Robert McNees
Herb Greenlee and Mel Shochet, representing the DZero and CDF experiments, respectively, simultaneously submitted papers to Physical Review Letters OTD in 1995. They were announcing that their collaborations had discovered the Top quark at Fermilab.
Image: FermiNews newsletter (https://history.fnal.gov/criers/FN_1995_03_17.PDF)
Robert McNees
That week, the meeting announcement for Fermilab's top quark research group read: "Since the top quark has been discovered, there will not be a top group meeting this week."
The top quark was found to have a mass of around 173 GeV/c², making it the heaviest of the six known quarks. It's an unusual value, given the Higgs boson mass of about 125 GeV/c².
Robert McNees
Assuming there isn't new physics out past the energies probed by the current generation of accelerators, these masses are consistent with the electroweak vacuum –– the field configuration that governs many features of the Standard Model of particle physics –– being "metastable."
If that were the case, then the arrangement of particle properties and interactions we're familiar with, would be unstable in the long term against quantum tunneling to a simpler configuration.
Robert McNees
Which is to say, we might exist in a quantum mechanically precarious reality which has the potential (no pun intended) to spontaneously deconstruct itself and revert to a simpler configuration.
It goes without saying that a reality in which the basic rules all change spontaneously, would not be compatible with physics or chemistry or us.
Robert McNees
Luckily, one recent estimate expects the lifetime of the present configuration of the Universe to last for at least 10⁶⁵ years (95% CL). So we've got a while.
Robert McNees
This all changes if there is new physics at higher energies. Stuff we're not yet aware of may shore up the stability of the electroweak vacuum, or it might provide new avenues for the catastrophic decay of everything.
The curiously precarious values of the Higgs and Top Quark masses is known as the "Higgs naturalness problem." It is often invoked as a reason to expect new physics around a TeV. What are the odds we'd occur in a Universe that was only sort of stable, instead of very stable?
Steffen Christensen
@mcnees How does the Higgs couple to other particles giving them mass, Robert?
Do we even know?
Robert McNees
@SnoopJ I agree. This is an simplification of course, but building bigger rings is an unsustainable plan.
SnoopJ
@mcnees it'd be a bit strange if there were new physics at ~1 TeV that LHC hasn't been able to sniff out at an order of magnitude higher CoM energy, but OTOH the Tevatron was definitely making Higgs, we just couldn't see them...
It might be a magnet-design bias, but I have some serious reservations about plans to push to higher energies just to see what's out there (i.e. FCC-hh), it feels like we should at least have an expected science case.
Maybe HL-LHC could find something, though?
Robert McNees
@Wikisteff We do! There is a very specific sort of coupling between the Higgs and fundamental fermions known as a Yukawa coupling. The value of the coupling for each particle determines its mass. (For composite particles, like protons, the Higgs is responsible for only a fraction of the mass.) We don’t know why these Yukawa couplings take the values they take; they are inputs of the Standard Model.
Robert McNees
@StrangeNoises @cstross Maybe we will find out! Or wait, maybe we will not find out? Or, uh… wont not find out?
Robert McNees
@cstross Never say never!
Charlie Stross
@mcnees So pleased we're probably not going to spontaneously vanish in a puff of exotic radiation due to a random quantum fluctuation erasing the universe we exist in and overwriting it with a simpler version ... at least, not any time soon!
Robert McNees
It seems, at the very least, a bit unjust.
Alexander Knochel
@mcnees My reaction to these stability calculations went the opposite way, as a reason for pessimism: if there were a considerable TeV scale modification to the SM, our position at the metastability bound of the higgs self coupling would be pure coincidence and meaningless. Only if there is no serious modification to the SM below the GUT scale can I think of reasons why we would be near metastability, either anthropic, from symmetry as in our 2012 papers, or from RG like Wetterich/Shaposhnikov
Christian Schwägerl
dbrand666
@mcnees
*... we might exist in a ... precarious reality which has the potential (no pun intended) to spontaneously deconstruct itself and revert to a simpler configuration"
You know... there are days I would welcome a little of that.
Steffen Christensen
@mcnees Cool!
How does a set of Yukawa coupling parameters for each fundamental particles provide more explanatory value than a set of arbitrary masses of fundamental particles?
Debbie Goldsmith 🏳️⚧️🏳️🌈
@mcnees If the many-worlds interpretation is correct, then vacuum decay is another form of the quantum suicide experiment: it could already have happened for some fraction of the wave function.
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