Primordial killers - excluding common dark matter with black holes

in steemstem •  2 months ago  (edited)

Weakly-interacting massive particles (aka WIMPs) are amongst the most popular candidates for dark matter. However, dark matter could also be made of primordial black holes, a special class of black holes that were formed right after the big bang.


[image credits: @pab.ink]

In a recent publication, physicists have explored the strongly-motivated idea of coexisting black-hole and WIMP dark matter. Their results are striking: observing a primordial black hole could rule out most popular extensions of the Standard Model of particle physics!


Primordial back holes and WIMPs

While it explains a large set of cosmological observations, dark matter still escapes detection on Earth. Consequently, there exists a multitude of dark matter models, some of them featuring WIMP and others primordial black hole dark matter.


[image credits: NASA (public domain)]

WIMPS are particles that rarely interact with normal matter and that appear in many theories extending the Standard Model of particle physics.

The weakness of their interactions allows them to exactly match the present dark matter abundance, and justifies that dark matter has not been detected yet.

Another appealing option for dark matter consists in primordial black holes formed in the early days of the universe, as resulting from gravitational collapses in regions where the (inhomogeneous) matter density was large.

Such black holes can however only account for a subdominant fraction of dark matter. In other words, they could be dark matter provided that dark matter has another component. Moreover, the latter could be a WIMP.


Primordial back holes as bullets for new phenomena in particle physics

Let’s focus on black hole detection for a moment.


[image credits: The SXS Project (CC BY-SA 4.0)]

Many experiments, like LIGO, Virgo or the Einstein Telescope, aim to track gravitational waves in a close future. They have hence the potential to directly observe primordial black holes.

On the other hand, we all know that black holes accrete matter.

The WIMP density around a primordial black hole is therefore enhanced, so that WIMP annihilation can take place. This however induce the production of gamma rays in a way strongly excluded by data.

Consequently, if we observe primordial black hole dark matter, WIMP annihilation must simultaneously be small enough to forbid the production of too many of these un-observed gamma rays.

This yields the results below.


[image credits: arxiv]

On this figure, the x-axis corresponds to different WIMP mass hypotheses, whilst the y-axis consists in the WIMP contribution to the dark matter annihilation rate (that is connected to the dark matter abundance).

The viable parameter space (containing all Standard Model extensions featuring a WIMP candidate) lies between the two grey dashed lines. Anything either above the horizontal dashed line at the top or below the diagonal dashed line at the right-bottom is irrelevant.

Let’s now assume that VIRGO/LIGO observe 1 primordial black hole. Any WIMP setup above the solid blue line turns out to be excluded. Taking the Einstein Telescope, anything above the solid orange line is this time excluded.

We can however get crazier. If VIRGO/LIGO observe 80 black holes, then anything above the dashed blue line would be excluded. This means that the entire viable parameter space is almost excluded!

Gravitational waves have hence an immense potential for particle physics!


Take-home message

Primordial black holes consist in a potential candidate for dark matter, provided that dark matter contains another component, like a WIMP. This multicomponent dark matter setup yields the production of gamma rays visible in the entire universe. Such gamma rays are however experimentally excluded.

On different lines, there are options for the potential observation of primordial black holes in a close future, thanks to gravitational-wave detection.

Consequently, observing a handful of primordial black hole could potentially entirely rule out the WIMP hypothesis (and thus a plethora theories extending the Standard Model and featuring a WIMP), as this would imply the existence of experimentally-excluded gamma rays.

Let us thus keep an eye on future gravitational wave observations!

PS: This article has been formatted for the steemstem.io front-end. Please see here for a better reading.


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I'm glad I waited (pressing schedule) a couple of days to read and comment on your latest post. I feel as though I'm sitting in on a senior seminar. The questions and answers are really quite provocative and enlightening.

I don't have a question I can clearly formulate...I'm just going to continue to read about wimps (I love that), Einstein telescopes, and the relationship between dark matter and the production of gamma rays.

Your posts are always mind-opening adventures into terrain I otherwise would not explore.

Thank you!

As said above (or below, it depends on which frontend one looks at ;) ), I really enjoy the comments. I am even starting to feel scary when the first one takes its time to appear ^^

If you have more questions later on, feel free to shoot! I will always be there to answer :)

I might take you up on that :) Thank you!

@lemouth,

So, gamma-rays are only considered to be a byproduct of WIMP annihilation if they are undetectable, and, therefore, possible to exclude from data?

Forgive me for this possibly mad question. I was very happy with my understanding until I read:

observing a handful of primordial black hole could potentially entirely rule out the WIMP hypothesis, as this would imply the existence of experimentally-excluded gamma rays.

I need some iced-tea now! :P

Hey Abi! Thanks for passing by (and for this first comment to my post)!

So, gamma-rays are only considered to be a byproduct of WIMP annihilation if they are undetectable, and, therefore, possible to exclude from data?

