01837nas a2200145   4500008004100000245007900041210006900120520133000189100002201519700002901541700002001570700002901590700002101619856005101640       2015                        en  d00aA class of Hamiltonians for a three-particle fermionic system at unitarity0 aclass of Hamiltonians for a threeparticle fermionic system at un3 aWe consider a quantum mechanical three-particle system made of two identical fermions of mass one and a different particle of mass $m$, where each fermion interacts via a zero-range force with the different particle. In particular we study the unitary regime, i.e., the case of infinite two-body scattering length. The   Hamiltonians describing the system are, by definition,  self-adjoint extensions  of the free Hamiltonian restricted on smooth functions vanishing at the two-body coincidence planes, i.e., where the positions of two interacting particles coincide.

It is known that  for $m$ larger than a critical value  $m^* \simeq (13.607)^{-1}$  a self-adjoint and lower bounded  Hamiltonian $H_0$ can be constructed, whose domain is characterized in terms of the standard point-interaction boundary condition at each coincidence plane. 

Here we prove that for $m\in(m^*,m^{**})$, where $m^{**}\simeq  (8.62)^{-1}$, there is a further family of self-adjoint and lower bounded Hamiltonians $H_{0,\beta}$, $\beta \in \mathbb{R}$, describing the system. Using a quadratic form method, we give a rigorous construction of such Hamiltonians and we show that the elements of their domains satisfy a further  boundary condition, characterizing the singular behavior when the positions of all the three particles coincide.1 aCorreggi, Michele1 aDell'Antonio, Gianfausto1 aFinco, Domenico1 aMichelangeli, Alessandro1 aTeta, Alessandro  uhttp://urania.sissa.it/xmlui/handle/1963/3446901607nas a2200157   4500008004100000245009600041210006900137260002100206520106500227100002201292700002901314700002001343700002901363700002101392856003601413       2012                        en  d00aStability for a System of N Fermions Plus a Different Particle with Zero-Range Interactions0 aStability for a System of N Fermions Plus a Different Particle w  bWorld Scientific3 aWe study the stability problem for a non-relativistic quantum system in\\r\\ndimension three composed by $ N \\\\geq 2 $ identical fermions, with unit mass,\\r\\ninteracting with a different particle, with mass $ m $, via a zero-range\\r\\ninteraction of strength $ \\\\alpha \\\\in \\\\R $. We construct the corresponding\\r\\nrenormalised quadratic (or energy) form $ \\\\form $ and the so-called\\r\\nSkornyakov-Ter-Martirosyan symmetric extension $ H_{\\\\alpha} $, which is the\\r\\nnatural candidate as Hamiltonian of the system. We find a value of the mass $\\r\\nm^*(N) $ such that for $ m > m^*(N)$ the form $ \\\\form $ is closed and bounded from below. As a consequence, $ \\\\form $ defines a unique self-adjoint and bounded from below extension of $ H_{\\\\alpha}$ and therefore the system is stable. On the other hand, we also show that the form $ \\\\form $ is unbounded from below for $ m < m^*(2)$. In analogy with the well-known bosonic case, this suggests that the system is unstable for $ m < m^*(2)$ and the so-called Thomas effect occurs.1 aCorreggi, Michele1 aDell'Antonio, Gianfausto1 aFinco, Domenico1 aMichelangeli, Alessandro1 aTeta, Alessandro  uhttp://hdl.handle.net/1963/606901175nas a2200133   4500008004300000245008500043210006900128260001300197520072500210100002900935700002000964700002100984856003601005       2010                        en_Ud  00aA time-dependent perturbative analysis for a quantum particle in a cloud chamber0 atimedependent perturbative analysis for a quantum particle in a   bSpringer3 aWe consider a simple model of a cloud chamber consisting of a test particle (the alpha-particle) interacting with two other particles (the atoms of the vapour) subject to attractive potentials centered in $a_1, a_2 \\\\in \\\\mathbb{R}^3$. At time zero the alpha-particle is described by an outgoing spherical wave centered in the origin and the atoms are in their ground state. We show that, under suitable assumptions on the physical parameters of the system and up to second order in perturbation theory, the probability that both atoms are ionized is negligible unless $a_2$ lies on the line joining the origin with $a_1$. The work is a fully time-dependent version of the original analysis proposed by Mott in 1929.1 aDell'Antonio, Gianfausto1 aFigari, Rodolfo1 aTeta, Alessandro  uhttp://hdl.handle.net/1963/396900908nas a2200145   4500008004300000245010400043210007000147260001300217520040600230100002000636700002900656700002000685700002100705856003600726       2004                        en_Ud  00aBlow-up solutions for the Schrödinger equation in dimension three with a concentrated nonlinearity0 aBlowup solutions for the Schrödinger equation in dimension three  bElsevier3 aWe present some results on the blow-up phenomenon for the Schroedinger equation in dimension three with a nonlinear term supported in a fixed point. We find sufficient conditions for the blow up exploiting the moment of inertia of the solution and the uncertainty principle. In the critical case, we discuss the additional symmetry of the equation and construct a family of explicit blow up solutions.1 aAdami, Riccardo1 aDell'Antonio, Gianfausto1 aFigari, Rodolfo1 aTeta, Alessandro  uhttp://hdl.handle.net/1963/299800418nas a2200121   4500008004100000245006600041210006600107260001800173100002900191700002000220700002100240856003500261       1998                        en  d00aDiffusion of a particle in presence of N moving point sources0 aDiffusion of a particle in presence of N moving point sources  bSISSA Library1 aDell'Antonio, Gianfausto1 aFigari, Rodolfo1 aTeta, Alessandro  uhttp://hdl.handle.net/1963/13401073nas a2200133   4500008004100000245003800041210003800079260001800117520069900135100002900834700002000863700002100883856003500904       1997                        en  d00aStatistics in space dimension two0 aStatistics in space dimension two  bSISSA Library3 aWe construct as a selfadjoint operator the Schroedinger hamiltonian for a system of $N$ identical particles on a plane, obeying the statistics defined by a representation $\\\\pi_1$ of the braid group. We use quadratic forms and potential theory, and give details only for the free case; standard arguments provide the extension of our approach to the case of potentials which are small in the sense of forms with respect to the laplacian. We also comment on the relation between the analysis given here and other approaches to the problem, and also on the connection with the description of a quantum particle on a plane under the influence of a shielded magnetic field (Aharanov-Bohm effect).1 aDell'Antonio, Gianfausto1 aFigari, Rodolfo1 aTeta, Alessandro  uhttp://hdl.handle.net/1963/13000341nas a2200097   4500008004100000245006400041210006400105260001800169100002100187856003500208       1990                        en  d00aQuadratic forms for singular perturbations of the Laplacian0 aQuadratic forms for singular perturbations of the Laplacian  bSISSA Library1 aTeta, Alessandro  uhttp://hdl.handle.net/1963/75700362nas a2200097   4500008004100000245008700041210006900128260001000197100002100207856003600228       1989                        en  d00aSingular perturbation of the Laplacian and connections with models of random media0 aSingular perturbation of the Laplacian and connections with mode  bSISSA1 aTeta, Alessandro  uhttp://hdl.handle.net/1963/6348