Why do scientists think Higgs fields is metastable? I have recently learn and read some articles about the false vacuum in quantum fields theory.
I wanted to know why scientists think that Higgs field could be in a metastable state instead of vacuum state like the others fields.
Can anyone explain me why ?
Vacuum state are when fields or particles have their lowest energy level possible
Metastable state are when the fields or particles reach a lower level but not the lowest one.
Am i right ?
Thank in advance, Creekorful
 A: 
I have recently learn and read some articles about the false vacuum in quantum fields theory.

Here is a definition:

In quantum field theory, a false vacuum is a metastable sector of space that appears to be a perturbative vacuum, but is unstable due to instanton effects that may tunnel to a lower energy state



A scalar field φ in a false vacuum. Note that the energy E is higher than that in the true vacuum or ground state, but there is a barrier preventing the field from classically rolling down to the true vacuum. Therefore, the transition to the true vacuum must be stimulated by the creation of high-energy particles or through quantum-mechanical tunneling.

The existence of a false vacuum  is a hypothesis that some theories may use, but it is not the Higgs mechanism.

I wanted to know why scientists think that Higgs field could be in a metastable state instead of vacuum state.

The Higgs field is not metastable in the sense of a false vacuum. It is dependent on the energy available and is symmetric for high enegies of the interactions involved ( order of 100 GeV) , and broken for lower energies.
An example of symmetry breaking analogous to what happens with the Higgs field:


Spontaneous symmetry breaking simplified: – At high energy levels (left) the ball settles in the center, and the result is symmetrical. At lower energy levels (right), the overall "rules" remain symmetrical, but the "Mexican hat" potential comes into effect: "local" symmetry is inevitably broken since eventually the ball must roll one way (at random) and not another.

At each energy the vacuum is stable, it is not a false vacuum. The difference between the vacuum for the other fields , like the electron field and the photon field, is in the vacuum expectation value.

In quantum field theory the vacuum expectation value (also called condensate or simply VEV) of an operator is its average, expected value in the vacuum.

For all other particles the vacuum expectation value in the standard model is zero, for the Higgs it is 246GeV, at the broken state . 
The conditions for symmetry existed at the beginning of the universe, according to the Big Bang model. The symmetry is broken at about 10^-10 seconds in the life of the universe (temperatures correspond to 100 GeV) and the Higgs field acquires the large vev.
