B Are Dark Matter Concentrations on Earth Seasonal?

[mfb]

Static electromagnetic fields have energy.

If universe were charged

What does that mean?

All known matter and fields slow down the acceleration. Dark energy is something fundamentally different.

Edit: Oops, wrong word

 

[snorkack]

What does that mean?

All known matter and fields slow down the acceleration.

Like masses attract. Like charges repel. What are expected consequences if universe had unbalanced electric charge, either positive or negative?

 

[mfb]

Both energy density and pressure slow down the expansion, I'm quite sure that a net charge will still lead to this effect.
@PeterDonis will know more.

 

[ohwilleke]

is there no dark matter that has no mass that doesn't interact with gravity? yet say it only interacts with matter...

or are there no dark matter that interacts with matter yet doesn't have any mass nor gravity?

Dark matter is something we infer to exist because from the dynamics of visible matter that would be explained if there were nearly collisionless particles that had mass. Mass is part of the definition of dark matter.

Everything that has mass or energy interacts via gravity. Everything that has neither mass nor energy doesn't exist.

 

[ohwilleke]

So the definition of dark matter is it has mass and interacts with gravity...

If there is a substance that interacts with matter but has no mass and doesn't interact with gravity.. then what is this substance called? And what laws of physics makes it not possible to exist?

There are two known particles (gravitons and gluons) and one hypothetical one (gravitons) that have no mass, but all of them have energy, and gravity interacts with anything that has mass or energy or both. All Standard Model particles with mass interact via the weak force. All quarks and gluons interact via the strong force. All quarks, charged leptons and massive weak force bosons emit and absorb photons as part of the electro-magnetic force. All Standard Model particles interact via gravity as does the hypothetical graviton.

If something had no mass and also had no energy, it could not have interactions and could not do work because energy is defined as the capacity to do work. Physics is defined so that only things with observable effects are considered. Something that has no interactions and cannot do work can't have any observable effects, ergo, they don't exist.

 

[ohwilleke]

[Gauge bosons always move with the speed of light.]

Not true. W and Z bosons are massive gauge bosons. Massless gauge bosons always move with the speed of light, but not all gauge bosons are massless. Massive gauge bosons do not move at the speed of light.

 

[ohwilleke]

At the limit of no energy and no frequency, photons convert to static electromagnetic fields. Which have no energy, but affect matter a lot.
If universe were charged, negative or positive, how would electrostatic repulsion affect expansion of universe?

At the limit of no energy and no frequency, photons don't exist. Anything that matters at all has either matter or energy or both. Photons with no energy would by definition be incapable of affecting anything.

 

[Stavros Kiri]

Not true. W and Z bosons are massive gauge bosons. Massless gauge bosons always move with the speed of light, but not all gauge bosons are massless. Massive gauge bosons do not move at the speed of light.

You're right of course. But here is what I was referring to (not including the W and Z bosons):

But in Elementary Particle Physics, [at least] two particles (sets of particles) are known to be massless (in the relativistic sense though): the two gauge bosons, i.e. photons and gluons. Gravitons would be as well, but they haven't been discovered yet. [All these three mentioned [sets of] particles are force carriers (for EM, strong and gravitational forces, respectively). You might hear of them also as field particles.]

Also regarding:

At the limit of no energy and no frequency, photons don't exist. Anything that matters at all has either matter or energy or both. Photons with no energy would by definition be incapable of affecting anything.

But at that limit also electrostatics emerge (no photons - you're right), so partially in a sense he is right too.

 

[ohwilleke]

Without photons there are no electrostatics.

 

[Stavros Kiri]

Without photons there are no electrostatics.

Coulomb's law requires no photons! ...
[I think what you stated is a common misconception in fundamental physics. Here is why:]
Only accelerating charges or time-varying fields produce EM waves, thus ... when quantized, ... Photons. Static E or B fields produce no photons, (nor EM waves), unless charges move or fields vary in time ... . Other than that they are just static fields ... as dictated by Coulomb's law etc.
(QED and Feynman diagrams would have no choice but to agree with that as well.)

 

[Drakkith]

Without photons there are no electrostatics.

