“Overall, the resulting description of the history of the universe is complete and consistent, from the period of inflation to the present day. And unlike many older models, the individual important values can be calculated to a high level of precision, for example the time at which the universe starts heating up again after inflation,” emphasises Andreas Ringwald at DESY, a research institute in Hamburg Germany for high-energy and particle physics.
Extension of the standard
model provides complete and consistent description of the history of the
universe. The extremely successful standard model of particle physics has an
unfortunate limitation: the current version is only able to explain about 15
percent of the matter found in the universe. Although it describes and
categorizes all the known fundamental particles and interactions, it does so
only for the type of matter we are familiar with. However, astrophysical
observations suggest that the mysterious dark matter is more than five times as
common.
An international team of
theoretical physicists has now come up with an extension to the standard model
which could not only explain dark matter but at the same time solve five major
problems faced by particle physics at one stroke. Guillermo Ballesteros, from
the University of Paris-Saclay, and his colleagues are presenting their SMASH
model (“Standard Model Axion Seesaw Higgs portal inflation” model) in the
journal Physical Review Letters.
“The good thing about SMASH
is that the theory is falsifiable. For example, it contains very precise
predictions of certain features of the so-called cosmic microwave background.
Future experiments that measure this radiation with even greater precision could
therefore soon rule out SMASH – or else confirm its predictions,” explains
DESY’s Andreas Ringwald. DESY is a research institute in Hamburg Germany for
high-energy and particle physics as well as in the production and application
of synchrotron radiation.
The history of the universe
according to SMASH, denoting the different phases and the dominant energies of
the epochs since the Big Bang.
The history of the universe
according to SMASH, denoting the different phases and the dominant energies of
the epochs since the Big Bang.
“SMASH was actually
developed from the bottom up,” explains DESY’s Andreas Ringwald, who
co-authored the study. “We started off with the standard model and only added
as few new concepts as were necessary in order to answer the unresolved
issues.”
To do this, the scientist ultimately
combined various different existing theoretical approaches and finally came up
with a simple, a uniform model. SMASH adds a total of six new particles to the
standard model: three heavy, right-handed neutrinos and an additional quark, as
well as a so-called axion and the heavy rho (ρ) particle. The latter two form a
new field which extends throughout the entire universe.
Using these extensions, the
scientists were able to solve five problems: the axion is a candidate for dark
matter, which astrophysical observations suggest is five times more ubiquitous
than the matter we are familiar with, which is described by the standard model.
The heavy neutrinos explain the mass of the already known, very light
neutrinos; and the rho interacts with the Higgs boson to produce so-called
cosmic inflation, a period during which the entire young universe suddenly
expanded by a factor of at least one hundred septillion for hitherto unknown
reasons.
In addition, SMASH provides
explanations as to why our universe contains so much more matter than
antimatter, even though equal amounts must have been created during the big
bang, and it reveals why no violation of so-called CP symmetry is observed in
the strong force, one of the fundamental interactions.
“Overall, the resulting
description of the history of the universe is complete and consistent, from the
period of inflation to the present day. And unlike many older models, the
individual important values can be calculated to a high level of precision, for
example the time at which the universe starts heating up again after
inflation,” emphasises Ringwald.
Being able to calculate
these values with such precision means that SMASH could potentially be tested
experimentally within the next ten years.
A further test of the model
is the search for axions. Here too, the model is able to make accurate
predictions, and if axions do indeed account for the bulk of dark matter in the
universe, then SMASH requires them to have a mass of 50 to 200
micro-electronvolts, in the units conventionally used in particle physics.
Experiments that examine dark matter more precisely could soon test this
prediction too.