Final ExamFrom the last time…Symmetry and Symmetry breakingMassWhat is mass?Mass in the SMMass and the Higgs fieldThe Higgs bosonThe Higgs BosonHow can we ‘see’ the Higgs?Grand Unified TheoriesNot all that easySlide 13The price of unificationBeyond the standard model?What does the SM say?Grand Unified Theories: GUTsUnifications: now and the futureFermions and bosonsSupersymmetry (SuSy)Supersymmetry SuccessesChecklist SUSYGravityEinstein’s gravityGravity QuestionKaluza-Klein: EM & gravityExtra dimensions?Compactificaton in Kaluza-KleinQFT and GR don’t mixChecklist Kaluza-KleinString theoryPowerPoint PresentationSlide 33Scales we can probeString InteractionsSome problemsResults of the theorySuperstringsExtra dimensions in string theoryChecklist String TheoryPhy107 Fall 20061Final Exam•Thursday, Dec. 21: 2:45 - 4:45 pm113 Psychology Building•Note sheet: one double-sided page•Cumulative exam-covers all material, 40 questions–11 questions from exam 1 material–11 questions from exam 2 material–11 questions from exam 3 material–7 questions from post-exam 3 materialCourse evaluation Wednesday, Review FridayStudy Hint: download blank hour exams from web site and take them closed-book, with note sheet only. Solution for Exams will all be posted this week.Phy107 Fall 20062•The forces–Matter particles interact via the forces according to the types of charge they carry.–Each force carried by a particle.–Matter particles are fermions, force carriers are bosons. Described by quantum field theories.•Unification–Noticed that electromagnetic force and weak force carried by Z boson are nearly identical.–At high energy they are identical. Same types of interactions and same strength–Requires an extra particle. The Higgs boson.From the last time…Phy107 Fall 20063Symmetry and Symmetry breaking•The standard model says that at high energies, this symmetry is apparent–We see a single electroweak interaction.–Zo and interact exactly the same way with the same strength.•At low energies the symmetry is broken–We see distinct electromagnetic and weak interactions•However needs one more element. Something to give the W and Z massPhy107 Fall 20064Mass•Here’s the experimental masses of SM particles.•Original SM gives zero mass for all particles.•But can give particles mass by coupling to a new field, the Higgs field.•Higgs boson is the (unobserved) quanta of the Higgs field.Phy107 Fall 20065What is mass?•Think of inertial mass: –inertial mass is a particle’s resistance to changes in velocity. •When you apply the same force to particles, the smaller the mass, the larger the acceleration.•What is the origin of mass?Phy107 Fall 20066Mass in the SM•In the standard model (SM),particles have mass because they interact with something that pervades the universe.This something is the Higgs fieldParticles ‘hit’ the Higgs field when you try to accelerate themMass = (chance of hit) x (Higgs density)Coupling constantPhy107 Fall 20067Mass and the Higgs fieldImagine a party in a room packed full of people.Now a popular person enters the room, attracting a cluster of hangers-on that impede her motionshe has become more massivePhy107 Fall 20068The Higgs bosonThe Higgs boson is a quantum excitation of the Higgs field.In analogy, suppose an interesting rumor is shouted in thru the door.The people get quite excited.They cluster to pass on the rumor, and the cluster propagates thru the room.Looks very similar to the popular/massive person who entered the roomGood way to think of other quantum excitations. All the other force carriersPhy107 Fall 20069The Higgs BosonHow much mass do you thing the Higgs Boson hasA. No massB. Light like an up or down quarkC. Very massive like a top quarkPhy107 Fall 200610How can we ‘see’ the Higgs?e-Zoe+HZo•The Higgs boson needs to be created in order to see it. E = mc2•Not found yet•mH > 114GeV•mH < 186GeVPhy107 Fall 200611Grand Unified Theories•What do we really need to unify particle physics?•Maxwell unified the electric and magnetic interactions into electromagnetic (EM)•The standard model unified the EM and weak interactions into the electroweak interaction•Start with the strong force.•What kind of theory is needed to unify this?Phy107 Fall 200612Not all that easyPhy107 Fall 200613Grand Unified Theories•Flavor changing interactions in quarks(e.g. changing a top quark to a bottom quark by emitting a W+) suggest that quarks can be viewed as different ‘orientations’ of the same object.•Have found the same thing for leptons.•But maybe there should be a lepto-quark field?–Quarks could turn into leptons, leptons into quarks–All matter particles would be different ‘orientations’ of the same fundamental object.•If we unify leptons and quarks then weak and strong forces may be shown to be two aspects of one force.Phy107 Fall 200614The price of unification•When the SM unified EM and weak interactions, we ended with more force-carrying bosons (e.g. the Zo)•This is because our fundamental ‘particle’ increased in complexity–e.g. from an electron to an electron-neutrino pair•If our ‘particle’ now encompasses both leptons and quarks, the interaction also becomes more complex.•In one particular GUT, we get 24 exchange bosons (W+,W-,Z0, photon, 8 gluons, and 12 new ones)Phy107 Fall 200615Beyond the standard model?•Standard model has been enormously successful.•Consistent picture of particles and their interactions.•Predictive power with unusual accuracy.•Questions:–Why 3 generations?–What determines all the mass values and interaction strengths?–Can we relate the quarks and leptons and the forces?Phy107 Fall 200616What does the SM say?•We can calculate how interactions would work at energies like those of the big bang. –The results don’t make sense.•Astrophysics observations indicate that there is more mass in the galaxy and universe than we can see: Dark Matter –No standard model particle could explain this.•All the standard model interactions create electrons and positrons or quarks and antiquarks in pairs. –However, everything around us is made of quarks and electrons. Where did the positrons and antiquarks go?None of these things can be explained by the SM!Phy107 Fall 200617Grand Unified Theories: GUTs•Unify all the forces: strong force and
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