There are many ways to generate gamma rays in the universe. Dark matter annihilation is one of them.

The point here is that when induced by WIMP annihilation, gamma-ray production has specific properties that could be observed. But we have not observed them. Consequently, such a production mechanism can only occur with a tiny suppressed rate (connected to the y-axis of the last figure).

To rephrase what I said::

  1. Primordial black hole could be dark matter, but under the condition that we have a second dark matter particle.
  2. We assume that this second dark matter particle is a WIMP.
  3. In this case, it has been demonstrated that WIMPs generate many special gamma rays that should have been observed.
  4. We didn't observe those gamma rays.
  5. If WIMP and back hole dark matter coexist, then we have huge constraints on WIMPs as they would generate something unobserved. In other words, the value of the parameter displayed on the y-axis of the last figure has to be small enough to suppress this gamma ray production.

is it clearer?

such a production mechanism can only occur with a tiny suppressed rate (connected to the y-axis of the last figure).

Ok, ok, ok! That’s better.

The numbered list cleared all my doubts and confusion 😃 I got a bit confused today ! Thank you for taking the time to explain things further @lemouth. I truly appreciate it!

Bye for now & happy weekend for the family! ☀️

  ·  last month (edited)

I am happy this clarified!

Enjoy your week-end as well! Here, it seems fall is starting to really be there... It is coldish (so perfect for construction and gardening) :)

🍁😊🍁

  ·  last month (edited)

WIMP-annihilation ... sounds almost like a cosmic purge, as always every post is both very interesting but also mostly confusing as one click leads to another and before i know it i find myself in need of reading the popcult hit by Tyson again to make me feel a little smart hahah.
I don't think there's any need to be apologetic here, @abigail-dantes , certainly not to the sensei here who has been proven (lol-pun) to not look down and always willing to explain. I always imagine a meeting of theoritical and particle physicist to be much like a tea party at Carroll's , with the mad hatter at the head, everyone spouting the most crazy ideas and a cloud of numbers and magic symbols hanging above. After all, they have to question everything in order to be able to prove anything at all, heretics maybe even :) (like galileo would have been i guess) . Longwinding and #offtopic as usual but i chose the name well this time.
I gave up on the link to the article from cornell, lol. Those things are above my braingrade due to the sheer amount of numbers but i think maybe mostly due to the technical jargon, which to a 'pro' in the field is very likely daily language, the links through wikipedia, however ,despite most of them begging for someone who is a 'pro in the field' (lol) to give it a revision to make sure, and some warning that this 'might encourage ideas' that havent been proven. But the way i see it most of it isn't proven.
Without going into a chaotic dissertation on how i feel time has not been proven to exist, it, time after time, strikes me, on how the whole universe is hanging by a thread. Again here clicking through from the primordial black hole to baryonic matter - coming down do "we are not even made of the most common matter in the universe" , assuming with a big capital if that it's actually matter as such because it hasnt really been proven, about 95% ( give or take a few, sensei) of existence has been "potentially observed" but as you so eloquently say "not on earth" (lol its not ...mwell, its funny to me because of the total absurdity and im grateful at least Newtonian Physics has tangible effects or planes and trains would act really funny and there would be no rover on Mars). It's basically the search for god, i could almost quote Tesla on it
->

51wXAZfOS4L._SX466_.jpg

(and should maybe state that i'm neither or a dis-believer as i feel both are dogmatic, one accepts blindly that it is and the other accepts blindly that it is NOT, both accept without proof of the other being wrong or they being right, but im a weird and ill-behaved particle myself, especially when observed)

And that's why it's theoretical physics, but from Galileo and (one of my personal favourite pioneers, also a heretic ofcourse) Paracelsus , if it wasn't for them coming up with the craziest ideas that went against everything accepted, and them who called out to burn everything you know and RE-search it yourself to make sure its true, and all their experiments we probably wouldnt be here at the table with Alice (and Bob :p) listening to the next-generation of heretics coming up with the craziest ideas and tearing down the know universe, looking for proof that it actually exists ...

I had a small question too, btw sensei @lemouth, it says somewhere inthere in one of the wikipedias that, according to Hawking, primordial black holes can be as small as (that means mass i assume) 10-8 10 to the minues eight ? isnt that like REALLY small , i mean like how would that be detected in a cosmic background or am i reading that minus wrong ? It's not like i have a degree in mathematics or something ...
somewhere here, something about planck relics guessing that's some "spacedust" left from the few moments after the bang (do correct me thats why im here) ... but the term particle chauvinism also put a smile on my face

i do have a weird sense of humour but im also sincere on the matter here , bit of a brainbuster but always a #goodread, tyvm !!!

