The Form of the Electron at the Root of the Matter-antimatter Imbalance?

The matter-antimatter imbalance is one of the major puzzles of Modern Cosmology and therefore represents a very active area of research within the scientific community. Indeed, the Big Bang model provides for that matter and antimatter were created in equal amounts during the first moments of the universe. Later, through an unknown mechanism, antimatter has disappeared, yielding his place to the matter that makes up our universe today.

In recent years, physicists have developed various theories trying to explain the phenomenon at the origin of this asymmetry. One of these assumptions attaches to the shape of the electron, and specifically to the presence or not of a moment electric dipole (MED). If a such MED exists, this would be a direct consequence on the Standard model, which could explain the disappearance of antimatter.

Form of the electron and electric dipole moment

The electric dipole moment of a system (for example a particle) is a measure of the distribution of positive and negative electrical charges in this system; This goes back to measure its polarity. The Standard model provides a homogeneous distribution of charges within the electron and the neutron, and so a moment Dipole electrical draw.

So far, physicists think that maybe this isn't the case; that's why a number of current experiments are trying to accurately measure the electric dipole moment of the electron and the neutron. Motivation of researchers lies in the fact that a MED nonzero would result in significant implications in particle physics.

First of all, in the case of the electron, a MED nonzero would imply an inhomogeneous distribution of negative charge, forming a "more negative" area and a "less negative" area inside the electron Such a skewed distribution distort the electron, making it lose its spherical shape and making it adopt an ' egg crushed"shape.

For the past 30 years, physicists were able to experimentally constrain the dimensions of this deformation. According to the data collected, if there is a distortion in the shape of the electron, the size of it is necessarily less than 10-27 mm. Also small deformation partly explains the reason why physicists have always failed to measure a MED nonzero with current technologies.

Time electric dipole nonzero: what consequences for the Standard model?

In the case of the electron (but also of the neutron), a time electric dipole nonzero would lead to a disruption of the Standard model of particles and so potentially offer an explanation to the matter-antimatter imbalance. Indeed, a MED nonzero results in the violation of two fundamental symmetries.

First of all, a violation of symmetry of parity (P symmetry), which is the symmetry leaving any theory unchanged under reversal of space. In other words, a theory remains the same when switching from the coordinates x, y, z coordinates to - x,-y,-z. Then, a violation of the temporal symmetry (symmetry T), which is the symmetry leaving unchanged all theory under a time reversal (from T to-T).

More specifically, with a MED nonzero, a reversal of time would change the direction of the magnetic dipole moment (spin) of the electron while his MED would remain unchanged. These two characteristics are more "in phase" with the other. The violation of P and T symmetries in this context would mean a necessary Standard to add more model change of elementary particles that it is currently planning.

The presence of a MED nonzero of the electron, and the violations of related symmetries, offering therefore an explanation concrete to the matter-antimatter asymmetry. First, where the electron would have a nonzero while the positron would present, MED, MED perfectly zero, this difference between the two particles would explain how matter has "defeated" antimatter.

Secondarily, the massive addition of new elementary particles in the Standard model there would also allow to explain the disappearance of antimatter, in which case the number of added matter particles would be higher than particle antimatter.

A new method to determine the shape of the electron

If the electron has a MED nonzero, then it should present a movement of rotation when placed in an electric field. Simply place it between two electrodes to generate an electric field and observe. However, in one such experiment, the electron would stick to the positive electrode before even starting to turn.

To work around this problem, physicists generally study the electrons within atoms or neutral molecules in which fields are used to stabilize the electrons. Physicists track so the radiation that can issue the atoms and molecules because these radiation would prove the existence of a rotational movement of the electrons and so of a MED nonzero. But in most cases, the radiation is emitted on well too short a period for a precise measurement.

In a recent study published in the journal Physical Review Letters , a team of physicists from the JILA (Joint Institute for Laboratory Astrophysics) led by Eric Cornell offers a new method to study electrons over a period of time longer than previous experiences.

To do this, the authors have confined molecular ions of fluoride of hafnium within an electric field in rotation, to stabilize ions and electrons. They were able to study the (gradual change in the axis of rotation) precession of the spin of the electrons for 0.7 seconds, is 1,000 times longer than the old technique using radiation.

This new technique has however failed to drastically increase the accuracy already established on the shape of the electron. 'Simply', the authors were able to ask a constraint of 1.3 × 10-28 cm on the maximum dimensions of the deformation of the electron in the case of MED nonzero. Nevertheless, physicists have already started new experiences involving more powerful electric fields and lasers in order to increase the accuracy of 10 to 1000 times in the next five years.