arXiv subjects

Saidakhmat N. Lakaev

Publications and source records attributed to Saidakhmat N. Lakaev.

25 records · Page 2Linked to original sources

arXiv2005

On the spectrum of an Hamiltonian in Fock space. Discrete spectrum Asymptotics

A model operator $H$ associated with the energy operator of a system describing three particles in interaction, without conservation of the number of particles, is considered. The precise location and structure of the essential spectrum of $H$ is described. The existence of infinitely many eigenvalues below the bottom of the essential spectrum of $H$ is proved for the case where an associated generalized Friedrichs model has a resonance at the bottom of its essential spectrum. An asymptotics for the number $N(z)$ of eigenvalues below the bottom of the essential spectrum is also established. The finiteness of eigenvalues of $H$ below the bottom of the essential spectrum is proved if the associated generalized Friedrichs model has an eigenvalue with energy at the bottom of its essential spectrum.

math-ph↗

arXiv2005

Estimates on the number of eigenvalues of two-particle discrete Schrödinger operators

Two-particle discrete Schrödinger operators $H(k)=H_{0}(k)-V$ on the three-dimensional lattice $\Z^3,$ $k$ being the two-particle quasi-momentum, are considered. An estimate for the number of the eigenvalues lying outside of the band of $H_{0}(k)$ via the number of eigenvalues of the potential operator $V$ bigger than the width of the band of $H_{0}(k)$ is obtained. The existence of non negative eigenvalues below the band of $H_{0}(k)$ is proven for nontrivial values of the quasi-momentum $k\in \T^3\equiv (-π,π]^3$, provided that the operator H(0) has either a zero energy resonance or a zero eigenvalue. It is shown that the operator $H(k), k\in \T^3,$ has infinitely many eigenvalues accumulating at the bottom of the band from below if one of the coordinates $k^{(j)},j=1,2,3,$ of $k\in \T^3$ is $π.$

math-ph↗

arXiv2005

The number of eigenvalues for an Hamiltonian in Fock space

A model operator $H$ corresponding to the energy operator of a system with non-conserved number $n\leq 3$ of particles is considered. The precise location and structure of the essential spectrum of $H$ is described. The existence of infinitely many eigenvalues below the bottom of the essential spectrum of $H$ is proved if the generalized Friedrichs model has a virtual level at the bottom of the essential spectrum and for the number $N(z)$ of eigenvalues below $z<0$ an asymptotics established. The finiteness of eigenvalues of $H$ below the bottom of the essential spectrum is proved if the generalized Friedrichs model has a zero eigenvalue at the bottom of its essential spectrum.

math-ph↗

arXiv2005

On the essential and discrete spectrum of a model operator related to three-particle discrete Schrödinger operators

A model operator $H$ corresponding to a three-particle discrete Schrödinger operator on a lattice $\Z^3$ is studied. The essential spectrum is described via the spectrum of two Friedrichs models with parameters $h_α(p),$ $α=1,2,$ $p \in \T^3=(-π,π]^3.$ The following results are proven: 1) The operator $H$ has a finite number of eigenvalues lying below the bottom of the essential spectrum in any of the following cases: (i) both operators $h_α(0), α=1,2,$ have a zero eigenvalue; (ii) either $h_1(0)$ or $h_2(0)$ has a zero eigenvalue. 2) The operator $H$ has infinitely many eigenvalues lying below the bottom and accumulating at the bottom of the essential spectrum, if both operators $h_α(0),α=1,2,$ have a zero energy resonance.

math-ph↗

arXiv2005

The Threshold effects for the two-particle Hamiltonians on lattices

For a wide class of two-body energy operators $h(k)$ on the three-dimensional lattice $\bbZ^3$, $k$ being the two-particle quasi-momentum, we prove that if the following two assumptions (i) and (ii) are satisfied, then for all nontrivial values $k$, $k\ne 0$, the discrete spectrum of $h(k)$ below its threshold is non-empty. The assumptions are: (i) the two-particle Hamiltonian $h(0)$ corresponding to the zero value of the quasi-momentum has either an eigenvalue or a virtual level at the bottom of its essential spectrum and (ii) the one-particle free Hamiltonians in the coordinate representation generate positivity preserving semi-groups.

math-ph↗

arXiv2003

On the structure of the essential spectrum of the three-particle Schrödinger operators on a lattice

A system of three quantum particles on the three-dimensional lattice $\Z^3$ with arbitrary "dispersion functions" having non-compact support and interacting via short-range pair potentials is considered. The energy operators of the systems of the two-and three-particles on the lattice $\Z^3$ in the coordinate and momentum representations are described as bounded self-adjoint operators on the corresponding Hilbert spaces. For all sufficiently small nonzero values of the two-particle quasi-momentum $k\in (-π,π]^3$ the finiteness of the number of eigenvalues of the two-particle discrete Schrödinger operator $h_α(k)$ below the continuous spectrum is established. A location of the essential spectrum of the three-particle discrete Schrödinger operator $H(K),K\in (-π,π]^3$ the three-particle quasi-momentum, by means of the spectrum of $h_α(k)$ is described. It is established that the essential spectrum of $H(K), K\in (-π,π]^3$ consists of a finitely many bounded closed intervals.

math-ph↗

arXiv2003

Schrödinger operators on lattices. The Efimov effect and discrete spectrum asymptotics

The Hamiltonian of a system of three quantum mechanical particles moving on the three-dimensional lattice $\Z^3$ and interacting via zero-range attractive potentials is considered. For the two-particle energy operator $h(k),$ with $k\in \T^3=(-π,π]^3$ the two-particle quasi-momentum, the existence of a unique positive eigenvalue below the bottom of the continuous spectrum of $h(k)$ for $k\neq0$ is proven, provided that $h(0)$ has a zero energy resonance. The location of the essential and discrete spectra of the three-particle discrete Schrödinger operator $H(K), K\in \T^3$ being the three-particle quasi-momentum, is studied. The existence of infinitely many eigenvalues of H(0) is proven. It is found that for the number $N(0,z)$ of eigenvalues of H(0) lying below $z<0$ the following limit exists $$ \lim_{z\to 0-} \frac {N(0,z)}{\mid \log\mid z\mid\mid}=\cU_0 $$ with $\cU_0>0$. Moreover, for all sufficiently small nonzero values of the three-particle quasi-momentum $K$ the finiteness of the number $ N(K,τ_{ess}(K))$ of eigenvalues of $H(K)$ below the essential spectrum is established and the asymptotics for the number $N(K,0)$ of eigenvalues lying below zero is given.

math-ph↗