Search results for "Mathematical physics"
showing 10 items of 2687 documents
Killing (absorption) versus survival in random motion
2017
We address diffusion processes in a bounded domain, while focusing on somewhat unexplored affinities between the presence of absorbing and/or inaccessible boundaries. For the Brownian motion (L\'{e}vy-stable cases are briefly mentioned) model-independent features are established, of the dynamical law that underlies the short time behavior of these random paths, whose overall life-time is predefined to be long. As a by-product, the limiting regime of a permanent trapping in a domain is obtained. We demonstrate that the adopted conditioning method, involving the so-called Bernstein transition function, works properly also in an unbounded domain, for stochastic processes with killing (Feynman-…
Unitary time-dependent superconvergent technique for pulse-driven quantum dynamics
2003
We present a superconvergent Kolmogorov-Arnold-Moser type of perturbation theory for time-dependent Hamiltonians. It is strictly unitary upon truncation at an arbitrary order and not restricted to periodic or quasiperiodic Hamiltonians. Moreover, for pulse-driven systems we construct explicitly the KAM transformations involved in the iterative procedure. The technique is illustrated on a two-level model perturbed by a pulsed interaction for which we obtain convergence all the way from the sudden regime to the opposite adiabatic regime.
Perturbative Treatment of the Evolution Operator Associated with Raman Couplings
2006
A novel perturbative treatment of the time evolution operator of a quantum system is applied to the model describing a Raman-driven trapped ion in order to obtain a suitable 'effective model'. It is shown that the associated effective Hamiltonian describes the system dynamics up to a certain transformation which may be interpreted as a 'dynamical dressing' of the effective model.
Interaction free and decoherence free states
2015
An interaction free evolving state of a closed bipartite system composed of two interacting subsystems is a generally mixed state evolving as if the interaction were a c-number. In this paper we find the characteristic equation of states possessing similar properties for a bipartite systems governed by a linear dynamical equation whose generator is sum of a free term and an interaction term. In particular in the case of a small system coupled to its environment, we deduce the characteristic equation of decoherence free states namely mixed states evolving as if the interaction term were effectively inactive. Several examples illustrate the applicability of our theory in different physical co…
Damping and pseudo-fermions
2012
After a short abstract introduction on the time evolution driven by non self-adjoint hamiltonians, we show how the recently introduced concept of {\em pseudo-fermion} can be used in the description of damping in finite dimensional quantum systems, and we compare the results deduced adopting the Schr\"odinger and the Heisenberg representations.
Ωb−→(Ξc+K−)π− decay and the Ωc states
2018
We study the weak decay ${\mathrm{\ensuremath{\Omega}}}_{b}^{\ensuremath{-}}\ensuremath{\rightarrow}({\mathrm{\ensuremath{\Xi}}}_{c}^{+}{K}^{\ensuremath{-}}){\ensuremath{\pi}}^{\ensuremath{-}}$, in view of the narrow ${\mathrm{\ensuremath{\Omega}}}_{c}$ states recently measured by the LHCb Collaboration and later confirmed by the Belle Collaboration. The ${\mathrm{\ensuremath{\Omega}}}_{c}(3050)$ and ${\mathrm{\ensuremath{\Omega}}}_{c}(3090)$ are described as meson-baryon molecular states, using an extension of the local hidden gauge approach in coupled channels. We investigate the $\mathrm{\ensuremath{\Xi}}D$, ${\mathrm{\ensuremath{\Xi}}}_{c}\overline{K}$, and ${\mathrm{\ensuremath{\Xi}}}_…
Effective Field Theories in a Finite Volume
2018
In this talk I present the formalism we have used to analyze Lattice data on two meson systems by means of effective field theories. In particular I present the results obtained from a reanalysis of the lattice data on the $KD^{(*)}$ systems, where the states $D^*_{s0}(2317)$ and $D^*_{s1}(2460)$ are found as bound states of $KD$ and $KD^*$, respectively. We confirm the presence of such states in the lattice data and determine the contribution of the $KD$ channel in the wave function of $D^*_{s0}(2317)$ and that of $KD^*$ in the wave function of $D^*_{s1}(2460)$. Our findings indicate a large meson-meson component in the two cases.
From loops to trees by-passing Feynman's theorem
2008
We derive a duality relation between one-loop integrals and phase-space integrals emerging from them through single cuts. The duality relation is realized by a modification of the customary +i0 prescription of the Feynman propagators. The new prescription regularizing the propagators, which we write in a Lorentz covariant form, compensates for the absence of multiple-cut contributions that appear in the Feynman Tree Theorem. The duality relation can be applied to generic one-loop quantities in any relativistic, local and unitary field theories. %It is suitable for applications to the analytical calculation of %one-loop scattering amplitudes, and to the numerical evaluation of %cross-section…
Interpolating between low and high energy QCD via a 5D Yang-Mills model
2005
We describe the Goldstone bosons of massless QCD together with an infinite number of spin-1 mesons. The field content of the model is SU(Nf)xSU(Nf) Yang-Mills in a compact extra-dimension. Electroweak interactions reside on one brane. Breaking of chiral symmetry occurs due to the boundary conditions on the other brane, away from our world, and is therefore spontaneous. Our implementation of the holographic recipe maintains chiral symmetry explicit throughout. For intermediate energies, we extract resonance couplings. These satisfy sum rules due to the 5D nature of the model. These sum rules imply, when taking the high energy limit, that perturbative QCD constraints are satisfied. We also il…
Infrared finite ghost propagator in the Feynman gauge
2007
We demonstrate how to obtain from the Schwinger-Dyson equations of QCD an infrared finite ghost propagator in the Feynman gauge. The key ingredient in this construction is the longitudinal form factor of the non-perturbative gluon-ghost vertex, which, contrary to what happens in the Landau gauge, contributes non-trivially to the gap equation of the ghost. The detailed study of the corresponding vertex equation reveals that in the presence of a dynamical infrared cutoff this form factor remains finite in the limit of vanishing ghost momentum. This, in turn, allows the ghost self-energy to reach a finite value in the infrared, without having to assume any additional properties for the gluon-g…