurl=https://web.archive.org/web/20150801001700/http://www.eso.org/public/news/eso1531/|archivedate=1 August 2015|df=dmy-all}}</ref>]]

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==Proposed solutions==

Possible solutions fall into three broad classes.

Numerous studies have been conducted in search of an explanation for this deficiency of lithium, all inconclusive.<ref name=coc>{{cite journal |last=Coc |first=A. |last2=Uzan |first2=J.-P. |last3=Vangioni |first3=E. |title=Standard big bang nucleosynthesis and primordial CNO abundances after Planck |date=2014 |journal=Journal of Cosmology and Astroparticle Physics |volume=2014 |doi=10.1088/1475-7516/2014/10/050 |arxiv=1403.6694}}</ref> One theory suggests that the lithium problem may be partially caused by faster destruction than synthesis of ⁷Li and its progenitor [[beryllium-7|⁷Be]] in [[nuclear reaction]]s, though no conclusive results on the reaction flow in Big Bang nucleosynthesis have been obtained. Newer theories involving physics beyond the [[standard model]], involving not well understood [[dark matter]], have also been proposed to explain the possible destruction of lithium, also inconclusively.<ref name=Bertulani>{{cite journal |last=Bertulani |first=C. A. |last2=Shubhchintak |last3=Mukhamedzhanov |first3=A.M. |title=Cosmological lithium problems |date=2018 |journal=EPJ Web of Conferences |volume=184 |pages=01002 |doi=10.1051/epjconf/201818401002 |arxiv=1802.03469|bibcode=2018EPJWC.18401002B }}</ref><ref name=MWoo>{{cite web |url=http://www.bbc.com/earth/story/20170220-the-cosmic-explosions-that-made-the-universe |title=The Cosmic Explosions That Made the Universe |last=Woo |first=M. |date=21 Feb 2017 |website=earth |publisher=BBC |access-date=21 Feb 2017 |quote=A mysterious cosmic factory is producing lithium. Scientists are now getting closer at finding out where it comes from |url-status=live |archiveurl=https://web.archive.org/web/20170221214442/http://www.bbc.com/earth/story/20170220-the-cosmic-explosions-that-made-the-universe |archivedate=21 February 2017 |df=dmy-all }}</ref> However, one new theory posits that strangeon dark matter (a hypothetical mix of [[strange matter|strange]] and dark matter) may be responsible for the destruction of ⁷Be before it decays to ⁷Li, as the low nuclear binding energy of ⁷Be renders it susceptible to destruction upon collision with strangeons.<ref name=Xu19>{{cite arxiv |last=Xu |first=R. |title=Trinity of strangeon matter |date=2019 |arxiv=1904.11153}}</ref>

=== '''Astrophysical solutions''' ===

Considering the possibility that BBN predictions are sound, the measured value of the primordial Lithium abundance should be in error and astrophysical solutions offer revision to it. For example, systematic errors, including ionization correction and inaccurate stellar temperatures determination could affect Li/H ratios in stars. Furthermore, more observations on Lithium depletion remain important since present Lithium level might not reflect the initial abundance in the star. In summary, accurate measurements of the primordial Lithium abundance is the current focus of progress, and it could be possible that the final answer does not lie in astrophysical solutions.<ref name="fields11" />

=== '''Nuclear Physics solutions''' ===

Now consider the possibility that the measured primordial Lithium abundance is correct and based on the [[Standard Model]] of particle physics and the standard cosmology, then the Lithium problem implies errors in the BBN light element predictions. Although standard BBN rests on well-determined physics, the weak and strong interactions are complicated for BBN and therefore might be the weak point in standard BBN calculation.<ref name="fields11" />

