Constraints for New Fundamental Force

[Rodsw]

What are the constraints (is this the right word) for introducing new fundamental force? Can our Standard Model accommodate a fifth one? Or would it mess up the math so badly that the present four fundamental forces is the final limit?

 

[phinds]

Do you believe that there is a fundamental force that has not been discovered? What is your evidence?

 

[Rodsw]

Do you believe that there is a fundamental force that has not been discovered? What is your evidence?

I was just asking if our physics like symmetries in gauge theory forbid them from existing much like the Higgs bosons mass being constrained to be certain energy close to 125 Gev.

 

[jimgraber]

@Phinds
On evidence:
There are at least four substantial bodies of evidence which require either a new fundamental force or a significantly different combination of the known forces.
They are dark matter, dark energy, MOND, and the inflationary universe.

Jim Graber

 

[phinds]

@Phinds
On evidence:
There are at least four substantial bodies of evidence which require either a new fundamental force or a significantly different combination of the known forces.
They are dark matter, dark energy, MOND, and the inflationary universe.

Jim Graber

I was not aware that dark matter would likely require a new force. WIMPs are the currently favored candidate and I don't believe they require any new force.

I think MOND is a wild goose chase.

What is your distinction between dark energy and "inflationary universe" [by which, and correct me if I'm wrong, I assume you mean the accelerating expansion of the universe]. I do agree w/ you that there is at least a possibility that dark energy / accelerating expansion MAY require a new force.

 

[humanino]

One specific proposal currently pursued by several experiments is here
A Theory of Dark Matter

 

[Rodsw]

Why isn't the Higgs field a new force?

How do you differentiate between a new force and a new field? Electromagnetic field, gravitational field, weak field, strong field are forces while higgs field are not. Would anyone happen to know why?

 

[phinds]

One specific proposal currently pursued by several experiments is here
A Theory of Dark Matter

Interesting ... so if they are right, the there WOULD be a new force associated with dark matter. I'm dubious, but that's based on total ignorance.

 

[jimgraber]

Phinds wrote:

"I was not aware that dark matter would likely require a new force. WIMPs are the currently favored candidate and I don't believe they require any new force.

I think MOND is a wild goose chase.

What is your distinction between dark energy and "inflationary universe" [by which, and correct me if I'm wrong, I assume you mean the accelerating expansion of the universe]. I do agree w/ you that there is at least a possibility that dark energy / accelerating expansion MAY require a new force."

The most popular form of WIMP is the neutralino, which requires or is based on supersymmetry.
I would call supersymmetry a major new principle, if not a new "force".

MOND theories are highly questionable.
MOND experimental evidence is many sigmas strong. If it's not a new "force", it requires an as yet not understood combination of existing partcles or forces.

Dark energy or the cosmological constant (a new "force" or "principle" in my opinion), is the current slow acceleration in the expansion of the universe.
The inflationary universe is Alan Guth's proposed very rapid expansion of the universe right at the beginning.


Jim Graber

 

[torquil]

Why isn't the Higgs field a new force?

How do you differentiate between a new force and a new field? Electromagnetic field, gravitational field, weak field, strong field are forces while higgs field are not. Would anyone happen to know why?

The Higgs particle is not a gauge boson.

 

[Rodsw]

The Higgs particle is not a gauge boson.

Why not? What is the requirement for being a gauge boson?

 

[tom.stoer]

On evidence:
There are at least four substantial bodies of evidence which require either a new fundamental force or a significantly different combination of the known forces.
They are dark matter, dark energy, MOND, and the inflationary universe.

I think one should rephrase this:
1) there are indications that astrophysical observations (e.g. rotation of galaxies, galaxy formation, gravitational lensing) require something like dark matter, MOND etc.; it's not the case that we know for sure that DM exists, but we have obsrvational facts for which DM (or MOND) may provide an explanation
2) there are indications that astrophysical observations (cosmological redshift) require something like dark energy or simply the cosmological constant; note that a cosmological constant need not be identified with a new force or field but can be introduced as a pure number

So most of what you are proposing is not "body of evidence" but are ideas how to solve currently known problems.

 

[torquil]

Why not? What is the requirement for being a gauge boson?

The Higgs field behaves differently due to the different mathematical laws that govern it. Please read up on quantum gauge field theory to understand more about that.

