
Note on path integration in a space with a dispirationS. A. Ali, A. InomataDepartment of Physics, State University of New York at Albany, 1400 Washington Avenue, Albany, NY 12222, USA Path integration is carried out in the field of topological defects. The topological defects being considered include a screw dislocation and a disclination in solid. The screw dislocation give rise to torsion, while the disclination generates curvature in the surrounding space. We consider a particle bound in the vicinity of the defect by a short range repulsive and long range attractive force. By path integration we obtain the energy spectrum and the corresponding eigenfunctions.
PACS: 02.40Ky, 61.72Lk Keywords: Riemannian geometries, linear defects, dislocations, disclinations File size: 139 KB Non perturbative series for the calculation of one loop integrals at finite temperatureP. AmoreFacultad de Ciencias, Universidad de Colima, Bernal Diaz del Castillo no. 340, Col. Villa San Sebastian, Colima, Colima, Mexico The calculation of one loop integrals at finite temperature requires the evaluation of certain series, which converge very slowly or can even be divergent. Here we review a new method, recently devised by the author, for obtaining accelerated analytical expressions for these series. The fundamental properties of the new series are studied and an application to a physical example is considered. The relevance of the method to other physical problems is also discussed.
PACS: 11.10.wx,11.10.z Keywords: finite temperature, Riemann zeta function, Hurwitz zeta function File size: 125 KB Path integrals in curved space and the worldline formalismF. BastianelliDipartimento di Fisica, Universita di Bologna and INFN, Sezione di Bologna, Via Irnerio 46, I40126 Bologna, Italy We describe, how to construct and compute unambiguously path integrals for particles moving in a curved space, and how these path integrals can be used to calculate Feynman graphs and effective actions for various quantum field theories with external gravity in the framework of the worldline formalism. In particular, we review a recent application of this worldline approach and discuss vector and antisymmetric tensor fields coupled to gravity. This requires the construction of a path integral for the N=2 spinning particle, which is used to compute the first three SeeleyDeWitt coefficients for all pform gauge fields in all dimensions and to derive exact duality relations.
PACS: 03.65.w, 04.62.+v Keywords: path integrals, worldline formalism File size: 212 KB Nonperturbative approach to (Wiener) functional integral with φ^{4} interactionJ. BohacikInstitute of Physics, Slovak Academy of Sciences, Dubravska cesta 9, 811 45 Bratislava, Slovakia P. Presnajder Department of Theoretical Physics and Physics Education, Faculty of Mathematics, Physics and Informatics, Comenius University, Mlynska dolina F2, 842 48 Bratislava, Slovakia We propose the another, in principe nonperturbative, method of the evaluation of the Wiener functional integral for φ^{4} term in the action. All infinite summations in the results are proven to be convergent. We find the "generalized" GelfandYaglom differential equation implying the functional integral in the continuum limit.
PACS: 11.15.Tk, 12.38.Lg Keywords: functional integral, φ^{4} interaction, nonperturbative approach File size: 102 KB Path integral method and rapid quantum computationH. CuiDepartment of Physics, Beihang University, Beijing, 100083, China A path integral method was developed according to the usual momentumwavefunction relation, it is different from the Feynman's path integral. In order to investigate its validity and usefulness, the path integral method was applied to hydrogen atom,the energy levels were calculated out with the same fine structure as the calculation of the Dirac wave equation, the electronic spin effect was also calculated out correctly when the hydrogen atom is put in a magnetic field. The path integral method would be useful for some physical systems when for which the Dirac equation can not be solved exactly, it was pointed out that the path integral method is a rapid quantum computation method.
