Primordial neutron star -- a new candidate for dark matter

[kodama]

TL;DR Summary

Primordial neutron stars may provide a mechanism of giving a part or the whole of the dark matter in the present universe

could this explains the 3rd peak of the CMB and dark matter
cold Primordial neutron star

High Energy Physics - Phenomenology
[Submitted on 7 Sep 2022 (v1), last revised 12 Sep 2022 (this version, v2)]
Primordial neutron star; a new candidate of dark matter
M. Yoshimura

Z-boson exchange interaction induces attractive force between left-handed neutrino and neutron. The Ginzburg-Landau mean field calculation and the Bogoliubov transformation suggest that this attractive force leads to neutrino-neutron pair condensate and super-fluidity. When the result of super-fluid formation is applied to the early universe, horizon scale pair condensate may become a component of dark energy. A further accretion of other fermions from thermal cosmic medium gives a seed of primordial neutron stars made of proton, neutron, electron, and neutrino in beta-equilibrium. Primordial neutron stars may provide a mechanism of giving a part or the whole of the dark matter in the present universe, if a properly chosen small fraction of cosmic thermal particles condenses to neutrino-neutron super-fluid and primordial neutron star not to over-close the universe. The proposal can be verified in principle by measuring neutrino burst at primordial neutron star formation and by detecting super-fluid relic neutrinos in atomic experiments at laboratories.

Comments: A sign mistake corrected. 13 pages, 5 figures
Subjects: High Energy Physics - Phenomenology (hep-ph); Cosmology and Nongalactic Astrophysics (astro-ph.CO); High Energy Physics - Theory (hep-th)
Cite as: arXiv:2209.02985 [hep-ph]

 

[ohwilleke]

TL;DR Summary: Some papers are so wrong that it is hard to even know where to begin. This is one of them.

But, for sh*ts and grins, I'll give it a try.

Primordial neutron stars may provide a mechanism of giving a part or the whole of the dark matter in the present universe could this explains the 3rd peak of the CMB and dark matter cold Primordial neutron star.

The paper doesn't actually make this claim or anything close to it.

It merely argues at length that something like a primordial neutron star could exist, and that because it might have the same impact on one part of Einstein's field equations as DM at some point, that it is imaginable that it could be a DM candidate.

It is basically a form of the MACHO hypothesis that was ruled out decades ago. From the link:

Several groups have searched for MACHOs by searching for the microlensing amplification of light. These groups have ruled out dark matter being explained by MACHOs with mass in the range 1×10^−8 solar masses (0.3 lunar masses) to 100 solar masses.

Neutron stars of any kind are MACHOs and should be in this mass range if they exist.

One group, the MACHO collaboration, claimed in 2000 to have found enough microlensing to predict the existence of many MACHOs with mean mass of about 0.5 solar masses, enough to make up perhaps 20% of the dark matter in the galaxy. This suggests that MACHOs could be white dwarfs or red dwarfs which have similar masses.

A claim was made that MACHOs were out there as late as 2000, but this was subsequently debunked as explained below:

However, red and white dwarfs are not completely dark; they do emit some light, and so can be searched for with the Hubble Space Telescope and with proper motion surveys. These searches have ruled out the possibility that these objects make up a significant fraction of dark matter in our galaxy.

Another group, the EROS2 collaboration, does not confirm the signal claims by the MACHO group. They did not find enough microlensing effect with a sensitivity higher by a factor 2.

Observations using the Hubble Space Telescope's NICMOS instrument showed that less than one percent of the halo mass is composed of red dwarfs. This corresponds to a negligible fraction of the dark matter halo mass. Therefore, the missing mass problem is not solved by MACHOs.

This statement at page 5 is also not confidence inspiring:

Pairs made of νLdL can attract uL , uR by strong Coulomb force. It is likely that this develops into bound pair formation of two neutrals, νL and left-handed neutron nL. This hadron formation is a complicated process, since the majority of internal energy of nucleons is made of QCD gluons. We shall simply assume that there is no difficulty of νLnL bound-pair formation of spin-singlet (~p, −~p) configuration.

