Swampland (physics)

In physics, the term swampland refers to effective low-energy physical theories which are not compatible with string theory, in contrast to the so-called "string theory landscape" of compatible theories. In other words, the swampland is the set of consistent-looking theories with no consistent ultraviolet completion in string theory.

Developments in string theory suggest that the string theory landscape of false vacua is vast, so it is natural to ask if the landscape is as vast as allowed by consistent-looking effective field theories. Some authors, such as Cumrun Vafa,[1] suggest that is not the case and that the swampland is in fact much larger than the string theory landscape.

Swampland conjectures

The swampland conjectures are a set of conjectured criteria for theories in the string theory landscape. Some proposed swampland criteria:[2]

If there is a charge symmetry, that symmetry has to be a gauge symmetry, not a global one, and at least one charged particle must have a mass in Planck units less than the gauge coupling strength. However, not all charged particles are necessarily light. The same applies to magnetic monopoles as well. This criterion would imply the weak gravity conjecture.
The sign of some higher order terms in the effective action is constrained by the absence of superluminal propagation.
There are finitely many types of massless particles.

References

Vafa, Cumrun (2005). "The String Landscape and the Swampland". arXiv:hep-th/0509212.
Arkani-Hamed, Nima; Motl, Luboš; Nicolis, Alberto; Vafa, Cumrun (15 June 2007). "The String Landscape, Black Holes and Gravity as the Weakest Force". Journal of High Energy Physics. 2007 (6): 060. arXiv:hep-th/0601001. Bibcode:2007JHEP...06..060A. doi:10.1088/1126-6708/2007/06/060. S2CID 16415027.

External links

Lecture by Cumrun Vafa, String Landscape and the Swampland, March 2018

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[1] Vafa, Cumrun (2005). "The String Landscape and the Swampland". arXiv:hep-th/0509212.

[2] Arkani-Hamed, Nima; Motl, Luboš; Nicolis, Alberto; Vafa, Cumrun (15 June 2007). "The String Landscape, Black Holes and Gravity as the Weakest Force". Journal of High Energy Physics. 2007 (6): 060. arXiv:hep-th/0601001. Bibcode:2007JHEP...06..060A. doi:10.1088/1126-6708/2007/06/060. S2CID 16415027.