PACS: 03.65.Ge, 32.10.Fn Keywords: path integral, hydrogen atom, rapid quantum computation File size: 183 KB Topological order and magnetic flux fractionalization in Josephson junction ladders with Mobius boundary conditions: a twisted CFT descriptionG. Cristofano, Vincenzo MarottaDipartimento di Scienze Fisiche, Universita di Napoli Federico II and INFN, Sezione di Napoli, Via Cintia, Compl. Universitario M. Sant'Angelo, 80126 Napoli, Italy A. Naddeo Dipartimento di Scienze Fisiche, Universita di Napoli Federico II and INFMCoherentia, Unita di Napoli, Via Cintia, Compl. Universitario M. Sant'Angelo, 80126 Napoli, Italy G. Niccoli Sissa and INFN, Sezione di Trieste, Via Beirut 1, 34100 Trieste, Italy We propose a CFT description for a closed onedimensional fully frustrated ladder of quantum Josephson junctions with Mobius boundary conditions; we show how such a system can develop topological order thanks to flux fractionalization. Such a property is crucial for its implementation as a protected solid state qubit.
PACS: 11.25.Hf, 74.50.+r Keywords: Josephson junction ladder, flux fractionalization, topological order File size: 212 KB A quantum field theory as emergent description of constrained supersymmetric classical dynamicsH. T. ElzeDipartimento di Fisica, Via Filippo Buonarroti 2, I56127 Pisa, Italia Deterministic dynamical models are discussed which can be described in quantum mechanical terms. In particular, a local quantum field theory is presented which is a supersymmetric classical model  the Hilbert space approach of Koopman and von Neumann is used to study the evolution of an ensemble of such classical systems. With the help of the supersymmetry algebra, the corresponding Liouville operator can be decomposed into two contributions with positive and negative spectrum, respectively. The unstable negative part is eliminated by a constraint on physical states, which is invariant under the Hamiltonian flow. In this way, choosing suitable phase space coordinates, the classical Liouville equation becomes a functional Schrödinger equation of a genuine quantum field theory. Quantization here is intimately related to the constraint, which selects the part of Hilbert space where the Hamilton operator is positive. This is interpreted as dynamical symmetry breaking in an extended model, introducing a mass scale which discriminates classical dynamics beneath from emergent quantum mechanical behaviour.
PACS: 03.65.Ta, 03.70+k, 05.20.y, 11.30.Pb Keywords: emergent quantum fields, supersymmetry constrained dynamics File size: 162 KB The second term of the semiclassical asymptotic expansion of Feynman path integrals with integrand of polynomial growthD. FujiwaraDepartment of Mathematics, Gakushuin University, 151 Mejiro, Toshimaku Tokyo 1718588, Japan N. Kumanogo GFM, Lisbon University, Av. Prof. Gama Pinto 2, P1649003 Lisboa, Portugal, Department of Mathematics, Kogakuin University, 1242 Nishishinjuku, Shinjukuku Tokyo 1638677, Japan Recently N. Kumanogo succeeded in proving that piecewise linear time slicing approximation to Feynman path integral with integrand F(γ) actually converges to the limit as the mesh of division of time goes to 0 if the functional F(γ) of paths γ belongs to a certain class of functionals with polynomial growth at the infinity. Moreover, he rigorously showed that the limit, which we call the Feynman path integral, has rich properties. The aim of this note is to explain that the use of piecewise classical paths naturally leads us to an analytic formula for the second term of the semiclassical asymptotic expansion of the Feynman path integrals under a little stronger assumptions than that in Kumanogo's. If F(γ)=1, this second term coincides with the one given by G. D. Birkhoff.
PACS: 03.65.Sq, 31.15.Kb Keywords: Feynman path integral, semiclassical asymptotics, stationary phase method File size: 130 KB Casimir energy, the cosmological constant and massive gravitonsR. GarattiniUniversita degli Studi di Bergamo, Facolta di Ingegneria, Viale Marconi 5, 24044 Dalmine (Bergamo), ITALY and INFN  sezione di Milano, Via Celoria 16, Milan, Italy The cosmological constant appearing in the WheelerDe Witt equation is considered as an eigenvalue of the associated SturmLiouville problem. A variational approach with Gaussian trial wave functionals is used as a method to study such a problem. We approximate the equation to one loop in a Schwarzschild background and a zeta function regularization is involved to handle with divergences. The regularization is closely related to the subtraction procedure appearing in the computation of Casimir energy in a curved background. A renormalization procedure is introduced to remove the infinities together with a renormalization group equation. The case of massive gravitons is discussed.
