Material against antimatter

Linas Juozenas

Matter vs. Antimatter: the imbalance that allowed matter to dominate

One of the deepest mysteries of modern physics and cosmology is why our The Universe consists almost entirely of matter, with very little antimatter. According to current understanding, matter and antimatter should have been formed in almost equal amounts in the very earliest moments after the Big explosion, so they should have completely annihilated – but that did not happen. A small matter excess (about one part in a billion) remained and formed galaxies, stars, planets, and ultimately life as we know it. This obvious matter and antimatter asymmetry is often referred to as baryonic Universe asymmetry term and closely related to phenomena called CP (English CP) violation and baryogenesis.

In this article, we will discuss:

A brief historical perspective on the discovery of antimatter.
The nature of the matter and antimatter imbalance.
CP (charge and parity) symmetry and its violation.
Sakharov conditions for baryogenesis.
Proposed hypotheses for the formation of matter and antimatter asymmetry (e.g., electroweak baryogenesis, leptogenesis).
Ongoing experiments and future directions.

By the end of the article, you will have a general understanding of why, in our view, there is more matter than antimatter, and you will learn how science attempts to to determine the exact mechanism causing this cosmic imbalance.

1. Historical context: the discovery of antimatter

The concept of antimatter was first theoretically predicted by the English physicist Paul Dirac in 1928 formulated a set of equations (the Dirac equation), describing relativistically moving electrons. This equation unexpectedly allowed finding solutions corresponding to particles with positive energy and negative energy. "Negative energy" solutions were later interpreted as particles having the same mass as the electron but with an electric charge of opposite sign.

Discovery of the positron (1932): In 1932, the American physicist Carl Anderson experimentally confirmed antimatter detecting the existence of the positron (the electron's antiparticle) in cosmic rays left in the tracks.
Antiproton and antineutron: The antiproton was discovered in 1955 by Emilio Segrè and Owen Chamberlain, and the antineutron was discovered in 1956.

These discoveries reinforced the idea that for every Standard Model particle type there exists an antiparticle with opposite quantum numbers (e.g., electric charge, baryon number), but the same mass and spins.

2. The nature of the matter and antimatter imbalance

2.1 Uniform formation in the early Universe

During the Big Bang, the Universe was extremely hot and dense, so the energy the level was high enough for matter and antimatter particles to form pair. According to common understanding, on average for each formed matter for each particle, a corresponding antiparticle had to be created. As the Universe expanded and cooling down, these particles and antiparticles had to almost completely annihilate, converting mass into energy (usually gamma-ray photons).

2.2 Remaining matter

However, observations show that the Universe is mostly composed of matter. The net the disproportion is small, but it was precisely this that was decisive. This ratio can be quantitatively assessed, looking at the density of baryons (matter) and photon density In the Universe, the ratio often denoted η = (n_B - n_̄B) / n_γ. Cosmic Microwave Background (CMB) – obtained from missions such as COBE, WMAP, and Planck – data shows:

η ≈ 6 × 10⁻¹⁰.

This means that for every billion photons left after the Big Bang, there is about one proton (or neutron) – but most importantly, that one the baryon exceeded its corresponding antibaryon. The question arises: how did this tiny but essential asymmetry arise?

3. CP symmetry and its violation

3.1 Symmetry in physics

In particle physics, K (charge conjugation) symmetry means particles and their antiparticles are swapped. P (parity) symmetry means spatial inverse reflection (changing the sign of spatial coordinates). If a physical law remains unchanged under both K and P transformations (i.e., "if the image remains is the same when particles are replaced by antiparticles, and left and right are swapped in places"), we say that CP symmetry is preserved.

3.2 Early discovery of CP violation

Initially, it was thought that CP symmetry could be a fundamental property of nature, especially after and in the 1950s only parity (P) violation was discovered. However, in 1964 James Cronin and Val Fitch found that neutral kaons (K⁰) decays violate CP symmetry (Cronin & Fitch, 1964 [1]). This revolutionary result showed that even CP sometimes can be violated in certain weak interaction processes.

3.3 CP violation in the Standard Model

In the Standard Model of particle physics, CP violation can arise from phases In the Cabibbo-Kobayashi-Maskawa (CKM) matrix, describing how quarks of different “flavors” transform into each other under the weak interaction. Later, in neutrino physics, another mixing matrix term appeared – Pontecorvo–Maki–Nakagawa–Sakata (PMNS) matrix, which can also to have CP-violating phases. However, so far the observed level of CP violation in these in the sectors is too small to explain the baryon asymmetry of the Universe asymmetry. Therefore, it is believed that there are additional sources of CP violation beyond the Standard Model.

4. Sakharov conditions for baryogenesis

In 1967, Russian physicist Andrei Sakharov formulated three necessary conditions for matter and antimatter to arise in the early Universe antimatter asymmetry (Sakharov, 1967 [2]):

Violation of baryon number: There must be an interaction or processes that change the net baryon number B. If the baryon number is strictly preserved, baryon and antibaryon asymmetry cannot form.
C and CP violation: Processes that distinguish matter and antimatter, are necessary. If C and CP were perfect symmetries, any process creating more baryons than antibaryons should have a mirror counterpart that creates as many antibaryons, thus "canceling out" any excess.
Departure from thermal equilibrium: In thermal equilibrium particle creation and annihilation processes occur equally in both directions, so balance is preserved. A non-thermally balanced environment, for example, rapidly expanding and cooling Universe allows certain processes "capture" the asymmetry.