However, there might be some freedom in what is called a "force", depending on which physicist you ask. The Higgs particle certainly represents a type of interaction between e.g. fermionic particles, so it wouldn't be too far off to call it a "force". But this is all semantics anyway, since the Higgs was already for a long time a proposed part of the Standard Model. So it was already agreed upon by most physicists to not call the Higgs a "new fundamental force", since it is not a gauge boson.

If new particle physics interactions are discovered that are described by an enlargment of the existing gauge symmetry group, thus leading to new gauge bosons, it would certainly be heralded as a "new fundamental force".

 

[Rodsw]

The Higgs field behaves differently due to the different mathematical laws that govern it. Please read up on quantum gauge field theory to understand more about that.

However, there might be some freedom in what is called a "force", depending on which physicist you ask. The Higgs particle certainly represents a type of interaction between e.g. fermionic particles, so it wouldn't be too far off to call it a "force". But this is all semantics anyway, since the Higgs was already for a long time a proposed part of the Standard Model. So it was already agreed upon by most physicists to not call the Higgs a "new fundamental force", since it is not a gauge boson.

If new particle physics interactions are discovered that are described by an enlargment of the existing gauge symmetry group, thus leading to new gauge bosons, it would certainly be heralded as a "new fundamental force".

Electromagnetic field is U(1)
Weak Force is SU(2)
Strong Force is SU(2) x SU(3)
Gravitational Force doesn't have any gauge symmetry group. So why is Gravity part of the fundamental forces?

 

[tom.stoer]

Electromagnetic field is U(1)
Weak Force is SU(2)
Strong Force is SU(2) x SU(3)
Gravitational Force doesn't have any gauge symmetry group. So why is Gravity part of the fundamental forces?

no, not really ;-)

Electromagnetic force corresponds to U(1)
=> electro-weak force corresponds to U(1) * SU(2)
strong force corresponds to SU(3)
gravitational 'force' corresponds to SL(2,C)

The gravitational 'force' can be formulated using a gauge symmetry, a 'local Lorentz gauge symmetry SO(3,1) ~ SL(2,C)' in tangent space which is not visible in second-order metric formulation but requires a first order formulation based on tetrads and connection. Afaik even a gauging of the full Poincare group (which is larger than the Lorentz group) is possible. Nevertheless the formulation differs significantly from ordinary gauge.

 

[torquil]

Electromagnetic field is U(1)
Weak Force is SU(2)
Strong Force is SU(2) x SU(3)
Gravitational Force doesn't have any gauge symmetry group. So why is Gravity part of the fundamental forces?

You have it a bit wrong:

* The strong colour force comes from the SU(3) gauge group factor.

* The electroweak force comes from the SU(2)xU(1) and includes both the weak and electromagnetic force. The U(1) gauge symmetry subgroub of the electromagnetic force is not the U(1) factor in the product written here, but rather a U(1) subgroup that comes from a combination of group elements in both factors. This has to do with the Higgs mechanism and spontaneous symmetry breaking.

* Gravity can be described as a gauge symmetry in some sense, as far as I know. It has to do with the diffeomorphism symmetry of spacetime. In any case, gravity is a special case, so this classification might not apply. The current theory of gravity is a classical one, and no scientifically accepted quantum theory of gravity exists yet, so the existence of gravitons is uncertain. It is hypothesized that gravity is described quantum mechanically by a spin-2 gauge bosons (gravitons), but this is all quite uncertain at the moment since there is not experimental information about this.

 

[tom.stoer]

Gravity is diff. inv. but the gauging is related to local Lorentz or Poincare inv.

 

[phinds]

... there are indications that astrophysical observations (e.g. rotation of galaxies, galaxy formation, gravitational lensing) require something like dark matter, MOND etc.; it's not the case that we know for sure that DM exists, but we have obsrvational facts for which DM (or MOND) may provide an explanation

Correct me if I'm wrong, but it was my impression that observations (gravitational lensiing in particular) are all completely consistent with dark matter, but some (gravitational lensing in particular) are NOT compatible with MOND. Is that not true?

 

[tom.stoer]

My intention was to 'scale down the demanding' from "substantial bodies of evidence ..." to "indications requiring something like ..."; but I agree that many would favour DM instead of MOND

 

[ohwilleke]

There are several ways you could get a new fundamental force:

1. In a "dark sector" like those of SUSY or sterile neutrinos that doesn't interact with ordinary matter significantly and hence is hard to observe.