PACS: 04.60.m, 04.62.+v, 11.10.Gh Keywords: Cosmological Constant, Renormalization, Quantum Gravity File size: 178 KB Electron spin dynamics in nanodevices and geometrical effectsD. GiulianoDipartimento di Scienze Fisiche Universita degli studi di Napoli Federico II, Napoli, Italy, Dipartimento di Fisica, Universita della Calabria and I.N.F.N., Gruppo collegato di Cosenza, Arcavacata di Rende, I87036, Cosenza, Italy P. Lucignano Dipartimento di Scienze Fisiche Universita degli studi di Napoli Federico II, Napoli, Italy, CoherentiaINFM, Monte S.Angelo  via Cintia, I80126 Napoli, Italy, SISSA and INFM Democritos National Simulation Center, Via Beirut 24, 34014 Trieste, Italy A. Tagliacozzo Dipartimento di Scienze Fisiche Universita degli studi di Napoli Federico II, Napoli, Italy, CoherentiaINFM, Monte S.Angelo  via Cintia, I80126 Napoli, Italy We discuss nonlocal quantum mechanical effects in mesoscopic devices,
for studying which, path integral has been shown to provide quite a
powerful and compact approach. In particular, we focus onto geometrical
phase effects. As a former example, we discuss how a geometrical phase
due to spinorbit coupling may affect AharonovBohm conductance
oscillations in a mesoscopic ring. As a latter example, we show that a
pertinent cycling in parameter space may induce a robust Berry phase in
a quantum dot tuned close to a threelevel degeneracy. In both cases, we
propose to detect geometrical phase effects by means of an appropriate
DC transport measurement.
PACS: 72.25.Dc, 72.25.Rb, 85.75.d Keywords: electronspin dynamics, nanodevice, geometrical effects File size: 328 KB Logarithmic corrections to the entropy of the exact string black holeD. GrumillerInstitute for Theoretical Physics, University of Leipzig, Augustusplatz 1011, D04109, Germany Exploiting a recently constructed target space action for the exact string black hole, logarithmic corrections to the leading order entropy are studied. There are contributions from thermal fluctuations and from corrections due to α'>0 which for the microcanonical entropy appear with different signs and therefore may cancel each other, depending on the overall factor in front of the action. For the canonical entropy no such cancellation occurs. Remarks are made regarding the applicability of the approach and concerning the microstates. As a byproduct a formula for logarithmic entropy corrections in generic 2D dilaton gravity is derived.
PACS: 04.70.Dy Keywords: black holes, space action File size: 249 KB On path integral for the radial Dirac equationT. IchinoseDepartment of Mathematics, Faculty of Science, Kanazawa University, Kanazawa, 9201192, Japan A path integral representation is given to the Green's function for the radial Dirac equation, by constructing a countably additive path space measure on the space of continuous paths living on the real halfline. An application is suggested to a problem in quantum field theory.
PACS: 03.65.Pm; 02.30.Sa Keywords: path integral, radial Dirac operator, Green's function File size: 170 KB Modification of Klauder's coherent statesA. Inomata and M. SadiqDepartment of Physics, State University of New York at Albany, Albany, New York 12222 A modified version of Klauder's coherent state is presented. Klauder's state is a generalized coherent state that can be constructed in terms of the energy eigenstates of a given nondegenerate system without referring to any symmetry group. It can be formed for continuous as well as discrete dynamics. The proposed modification allows us to deal with degenerate systems and to treat discrete states and continuous states in a unified manner. Some examples are given for illustration.