Coulomb's law requires no photons! ...
[I think what you stated is a common misconception in fundamental physics. Here is why:]
Only accelerating charges or time-varying fields produce EM waves, thus ... when quantized, ... Photons. Static E or B fields produce no photons, (nor EM waves), unless charges move or fields vary in time ... . Other than that they are just static fields ... as dictated by Coulomb's law etc.
(QED and Feynman diagrams would have no choice but to agree with that as well.)

QED does model electrostatic interactions using virtual photons though, and Feynman diagrams incorporate both real and virtual particles if I remember correctly.

 

[ohwilleke]

(QED and Feynman diagrams would have no choice but to agree with that as well.)

A field is just photons. If there is nothing to transmit electromagnetic interactions, there is no electromagnetism. Coulomb's law absolutely requires photons in QED.

 

[Stavros Kiri]

Coulomb's law absolutely requires photons in QED.

Do you see any from a static charge? Where are they? What frequency? Virtual perhaps but ... long story ...

 

[mfb]

Photons have to be possible to have static fields in QFT, even if there are no photons flying around.

 

[bluecap]

Everything with energy interacts with gravity. It doesn't even need mass.

And everything has energy, something without energy cannot have any impact on the world and we can simply assume it is not there.
This would violate special relativity, unless "near speed" means the speed of light. But massless particles would not clump together like dark matter does.
I'm not a dark matter expert, but as far as I can see, all the phase space for their assumed WIMP mass and cross section has been ruled out by orders of magnitude since that publication was published, mainly by PICO-60, PandaX-II and CDMS-lite. Here is a recent study.

What if there were dark matter that interacts only with photons and concentrated in the sun and it doesn't interact with any other particles.. does it mean this dark matter species doesn't interact with the weak force but only gravity and with photons.. what are these called then and isn't there any paper that mentions this?

 

[Drakkith]

What if there were dark matter that interacts only with photons and concentrated in the sun and it doesn't interact with any other particles.. does it mean this dark matter species doesn't interact with the weak force but only gravity and with photons.. what are these called then and isn't there any paper that mentions this?

Please stick to real science and avoid speculation such as this. We can't hope to answer every "what if..." scenario that people come up with.

 

[bluecap]

Please stick to real science and avoid speculation such as this. We can't hope to answer every "what if..." scenario that people come up with.

I mean why does dark matter obey the weak interaction.. does it really interact with the weak force? Why not just gravity?

 

[Drakkith]

I mean why does dark matter obey the weak interaction..

As far as we know, it doesn't. It only interacts via gravity.

 

[mfb]

We know it doesn’t interact with photons, otherwise we would see it.
For particles that interact only via gravity it is unclear how they could have been produced in the right amount in the early universe.

 

[bluecap]

We know it doesn’t interact with photons, otherwise we would see it.
For particles that interact only via gravity it is unclear how they could have been produced in the right amount in the early universe.

I thought WIMP interacts via the weak force.. i thought anything that comes from Supersymmetry should interact at least the weak force.. but if it only interacts via gravity.. how come experiments reported WIMP null results when they can't be detected except by gravity?

 

[mfb]

I thought WIMP interacts via the weak force..

By definition, yes (WI in WIMP). That doesn’t mean dark matter has to consist of WIMPs.

i thought anything that comes from Supersymmetry should interact at least the weak force.. but if it only interacts via gravity.. how come experiments reported WIMP null results when they can't be detected except by gravity?

Additional particles don’t have to participate in the weak interaction, it is just likely.
Null results of detectors looking for weak interactions are perfectly consistent with particles with no weak interaction.

 

[ohwilleke]

By definition, yes (WI in WIMP). That doesn’t mean dark matter has to consist of WIMPs.
Additional particles don’t have to participate in the weak interaction, it is just likely.
Null results of detectors looking for weak interactions are perfectly consistent with particles with no weak interaction.

Particles with no weak, strong or EM interactions are not only perfectly consistent with the non-detection of dark matter in direct detection experiments and the non-detection of DM at the LHC. They are also consistent with the absence of any compelling DM annihilation signature. So, while non-detection of DM in those channels is parameter bounding for DM theories, it certainly doesn't rule out DM that is "sterile" (i.e. that only interacts via gravity) or DM that only interacts with other DM in addition to gravity.

