Some open questions from this conference/workshop

Q 1 (Balents) Are quantum effects important for physics of hexagonal manganites (Eg: YMnO3)? What is the mechanism of coupling between electric polarization and spin order?

Q2 (Senthil) Theory of field-induced transition from heavy fermi liquid to fermi liquid with polarized local moments? Application to CeRu2Si2 or URu2Si2? Is there significant Fermi surface reconstruction at the metamagnetic transition in these materials?

Q3 (Vishwanath, Balents) In amorphous films undergoing a field-tuned ``superconductor-insulator” transition, to what extent can the vortices be regarded as quantum particles?

Q4 (Je-Geun Park) Experiments on a number of heavy fermion critical points (Fermi liquid to AF metal/spin glass) see non-trivial exponents for dynamical spin correlations. Thus far these exponents cluster around 2 values (2/3 and 1/3). Is there any systematics to these exponent values? Is there any theory?

Q5 (Oshikawa, Fisher, Senthil) Can non-trivial two dimensional quantum paramagnets be accessed by weakly coupling together spin-1/2 chains?

Q6 (Y.B. Kim, Senthil) Can the Oshikawa/Hastings arguments on structure of paramagnetic states of easy plane/axis magnets be generalized to SU(2) invariant systems? (Eg S = 1 on 2d square lattice believed not to have trivial paramagnetic ground state with SU(2) symmetry: can this be understood at the same level as generality as Oshikawa/Hastings?)

Q7 (Senthil) Are there any clear demonstrable instances of criticality in quantum systems where spatial correlations are mean-field like but time correlations are anamolous? (analogous to proposal of Si et al for heavy fermion critical points)

Q8 (Q. Si) Is there a microscopic model which can be demonstrated to have a deconfined Landau-forbidden deconfined quantum critical point? Spin systems, bosons on various lattices?

Q9 (Balents, Y.B. Kim, Senthil) Can one understand the theoretical problem of Fermi surface coupled to a gauge field in some controlled approximation? (Do better than work from 1990’s) Fate of monopoles? 2kf correlations? Luttinger theorem?

Q10 (Y.B. Kim, Oshikawa, Fisher, Senthil) Does the sigma model formulation for 2d deconfined quantum critical points have any power for analytic/numerical calculations? Is there a `sigma model’ description of stable two dimensional algebraic spin liquids in terms of a bosonic field theory perhaps with topological terms?

Q11 (Kwon Park) Is there a `solution’ to the sign problem in simulating Hamiltonians of quantum many particle systems? How well-defined is the sign problem? Are there classes of problems that have an `intrinsic’ sign problem that will not disappear in any useful reformulation? Will such systems have properties different from those without an `intrinsic’ sign problem?

Q12 (Si, Senthil) How do we describe the single impurity Kondo effect in a bosonic decription of the impurity spin?

Q13 (Vishwanath, Si, Senthil) Is there really `reduced’ dimensionality for spin fluctuations at heavy fermion critical points that show non-fermi liquid behavior? Does the reduced dimensionality play any direct role in giving the non-Fermi liquid physics?

Q14 (Senthil) Is gauge theory useful (necessary?) for understanding high-Tc cuprates? Is there a viable alternate to implement Mott/valence bond physics in doped Mott insulators?

Q15 (Balents) Is there a quasi-realistic spin/Hubbard model that can be shown to be in a spin liquid phase?

Q16 (Vishwanath, Fisher, Senthil) How correct is it to integrate out fermions in a Hertz-Millis theory of a metallic quantum phase transition? (Action in ordered and disordered phases is different; is this a problem?)

Q17 (Si) Is there interesting physics at a quantum first order transition in a metallic system?

Q18 (Balents, Fisher, Y.B. Kim, Senthil) Cs2CuCl4 1. Where in q-space are there ``gapless” excitations associated with power law tails in inelastic neutron scattering? 2. To what extent is the scattering in these tails polarized in easy plane? 3. What is the theoretically expected answer for 1d-2d crossover?

Q19 (Furusaki) What is the phase diagram of the 2d Hubbard model at half-filling on a frustrated lattice? Eg: Triangular or Kagome lattices

Q20 (Senthil) Do there exist non-Fermi liquid states of matter with Fermi arcs? Can we construct an example?