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Constraints for New Fundamental Force

by Rodsw
Tags: constraints, force, fundamental
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Rodsw
#1
Jan6-12, 05:21 PM
P: 32
What are the constraints (is this the right word) for introducing new fundamental force? Can our Standard Model accomodate a fifth one? Or would it mess up the math so badly that the present four fundamental forces is the final limit?
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phinds
#2
Jan6-12, 05:56 PM
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Do you believe that there is a fundamental force that has not been discovered? What is your evidence?
Rodsw
#3
Jan6-12, 07:56 PM
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Quote Quote by phinds View Post
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
#4
Jan7-12, 04:22 AM
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Constraints for New Fundamental Force

@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.
Best,
Jim Graber
phinds
#5
Jan7-12, 05:29 PM
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Quote Quote by jimgraber View Post
@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.
Best,
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
#6
Jan7-12, 10:38 PM
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One specific proposal currently pursued by several experiments is here
A Theory of Dark Matter
Rodsw
#7
Jan7-12, 11:23 PM
P: 32
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
#8
Jan8-12, 07:21 AM
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Quote Quote by humanino View Post
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
#9
Jan8-12, 07:21 AM
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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.

Best,
Jim Graber
torquil
#10
Jan8-12, 10:11 AM
P: 641
Quote Quote by Rodsw View Post
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
#11
Jan8-12, 04:06 PM
P: 32
Quote Quote by torquil View Post
The Higgs particle is not a gauge boson.
Why not? What is the requirement for being a gauge boson?
tom.stoer
#12
Jan9-12, 01:29 AM
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Quote Quote by jimgraber View Post
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
#13
Jan9-12, 03:28 AM
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Quote Quote by Rodsw View Post
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
#14
Jan9-12, 03:34 AM
P: 32
Quote Quote by torquil View Post
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
#15
Jan9-12, 04:18 AM
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Quote Quote by Rodsw View Post
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
#16
Jan9-12, 04:20 AM
P: 641
Quote Quote by Rodsw View Post
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
#17
Jan9-12, 04:56 AM
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Gravity is diff. inv. but the gauging is related to local Lorentz or Poincare inv.
phinds
#18
Jan9-12, 07:06 AM
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Quote Quote by tom.stoer View Post
... 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?


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