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Why not more particles?

by Garrulo
Tags: particles, ¿why
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Garrulo
#1
Apr28-14, 12:21 AM
P: 10
¿How we know that a energy scale, for example, standard model typical energies, there is not more particles?
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The_Duck
#2
Apr28-14, 02:16 AM
P: 846
We don't. Dark matter direct detection experiments are trying to detect new particles with masses comparable to the masses of standard model particles.

But if there are new particles at accessible energies, they have to satisfy a number of constraints. They can't couple too strongly to standard model particles or we would have produced them directly in accelerator experiments, or detected them in sensitive experiments like dark matter detectors, or seen them through their loop effects in precision tests of the standard model. Cosmology also provides some constraints: we can predict the implications of a new particle for the physics of the early universe and check if these implications contradict any cosmological observations (for example, see here).
Garrulo
#3
Apr28-14, 03:06 AM
P: 10
Quote Quote by The_Duck View Post
. Cosmology also provides some constraints: we can predict the implications of a new particle for the physics of the early universe and check if these implications contradict any cosmological observations (for example, see here).
I don´t find the constraints between the technicisms of the blog (I am not astrophysical). What is the conclusion about it in the old universe situation?

mfb
#4
Apr28-14, 02:08 PM
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P: 11,631
Why not more particles?

What is an "old universe situation"?
The conclusion: No other particles were found wherever experiments could look for them.

If there are undiscovered particles, they have to be [really heavy] or [uncharged, without a color charge, and really weakly interacting with any other particles].
Garrulo
#5
Apr28-14, 04:12 PM
P: 10
Quote Quote by mfb View Post
What is an "old universe situation"?


If there are undiscovered particles, they have to be [really heavy] or [uncharged, without a color charge, and really weakly interacting with any other particles].
¿How weight is really heavy? ¿What were the typical distance for these particles?
ChrisVer
#6
Apr28-14, 05:00 PM
P: 762
The Standard Model particle list, after the discovery of the Higgs particle, is closed and finished...
Standard Model alone cannot describe any more elementary particles...
The Dark Matter for example, is not within the Standard Model.

If any new elementary particle is to be discovered, it will be out of the Standard model...
(we already know that we must have 3 generations of quarks and leptons, we already know that the Higgs particle exists- and so the Higgs field can be used to give particles masses- and we know how interactions take place.)
Garrulo
#7
Apr28-14, 05:14 PM
P: 10
Quote Quote by ChrisVer View Post
The Standard Model particle list, after the discovery of the Higgs particle, is closed and finished...
Standard Model alone cannot describe any more elementary particles...
The Dark Matter for example, is not within the Standard Model.

If any new elementary particle is to be discovered, it will be out of the Standard model...
(
My question is about Universe, not about the Standard Model. It misses the graviton, minimally
ChrisVer
#8
Apr28-14, 05:28 PM
P: 762
The graviton is not within the Standard Model. The Standard model cannot quantize gravity due to Renormalizability issues... In other words, we are still using GR for gravity and Standard Model for elementary particles...
What do you mean about the Universe?
As for your question about "how heavy", well, they must be heavier than the energies we have achieved in colliders (>~1-10 TeV approximately)
mfb
#9
Apr28-14, 05:38 PM
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P: 11,631
Quote Quote by Garrulo View Post
What were the typical distance for these particles?
What do you mean with "typical distance"?

Really heavy means out of range for current accelerators, at least of the order of a TeV.
Garrulo
#10
Apr29-14, 12:08 AM
P: 10
Quote Quote by ChrisVer View Post
As for your question about "how heavy", well, they must be heavier than the energies we have achieved in colliders (>~1-10 TeV approximately)
But, how we know that when the particles that we don´t generate in acelerators, they can´t in another in the cotidian life
mfb
#11
Apr29-14, 02:36 AM
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Quote Quote by Garrulo View Post
But, how we know that when the particles that we don´t generate in acelerators, they can´t in another in the cotidian life
I don't understand that question.

There is always the possibility that they do not interact with other particles at all (just via gravity), then we have no way to find them in accelerators. So what? Where is the point?
ChrisVer
#12
Apr29-14, 03:05 AM
P: 762
It's a game of energy threshold and precision measurements. Both those two have for many decades confirmed the standard model particle content (or more precisely have built up the standard model), no other particle can exist within it.
However we know that Standard Model is not the perfect model for elementary interactions. Any discovery of a new particle will indicate physics beyond the standard model...Even if you create extra particles that you cannot detect at the moment, those particles are not coming/donnot behave in a well-known physical way (that's why there is a plurality of theories dealing beyond the standard model physics, and they all act as candidates- but they are not experimentally confirmed. Some have been experimentally disproven).
Garrulo
#13
Apr29-14, 11:26 AM
P: 10
Quote Quote by mfb View Post
I don't understand that question.

There is always the possibility that they do not interact with other particles at all (just via gravity), then we have no way to find them in accelerators. So what? Where is the point?

There is the point. How do we know this particles?
ChrisVer
#14
Apr29-14, 11:43 AM
P: 762
We don't... we can just make theories containing the particles we know and some extra features and those theories may contain those extra particles in them...
Or we know of the existence of Dark Matter but we don't know its particles - we build a model trying to explain them too in such a way that it'd answer us why we haven't detected them yet.
mfb
#15
Apr29-14, 01:29 PM
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P: 11,631
Quote Quote by Garrulo View Post
There is the point. How do we know this particles?
Which particles?
All particles we know of have been observed (that is a trivial statement).
Garrulo
#16
Apr29-14, 03:42 PM
P: 10
Quote Quote by mfb View Post
Which particles?
All particles we know of have been observed (that is a trivial statement).
Your interpretations are really convoluted. I refer to the particles that we don´t see in accelerators, no to particles that we see in their. Obviously, they exist (that is a trivial statement)
mfb
#17
Apr29-14, 04:42 PM
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P: 11,631
refer to the particles that we don´t see in accelerators
We don't know if there are particles we don't see in accelerators. There could be more - and actually it is expected that there are more, due to dark matter.
Garrulo
#18
Apr29-14, 09:56 PM
P: 10
Quote Quote by mfb View Post
We don't know if there are particles we don't see in accelerators. There could be more - and actually it is expected that there are more, due to dark matter.
Yeah, I read about dark matter, but there are many hypothesis (even that gravity is not always r-2 and dark matter doesn`t exist. But I refer to particles around ours that it can affect us pshychophysically and we don´t know about it.


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