The Standard Model has been very successful so far, and its latest success has been the discovery of the Brout-Englert-Higgs-Hagen-Guralnik-Kibble (BEHHGK) or Brout-Englert-Higgs (BEH) or Higgs particle, the first-known non-composite spin-0 particle.
But it has some deficiencies, both empirical and theoretical.
Empirical
There are still lots of things that don't fit.
Neutrino masses. Inferred from neutrino oscillations.
Matter-antimatter asymmetry. Requires baryon-number and lepton-number violation associated with C and CP violation (= time-symmetry violation), the "Sakharov criteria".
Gravity. The most successful theory so far is general relativity, a theory that can be interpreted as a gauge theory of space-time transformations. However, it's very hard to quantize.
Dark matter. Its only firm evidence is gravitational, and so far, it's most consistent with being Weakly Interactive Massive Particles (WIMP's). Nongravitational evidence has been claimed by some direct-detection experimenters and by the Fermi-telescope team, but neither looks very strong.
Dark energy. Its only evidence is also gravitational, where it acts like the cosmological constant.
Inflation. A phase of exponential expansion early in the Universe's history, when a spin-0 field acted like the cosmological constant. It ended with the field's energy getting dumped into ordinary particles ("reheating"). That field has been named the "inflaton" (no second i).
Theoretical
Sources of neutrino masses. If these are due to the Higgs mechanism, then they require very tiny Higgs coupling constants. An alternative is the seesaw model, where the Higgs mechanism coexists with right-handed neutrinos having large Majorana masses of 10^(12) GeV or so.
Strong CP violation. QCD can violate CP, but nucleons' electric dipole moments provide a strong upper limit. So it's either (1) very fine-tuned or (2) with an additional particle, the axion.
Higgs-particle instability. If one extrapolates to higher energies while adding no new particles along the way, one finds that our Higgs-vacuum state becomes unstable. But it has a rather sensitive dependence, and the decay time is longer than the lifetime of the Universe for typical parameter values. If it had a supersymmetry partner, that would stabilize it.
Elementary-fermion unification. Some of the simpler Grand Unification Theories are remarkably successful. SU(5) makes every generation 2 multiplets, and SO(10) makes each one 1 multiplet, though with right-handed neutrinos.
Gauge unification. The gauge-coupling constants converge at high energies. The convergence is best if the SM particles have TeV-scale SUSY partners (the MSSM), only a few percent at about 2*10^(16) GeV.
Prospects for improving?
Neutrino experiments have been improving, and we are likely to get a good handle on their masses and mixing angles. Experiments like neutrinoless beta decay will also help, though they still have yet to go down to expected values for massive neutrinos.
Measurements of nucleon electric dipole moments are steadily pushing down their upper limits, though they are still far above the Standard Model's predictions.
Proton decay, if observed, will give us some clues about GUT's, since the current lower limits on its mean life press into GUT energies. Both flavors of nucleon, protons and neutrons, will decay in this fashion, though it will only be observable if they are in otherwise-stable combinations.
Dark-matter detectors are steadily being improved, with the direct detectors using several different materials. If DM is detected with more than one detector, then their different responses may provide clues as to its nature. Silicon (Z = 14), for instance, has 1 neutron per proton, and tungsten (Z = 74) 1.5 neutrons per proton. So relative performance with silicon and tungsten-compound detectors may tell us how much DM bounces off of protons and neutrons.
Improvements in high-energy gamma-ray telescopes will also help resolve the question of DM annihilation radiation.
When the LHC restarts, it will be operating at twice the energy, advancing further into the possible masses of SUSY particles. A big challenge will be detecting the non-colored ones, those other than squarks and gluinos, since they will be produced at a much lower rate.
Improving observations of the cosmic microwave background may eventually make possible detection of inflation-generated gravitational waves. These will provide further clues as to how inflation ended, clues now emerging from the departure of the primordial-fluctuation spectrum from its steady-state value.
One can make improvements elsewhere also, like improving observations of post-Newtonian gravitational effects to compare to GR. But it will be difficult to improve in some places, like matter-antimatter asymmetry.