PACS: 75.45.+j Keywords: coherent states, discrete dynamics File size: 131 KB BeadFourier path integral molecular dynamics for identical particlesS. D. Ivanov, A. P. LyubartsevyDivision of Physical Chemistry, Arrhenius Laboratory, Stockholm University, S10691, Stockholm, Sweden The BeadFourier path integral molecular dynamics technique, introduced earlier [S.D. Ivanov, A.P. Lyubartsev, and A. Laaksonen, Phys. Rev. E 67 (2003) 066710] for the case of distinguishable particles is reformulated in order to achieve more efficient sampling. The reformulation is carried out on the basis of the staging transformation of beads' coordinates, yielding all dynamical variables to move on similar time scales. The formalism for identical particles is presented. It is shown, that the straightforward approach leads to impossibility of the sign changes. A recipe to overcome this problem is suggested. It is demonstrated, that the developed formalism for identical particles can also be reformulated, providing efficient molecular dynamics.
PACS: 05.30.d, 02.70.Ns Keywords: BeadFourier, path integral, molecular dynamics, identical particles File size: 215 KB Phase transitions in a generalized ψ^{4} modelW. Janke, E. BittnerInstitut für Theoretische Physik, Universität Leipzig, Augustusplatz 10/11, D04109 Leipzig, Germany Monte Carlo simulations are employed for studying a generalized threedimensional complex ψ^{4} field theory with an additional fugacity term controlling the vortexline density. It is shown that only with such an extra term, the XY type secondorder phase transitions of the standard model can be tuned in certain regions of the phase diagram to become firstorder. In particular, this settles a recent controversy in the standard model related to the measure of the functional integral. Also the topological excitations of the model (vortex networks) are carefully examined.
PACS: 02.70.Lq, 64.60.i Keywords: phase transitions, 3D XY model universality class, vortex networks File size: 504 KB On quantum mechanics as a constrained deterministic dynamicsM. BlasoneDipartimento di Fisica, Universita di Salerno, I84100 Salerno, Italy P. Jizba FNSPE, Czech Technical University, Brehova 7, 115 19 Praha 1, Czech Republic H. Kleinert Institut für Theoretische Physik, Freie Universität Berlin, Arnimallee 14 D14195 Berlin, Germany In this paper we review recent results obtained in [quantph/0504200] on the path integral formulation of 't Hooft's derivation of quantum from classical physics. In particular, we employ the FaddeevJackiw treatment of classical constrained systems to show how 't Hooft's loss of information condition may yield a genuine quantum mechanical system. With two simple examples we discuss some of the consequences that follow from our approach.
PACS: 03.65.w, 31.15.Kb, 45.20.Jj Keywords: path integral, constrained systems, FaddeevJackiw approach File size: 153 KB Path integrals, and classical and quantum constraintsJ. R. KlauderDepartment of Physics and Department of Mathematics, University of Florida, Gainesville, FL 32611, USA Systems with constraints pose problems when they are quantized. Moreover, the Dirac procedure of quantization prior to reduction is preferred. The projection operator method of quantization, which can be most conveniently described by coherent state path integrals, enables one to directly impose a regularized form of the quantum constraints. This procedure also overcomes conventional difficulties with normalization and second class constraints that invalidate conventional Dirac constraint quantization procedures.
PACS: 03.65.Ca, 03.65.Db Keywords: path integrals, operator formulation, quantum mechanics File size: 146 KB su(21) path integral for strongly correlated electrons: application to the pseudogap phenomenonE. KochetovBogoliubov Theoretical Laboratory, Joint Institute for Nuclear Research, 141980 Dubna, Russia We employ the su(21) superalgebra representation of the tJ model Hamiltonian to rigorously enforce the local constraint that guarantees a given lattice site to be either empty or singly occupied. This constraint arises because a Coulomb repulsive energy dominates over hopping energy and results in strong electron correlation which determines the basic physics of highT_{c} superconductors. We apply this technique to derive a bosonspinless fermion model for the tJ Hamiltonian, which provides a microscopic scenario to take into account local spin fluctuations to the pseudogap phenomenon.
