Beyond the Standard Model (New Physics “NP”)

Beyond the Standard Model(New Physics “NP”) Brian Meadows University of Cincinnati Brian Meadows, U. Cincinnati.

Outline • Grand Unification • Super-Symmetry • Neutrinos • Strings and Things • Particle Cosmology Brian Meadows, U. Cincinnati

Reminder: Success of electro-weak unification suggested to try to include strong The plot illustrates “running” of: Idea is that couplings converge at some high m (´ q) ¼ 1015 GeV2 The “GUT scale” is different for different GUT theories In all theories, all three interactions have a common coupling strength at the GUT scale energy Differences emerge at lower energies. Assumption is that nothing else intervenes betweenm2=MZ2andm2=GUT2 Grand Unification (GUT) “GUT scale” Brian Meadows, U. Cincinnati

Simplest way to combine QCD and EW(Georgi and Glashow): Incorporate leptons and quarks into families. E.g. “Left-handed”d quark with e and ne Gluons still convert one color to another Change color Change charge “Lepto-quarks” M2~ 1015 GeV2 • This also allows quarks to convert into/from leptons. • Leads to two new “lepto-quarks”XandYwith Change quark$ lepton Grand Unification (GUT) One coupling: aU = gU2/4p ~ 1/42 Brian Meadows, U. Cincinnati

Structure of Georgi and Glashow GUT • Theory is based on the group SU(5) with sub-groups: • SU(3)color • SU(2)L U(1)Y • First family is a {5}: • Other family is a {10}: • There are 24 gauge bosons: Brian Meadows, U. Cincinnati

Charges in Georgi and Glashow GUT • Theory requires that sum of charges in a “family” = ZERO: “Explains” why charge of d is –1/3 e : • First family is a {5}: • So 3Qd + e = 0 •  Qd = -1/3e • Can be shown also that • Qu = +2/3e  Qp = Qe (charge balance in baryonic matter !!) Brian Meadows, U. Cincinnati

Weinberg Angle qW • The ratio of couplings at low mass (~MZ) can be computed in terms of: • GUT scale MX ~ 1015and • aU = 1/42  sin2qW = 0.21 (experimental result is ~ 0.28) gs 0.10 g g’ 0.05 gs 0.10 g 0.05 g’ Brian Meadows, U. Cincinnati

Baryon Number Conservation ? • A feature of a GUT is that quarks can decay: • The vertices indicate that the quantity (NOT B) is conserved. Change quark$ lepton Brian Meadows, U. Cincinnati

d e+ d e+ u e+ Y X Y u u u u d u u u u u u u Proton Decay • Since baryon number is not conserved, protons can decay: • For example: p  e+ + p0 • Also: p  e+ + ne + + Change quark$ lepton Brian Meadows, U. Cincinnati

d e+ d e+ X u u u u Proton Lifetime • At proton mass, MX is extremely large, so can approximate • In analogy with the Fermi 4-Fermion coupling: • Proton lifetime (very sensitive to MX): BY Using E = Mp (proton mass) MX ~ 1015 GeV/c2 gU2/4 ~ 1/42 Brian Meadows, U. Cincinnati

Proton Decay Rate • For a lifetime of 1032 years, means there will be one proton decay per year in 300 tons of iron !! • Super-Kamiokande (in Japan) has searched for • Upper limit is quoted as • Giorgi-Glashow model predicts branching fraction: • Super-Symmetry predicts ~1032-1033 years, however. 0  ,  e+e-  Much Cherenkov light !! Appears to rule out this model Brian Meadows, U. Cincinnati

Super-Symmetry • Zumino and Wess (1974) introduced a symmetry involving scalar Boson and spin-½ Fermi fields  and , respectively • Particles have same mass if symmetry is unbroken • In fact, symmetry is badly broken, and SS particles are probably much more massive than their SM counterparts. • This implies that each SM Boson particle has a “supersymmetric” Fermion partner whose spin differs by ½ (and vice-versa). Brian Meadows, U. Cincinnati

Super-Symmetric Particles Brian Meadows, U. Cincinnati

Problems Solved by Super-Symmetry • Three major problems are solved by Super-Symmetry: • The introduction of new particles modifies the energy dependence of the three running coupling constants • “Hierarchy problem”: Loop corrections to the Higgs mass, when re-normalized, lead to a very large mass unless fine-tuning of the parameters is done. Boson and Fermion loops carry opposite signs, so cancellation is more natural. 3. Lightest, neutral super-symmetric particle, the , is a sensible candidate for dark matter. Brian Meadows, U. Cincinnati

Problems Solved by Super-Symmetry ALSO • Super-symmetry can lead to better agreement between the prediction of sin W and also of p (the proton lifetime). • The SM is unable to describe large enough CP violationto account for the asymmetry of matter and anti-matter. • The new particles lead to new CKM angles that can, potentially, introduce much more CP violation into the universe. Brian Meadows, U. Cincinnati

The Neutralino • Lightest, neutral Super-particle is (the neutralino) • A linear combination of • Most versions of SS require that Super-particles are produced in pairs. Therefore, decay of a Super-particle must lead to a Super-particle in the final state. • This implies, therefore, that the cannot decay • is a good candidate for “Dark Matter” Brian Meadows, U. Cincinnati

Detection of Super-Symmetric Particles • A simple way to produce Super-particles is followed by the decays • It is assumed that: • At high enough energy (e.g. at the ILC) production of pairs will have a cross-section that is comparable to that of ordinary pairs • The Super-particles will decay very rapidly (before reaching the detector) • The ‘s do not interact in the detector, since their interaction with ordinary matter is very weak. • Then events are recognized by • A large missing energy (average ~½ the total available) • A large missing 3-momentum • At the LHC, production is from pairs rather than Brian Meadows, U. Cincinnati

Beyond the Standard Model (New Physics “NP”)