Every successful baryogenesis theory or mechanism must meet these three conditions to explain the observed matter and antimatter imbalance.

5. Proposed mechanisms for the formation of matter and antimatter asymmetry

5.1 Electroweak baryogenesis

Electroweak baryogenesis states that baryon asymmetry formed roughly at the time when the electroweak phase transition stage occurred (~10⁻¹¹ seconds after the Big Bang). Main aspects:

The Higgs field acquires a nonlinear vacuum expectation value and thus spontaneously breaks the electroweak symmetry.
Non-perturbative processes called sphalerons can violate the total baryon and lepton number (B+L), but preserve baryon and lepton difference (B−L).
The phase transition, if it were first order (i.e., characterized by bubble formation), would create the necessary deviation from thermal equilibrium.
CP-violating interaction processes in the Higgs sector or during quark mixing would contribute to the matter-antimatter imbalance arising in bubbles.

Unfortunately, in the current Standard Model parameter range (especially with a 125 GeV mass Higgs boson discovery) it is unlikely that the electroweak phase transition stage was first order. Moreover, the CP violation provided by the CKM matrix is too small. Therefore, many theorists propose physics beyond the Standard Model – for example, additional scalar fields – so that electroweak baryogenesis becomes more realistic.

5.2 GUT baryogenesis

Grand Unified Theories (GUT) aim to unify the strong, weak and electromagnetic interactions under very high energy conditions (~10¹⁶ GeV). Daugelyje DVT modelių sunkieji kalbos bosons and Higgs bosons can mediate proton decay or other processes violating baryon number. If these processes occur out of thermal equilibrium in the early Universe environment, they can essentially generate baryon asymmetry. However, it is necessary that CP violation in these GUT scenarios is sufficiently large, but proton decay, predicted by GUT, has not yet been observed experimentally detected at the frequencies expected. This limits simpler GUT baryogenesis models.

5.3 Leptogenesis

Leptogenesis starts from the asymmetry of leptons and antileptons. This lepton asymmetry later, through sphaleron processes, affects the electroweak during the period is partially converted into baryon asymmetry, as these processes can leptons to convert into baryons. One popular mechanism:

“Seesaw” mechanism: Heavy right-handed neutrinos (or other heavy leptons).
These heavy neutrinos can decay through CP violation, creating a lepton sector asymmetry.
The sphaleron interactions convert part of this leptonic asymmetry into baryonic asymmetry.

Leptogenesis is attractive because it links the origin of neutrino masses (observable in neutrino oscillations) with the cosmic matter and antimatter imbalance. Moreover, it lacks some limiting factors that hinder for electroweak baryogenesis, so it is often mentioned as one of the main components of new physics theories.

6. Experiments conducted and future directions

6.1 High-energy accelerators

Accelerators like the Large Hadron Collider (LHC) – especially the LHCb experiment – may be sensitive to CP violation in various meson (B, D, etc.) decays. By measuring the extent of CP violation and by comparing it with Standard Model predictions, scientists hope to find discrepancies that could indicate new physics beyond the Standard Model.

LHCb: Specializes in precise measurements of rare decays and CP violation in the b-quark sector studies.
Belle II (KEK in Japan) and the already completed BaBar (SLAC) also studied CP violation in B-meson in systems.

6.2 Neutrino experiments

Next-generation neutrino oscillation experiments, such as DUNE (Deep Underground Neutrino Experiment) in the USA and Hyper-Kamiokande in Japan aims for high precision measurements CP violation phase in the PMNS matrix. If neutrinos showed a significant CP violation, this would further support leptogenesis as the cause of the matter-antimatter imbalance solution, hypothesis.

6.3 Proton Decay Search

If GUT baryogenesis scenarios are correct, proton decay could be an important source of clues. Experiments such as Super-Kamiokande (and in the future Hyper-Kamiokande) strictly sets limits on the proton's lifetime for different decay channels. Any discovery of proton decay would be extremely important as it would provide serious clues about baryon number violation at high energy levels.

6.4 Axion Search

Although axions (hypothetical particles related to the strong CP problem solution) are not directly related to baryogenesis in the usual sense, they also could play a certain role in the early Universe's thermal history and to determine possible matter and antimatter imbalances. Therefore, axion searches remains an important part in solving the overall puzzle of the Universe.

Conclusion

The cosmic dominance of matter over antimatter remains one of the main open physics questions. The Standard Model predicts a certain CP violation, but insufficient to explain the observed scale of asymmetry. This discrepancy the need for new physics – or higher energy (e.g., at the DVT scale), or by introducing additional particles and interactions, which have not yet not found.

Although electroweak baryogenesis, DVT baryogenesis and leptogenesis are possible mechanisms, further experimental and theoretical analysis is necessary. High-precision experiments in accelerator physics, neutrino oscillation studies, and rare decay studies and astrophysical observations continue to test these theories. The answer to the question of why matter won over antimatter can not only expand our understanding of the origin of the Universe, but also reveal completely new aspects of our reality aspects.

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