In theoretical physics, Q-ball is a type of non-topological soliton.
A soliton is a localized field configuration that is stable—it cannot spread out and dissipate.
In the case of a non-topological soliton, the stability is guaranteed by a conserved charge: the soliton has lower energy per unit charge than any other configuration.
(In physics, charge is often represented by the letter "Q", and the soliton is spherically symmetric, hence the name.)
Loosely speaking, the Q-ball is a finite-sized "blob" containing a large number of particles.
However, nickel-62 is not a Q-ball, in part because neutrons and protons are fermions, not bosons.)
For non-interacting particles, the potential would be just a mass term
to ensure that the potential has a lower bound), then there are values of
This corresponds to saying that one can create blobs of non-zero field (i.e. clusters of many particles) whose energy is lower than the same number of individual particles far apart.
Those blobs are therefore stable against evaporation into individual particles.
The Q-ball solution is a state that minimizes energy while keeping the charge Q associated with the global
A particularly transparent way of finding this solution is via the method of Lagrange multipliers.
In particular, in three spatial dimensions we must minimize the functional where the energy is defined as and
The time dependence of the Q-ball solution can be obtained easily if one rewrites the functional
In this case, a volume of space with the field at that value can have an energy per unit charge that is less than
, meaning that it cannot decay into a gas of individual particles.
If it is large enough, its interior is uniform and is called "Q-matter".
[1] The thin-wall Q-ball was the first to be studied, and this pioneering work was carried out by Sidney Coleman in 1986.
We can think of this type of Q-ball a spherical ball of nonzero vacuum expectation value.
We can therefore state that a Q-ball solution of the thin-wall type exists if and only if When the above criterion is satisfied the Q-ball exists and by construction is stable against decays into scalar quanta.
The mass of the thin-wall Q-ball is simply the energy Although this kind of Q-ball is stable against decay into scalars, it is not stable against decay into fermions if the scalar field
This decay rate was calculated in 1986 by Andrew Cohen, Sidney Coleman, Howard Georgi, and Aneesh Manohar.
[4] Stable configurations of multiple scalar fields were studied by Friedberg, Lee, and Sirlin in 1976.
Interest in Q-balls was stimulated by the suggestion that they arise generically in supersymmetric field theories (Kusenko 1997[10]), so if nature really is fundamentally supersymmetric, then Q-balls might have been created in the early universe and still exist in the cosmos today.
It has been hypothesised that the early universe had many energy lumps that consisted of Q-balls.
When these eventually interacted with each other they ‘’popped’’, i.e., dispersed, creating more matter particles than antimatter particles and explaining why matter predominates in the visible universe.
It should be possible to verify this by detecting gravitational waves propagated by the ''popping'' of the Q-balls.