Weakless universe
A weakless universe is a hypothetical universe that contains no weak interactions, but is otherwise very similar to our own universe.
In particular, a weakless universe is constructed to have
Motivation and anthropics
The strength of the weak interaction is an outstanding problem in modern
An alternative approach to explaining the hierarchy problem is to invoke the
Anthropic arguments have recently been boosted by the realization that
The hypothetical universe without the weak interaction is meant to serve as a counter-example to the anthropic approach to the hierarchy problem. For this “weakless universe”, other parameters are varied as the electroweak breaking scale is changed. Indeed, string theory implies that the landscape is very big and diverse. The ostensible habitability of the weakless universe implies that anthropic reasoning alone cannot explain the hierarchy problem, unless the available vacua in the landscape are severely restricted for some other reason.
Obstacles
Weakless stars
One of the biggest obstacles for a habitable weakless universe is the necessary existence of stars. Main sequence stars work through fusing two protons to
He.
Oxygen abundance
Another potential problem for a weakless universe is that supernova explosions are necessarily neutrinoless. The resulting efficiency of production and dispersion of heavy elements (in particular, oxygen) into the interstellar medium for subsequent incorporation into habitable planets has been questioned by Clavelli and White.[2]
Baryogenesis
Baryogenesis and leptogenesis within the Standard Model rely on the weak interaction: For matter not to be wiped off by anti-matter at the very early universe, the universe must either have to start with a different amount of each (i.e. initial non-zero baryon number), or admit Sakharov's conditions to baryogenesis. In the latter case, there are two options:
- Baryon number conservation is broken exotic particlesthat are also created abundantly in the universe and interact in peculiar ways with the baryonic matter, or very weak, or both. If the particles interacting with baryons are not strongly (and/or electromagnetically) interacting themselves, the strong interaction (and/or electromagnetic interaction) has to be part of a larger, spontaneously broken, gauge symmetry.
- Baryon number conservation is broken non-perturbatively, i.e. by quantum anomaly. At least one such mechanism is chiral anomaly, which requires the existence of the weak interaction, or at least something very similar to it: [3]
- There has to be a chiral gauge interaction, where the fermions are in its fundamental representation.
- In order not to be anomalous itself (as gauge interaction anomaly leads to inconsistency), the gauge group is highly restricted, with SU(2) symmetry being the only option among SU(N) groups.
- Mass terms break chiral symmetry, so in order for baryon masses to be possible, the chiral gauge interaction has to be spontaneously broken, leading to a Higgs mechanism.
- Since the electromagnetic and the strong gauge groups also need to be non-anomalous, this leads to additional constraints. For example, if the sum of electromagnetic charges of all quark types is positive (more generally, non-zero), then there have to be additional, negatively charged particles, coupled to the chiral gauge group, which will also be created during baryogenesis - namely, the leptons.
Harnik, Kribs, and Perez argue that the Standard Model does not explain the observed size of the baryon asymmetry either, and that their weakless universe model only focuses on the time where the asymmetry already exists.[1]
References
- ^ S2CID 14340180.
- arXiv:hep-ph/0609050v1.
- ^ Peskin, M. (2018). An introduction to quantum field theory. CRC press.
External links
- Jenkins, Alejandro; Perez, Gilad (December 2009). "Looking for life in the multiverse". Scientific American.