At high enough temperature all elementary particles become massless?

[Silvestru]

I was reading that in the early universe, the temperature was above the electroweak symmetry breaking scale so particles probably had no mass.

Would this theoretically be possible to reproduce in a laboratory? Raising the temperature (somehow) of an elementary massive particle so that it becomes massless?

https://arxiv.org/pdf/1512.08749.pdf

(I understand that the reason particles had no mass is because of the Higgs field that could not give mass to particles and not that the particles had a high temperature. So my question is not if we can raise the temperature of the particle but somehow "block" the effect of the Higgs field.)

 

Edited April 12, 2018 by Silvestru

[swansont]

AFAIK, massive particles didn't exist. Quarks and electrons were created after it cooled (but it only took a small fraction of a second to cool to that point)

[timo]

In a sense, getting to massless SM particles could be achieved by increasing the temperature in some region. But it would be more like an activation of the frozen Higgs field than a blocking. It is easier to explain coming from the high-energy side (high temperature), since that is the standard explanation for the Higgs mechanism:

 

The Higgs proto-field (*) can be considered as an additional particle class to a Standard Model in which all of the other Standard Model particles are massless (**). It interacts with most of the other particle fields. But it also has a weird self-interaction which causes the energetically lowest state to not be at "no proto field" but at "some value of the proto-field". At low temperatures, where the Higgs proto-field is just lying around in its minimum, this means that the dynamic interaction terms of the Higgs proto-field with the other particles become some dull interaction of those particles with some sticky stuff that seems to lie around everywhere (***). In the mathematical description of the Standard Model time evolution, the associated terms that originally were terms of a dynamic interaction now become the mass terms for the other particles. If the minimum was at "no field", they would simply drop out (****).

 

This "low-energy" limit actually covers almost all of the temperature ranges we can create on earth, and only recently did we manage to even create and see a few excitations of the Higgs proto-field around its minimum in specialized, very expensive experiments (-> confirmation of the Higgs-Boson at the LHC). So technically, I think we are very far away from creating the "massless particles" state in an experiment. But there is no theoretical reason why this would not be possible (*****). But as described, I would understand it to be less of a shielding of the Higgs field and more of an activation. And as a state with such a high amount of  interaction between the fields. So I am not even sure if the common view of a few particles flying through mostly empty space and only rarely kicking into other free-flying particles would still make sense.

 

Remarks:

(*) I would just call it Higgs-field(s), but since the paper you cited seems to explicitly avoid using the name at this stage I may be wrong about common usage of the terms. Haven't been working in the field for over ten years. So I have invented the term proto-field for the scope of this post - it is also easier to understand than "doublet of complex scalar fields".

(**) This is not exactly true because the particles are mixed and get renamed under the Higgs mechanism. But I'll pretend that does not happen for the sake of providing an answer that is easier to understand than reading a textbook.

(***) Sidenote: In this state, the few excitations of the Higgs proto-field around its minimum are the infamous Higgs Boson.

(****) Which is why you can always invent new fields that just happen to have no effect on anything we can see but magically make your particle cosmology equations work at very, very high energies

(****) Except for the fact that some people still expect new physics and associated new particles at such high temperatures, which then again would have mass from another Higgs-like mechanism

 

[YaDinghus]

@Timo this is actually the best explanation of the Higgs Mechanism I've read so far. The Higgs Mechanism has eluded me, and I usually understand everything

[Strange]

Excellent post @timo 

On 23/05/2018 at 3:42 AM, timo said:

(**) This is not exactly true because the particles are mixed and get renamed under the Higgs mechanism. But I'll pretend that does not happen for the sake of providing an answer that is easier to understand than reading a textbook.

Is this mixing the same thing we see with the mass/types of neutrinos? So does it mean that in this "massless era", the particles we know and love would not exist as the separate entities we see now, but as various permutations of those properties?

[Mordred]

The Higgs interaction with the neutrino mixing is what gives rise to the mass value to those neutrinos. As the mass value is one of the properties in particle identification then without that mass value it wouldn't exist as that particular type of neutrino. The Higgs field is oft treated as 4 seperate fields each dealing with each individual mixing angle with the three neutrinos and 1 left unused. 

 That being said another factor is the temperatures involved during EWSB is also high enough many of the SM particles would be indistinquishable from one another via thermal equilibrium.

 A side note this is one of the possible processes involved in Higgs inflation which instead of requiring an inflaton would be explainable as a thermal phase transition.

 The paper being focussed on the Higgs interaction during EWSB doesn't detail thermal equilibrium but under cosmology this process is also occuring.

 Prior to inflation the quark gluon plasma state Swansont mentioned above is a thermal equilibrium state which would exist at this time.

Edited May 24, 2018 by Mordred

[Silvestru]

On 23/05/2018 at 3:42 AM, timo said:

In a sense, getting to massless SM particles could be achieved by increasing the temperature in some region. But it would be more like an activation of the frozen Higgs field than a blocking. It is easier to explain coming from the high-energy side (high temperature), since that is the standard explanation for the Higgs mechanism........

Thank you timo . You even answered some questions that I would follow after the first ones.

I love this "remarks" section for longer answers. More people should start doing this when things get cloudy.

I think you forgot to add your remark for point 5 "(*****)". Was it like a "Easter egg" or a "Trailer" for your next post haha.

Edited May 24, 2018 by Silvestru