Spin 1 Gauge Bosons.. How will we sleep?!
(Originally posted October 13, 2016 on Blogger)
Dark matter. It makes up 27% of our Universe's mass... and we don't yet know what dark matter is. There are some very interesting hypotheses floating around out there (pun) as to what it might be; one cool hypothesis being that of primordial black holes. If you look at the Cosmic Background Radiation (CMB), you'll see small differences in temperature across the observable Universe. The temperature of the CMB is not exactly the same in all directions, which is to say it is anisotropic.
The further we look into the Universe, the older the 'light' is, as it takes light time to reach our eyes from such unfathomable distances. Of course, our Universe is expanding, so that light from faraway stars red-shifts to longer wavelengths of the electromagnetic spectrum. It's not just expanding, but it's accelerating its expansion rate, so the further you look into our Universe, the more pronounced that red-shifting becomes. So much so that there's a point when the light of faraway stars shifts right out of the visible light portion of the spectrum. And a good thing too I suppose, because if it didn't, we wouldn't have dark skies at night! The Universe would light up Earth far more than the Sun does already. Talk about getting no sleep! So as scary as the thought of the Universe expanding into oblivion might be, be grateful it at least allows you to sleep at night. How is THAT for ironic! Get it? Staying up awake at night because of impending oblivion, yet being able to sleep... I'll stick to my day job.
We may not be able to see that ultra-red-shifted light from what is effectively the 'distant' past, but the WMAP and Planck satellites could see it, and the CMB shown in the image above is our Universe when it was only 380,000 years post inflation. Aha! You might have expected me to say "when it was 380,000 years old", but there is mounting academic research that undermines the very notion that the Universe had a beginning at all! Want to learn more on that? Visit my friend's YouTube channel (SkyDivePhil) to learn about some of the alternatives to there being a beginning:
Eternal Inflation & the Multiverse
(I was fortunate enough to participate in this particular documentary)
He is currently planning a 5th documentary in his series, "Before the Big Bang", and I hope to be a part of that project as we wait for interview confirmations. All in good spacetime my friends.. all in good spacetime!
Back to the CMB... the blues and oranges you see are tiny temperature fluctuations that existed as you see them about (ok I'm about to nerd out here) 13,819,620,000 years ago... give or take a day or two... heh heh. These fluctuations seen in the CMB stemmed from a time when the Universe was smaller than an atom (watch the Eternal Inflation & Multiverse documentary linked above for more on this). Some of these fluctuations were strong enough to collapse into primordial black holes (PBHs )despite the opposing force of the Universe's expansion. SkyDivePhil and I also inquire about bubble collisions, which could also lead to the formation of PBHs, so go check out that video!
It is theorized that these PBHs have roamed our Universe ever since their theoretical creation, and over time--due to Hawking radiation--the mass of these PBHs would have decreased considerably... should they exist. Now imagine, billion-ton black holes (with event horizons about the size of a proton) being possible dark matter candidates! Awesome yes?! Perhaps not, but still possible! To see how these could possibly be detected (Geology nerds will love this), check out PBSspactime's YouTube video here:
That's one possible candidate for dark matter. There are others... (see that inflation video!). But so far, these are all just speculative hypotheses. Since dark matter is, well, dark, it is going to be quite challenging for scientists to detect what it is. Though in recent years, studies have shown that light-neutral bosons in the 10 MeV to 10 GeV mass range might be dark-matter candidates.
This is where a paper published back in January comes in. It was published in the Physical Review Letters by A.J. Krasznahorkay et al. (you can read that paper here). Their paper discusses an anomaly observed when excited electrons, on very rare occasion, drop to their ground state in beryllium-8. Normally, the highly unstable isotopes such as beryllium-8 decay into other atomic isotopes and free-ranging protons, but sometimes... sometimes... those highly-excited electrons can relax back down to the ground state. As we'll remember from high school physics, when excited electrons drop down energy levels or to the ground state, they release the energy they 'absorbed' when excited. And we'll remember that these energies are quantized, not constant. This being one of the legacies of Neils Bohr. With Beryllium-8, one of these energy levels (orbitals or clouds) exist at 18.15 MeV. In the Beryllium-8 isotope, there is a very rare occurrence wherein an electron-positron pair (internal pair creation) occurs when an electron relaxes from this energy level to its ground state.