2. As part of a see-saw or Majorana mass scenario mediating between fertile and sterile neutrinos, for example.

3. As a binding force of preons at a very small distance scale and very high energy scale undetectable at LHC that make up "fundamental" particles in the Standard Model.

4. At long distances that are only visible in weak gravitational fields (e.g. some force related in some way to dark matter or dark energy effects).

5. In low energy quantum scale contexts. LHC, etc. can measure high energy contexts at the quantum scale, but not low energy contexts, there could be unknown forces acting within confined composite particles that are hard to see as a result since we don't have the tools to see them.

6. In high pressure complex systems (e.g. Fermi contact forces) in neutron stars and the like.

7. Some force that seems unified, may actually decompose into more than one force in the right conditions. For example, maybe the Yang-Mills QCD equations really describe three separate forces collectively that can really be parsed out into separable independent forces that are capable of separate observation in the right conditions that only happen to coincide most of the time. Or, perhaps the CP violating component of the weak force is actually separable from the remaining effects of the weak force even though we observe them as a single combined phenomena.

 

[ohwilleke]

Correct me if I'm wrong, but it was my impression that observations (gravitational lensiing in particular) are all completely consistent with dark matter, but some (gravitational lensing in particular) are NOT compatible with MOND. Is that not true?

Gravitational lensing is perfectly consistent with MOND as are a surprisingly large range of gravitational phenomena. There are basically two phenomena that potentially are inconsistent with its relativistic version TeVeS: (1) the bullet cluster, (2) the lack of proper scaling from galactic to cluster level phenomena (i.e. TeVeS expects some dark matter beyond its force modification in clusters).

A similar but different formulation by Moffat claims to do better.

There are also a number of papers that claim that simply better modeling relativistic effects in complex systems rather than modeling them as effectively Newtonian can decrease the magnitude of the potential dark matter effects.

Recent data on "dim" ordinary matter from star censuses of ellipical data also suggest that the conventional 80% of matter is dark statement is wildly off and that the real figure is much closer to 50% than 80%.

Finally, it is worth noting that particle based dark matter theories aren't terribly healthy either. Candidate particles in the right mass range have been ruled out by a variety of evidence from precision electro-weak decays to direct detection efforts to constraints from the Bullet Cluster to the scales at which different kinds of large scale structures are seen.

Traditional cold dark matter with WIMP theories are pretty much inconsistent with the data - they give rise to the wrong distributions of dark matter. "Warm dark matter" theories are state of the art with hypothetical particles moving at speeds one would typically associated with keV scale particles that are ruled out to the extent that they are weak force interacting under the leptogenesis scenarios proposed.

 

[jimgraber]

@phinds:
My understanding of the observational evidence is that cluster scale evidence favors conventional cold dark matter (CDM) but galaxy and smaller scale observations are more compatible with MOND. Even ignoring the bullet cluster, MOND requires neutrinos or something else to match cluster scale gravitation with the same parameters used at the galactic scale. CDM on the other hand can be made compatible with galaxy (especially small galaxy and spiral arm scale) rotation curves only with considerable fine tuning of the location and composition of the dark matter, which is not very easy to square with the simpler cluster scale picture.

@tom.stoer:
Dark matter and dark energy seem to be widely accepted now.
MOND is still very controversial, and a minority opinion.
(However, the observational evidence for some effect different from standard CDM is in much better shape than the original theory or modern replacements)
The inflationary universe seems to have a moderate majority among cosmologists, and to be pretty much ignored by everyone who is not a cosmologist.
(I could be wrong, and of course these opinions have changed substantially in the last fifteen or twenty years.)

In my view, the stronger “substantial body of evidence” as opposed to the weaker “indications …” is certainly appropriate for dark matter and dark energy, and arguably so for MOND. The inflationary universe has somewhat less support in my view, and is more subject to interpretation, but you should argue with Alan Guth or Andrei Linde about that.


There is a whole other question as to what constitutes a “new fundamental force” or principle. (In my lifetime, I actually remember the overthrow of parity conservation fifty-six years ago. Also more recently non-zero neutrino mass was a surprise.)
Without arguing about words, I would regard even a confirmed WIMP as a significantly new something-or-other. Same for an axion. I propose supersymmetry or a fortiori string theory would certainly qualify. On a weaker scale an SO(10) GUT or anything beyond SU(3)x SU(2)xU(1) would float my boat.