First, reactions missing or incorrect could lead to Lithium problem. For incorrect reactions, major thoughts lie within revision to cross-section errors and standard thermonuclear rates according to recent studies.<ref>{{Cite journal|last=Angulo|first=C.|last2=Casarejos|first2=E.|last3=Couder|first3=M.|last4=Demaret|first4=P.|last5=Leleux|first5=P.|last6=Vanderbist|first6=F.|last7=Coc|first7=A.|last8=Kiener|first8=J.|last9=Tatischeff|first9=V.|last10=Davinson|first10=T.|last11=Murphy|first11=A. S.|date=2005-09|title=The 7Be(d,p)2α Cross Section at Big Bang Energies and the Primordial 7Li Abundance|url=https://ui.adsabs.harvard.edu/abs/2005ApJ...630L.105A/abstract|journal=ApJL|language=en|volume=630|issue=2|pages=L105–L108|doi=10.1086/491732|issn=0004-637X}}</ref><ref>{{Cite journal|last=Boyd|first=Richard N.|last2=Brune|first2=Carl R.|last3=Fuller|first3=George M.|last4=Smith|first4=Christel J.|date=2010-11|title=New nuclear physics for big bang nucleosynthesis|url=https://ui.adsabs.harvard.edu/abs/2010PhRvD..82j5005B/abstract|journal=PhRvD|language=en|volume=82|issue=10|pages=105005|doi=10.1103/PhysRevD.82.105005|issn=1550-7998}}</ref>

Second, starting from [[Fred Hoyle]]'s great discovery of [[carbon-12]] resonance, [[Resonance (particle physics)|resonance]] reactions, some of which might have evaded experimental detection or whose effects have been underestimated, become possible solutions to the Lithium problem and are studied by many recently.<ref>{{Cite journal|last=Hammache|first=F.|last2=Coc|first2=A.|last3=de Séréville|first3=N.|last4=Stefan|first4=I.|last5=Roussel|first5=P.|last6=Ancelin|first6=S.|last7=Assié|first7=M.|last8=Audouin|first8=L.|last9=Beaumel|first9=D.|last10=Franchoo|first10=S.|last11=Fernandez-Dominguez|first11=B.|date=2013-12|title=Search for new resonant states in 10C and 11C and their impact on the cosmological lithium problem|url=https://ui.adsabs.harvard.edu/abs/2013PhRvC..88f2802H/abstract|journal=PhRvC|language=en|volume=88|issue=6|pages=062802|doi=10.1103/PhysRevC.88.062802|issn=0556-2813}}</ref><ref>{{Cite journal|last=O'Malley|first=P. D.|last2=Bardayan|first2=D. W.|last3=Adekola|first3=A. S.|last4=Ahn|first4=S.|last5=Chae|first5=K. Y.|last6=Cizewski|first6=J. A.|last7=Graves|first7=S.|last8=Howard|first8=M. E.|last9=Jones|first9=K. L.|last10=Kozub|first10=R. L.|last11=Lindhardt|first11=L.|date=2011-10|title=Search for a resonant enhancement of the 7Be + d reaction and primordial 7Li abundances|url=https://ui.adsabs.harvard.edu/abs/2011PhRvC..84d2801O/abstract|journal=PhRvC|language=en|volume=84|issue=4|pages=042801|doi=10.1103/PhysRevC.84.042801|issn=0556-2813}}</ref>

All these nuclear physics solutions are accessible in experimental validation, which make them highly possible resulted in a true answer.

=== '''Beyond the Standard Model solutions''' ===

Under the assumptions of all correct calculation, solutions beyond the existing Standard Model or standard cosmology might be needed.<ref name="fields11" />

Dark Matter Decay and [[Supersymmetry]] provide one possibility, in which  decaying dark matter scenarios introduce a rich array of novel processes that can alter light elements during and after BBN, and find the well-motivated origin in supersymmetric cosmologies. With fully operational [[Large Hadron Collider|LHC]], much of minimal supersymmetry lies within reach, which would revolutionize particle physics and cosmology if discovered.<ref name="fields11" />

Changing Fundamental Constants can be one possible solution, and it implies that first, atomic transitions in metals residing in high-redshift regions might behave differently from our own; second, Standard Model couplings and particle masses might vary; third, variation in nuclear physics parameters is needed.<ref name="fields11" />

Nonstandard Cosmologies indicate variation of baryon to photon ratio in different regions. One proposal is a result of large-scale inhomogeneities in cosmic density, different from homogeneity defined in the [[cosmological principle]]. However, this possibility requires a large amount of observations to test it.<ref>{{Cite journal|last=Holder|first=Gilbert P.|last2=Nollett|first2=Kenneth M.|last3=van Engelen|first3=Alexander|date=2010-06|title=On Possible Variation in the Cosmological Baryon Fraction|url=https://ui.adsabs.harvard.edu/abs/2010ApJ...716..907H/abstract|journal=ApJ|language=en|volume=716|issue=2|pages=907–913|doi=10.1088/0004-637X/716/2/907|issn=0004-637X}}</ref>

==See also==