oh, btw, probably not noticeable, but i only vote witnesses on one account, so if you saw it gone somewhere else its now here ...
im sure you will agree to my reasoning after reading the introductory post on @stem.witness here
the way i see it, i am a multiple account-holder myself but i only have one free one and the 15 sp delegation from steemit didnt last very long there so most of it in all of it is mine and actually most of it is mine i paid for as i dont do the marketing thing very well and i dont bother with adjusting my opinion per qualche votes in più (yea clint eastwood and stuff i think, i dont speak italian) and so, if i choose to have 10 accounts and disperse my steem across them i actually lose on curation over the whole and the overall effect on the pool remains the same (or is even maybe less as its smaller amounts). Witness-voting however is a different thing, if all my accounts vote once on all my favourite witnesses i would consider that cheating and i think that would do way more damage to the eco-system as a whole over time b/c rich witnesses could simply burn a few thousand steem , create accounts and keep themselves on top (luckily that is technically right now not possible 22 hardforks deep into advancement cough cough cough and luckily , despite my talent for making friends in high places, everyone will ofcourse do the right thing because that is how its done.

So (allow me to apologize for the #offtopic again, sensei, but you know i have a hard time keeping myself in one time-line at once heheh), just so to say the witness vote isnt gone, its just here now, not there ... (like that foton you were trying to track yesterday ;-)

that said, ... my prozaic metaphysics doesn't matter, matter matters ... (glad i made this account so i can spread my raving lunacy to my hearts content when i feel like it) and ofcourse

animated-have-a-nice-day-image-0008.gif

It is sometimes the case that a comment is as delightful and enlightening as a post...this one does that. It raises and answers questions--may I say, almost irreverently....which I know @lemouth welcomes. He leads us down a dark, uncertain path and makes no promises. We follow, learn and question.

I don't have mathematical references or even a superficial understanding of physics (beyond which I am acquiring through these blogs), but I kept thinking as I read your comment of a book by Miguel de Unamuno: "La Niebla". Poor confused Augusto, the main character--cannot call him a protagonist because he learns he is just a character in a book. He doesn't write the script of his life--it is written for him.
Anyway, the intersection of physics and our perception of reality--that's where your comment took me. A very interesting journey. I won't go on, because my mind continues to make associations that go back to your comment, and @lemouth's journey into the primordial and the dark....nothing wimpy about that.

He leads us down a dark, uncertain path and makes no promises.

I promise, the next step will be as invisible, but less dark. I just cannot make any promise with respect to the time of delivery :)

Thanks for passing by and reading what I write week after week :)

Dark is Ok. I don't see science as separate from everyday life. Just takes specialized training to understand it sometimes. But that's what we have you for :))
It's a privilege to be in on the conversation.

Oh it is you! I didn’t make the connection quickly this time.

I always imagine a meeting of theoritical and particle physicist to be much like a tea party at Carroll's , with the mad hatter at the head, everyone spouting the most crazy ideas and a cloud of numbers and magic symbols hanging above

This depends. Those meetings can sometimes be quite… errrhh well… lively ;)

But the way i see it most of it isn't proven

This is exactly the problem with dark matter: it works extremely well, but somehow we are missing the direct proof of its existence.

I had a small question too, btw sensei @lemouth, it says somewhere inthere in one of the wikipedias that, according to Hawking, primordial black holes can be as small as (that means mass i assume) 10-8 10 to the minues eight ? i

You are missing the units. A number without a unit has no meaning ;)

Indeed, primordial black holes can be as light as 10-8 kg. But those black holes are not there anymore today, because whilst black holes accrete matter (i.e. they grow), they also evaporate (i.e. they shrink). Small black holes shrink faster than they grow. Inversely, large black holes grow faster than they shrink. In other words, light black holes have fully evaporated since a long long time. 1011 kg is the limit: anything lighter is totally gone today.

For the witness stuff: the easiest is to use proxy: one account votes and all the others follow. In any case, thanks for supporting stem.witness. But why do you need so many accounts?

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Thank you @yapcat :)

You're right, @lemouth does put me at ease when it comes to my (limited) understanding of his blogs. So much so I keep coming back for more. I feel particularly curious about dark matter these days and have even found similarities between his journey in his field and my own in mine. It also helps having people like you whose knowledge on physics surpasses mine by 1000 fold, but also have a kind attitude towards my queries and doubts.

Lovely, lovely gif by the way.
Have a great week.

Best,
Abigail

Having a new comment to my post with questions always makes me happy and I appreciate my regular readers (which set includes you) passing by and letting me know their thoughts. Also I like feeling useful in answering questions ^^

As a researcher, I find it (very) important to communicate about my field, about what I do, in simple terms. There is no secret, which means no secret both for researchers from my community and for the general audience. However, communication in simple terms is not always easy (which is where questions matter; this is also how I can improve myself).

Also, such a thing like a stupid question does not exist. Only stupid answers exist! ^^

I love the drawing, especially your labcoat! :)

I somehow got an official illustrator ;)

Thanks for sharing amezing blog.

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