@ohwilleke:
Thanks for all the details.


Jim Graber

 

[Rodsw]

There are several ways you could get a new fundamental force:

1. In a "dark sector" like those of SUSY or sterile neutrinos that doesn't interact with ordinary matter significantly and hence is hard to observe.

2. As part of a see-saw or Majorana mass scenario mediating between fertile and sterile neutrinos, for example.

3. As a binding force of preons at a very small distance scale and very high energy scale undetectable at LHC that make up "fundamental" particles in the Standard Model.

4. At long distances that are only visible in weak gravitational fields (e.g. some force related in some way to dark matter or dark energy effects).

5. In low energy quantum scale contexts. LHC, etc. can measure high energy contexts at the quantum scale, but not low energy contexts, there could be unknown forces acting within confined composite particles that are hard to see as a result since we don't have the tools to see them.

6. In high pressure complex systems (e.g. Fermi contact forces) in neutron stars and the like.

7. Some force that seems unified, may actually decompose into more than one force in the right conditions. For example, maybe the Yang-Mills QCD equations really describe three separate forces collectively that can really be parsed out into separable independent forces that are capable of separate observation in the right conditions that only happen to coincide most of the time. Or, perhaps the CP violating component of the weak force is actually separable from the remaining effects of the weak force even though we observe them as a single combined phenomena.

Since a new force has to be at least SU(4) gauge group or higher.. then all of the above needs to be at least SU(4)? Can't they also be U(1) or U(1)xSU(2) or SU(3) also?

 

[Vanadium 50]

Since a new force has to be at least SU(4) gauge group or higher..

Untrue.

 

[ohwilleke]

Since a new force has to be at least SU(4) gauge group or higher.. then all of the above needs to be at least SU(4)? Can't they also be U(1) or U(1)xSU(2) or SU(3) also?

Why? It seems to me that the main requirement for a new force is that it is someplace that we aren't equipped to have seen it already. Being "new" one can't make any real a priori assumptions about it.

There is no tremendously compelling logical reason that a force has to correspond to any gauge group, and indeed, LQG is to a great extent notable because it gets out of the gauge group rut.

 

[Rodsw]

Why? It seems to me that the main requirement for a new force is that it is someplace that we aren't equipped to have seen it already. Being "new" one can't make any real a priori assumptions about it.

There is no tremendously compelling logical reason that a force has to correspond to any gauge group, and indeed, LQG is to a great extent notable because it gets out of the gauge group rut.

Don't forget the reply of Torquil in message #13 in which he mentioned:

"The Higgs field behaves differently due to the different mathematical laws that govern it. Please read up on quantum gauge field theory to understand more about that.

However, there might be some freedom in what is called a "force", depending on which physicist you ask. The Higgs particle certainly represents a type of interaction between e.g. fermionic particles, so it wouldn't be too far off to call it a "force". But this is all semantics anyway, since the Higgs was already for a long time a proposed part of the Standard Model. So it was already agreed upon by most physicists to not call the Higgs a "new fundamental force", since it is not a gauge boson.

If new particle physics interactions are discovered that are described by an enlargment of the existing gauge symmetry group, thus leading to new gauge bosons, it would certainly be heralded as a "new fundamental force"."

 

[jimgraber]

http://arxiv.org/abs/1201.1697 is a professional level discussion mentioning the same four topics of MOND, inflation, dark matter and dark energy.
Enjoy!
Jim Graber

 

[PhizzyQs]

Regarding dark matter, energy, and the inflationary universe, it is possible to extend gravity (or, more precisely, geometrodynamics) to account for those effects.

The Einstein field equations, which are the main equations used to define gravity, may be derived from an Einstein-Hilbert action, with Lagrangian L = R(-g)^1/2 + L_matter, where are is the Ricci scalar curvature, and g is the determinant of the metric tensor. Using variational principles, the stress energy tensor may be obtained from L_matter.

However, this is not the only configuration (see Wikipedia: f(R) gravity). Indeed, it is possible to draft more general actions, which include different curvature terms. For example, there is Gauss-Bonnet gravity, where L is given by (-g^1/2)(R^2 - 4<Ric, Ric> + <Riemann, Riemann>).

Some theorists have suggested that f(R) gravity may be used to account for dark matter observations, etc. See arXiv:1010.2403v1 [physics.gen-ph] as an example.

