Topics discussed in the Lectures 11/6-11/15 for Graduate Nuclear Physics 
(PHYS722/822 Fall 2018)

Lecture 1

Nucleon-Nucleon Interaction Models

  1. Gluon and Quark exchange, plus Pauli-repulsion between like quarks in overlapping nucleons
    1. Gluon exchange based on Constituent Quark model plus 1-gluon exchange potential - not a good description for reasonable distances (because of confinement of non-color singletts)
    2. Pauli repulsion related to minimum energy to excite a nucleon (i.e. to move a quark into a different state) of 300 MeV
    3. Quark exchange between nucleons can change their charge (p->n and at the same time n->p)
    4. Gives reasonable (semi-quantitative) description of short range repulsive part of the nucleon-nucleon potential (plus maybe intermediate range)
  2. Quark-antiquark pair (= meson) exchange
    1. Similar to quark exchange (just reverse direction of one quark in time)
    2. Very good description of many aspects of NN potential
    3. Preferred because meson states are color-neutral and have relatively low mass (longer range)
    4. E.G.: pion mass = 140 MeV corresponds to range of 1.4 fm
    5. Will study one-pion exchange potential (OPEP) and generalizations to other mesons - so far only model that gives perfect agreement with data, especially long range part
  3. Chiral Symmetry and ChPT
    1. Based on chiral symmetry of QCD Lagrangian (quarks of opposite helicity are indistinguishable and don't couple to each other except for their masses)
    2. Chiral symmetry is spontaneously broken (because QCD prefers quark-antiquark pairs with negative parity over quark-quark pairs with positive ones). Consequence: Low (theoretically, zero) mass modes of the "quark condensate" called Goldstone bosons (pions, kaons and etas). This constrains the Lagrangian for processes involving nucleons and pseudoscalar mesons.
    3. Chiral symmetry is also violated by the (small) quark masses, so Goldstone bosons are not totally massless. But one can expand the interaction in small parameters like mp/mN to make definite predictions (Chiral Perturbation Theory).
  4. Effective Field Theory (EFT) approaches
    1. Describe Nature on different, separate length and mass scales without using underlying theory except for its symmetries
    2. Example: Chiral symmetry, see above
    3. In the context of NN interaction, EFT means applying all symmetries (including chiral symmetry) of the QCD lagrangian but not explicitely taking into account underlying degrees of freedom like pions or quarks. This gives a most general lagrangian which contains many parameters one can constrain with data.
  5. General form of potential allowed by symmetries like rotation, translation, isospin,... (see Wong)
    1. Somewhat in the same spirit as EFT, but much older and restricted to space-time and isospin symmetries
    2. 4 important terms: Central potential V(r), spin-spin (ss) interaction, spin-orbit (Ls) interaction and tensor (S12) interaction.
    3. Each term occurs twice: once without isospin dependence, and once with t1.t2 (which measures total isospin of NN combination). The latter terms are responsible for charge-changing pion exchange etc.
    4. Tensor term is important for long-range part of potential and arises "naturally" from pion exchange. QED analogy: magnetic dipole-dipole interaction

Lecture 2

NN potentials and phase shifts continued

Lecture 3

The deuteron - ground state properties

If/as time permits:

Lecture 4

Few body nuclei (A = 2,...,8) - ground state properties

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