PACS: 74.20.Mn, 75.10.Jm Keywords: su(21) path integral, highT_{c} superconductors, tJ model, pseudogap File size: 136 KB Smooth functional derivatives in Feynman path integralsN. KumanogoGFM, Lisbon University, Av. Prof. Gama Pinto 2, P1649003 Lisboa, PORTUGAL, Department of Mathematics, Kogakuin University, 1242 Nishishinjuku, Shinjukuku, Tokyo 1638677, JAPAN D. Fujiwara Department of Mathematics, Gakushuin University, 151 Mejiro Toshimaku Tokyo 1718588, JAPAN This note is an exposition of our resent papers. We give a fairly general class of functionals on a path space so that Feynman path integral has a mathematically rigorous meaning. More precisely, for any functional belonging to our class, the time slicing approximation of Feynman path integral converges uniformly on compact subsets of the configuration space. Our class of functionals is closed under addition, multiplication, translation, real linear transformation and functional differentiation. The integration by parts and Taylor's expansion formula with respect to functional differentiation holds in Feynman path integral. Feynman path integral is invariant under translation and orthogonal transformation. The interchange of the order with RiemannStieltjes integrals, the interchange of the order with a limit, the perturbation expansion formula, the semiclassical approximation and the fundamental theorem of calculus holds in Feynman path integral.
PACS: 31.15.Kb, 02.30.Nw, 02.50.Fz Keywords: Feynman path integral, oscillatory integral, stochastic analysis File size: 176 KB Development of the Green function method on a basis of deterministic approach to approximate functional integrationY. Y. Lobanov and V. D. RushaiJoint Institute for Nuclear Research, Dubna Within the general approach which is understood as the Green function method, we develop a numerical method based on representation of the Green functions for a class of problems in the form of functional integrals with respect to Gaussian measures, and subsequent calculation of the integrals with the help of a deterministic approach. In this case the solving of the problems is reduced to evaluation of usual (Riemann) integrals of relatively low multiplicity. The method was applied to numerical solving of the Schrödinger equation and the related diffusion equation, and also to description of time evolution of some Markovian open quantum systems. The features of the method and possible area of its application are discussed.
PACS: 02.60.x, 02.70.c, 03.65.w Keywords: green function, approximate functional integration File size: 213 KB On the quantization of the superparticle action in proper time and the Lorentz group SO(3,1)D. J. CiriloLombardoBogoliubov Laboratory of Theoretical Physics, Joint Institute of Nuclear Research, 141980, Dubna, Russia In this work the problem of the square root operator is analyzed. To this end we
considered a relativistic geometrical action of a particle in the superspace in order to
quantize it and to obtain the spectrum of physical states but remaind the Hamiltonian
in the natural square root form. We show, after complete quantization of the model,
that the physical states that the square root Hamiltonian can operate correspond to the
representations with the lowest weights λ=1/4 and λ=3/4.
PACS: 12.60.Jv, 11.10.Ef, 11.30.Cp Keywords: superparticle, Hamiltonian formulation, relativistic theories File size: 141 KB The functional integration and the twopoint correlation functions of the trapped Bose gasC. Malyshev, N. M. BogoliubovSt.Petersburg Department of Steklov Mathematical Institute (PDMI), 27, Fontanka, St.Petersburg, 191023, RUSSIA A quantum fieldtheoretical model, which describes spatially nonhomogeneous repulsive Bose gas in an external harmonic potential is considered. Twopoint thermal correlation functions of the Bose gas are calculated in the framework of the functional integration approach. Successive integration over the highenergy functional variables first and then over the lowenergy ones is used. The effective action functional for the lowenergy variables is obtained in one loop approximation. The functional integral representations for the correlation functions are estimated by means of the stationary phase approximation. A powerlaw asymptotical behaviour of the correlators of the onedimensional Bose gas is demonstrated in the limit, when the temperature is going to zero, while the volume occupied by the nonhomogeneous Bose gas infinitely increases. The powerlaw behaviour is governed by the critical exponent dependent on the spatial arguments.
