The Rev Dodgson said:
mollwollfumble said:
mollwollfumble said:
IF supersymmetry had proved correct then this would be a given. ie. that dark matter is similar in occurrence to ordinary matter because they are converted from one to another. Similar to the hydrogen-helium ratio. And perhaps (I haven’t seen a paper about this) the fine tuning of the number of neutrinos matching the number of photons in the universe. Three fine tuning problems solved by a single sensible theoretical model.
It was a sad day for science when the LHC proved that supersymmetry doesn’t exist.
Thinking further.
Supersymmetry, if it existed, would solve all three of the above fine tuning problems. hydrogen-helium, neutrino-photon & baryon-dark matter.
With the addition of supergravity it would also solve the fine tuning of gravity + electromagnetism.
But even with supergravity it doesn’t explain the fine tuning of dark energy + dark matter.
Or does it? If supergravity existed, could it solve the dark energy problem?
ie. is the magnitude of the cosmological constant somehow linked in with the supersymmetric properties of the graviton?
Don’t the proponents of supersymmetry still consider it to be a possibility?
Regarding fine tuning – I don’t see why that is seen as a problem.
If fine tuning is required for life, then only the finely tuned universes will have things capable of wondering why their universe happens to be fine tuned.
Appreciate the comments, Rev D.
Only certain aspects of fine tuning are necessary for life. In particular the hydrogen-helium ratio is necessary because that gives us the periodic table of stable elements. That only accounts for one of the five types of fine tuning, or at most two. The others are not necessary for life. On top of the five types of fine tuning, there is a non-fine-tuning problem to consider. To whit, the asymmetry between matter and antimatter, because simple physics suggests that they should be present in approximately equal amounts.
I went looking for papers about supergravity + dark energy as a coherent whole as opposed to as a bolt-on decoration.
Let’s see if https://arxiv.org/pdf/1909.05599.pdf fits the bill
“Inflation, Dark Energy and Dark Matter in Supergravity”
“The Dark Side of the Universe, which includes the cosmological inflation in
the early Universe, the current dark energy and dark matter, can be theoretically
described by supergravity, though it is non-trivial. We recall the arguments pro
and contra supersymmetry and supergravity, and define the viable supergravity
models describing the Dark Side of the Universe in agreement with all current ob-
servations. Our approach to inflation is based on the Starobinsky model, the dark
energy is identified with the positive cosmological constant (de Sitter vacuum),
and the dark matter particle is given by the lightest superparticle identified with
the supermassive gravitino. The key role is played by spontaneous supersymme-
try breaking.”
So far so good.
“The standard approach to the Dark Side of the (current) Universe is based on the
Cosmological Concordance Model that assumes (i) the dark energy described by
the cosmological constant and (ii) the dark matter (DM) described by unknown
(electrically neutral and stable) massive particles. In addition, the standard
(single-field) approach to cosmological inflation in the early Universe assumes
the existence of another scalar field (called inflaton) driving inflation. The early
Universe inflation can be considered as the primordial dark energy because ”dark
energy” is merely the substitute for the accelerating expansion of the Universe,
though the underlying physics of inflation and (current) dark energy are different:
one needs an appropriate scalar potential describing inflaton slow roll for inflation,
whereas a de Sitter vacuum (the positive cosmological constant) suffices for dark
energy. As regards the cold dark matter particle, one needs to explain its origin
and find the reason for its stability.”
So far so good.
“In supergravity theory, getting all those features is highly non-trivial, because
they have to be compatible with local supersymmetry of the acton. However,
this problem simultaneously offers the opportunity to severely constrain possible
options for embedding the Cosmological Concordance Model into supergravity
and connect it to the Standard Model (SM) of elementary particles.”
Good.
“Supergravity has many attractive features:
- SUSY unifies bosons and fermions;
- supergravity automatically includes General Relativity (GR);
- supergravity is the conservative extension of GR and field theory, which
restricts the number of independent parameters (coupling constants);
- SUSY Grand Unified Theories (super-GUTs) result in the perfect unifica-
tion of electro-weak and strong interactions;
- the spectrum of matter-coupled supergravities with spontaneously broken
SUSY has the natural DM candidate given by the Lightest SUSY Particle
(LSP), provided that R-parity is conserved;
- SUSY helps to stabilize the fundamental scales (the hierarchy problem),
such as the electro-weak scale and the GUT scale;
- SUSY leads to cancellation of the quadratic UV-divergences in quantum
field theory;
- supergravity is the only way to consistently describe coupling of spin 3/2
particles to gravity;
- it is unknown how many degrees of freedom (d.o.f.) were present during
inflation. Supergravity may be the answer;
• supergravity can be considered as the low-energy effective action of super-
strings (quantum gravity).”
Nicely explained.
“In this paper we very briefly review the standard approach to cosmology in
supergravity and its problems (Sec. 2). Then we outline our approach and its
tools based on the vector supermultiplet unifying inflaton and goldstino (Sec. 3).
The DM in our approach is given by the superheavy gravitino LSP in the context
of high-scale SUSY (Sec. 4). In Sec. 5 we outline the minimalistic approach
entirely based on the use of a single massive vector multiplet with the Born-Infeld
(BI) structure and the alternative Fayet-Iliopoulos (FI) terms. We conclude in
Sec. 6 where we also comment on a description of the primordial black holes in
supergravity.”
So far so good, but no mention of dark energy in that paragraph.
I haven’t seen this before. So quintessence gives cosmological inflation and constant cosmological constant gives dark energy, the two are perfectly compatible. This can count as a unification of cosmological inflation and dark energy.
That’s what I was looking for. An inclusion of dark energy (a general relativity construct) into the quantum mechanics of supergravity. This goes a long way towards unifying GR and QM.
Aha, that clears up a concern of mine. I see now that there are two types of f( R ) gravity. The modification of gravity to account for cosmological inflation is the one that needs to be taken seriously.
Ah, the old problem remains. The graviton alone fails to account for gravity, it would need to be stabilised by a cascade of heavier gravitons and no way to do this has yet been found.