It doesn't explain why the strong force wouldn't utterly overwhelm the Z boson mediate weak force interactions in these hadrons as they do in ordinary hadrons. This sounds a lot like:

Think up PNS --> ? --> Explain DM and DE.

Neutron stars also simply don't have the right properties to be dark matter.

They are luminous.

They interact by means other than gravity with each other and with other matter.

If you have a DM particle candidate it needs to be collisionless or nearly so to get the right dynamics like the cosmic microwave background radiation peaks.

It needs to be extremely stable over time frames approaching the age of the universe, while this paper doesn't even assert or show that the structures would be gravitationally bound and persist at lower temperatures.

It needs to be undetectable today. This part is simply not discussed or explained except by a passing indirect suggestion that maybe primordial neutron stars collapse into primordial black holes (a DM hypothesis that has been basically ruled out observationally).

It needs to be consistent with the baryonic matter budget for the universe and Big Bang nucleosynthesis (BBN). This is a very serious constraint that the author, who references BBN research in the very first paragraph of the paper at footnote number one, should know about and engage with. But the paper doesn't do that.

The particles that make up DM need to have an average velocity in a particular range that makes it "cold", but not too cold (in order to get the right amount of structure in the universe). The paper doesn't even try to consider whether its primordial neutron stars would have the right average velocity.

This quote from page 12 (broken up to interject commentary bit by bit), in particular, raised eyebrows of skepticism for multiple reasons:

The created aggregate of beta-equilibrium may be called primordial neutron star (PNS), but its internal structure, in particular, the stratified onion skin structure, of ordinary neutron stars is not realized, since ordinary neutron stars are gravitationally bound.

If it isn't gravitationally bound, it isn't stable at lower temperature eras in the universe. It should also have a mass-energy density profoundly lower than an ordinary neutron star, because the weak force can't hold particles together tightly enough to do so. This force is profoundly weaker than the forces that bind ordinary neutron stars.

Indeed, in the SM (or for that matter even in the Minimal Supersymmetric Model a.k.a. the MSSM), the weak force should be weaker at the energies where the papers states that this phenomena is supposed to be occurring (which is nonetheless within the energies of what has been explored in collider physics and not at immediately after the Big Bang energies) than it is at lower energies.

These kind of structures have not been observed in those collider experiments (e.g. the LEP, Tevatron, and the LHC), although there are plausible reasons why that could be the case that don't totally undermine the analysis (basically because the size of the observable universe was so much smaller in the epoch in question, so the mass-energy density and the total available pool of mass-energy was higher then, than in the colliders).

Gravity affects νLnL condensates and PNS’s at later epochs, and may form bosonic stars of mass ∼ 10^13 gr, made of νLnL condensates this time, while axion stars have a different mass, ∼ 10^28gr (ma/µeV)−1 .

There is absolutely no evidence that there have ever been boson stars or axion stars, or that axions even exist. These concepts are just twinkles in theoretical astrophysicists' minds. But, they do confirm that the proposal involves MACHO scale masses.

Important corrections may arise due to that νLnL pairs are more fragile than axions.

If it is "fragile", it won't be stable over many, many billions of years, as it must be in order to conform to observational and model constraints on DM properties.

Number and energy density densities of νLnL condensates stays constant with cosmological time evolution, hence they behave as dark energy.

The proposition that "Number and energy density densities of νLnL condensates stays constant with cosmological time evolution" is inconsistent with the conservation of mass-energy.

This is all good and well in the case of a cosmological constant that is part of Einstein's field equations in GR, but it doesn't work in a paper proposing a particle DM candidate that purports to be confining itself to Standard Model physics.

This paper notes on page 1 that: "Other works concentrates on neutrino interaction alone, and for condensate formation are forced to extend the standard particle physics model. We insist on the standard model with finite neutrino masses." But the standard particle physics model conserves mass-energy.

In other words, the neutrino condensate half of the theory to explain dark energy just completely doesn't work at all.

On the other hand, the energy density of PNS may be dominated by mass density of moving nucleons in beta equilibrium, hence they are classified and behave as dark matter.

