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Cosmic Superstrings: Insights from Superstring Theory

Explore the fascinating world of cosmic superstrings and their relevance in modern superstring theory, including their origins, potential instabilities, and observational possibilities in gravitational lensing, pulsar timing, cosmic microwave background, and gravitational radiation. Learn about the diverse types of strings and branes, the M-theory conjecture, dualities, and the evolution of string theories post-1995.

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Cosmic Superstrings: Insights from Superstring Theory

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  1. Cosmic Superstrings

  2. Strings (or linear defects) appear in many physical systems: • vortex lines in liquid helium • magnetic flux tubes in Type II superconductors • disclination lines in liquid crystals

  3. Could the fundamental strings of superstring theory appear as cosmic strings? X superstrings cosmic strings E. Witten (1985): NO!!

  4. Problems, Problems, Problems (pre-1995) • microscopic details make strings unstable! Type I: open strings fragment Heterotic & Type II: closed strings domain walls, • fundamental strings have tension close • to Planck scale, but isotropy of CMB constrains • inflation would dilute away any such relic strings • from Planck scale era

  5. 2nd Superstring Revolution(circa 1995): • M-theory Conjecture: all known string theories are • different solutions of single fundamental theory

  6. Essential ingredients for M-theory conjecture: Different perturbative constructions related by “Dualities” • Dualites: two mathematical descriptions describe • identical physical phenomena “String theory is more than a theory of strings” • D-branes: string theory contains other kinds of • objects extended in 0, 1, 2, . . . dimensions D-particles Dp-branes D-strings D-membranes • NS5-branes, M2-branes, M5-branes

  7. After the 2nd superstring revolution: • More kinds of strings: • fundamental strings, D-strings, • partially wrapped D-, M- or NS5-branes (Dualities may relate these objects)

  8. After the 2nd superstring revolution: • More kinds of strings: • fundamental strings, D-strings, • partially wrapped D-, M- or NS5-branes (Dualities may relate these objects) 2. More “exotic” kinds of compactifications: - large extra dimensions - warped compactifications We should reconsider cosmic superstrings

  9. Strings have Planck scale tension • Strings are diluted away by inflation • Strings are unstable Pre-1995 thinking on cosmic superstrings:

  10. 1. string tension reduced in “exotic” compactifications: in “warped” compactifications, tension is redshifted by internal metric factors Bulk: Throat:

  11. Strings have Planck scale tension • Strings are diluted away by inflation • Strings are unstable Pre-1995 thinking on cosmic superstrings: String tension decoupled from Planck scale

  12. Burgess et al; Jones, Stoica & Tye; Sarangi & Tye 2. Cosmic strings from brane inflation: D1-strings form in D3-D3 annihilation as defects in tachyon field by standard Kibble mechanism Radiation (p,q)-strings D3 D3 Theory contains Dirichlet strings, fundamental strings, and also bound state strings (p,q)-strings

  13. Strings have Planck scale tension • Strings are diluted away by inflation • Strings are unstable Pre-1995 thinking on cosmic superstrings: String tension decoupled from Planck scale Rich network of strings may be generated at end of brane inflation

  14. 3. Many potential sources of instability, e.g., • Breaking on D-branes • Collapsing with domain walls • “Baryon decay” • Tachyon decay But instabilities are model specific!! One can find scenarios where: i) (p,q)-strings are stable ii) only D-strings are stable iii) no strings are stable

  15. Strings have Planck scale tension • Strings are diluted away by inflation • Strings are unstable Pre-1995 thinking on cosmic superstrings: String tension decoupled from Planck scale Rich network of strings may be generated at end of brane inflation Many potential instabilities , but model specific!!

  16. What are the numbers? Producing reasonable inflationary parameters constrains models with warped compactifications: Kachru, Kallosh, Linde, Maldacena, McAlister & Trivedi Similarly for large extra dimensions models: Jones, Stoica & Tye; Sarangi & Tye

  17. Seeing Cosmic Superstrings? There are a number of experimental opportunities to observe cosmic superstrings: a) Gravitational Lensing b) Pulsar Timing c) Cosmic Microwave Background d) Gravitational Radiation

  18. c) Cosmic Microwave Background: cosmic strings give no acoustic peaks! Landriau & Shellard; Pogosian et al Non-gaussianities: Jeong & Smoot Future polarization measurements!

  19. d) Gravitational Radiation: Oscillating loops of string can be very wiggly! Cusps: for an instant in an oscillation – rare Kinks: sharp bends appear every intercommutation – common Both produce beams of gravity waves, but cuspsare much more powerful!!

  20. d) Gravitational Radiation: Gravitational radiation bursts from cusps (and kinks) may be observed by gravity wave observatories: Hanford, WA (Livingston, LA) LIGO LISA

  21. Damour & Vilenkin d) Gravitational Radiation: Gravitational radiation bursts from cusps (and kinks): • LIGO I: • LIGO II: • LISA: LIGO I cusps LIGO II kinks

  22. Conclusions: Modern superstring theory admits scenarios where macroscopic superstrings satisfy: a) small tension (compared to Planck scale) b) copiously produced (after inflation) c) stable (on cosmological timescales) Cosmic Superstrings may present a remarkable astronomical window on the microphysics of superstring theory!!!

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