30 YEARS OF COSMIC STRINGS Alex Vilenkin Tufts Institute of Cosmology

30 YEARS OF COSMIC STRINGS String evolution Detection (bounds) FOCUS ON:

30 YEARS OF COSMIC STRINGS Superconducting strings Vortons Semilocal strings String formation Strings in GUTs Strings in condensed matter … LEAVE OUT:

Strings are seeds of galaxies! Strings are dead! Cosmic super- strings! A BRIEF HISTORY Publications per year Kibble 1976

OLD STRING EVOLUTION SCENARIO Distance between strings: Loop sizes: Loops decay by gravitational radiation: Kibble (1976), A.V. (1981) Mass per unit length of string

THE FIRST COSMIC STRING REVOLUTION

High-resolution simulations: the loops are tiny Bennett & Bouchet (1990) Allen & Shellard (1990) (below the resolution) Small-scale wiggles rad. 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”)

THE SECOND COSMIC STRING REVOLUTION (still in progress!)

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 production develops at after a long transient regime. Radiation era

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

The picture that seems to emerge is 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 SUPERSTRINGS Reconnection 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 >> 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 << 1 there is a large number of strings per Hubble volume. Direct observational test of string theory.

EVOLUTION OF FD-NETWORKS Vachaspati & A.V. (1987) McGraw (1998) Tye, Wasserman & Wyman (2005) Simple models Scaling: depends on energy dissipation. Spergel & Pen (1997) Copeland & Saffin (2005) Hindmarsh & Saffin (2006) Global string network simulations If the dominant energy loss is gravitational radiation: Goldstone radiation String domination

Urrestilla Gauge strings U(1)xU(1) Scaling: Loop production?

OBSERVATIONAL BOUNDS

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

GRAVITATIONAL RADIATION Stochastic GW background & GW bursts from cusps. Vachaspati & A.V. (1984) Hogan & Rees (1984) Caldwell & Allen (1992) Battye, Caldwell & Shellard (1996) … Comparable power in bursts and in low harmonics. Bursts may be detectable for. Better for p << 1. LIGO search is underway! Damour & A.V. (2000,2005) Siemens et. al. (2006) Hogan (2006)

BOUNDS FROM PULSAR OBSERVATIONS 8 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 BOUNDS CMB anisotropies Pogosian, Wasserman & Wyman (2006) CMB polarization B-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 below the GUT scale. We are not likely to detect strings through gravitational lensing or CMB anisotropies. Gravitational waves, CMB polarization Constraint is much weaker for global strings:

CONCLUSIONS A 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!