Or, it may not. The paper doesn't really answer this question and at one point argues that somehow, some of these composite fermions are massless because superfluidity. See page 8.

The criterion of either dark energy or dark matter is in the form of energy-momentum tensor, its simplest criterion given by the ratio of pressure p and energy density ρ in isotropic medium w = p/ρ (called the equation of state factor): w = −1 for dark energy and w = 0 for cold dark matter made of non-relativistic particles.

The statement is necessary, but not sufficient, for a substance to be equivalent to dark matter or dark energy.

As noted above, the dark energy part simply doesn't work, not even remotely, for obvious reasons, because it doesn't conserve mass-energy contrary to the SM physics boundaries that the paper imposed upon itself.

DM, meanwhile, has to have far more properties than merely having w=0 and being made of non-relativistic particles, something that is also true of almost all ordinary baryonic matter.

Masses of individual PNS’s may vary, although they have a mass range of astrophysical scale, quite unlike a definite mass assigned to particle physics dark matter; WIMP and axion.

If PNS's are very massive than the same observations that almost entirely rule out primordial black holes and entirely rule out MACHOs also rule out PNS's, but more so, since PNS's if they persisted to the present would be visible luminous matter. The paper similarly leaves no explanation for why we can't see it in the current era.

Also, for what it's worth, direct DM searches rule out DM particles that couple to ordinary matter as strong as the weak force interaction for DM particle masses of about 3 GeV to 1 TeV (and perhaps even into the low single digit TeV masses).

It is an attractive idea that two different forms of constituents of universe originate from a single event, since the dark energy and the dark matter are roughly comparable energetically at the present epoch.

Lots of cool things that we would love to be true aren't. Basically, the paper concludes that it is conceivably maybe possible that primordial neutron stars could be a DM particle candidate without doing anything more to explore or corroborate this bare speculation.

The fact that conservation of mass-energy forbids this theory from explaining dark energy also immediately eliminates much of the beauty and attractiveness of this proposal as articulated in this quote.

Some sort of brief episode in the history of the cosmos around temperature 71 GeV (per equation 39 at page 8) in which primordial neutron stars are formed before they fall apart isn't entirely out of the question.

But, the notion that primordial neutron stars meaningful explain dark matter or dark energy phenomena, in contrast, simply doesn't hold water. It is so far off the mark the serious consideration of further theory or experimental searches to develop this hypothesis aren't warranted.

It isn't clear that this paper could even rise above the quite low threshold necessary to overcome the barrier of peer review to be published, without heavy revision and greatly scaled back claims about what it's author can show or justify speculating about.

About the Author

I attempted to get sense of how this paper fit into the author's larger research agenda.

The author appears to be Motohiko Yoshimura from the Research Institute for Interdisciplinary Science, Okayama University. But since the paper is authored as M. Yoshimura, a search of arXiv publications on that name is conflated with several other M. Yoshimura's who are different people who have collectively posted 131 pre-prints.

It takes a fair amount of work to figure out which of the papers are from this author. This author has what appear to be 8 papers in 2020-2022, which are all over the place in speculative astrophysics and fundamental physics, in addition to several more mainstream papers as one of several non-lead co-authors in each case and a few more speculative papers back to at least 2016.

I sympathize with using a first initial to degender authorship impressions, which is a modern academic trend.

But this desirable approach is complicated by the fact that Japan, while its surname deficit is not as bad as Korea or China or Vietnam (it is more in the same ballpark as Mexico), still has lots of people with the same surname and the same first initials even when you narrow it down to a small group of people like publishing physicists. Perhaps physicists need to get ID numbers, so that we can properly distinguish them.

The author appears to currently be about 72 years old and growing more ambitious and free ranging in the author's late career, but still very prolific in publishing preprints at least, after publishing lots of papers earlier in the author's career which were heavy on far more concrete topics related to instrumentation, nuclear physics, hadron physics, solid state physics, experimental neutrino physics, and inorganic physical chemistry.

The author's recent speculative papers on astrophysics and fundamental physics are far outside the specialties that the author pursued until about the time the author reached what would normally be retirement age, so the author may not be as familiar with the literature and common ways to vet concepts in these areas.

