All Questions
Tagged with sp.spectral-theory differential-equations
25 questions
6
votes
0
answers
201
views
Dependence of Neumann eigenvalues on the domain
I have the following problem in hands, in the context of a broader investigation:
Let $V\in L^{n/2}$ compactly supported, where $n\geq 3$ is the dimension. I want to prove the following:
For any $\...
- 101
3
votes
1
answer
209
views
Must solutions to the time-independent Schrodinger equation that have discrete or negative eigenvalues be square-integrable?
This is a very straightforward question (although the answer may not be!) about a ubiquitous textbook physics situation. I assume that the answer is probably well-known, but I asked it on both Math ...
- 1,311
5
votes
1
answer
260
views
Resources on the stationary Schrödinger equation with the soliton potential
I am studying the following Lamé equation in the Jacobi form
\begin{equation}
-\frac{d^2 v}{dx^2} - \left(2k^2 \operatorname{cn}^{2}\left [x\;|\;k\right ]\right)v = \lambda v,
\end{equation}
...
- 51
1
vote
0
answers
69
views
Show that an integral operator with Bessel function kernel is bounded on $L^2(0,\infty)$
Let $J_0$ denote the Bessel function of the first kind of order $\nu = 0$ (see DLMF 10.2),
$$
J_0(z) = \sum_{k = 0}^\infty (-1)^k \frac{(\tfrac{1}{4} z^2)^k }{k! \Gamma(k + 1)}.
$$
Put $u_0(r) = r^{1/...
- 481
1
vote
0
answers
119
views
Sturm-Liouville Problem: When does $w y^2$ vanish at a singular boundary point?
It is well known (e.g. Courant, Hilbert - Methods of Mathematical Physics) that solutions of the Sturm-Liouville problem on an interval $J=(a,b)$
\begin{equation} \tag{1}
\left(p y' \right)' - qy \; = ...
- 183
7
votes
1
answer
767
views
Singular Sturm-Liouville problems: criterion for discrete spectrum for zero potential ($q=0$) and Hermite Polynomials
There are some known criteria for the Sturm-Liouville Problem
\begin{equation} \tag{1}
\frac {\mathrm {d} }{\mathrm {d} x}\left[p(x){\frac {\mathrm {d} y}{\mathrm {d} x}}\right]+q(x)y=-\lambda w(x)y
\...
- 183
14
votes
1
answer
1k
views
Computing spectra without solving eigenvalue problems
There is a rather remarkable conjecture formulated in this paper, "Computing spectra without solving eigenvalue problems," https://arxiv.org/pdf/1711.04888.pdf and in this talk by Svitlana Mayboroda ...
- 649
2
votes
0
answers
150
views
Limit circle/point of an ODE with finite eigenvalues
Consider the following Sturm–Liouville (SL) eigenvalue problem defined in $(-\infty,0]$ or $[0,\infty)$ or $(-\infty,+\infty)$ $$(py')'-qy=-\lambda^2wy,$$ in which $p(x)=x^2$, $w(x)=1$, and $q(x)=(x/2+...
- 155
4
votes
0
answers
410
views
Spectral Gap of Elliptic Operator
Under what conditions on $a(x)$ and domain $D$, the spectral gap of the elliptic operator $ \nabla \cdot(a(x)\cdot \nabla)$ defined on $D$, can be controlled?
The boundary condition is that the ...
- 325
2
votes
3
answers
487
views
Non-linear Basis for PDE's
Asked this on stack exchange and got no response, so I'll try here.
An idea popped into my head awhile ago while doing a project on non-linear effects of systems of coupled oscillators, but I'm not ...
- 131
2
votes
1
answer
132
views
A nodal theorem in 1D
Consider a 1D zero-energy Schrödinger equation on the half-line,
$(-\partial_x^2 + V(x))\psi(x)=0, \quad x \in (0, \infty)$
with a zero boundary condition $\psi(0) = 0$.
Is it true that if the zero-...
- 151
0
votes
1
answer
181
views
Does asymptotic behavior guarantee uniqueness?
Suppose $w$ is a solution of
$$\frac{d^2}{dx^2}w+\{u(x)+k^2\}w=0$$
with asymptotic condition
$$\lim_{x\rightarrow \infty}w(x)e^{ikx}=1$$
and $u\in L^1_1(\mathbb{R})=\{f:\int_\mathbb{R}(1+|x|)|f|dx<...
