Does a fundamental scalar field (the Higgs field) permeate all of space and give elementary particles their mass through their interaction with it, as predicted by electroweak theory in the 1960s?
#quantum
Post a problemDo isolated magnetic north or south poles (magnetic monopoles) exist as fundamental particles, as predicted by some grand unified theories, or is magnetic charge always found in inseparable north-south pairs as observed so far?
Why did every experiment from the 1960s through the 1990s detect only about one-third to one-half of the electron neutrinos from the Sun's fusion reactions that Standard Solar Model calculations predicted?
Can a dilute gas of atoms be cooled and compressed into a single, coherent quantum state (a Bose-Einstein condensate), and how well does phase-transition theory describe such ultracold systems?
Do neutrinos have mass and change ('oscillate') between flavor types as they travel, explaining why fewer solar and atmospheric neutrinos than expected reach detectors on Earth?
What does quantum mechanics actually tell us about physical reality — is the wavefunction real, does measurement cause genuine collapse, and could hidden variables restore classical determinism?
In the classic Millikan oil-drop experiment, tiny charged droplets are also jostled by random molecular collisions (Brownian motion): how much does this fundamentally limit the precision of measuring the electron's charge this way?
Proton radius puzzle
Research level
Why did early 2010s measurements of the proton's charge radius using muonic hydrogen come out about 4% smaller than the previously accepted value from electron-based measurements, and which value is correct?
Internal structure of pentaquarks and exotic hadrons
Research level
Now that pentaquark particles (five-quark states) have been confirmed to exist, are they tightly bound compact five-quark objects, or loosely bound 'molecules' of a meson and a baryon stuck together, and which quark combinations are actually possible?
Hadron mass spectrum, QCD, and the quark-gluon plasma
Research level
Can the masses of protons, neutrons and other hadrons be computed from the underlying quark-gluon theory (QCD), and can the free quark-gluon plasma believed to have filled the early universe be created and studied in the laboratory?
Electroweak unification and the Higgs boson
Research level
Does the electroweak theory unifying electromagnetism and the weak nuclear force correctly predict a Higgs boson responsible for elementary-particle masses, and can that particle actually be found?
CP violation and the matter-antimatter asymmetry
Research level
Where and how strongly does nature violate the combined charge-parity (CP) symmetry, and can the observed amount explain why the universe is made of matter rather than antimatter?