Decay of correlations in the dissipative two-state system

We study the equilibrium correlation function of the polaron-dressed tunnelling operator in the dissipative two-state system and compare the asymptoptic dynamics with that of the position correlations. For an Ohmic spectral density with the damping strength $K=1/2$, the correlation functions are obtained in analytic form for all times at any $T$ and any bias. For $K<1$, the asymptotic dynamics is found by using a diagrammatic approach within a Coulomb gas representation. At T=0, the tunnelling or coherence correlations drop as $t^{-2K}$, whereas the position correlations show universal decay $\propto t^{-2}$. The former decay law is a signature of unscreened attractive charge-charge interactions, while the latter is due to unscreened dipole-dipole interactions.Comment: 5 pages, 5 figures, to be published in Europhys. Let

From GM Law to A Powerful Mean Field Scheme

A new and powerful mean field scheme is presented. It maps to a one-dimensional finite closed chain in an external field. The chain size accounts for lattice topologies. Moreover lattice connectivity is rescaled according to the GM law recently obtained in percolation theory. The associated self-consistent mean-field equation of state yields critical temperatures which are within a few percent of exact estimates. Results are obtained for a large variety of lattices and dimensions. The Ising lower critical dimension for the onset of phase transitions is $d_l=1+\frac{2}{q}$. For the Ising hypercube it becomes the Golden number $d_l=\frac{1+\sqrt 5}{2}$. The scheme recovers the exact result of no long range order for non-zero temperature Ising triangular antiferromagnets.Comment: 3M Conference Proceedings, San Jose, California (November, 1999

Characterization of coherent impurity effects in solid state qubits

We propose a characterisation of the effects of bistable coherent impurities in solid state qubits. We introduce an effective impurity description in terms of a tunable spin-boson environment and solve the dynamics for the qubit coherences. The dominant rate characterizing the asymptotic time limit is identified and signatures of non-Gaussian behavior of the quantum impurity at intermediate times are pointed out. An alternative perspective considering the qubit as a measurement device for the spin-boson impurity is proposed.Comment: 4 pages, 5 figures. Replaced with published version, minor change

The core helium flash revisited: II. Two and three-dimensional hydrodynamic simulations

We study turbulent convection during the core helium flash close to its peak by comparing the results of two and three-dimensional hydrodynamic simulations. We use a multidimensional Eulerian hydrodynamics code based on state-of-the-art numerical techniques to simulate the evolution of the helium core of a $1.25 M_{\odot}$ Pop I star. Our three-dimensional hydrodynamic simulations of the evolution of a star during the peak of the core helium flash do not show any explosive behavior. The convective flow patterns developing in the three-dimensional models are structurally different from those of the corresponding two-dimensional models, and the typical convective velocities are smaller than those found in their two-dimensional counterparts. Three-dimensional models also tend to agree better with the predictions of mixing length theory. Our hydrodynamic simulations show the presence of turbulent entrainment that results in a growth of the convection zone on a dynamic time scale. Contrary to mixing length theory, the outer part of the convection zone is characterized by a sub-adiabatic temperature gradient.Comment: 19 pages, 18 figure

Ground state energy of a homogeneous Bose-Einstein condensate beyond Bogoliubov

The standard calculations of the ground-state energy of a homogeneous Bose gas rely on approximations which are physically reasonable but difficult to control. Lieb and Yngvason [Phys. Rev. Lett. 80, 2504 (1998)] have proved rigorously that the commonly accepted leading order term of the ground state energy is correct in the zero-density-limit. Here, strong indications are given that also the next to leading term is correct. It is shown that the first terms obtained in a perturbative treatment provide contributions which are lost in the Bogoliubov approach.Comment: 6 pages, accepted for publication in Europhys. Lett. http://www.epletters.ch

A Single Impurity in Tomonaga-Luttinger Liquids

The problem of a single impurity in one dimensional Tomonaga-Luttinger liquids with a repulsive electron-electron interaction is discussed. We find that the renormalization group flow diagram for the parameters characterizing the impurity is rather complex. Apart from the fixed points corresponding to two weakly connected semi-infinite wires, the flow diagram contains additional fixed points which control the low temperature physics when the bare potential of the impurity is not strong.Comment: To be published in the Philosophical Magazine in the Proceedings of the "MINERVA WORKSHOP on MESOSCOPICS, FRACTALS and NEURAL NETWORKS", Eilat, Israel, March 199

Rapidity gap survival in the black-disk regime

We summarize how the approach to the black-disk regime (BDR) of strong interactions at TeV energies influences rapidity gap survival in exclusive hard diffraction pp -> p + H + p (H = dijet, Qbar-Q, Higgs). Employing a recently developed partonic description of such processes, we discuss (a) the suppression of diffraction at small impact parameters by soft spectator interactions in the BDR; (b) further suppression by inelastic interactions of hard spectator partons in the BDR; (c) correlations between hard and soft interactions. Hard spectator interactions substantially reduce the rapidity gap survival probability at LHC energies compared to previously reported estimates.Comment: 4 pages, 3 figures. Proceedings of XV International Workshop on Deep-Inelastic Scattering and Related Subjects (DIS 2007), Munich, Germany, Apr. 16-20, 200

Violation of the Leggett-Garg Inequality in Neutrino Oscillations

The Leggett-Garg inequality, an analogue of Bell's inequality involving correlations of measurements on a system at different times, stands as one of the hallmark tests of quantum mechanics against classical predictions. The phenomenon of neutrino oscillations should adhere to quantum-mechanical predictions and provide an observable violation of the Leggett-Garg inequality. We demonstrate how oscillation phenomena can be used to test for violations of the classical bound by performing measurements on an ensemble of neutrinos at distinct energies, as opposed to a single neutrino at distinct times. A study of the MINOS experiment's data shows a greater than $6{\sigma}$ violation over a distance of 735 km, representing the longest distance over which either the Leggett-Garg inequality or Bell's inequality has been tested.Comment: Updated to match published version. 6 pages, 2 figure

Transverse imaging of the proton in exclusive diffractive pp scattering

In a recent paper (hep-ph/0608271) we describe a new approach to rapidity gap survival (RGS) in the production of high-mass systems (H = dijet, Higgs, etc.) in exclusive double-gap diffractive pp scattering, pp -> p + H + p. It is based on the idea that hard and soft interactions are approximately independent (QCD factorization), and allows us to calculate the RGS probability in a model-independent way in terms of the gluon generalized parton distributions (GPDs) in the colliding protons and the pp elastic scattering amplitude. Here we focus on the transverse momentum dependence of the cross section. By measuring the "diffraction pattern," one can perform detailed tests of the interplay of hard and soft interactions, and even extract information about the gluon GPD in the proton from the data.Comment: 4 pages, 2 figures, uses ws-procs9x6.cls. Proceedings of XIV International Workshop on Deep Inelastic Scattering (DIS2006), Tsukuba City, Japan, Apr 20 - 24, 200

Metastable states and macroscopic quantum tunneling in a cold atom Josephson ring

We study macroscopic properties of a system of weakly interacting neutral bosons confined in a ring-shaped potential with a Josephson junction. We derive an effective low energy action for this system and evaluate its properties. In particular we find that the system possesses a set of metastable current-carrying states and evaluate the rates of transitions between these states due to macroscopic quantum tunneling. Finally we discuss signatures of different metastable states in the time-of-flight images and argue that the effect is observable within currently available experimental technique.Comment: 4 pages, 2 figure