- 145
2
votes
1
answer
195
views
the asymptotic behaviour of function as $\lambda \to -\infty$
Let's consider the following differential equation on $\mathbb{R}$:
$$-u''(x)+u(x)-V(x)u(x)=\lambda u(x),$$ where $\lambda<1$ and $V$ is a bounded.
We consider only that solution $u(x) \in C^1$ ...
- 195
3
votes
1
answer
232
views
what is about the corresponding power series?
According to the papers The absolutely continuous spectrum of Jacobi matrices and these lecture notes:
periodicity ~ potential well or lattice (order)
lack of absolutely continued spectrum ~ Anderson ...
- 3,094
1
vote
0
answers
93
views
inverse problem to resolution of the identity
Suppose $f_\lambda(x),\lambda \in \mathbb{R}$ is a continuous/smooth family of bounded function on $\mathbb{R}$. Given a measurable set $\mathfrak{m}$ on $\mathbb{R}$, define $$E_\mathfrak{m}:L^2\...
- 587
6
votes
3
answers
916
views
Non-self adjoint Sturm-Liouville problem
I'm new to this site, but I felt the need to post when I recently came in to an ordinary differential equation/boundary value problem with this form:
$(1)- \frac{d^2 y}{d x^2} + \frac{m(m+1)} {x^2(...
- 71
3
votes
1
answer
205
views
Bounds for smallest eigenvalue of Schrödinger equation with a superpotential and periodic boundary conditions
A very specific question, but posted on the off-chance that someone may be able to help. If we have a Schrödinger equation with arbitrary "superpotential"
\begin{equation}
-\frac{d^2 \psi}{dx^2} ...
- 71
-1
votes
1
answer
360
views
Which operators other than self-adjoint operators have no purely imaginary eigenvalues? [closed]
Given an operator mapping between suitable spaces, what is the condition that guarantees all eigenvalues have nonzero real part? Obviously self-adjointness implies all eigenvalues are real, but how ...
- 7
4
votes
2
answers
590
views
Examples of potentials for which Schrödinger equation lacks discrete points in continuous spectrum
In Landau, Lifshitz, "Quantum Mechanics, non-relativistic theory" in $\S18$ "The fundamental properties of Schrödinger's equation" the following is said about potential $U(x,y,z)$ in a footnote:
it ...
- 285
0
votes
1
answer
393
views
Legendre differential equation with additional term
In an application I encountered the ODE
$$ \left( {x}^{2}-1 \right) {\frac {{\rm d}^{2}}{{\rm d}{x}^{2}}}f
\left( x \right) +x \left( {\frac {\rm d}{{\rm d}x}}f \left( x
\right) \right) \left( 8\,...
user37929
2
votes
2
answers
1k
views
What is the right initial domain for the Dirichlet-Laplacian on a bounded domain?
Given some bounded domain $\Omega\subset \mathbb{R}^n$ with sufficiently regular boundary (e.g. smooth boundary). Then I saw two slightly different definitions for the Dirichlet-Laplacian.
Some books ...
- 675
10
votes
2
answers
1k
views
What are first eigenfunctions of Laplacian for $CP^n$ with Fubini-Study metric?
I know the round $n$-sphere has $f_i=\cos(dist(e_i, x))$ as the set of first eigenfunctions for $e_i=(0, \cdots, 1, \cdots, 0)\in \mathbb R^{n+1}$. i.e. $\Delta f_i=\lambda_1 f$, where $\lambda_1$ is ...
- 2,623
1
vote
0
answers
137
views
Decay rate of Discrete Prolate Spheroidal Sequences in frequency
What is the decay rate of DPSS sequences in frequency?
Consider an interval $T\subset\mathbb{Z}$ of length N in time. Consider another interval $[-W,W]$ in frequency with $W<1/2$. Let $\phi_0$ ...
1
vote
1
answer
591
views
Parametrizing eigenvectors
I'm looking for a proof in the literature of the following fact:
Let $A_t$ be a $C^1$-function of one argument $t \in (a,b)$ taking values in the self-adjoint $N \times N$ matrices. Suppose that for ...
- 3,343
7
votes
2
answers
614
views
Does there exist a potential which realizes this strange quantum mechanical system?
I have done some courses on quantum mechanics and statistical mechanics in the past. Since I also do math, I wonder about converge issues which are usually not such a problem in physics. One of those ...
- 8,167