26,794 research outputs found

    String Evolution with Friction

    Get PDF
    We study the effects of friction on the scaling evolution of string networks in condensed matter and cosmological contexts. We derive a generalized `one-scale' model with the string correlation length LL and velocity vv as dynamical variables. In non-relativistic systems, we obtain a well-known Lt1/2L\propto t^{1/2} law, showing that loop production is important. For electroweak cosmic strings, we show transient damped epoch scaling with Lt5/4L\propto t^{5/4} (or, in the matter era, Lt3/2L\propto t^{3/2}). A low initial density implies an earlier period with Lt1/2L\propto t^{1/2}. For GUT strings, the approach to linear scaling LtL\propto t is faster than previously estimated.Comment: 8 pages, uuencoded gziped .ps file. Paper submitted to Phys. Rev. Let

    Effects of Inflation on a Cosmic String Loop Population

    Full text link
    We study the evolution of simple cosmic string loop solutions in an inflationary universe. We show, for the particular case of circular loops, that periodic solutions do exist in a de Sitter universe, below a critical loop radius RcH=1/2R_c H=1/2. On the other hand, larger loops freeze in comoving coordinates, and we explicitly show that they can survive more ee-foldings of inflation than point-like objects. We discuss the implications of these findings for the survival of realistic cosmic string loops during inflation, and for the general characteristics of post-inflationary cosmic string networks. We also consider the analogous solutions for domain walls, in which case the critical radius is RcH=2/3R_c H=2/3.Comment: 5 pages, 5 figures, accepted for publication in Physical Review

    Contribution of domain wall networks to the CMB power spectrum

    Get PDF
    We use three domain wall simulations from the radiation era to the late time dark energy domination era based on the PRS algorithm to calculate the energy-momentum tensor components of domain wall networks in an expanding universe. Unequal time correlators in the radiation, matter and cosmological constant epochs are calculated using the scaling regime of each of the simulations. The CMB power spectrum of a network of domain walls is determined. The first ever quantitative constraint for the domain wall surface tension is obtained using a Markov chain Monte Carlo method; an energy scale of domain walls of 0.93 MeV, which is close but below the Zel'dovich bound, is determined.Comment: Submitted to Physics Letters

    Vorton Formation

    Get PDF
    In this paper we present the first analytic model for vorton formation. We start by deriving the microscopic string equations of motion in Witten's superconducting model, and show that in the relevant chiral limit these coincide with the ones obtained from the supersonic elastic models of Carter and Peter. We then numerically study a number of solutions of these equations of motion and thereby suggest criteria for deciding whether a given superconducting loop configuration can form a vorton. Finally, using a recently developed model for the evolution of currents in superconducting strings we conjecture, by comparison with these criteria, that string networks formed at the GUT phase transition should produce no vortons. On the other hand, a network formed at the electroweak scale can produce vortons accounting for up to 6% of the critical density. Some consequences of our results are discussed.Comment: 41 pages; color figures 3-6 not included, but available from authors. To appear in Phys. Rev.

    Topological Defects in Contracting Universes

    Get PDF
    We study the behaviour and consequences of cosmic string networks in contracting universes. They approximately behave during the collapse phase as a radiation fluids. Scaling solutions describing this are derived and tested against high-resolution numerical simulations. A string network in a contracting universe, together with the gravitational radiation it generates, can affect the dynamics of the universe both locally and globally, and be an important source of radiation, entropy and inhomogeneity. We discuss possible implications for bouncing and cyclic models.Comment: Shorter version of astro-ph/0206287. To appear in Phys. Rev. Let

    Probing dark energy beyond z=2z=2 with CODEX

    Full text link
    Precision measurements of nature's fundamental couplings and a first measurement of the cosmological redshift drift are two of the key targets for future high-resolution ultra-stable spectrographs such as CODEX. Being able to do both gives CODEX a unique advantage, allowing it to probe dynamical dark energy models (by measuring the behavior of their equation of state) deep in the matter era and thereby testing classes of models that would otherwise be difficult to distinguish from the standard Λ\LambdaCDM paradigm. We illustrate this point with two simple case studies.Comment: 4 pages, 4 figures; submitted to Phys. Rev.
    corecore