So we have a lot to look forward to.
But it has some deficiencies, both empirical and theoretical.
Empirical
There are still lots of things that don't fit.
Neutrino masses. Inferred from neutrino oscillations.
Matter-antimatter asymmetry. Requires baryon-number and lepton-number violation associated with C and CP violation (= time-symmetry violation), the "Sakharov criteria".
Gravity. The most successful theory so far is general relativity, a theory that can be interpreted as a gauge theory of space-time transformations. However, it's very hard to quantize.
Dark matter. Its only firm evidence is gravitational, and so far, it's most consistent with being Weakly Interactive Massive Particles (WIMP's). Nongravitational evidence has been claimed by some direct-detection experimenters and by the Fermi-telescope team, but neither looks very strong.
Dark energy. Its only evidence is also gravitational, where it acts like the cosmological constant.
Inflation. A phase of exponential expansion early in the Universe's history, when a spin-0 field acted like the cosmological constant. It ended with the field's energy getting dumped into ordinary particles ("reheating"). That field has been named the "inflaton" (no second i).
Theoretical
Sources of neutrino masses. If these are due to the Higgs mechanism, then they require very tiny Higgs coupling constants. An alternative is the seesaw model, where the Higgs mechanism coexists with right-handed neutrinos having large Majorana masses of 10^(12) GeV or so.
Strong CP violation. QCD can violate CP, but nucleons' electric dipole moments provide a strong upper limit. So it's either (1) very fine-tuned or (2) with an additional particle, the axion.
Higgs-particle instability. If one extrapolates to higher energies while adding no new particles along the way, one finds that our Higgs-vacuum state becomes unstable. But it has a rather sensitive dependence, and the decay time is longer than the lifetime of the Universe for typical parameter values. If it had a supersymmetry partner, that would stabilize it.
Elementary-fermion unification. Some of the simpler Grand Unification Theories are remarkably successful. SU(5) makes every generation 2 multiplets, and SO(10) makes each one 1 multiplet, though with right-handed neutrinos.
Gauge unification. The gauge-coupling constants converge at high energies. The convergence is best if the SM particles have TeV-scale SUSY partners (the MSSM), only a few percent at about 2*10^(16) GeV.
Prospects for improving?
Neutrino experiments have been improving, and we are likely to get a good handle on their masses and mixing angles. Experiments like neutrinoless beta decay will also help, though they still have yet to go down to expected values for massive neutrinos.
Measurements of nucleon electric dipole moments are steadily pushing down their upper limits, though they are still far above the Standard Model's predictions.
Proton decay, if observed, will give us some clues about GUT's, since the current lower limits on its mean life press into GUT energies. Both flavors of nucleon, protons and neutrons, will decay in this fashion, though it will only be observable if they are in otherwise-stable combinations.
Dark-matter detectors are steadily being improved, with the direct detectors using several different materials. If DM is detected with more than one detector, then their different responses may provide clues as to its nature. Silicon (Z = 14), for instance, has 1 neutron per proton, and tungsten (Z = 74) 1.5 neutrons per proton. So relative performance with silicon and tungsten-compound detectors may tell us how much DM bounces off of protons and neutrons.
Improvements in high-energy gamma-ray telescopes will also help resolve the question of DM annihilation radiation.
When the LHC restarts, it will be operating at twice the energy, advancing further into the possible masses of SUSY particles. A big challenge will be detecting the non-colored ones, those other than squarks and gluinos, since they will be produced at a much lower rate.
Improving observations of the cosmic microwave background may eventually make possible detection of inflation-generated gravitational waves. These will provide further clues as to how inflation ended, clues now emerging from the departure of the primordial-fluctuation spectrum from its steady-state value.
One can make improvements elsewhere also, like improving observations of post-Newtonian gravitational effects to compare to GR. But it will be difficult to improve in some places, like matter-antimatter asymmetry.
So we have a lot to look forward to.
via JREF Forum http://forums.randi.org/showthread.php?t=263630&goto=newpost
Aucun commentaire:
Enregistrer un commentaire