30 YEARS OF COSMIC STRINGS Alex Vilenkin Tufts Institute of Cosmology

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    Alex Vilenkin

    Tufts Institute of Cosmology

  • 30 YEARS OF COSMIC STRINGSString evolutionDetection (bounds)FOCUS ON:

  • 30 YEARS OF COSMIC STRINGSSuperconducting strings VortonsSemilocal stringsString formation Strings in GUTsStrings in condensed matter LEAVE OUT:

  • A BRIEF HISTORYPublications per yearKibble 1976

  • OLD STRING EVOLUTION SCENARIODistance between strings:

    Loop sizes:

    Loops decay by gravitational radiation:

    Kibble (1976), A.V. (1981)Mass per unit length of string


  • High-resolution simulations: the loops are tinyBennett & Bouchet (1990)Allen & Shellard (1990) (below theresolution)Small-scale wigglesrad. matter Loop sizes are set by the scale of wiggles.

  • SCENARIOS:is determined by gravitational back-reaction:Bennett & Bouchet (1990)Siemens & Olum (2001)Siemens, Olum & A.V. (2002)No scaling:Vincent, Hindmarsh & Sakellariadou (1997)Observational predictions are sensitive to !(standard model)


  • Small-scale wiggles and loops are resolved!Ringeval, Sakellariadou & Bouchet (2005):Olum & Vanchurin (2006):Shellard & Martins (2005):Most of the energy goes Into loops with .

    Requires a cutoff.Loop formation on scales . Scaling peak in loop productiondevelops atafter a long transient regime. Radiation era

  • after a long transient regime.Flat-space exact simulationVanchurin, Olum & A.V. (2005)

  • The picture that seems to emergeis close to the old string scenario: Broad distribution of loops and small-scale wiggles.(?)

  • Analytic models:Kibble (1985)Bennett (1986)Copeland, Kibble & Austin (1992)Martins & Shellard (1996) Copeland, Kibble & Steer (1998)Polchinski & Rocha (2006)To reach full understanding, we will need to combine numerical and analytic techniques.

  • COSMIC SUPERSTRINGSReconnection probability may be small: .Jackson, Jones & Polchinski (2004)Witten (1985)Sarangi & Tye (2002)Majumdar & A. Davis (2002)F, D and FD strings; FD networks.Copeland, Myers & Polchinski (2004)Dvali & A.V. (2004)Metastable, but the lifetime can be >> 1010 yrs.In models of brane inflation: .Jones, Stoica & Tye (2003)[Similar range in hybrid inflation GUT models]Jeannerot & Postma (2005)

  • How does affect string evolution?Sakellariadou & A.V. (1990)Sakellariadou (2005)Avgoustidis & Shellard (2006)Simple argument suggests

    Numerical evidence is inconclusive.But in any case, for p

  • EVOLUTION OF FD-NETWORKSVachaspati & A.V. (1987)McGraw (1998)Tye, Wasserman & Wyman (2005)Simple modelsScaling: depends on energy dissipation.Spergel & Pen (1997)Copeland & Saffin (2005)Hindmarsh & Saffin (2006)Global string network simulationsIf the dominant energy lossis gravitational radiation:Goldstone radiation String domination

  • UrrestillaGauge stringsU(1)xU(1)Scaling:Loop production?


  • STRING SIGHTINGS:Sazhin et. al. (2003) Cowie & Hu (1987)Schild et. al. (2004)

  • GRAVITATIONAL RADIATIONStochastic GW background & GW bursts from cusps. Vachaspati & A.V. (1984) Hogan & Rees (1984) Caldwell & Allen (1992)Battye, Caldwell & Shellard (1996) Comparable power in bursts andin low harmonics.Bursts may be detectable for .Better for p
  • BOUNDS FROM PULSAR OBSERVATIONS8 yrs:Kaspi, Taylor & Ryba (1994)17 yrs:Lommen (2002)Hogan (2006)(disputed)PTA:Jenet et. al. (2006)Full PTA (Pulsar Timing Array)(20 pulsars for 5 yrs)

  • Implications of large loops Nucleosynthesis bound:Vanchurin, Olum & A.V. (2005)Reionization:Olum & A.V. (2006)loops seed early galaxy formation.

  • CMB BOUNDSCMB anisotropiesPogosian, Wasserman & Wyman (2006)CMB polarizationB-type polarization due to vector perturbations induced by strings.may be detectable.Seljak & Slosar (2006)

  • Bad news: GUT-scale strings are ruled out.Good news: strings can be detected well belowthe GUT scale.We are not likely to detect strings through gravitational lensing or CMB anisotropies. Gravitational waves, CMB polarizationConstraint is much weaker for global strings:

  • CONCLUSIONSA new generation of string simulations is underway.Strong indications of loop scaling; (?) important observational implications. The strongest present bound on strings:(PTA)The most promising detection methods:pulsar timing, GW bursts, CMB polarization. May get to in ~ 5 yrs. The field is as vibrant as ever!