PACS: 05.30.Jp, 31.15.Kb Keywords: functional integration, Bose gas, correlation functions File size: 194 KB Cancellation of anomalies in a path integral formulation for classical field theoriesD. MauroDepartment of Theoretical Physics, University of Trieste, Strada Costiera 11, MiramareGrignano, 34014 Trieste, Italy Some symmetries can be broken in the quantization process (anomalies) and this breaking is signalled by a noninvariance of the quantum path integral measure. In this talk we show that it is possible to formulate also classical field theories via path integral techniques. The associated classical functional measure is larger than the quantum one, because it includes some auxiliary fields. For a fermion coupled with a gauge field we prove that the way these auxiliary fields transform compensates exactly the Jacobian which arises from the transformation of the fields appearing in the quantum measure. This cancels the quantum anomaly and restores the symmetry at the classical level.
PACS: 11.30.Rd, 45.20 Keywords: chiral anomalies, classical and quantum functional methods File size: 110 KB Path integral calculation for asymmetric doublewell potential: cumulant, DebyeWaller factor and chemical reactionT. Miyanaga, K. NittaDepartment of Materials Science and Technology, Faculty of Science and Technology, Hirosaki University, Hirosaki, Aomori 0368561, Japan T. Fujikawa Graduate School of Science, Chiba University, Yayoicho 133, Inage, Chiba, 2638522, Japan Path integral effective potential method is applied to symmetric and asymmetric doublewell potential systems. We calculate the temperature dependence of 2nd, 3rd and 4th order cumulants, which are useful to study vibrational effects in various spectroscopic techniques. We evaluate the DebyeWaller factors in EXAFS, EELFS and XPD and discuss the characteristic features caused by asymmetric doublewell potential. We also relate this method to the quantum tunneling effect in the simple chemical reaction rate constant.
PACS: 61.10.Ht Keywords: path integral, DebyeWaller factor, EXAFS, doublewell potential File size: 524 KB Design of highorder shorttime approximations as a problem of matching the covariance of a Brownian motionC. PredescuDepartment of Chemistry and Kenneth S. Pitzer Center for Theoretical Chemistry, University of California, Berkeley, California 94720 One of the outstanding problems in the numerical discretization of the FeynmanKac formula calls for the design of arbitraryorder shorttime approximations that are constructed in a stable way, yet only require knowledge of the potential function. In essence, the problem asks for the development of a functional analogue to the Gauss quadrature technique for onedimensional functions. In PRE 69 (2004) 056701, it has been argued that the problem of designing an approximation of order ny is equivalent to the problem of constructing discretetime Gaussian processes that are supported on finitedimensional probability spaces and match certain generalized moments of the Brownian motion. Since Gaussian processes are uniquely determined by their covariance matrix, it is tempting to reformulate the momentmatching problem in terms of the covariance matrix alone. Here, we show how this can be accomplished.
PACS: 02.70.Ss, 05.40.Jc Keywords: FeynmanKac formula, Brownian motion, shorttime approximations, order of convergence File size: 157 KB The TitiusBode law and a quantumlike description of the planetary systemsF. ScardigliCENTRA, Departamento de Fisica, Instituto Superior Tecnico, Av. Rovisco Pais 1, 1049001 Lisboa, Portugal The TitiusBode law for planetary distances is reviewed. A model describing the basic features of this law in the "quantumlike" language of a wave equation is proposed. Some considerations about the 't Hooft idea on the quantum behaviour of deterministic systems with dissipation are discussed.