The trouble is that the amount of correlation between inferred DM distributions and baryonic matter distributions is too tight to be explained by gravity alone and the shape of the DM distributions aren't what we would theoretically predict if DM was truly sterile or only interacted with other DM. So, truly sterile DM or DM that only interacts with other DM isn't enough to explain the phenomenology.

This leaves you looking for a fifth force that predominantly governs DM-ordinary matter interactions (and possibly also DM to DM interactions), such as the paper described below, in a dark matter particle theory.

Dark matter and neutrinos provide the two most compelling pieces of evidence for new physics beyond the Standard Model of Particle Physics but they are often treated as two different sectors. The aim of this paper is to determine whether there are viable particle physics frameworks in which dark matter can be coupled to active neutrinos. We use a simplified model approach to determine all possible renormalizable scenarios where there is such a coupling, and study their astrophysical and cosmological signatures. We find that dark matter-neutrino interactions have an impact on structure formation and lead to indirect detection signatures when the coupling between dark matter and neutrinos is sufficiently large. This can be used to exclude a large fraction of the parameter space. In most cases, dark matter masses up to a few MeV and mediator masses up to a few GeV are ruled out. The exclusion region can be further extended when dark matter is coupled to a spin-1 mediator or when the dark matter particle and the mediator are degenerate in mass if the mediator is a spin-0 or spin-1/2 particle.

Andres Olivares-Del Campo, et al., "Dark matter-neutrino interactions through the lens of their cosmological implications" (November 14 2017).

 

[bluecap]

Particles with no weak, strong or EM interactions are not only perfectly consistent with the non-detection of dark matter in direct detection experiments and the non-detection of DM at the LHC. They are also consistent with the absence of any compelling DM annihilation signature. So, while non-detection of DM in those channels is parameter bounding for DM theories, it certainly doesn't rule out DM that is "sterile" (i.e. that only interacts via gravity) or DM that only interacts with other DM in addition to gravity.

The trouble is that the amount of correlation between inferred DM distributions and baryonic matter distributions is too tight to be explained by gravity alone and the shape of the DM distributions aren't what we would theoretically predict if DM was truly sterile or only interacted with other DM. So, truly sterile DM or DM that only interacts with other DM isn't enough to explain the phenomenology.

May I know what this "correlation" you were referring to that indicates the amount of correlation between inferred DM distributions and baryonic matter distributions is too tight to be explained by gravity alone? Some references directly about it perhaps? Thank you

This leaves you looking for a fifth force that predominantly governs DM-ordinary matter interactions (and possibly also DM to DM interactions), such as the paper described below, in a dark matter particle theory.
Andres Olivares-Del Campo, et al., "Dark matter-neutrino interactions through the lens of their cosmological implications" (November 14 2017).

 

[Arman777]

Particles with no weak, strong or EM interactions are not only perfectly consistent with the non-detection of dark matter in direct detection experiments and the non-detection of DM at the LHC. They are also consistent with the absence of any compelling DM annihilation signature. So, while non-detection of DM in those channels is parameter bounding for DM theories, it certainly doesn't rule out DM that is "sterile" (i.e. that only interacts via gravity) or DM that only interacts with other DM in addition to gravity.

The trouble is that the amount of correlation between inferred DM distributions and baryonic matter distributions is too tight to be explained by gravity alone and the shape of the DM distributions aren't what we would theoretically predict if DM was truly sterile or only interacted with other DM. So, truly sterile DM or DM that only interacts with other DM isn't enough to explain the phenomenology.

This leaves you looking for a fifth force that predominantly governs DM-ordinary matter interactions (and possibly also DM to DM interactions), such as the paper described below, in a dark matter particle theory.
Andres Olivares-Del Campo, et al., "Dark matter-neutrino interactions through the lens of their cosmological implications" (November 14 2017).

It says it solves some problems for CDM also it can simulate on large scales.

But in general it doesn't seem to me a perfect candidate to understand the general description of CDM. As ohwilleke pointed out we need a new model and maybe even a new force.