There is also this nice presentation here: http://vipac.desy.de/Common/vipac1207/Winitzki_f%28R%29_2007.pdf

 

[Rodsw]

Since a new force has to be at least SU(4) gauge group or higher..

Untrue.

Why untrue. You mean a new force can belong to one of the lower symmetry group like U(1) or SU(3) which the electromagnetic and strong force also use?

 

[PhizzyQs]

Certainly, if a different symmetry is observed which can be described by a group action of U(1), SU(2), etc. The point is that we'll now have two different classes of gauge fields, accounting for two different local transformations.

 

[czes]

In the Holographic Universe hypothesis there aren't the forces at all. The effect of the force appeares according to the entropy due to the relation between the quantum information. Each relation causes a Planck time dilation and it causes the inertia and time flow. The sum of the relation creates the Dark Energy and te relative distribution causes an effect of the Dark Matter.
There aren't particles in the fundamental level.
http://en.wikipedia.org/wiki/Quantum_decoherence

 

[Rodsw]

Certainly, if a different symmetry is observed which can be described by a group action of U(1), SU(2), etc. The point is that we'll now have two different classes of gauge fields, accounting for two different local transformations.

Let's go back to this before we totally forgot about it.

So gauge field 1 Electroweak is described by U(1) x SU(2)

And gauge field 2 Dark Matter coupling (just example) is described also by U(1) x SU(2)

But how can two similar gauge symmetry group produce two different local transformations. Can you give an example of how it do it (if this is valid at all)?

 

[fzero]

Let's go back to this before we totally forgot about it.

So gauge field 1 Electroweak is described by U(1) x SU(2)

And gauge field 2 Dark Matter coupling (just example) is described also by U(1) x SU(2)

But how can two similar gauge symmetry group produce two different local transformations. Can you give an example of how it do it (if this is valid at all)?

The idea is that the new group can be of the same type, but it is a different copy. To be clear, we have the Standard Model group, G_{\textrm{SM}}=SU(3)\times SU(2)\times U(1), while the hypothetical new force is associated with some new group G_{\mathrm{new}}. The group G_{\mathrm{new}} can be U(1), SU(2), or something more complicated, but it is a completely different group, with its own transformation and associated gauge fields. The total gauge group of the model for new physics would be G_{\textrm{SM}}\times G_{\mathrm{new}}.

 

[nazarbaz]

What would be the effects of this hypothetical discovery on the quantum gravity approach ? Something that could ruin the attempt ?
The underlying idea is the "possibility" that the fundamental forces of our known physics are the proprieties of our actual universe, not of the targeted epochs or phenomena of quantum gravity...
Please correct me if you think this is silly...

 

[ohwilleke]

"two similar gauge symmetry group produce two different local transformations. Can you give an example of how it do it (if this is valid at all)?"

Imagine that there is regular matter that has regular electromagnetic charge and weak isospin.

Imagine that dark matter is composed of something called "mirror matter" and that mirror matter has mirror charge and mirror isospin that is mediated by the futon, the V boson and the Y boson, which follow precisely the same laws as and have the same properties as the photon, W boson and Z boson respectively do with respect to the corresponding properties of mirror matter. Imagine further that futons, V bosons and Y bosons never couple to regular matter, while photons, W bosons and Z bosons never couple to mirror matter.

Voila, I have just completely described how two identical gauge symmetry groups of the SU(2)xU(1) type produced two different local transformations.

Another fairly common proposal would be to propose something along the line of a theory in which quarks are themselves composed of three "preons" bound together by an exchange of "supergluons" that come in three "tints" which we might call black, gray and white, that we would call the "superstrong force" that is identical in all respects to the SU(3) gauge group of QCD except that the coupling constant of the superstrong force was much larger than the coupling constant of QCD. Not very original, I agree. But, honestly, how original is nature in always giving us gauge boson mediated gauge group forces that propogate bosons in essentially the same way the QED does?

 

[BDOA]

The first constraint is the anomally triangle diagrams, any new force needs to satisfy these constraints. However adding addition fermions could allow extra forces to exist. After that, the symmetry group
and the mass of the force carriers need to be found.

Any new force, needs to have hidden from previous investigation, this might happen if

If the force carrier has a large mass,
if the force is confined like QED,
if the force constant is very small, or
if the force is screened by very light particles.