PACS: 03.65.Ta, 96.35.j Keywords: foundations of quantum mechanics, planetary systems File size: 189 KB Feynman path integrals for exponents of polynomially growing functionalsE. T. ShavgulidzeDepartment of Mechanics and Mathematics, Lomonosov Moscow State University, Vorobievy Gory, 119899 Moscow, Russia A general class of functional integrals of the exponents of polynomially growing functionals on the Hilbert space be studied. A representation formula by integrals for Gaussian measures is given for this class of functional integrals. These results are applied to provide a rigorous Feynman path integral representations for the solutions of the time dependent Schrodinger equations with a polynomially growing potentials (it is possible with alternating signs). Special selfadjoint extensions for Schrodinger differential operators with a polynomially growing potentials are obtained.
PACS: 03.65.Ge, 11.10.Lm, 74.20.Kk Keywords: polynomially growing functionals, functional integrals File size: 99 KB Unidirectional diffusion flux, Brownian and Langevin simulationsA. Singer, Z. SchussDepartment of Mathematics, TelAviv University, RamatAviv, 69978 TelAviv, Israel B. Nadler Department of Mathematics, Yale University, 10 Hillhouse Avenue P.O. Box 208283, New Haven, Connecticut 065208283, USA The Wiener path integral splits the net diffusion flux into infinite unidirectional fluxes, whose difference is the classical diffusion flux. The infinite unidirectional flux is an artifact of the diffusion approximation to Langevin's equation, an approximation that fails on time scales shorter than the relaxation time 1/γ. The probability of onedimensional Brownian trajectories that cross a point in one direction per unit time Δt equals that of Langevin trajectories if γΔt=2. This result is relevant to Brownian and Langevin dynamics simulation of particles in a finite volume inside a large bath. We describe the sources of new trajectories at the boundaries of the simulation that maintain fixed average concentrations and avoid the formation of spurious boundary layers.
PACS: 31.15.Kb, 02.50.r Keywords: Wiener's path integral, diffusion, Brownian simulations, Langevin File size: 300 KB Pathintegrals and the BEC/BCS crossover in dilute atomic gasesJ. TempereTFVS, Universiteit Antwerpen, Universiteitsplein 1, B2610 Antwerpen, Belgium J. T. Devreese TFVS, Universiteit Antwerpen, Universiteitsplein 1, B2610 Antwerpen, Belgium Both the trapping geometry and the interatomic interaction strength of a dilute ultracold fermionic gas can be well controlled experimentally. When the interactions are tuned to strong attraction, Cooper pairing of neutral atoms takes place and a BCS super fluid is created. Alternatively, the presence of Feshbach resonances in the interatomic scattering allow populating a molecular (bound) state. These molecules are more tightly bound than the Cooper pairs and can form a BoseEinstein condensate (BEC). In this contribution, we describe both the BCS and BEC regimes, and the crossover, from a functional integral point of view. The pathintegral description allows to derive the properties of the superfluid (such as vortices and Josephson tunneling) and follow them as the system is tuned from BCS the BEC.
PACS: 03.75.b, 03.75.Lm Keywords: super fluidity, BEC/BCS crossover File size: 233 KB Pathintegral evaluation of the kinetic isotope effects based on the quantuminstanton approximationJ. Vanicek, W. H. MillerDepartment of Chemistry and Kenneth S. Pitzer Center for Theoretical Chemistry, University of California, Berkeley, CA 94720, USA A general method for computing kinetic isotope effects is described. The method uses the quantuminstanton approximation and is based on the thermodynamic integration with respect to the mass of the isotopes and on the pathintegral MonteCarlo evaluation of relevant thermodynamic quantities. The central ingredients of the method are the MonteCarlo estimators for the logarithmic derivatives of the partition function and the deltadelta correlation function. Several alternative estimators for these quantities are described here and their merits are compared on the benchmark hydrogenexchange reaction, H+H_{2}>H_{2}+H on the TruhlarKuppermann potential energy surface. Finally, a qualitative discussion of issues arising in manydimensional systems is provided.
PACS: 05.10.a, 05.30.d Keywords: kinetic isotope effect, quantum instanton approximation File size: 195 KB 