 

[ohwilleke]

Some references directly about it perhaps? Thank you

Some references can be found in thIs post. I don't specifically mention it there but collisionless bosonic dark matter models also don't work.

 

[bluecap]

Particles with no weak, strong or EM interactions are not only perfectly consistent with the non-detection of dark matter in direct detection experiments and the non-detection of DM at the LHC. They are also consistent with the absence of any compelling DM annihilation signature. So, while non-detection of DM in those channels is parameter bounding for DM theories, it certainly doesn't rule out DM that is "sterile" (i.e. that only interacts via gravity) or DM that only interacts with other DM in addition to gravity.

The trouble is that the amount of correlation between inferred DM distributions and baryonic matter distributions is too tight to be explained by gravity alone and the shape of the DM distributions aren't what we would theoretically predict if DM was truly sterile or only interacted with other DM. So, truly sterile DM or DM that only interacts with other DM isn't enough to explain the phenomenology.

This leaves you looking for a fifth force that predominantly governs DM-ordinary matter interactions (and possibly also DM to DM interactions), such as the paper described below, in a dark matter particle theory.
Andres Olivares-Del Campo, et al., "Dark matter-neutrino interactions through the lens of their cosmological implications" (November 14 2017).

Just for sake of understanding of your "fifth force that predominantly governs DM-ordinary matter interactions (and possibly also DM to DM interactions)", supposed you had a dark matter jacket that somehow got binded to your body and the dark matter jacket weights 50 lbs and you weight 100 lbs.. what would happen if you put yourself in a weighting scale. Would it register 150 pounds or 100 pounds? I know the dark matter jacket won't affect the weighing scale directly and it won't be pull down because the Earth won't attract it.. so I guess it can just cause a drag in your body when you run.. can this drag be measured? In cosmological setting.. what are the results of attempts to measure this drag?

 

[Drakkith]

I know the dark matter jacket won't affect the weighing scale directly and it won't be pull down because the Earth won't attract it..

It would certainly be attracted to the Earth, as dark matter interacts gravitationally with normal matter. If you could somehow attach this jacket to yourself you would find that you weighed more. There would be no drag though, as that requires an EM interaction, which dark matter doesn't have.

 

[bluecap]

It would certainly be attracted to the Earth, as dark matter interacts gravitationally with normal matter. If you could somehow attach this jacket to yourself you would find that you weighed more. There would be no drag though, as that requires an EM interaction, which dark matter doesn't have.

Hmm... don't they make weighing scale in the labs that can measure the dark matter flux by coupling using the fifth force with dark matter moving all around.. it should register different readings.. shouldn't it?

 

[bluecap]

There are two known particles (gravitons and gluons) and one hypothetical one (gravitons) that have no mass, but all of them have energy, and gravity interacts with anything that has mass or energy or both. All Standard Model particles with mass interact via the weak force. All quarks and gluons interact via the strong force. All quarks, charged leptons and massive weak force bosons emit and absorb photons as part of the electro-magnetic force. All Standard Model particles interact via gravity as does the hypothetical graviton.

If something had no mass and also had no energy, it could not have interactions and could not do work because energy is defined as the capacity to do work. Physics is defined so that only things with observable effects are considered. Something that has no interactions and cannot do work can't have any observable effects, ergo, they don't exist.

Are there dark matter candidates which don't contain mass but only pure energy (which can still interact with gravity)?

If a particle has no mass (like photons) it moves at the speed of light... but photons have energy... I mean.. if dark matter contains no mass but only energy.. should it move at speed of light too?

 

[ohwilleke]

Are there dark matter candidates which don't contain mass but only pure energy (which can still interact with gravity)?

If a particle has no mass (like photons) it moves at the speed of light... but photons have energy... I mean.. if dark matter contains no mass but only energy.. should it move at speed of light too?

A massless particle moves at the speed of light which is inconsistent with dark matter which has sub-relativistic speeds (i.e. it is 'warm" or "cold" dark matter, not "hot" dark matter) if it exists in the form of a particle, although massless particles could, in principle be confined in a massive composite particle (e.g. a "glueball"). For the same reason, ordinary neutrinos cannot be dark matter because they are too "hot" which is to say that their average velocity is too large.