Will Baryogenesis Be Finally Able To Solve The Mystery Of The Missing Antimatter In Our Universe?
According to the Quantum Field Theory, there are a multitude of quantum fields everywhere. Whether this everywhere can be expanded into infinity is a much bigger question. According to my own understanding of quantum mechanics, vacuum should be infinite and should have quantum fields in it. Infinite presence of quantum fields in an infinite vacuum should yield infinite creation of matter, antimatter and thus, an infinite possibility of universe creation.
However, is it not necessary that the quantum fields residing in the vacuum of space within our universe should be the same outside our universe, as the laws of physics outside our universe might be different. You can read more about why vacuum should be infinite here .
As for the generation of particles, a particle is a localized vibration of a field moving around in the form of vibrations instead of matter and thus having no mass, if we look at it from the perspective of pure energy. As we know from Einstein’s E = mc2, matter and energy are incontrovertible. What we know about these fields is that they are not stable in the entirety of their existence. They do have localized vibrations in them which can be converted into matter, antimatter in certain cases depending on the intensity of these vibration.
These vibrations are termed quantum fluctuations or simply fluctuating fields at a quantum level due to being in a non-zero or near-zero energy state. I am pretty sure you would have heard about the term “quantum fluctuations” before, if you are curious about why there is something rather than nothing. I used the term near-zero because we do not know if vacuum state in a localized environment can ever be absolute zero. The Uncertainty Principle demands that there can be no pure and perfect vacuum with a state of zero energy.
These particles get created in pairs of matter-antimatter. For every particle being created, an anti-particle needs to be created as well, or that is how we think of it according of our current understanding of modern physics.
One of the biggest questions in modern day physics is where is the missing anti-matter? It needed to be in our universe in equal proportion but if it did, it would have annihilated all of the matter we see today. In fact, almost all anti-matter got destroyed within micro seconds after the creation of the universe. There needs to be some form of matter-antimatter asymmetry which would have resulted in anti-matter being annihilated and matter being retained, even if they were created in the exact 50–50 proportion either as a result of spontaneous quantum fluctuations of very high measures or any other scientific phenomenon we might not be aware of.
Continuing on, to find this missing piece of the puzzle, Andrei Sakharov proposed three necessary conditions that a baryon generating interaction must satisfy to create matter and antimatter in different numbers. Baryons are massive particles which are made up of three quarks in the standard model. Protons and neutrons which are composed of three quarks each are classified as baryons. Protons have two up quarks and one down quark (uud), neutrons have one up quark and two down quarks (udd).
We call this process Baryogenesis, or simply the process that created asymmetry between matter-antimatter annihilation milliseconds after the creation of the universe.
The three necessary conditions for baryogenesis are:
- C-symmetry and CP-symmetry violation.
- Interactions out of thermal equilibrium.
- Baryon number violation.
CP- Symmetry Violation:
“C” here means charge and “P” means Parity.
C-symmetry or charge reversal is when you keep the mass of the particle same but change the charge with an opposite charge.
P-symmetry is what you will see if you reflect particles in a mirror. For example, a ball turning clockwise, if seen in the mirror, would seem to be turning counterclockwise.
There is also T-symmetry or time reversal symmetry which is time reversal from any moment in time to another.
Although, CPT is conserved in every interaction in the standard model, the individual entities of C,P and T can be violated. CP combined can also be violated as observed in the weak interactions. In simple words, if you reverse the charge [c] as well as the spinning direction [p] on a set of particles without considering the time constraint [t] thus making its symmetry CP-, you can get different values from their CP- interactions compared to the values from their CP interactions. These different values are mostly observed in the weak interactions involving strange, charm, and bottom quarks and their antiquarks.
CP violation was first observed in the 1964 Fitch-Cronin experiment with neutral kaons where particles known as mesons displayed some differences in particles properties. Direct CP violation was confirmed again in the 1990s when the NA31 experiment at CERN suggested evidence for direct CP violation in the decay process of very same neutral kaons . At the time, the observation was somewhat controversial, but was finally confirmed in 1999 by the KTeV experiment and the NA48 experiment .
Because of this, the standard model in physics allows the violation of CP- symmetry after having been confirmed in multiple experiments over the years. If CP is violated, the decay pathways can be different for particles compared to their anti-particles which can result in creation of more matter over anti-matter or vice versa.
Interactions Out Of Thermal Equilibrium :
A thermal equilibrium can only occur in a confined area which, in this case is the space-time within which the early universe existed, for all the particles in it to have enough time to interact with each other and exchange information (like temperature) equally, or in case of particles/antiparticles to have enough time to annihilate each other completely. Because the expansion of the universe was so rapid, the particles and antiparticles in it would not have had the opportunity to exchange information or annihilate themselves completely. Even to this day, because of the expanding universe, the universe in not in a thermal equilibrium state and because of it, filled with unstable particles (and/or antiparticles).
Baryon Number Violation :
Baryons are composite subatomic particles made up of three quarks. The most stable baryons are protons and neutrons having 3 quarks each, so most building blocks of matter are baryons.
Each Baryon is assigned a baryon number B=1. In case of baryons with 3 quarks (protons, neutrons), this can be considered to be equivalent to assigning each quark a baryon number of 1/3. This implies that the mesons, with one quark and one antiquark, have a baryon number B=0. Each baryon has a corresponding antiparticle (antibaryon) having a baryon number of −1, where the quarks are replaced by the corresponding antiquarks . No known decay process or interaction in nature changes the net baryon number.
Currently, there is no experimental evidence of particle interactions where the conservation of baryon number is broken or in simple terms, lets say a trillion protons interact with a trillion anti-protons and the result is “not” complete annihilation.
This also applies to quarks (3 quarks make 1 baryon) and leptons (electron is a lepton for example) and their corresponding antiquarks and antileptons.
The Standard Model of particle physics, however, does not have a law regarding the conservation of baryon number. However, the Baryon-Lepton number difference (B-L) is conserved in the standard model.
For now, we know that the balance of quarks to antiquarks and leptons to antileptons is conserved but that can change in the future.
Although, the current Standard Model of particle physics does allow baryon number violation but no experimental evidence for it violating net baryon number exists. However, its a matter of time when we will come up with a better explanation of baryon number violation and what could have caused more baryons along with their respective leptons to outnumber the antibaryons along with their antileptons in the giant primordial soup of particles in the early universe, which caused more matter to retain over antimatter, thus allowing this universe to exist and not go into non-existence (sort of ) again.