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First year grad student at UC Berkeley. Here to ask naive questions.

I miss the theoretical physics stackexchange and think this whole website should be a bit more lax.


Jul
16
comment Is there a physical system whose phase space is the torus?
pi_1 is also Z plus Z...
Jul
16
comment Is there a physical system whose phase space is the torus?
H_1 is Z plus Z. Flat connections are maps from this to U(1).
Jul
15
comment Is there a physical system whose phase space is the torus?
Only long-range effective theories like I mention. By the way, I don't know any theories with higher genus surfaces as their phase space...
Jul
15
revised Is there a physical system whose phase space is the torus?
added 244 characters in body
Jul
15
answered Is there a physical system whose phase space is the torus?
Jul
7
comment can gapped systems have gravitational anomalies?
@Idear Sorry, I misunderstood. That question is more general than mine. If the topological order is to be the anomaly theory for the boundary, then it should be invertible (no topological ground state degeneracy). My question is if any of these admit gapped boundaries.
Jul
7
comment can gapped systems have gravitational anomalies?
Thanks for your answer. It does not yet answer my question, though. In these examples it is the boundary which has a gravitational anomaly. My analogous question for these sorts of gravitational anomalies is "which topological orders admit gapped boundaries?"
Jul
6
revised can gapped systems have gravitational anomalies?
edited tags
Jul
6
comment can gapped systems have gravitational anomalies?
Separate from the condensed matter motivation, gapped systems are ones whose long range effective field theory is topological. I'm more generally interested in what sorts of anomalies can be realized by topological field theories.
Jul
5
awarded  Yearling
Jul
4
comment can gapped systems have gravitational anomalies?
Some systems have edge modes with robust gaplessness. In the case that this robustness is symmetry protection, then we can explain this by saying the boundary has a 't Hooft anomaly. Sometimes the same argument is made for systems (eg. the E8 state) via a gravitational anomaly for the bulk. Making these arguments rigorous requires understanding which gravitational anomalies (if any) can be realized by gapped theories.
Jul
3
comment can gapped systems have gravitational anomalies?
A gravitational anomaly is some problem with formulating the field theory on a manifold that isn't Minkowski space. In some sense we are coupling to a background gravitational field.
Jul
3
comment can gapped systems have gravitational anomalies?
I mean systems with an energy gap above the ground state(s), so yes the effective field theory of an electron in an insulating material is gapped.
Jul
3
asked can gapped systems have gravitational anomalies?
Jul
3
comment quantum field theoretic models of decoherence
Thanks for taking the time to answer an old question of mine and for providing another interesting perspective!
Jul
2
awarded  Curious
Jun
29
awarded  Self-Learner
Mar
1
comment Questions on the $N=2$ superconformal algebra
Note one can define the A model even if the manifold is just Kahler.
Feb
14
awarded  Nice Question
Jan
17
comment Is mean field theory self-consistency analogous to string theory consistency?
Thanks for your answer, Lubos, things are certainly looking a bit clearer. Just because the perturbation theory is unique doesn't mean it's exact. Does summing over worldsheets include the effects of say D-branes created from the vacuum? What about tunneling effects between different vacua?