Alternative dark matter particle could explain the universe’s lithium shortage

After H and helium , lithium is the light-headed and simplest element in the world . It should have been everywhere right after the Big Bang … but the data shows a deep shortage . The explanation may point to an unlikely dark matter candidate .

The leading explanation for the creative activity of the wanton elements at the starting time of the universe of discourse is known as Big Bang Nucleosynthesis . AsPhysics World explains , the idea is that the primordial universe was once a fatheaded soup of super - het up protons and neutrons . Those two corpuscle began tack into nuclear nuclei , produce the hydrogen isotope deuterium as well as atomic number 2 and lithium isotope . negatron put down the picture as temperatures dropped , and the afterglow of this process is what we now live as the Cosmic Microwave Background .

There ’s just one problem with this whole mind – our reflection of the cosmic background radiation suggest that there is n’t enough lithium-7 . In fact , there ’s only about a third the presage amount , which is a fairly gaping hole in an otherwise satisfying hypothesis . To fill that gap , University of Florida physicists led by Pierre Sikivie point to the axion , a hypothetical particle that has long been discourse as a potential alternative prospect for dark topic . If the axion exists , it ’s a very light corpuscle that barely interact at all with affair . ( For more on the axion , and other sorry subject candidate , check out ourprimer . )

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https://gizmodo.com/the-undiscovered-particles-on-the-edge-of-known-physics-5640527

If the axion does live – and that ’s still a pretty huge “ if ” – then some of its less recognize property could actually be put to use explaining the lithium-7 discrepancy . Physics World has more :

Sikivie and fellow worker point out that axions can work a Bose – Einstein condensation ( BEC ) . Such condensates hold molecule that have all fallen into their lowest energy DoS , and are best known to occur in low - density gas at temperatures stuffy to absolute zero . But since the critical temperature for changeover to a BEC depends on density , say the Florida researchers , particles can form BECs at gamey temperature as long as they are heavy enough . Even in the primordial heat of the Big Bang , the researcher say , axions would well be dense enough to form a BEC .

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An axion condensate would have a pronounced issue on Big Bang nucleosynthesis . Passing photon would make waves in it , transferring heat and , ultimately , depleting in number . This signify that the heavy particle - to - photon ratio would increase towards the time of recombination , giving cosmologists today a falsely in high spirits stamp of the amount of atomic number 3 that should have been create .

It ’s an interesting opening , and it certainly takes attention of the lithium-7 trouble – not to mention bolster axion ’s political campaign for dark matter – but it has some hearty drawbacks . essentially , to puzzle out the lithium-7 problem with axions , you ’re creating two whole new problems . The mien of axions would do deuterium levels to be much high-pitched than what we observe in the CMB , so you ’re basically merchandise one discrepancy for another .

What ’s more , the number of neutrino case would have to increase from its current economic value of 3 or 4 to about 7 for this to work . According to Physics World , Sikivie recognise both of these problems , but he also manoeuvre to one the fact that the European Space Agency ’s Planck Space Observatory is still appraise the issue of neutrinos , and we can expect a novel , more precise measurement next year . If that figure fortify up close to 7 , then we might involve to take a much closer look at this axion explanation .

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