A Pedestrian Introduction to Gamow Vectors

Relativistic Gamow Vectors I Derivation from Poles of the S-Matrix

A state vector description for relativistic resonances is derived from the first order pole of the $j$-th partial $S$-matrix at the invariant square mass value $\sm_R=(m-iΓ/2)^2$ in the second sheet of the Riemann energy surface. To associate a ket, called Gamow vector, to the pole, we use the generalized eigenvectors of the four-velocity operators in place of the customary momentum eigenkets of Wigner, and we replace the conventional Hilbert space assumptions for the in- and out-scattering states with the new hypothesis that in- and out-states are described by two different Hardy spaces with …

Gamow vectors formalism applied to the Loschmidt echo

Gamow vectors have been developed in order to give a mathematical description for quantum decay phenomena. Mainly, they have been applied to radioactive phenomena, scattering and to some decoherence models. They play a crucial role in the description of quantum irreversible processes, and in the formulation of time asymmetry in quantum mechanics. In this paper, we use this formalism to describe a well-known phenomenon of irreversibility: the Loschmidt echo. The standard approach considers that the irreversibility of this phenomenon is the result of an additional term in the backward Hamiltonia…

Nonlinear Gamow vectors, shock waves and irreversibility in optically nonlocal media

Dispersive shock waves dominate wave-breaking phenomena in Hamiltonian systems. In the absence of loss, these highly irregular and disordered waves are potentially reversible. However, no experimental evidence has been given about the possibility of inverting the dynamics of a dispersive shock wave and turn it into a regular wave-front. Nevertheless, the opposite scenario, i.e., a smooth wave generating turbulent dynamics is well studied and observed in experiments. Here we introduce a new theoretical formulation for the dynamics in a highly nonlocal and defocusing medium described by the nonl…

Resonances from Higher Order S-Matrix Poles with Exponential Decay

In analogy to Gamow vectors describing resonance states from first order S-matrix poles, one can define Gamow vectors from higher order poles of the S-matrix. With these vectors we are going to discuss a density operator that describes exponentially decaying resonances from higher order poles.

Relativistic Gamow Vectors II

Motivated by the debate of possible definitions of mass and width of resonances for $Z$-boson and hadrons, we suggest a definition of unstable particles by ``minimally complex'' semigroup representations of the Poincaré group characterized by $(j,{\mathsf s}=(m-iΓ/2)^{2})$ in which the Lorentz subgroup is unitary. This definition, though decidedly distinct from those based on various renormalization schemes of perturbation theory, is intimately connected with the first order pole definition of the $S$-matrix theory in that the complex square mass $(m-iΓ/2)^{2}$ characterizing the representatio…

量子力学的Rigged Hilbert空间表述及其对不可逆性的意义

The Rigged Hilbert Space Formulation of Quantum Mechanics and its Implications for Irreversibility

量子力学在Rigged Hilbert空间表述中用伽莫夫向量严格地描述了准稳态现象。我们表明，这些向量表现出微观物理的不可逆性，相关的内在量子力学箭头的时间，这表明，一个国家的准备必须在此状态下的一个观察之前登记。此外，Rigged Hilbert空间形式主义允许导出一个精确的黄金法则，描述纯伽莫夫态转变为无相互作用衰变产物的混合物。

行人通往Baxter周期XYZ链Bethe拟设之路

A Pedestrian's Way to Baxter's Bethe Ansatz for the Periodic XYZ Chain

本文提出手性坐标Bethe拟设方法研究周期XYZ链，构造手性向量基，在单位根条件下推导齐次Bethe方程，精确求解能量和本征态，与Baxter结果一致并经数值验证。

Rigged Hilbert Space Resonances and Time Asymmetric Quantum Mechanics

The Rigged Hilbert Space (RHS) theory of resonance scattering and decay is reviewed and contrasted with the standard Hilbert space (HS) theory of quantum mechanics. The main difference is in the choice of boundary conditions. Whereas the conventional theory allows for the in-states $ϕ^+$ and the out-states (observables) $ψ^-$ of the S-matrix elements $(ψ^-,ϕ^+)=(ψ^{out},S ϕ^{in})$ any elements of the HS $\H$, $\{ψ^-\}=\{ϕ^+\}(=\H)$, the RHS theory chooses the boundary conditions~: $ϕ^+\inΦ_-\subset\H\subsetΦ_-^\times$, $ψ^-\inΦ_+\subset \H\subset Φ_+^\times$, where $Φ_-$ ($Φ_+$) are Hardy clas…

Time Asymmetric Quantum Theory - II. Relativistic Resonances from S-Matrix Poles

Relativistic resonances and decaying states are described by representations of Poincaré transformations, similar to Wigner's definition of stable particles. To associate decaying state vectors to resonance poles of the $S$-matrix, the conventional Hilbert space assumption (or asymptotic completeness) is replaced by a new hypothesis that associates different dense Hardy subspaces to the in- and out-scattering states. Then one can separate the scattering amplitude into a background amplitude and one or several ``relativistic Breit-Wigner'' amplitudes, which represent the resonances per se. Thes…

Irreversible Evolution of a Wave Packet in The Rigged Hilbert Space Quantum Mechanics

It is well known that a state with complex energy cannot be the eigenstate of a self-adjoint operator, like the Hamiltonian. Resonances, i.e. states with exponentially decaying observables, are not vectors belonging to the conventional Hilbert space. One can describe these resonances in an unusual mathematical formalism, based on the so-called Rigged Hilbert Space (RHS). In the RHS, the states with complex energy are denoted as Gamow Vectors (GV), and they model decay processes. We study GV of the Reversed Harmonic Oscillator (RHO), and we analytically and numerically investigate the unstable …