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S Feb 14, 2014 at 20:06 history suggested Sebastien Palcoux CC BY-SA 3.0
Several minor edits.
Feb 14, 2014 at 19:39 review Suggested edits
S Feb 14, 2014 at 20:06
Oct 14, 2013 at 20:42 vote accept André Henriques
S Oct 11, 2013 at 13:25 history suggested Sebastien Palcoux CC BY-SA 3.0
I have improved the shape of the table and of some lists. I have added the tag "subfactors".
Oct 11, 2013 at 13:19 review Suggested edits
S Oct 11, 2013 at 13:25
Oct 11, 2013 at 13:18 answer added Sebastien Palcoux timeline score: 16
Jul 20, 2011 at 19:14 comment added André Henriques Thank you Marcel for the link. I think that I now understand the general picture.
Jul 20, 2011 at 18:49 comment added Marcel Bischoff Btw on wikipedia the example is discussed en.wikipedia.org/wiki/Finite_potential_well and it is actually not so simple to calculate the discrete eigenvalues because there is no closed solution. @Theo in your Hamiltonian is missing a square for $(-i\frac\partial{\partial x})$
Jul 20, 2011 at 1:25 comment added Theo Johnson-Freyd @André: Yes, I meant for $V$ to be bounded, not just bounded below. I rewrote my comment a few times, and somehow that got lost. Marcel's example is spot on, even if it doesn't quite satisfy my fairly restrictive conditions.
Jul 19, 2011 at 11:44 history edited André Henriques CC BY-SA 3.0
added 178 characters in body
Jul 18, 2011 at 16:01 comment added Marek @André, something like this: etsf.eu/system/files/born-oppenheimer-m.png -- as one gets closer to the "top of the well" the energy levels are getting finer and eventually they become continuous (it depends on the precise profile whether there is a finite or infinite number of the discrete levels though). I am not sure what is the picture of but qualitatively it resembles the radial part of a Coulomb potential (as felt e.g. by an electron orbiting a nucleus).
Jul 18, 2011 at 15:34 answer added Eric Rowell timeline score: 5
Jul 18, 2011 at 13:00 comment added Marcel Bischoff ok maybe not a good example because it has finite discrete spectrum...
Jul 18, 2011 at 12:54 comment added Marcel Bischoff The simplest examples of what Theo is talking about is probably $V(x) = -1_{[-1,1]}(x)$ the negative characteristic function of an interval. For energy $-1< E<0$ the spectrum of the Hamiltonian is discrete for $E>0$ continuous.
Jul 18, 2011 at 12:36 comment added André Henriques @Theo: In your example, is V(x) is a bounded function? (if not: what do you mean by "top of the mountains"?). What is the simplest example of a function V(x) that exhibits the kind of behavior that you describe?
Jul 18, 2011 at 11:40 comment added Theo Johnson-Freyd Maybe Qiaochu's question is the following. As physicists, we're very used to the following phenomenon: let $V(x)$ be a potential energy function which bounded below and has finitely many local minima (I probably can relax something). Then the spectrum of the Hamiltonian $(i\hbar\frac{\partial}{\partial x}) + V(x)$ has a discrete part, roughly corresponding to valleys in the graph of $V$, and a continuous part, starting near the tops of the mountains and going higher. Here the role of $c,\delta$ is played by the energy $E$ = eigenvalue. So your remarked upon behavior is not a priori surprising.
Jul 18, 2011 at 1:37 answer added Stephen timeline score: 15
Jul 18, 2011 at 1:15 history edited André Henriques CC BY-SA 3.0
added the positive energy constraint. Without it, the stated facts about Rep(Vir_c) aren't correct.; added 70 characters in body; deleted 4 characters in body
Jul 18, 2011 at 0:27 history edited André Henriques CC BY-SA 3.0
edited title
Jul 18, 2011 at 0:27 comment added André Henriques @Qiaochu: What do you mean by "objects of this type"?
Jul 17, 2011 at 23:55 comment added Qiaochu Yuan Is it clear that this isn't the generic expected behavior for objects of this type?
Jul 17, 2011 at 23:12 history edited André Henriques CC BY-SA 3.0
edited title
Jul 17, 2011 at 22:28 history asked André Henriques CC BY-SA 3.0