 

[kodama]

the lower bound of a neutron star is theoretically calculated to be 0.1 solar Mass, which is below the threshold of those microlensing survey.

MACHO candidates include black holes or neutron stars as well as brown dwarfs and unassociated planets. White dwarfs and very faint red dwarfs have also been proposed as candidate MACHOs. The term was coined by astrophysicist Kim Griest.[1]

One group, the MACHO collaboration, claimed in 2000 to have found enough microlensing to predict the existence of many MACHOs with mean mass of about 0.5 solar masses, enough to make up perhaps 20% of the dark matter in the galaxy.[2] This suggests that MACHOs could be white dwarfs or red dwarfs which have similar masses.Neutron stars, unlike black holes, are not heavy enough to collapse completely, and instead form a material rather like that of an atomic nucleus (sometimes informally called neutronium). After sufficient time these stars could radiate away enough energy to become cold enough that they would be too faint to see.ref

The theoretical lower limit to the neutron star mass is about 0.1−0.2M⊙, but none have been​

https://astronomy.stackexchange.com...han-about-1-44-solar-masses-the-chandrasekharPrimordial neutron stars would have been formed during the Big Bang and direct collapse, so it is theoretically possible they could have 0.1 M

Stacy McGaugh on his blog states neutrons could have been good dark matter candidates except they are unstable.This paper of course posits neutron stars which are known to be stable.

Primordial neutron stars might be collisionless or nearly so to get the right dynamics like the cosmic microwave background radiation peaks.

what exactly are the properties of a 0.1M Primordial neutron stars , not stellar collapse, formed from direct collapse during the Big Bang?

 

[ohwilleke]

the lower bound of a neutron star is theoretically calculated to be 0.1 solar Mass, which is below the threshold of those microlensing survey.

ref

The theoretical lower limit to the neutron star mass is about 0.1−0.2M⊙, but none have been​

https://astronomy.stackexchange.com...han-about-1-44-solar-masses-the-chandrasekhar

Primordial neutron stars would have been formed during the Big Bang and direct collapse, so it is theoretically possible they could have 0.1 M

Stacy McGaugh on his blog states neutrons could have been good dark matter candidates except they are unstable.

This paper of course posits neutron stars which are known to be stable.

Primordial neutron stars might be collisionless or nearly so to get the right dynamics like the cosmic microwave background radiation peaks.

what exactly are the properties of a 0.1M Primordial neutron stars , not stellar collapse, formed from direct collapse during the Big Bang?

To form a gravitationally bound neutron star at the lower mass limit of 0.1-0.2M (I'm assuming you are correct on that). In that system you have fermi statistics and the strong force resisting gravity, and you have gravity squeezing it together. But, for gravity to get that strong the mass has to be much more concentrated than it would be in a weak force bound PNS which isn't a neutron star in terms of structure or the forces holding it together. To get a gravitationally bound system in a much less dense weak force bound PNS you'd need much more mass because it would be more spread out. (Analogously the volume within the event horizon in a black hole grows much faster than the mass needed to support that event horizon.)

The stability of the PNS in the paper is an equilibrium between the neutrons, the neutrinos, other fundamental particles, which is temperature dependent. Ordinarily bound neutrons overcome the instability of a neutron and are stable due to a dynamic equilibrium between neutrons emitting neutrinos and turning into protons and protons absorbing neutrinos and becoming neutrons, and due to conservation of mass-energy considerations in the bound system. But, in this system, once the PNS gets cold enough it would cease to be stable.

Primordial neutron stars might be collisionless or nearly so to get the right dynamics like the cosmic microwave background radiation peaks.

This is certainly not true (and the author doesn't claim that this is true). The neutrons interact via the nuclear force. The neutrons are bound to the neutrinos via the weak force. The system isn't even perfectly electromagnetically neutral since while neutrinos have zero electromagnetic charge, neutrons are composite particles that are net electromagnetically neutral but are made of charged quark components. Neutron stars can't just pass through each other like they weren't there, they spiral into each other and merge in an event that makes a big gravitational wave.