2,004 research outputs found

    Instabilities of Twisted Strings

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    A linear stability analysis of twisted flux-tubes (strings) in an SU(2) semilocal theory -- an Abelian-Higgs model with two charged scalar fields with a global SU(2) symmetry -- is carried out. Here the twist refers to a relative phase between the two complex scalars (with linear dependence on, say, the zz coordinate), and importantly it leads to a global current flowing along the the string. Such twisted strings bifurcate with the Abrikosov-Nielsen-Olesen (ANO) solution embedded in the semilocal theory. Our numerical investigations of the small fluctuation spectrum confirm previous results that twisted strings exhibit instabilities whose amplitudes grow exponentially in time. More precisely twisted strings with a single magnetic flux quantum admit a continuous family of unstable eigenmodes with harmonic zz dependence, indexed by a wavenumber k[km,km]k\in[-k_{\rm m},k_{\rm m}]. Carrying out a perturbative semi-analytic analysis of the bifurcation, it is found that the purely numerical results are very well reproduced. This way one obtains not only a good qualitative description of the twisted solutions themselves as well as of their instabilities, but also a quantitative description of the numerical results. Our semi-analytic results indicate that in close analogy to the known instability of the embedded ANO vortex a twisted string is also likely to expand in size caused by the spreading out of its magnetic flux.Comment: 27 pages, 18 figures. Typos corrected, references adde

    Renormalization group approach to Fermi Liquid Theory

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    We show that the renormalization group (RG) approach to interacting fermions at one-loop order recovers Fermi liquid theory results when the forward scattering zero sound (ZS) and exchange (ZS') channels are both taken into account. The Landau parameters are related to the fixed point value of the ``unphysical'' limit of the forward scattering vertex. We specify the conditions under which the results obtained at one-loop order hold at all order in a loop expansion. We also emphasize the similarities between our RG approach and the diagrammatic derivation of Fermi liquid theory.Comment: 4 pages (RevTex) + 1 postcript file, everything in a uuencoded file, uses epsf (problem with the figure in the first version

    Interaction of a surface acoustic wave with a two-dimensional electron gas

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    When a surface acoustic wave propagates on the surface of a GaAs semiconductor, coupling between electrons in the two-dimensional electron gas beneath the interface and the elastic host crystal through piezoelectric interaction will attenuate the SAW. The coupling coefficient is calculated for the SAW propagating along an arbitrary direction. It is found that the coupling strength is largely dependent on the propagating direction. When the SAW propagates along the [011] direction, the coupling becomes quite weak.Comment: 3 figure

    High Density Effective Theory Confronts the Fermi Liquid

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    The high density effective theory recently introduced by Hong and Hsu to describe ultradense relativistic fermionic matter is used to calculate the tree-level forward scattering amplitude between two particles at the Fermi surface. While the direct term correctly reproduces that of the underlying gauge theory, the exchange term has the wrong sign. The physical consequences are discussed in the context of Landau's theoretical description of the Fermi liquid.Comment: 15 pages, 2 figures; conclusion expanded, reference adde

    Empirical Emission Functions for LPM Suppression of Photon Emission from Quark-Gluon Plasma

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    The LPM suppression of photon emission rates from the quark gluon plasma have been studied at different physical conditions of the plasma given by temperature and chemical potentials.The integral equation for the transverse vector function (f(p_t)) consisting of multiple scattering effects is solved for the parameter set {p,k,kappa,T}, for bremsstrahlung and AWS processes. The peak positions of these distributions depend only on the dynamical variable x=(T/kappa)|1/p-1/(p+k)|. Integration over these distributions multiplied by x^2 factor also depends on this variable x,leading to a unique global emission function g(x) for all parameters. Empirical fits to this dimensionless emission function, g(x), are obtained. The photon emission rate calculations with LPM suppression effects reduce to one dimensional integrals involving folding over the empirical g(x) function with appropriate distribution functions and the kinematic factors. Using this approach, the suppression factors for both bremsstrahlung and AWS have been estimated for various chemical potentials and compared with the variational method

    Realistic Electron-Electron Interaction in a Quantum Wire

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    The form of an effective electron-electron interaction in a quantum wire with a large static dielectric constant is determined and the resulting properties of the electron liquid in such a one-dimensional system are described. The exchange and correlation energies are evaluated and a possibility of a paramagnetic-ferromagnetic phase transition in the ground state of such a system is discussed. Low-energy excitations are briefly described.Comment: 10 pages, 6 figure

    Mass singularity and confining property in QED3QED_3

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    We discuss the properties of the position space fermion propagator in three dimensional QED which has been found previouly based on Ward-Takahashi-identity for soft-photon emission vertex and spectral representation.There is a new type of mass singularity which governs the long distance behaviour.It leads the propagator vanish at large distance.This term corresponds to dynamical mass in position space.Our model shows confining property and dynamical mass generation for arbitrary coupling constant.Since we used dispersion retation in deriving spectral function there is a physical mass which sets a mass scale.For finite cut off we obtain the full propagator in the dispersion integral as a superposition of different massses.Low energy behaviour of the proagator is modified to decrease by position dependent mass.In the limit of zero infrared cut-off the propagator vanishes with a new kind of infrared behaviour.Comment: 22pages,4figures,revtex4,Notational sloppiness are crrected.Submitted to JHE

    The quantum theory of the Penning trap

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    We present the quantum theory of the Penning trap in terms of individual x and y radial modes of the motion of a single charged particle in the trap, and demonstrate how the conventional rotating frame used to examine these individual dynamics fails in the quantum regime. In solving the radial Hamiltonian in the {x,y} basis, we show how canonical transformation of the variables must take place after quantization, in order that these separate motions can be consistently tracked. This is in contrast to previous work. The results of the discussion lend themselves to a fully quantum treatment of mode coupling in the trap, leading to an avoided crossing between the coupled energy levels of the system. Exploiting the algebraic structure of the problem allows employment of a dressed-atom formalism within quantum Penning trap theory, and future applications resulting from this are proposed

    Flat coordinates and dilaton fields for three--dimensional conformal sigma models

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    Riemannian coordinates for flat metrics corresponding to three--dimensional conformal Poisson--Lie T--dualizable sigma models are found by solving partial differential equations that follow from the transformations of the connection components. They are then used for finding general forms of the dilaton fields satisfying the vanishing beta equations of the sigma models.Comment: 16 pages, no figure

    The Equation of State for Cool Relativistic Two-Constituent Superfluid Dynamics

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    The natural relativistic generalisation of Landau's two constituent superfluid theory can be formulated in terms of a Lagrangian LL that is given as a function of the entropy current 4-vector sρs^\rho and the gradient φ\nabla\varphi of the superfluid phase scalar. It is shown that in the ``cool" regime, for which the entropy is attributable just to phonons (not rotons), the Lagrangian function L(s,φ)L(\vec s, \nabla\varphi) is given by an expression of the form L=P3ψL=P-3\psi where PP represents the pressure as a function just of φ\nabla\varphi in the (isotropic) cold limit. The entropy current dependent contribution ψ\psi represents the generalised pressure of the (non-isotropic) phonon gas, which is obtained as the negative of the corresponding grand potential energy per unit volume, whose explicit form has a simple algebraic dependence on the sound or ``phonon" speed cPc_P that is determined by the cold pressure function PP.Comment: 26 pages, RevTeX, no figures, published in Phys. Rev. D. 15 May 199
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