NGB and their parameters

1. NGB and their parameters Gradient expansion: parameters of the NGB’s Masses of the NGB’s The role of the chemical potential for scalar fields: BE condensation Dispersion relations for the gluons

2. Hierarchies of effective lagrangians Integrating out heavy degrees of freedom we have two scales. The gap Dand a cutoff, d above which we integrate out. Therefore: two different effective theories, LHDET and LGolds

3. Gradient expansion: NGB’s parameters Recall from HDET that in the CFL phase and in the basis

4. Propagator Coupling to the U(1) NGB: Invariant couplings

5. Consider now the case of the U(1)B NGB. The invariant Lagrangian is: At the lowest order ins generates 3-linear and 4-linear couplings

6. Generating functional:

7. At the lowest order:

8. Feynman rules For each fermionic internal line For each vertex a term iLint For each internal momentum not constrained by momentum conservation: Factor 2x(-1) from Fermi statistics and spin. A factor 1/2 from replica trick. A statistical factor when needed.

9. + Goldstone theorem: Expanding in p/D:

10. CFL

11. For the V NGB same result in CFL, whereas in 2SC 2SC With an analogous calculation:

12. Dispersion relation for the NGB’s Different way of computing: Current conservation:

13. Masses of the NGB’s QCD mass term:

14. Calculation of the coefficients from QCD Mass insertion in QCD Effective 4-fermi Contribution to the vacuum energy

15. Consider: Solving for as in HDET like chemical potential

16. Consider fermions at finite density: as a gauge field A0 Invariant under: Define: Invariance under:

17. The same symmetry should hold at the level of the effective theory for the CFL phase (NGB’s), implying that The generic term in the derivative expansion of the NGB effective lagrangian has the form

18. Compare the two contribution to quark masses: kinetic term mass insertion Same order of magnitude for since

19. The role of the chemical potential for scalar fields: Bose-Einstein condensation A conserved current may be coupled to the a gauge field. Chemical potential is coupled to a conserved charge. The chemical potential must enter as the fourth component of a gauge field.

20. Complex scalar field: breaks C negative mass term Mass spectrum: For m< m

21. At m = m, second order phase transition. Formation of a condensate obtained from: Charge density Ground state = Bose-Einstein condensate

22. Mass spectrum At zero momentum

23. At small momentum

24. Back to CFL. From the structure First term from “chemical potential” like kinetic term, the second from mass insertions

25. For large values of ms: and the masses of K+and K0 are pushed down. For the critical value masses vanish

26. For larger values of ms these modes become unstable. Signal of condensation. Look for a kaon condensate of the type: (In the CFL vacuum, S = 1) and substitute inside the effective lagrangian positive contribution from mass insertion negative contribution from the “chemical potential”

27. Defining with solution and hypercharge density

28. Mass terms break original SU(3)c+L+Rto SU(2)IxU(1)Y. Kaon condensation breaks this to U(1) breaking through the doublet as in the SM Only 2 NGB’s from K0, K+ instead of expected 3 (see Chada & Nielsen 1976)

29. Chada and Nielsen theorem: The number of NGB’s depends on their dispersion relation If E is linear in k, one NGB for any broken symmetry If E is quadratic in k, one NGB for any two broken generators In relativistic case always of type I, in the non-relativistic case both possibilities arise, for instance in the ferromagnet there is a NGB of type II, whereas for the antiferromagnet there are to NGB’s of type I

30. Dispersion relations for the gluons The bare Meissner mass The heavy field contribution comes from the term

31. Notice that the first quantized hamiltonian is: Since the zero momentum propagator is the density one gets spin

32. Gluons self-energy Vertices from Consider first 2SC for the unbroken gluons:

33. Bare Meissner mass cancels out the constant contribution from the s.e. All the components of the vacuum polarization have the same wave function renormalization Dielectric constant e = k+1, and magnetic permeabilityl =1

34. Broken gluons

35. But physical masses depend on the wave function renormalization Rest mass defined as the energy at zero momentum: The expansion in p/D cannot be trusted, but numerically

36. In the CFL case one finds: from bare Meissner mass Recall that from the effective lagrangian we got: implying and fixing all the parameters.

37. We find: Numerically

38. LOFF phase Different quark masses LOFF phase Phonons

39. Different quark masses We have seen that for one massless flavors and a massive one (ms), the condensate may be disrupted for The radii of the Fermi spheres are: As if the two quarks had different chemical potential (ms2/2m)

40. Simulate the problem with two massless quarks with different chemical potentials: Can be described by an interaction hamiltonian Lot of attention in normal SC.

41. LOFF:ferromagnetic alloy with paramagnetic impurities. • The impurities produce a constant exchange fieldacting upon the electron spins giving rise to aneffective difference in the chemical potentials of the opposite spins. • Very difficult experimentally but claims of observations in heavy fermion superconductors (Gloos & al 1993) and in quasi-two dimensional layered organic superconductors (Nam & al. 1999, Manalo & Klein 2000)

42. HIchanges the inverse propagator and the gap equation (for spin up and down fermions): This has two solutions:

43. Grand potential: Also: Favored solution

44. Also: First order transition to the normal state at For constant D, Ginzburg-Landau expanding up toD6

45. LOFF phase In 1964 Larkin, Ovchinnikov and Fulde, Ferrel, argued the possibility that close to the first order-line a new phase could take place. According LOFF possible condensation withnon zero total momentum of the pair More generally

46. Non zero total momentum fixed variationally chosen spontaneously Gap equation:

47. For T T0 blocking region The blocking region reduces the gap:

48. Possibility of a crystalline structure (Larkin & Ovchinnikov 1964, Bowers & Rajagopal 2002) see later The qi’s define the crystal pointing at its vertices. The LOFF phase has been studied via a Ginzburg-Landau expansion of the grand potential

49. (for regular crystalline structures all the Dq are equal) The coefficients can be determined microscopically for the different structures (Bowers and Rajagopal (2002))

50. General strategy • Gap equation • Propagator expansion • Insert in the gap equation