Fluctuations and long-range order in finite-temperature pion condensates

We study the stability of the neutral and charged pion-condensed phases of nuclear matter against fluctuations of the order parameter. At finite temperatures pion condensates with an order parameter varying in only one dimension are, as we show, prohibited, while such condensates are allowed at zero temperature. Condensates that vary in two and three dimensions can be stable at all temperatures. Another allowed state, which may be favored energetically, is a quasi-ordered one-dimensional condensate characterized by long-range pion field correlations decaying only algebraically in space; insufficient experimental resolution may, however, limit one's ability to distinguish such a one-dimensional structure from true one-dimensional long-range order. Finally, we calculate the normal modes and the pion propagator in a charged one-dimensional running-wave condensate, explicitly illustrating the effect of long-range Coulomb forces on the order-parameter fluctuations.     

Magnetic flux penetration and destruction of pion condensates

We show that an external magnetic field can destroy a pion condensate or lead to a vortex ground state stimilar to the mixed phase of a type II superconductor. Critical magnetic fields, determined for the ground state phases of the sigma model, are comparable to those which may be present in neutron stars.     

Gluon condensates,chiral symmetry breaking and pion wave-function

We consider here chiral symmetry breaking in quantum chromodynamics arising from gluon condensates in vacuum. Through coherent states of gluons simulating a mean field type of approximation, we show that the off-shell gluon condensates of vacuum generate a mass-like contribution for the quarks, giving rise to chiral symmetry breaking. We next note that spontaneous breaking of global chiral symmetry links the four component quark field operator to the pion wave function. This in turn yields many hadronic properties in the light quark sector in agreement with experiments, leading to the conclusion that low energy hadron properties are primarily driven by the vacuum structure of quantum chromodynamics.     

Correlation effects in pion double charge exchange in the f72 shell

Analog and non-analog transitions have been measured in the reactions ⁴⁸Ca(π⁺, π⁻)⁴⁸Ti and ⁴⁸Ti(π⁺, π⁻)⁴⁸ Cr at pion energies of 130, 180, 235, and 292 MeV, and θ=5°. The ratios of cross sections for the different transitions are discussed in terms of different models of DCX which offer contrasting explanations.     

Josephson effects in dilute bose-einstein condensates

We propose an experiment that would demonstrate the dc and ac Josephson effects in two weakly linked Bose-Einstein condensates. We consider a time-dependent barrier, moving adiabatically across the trapping potential. The phase dynamics are governed by a "driven-pendulum" equation, as in current-driven superconducting Josephson junctions. At a critical velocity of the barrier (proportional to the critical tunneling current), there is a sharp transition between the dc and ac regimes. The signature is a sudden jump of a large fraction of the relative condensate population. Analytical results are compared with a numerical integration of the Gross-Pitaevskii equation, in an experimentally realistic situation.     

Studying pion effects in the quark propagator

Within the framework of Schwinger-Dyson and Bethe-Salpeter equations we investigate the importance of pions for the quark-gluon interaction. To this end we choose a truncation for the quark-gluon vertex that includes intermediate pion degrees of freedom and adjust the interaction such that unquenched lattice results for various current quark masses are reproduced. After extrapolation to the physical point we find a considerable contribution of the pion back reaction to the quark mass function as well as to the chiral condensate.     

RPA correlation effects in radiative pion capture

A sum rule approach to radiative pion capture is given in terms of the energy-weighted and inverse-energy weighted sum rules. They are evaluated with RPA accuracy for Skyrme-like interactions. The static polarizabilities of the dipole, quadrupole and octupole isovector modes turn out to be the relevant quantities to determine the total branching ratios and mean photon energies.     

Nonlinear effects in interference of bose-einstein condensates

Nonlinear effects in the interference of Bose-Einstein condensates are studied using exact solutions of the one-dimensional nonlinear Schrodinger equation, which is applicable when the lateral motion is confined or negligible. With the inverse scattering method, the interference pattern is studied as a scattering problem with the linear Schrodinger equation, whose potential is profiled by the initial density distribution of the condensates. Our theory not only provides an analytical framework for quantitative predictions for the one-dimensional case, it also gives an intuitive understanding of some mysterious features of the interference patterns observed in experiments and numerical simulations.     

Nonlocal quantum effects with Bose-Einstein condensates

We study theoretically the properties of two Bose-Einstein condensates in different spin states, represented by a double Fock state. Individual measurements of the spins of the particles are performed in transverse directions, giving access to the relative phase of the condensates. Initially, this phase is completely undefined, and the first measurements provide random results. But a fixed value of this phase rapidly emerges under the effect of the successive quantum measurements, giving rise to a quasiclassical situation where all spins have parallel transverse orientations. If the number of measurements reaches its maximum (the number of particles), quantum effects show up again, giving rise to violations of Bell type inequalities. The violation of Bell-Clauser-Horne-Shimony-Holt inequalities with an arbitrarily large number of spins may be comparable (or even equal) to that obtained with two spins.     

Isospin squeezed states, disoriented chiral condensates and pion production: a dynamic group theoretical approach

We make a complete dynamical study of isotopic spin conservation effects on the multiplicity distributions of both hard and soft pions emitted in a quark gluon plasma undergoing a non-equilibrium phase transition.     

Quark condensates in nuclear matter with vacuum effects

On the basis of a bosonized Nambu- Jona-Lasinio (NJL) model with derivative expansions, quark condensates in nuclear matter are studied at one-quark loop level and the dependence of meson masses and couplings on the constituent quark mass is investigated. The condensate ratio obtained here < q?q > _ρB / < q?q > _vac is roughly 0.66 with constituent quark mass of 313 MeV, which yields a corresponding σ _N value to be roughly 42.2 MeV at the mean field level and σ _N =31.4 MeV with the vacuum dependence, where the model parameters describing a Lorentz scalar and a vector field are self-determined.     

Nonlinearity effects in wave propagation in multicomponent Bose-Einstein condensates

We consider a spinor Bose-Einstein condensate in its polar ground state. We analyze magnetization waves of a finite amplitude and show that their nonlinear coupling to density waves dramatically changes the dependence of the frequency on the wave number. On the contrary, the density wave propagation is much less modified by nonlinearity effects. A similar phenomenon in a miscible two-component condensate is also studied.     

Comments on Lorentz-Lorenz effects in low energy pion scattering

The differences between a full Lorentz-Lorenz potential modification, and a ?² approximation to this modification are examined for low energy pion-nucleus elastic scattering. The relationship between these approaches and the single-scattering impulse approximation is also investigated.     

Second order density effects in low energy pion scattering

The differences between a full Lorentz-Lorenz potential modification and a ?² approximation are examined for low energy pion-nucleus elastic scattering. It is found that the two methods give comparable results when Coulomb, absorption and kinematic effects are taken into account.     

How to observe dipolar effects in spinor Bose-Einstein condensates

We propose an experiment which proves the possibility of spinning gaseous media via dipolar interactions in the spirit of the famous Einstein-de Haas effect for ferromagnets. The main idea is to utilize resonances that we find in spinor condensates of alkali atoms while these systems are placed in an oscillating magnetic field. A significant transfer of angular momentum from spin to motional degrees of freedom observed on resonance is a spectacular manifestation of dipolar effects in spinor condensates.