In physics, the term swampland refers to effective low-energy physical theories which are not compatible with string theory. Physical theories which are compatible are called "landscape". Recent developments in string theory suggest that the string theory landscape of false vacua is vast.
It is natural to ask if the landscape is as vast as allowed by consistent-looking effective field theories. Some authors (e.g. Cumrun Vafa[1]) suggest that is not the case and that the landscape is surrounded by an even larger swampland of consistent-looking semiclassical effective field theories, which are actually inconsistent.
Some proposed swampland criteria[2] are the following:
If there is a charge symmetry, that symmetry has to be a gauge symmetry, not a global one, and in the spectrum of charged particles, there has to be at least a particle with a mass in Planck units less than the gauge coupling strength. However, not all charged particles are necessarily light.
That applies to magnetic monopoles as well.
The sign of some higher order terms in the effective action is constrained by the absence of superluminal propagation.
It has been shown that the swampland criteria are inconsistent with the idea of single-field slow-roll inflation given current cosmological data[3].
See also
Weak gravity conjecture
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.
Kinney, William H.; Vagnozzi, Sunny; Visinelli, Luca (2018). "The zoo plot meets the swampland: mutual (in)consistency of single-field inflation, string conjectures, and cosmological data".arXiv:1808.06424.
External links
Lecture by Cumrun Vafa - | String Landscape and the Swampland March 2018
Hellenica World - Scientific Library
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