Like a kid burnt out on a prolonged sugar rush (which is to say a prolonged placebo), an electron eventually loses its excitement and calms the f&*!% back down to its ground state as depicted in the image to the right. When it does this, it releases that quantized energy at a frequency equal to the frequency absorbed when it was excited in the first place. In the case of Beryllium-8, an electron-positron pair is—on very rare occasion—created.
This elementary particle and its antiparticle counterpart (electron-positron pair) created from that squiggly photon (a neutral boson) you see in the illustration above, is where Krasznahorkay et al. observed an anomaly. They observed an excess of events with large opening angles of these electron-positron pairs... particularly at 140 degrees where it forms a bump in the number of internal-pair creation events. One of the authors (Philip Tanedo) of a more recent, and related paper titled, "Particle Physics Models for the 17 MeV Anomaly in Beryllium Nuclear Decays" says that this bump is of interest because bumps like this could be a sign of a new particle! ...or not (he says that too)..
Above we see that 'bump'. It's as if something with a mass-energy equivalence of 17 MeV is decaying into these electron-positron pairs. This is pretty exciting, because unlike that 750 GeV fiasco earlier this year, which turned out to be nothing, THIS anomaly is more likely to be something.
Why is it more likely to be something? Statistically, these anomalous events have a probability value (p-value) of 6.8 sigma. Check out my blog entry here I posted several months ago to learn more about p-values... about a dozen or so paragraphs down! :) I briefly explain the 'value' of x sigma excess.
6.8 sigma excess is definitely NOT a statistical fluctuation like that apparent 750 GeV diphoton excess anomaly turned out to be that I wrote about several months ago. Not only does this anomaly at this specific transition result in different energies, but also different spin parity and isospin. And it seems that the best way to explain this is if a spin-1 gauge boson is created.. more on this in a bit. So is there some new particle with an energy-mass equivalence of 17 MeV? They don't know yet, but they're on it! And this brings us to that more recent paper co-authored by Tanedo:
Let me start with the caveat... this could be nothing! Even the authors warn of this. But they also say it could be something. So, since I don't want it to be nothing, let's go ahead and ignore the what-if-it's-nothing scenario, and look at the what-if-it-is-something scenario instead! Much more interesting!
Check out Tanedo's blog on quantumdiaries.org; scroll down to his theories of what this excess event bump may or may not be... He lists 4 theories and their implications should some new particle actually exist. Obviously, coming from one of the authors of the above-mentioned paper, Tanedo's write up is an excellent read:
Now, imagine this possibility... the anomaly is caused by a spin-1 gauge boson! A gauge boson, as you might recall from my blog on what might lurk at 750 GeV at the LHC a few months ago, is a force-carrier particle. Just a quick recap; there are (as of now) four fundamental forces... from strongest to weakest they are:
1. Strong force (largely responsible for binding nucleons in atomic nuclei)
2. Electromagnetic force (force between charged particles)
3. Weak force (responsible for radioactive decay and quantum tunneling *wink wink)
4. Gravity (responsible for apples falling from trees)... though I'm not convinced this is a force. We'll get to that in some future blog.
Matter particles exchange small amounts of these energies between each other using gauge bosons, or force-carrier particles.
The gauge boson family includes the gluon, photon, Z-boson, W-boson, and the Higgs. The Gluon carries the strong force... it's the "glue" that allows the strong force to bind nucleons in atomic nuclei! That's an easy way to remember it! :) The photon, obviously, carries the electromagnetic force (ie. visible light). The W & Z bosons carry the weak force...
What about gravity? Well, one... gravity hasn't exactly been figured out yet. Gravity sort of doesn't want to behave at the Planck scale, so until Newtonian gravity and quantum gravity find common ground, it may be awhile before we find its theoretical gauge boson, the graviton. (I should mention that some believe gravity isn't a force at all, but an effect... and I'll admit that I'm in this camp.)
Now we mention that these differences in energies, spin parity, isospin and other quantum stuff like that can best be explained by the decay of a spin-1 gauge boson... GAUGE BOSON my friends! That means this, if it exists, could be a force-carrier particle for.......drum roll please....... dark matter!
As Matt O'Dowd says in his PBS Spacetime video titled, "Is There a Fifth Fundamental Force?...", this potentially-new gauge boson could communicate between the "so-called dark sector and the observable Universe"! Whoa indeed!
I know... too excited to sleep now? Me too! But thankfully we exist in a Universe undergoing accelerated expansion and have that to thank for keeping our skies dark at night! ...unless you live in or near a city.